Bis(fluorosulfonyl)imide ionic liquid

Abstract

The present invention relates to a compound of formula (I): TIFF2024504040000020.tif27170 anion and at least one onium cation; The ionic liquid comprises The ionic liquid has a color of less than 115 Hazen units on the APHA scale. The present invention also relates to a method for purifying an ionic liquid comprising an anion of formula (I) and at least one onium cation.

Description

Technical Field

[0001] The present invention relates to an ionic liquid containing a bis(fluorosulfonyl)imide (FSI) anion suitable for use as an electrolyte in a battery, and a method for purifying the ionic liquid.

Background Art

[0002] Lithium (Li) batteries such as lithium-ion batteries are commonly used in electric vehicles as well as in portable and mobile devices.

[0003] A lithium-ion battery or a lithium-sulfur battery includes at least a negative electrode (anode), a positive electrode (cathode), an electrolyte, and preferably a separator. The electrolyte generally consists of a lithium salt dissolved in a solvent that is usually a mixture of organic solvents in order to achieve a good balance between the viscosity and the dielectric constant of the electrolyte.

[0004] Additives can be added to improve the stability of the electrolyte salt or the passivation layer. In fact, the passivation layer formed during the first charge / discharge cycle of the battery is extremely important for the battery life. The passivation layers that can be mentioned include, in particular, passivated aluminum, which is generally a current collector used in the cathode, and the solid electrolyte interface (SEI), which is an inorganic and polymer layer formed at the anode / electrolyte interface and the cathode / electrolyte interface. The stability of these interfaces is a substantial challenge for improving battery life.

[0005] Another major challenge is to improve the overall battery safety, especially for electric vehicle applications. In fact, the flammability of the solvents used in the electrolyte is a problem. There are various solutions for avoiding the flammability of the electrolyte, such as the use of fluorinated solvents or ionic liquids.

[0006] The use of fluorinated solvents has the disadvantage of reducing the ionic conductivity of the electrolyte. Ionic liquids do not have this drawback, but a considerable amount of ionic liquid must be used to make the electrolyte non-flammable. Under these conditions, it is especially important to use an ionic liquid that exhibits good electrochemical stability in order to obtain a battery with sufficient lifespan.

[0007] Ionic liquids can be used for applications other than lithium batteries.

[0008] International Publication No. 2016 / 049391 describes ionic liquids, particularly for surface treatment and cleaning.

[0009] International Publication No. 99 / 40025 relates to low-melting-point ionic compounds in which the cation is an onium cation and the anion is an imide ion.

[0010] Therefore, it is truly necessary to provide ionic liquids with improved electrochemical stability, thereby enabling the creation of batteries with extended lifespan. [Overview of the Initiative]

[0011] The present invention first relates to formula (I): [ka] The anion and At least one onium cation, Regarding ionic liquids containing, The ionic liquid has a color of less than 115 Hazen units on the APHA scale.

[0012] In some embodiments, the onium cation is a quaternary ammonium ion, a pyridinium ion, an imidazolium ion, an oxazolidinium ion, a piperidinium ion, and / or a phosphonium ion.

[0013] In some embodiments, the ionic liquid has a color of 100 Hasen units or less on the APHA scale, preferably 75 Hasen units or less, more preferably 50 Hasen units or less, even more preferably 25 Hasen units or less, and even more preferably 20 Hasen units or less.

[0014] In some embodiments, the ionic liquid essentially consists of an anion of formula (I) and an onium cation.

[0015] In some embodiments, the ionic liquid is 0-20 ppm F - Ions, 0-20 ppm Cl - Ions, 0-50 ppm SO4 2- Ions, 0-20 ppm Na + Ions and K at 0-20 ppm + It contains even more ions.

[0016] The present invention also relates to a method for purifying ionic liquids, and this method is described below. Equation (I): [ka] A step of supplying an initial ionic liquid containing an anion and an onium cation, The process involves contacting the initial ionic liquid with activated carbon to recover the decolorized ionic liquid, The process involves washing the decolorizing ionic liquid with aqueous solution at least once, The process of recovering the purified ionic liquid, Includes.

[0017] In some embodiments, the initial ionic liquid has a color of 115 Hazen units or more on the APHA scale.

[0018] In some embodiments, the purified ionic liquid has a color of less than 115 Hazen units on the APHA scale.

[0019] In some embodiments, the initial ionic liquid is preferably dissolved in a polar organic solvent selected from the group consisting of esters, ethers, nitriles, carbonates, and mixtures thereof.

[0020] In some embodiments, the activated carbon is 300m 2 It has a specific surface area of ​​1 / g or more.

[0021] In some embodiments, the mass ratio of activated carbon to the initial ionic liquid is 0.05 to 0.5.

[0022] In some embodiments, the aqueous washing step includes contacting a decolorizing ionic liquid dissolved in a non-water-soluble polar organic solvent with a large amount of desalinated water.

[0023] The present invention also relates to ionic liquids obtained by the above method.

[0024] The present invention also relates to an electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte, wherein the electrolyte contains the above-mentioned ionic liquid.

[0025] The present invention also relates to a battery comprising at least one of the above-described electrochemical cells.

[0026] The present invention makes it possible to satisfy the above-mentioned needs. More specifically, it provides an ionic liquid that exhibits improved electrochemical stability, which can be used, for example, in the manufacture of longer-lasting electrochemical cells present in batteries.

[0027] This is achieved by ionic liquids with a color value of less than 115 Hazen units on the APHA scale. Surprisingly, it has been found that ionic liquids based on FSI anions and onium cations, with color values ​​strictly less than 115 Hazen units, can possess the electrochemical properties necessary for use in Li-ion batteries. While we do not wish to be bound by any theory, if an ionic liquid has a color value greater than 115 Hazen units, it is thought that the coloring impurities present in the ionic liquid, which are responsible for its color, trigger secondary reactions when the ionic liquid is used in an electrolyte. These secondary reactions are characterized by a high oxidation current in Li-ion batteries and cause a decrease in capacity over time. By removing at least some of the coloring impurities, secondary reactions can be reduced, and the battery life can be improved.

