Electrolyte for electrochemical generator

Abstract

Thermotropic ionic liquid crystal molecules, comprising a so-called rigid part, a so-called flexible part bonded covalently, directly or via a spacer, to said rigid part, and one or more ionic groups bonded covalently to said rigid part. Said molecules can be used as electrolytes in an electrochemical device, in particular a lithium-ion battery.

Claims

1. An electrolyte, comprising a thermotropic ionic liquid crystal molecule, in a mesomorphic state, wherein the molecule comprises: a rigid part, comprising a polycyclic group Ar formed from 2 to 6 rings, at least one of which is aromatic, the rings being, independently of each other, 4- to 6-membered, the polycyclic group optionally including up to 18 heteroatoms; a flexible part, formed from one or more linear or branched, saturated or unsaturated, fluorinated or nonfluorinated aliphatic chains, the chain(s) being optionally interrupted with one or more heteroatoms, metalloids, and/or aromatic or nonaromatic, 4- to 6-membered (hetero)cycles, and optionally substituted with one or more hydroxyl, NH.sub.2, and/or oxo groups, the flexible part being covalently bonded, directly or via a spacer, to the rigid part; and an ionic group -A.sup.xC.sup.x+, wherein -A.sup.x is an anionic group covalently bonded to the rigid part, with x being an integer equal to 1 or 2, -A.sup.x being a sulfonate anion, sulfonylimide of formula SO.sub.2N.sup.SO.sub.2C.sub.yF.sub.2y+1 with y being an integer ranging from 0 to 4, borate, borane, phosphate, phosphinate, phosphonate, silicate, carbonate, sulfide, selenate, nitrate, and/or perchlorate, and wherein C.sup.x+ is a counter-cation of -A.sup.x, and C.sup.x+ is H.sup.+, an alkali metal cation, and/or an alkaline-earth metal cation.

2. The electrolyte of claim 1, wherein, in the molecule, the polycyclic group Ar has one of the following backbones: ##STR00022##

3. The electrolyte of claim 1, wherein, in the molecule, the polycyclic group Ar is an aromatic bicyclic group.

4. The electrolyte of claim 1, wherein, in the molecule, the flexible part is formed from: a single branched aliphatic chain, comprising a linear sequence of at least 6 covalent bonds; or at least two linear or branched aliphatic chains, each of the chains comprising a linear sequence of at least 6 covalent bonds.

5. The electrolyte of claim 1, wherein, in the molecule, each of the aliphatic chains is formed from a single chain segment or from a linear sequence of at least two chain segments.

6. The electrolyte of claim 1, wherein, in the molecule, the aliphatic chain(s) forming the flexible part are covalently bonded directly to one or more carbon atoms or heteroatoms of the group Ar forming the rigid part.

7. The electrolyte of claim 1, wherein, in the molecule, the aliphatic chain(s) forming the flexible part are covalently bonded via a spacer to one or more carbon atoms or heteroatoms of the group Ar forming the rigid part.

8. The electrolyte of claim 7, wherein the aliphatic chain(s) are covalently bonded to a carbon atom of the group Ar via an atom of valency greater than or equal to 2.

9. The electrolyte of claim 8, wherein the atom of valency greater than or equal to 2 is a nitrogen atom.

10. The electrolyte of claim 7, wherein, in the molecule, the flexible part is formed from two linear alkyl chains, comprising from 4 to 18 carbon atoms, optionally substituted with one or more hydroxyl groups, optionally interrupted with one or more oxygen atoms, wherein the chains are bonded to a carbon atom of the group Ar via a nitrogen atom.

11. The electrolyte of claim 1, wherein, in the molecule, the anionic groups -A.sup.x are sulfonate anions and/or anions of formula SO.sub.2N.sup.SO.sub.2C.sub.yF.sub.2y+1 with y ranging from 0 to 4.

12. The electrolyte of claim 1, wherein, in the molecule, C.sup.x+ is H.sup.+ or a Li.sup.+ cation.

13. The electrolyte of claim 1, wherein the molecule has the structure: ##STR00023## wherein E.sub.1 and E.sub.2 represent identical or different linear or branched, saturated or unsaturated, fluorinated or nonfluorinated aliphatic chains, the chain(s) being optionally interrupted with one or more heteroatoms, metalloids, and/or aromatic or nonaromatic, 4- to 6-membered (hetero)cycles, and optionally substituted with one or more groups selected from the group consisting of hydroxyl, NH.sub.2 and oxo groups.

