Electrolytes for electrochemical generator

Abstract

The present invention relates to thermotropic ionic liquid crystal molecules of general formula (I) ##STR00001##
With E.sub.1 and E.sub.2, which may be identical or different, representing, independently of one another, a linear, saturated and unsubstituted C.sub.10 to C.sub.14 hydrocarbon-based radical, A.sup.x− representing a sulfonate anion or a sulfonylimide anion of formula —SO.sub.2—N.sup.−—SO.sub.2C.sub.yF.sub.2y+1 with y being an integer ranging from 0 to 2 and C.sup.x+ a sodium, lithium or potassium ion, most particularly advantageous for their conductivity performance qualities as an electrolyte in particular for lithium batteries.

Claims

1. A process for preparing an electrochemical system comprising: preparing an electrolyte comprising thermotropic ionic liquid crystal molecules according to formula (I): ##STR00010## wherein: E.sub.1 and E.sub.2, which may be identical or different, represent, independently of one another, a linear, saturated, and unsubstituted C.sub.11 to C.sub.13 alkyl radical, A.sup.x− represents a sulfonate anion or a sulfonylimide anion —SO.sub.2—N.sup.−—SO.sub.2CF.sub.3, C.sup.x+ is an Li.sup.+ cation, and wherein thermotropic ionic liquid crystal molecules are in a mesomorphic state; and employing said electrolyte in the electrochemical system.

2. The method according to claim 1, wherein E.sub.1 and E.sub.2 are identical.

3. The method according to claim 1, wherein -A.sup.x− is the sulfonate anion.

4. The method according to claim 1, wherein the thermotropic ionic liquid crystal molecules have a structure: ##STR00011##

5. The method according to claim 1, wherein E.sub.1 and E.sub.2 are dodecyl radicals.

6. An electrolyte comprising thermotropic ionic liquid crystal molecules having formula (I): ##STR00012## wherein: E.sub.1 and E.sub.2, which may be identical or different, represent, independently of one another, a linear, saturated, and unsubstituted C.sub.11 to C.sub.13 alkyl radical, A.sup.x− represents a sulfonate anion or a sulfonylimide anion —SO.sub.2—N.sup.−—SO.sub.2CF.sub.3, C.sup.x+ is an Li.sup.+ cation, and wherein thermotropic ionic liquid crystal molecules are in a mesomorphic state.

7. The electrolyte according to claim 6, wherein the electrolyte has a viscosity of greater than or equal to 10 mPa.s at a temperature of between −60° C. and 300° C.

8. The electrolyte according to claim 6, wherein the electrolyte has an ion conductivity at 20° C. of greater than or equal to 10.sup.−7 S.cm.sup.−1.

9. The electrolyte according to claim 6, wherein the electrolyte has an ionic conductivity of greater than 10.sup.−4 S.cm.sup.−1 at 100° C. and an ionic conductivity at 150° C. of greater than or equal to 10.sup.−3 S.cm.sup.−1.

10. An electrochemical system comprising the electrolyte according to claim 6 and an electrode.

11. The electrochemical system according to claim 10, wherein the electrochemical system is a battery.

12. The electrochemical system according to claim 11, wherein the electrochemical system is a lithium battery.

13. The electrochemical system according to claim 10, wherein the electrolyte is impregnated in a porous separator.

14. A porous separator impregnated with the electrolyte according to claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: FTIR analysis of compound Ia.

(2) FIG. 2: calorimetric analysis of compound Ia by DSC under argon and with a heating rate of 10° K/min

(3) FIG. 3: Analysis of compound Ia by SAXS.

(4) FIG. 4: FTIR analysis of compound Ib.

(5) FIG. 5: Analysis of compound Ib by SAXS.

(6) FIG. 6: Ion conductivity analysis, in temperature increase and temperature decrease, of compounds Ia and Ib versus products not in accordance with the invention.

EXAMPLE 1

(7) Preparation of Compound Ia in Accordance with the Invention

(8) ##STR00005##

(9) 1.25 g of 4-aminonaphthalenesulfonic acid, 3.50 g of 1-bromododecane and 2.3 ml of triethylamine are dissolved in 50 ml of DMF. The solution is stirred at 70° C. for 48 h. 40 ml of deionized water and 2 ml of 2 M HCl aqueous solution are added thereto and the aqueous phase is extracted three times with 30 ml of dichloromethane. The product is purified on a silica column (MeOH/DCM) and the fractions containing the desired product are combined and evaporated. 1.74 g of disubstituted product is obtained in the form of a yellowish powder. Following neutralization with a dilute solution of LiOH, the product A is obtained.