[0028] The present invention also provides a method for obtaining ionic liquids exhibiting the above-mentioned advantages.

[0029] This is achieved by a combination of activated carbon decolorization of the ionic liquid and at least one aqueous wash. The reason for doing this is that while treating the ionic liquid with activated carbon can reduce the level of coloring impurities, impurities are introduced into the ionic liquid. Therefore, these impurities are removed or reduced by the aqueous wash of the ionic liquid. [Brief explanation of the drawing]

[0030] [Figure 1] The flash point (y axis, °C) of the composition described in Example 1 is shown as a function of the mass percentage (x axis, mass%) of the ionic liquid EMIM:FSI in the composition. [Figure 2]The ionic conductivity (y-axis, mS / cm) of the electrolyte described in Example 1, as a function of the mass percentage x (x-axis, mass%) of the ionic liquid EMIM:FSI in the composition, is shown for the following electrolytes: an electrolyte containing 3 / 7 volume ratio EC / EMC mixture (100-x)% and 0.7 mol / L concentration LiFSI (curve A), an electrolyte containing 3 / 7 volume ratio EC / EMC mixture (100-x)% and 0.8 mol / L concentration LiFSI (curve B), an electrolyte containing 3 / 7 volume ratio EC / EMC mixture (100-x)% and 0.9 mol / L concentration LiFSI (curve C), and an electrolyte containing 3 / 7 volume ratio EC / EMC mixture (100-x)% and 1 mol / L concentration LiFSI (curve D). [Modes for carrying out the invention]

[0031] The present invention will be described in more detail, without limitation, in the following description.

[0032] Unless otherwise specified, all percentages and proportions are mass percentages and mass proportions, and all ratios of two quantities are mass ratios.

[0033] Ionic liquid The present invention first relates to formula (I): [ka] The anion and One or more onium cations, This concerns ionic liquids that include [specific components / liquids].

[0034] An ionic liquid is a salt having a melting temperature of less than 100 °C, preferably less than room temperature (i.e., a temperature in the range of 15 to 35 °C). Thus, an "ionic liquid" refers to a salt that exists in liquid form at 100 °C, i.e., an ionic compound containing at least an anion and a cation. An ionic liquid contains only ionic species (cations and anions), excluding the possibility of the presence of non-ionic impurities. Thus, in the context of the present invention, an ionic liquid contains at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, more preferably at least 99% by weight, still more preferably at least 99.5% by weight, and still more preferably 99.9% by weight or more of ionic species.

[0035] The anion of formula (I) is a bis(fluorosulfonyl)imide anion, also referred to as the FSI anion.

[0036] The ionic liquid according to the present invention contains at least one onium ion as a cation. The onium ion is preferably selected from the group consisting of a quaternary ammonium ion, a pyridinium ion, an imidazolium ion, an oxazolidinium ion, a piperidinium ion, a phosphonium ion, and mixtures thereof.

[0037] The quaternary ammonium ion is preferably an ion of the formula NR4 + wherein R represents an alkyl chain having 1 to 14 carbon atoms, optionally containing one or more heteroatoms such as heteroatoms N, O, S, and / or Si.

[0038] "Pyridinium ion" means an ion of the formula C5H5NH + and derivatives thereof, i.e., an ion of the formula C5H5NH in which one or more hydrogen atoms are substituted with a group, preferably an alkyl chain optionally containing one or more heteroatoms such as heteroatoms N, O, S, and / or Si, more preferably an alkyl chain containing 1 to 14 carbon atoms. + of the formula C5H5NH.

[0039] "Imidazolium ion" means an ion of the formula C3H5N2+ Ions and derivatives thereof, i.e., C3H5N2, in which one or more hydrogen atoms are substituted with groups, preferably alkyl chains containing one or more heteroatoms such as heteroatoms N, O, S and / or Si, more preferably alkyl chains containing 1 to 14 carbon atoms. + It means the ion.

[0040] The "oxazolidinium ion" is represented by the formula C3H8NO + Ions and derivatives thereof, i.e., C3H8NO3, in which one or more hydrogen atoms are substituted with groups, preferably alkyl chains containing one or more heteroatoms such as heteroatoms N, O, S and / or Si, more preferably alkyl chains containing 1 to 14 carbon atoms. + It means the ion.

[0041] The "piperidinium ion" is represented by the formula C5H 12 N + C5H ions and derivatives thereof, i.e., C5H ions in which one or more hydrogen atoms are substituted with groups, preferably alkyl chains containing one or more heteroatoms such as heteroatoms N, O, S and / or Si, more preferably alkyl chains containing 1 to 14 carbon atoms. 12 N + It means the ion.

[0042] The "phosphonium ion" is represented by formula PR'4 + This represents an ion, where R' represents an alkyl chain of preferably 1 to 14 carbon atoms, optionally containing one or more heteroatoms such as N, O, S and / or Si.

[0043] The ionic liquid may essentially consist of the anion of formula (I) and one (or more) onium cations, meaning that the anion of formula (I) and one (or more) onium cations may be present in an amount of 90% by weight or more, preferably 95% by weight or more, more preferably 98% by weight or more, more preferably 99% by weight or more, even more preferably 99.5% by weight or more, and even more preferably 99.9% by weight or more, relative to the total weight of the ionic liquid.

[0044] In some embodiments, the ionic liquid may contain one or more other anions and / or one or more other cations.