14. The electrolyte of claim 13, wherein the chains E.sub.1 and E.sub.2 represent identical or different linear alkyl chains, comprising from 6 to 16 carbon atoms, each being substituted with a hydroxyl group, optionally fluorinated, and optionally interrupted with an oxygen atom.

15. The electrolyte of claim 1, having a viscosity of greater than or equal to 10 mPa.Math.s at a temperature of between 60 C. and 300 C.

16. The electrolyte of claim 1, having an ion conductivity at 20 C. of greater than or equal to 10.sup.9 S/cm, and an ion conductivity at 200 C. of greater than or equal to 10.sup.5 S/cm.

17. The electrolyte of claim 1, wherein, in the molecule, the polycyclic group Ar is an aromatic bicyclic group with a naphthalene aromatic backbone.

18. The electrolyte of claim 1, wherein, in the molecule, the polycyclic group Ar is a naphthalene group.

19. The electrolyte of claim 1, wherein, in the molecule, each of the aliphatic chains is formed from a linear sequence of two or three chain segments of different chemical nature.

20. The electrolyte of claim 1, wherein, in the molecule, the anionic groups -A.sup.x are sulfonate anions.

21. The electrolyte of claim 1, wherein the molecule comprises: ##STR00024## ##STR00025## ##STR00026##

22. An electrochemical system comprising the electrolyte of claim 1.

23. The electrochemical system of claim 22, which is a battery.

24. The electrochemical system of claim 23, wherein the system is a lithium battery.

25. A porous separator, which is impregnated with the electrolyte of claim 1.

Description

(1) The invention will now be described by means of the examples and figures that follow, which are obviously given as nonlimiting illustrations of the invention.

(2) FIG. 1: Calorimetric analysis of the product 12-HAN by DSC under argon and with a heating rate of 10 K/min.

(3) FIG. 2: Analysis of the product 12-HAN by XRD.

(4) FIG. 3: Isotherms of sorption/desorption of water at 25 C. for the product 12-HAN.

(5) FIG. 4: Analysis of the product 12-HAN by SAXS, as a function of its degree of hydration.

(6) FIG. 5: Calorimetric analysis of the product 12-LiAN by DSC under argon and with a heating rate of 10 K/min.

(7) FIG. 6: Analysis of the product 12-LiAN by XRD.

(8) FIG. 7: Isotherms of sorption/desorption of water at 25 C. for the product 12-LiAN.

(9) FIG. 8: Ion conductivity analysis, in temperature rise and fall, of the products 12-LiAN and 14-LiAN.

(10) FIG. 9: Ion conductivity analysis, in temperature rise and fall, of the products 12-LiAN, 14-LiAN, 16-LiAN, 12-LiAN and 16-LiAN.

EXAMPLES

Preparation of Synthetic Intermediates

Preparation of Lithium 4-amino-1-naphthalenesulfonate (LiAN)

(11) ##STR00008##

(12) 1.340 g of 4-amino-1-naphthalenesulfonic acid (HAN) and 0.210 g of lithium hydroxide monohydrate (LiOH.H.sub.2O) were placed in 20 mL of distilled water. The reaction medium was stirred overnight at room temperature. The excess HAN was removed by filtration. The filtrate was then concentrated by evaporating off the solvent under reduced pressure. After washing twice with ethanol, a pink powder (LiAN) was obtained.

(13) .sup.1H NMR (400 MHz; DMSO-d6; 300 K): ppm 7.89 (dd, 1H); 7.18 (dd, 1H); 6.83 (d, 1H); 6.52 (m, 2H); 5.68 (d, 1H); 4.96 (s, 2H).

(14) .sup.13C NMR (400 MHz; DMSO-d6; 300 K): ppm 146.11; 132.34; 130.61; 128.10; 126.45; 125.33; 123.56; 122.94; 122.26; 105.17.

Preparation of Lithium 5-amino-1-naphthalenesulfonate (LiAN)

(15) ##STR00009##

(16) 24.441 g of 4-amino-1-naphthalenesulfonic acid (HAN) and 4.282 g of lithium hydroxide monohydrate (LiOH.H.sub.2O) were placed in 500 mL of distilled water. The reaction medium was stirred overnight at room temperature. The excess HAN was removed by filtration. The filtrate was then concentrated by evaporating off the solvent under reduced pressure. After washing twice with ethanol, a pink powder (LiAN) was obtained.

