Composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole and preparation process

Abstract

The invention relates to a composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) of formula (1) comprising an amount of non-cyclized products of formula (1a) and (1b) less than or equal to 100 ppm by weight, as well as a preparation process.

Description

[0001] Composition comprising a sodium 4,5-dicyano-2-tifluoromethylimidazole salt and method of preparation.

[0002] Scope of the invention

[0003] The present invention relates to a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) salt and a method for its preparation. More particularly, the present invention relates to a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) salt containing less than 100 ppm by weight of uncyclized products of formula (1a) and (1b).

[0004] Technical background

[0005] Sodium-ion (Na-ion) batteries are an alternative to lithium-ion batteries because they are more environmentally friendly. A Na-ion battery consists of at least one negative electrode (anode), one positive electrode (cathode), an electrolyte, and preferably a separator. The electrolyte is usually made from a sodium salt dissolved in a solvent, which may be a mixture of organic solvents, to achieve a good balance between the viscosity and the dielectric constant of the electrolyte.

[0006] The passivation layers formed during the first charge / discharge cycles of a battery are crucial for its lifespan. Examples of passivation layers include the aluminum passivation, which is generally used as the current collector at the cathode, and the solid-electrolyte interface (SEI), which is the inorganic and polymeric layer that forms at the anode / electrolyte and cathode / electrolyte interfaces. The stability of these interfaces is a key factor in improving battery lifespan.

[0007] Regarding the state of the art of Na-ion batteries, reference is made to the following review articles:

[0008] - Hwang et al., Sodium-ion batteries: present and future, in Chem. Soc. Rev., 46:3529-2614 (2017);

[0009] - Chen et al., Readiness Level of Sodium-Ion Battery Technology: A Materials Review, in Adv. Sus. Sys., DOi: 10.1002 / adsu.201700153 (2018);- Eshetu et al., Electrolytes and Interphases in Sodium-Based Rechargeable Batteries: Recent Advances and Perspectives, in Adv. Energy Mater, 10:2000093 (2020).

[0010] Sodium 4,5-dicyano-2-(trifluoromethyl)imidazole (NaTDI) can be used as an additive for sodium-ion battery electrolytes. The resulting electrolytes have high ionic conductivity at room temperature and good electrochemical stability up to 4.5V compared to metal sodium. Furthermore, the NaTDI salt is not corrosive to aluminum.

[0011] We are familiar with document WO 2013 / 072591 A1, which concerns a process for preparing 4,5-dicyano-2-(trifluoromethyl)imidazole, comprising a step of reacting diaminomaleonitrile (DAMN) with a trifluoroacetic acid derivative at a temperature T1, followed by dehydration of the salified compound or the corresponding amine at a temperature T2 higher than T1 to form HTDI. However, the product must have a very low water content and a very low content of impurities harmful to battery operation.

[0012] The NaTDI synthesis process from diaminomaleonitrile generates non-cyclized impurities containing labile protons. These impurities can react electrochemically to produce degradation products that are detrimental to battery life.

[0013] It is therefore necessary to propose an efficient process for the synthesis of NaTDI with good yield and good purity, which in particular allows the elimination of non-cyclized products from diaminomaleonitrile.

[0014] Summary of the invention

[0015] The invention relates to a composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) of formula (1)

[0016]

[0017] comprising a quantity of non-cyclized products of formula (1a) and (1b)o

[0018] (1a)

[0019]

[0020] less than or equal to 100 ppm by weight.

[0021] In embodiments, the quantity of non-cyclized products of formula (1a) and (1b) is less than or equal to 50 ppm by weight.

[0022] In embodiments, the quantity of non-cyclized products of formula (1a) and (1b) is between 0.1 and 25 ppm by weight.

[0023] In embodiments, the water content is less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight.

[0024] In some embodiments, the water content is between 0.1 and 25 ppm by weight.

[0025] In embodiments, sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt is present in an amount greater than or equal to 99.5% by weight relative to the total weight of the composition.

[0026] In embodiments, the composition according to the invention has a color less than 500 Hazen units, preferably a color less than or equal to 400 Hazen units, preferably a color less than or equal to 300 Hazen units, preferably a color less than or equal to 200 Hazen units, preferably a color less than or equal to 100 Hazen units, preferably less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units and even more preferably less than or equal to 20 Hazen units, on the APHA scale.