[0045] The ionic liquid of the present invention contains, in addition to the anion of formula (I), Cl - , Br - , I - NO3 - , M(R 1 )4 - , A(R 1 )6 - , R 2 O2 - [R 2 ONZ 1 ] - [R 2 YOCZ 2 Z 3 ]-,4,5-dicyano-1,2,3-triazole,3,5-bis(R F The product may also contain at least one other anion selected from )-1,2,4-triazole, tricyanomethane, pentacyanocyclopentadiene, pentakis(trifluoromethyl)cyclopentadiene, derivatives of barbituric acid and meldrumic acid, and their substituted products, where, M is B, Al, Ga, or Bi. A is P, As, or Sb. R 1 It is a halogen, R 2This represents an H, F, alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, dialkylamino, alkoxy, or thioalkoxy group, each having 1 to 18 carbon atoms, being unsubstituted or substituted with one or more oxa, thia, or aza substituents, with one or more hydrogen atoms optionally replaced by halogens in a proportion of 0 to 100%, and may form part of a polymer chain. Y is C, SO, S=NCN, S=C(CN)2, POR 2 P(NCN)R 2 P(C(CN)2)R2, alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl or alkenylaryl group having 1 to 18 carbon atoms and optionally substituted with one or more oxa, thia or aza substituents, or dialkylamino group N(R 1 ) 2 This represents, Z 1 From Z 3 R is independent 2 , R 2 Representing YO or CN, this group may be capable of forming part of a polymer chain.

[0046] Advantageously, ionic liquids have a concentration of 0-20 ppm F - Ions and / or 0-20 ppm Cl - Ions and / or 0-50 ppm of SO4 2 -ions, and / or 0-20 ppm of Na + Ions and / or 0-20 ppm of K + Contains ions.

[0047] The ionic liquid according to the present invention has a color of less than 115 Hazen units on the APHA scale (also known as the Hazen scale, platinum-cobalt scale, or Pt-Co scale). The color of the ionic liquid may be determined by spectrophotometric measurement in accordance with ISO 6271:2015.

[0048] More preferably, the ionic liquid has a color of 100 Hazen units or less on the APHA scale, more preferably 75 Hazen units or less, more preferably 50 Hazen units or less, more preferably 25 Hazen units or less, and even more preferably 20 Hazen units or less. In some embodiments, the color of the ionic liquid may be 1 to 5 Hazen units, or 5 to 10 Hazen units, or 10 to 15 Hazen units, or 15 to 20 Hazen units, or 20 to 25 Hazen units, or 25 to 30 Hazen units, or 30 to 35 Hazen units, or 35 to 40 Hazen units, or 40 to 45 Hazen units, or 45 to 50 Hazen units, or 50 to 60 Hazen units, or 60 to 70 Hazen units, or 70 to 80 Hazen units, or 80 to 90 Hazen units, or 90 to 100 Hazen units, or 100 to 110 Hazen units, or less than 110 to 115 Hazen units on the APHA scale.

[0049] Method for preparing ionic liquids An ionic liquid containing the anion of formula (I) and at least one onium cation is as follows: The process of supplying the salt of the FSI anion, A process of supplying the salt of the onium cation, A step to obtain an ionic liquid containing an FSI anion and an onium cation by combining a salt of an FSI anion and a salt of an onium cation, It may be prepared by [method].

[0050] Therefore, ionic liquids can be synthesized by exchange reactions according to the following diagram. [ka] Here, TIFF0007853304000005.tif7170 is an onium cation, TIFF0007853304000006.tif7170 is a cation, TIFF0007853304000007.tif6170 is an anion.

[0051] TIFF0007853304000008.tif7170 may, in particular, represent a hydrogen cation, or an alkali metal or alkaline earth metal cation, or a quaternary ammonium cation. This could be, for example, hydrogen, lithium, sodium, potassium, or ammonium (NH4). + ) A cation may also be used.

[0052] TIFF0007853304000009.tif6170 is, for example, Cl - , Br - BF4 - F - CH3COO - , OH - NO3 - Or I - It may be an anion or a sulfonate anion.

[0053] The reaction may be carried out, for example, in water, a polar organic solvent, or a mixture of polar organic solvents.

[0054] Therefore, preferably, the salt of the FSI anion is supplied in the form of a solution of the salt of the FSI anion in water, an organic solvent such as nitromethane, or a mixture of polar organic solvents.

[0055] Preferably, the onium cation salt is supplied in the form of a solution of the onium cation salt in water, an organic solvent such as nitromethane, or a mixture of polar organic solvents.

[0056] An ionic liquid containing FSI anions and onium cations is purified to obtain an anionic TIFF0007853304000010.tif7170 and cationic TIFF0007853304000011.tif7170 Impurities may be removed.

[0057] For example, this method comprises one or more steps of dissolving a combination of an FSI anion salt and an onium cation salt in an organic solvent such as butyl acetate, and washing with an aqueous solution, preferably water, wherein the ionic liquid is present in the organic phase and the anionic TIFF0007853304000012.tif6170 and cationic TIFF0007853304000013.tif6170 This may include a step in which impurities are present in the aqueous phase. The organic phase may then be evaporated, preferably under reduced pressure, to recover the ionic liquid.

[0058] Before dissolving the combination of the FSI anion salt and the onium cation salt in an organic solvent, the combination may be subjected to an evaporation step, preferably under reduced pressure, to remove the reaction solvent.

[0059] Before or after dissolving the combination of the FSI anion salt and the onium cation salt in an organic solvent, the combination may be filtered through, for example, a PTFE (polytetrafluoroethylene) membrane.

[0060] Method for purifying ionic liquids The present invention also relates to a method for purifying ionic liquids. This method is as follows: Equation (I): [ka] A step of supplying an initial ionic liquid containing an anion and an onium cation, The process involves contacting the initial ionic liquid with activated carbon to recover the decolorized ionic liquid, The process involves washing the decolorizing ionic liquid with aqueous solution at least once, The process of recovering the purified ionic liquid, Includes.

[0061] This process can reduce the amount of colored impurities in the ionic liquid.

[0062] A "decolorized ionic liquid" refers to an ionic liquid that, when measured on an APHA scale, has a lower color than the ionic liquid before the step of contacting it with activated carbon.

[0063] "Purified ionic liquid" refers to an ionic liquid in which the molar concentration ratio of [liquid salt of the anion and onium cation of formula (I)] / [total impurities] is greater than that of the decolorized ionic liquid before washing.