(10) Characterization of the Liquid Crystal

(11) .sup.1HNMR (400 MHz; MeOD; 300 K): δ ppm 8.7 (d, 1H); 8.0 (d, 1H); 7.9 (d, 1H); 7.5 (dd, 1H); 7.4 (dd, 1H); 6.5 (d, 1H); 3.2 (d, 2H); 3.0 (d, 2H); 1.4 (m, 40H); 0.88 (t, 6H)

(12) .sup.13C NMR (400 MHz; MeOD; 300 K): δ ppm 131.6; 129.0; 128.1; 127.3; 125.4; 124.9; 122.0; 101.6; 53.8; 44.8; 33.1; 30.8; 30. 7; 30.5; 29.9; 28.5; 23.8; 22.6; 14.4; 7.6

(13) Its ATR 2-FTIR spectrum recorded on a Thermo Scientific Nicolet 6700 apparatus is represented in FIG. 1.

(14) The product Ia was characterized by DSC under argon and with a heating rate of 10° K/min. The results of the calorimetric analysis are represented in FIG. 2. The analysis is carried out with a temperature gradient of 10° C./min under an inert atmosphere. The sample is heated from ambient temperature to 180° C. during a first heating not represented in FIG. 2, then a cooling cycle down to −50° C., followed by a second heating up to 180° C. is applied and the points measured are represented below.

(15) The product shows five transitions in heating at 52° C., 78° C., 109° C., 131.5° C. and 147.2° C., and four in cooling at 102° C., 66.4° C., 40.5° C. and −24° C.

(16) For the SAXS analysis, a sample of powder of compound Ia is placed between two kapton films under an inert atmosphere and measured on a SAXS line. A rotating copper anode and a Vantec 2000 detector are used. The signal obtained is a ring of equivalent density (therefore the material is isotropic); after radial integration, the 2D spectrum represented in FIG. 3 is obtained. The organized state of this material is characterized by the presence of thin and intense Bragg peaks. The SAXS image of the product Ia corresponds to a columnar rectangular structure at ambient temperature.

EXAMPLE 2

(17) Synthesis of Compound Ib

(18) ##STR00006##

(19) Synthesis of the ANTFSI Synthon:

(20) ##STR00007##
Step n.sup.o1:

(21) Amino-4-naphthalenesulfonic acid—ANH (14.97 g, 67.13 mmol) is weighed into a 500 ml single-necked round-bottomed flask under an inert atmosphere. 100 ml of pyridine are added dropwise to the ANH still under an inert atmosphere, then 13 ml (1.3 eq) of phthaloyl chloride are added with stirring. As soon as the first drop of phthaloyl chloride is added, fumes are given off and the solution begins to turn amber in color. The reaction medium is stirred at reflux for 24 h. The pyridine is evaporated off and the residue is recrystallized three times from methanol until the product A is obtained (21.698 g, 75% yield after purification).

(22) Step n.sup.o2:

(23) The product A (21.698 g, 50.290 mmol) is added to 100 ml of anhydrous DMF in a three-necked 500 ml round-bottomed flask inserted under argon. Once the product has dissolved, the reaction medium is placed in an ice bath at 3-5° C. and thionyl chloride (7.5 ml, 2 eq) is added dropwise via a dropping funnel. At the end of the addition, the reaction medium is reheated to ambient temperature with stirring. After reaction for 1 h, the reaction medium is poured dropwise into cold water. The product 2 is filtered through a Buchner funnel and dried under vacuum at 80° C. for 12 h. The product B obtained is a white powder (22.7 g, 98% yield).

(24) Step n.sup.o3:

(25) The product B (22.7 g, 61.0 mmol) is added to 200 ml of anhydrous acetone contained in a single-necked 500 ml round-bottomed flask. Trifluoromethanesulfonamide (34.4 g, 2 eq) and, finally, triethylamine (20 ml, 2.5 eq) are then added. The reaction medium is stirred at ambient temperature for 24 h; according to the thin layer chromatography (TLC) carried out with the 1:1 mixture of DCM/MeOH solvent as eluent, the conversion of the product 2 is total. The solvent and the excess triethylamine are evaporated off under reduced pressure and the dry residue is purified on a silica column. The product C is obtained (35.97 g, 95% yield).