Example 1Preparation of a Liquid Crystal 12-HAN in Accordance with the Invention

(17) ##STR00010##

(18) 2.0 g (8.96 mmol) of 4-amino-1-naphthalenesulfonic acid (HAN) and 3.29 g (17.9 mmol) of 1,2-epoxydodecane (i.e. 2 equivalents of epoxide per 1 of amine) in 10 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated at a temperature of 80 C. at the start of the reaction and then raised to 100 C. for 2 days until a brown two-phase mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel. The solid phase was then dissolved in methanol, this methanol being removed on a rotary evaporator.

(19) The product obtained (12-HAN) was dried under reduced pressure and a brown paste was obtained.

(20) Characterization of the Liquid Crystal 12-HAN The product 12-HAN was characterized by DSC under argon and with a heating rate of 10 K/min. The results of the calorimetric analysis are shown in FIG. 1.

(21) The DSC spectrum shows the phase transition at 38 C. (corresponding to the melting point) and an endothermic peak at 193 C. (corresponding to the clarification temperature). The liquid crystal 12-HAN was observed by PLM. The liquid crystal is placed between two hydrophilic glass plates (thickness of the deposit: 3-5 m), slid inside a hotplate and under a controlled atmosphere (nitrogen), which is itself mounted between the polarizer and the analyzer of the microscope.

(22) The PLM image obtained after shear under the glass plates at 185 C. shows the appearance of very small birefringent zones representative of the observation of mesomorphic phase defects. A deposit of 12-HAN powder was produced on a glass support for XRD analysis.

(23) The x-ray diffractogram, shown in FIG. 2, shows that the liquid crystal 12-HAN has a hexagonal lamellar phase with different peaks in ratios {square root over (3)}, {square root over (4)}, {square root over (7)}. Evaluation of the hygroscopicity of the liquid crystal 12-HAN was performed by conducting the study of the isotherm of sorption/desorption of water in the vapor phase in accordance with the method described below.

(24) The sorption balance was equipped with an electronic microbalance and a dew point analyzer. The liquid crystal 12-HAN was predried at 60 C. in an oven under vacuum. The liquid crystal 12-HAN was then dried again in the balance at 60 C. with a ramp of 5 C./min until an equilibrium of 0.0010% mass uptake over 10 minutes was achieved. If these conditions were not met, the liquid crystal was dried up to a maximum time of 600 minutes. The end condition used was 0.005% mass change for a time of 20 minutes. During the sorption/desorption cycle, the maximum time required to reach equilibrium was 1000 minutes.

(25) FIG. 3 shows the isotherms of sorption/desorption of water at 25 C., showing that the liquid crystal 12-HAN is hydrophilic. The liquid crystal 12-HAN was also characterized by SAXS, as a function of its degree of hydration.

(26) The degree of hydration of the samples was controlled using a controlled atmosphere. The liquid crystal 12-HAN was dried in an oven at 60 C. for one week under vacuum to obtain a dry sample. The liquid crystal 12-HAN was then analyzed by SAXS and the relative humidity of the room was measured using a hygrometer. The sample was then left to equilibrate for 1, 3 and 6 hours. To obtain a hydrated sample in an atmosphere containing 100% humidity, it was placed in a crucible to avoid direct contact with water. This same crucible was placed in a hermetic system filled with water. A water-saturated system in which the sample can become hydrated was then obtained.

(27) A shift of the ionomer peak with hydration of the liquid crystal 12-HAN is observed (FIG. 4).

(28) The ionomer peak is the signature of phase separation between the hydrophilic and hydrophobic domain at the nanometric scale. Its position (q) directly reflects the state of nanometric swelling or the correlation distance between the hydrophilic (or hydrophobic) domains (d=2/q). The more this peak is shifted toward the small values of q (the more d increases), the greater the amount of water in the product.

Example 2Preparation of a Liquid Crystal 12-LiAN in Accordance with the Invention

(29) ##STR00011##

(30) This product was synthesized via a protocol similar to that described in example 1, using 1.050 g of LiAN (4.73 mmol) instead of HAN with 1.741 g (9.46 mmol) of 1,2-epoxydodecane in 10 mL of DMF. The reaction is maintained at 70 C. for 3 days. A yellow-brown powder (12-LiAN) is obtained.