[0064] The onium cation may be one of those described in a previous paragraph.

[0065] The initial ionic liquid may essentially consist of the anion of formula (I) and the onium cation, as described in the previous paragraph, and / or may contain one or more other anions and / or one or more other cations.

[0066] The purified ionic liquid preferably has a color of less than 115 Hasen units on the APHA scale. The color of the ionic liquid may be measured as described above. More preferably, the purified ionic liquid has a color of 100 Hasen units or less on the APHA scale, more preferably 75 Hasen units or less, more preferably 50 Hasen units or less, more preferably 25 Hasen units or less, and even more preferably 20 Hasen units or less. In particular, the color of the purified ionic liquid may be less than 1-5 Hazen units, or 5-10 Hazen units, or 10-15 Hazen units, or 15-20 Hazen units, or 20-25 Hazen units, or 25-30 Hazen units, or 30-35 Hazen units, or 35-40 Hazen units, or 40-45 Hazen units, or 45-50 Hazen units, or 50-60 Hazen units, or 60-70 Hazen units, or 70-80 Hazen units, or 80-90 Hazen units, or 90-100 Hazen units, or 100-110 Hazen units, or less than 110-115 Hazen units on the APHA scale.

[0067] The color of the decolorizing ionic liquid is preferably as described above.

[0068] The initial ionic liquid may be obtained as described in the previous paragraph.

[0069] The initial ionic liquid preferably has a color of 115 Hazen units or more on the APHA scale. It may also have a color of 120 Hazen units, or 140 Hazen units, or 160 Hazen units, or 180 Hazen units, or 200 Hazen units, or 220 Hazen units, or 240 Hazen units, or 260 Hazen units, or 280 Hazen units, or 300 Hazen units, or 320 Hazen units, or 340 Hazen units, or 360 Hazen units, or 380 Hazen units, or 400 Hazen units or more on the APHA scale.

[0070] The initial ionic liquid may be supplied dissolved in a polar organic solvent (or a mixture of polar organic solvents). The polar organic solvent may be classified as an ester, ether, nitrile, carbonate, ketone, or a combination thereof. Examples of polar organic solvents suitable for the method according to the present invention are butyl acetate, ethyl acetate, tert-butyl acetate, acetonitrile, butyronitrile, isobutyronitrile, glutalonitrile, diethyl ether, cyclopentyl methyl ether, tetrahydrofuran, methyl isobutyl ketone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate. The mass ratio of the ionic liquid to the polar organic solvent may be advantageously 0.001 to 100, preferably 0.01 to 10, for example, 0.001 to 0.01, or 0.01 to 0.1, or 0.1 to 1, or 1 to 10, or 10 to 100.

[0071] Alternatively, the initial ionic liquid may be brought into contact with activated carbon only, that is, without being combined with a solvent beforehand.

[0072] Contact of the initial ionic liquid with activated carbon may be carried out, for example, by mixing the activated carbon into the ionic liquid. The mass ratio of activated carbon to the ionic liquid is advantageously 0.05 to 0.5, preferably 0.1 to 0.5. In particular, this ratio may be 0.05 to 0.1, or 0.1 to 0.2, or 0.2 to 0.3, or 0.3 to 0.4, or 0.4 to 0.5.

[0073] Activated carbon is preferably 300 m 2 Specific surface area exceeding / g, for example, 350m² 2 / g or more, or 400m 2 / g or more, or 500m 2 / g or more, or 600m 2 / g or more, or 800m 2 / g or more, or 1000m 2 It has a specific surface area greater than / g. The specific surface area of ​​activated carbon can be measured by the BET method. The specific surface area of ​​the powder is estimated from the boiling point of liquid nitrogen and the amount of nitrogen adsorbed relative to its pressure under standard atmospheric pressure. The data are interpreted according to the Brunauer, Emmett, and Teller model (BET method).

[0074] The contact time between the ionic liquid and the activated carbon may be 1 to 72 hours, preferably 5 to 48 hours. In some embodiments, the contact time between the ionic liquid and the activated carbon is 1 to 5 hours, or 5 to 12 hours, or 12 to 24 hours, or 24 to 36 hours, or 36 to 48 hours, or 48 to 72 hours.

[0075] The step of contacting the initial ionic liquid with activated carbon may be carried out at a temperature ranging from 10°C to below the boiling point of the polar organic solvent, for example, room temperature (i.e., 15-35°C), if the initial ionic liquid is dissolved in a polar organic solvent.

[0076] The step of contacting the initial ionic liquid with activated carbon is advantageously carried out at a temperature higher than the melting point of the ionic liquid when it comes into contact with activated carbon alone.

[0077] At the end of the activated carbon treatment process, the activated carbon is advantageously separated from the decolorized ionic liquid by filtration, for example, using a PTFE membrane, or via a poly(vinylidene fluoride) (PVDF) membrane, or via a cellulose membrane, or via a filtration medium (silica, alumina, diatomaceous earth).

[0078] If the ionic liquid that has come into contact with the activated carbon is dissolved in a polar organic solvent, this solvent can be removed after the activated carbon contact step, or preferably after separating the activated carbon from the decolorized ionic liquid. Removal may be carried out, for example, by evaporation of the solvent, preferably under reduced pressure.

[0079] Alternatively, (for example, if this solvent is not water-soluble) polar organic solvents are not removed.

[0080] A "water-insoluble solvent" refers to a solvent whose solubility in water at 25°C is less than 10% by weight. The solubility of a solvent can be measured by gradually adding the solvent to a large amount of water until separation is observed.

[0081] The decolorizing ionic liquid is subjected to one or more aqueous washes. "Aqueous wash" means bringing the ionic liquid into contact with an aqueous solution, preferably water, and more preferably desalinated water.