[0027] Another object of the invention relates to a process for preparing a composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) comprising the following steps:

[0028] - a reaction step between diaminomaleonitrile (DAMN) and a trifluoroacetic acid derivative at temperature T1 in a solvent leading to the production of compounds of formula (1a) and (1b); NC. NI-£

[0029] Tl 0

[0030] NC NH CF3

[0031]

[0032] (1a)

[0033] - a cyclization step at a temperature T2 higher than T1 allowing the 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) of formula (1c);

[0034] NC CF

[0035]

[0036] (1c)

[0037] - a neutralization step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) with a sodium base to form the sodium salt of 4,5-dicyano-2-trifluoromethyl-imidazole of formula (1)

[0038] NC

[0039]

[0040] - a recrystallization step to obtain a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt comprising an amount of uncyclized products of formula (1a) and (1b) less than or equal to 100 ppm by weight.

[0041] In an alternative embodiment, the process for preparing a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) salt includes a step of supplying a composition comprising a sodium 4,5-dicyano-2-trifluoromethylimidazole salt of formula (1) followed by a recrystallization step to obtain a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt comprising an amount of uncyclized products of formula (1a) and (1b) of less than 100 ppm by weight.

[0042] In some embodiments, the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt at the end of the recrystallization step also has a water content of less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight. In some embodiments, the temperature T1 is between 0°C and 50°C, preferably between 5°C and 20°C, more preferably between 5°C and 10°C.

[0043] In embodiments, the trifluoroacetic acid derivative in the reaction step with DAMN is an acid halide, preferably selected from trifluoroacetyl chloride, trifluoroacetyl bromide, trifluoroacetic anhydride, more preferably the trifluoroacetic acid derivative is trifluoroacetic anhydride.

[0044] In embodiments, the solvent for the reaction step between DAMN and the trifluoroacetic acid derivative is an organic solvent, preferably an ether selected from 1,4-dioxane, tetrahydrofuran (THF), methyl tert-butyl ether (MTBE), diisopropyl ether or cyclopentyl methyl ether (CPME), more preferably cyclopentyl methyl ether.

[0045] In preferred embodiments, the reaction step between DAMN and the trifluoroacetic acid derivative is carried out in the absence of phosphorus pentoxide (P2O5).

[0046] In embodiments, the molar ratio between the trifluoroacetic acid derivative and DAMN is between 0.9 and 2, preferably between 1 and 1.2.

[0047] In embodiments, the weight concentration of DAMN in the solvent is between 5% and 50%, preferably between 10% and 30%, more preferably between 10% and 20% by weight relative to the total weight of the solvent.

[0048] In embodiments, the duration of the reaction step between DAMN and the trifluoroacetic acid derivative is between 0.5 hours and 12 hours, preferably between 1 hour and 8 hours, more preferably between 1 hour and 3 hours.

[0049] In some embodiments, the temperature T2 is between 50°C and 150°C, preferably between 75°C and 130°C, preferably between 80°C and 110°C.

[0050] In embodiments, the duration of the cycling step is between 0.5 hours and 12 hours, preferably between 1 hour and 8 hours, more preferably between 1 hour and 3 hours.

[0051] In some embodiments, the process according to the invention further comprises a step of purifying the sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt after the cyclization step and before the neutralization step. Preferably, the purification step is carried out by filtration through activated carbon.

[0052] In some embodiments, the purification step is carried out in the solvent of the reaction step between DAMN and the trifluoroacetic acid derivative.

[0053] In embodiments, the sodium base during the neutralization step is chosen from sodium carbonate Na2CO3, sodium hydroxide NaOH, sodium fluoride NaF, sodium hydride NaH, sodium acetate NaOAc, preferably sodium carbonate.

[0054] In some embodiments, the neutralization reaction is carried out in an organic solvent.

[0055] In some embodiments, the organic solvent in the neutralization reaction is chosen from a nitrile or an organic carbonate.

[0056] In some embodiments, the molar ratio between the sodium base and the HTDI during the neutralization reaction is between 1 and 2 (in Na equivalents) and preferably between 1 and 1.1.

[0057] In some embodiments, the molar ratio between sodium carbonate and HTDI during the neutralization reaction is between 0.5 and 0.55 in the case of sodium carbonate.

[0058] In some embodiments, the process according to the invention includes, before the neutralization step, a titration step of the HTDI with sodium hydroxide.

[0059] In some embodiments, the neutralization step is carried out at a temperature between 0°C and 30°C, preferably between 5°C and 15°C.