(26) Step n.sup.o4:

(27) The product C (1 g, 2.1 mmol) is placed in a 500 ml single-necked round-bottomed flask. 300 ml of anhydrous acetone are added in order to totally dissolve the product 3. Hydrazine (2 eq) is then added to the reaction medium which is subsequently stirred for 24 h at ambient temperature. The formation of a white precipitate during the reaction is noted. The solid is then filtered off and analyzed by .sup.1H NMR so as to confirm its chemical structure. The filtrate is evaporated and directly purified on a silica column. The fractions containing the desired product are combined and the solvent is evaporated off. The weight of product D obtained is 0.51 g, i.e. a synthesis yield of 69%.

(28) The grafting of the chains was carried out in two steps:

(29) ##STR00008##
Step n.sup.o1:

(30) The product D (0.500 g, 1.4 mmol) is dissolved in 50 ml of DMF, in a 100 ml round-bottomed flask under an inert atmosphere. Triethylamine (0.59 ml, 3 eq) is added to the reaction medium with stirring. Finally, 1-bromododecane (0.84 ml, 2.5 eq) is added to the solution. The reaction medium is stirred at 70° C. for 48 h. 40 ml of deionized water and 2 ml of 2M HCl aqueous solution are added and the aqueous phase is extracted three times with 30 ml of dichloromethane. The product is purified on a silica column (MeOH/DCM) and the fractions containing the desired product are combined and evaporated. The monosubstituted product E is obtained in the form of a yellowish powder (0.460 g, 64% synthesis yield).

(31) Step n.sup.o2:

(32) The product E (0.460 g, 0.8 mmol) is dissolved in 50 ml of DMF, in a 100 ml round-bottomed flask under an inert atmosphere. Triethylamine (0.37 ml, 3 eq) is added to the reaction medium with stirring. Finally, 1-iodododecane (0.55 ml, 2.5 eq) is added to the solution. The reaction medium is stirred at 70° C. for 48 h. 40 ml of deionized water and 2 ml of 2M HCl aqueous solution are added and the aqueous phase is extracted three times with 30 ml of dichloromethane. The product is purified on a silica column (MeOH/DCM) and the fractions containing the desired product are combined and evaporated. The product F is obtained in the form of a brown powder (0.503 g, 82% synthesis yield).

(33) Characterization of the Liquid Crystal

(34) .sup.1H NMR (400 MHz; MeOD; 300 K): δ ppm 8.7 (d, 1H); 8.0 (d, 1H); 7.9 (d, 1H); 7.5 (dd, 1H); 7.4 (dd, 1H); 6.6 (d, 1H); 3.2 (d, 2H); 3.0 (d, 2H); 1.6 (m, 4H); 1.4 (m, 36H); 0.88 (t, 6H)

(35) Its ATR 2-FTIR spectrum recorded on a Thermo Scientific Nicolet 6700 apparatus is represented in FIG. 4.

(36) For the SAXS analysis, the sample is placed between two kapton films under an inert atmosphere and measured on a SAXS line. A rotating copper anode and a Vantec 2000 detector are used. The signal obtained is a ring of equivalent density (thus the material is isotropic); after radial integration, the 2D spectrum represented in FIG. 5 is obtained. The organized state of this material is characterized by the presence of Bragg peaks. The spectrum of the product Ib is characteristic of a structure in the form of lamellae (ratio 1:2).

EXAMPLE 3

Characterization of the Ionic Conductivities of the Compounds of Examples 2 and 3

(37) The conductivity measurements are carried out in a CESH cell (Biologic) between two blocking electrodes. A potential difference of 50 mV is applied between the two blocking electrodes and a frequency scan between 5 MHz and 100 mHz is used. The EIS spectra obtained are modeled by equivalent electrical circuits (R1+R2/Q2+W) to determine the resistance of the electrolyte.

(38) The results obtained are represented in FIG. 6 (ionic conductivity in S.Math.cm.sup.−1 as a function of 1000/T, where T is the temperature in Kelvin). For the purposes of comparison, compounds not in accordance with the invention, termed 16-ANLi and 14-AN-Li, having the following formulae,

(39) ##STR00009##
were prepared according to the indications given in document EP 3 353 262 and tested under the same conditions as compounds Ia and Ib according to the invention.

(40) It appears that only the thermotropic ionic liquid crystal molecules Ia and Ib in accordance with the invention have an ionic conductivity that can reach up to 10.sup.−5 S.Math.cm.sup.−1 at 103° C., i.e. 100 times greater than that measured for the compounds not in accordance with the invention. In addition, compound Ib has a conductivity that is up to an order of magnitude greater than that of compound Ia. A conductivity of 10.sup.−4 S.Math.cm.sup.−1 is in fact obtained from 75° C.

(41) These results demonstrate the great efficiency of the thermotropic ionic liquid crystal molecules in accordance with the invention as an electrolyte in an electrochemical system, in particular in a lithium battery.