[0082] It is particularly preferable that the ionic liquid, which is washed with aqueous solution once or multiple times, is dissolved in a water-insoluble polar organic solvent. In particular, if the ionic liquid is brought into contact with activated carbon without being dissolved in a solvent, or if the solvent is removed after the activated carbon contact step, the ionic liquid is dissolved in a water-insoluble polar organic solvent. Alternatively, the water-insoluble polar organic solvent in which the ionic liquid is dissolved for aqueous washing may be the polar organic solvent in which the ionic liquid was dissolved for the activated carbon contact step. The water-insoluble polar organic solvent is selected from the group consisting of butyl acetate, ethyl acetate, tert-butyl acetate, butyronitrile, isobutyronitrile, glutaronitrile, diethyl ether, cyclopentyl methyl ether, tetrahydrofuran, methyl isobutyl ketone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate.

[0083] One or more aqueous washes can reduce and remove impurities present in the decolorized ionic liquid, particularly those generated by the process of treating the ionic liquid with activated carbon, such as chloride ions, fluoride ions, sodium ions, and / or potassium ions.

[0084] During each aqueous wash, the mass ratio of the aqueous washing solution, preferably demineralized water, to the ionic liquid is preferably 0.01 to 1, for example, 0.01 to 0.05, or 0.05 to 0.1, or 0.1 to 0.5, or 0.5 to 1.

[0085] The contact time between the ionic liquid and the aqueous cleaning solution may vary from 10 minutes to 5 hours. In particular, this time may be 10 minutes to 30 minutes, or 30 minutes to 1 hour, or 1 hour to 2 hours, or 2 hours to 3 hours, or 3 hours to 4 hours, or 4 hours to 5 hours.

[0086] Next, the aqueous phase is advantageously separated from the organic phase by decanting. The organic phase is rich in ionic liquids and devoid of impurities (e.g., chloride ions, fluoride ions, sodium ions, and / or potassium ions), meaning that in the organic phase, the molar concentration ratio of ionic liquids to impurities (more specifically, chloride, fluoride, sodium, and / or potassium ions) is greater than the molar concentration ratio of the decolorizing ionic liquid. The aqueous phase is rich in impurities (e.g., rich in chloride, fluoride, sodium, and / or potassium ions), meaning that in the aqueous phase, the molar concentration ratio of ionic liquids to impurities (more specifically, chloride, fluoride, sodium, and / or potassium ions) is smaller than the molar concentration ratio of the decolorizing ionic liquid.

[0087] Next, the aqueous phase may be removed.

[0088] Several aqueous washes, particularly 2 to 11 aqueous washes (for example, 2, 3, 4, 5, or 10 washes), may be performed. If several washes are performed, each may be performed independently as described above. Subsequent washes are preferably performed on the organic phase obtained after the final decant of the previous wash.

[0089] The solvent in the organic phase may be removed, for example, by evaporation of the solvent, preferably under reduced pressure. A purified ionic liquid is obtained.

[0090] The present invention also relates to ionic liquids that can be obtained or obtained by the above-described method.

[0091] Electrochemical cells and batteries The present invention also relates to an electrolyte comprising the above-mentioned ionic liquid and at least one other component selected from metal salts, polar polymers and / or aprotic solvents.

[0092] The metal salt preferably contains hydrogen cations, alkali metal cations, alkaline earth metal cations, transition metal cations, or rare earth cations as cations, with lithium being particularly preferred.

[0093] As a non-limiting example, lithium salts (or multiple lithium salts) can be selected from LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), LiPOF2, LiB(C2O4)2, LiF2B(C2O4)2, LiBF4, LiNO3, or LiClO4.

[0094] The polar polymers preferably include monomer units derived from ethylene oxide, propylene oxide, epichlorohydrin, epifluorohydrin, trifluoroepoxypropane, acrylonitrile, methacrylonitrile, esters and amides of acrylic and methacrylic acids, vinylidene fluoride, N-methylpyrrolidone, and / or polycationic or polyanionic polymer electrolytes. If the electrolyte composition contains multiple polymers, at least one of them may be crosslinked.

[0095] One or more aprotic solvents can be selected from the following, non-exclusively listed, namely ethers, esters, ketones, alcohols, nitriles, carbonates, amides, sulfamides and sulfonamides, and mixtures thereof.

[0096] Examples of ethers include linear or cyclic ethers, such as dimethoxyethane (DME), methyl ethers of oligoethylene glycols with 2 to 5 oxyethylene units, dioxolane, dioxane, dibutyl ether, tetrahydrofuran, and mixtures thereof.

[0097] Examples of esters include phosphate esters or sulfite esters. For example, methyl formate, methyl acetate, methyl propionate, ethyl acetate, butyl acetate, gamma-butyrolactone, or mixtures thereof.

[0098] Among ketones, cyclohexanone is a particularly noteworthy example.

[0099] Examples of alcohols include ethyl alcohol or isopropyl alcohol.

[0100] Examples of nitriles include acetonitrile, pyronitrile, propionitrile, methoxypropionitrile, dimethylaminopropionitrile, butyronitrile, isobutyronitrile, valeronitrile, pivalonitrile, isovaleronitrile, glutaronitrile, methoxyglutaronitrile, 2-methylglutaronitrile, 3-methylglutaronitrile, adiponitrile, malononitrile, 1,2,6-tricyanohexane, and mixtures thereof.

[0101] Among carbonates, for example, ethylene carbonate (EC) (CAS: 96-49-1), propylene carbonate (PC) (CAS: 108-32-7), butylene carbonate (BC) (CAS: 4437-85-8), dimethyl carbonate (DMC) (CAS: 616-38-6), diethyl carbonate (DEC) (CAS: 105-58-8), ethyl methyl carbonate (EMC) (CAS: 623-53-0), diphenyl carbonate (CAS: 102-09-0), methylphenyl carbonate Examples of cyclic carbonates include tetrapropyl carbonate (CAS: 13509-27-8), dipropyl carbonate (DPC) (CAS: 623-96-1), methylpropyl carbonate (MPC) (CAS: 1333-41-1), ethylpropyl carbonate (EPC), vinylene carbonate (VC) (CAS: 872-36-6), fluoroethylene carbonate (FEC) (CAS: 114435-02-8), trifluoropropylene carbonate (CAS: 167951-80-6), or mixtures thereof.