[0060] In some embodiments, the process according to the invention further comprises a filtration step. Preferably, the filtration step is carried out after the neutralization step and before the recrystallization step.

[0061] In some embodiments, the filtration step is carried out on a filtration membrane.

[0062] In embodiments, the pore size of the filtration membrane is less than or equal to 10 pm, preferably less than or equal to 1 pm, preferably less than or equal to 0.5 pm.

[0063] In some embodiments, the filtration membrane is chosen from a microfiltration membrane, a nanofiltration membrane, an ultrafiltration membrane.

[0064] In embodiments, the process according to the invention further comprises a step of precipitation of the sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt after the cyclization step and before the neutralization step.

[0065] Preferably, the precipitation step takes place after the filtration step and before the recrystallization step.

[0066] In some embodiments, the step of precipitation of the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt is carried out by concentration of the filtrate and then addition of a non-solvent.

[0067] In embodiments, the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt at the end of the recrystallization step further exhibits a color of less than 500 Hazen units, preferably a color of less than or equal to 400 Hazen units, preferably a color of less than or equal to 300 Hazen units, preferably a color of less than or equal to 200 Hazen units, preferably a color of less than or equal to 100 Hazen units, preferably less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units and even more preferably less than or equal to 20 Hazen units, on the APHA scale.

[0068] In some embodiments, the recrystallization step of sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt is carried out in a solvent and non-solvent mixture.

[0069] In some embodiments, the solvent is an alcohol selected from methanol, ethanol, propanol or isopropanol, and / or an organic carbonate selected from dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC), and their combinations.

[0070] Preferably, the solvent is an alcohol and more preferably ethanol.

[0071] In some embodiments, the non-solvent is a chlorinated solvent selected from dichloromethane or dichloroethane, an aromatic solvent selected from toluene, xylenes, chlorobenzene or dichlorobenzenes, or a hydrocarbon selected from pentane, hexane, heptane or cyclohexane, and combinations thereof.

[0072] Preferably, the non-solvent is a chlorinated solvent and more preferably dichloromethane.

[0073] In some embodiments, the recrystallization step is followed by a vacuum drying step at a temperature between 20°C and 100°C. In some embodiments, the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt before the recrystallization step has a color of at least 3 units on the Gardner scale.

[0074] Another object of the invention is a composition obtained by the process according to the invention

[0075] The invention also relates to an electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte comprising the composition according to the invention.

[0076] The invention also relates to a battery comprising at least one electrochemical cell according to the invention.

[0077] Detailed description

[0078] The invention is now described in more detail and in a non-limiting manner in the following description.

[0079] Unless otherwise stated, all percentages relating to quantities are mass percentages.

[0080] In this text, the quantities indicated for a given species may apply to that species according to all its definitions (as mentioned in this text), including more restricted definitions.

[0081] In this text, unless otherwise stated, ranges of values ​​include the bounds of those ranges.

[0082] Composition

[0083] The invention relates to a composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) of formula (1)

[0084]

[0085] including a quantity of non-cycled products of formula:

[0086] o

[0087]

[0088] (1a) (W) less than or equal to 100 ppm by weight.

[0089] For example, the quantity of non-cycled products may be between 0.001 ppm and 10 ppm by weight, from 10 ppm to 20 ppm by weight, from 20 ppm to 30 ppm by weight, from 30 ppm to 40 ppm by weight, from 40 ppm to 50 ppm by weight, from 50 ppm to 60 ppm by weight, from 60 ppm to 70 ppm by weight, from 70 ppm to 80 ppm by weight, from 80 ppm to 90 ppm by weight, from 90 ppm to 100 ppm by weight.

[0090] Preferably, the amount of non-cyclized products of formula (1a) and (1b) is less than or equal to 50 ppm by weight. For example, the amount of non-cyclized products of formula (1a) and (1b) is between 0.001 ppm and 50 ppm by weight, preferably between 0.001 ppm and 25 ppm by weight.

[0091] Preferably, the water content is less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight. For example, the water content may be between 0.001 ppm and 10 ppm by weight, from 10 ppm to 20 ppm by weight, from 20 ppm to 30 ppm by weight, from 30 ppm to 40 ppm by weight, from 40 ppm to 50 ppm by weight, from 50 ppm to 60 ppm by weight, from 60 ppm to 70 ppm by weight, from 70 ppm to 80 ppm by weight, from 80 ppm to 90 ppm by weight, from 90 ppm to 100 ppm by weight.