(31) Characterization of the Liquid Crystal 12-LiAN The results of the DSC analysis under argon and with a heating rate of 10 K/min are shown in FIG. 5. The DSC spectrum shows the phase transition at 6.25 C. (corresponding to the melting point) and an endothermic peak at 226 C. (corresponding to the clarification temperature). A deposit of 12-LiAN powder was produced on a glass support for X-ray diffraction analysis.

(32) The XRD analysis shown in FIG. 6 shows that the compound 12-LiAN has a lamellar phase with different peaks in ratios 2, 3, 4, 5. Evaluation of the hygroscopicity of the liquid crystal 12-LiAN was performed by conducting the study of the sorption/desorption isotherm of water in the vapor phase, according to the protocol detailed in example 1.

(33) FIG. 7 shows the isotherms of sorption/desorption of water at 25 C., showing that the liquid crystal 12-LiAN is hydrophilic.

Example 3Preparation of the Liquid Crystal 6-HAN in Accordance with the Invention

(34) ##STR00012##

(35) 3.101 g (13.47 mmol) of HAN and 3.35 mL (26.94 mmol) of 1,2-epoxyhexane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 100 C. for 120 hours until a homogeneous brown mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(36) The product obtained (6-HAN) was dried under reduced pressure and a brown paste was obtained.

Example 4Preparation of the Liquid Crystal 6-LiAN in Accordance with the Invention

(37) ##STR00013##

(38) 3.122 g (13.62 mmol) of LiAN and 3.39 mL (27.24 mmol) of 1,2-epoxyhexane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 100 C. for 144 hours until a very dark red homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(39) The product obtained (6-LiAN) was dried under reduced pressure and a bordeaux-red paste was obtained.

(40) The SAXS temperature observations confirmed the existence of an organized structure, proving that 6-LiAN is a thermotropic ionic liquid crystal.

Example 5Preparation of the Liquid Crystal 8-LiAN in Accordance with the Invention

(41) ##STR00014##

(42) 3.03 g (13.19 mmol) of LiAN and 4.21 mL (26.38 mmol) of 1,2-epoxyoctane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 60 C. for 96 hours, then at 65 C. for 144 hours, then at 75 C. for 264 hours and then at 85 C. for 3 weeks until a very dark homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(43) The product obtained (8-LiAN) was dried under reduced pressure and a dark red powder was obtained.

Example 6Preparation of the Liquid Crystal 14-HAN in Accordance with the Invention

(44) ##STR00015##

(45) 3.136 g (13.62 mmol) of HAN and 8.057 mL (27.25 mmol) of 1,2-epoxytetradecane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 90 C. for 144 hours until a very dark red homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(46) The product obtained (14-HAN) was dried under reduced pressure and an orange-red powder was obtained.

Example 7Preparation of the Liquid Crystal 14-LiAN in Accordance with the Invention

(47) ##STR00016##

(48) 3.008 g (13.12 mmol) of LiAN and 7.76 mL (26.25 mmol) of 1,2-epoxytetradecane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 90 C. for 144 hours until a very dark brown homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(49) The product obtained (14-LiAN) was dried under reduced pressure and a red powder was obtained.

(50) The observations by DSC, PLM and SAXS confirmed that 14-LiAN is a thermotropic ionic liquid crystal.

(51) The DSC spectrum does not show the phase transition corresponding to the melting point (since it is below the minimum measurement temperature) but shows three endothermic peaks characteristic of three mesomorphic phase changes.

(52) The changes in the SAXS spectra on temperature rise and fall, and also the PLM images, made it possible to identify the three mesomorphic phases: lamellar, lamello-columnar and columnar.

Example 8Preparation of the Liquid Crystal 16-LiAN in Accordance with the Invention

(53) ##STR00017##

(54) 2.991 g (13.12 mmol) of LiAN and 7.380 g (26.10 mmol) of 1,2-epoxyhexadecane in 25 mL of dimethylformamide DMF were placed in a 100 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 100 C. for 2 weeks until a very dark brown homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(55) The product obtained (16-LiAN) was dried under reduced pressure and a red powder was obtained.

(56) The observations by DSC and SAXS confirmed that 16-LiAN is a thermotropic ionic liquid crystal with two main mesomorphic phases of lamellar type with a mesomorphic phase transition at about 50 C.