[0102] Examples of amides include dimethylformamide and N-methylpyrrolidinone.

[0103] The aprotic solvent is more preferably selected from EC, EMC, a mixture of EC and EMC, a mixture of EC and DMC, a mixture of EC and DEC, PC, and a mixture of EC, DMC, and EMC.

[0104] The electrolyte preferably comprises or consists of an ionic liquid as described above, one or more lithium salts (as described above) dissolved in a solvent or a mixture of solvents (as described above), and optionally one or more additives.

[0105] One or more additives may be selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate, 4-vinyl-1,3-dioxolan-2-one, pyridazine, vinylpyridazine, quinoline, vinylquinoline, butadiene, sebaconitrile, alkyl disulfide, fluorotoluene, 1,4-dimethoxytetrafluorotoluene, t-butylphenol, di(t-butyl)phenol, tris(pentafluorophenyl)borane, oxime, aliphatic epoxide, halogenated biphenyl, methacrylic acid, allyl ethyl carbonate, vinyl acetate, divinyl adipate, propanesultone, acrylonitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonate, vinyl and / or 2-cyanofuran compounds.

[0106] Advantageously, the ionic liquid is present in the electrolyte in an amount of 10% to 90% by weight, preferably 20% to 80% by weight, and more preferably 40% to 80% by weight, relative to the total weight of the electrolyte. In some embodiments, the electrolyte may contain 10% to 20% by weight, or 20% to 30% by weight, or 30% to 40% by weight, or 40% to 50% by weight, or 50% to 60% by weight, or 60% to 70% by weight, or 70% to 80% by weight, or 80% to 90% by weight, relative to the total weight of the electrolyte.

[0107] The present invention also relates to an electrochemical cell comprising an electrolyte containing the above-mentioned ionic liquid. The electrochemical cell also comprises a negative electrode (or anode) and a positive electrode (or cathode).

[0108] Electrochemical cells may also include a separator impregnated with an electrolyte.

[0109] The electrolytes can be as described above.

[0110] The term "negative electrode" refers to the electrode that acts as the anode when the cell is conducting current (i.e., discharging) and as the cathode when the cell is charging.

[0111] The negative electrode typically comprises an electrochemical active material, optionally a conductive material, and optionally a binder.

[0112] The term "positive electrode" refers to the electrode that acts as the cathode when the cell is conducting current (i.e., discharging) and as the anode when the cell is charging.

[0113] The positive electrode typically comprises an electrochemical active material, optionally a conductive material, and optionally a binder.

[0114] The term "electrochemically active material" is understood to mean a material into which ions can be reversibly inserted.

[0115] The term "conductive material" is understood to mean a material that can conduct electrons.

[0116] The negative electrode of an electrochemical cell is particularly made of graphite, lithium, lithium alloy, or Li4Ti5O as the electrochemical active material. 12 It may contain lithium titanate or titanium oxide (TiO2), silicon or lithium-silicon alloys, tin oxide, lithium intermetallic compounds, or mixtures thereof.

[0117] When the negative electrode contains lithium, the lithium can be in the form of a film of metallic lithium or an alloy containing lithium. Among the lithium-based alloys that can be used, for example, lithium-aluminum alloy, lithium-silica alloy, lithium-tin alloy, Li-Zn, Li3Bi, Li3Cd, and Li3SB can be mentioned. As an example of the negative electrode, it can include an active lithium film produced by rolling a strip of lithium between rollers.

[0118] The positive electrode contains an oxide-based electrochemically active material. Preferably, lithium iron phosphate (Li x FePO4, 0 < x < 1), or a lithium / nickel / manganese / cobalt composite oxide with a high nickel content (LiNi x Mn y Co z O2, where x + y + z = 1, abbreviated as NMC, and x > y and x > z), or a lithium / nickel / cobalt / aluminum composite oxide with a high nickel content (LiNi x’ Co y’ Al z , where x' + y' + z' = 1, abbreviated as NCA, and x' > y' and x' > z').

[0119] Specific examples of these oxides are NMC532 (LiNi 0.5 Mn 0.3 Co 0.2 O2), NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) and NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O2).

[0120] Mixtures of these oxides can be used. The above oxide materials, when appropriate, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium / manganese composite oxide (such as Li x Mn2O4 or Li x M n O2), lithium / nickel oxide composition (such as Li xNiO2), a lithium / cobalt oxide composition (e.g., Li x CoO2), a lithium / nickel / cobalt composite oxide (e.g., LiNi 1-y Co y O2), a lithium and transition metal composite oxide, a lithium / manganese / nickel composite oxide with a spinel structure (e.g., Li x Mn 2-y Ni y O4), vanadium oxide, NMC and NCA oxides with a low nickel content, and can be combined with other oxides such as mixtures thereof.

[0121] Preferably, the NMC or NCA oxide with a high nickel content corresponds to at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, and more preferably essentially all of the oxide material present in the positive electrode as an electrochemically active material.

[0122] Alternatively or additionally, the positive electrode may contain sulfur, Li2S, O2, and / or LiO2 as an electrochemically active material.

[0123] The material of each electrode can also contain, in addition to the electrochemically active material, a conductive material such as, for example, carbon black, Ketjen (registered trademark) carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (e.g., vapor-grown carbon fibers or VGCF), non-powdery carbon obtained by carbonization of an organic precursor, or a carbon source containing a combination of two or more of these. A lithium salt, or other additives such as inorganic particles of ceramics or glasses, or other compatible active substances (e.g., sulfur) can also be present in the material of the positive electrode.

[0124] The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched and / or crosslinked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO) or poly(propylene oxide) (PPO), or mixtures thereof (or EO / PO copolymers), which may include crosslinkable units), water-soluble binders (e.g., SBR (styrene / butadiene rubber), NBR (acrylonitrile / butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluoropolymer binders (e.g., PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene)), and combinations thereof. Some binders, such as those that are water-soluble, may also include additives such as CMC (carboxymethylcellulose).

[0125] The separator may be a porous polymer membrane. In non-limiting examples, the separator may consist of a porous polyolefin membrane such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, or a multilayer structure of the above polymers. Alternatively, the separator may consist of glass fibers.

[0126] The present invention also relates to a battery comprising at least one, preferably two or more of the above-described electrochemical cells. The electrochemical cells can be assembled in series and / or parallel within the battery.

[0127] Other uses The ionic liquid according to the present invention may also be used in the electrolyte of an electrochromic light modulation system comprising at least one electrochromic material. In such a system, the electrochromic material is advantageously deposited on a layer of a semiconductor transparent in the visible range, preferably tin oxide or an indium oxide derivative, on a glass or polymer substrate. Examples of preferred electrochromic materials include molybdenum, tungsten, titanium, vanadium, niobium, cerium, and tin oxide, as well as mixtures thereof. The electrochromic material may be dissolved in the electrolyte.

[0128] The ionic liquid according to the present invention may also be used in a composition as a reaction medium for chemical or electrochemical reactions, preferably Diels-Alder reactions, Friedel-Crafts reactions, mixed aldol reactions, condensation and polymerization reactions, and nucleophilic and electrophilic substitutions. If the ionic liquid contains a chiral onium cation, the ionic liquid may also be used in a composition as a reaction medium for enantioselective reactions.

[0129] The ionic liquid according to the present invention may also be used for surface treatment, for example, cleaning the surface. [Examples]

[0130] The following examples will be described without limiting the present invention.

[0131] Example 1 - Effect of the presence of ionic liquid in electrolytes flash point An ionic liquid of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM:FSI) having a color of 20 Hazen units was prepared as described in Example 2.

[0132] EMIM:FSI was added in various mass ratios to a carbonate mixture (EC / EMC with a volume ratio of 3 / 7) conventionally used in lithium-ion battery electrolytes.

[0133] For each proportion of EMIM:FSI, the flash point of the composition was measured according to ISO 3679.

[0134] The results are shown in Figure 1.

[0135] It has been observed that adding the ionic liquid EMIM:FSI to a composition increases its flash point, thus suppressing the flammability of the battery electrolyte. Furthermore, when the amount of EMIM:FSI is 70% or more, the composition achieves a sufficient flash point to allow for a change in classification in the context of transport regulations (the upper limit of the flash point for flammable products under transport regulations is set at 60°C). Therefore, at such amounts, it is important that the ionic liquid has good electrochemical stability.

[0136] Ionic conductivity Various electrolytes were prepared, each containing various mass proportions of ionic liquid EMIM:FSI in a carbonate mixture (EC / EMC in a volume ratio of 3 / 7), and also containing various concentrations of LiFSI (0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L).

[0137] For each electrolyte prepared in this manner, the ionic conductivity of the electrolyte was determined by impedance spectroscopy. To this end, a conductive cell was immersed in each solution, and impedance spectroscopy measurements were performed three times. These spectroscopic measurements were performed at 500 mHz to 100 kHz with an amplitude of 10 mV. The cell constant used was 1.12, and the ionic conductivity σ was calculated according to the following formula.

number

[0138] The results are shown in Figure 2.

[0139] It has been observed that adding EMIM:FSI to an electrolyte can significantly increase its ionic conductivity. Furthermore, optimal conductivity can be obtained for a considerable proportion of ionic liquids. Therefore, it is essential to use ionic liquids with good electrochemical stability and thus high purity.

[0140] This embodiment demonstrates the importance of obtaining high-purity usable ionic liquids, considering that the electrolyte must contain a very large amount of ionic liquid to obtain better conductivity and lower flammability.

[0141] Example 2 - Preparation of Ionic Liquid EMIM:FSI In a 250 mL reactor, dissolve 30 g of 1-ethyl-3-methylimidazolium chloride in 60 g of nitromethane. Once the reaction mixture is homogeneous, add a solution of potassium bis(fluorosulfonyl)imide (42.73 g) in 120 g of nitromethane. Allow the reaction mixture to stand for 12 hours while stirring.

[0142] The reaction mixture is filtered through a 0.45 μm PTFE membrane. The filtrate is then evaporated under reduced pressure to remove the residual solvent.

[0143] Next, the resulting residue is diluted with 50 g of butyl acetate. This solution is then brought into contact with 25 g of water. After decanting, the organic phase containing the ionic liquid is recovered, and the aqueous phase is discarded. This washing is repeated three times with the same amount of water. The organic phase is then evaporated under reduced pressure, and the ionic liquid is recovered in a yield of 71% (39.29 g). The color of the obtained ionic liquid is 115 Hazen units. The color of the obtained ionic liquid is measured using a Lico spectrophotometer according to ISO 6271:2015.

[0144] The previously obtained ionic liquid is dissolved in 80 g of butyl acetate. Activated carbon (6 g) is added, and the solution is left to stand for 4 hours while stirring. Next, the carbon is removed by filtration through a 0.45 μm PTFE membrane, and the solution is rinsed three times with 20 g of butyl acetate. The filtrate is then evaporated under reduced pressure, and the ionic liquid is recovered in a yield of 96.65%. The color of the purified ionic liquid is 20 Hasen units. However, the ionic liquid contains cationic and anionic impurities such as chlorides, fluorides, sodium, and potassium.

[0145] Next, further purification is performed. The previously obtained ionic liquid is dissolved in 40 g of butyl acetate. This solution is washed four times with 20 g of water. The aqueous phase is removed, and the organic phase is evaporated under reduced pressure to obtain 29.7 g of ionic liquid having a color of 20 Hazen units.

[0146] Example 3 - Preparation of ionic liquid PYR14:FSI (1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide) In a 1 L reactor, dissolve 120 g of 1-butyl-1-methylpyrrolidinium chloride in 250 g of nitromethane. Once the reaction mixture is homogeneous, add the solution of potassium bis(fluorosulfonyl)imide (140.7 g) in 120 g of nitromethane. Allow the reaction mixture to stand for 24 hours while stirring.