Example 9Preparation of the Liquid Crystal 8F-HAN in Accordance with the Invention

(57) ##STR00018##

(58) 1.00 g of HAN (4.48 mmol) and 4.26 g (8.95 mmol) of 1,2-epoxy-1H,1H,2H,3H,3H-heptadecafluorodecane in 10 mL of DMF were placed in a round-bottomed flask equipped with a condenser and a magnetic bar. The reaction mixture was stirred and heated under argon at 80 C. in air for 2 days until a homogeneous mixture was obtained. The compound was precipitated from diethyl ether and filtered off on a Bchner funnel. The product was dried under reduced pressure, and a stable reddish gel was obtained (8F-HAN).

Example 10Preparation of the Liquid Crystal BGE-LiAN in Accordance with the Invention

(59) ##STR00019##

(60) 3.034 g (13.24 mmol) of LiAN and 3.99 mL (26.48 mmol) of butyl glycidyl ether were placed in a 25 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 70 C. for 24 hours, then at 80 C. for 96 hours and then at 90 C. for 1 week until a very dark homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(61) The product obtained (BGE-LiAN) was dried under reduced pressure and a red powder was obtained.

Example 11Preparation of the Liquid Crystal 12-LiAN in Accordance with the Invention

(62) ##STR00020##

(63) 2.903 g (12.67 mmol) of LiAN and 6.15 g (25.33 mmol) of 1,2-epoxydodecane in 15 mL of dimethylformamide DMF were placed in a 50 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 100 C. for 2 weeks until a very dark brown homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(64) The product obtained (12-LiAN) was dried under reduced pressure and a red powder was obtained.

(65) The observations by DSC and SAXS confirmed that 12-LiAN is a thermotropic ionic liquid crystal with an undefined organization between 10 C. and 70 C., and then an organization of lamellar type above 70 C.

Example 12Preparation of the Liquid Crystal 16-LiAN in Accordance with the Invention

(66) ##STR00021##

(67) 3.160 g (13.79 mmol) of LiAN and 7.80 g (27.57 mmol) of 1,2-epoxyhexadecane in 25 mL of dimethylformamide DMF were placed in a 100 mL round-bottomed flask mounted on a reflux assembly equipped with a condenser and a magnetic bar, and also an oil bath on a hotplate. The reaction mixture was stirred and heated under argon at a temperature of 90 C. for 2 weeks until a very dark brown homogeneous mixture was obtained. The reaction products were precipitated from a large volume of diethyl ether and then filtered off on a Bchner funnel.

(68) The product obtained (16-LiAN) was dried under reduced pressure and a red powder was obtained.

(69) The observations by DSC and SAXS confirmed that 16-LiAN is a thermotropic ionic liquid crystal with a columnar organization from room temperature to 80 C., and then a lamellar phase up to 160 C. (clarification temperature).

Example 13Ion Conductivity Measurements

(70) The measurements were taken between the upper and lower plate of a plate/plate rheometer using disposable geometries in an oven allowing conductivity measurements up to 250 C. The two parallel plates represent the two electrodes of electrochemical impedance spectroscopy measurements and were connected to the working electrode and to the counter-electrodes of an impedance spectrometer.

(71) The test product was placed on the lower geometry and the upper geometry was descended up to an applied force of 5 N. The system was heated to melt the product while maintaining a force of 5 N, so as to ensure a perfect contact surface between the sample and the electrodes. Gradually as the temperature increased, the measurement gap decreased and the value (displayed digitally on the rheometer) was recorded so as to be able to calculate the ion conductivity. Impedance spectroscopy was performed with an amplitude of 10 mV from 1 MHz to 10 MHz for each temperature.

(72) The results obtained are indicated in FIGS. 8 and 9 (ion conductivity in S/cm as a function of 1000, where T is the temperature in kelvins).

(73) The thermotropic ionic liquid crystal molecules in accordance with the invention 12-LiAN, 12-LiAN, 14-LiAN, 16-LiAN and 16-LiAN have ion conductivity over a broad temperature range, from about 10.sup.9 S/cm at about 60 C. to about 10.sup.5 S/cm at about 200 C.

(74) These thermotropic ionic liquid crystal molecules in accordance with the invention are suitable for use as electrolyte in an electrochemical system, in particular in a lithium battery.