[0147] The reaction mixture is filtered through a 0.45 μm PTFE membrane. The filtrate is then evaporated under reduced pressure to remove the residual solvent.

[0148] Next, the resulting residue is diluted with 200 g of butyl acetate. Then, this solution is brought into contact with 100 g of water. After decanting, the organic phase containing the ionic liquid is recovered, and the aqueous phase is discarded. This washing is repeated three times with the same amount of water. Next, the organic phase is evaporated under reduced pressure, and the ionic liquid is recovered in a yield of 82% (169.9 g). The color of the obtained ionic liquid is 135 Hazen units.

[0149] The previously obtained ionic liquid is dissolved in 250 g of butyl acetate. Activated carbon (30 g) is added, and the solution is left to stand for 20 hours while stirring. Next, the carbon is removed by filtration through a 0.45 μm PTFE membrane, and the mixture is rinsed three times with 100 g of butyl acetate. The filtrate is then evaporated under reduced pressure, and the ionic liquid is recovered in a yield of 94.3%. The color of the purified ionic liquid is 20 Hasen units. However, the ionic liquid contains cationic and anionic impurities such as chlorides, fluorides, sodium, and potassium.

[0150] Next, further purification is performed. The previously obtained ionic liquid is dissolved in 250 g of butyl acetate. This solution is washed four times with 50 g of water. The aqueous phase is removed, and the organic phase is evaporated under reduced pressure to obtain 152.2 g of ionic liquid having a color of 20 Hazen units.

[0151] Example 4 - Color Effects Ionic liquids EMIM:FSI having 115 Hasen units and 20 Hasen units of color were prepared as described in Example 2. Furthermore, a third ionic liquid EMIM:FSI was prepared in the same manner as the ionic liquids with 115 Hasen units of color, except that the step of purifying the starting materials before synthesis was omitted (the ionic liquids with 115 Hasen units and 20 Hasen units of color are obtained by purifying the raw materials by contact with activated carbon and aqueous washing). This third ionic liquid has a color of 360 Hasen units.

[0152] The electrochemical stability of each ionic liquid is determined by cyclic voltammetry. For this purpose, CR2032 button batteries are manufactured. These button batteries consist of a 20mm diameter aluminum foil as the working electrode, an 8mm diameter lithium metal pellet as the reference electrode, and an 18mm diameter glass fiber separator impregnated with 12 drops (0.6mL) of electrolyte consisting of the ionic liquid EMIM:FSI. Next, a voltage sweep is performed at the button battery terminals, and the generated current is measured and recorded. The voltage sweep is performed at 2-5V. The oxidation current is measured in the third cycle. The two preceding sweeps enable the formation of passivation layers such as the SEI (solid-electrolyte interface) and the passivation of aluminum.

[0153] Furthermore, the approximate lifespan of 4mAh batteries containing electrolytes with one of the three ionic liquids mentioned above will also be measured. Lifespan is determined as the number of cycles performed until 80% of the initial capacity is lost. In each cycle, each battery loses a capacity equivalent to the oxidation current of the ionic liquid at 4.3V. When this loss reaches 0.8mAh, the battery is considered to have reached the end of its lifespan.

[0154] The results are shown in the table below (the oxidation current in the table below was measured at 4.3V, which is the conventional operating voltage for Li-ion batteries). [Table 1]

[0155] It has been found that the color of an ionic liquid affects the battery life. In fact, an ionic liquid with 20 Hasen units of color can extend the battery life by 35 times compared to an ionic liquid with 115 Hasen units of color.

[0156] Furthermore, measurements of oxidation current have shown that ionic liquids with a color of 20 Hasen units exhibit better electrochemical stability than ionic liquids with a color of 115 Hasen units.

Claims

1. Equation (I): 【Transformation 6】 The anion and At least one onium cation, 0-20 ppm F- ions, 0-20 ppm Cl- ions, 0-50 ppm SO4 2- ions, 0-20 ppm Na+ ions, and 0-20 ppm K+ ions An ionic liquid containing, The ionic liquid is a liquid having a color of less than 115 Hasen units on the APHA scale.

2. The ionic liquid according to claim 1, wherein the onium cation is a quaternary ammonium ion, a pyridinium ion, an imidazolium ion, an oxazolidinium ion, a piperidinium ion, and / or a phosphonium ion.

3. The ionic liquid according to claim 1 or 2, having a color of 100 Hazen units or less on the APHA scale.

4. The ionic liquid according to any one of claims 1 to 3, wherein the anion of formula (I) and the onium cation are present in an amount of 90% by weight or more relative to the total weight of the ionic liquid.

5. A method for purifying ionic liquids, Equation (I): 【Transformation 7】 A step of supplying an initial ionic liquid containing an anion and an onium cation, The process involves contacting the initial ionic liquid with activated carbon to recover the decolorized ionic liquid, The process involves washing the decolorizing ionic liquid with aqueous solution at least once. A process for recovering a purified ionic liquid having a color of less than 115 Hazen units on the APHA scale, A method that includes this.

6. The method according to claim 5, wherein the initial ionic liquid has a color of 115 Hazen units or more on the APHA scale.

7. The method according to claim 5 or 6, wherein the initial ionic liquid is dissolved in a polar organic solvent or a mixture thereof.

8. The activated carbon is 300 m ２ The method according to any one of claims 5 to 7, having a specific surface area of ​​1 / g or more.

9. The method according to any one of claims 5 to 8, wherein the mass ratio of the activated carbon to the initial ionic liquid is 0.05 to 0.

5.

10. The method according to any one of claims 5 to 9, wherein the aqueous washing step includes contacting the decolorizing ionic liquid dissolved in a non-water-soluble polar organic solvent with a large amount of desalinated water.

11. An electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte, wherein the electrolyte contains an ionic liquid according to any one of claims 1 to 4.

12. A battery comprising at least one electrochemical cell as described in claim 11.

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