[0092] The sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt may be present in an amount greater than or equal to 99.5% by weight relative to the total weight of the composition, preferably in an amount greater than or equal to 99.7%.

[0093] The purity of salts can be determined by various methods well known to those skilled in the art. In particular, the degree of purity of the composition according to the invention can be determined by NMR. 1 H and 19F in DMSO-de solvent. NMR spectra can be acquired on a Bruker AVI 11400 spectrometer equipped with a 5 mm BBFO+ probe. The sample is dissolved in DMSO-de and examined by NMR. 1 H and 19 F. An internal standard such as trifluorotoluene is used.

[0094] Such sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salts with a high degree of purity and / or low levels of uncycled reaction products and / or water are particularly suitable as additives for ionic liquids and electrolytes. These compositions exhibit improved electrochemical stability and can be used in the production of electrochemical cells, such as those found in batteries, with a longer lifespan.

[0095] The composition according to the invention may have a color value of less than 500 Hazen units, preferably less than or equal to 400 Hazen units, preferably less than or equal to 300 Hazen units, preferably less than or equal to 200 Hazen units, preferably less than or equal to 100 Hazen units, preferably less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units, and even more preferably less than or equal to 20 Hazen units, on the APHA scale (also called the Hazen scale, platinum-cobalt scale, or Pt-Co scale). The determination of the color on the Hazen scale can be carried out in accordance with ISO 6271:2015.

[0096] Method according to the invention

[0097] The invention further relates to a process for preparing a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) salt according to the invention comprising the following steps:

[0098] - a reaction step between diaminomaleonitrile (DAMN) and a derivative of trifluoroacetic acid at a temperature T1 in a solvent leading to the production of compounds of formula (1a) and (1b);

[0099] o

[0100]

[0101] Ua) ( 1 b )

[0102] - a cyclization step at a temperature T2 higher than T1 allowing the 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) of formula (1c);

[0103]

[0104] (1c)

[0105] - a neutralization step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) with a base to form the sodium salt of 4,5-dicyano-2-trifluoromethyl-imidazole of formula (1)NC K.N.

[0106] J

[0107] (

[0108]

[0109] 1) NC N N / A + , et

[0110] - a recrystallization step allowing the production of a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt. In one embodiment, the process according to the invention may include the steps of supplying an ionic liquid followed by a recrystallization step as described allowing the production of a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt according to the invention.

[0111] The process according to the invention makes it possible to obtain a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt, the composition comprising an amount of uncyclized products of formula (1a) and (1b) of less than 100 ppm by weight, and / or an amount of water of less than 100 ppm by weight. The ppm contents are expressed by weight, relative to the total weight of the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt obtained after the recrystallization step.

[0112] Preferably, at the end of the recrystallization step, the quantity of uncycled products is less than or equal to 100 ppm by weight. For example, the quantity of uncycled products may be between 0.001 ppm and 10 ppm by weight, from 10 ppm to 20 ppm by weight, from 20 ppm to 30 ppm by weight, from 30 ppm to 40 ppm by weight, from 40 ppm to 50 ppm by weight, from 50 ppm to 60 ppm by weight, from 60 ppm to 70 ppm by weight, from 70 ppm to 80 ppm by weight, from 80 ppm to 90 ppm by weight, from 90 ppm to 100 ppm by weight.

[0113] Preferably, the water content is less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight. For example, the water content may be between 0.001 ppm and 10 ppm by weight, from 10 ppm to 20 ppm by weight, from 20 ppm to 30 ppm by weight, from 30 ppm to 40 ppm by weight, from 40 ppm to 50 ppm by weight, from 50 ppm to 60 ppm by weight, from 60 ppm to 70 ppm by weight, from 70 ppm to 80 ppm by weight, from 80 ppm to 90 ppm by weight, from 90 ppm to 100 ppm by weight.

[0114] During the first reaction step between DAMN and the trifluoroacetic acid derivative, the temperature T1 is between 0°C and 50°C, preferably between 5°C and 20°C, and more preferably between 5°C and 10°C.

[0115] The trifluoroacetic acid derivative in the reaction step between DAMN and HTDI is an acid halide. Preferably, the acid halide is chosen from trifluoroacetyl chloride, trifluoroacetyl bromide, trifluoroacetic anhydride, and more preferably trifluoroacetic anhydride.

[0116] The reaction between DAMN and the trifluoroacetic acid derivative preferably takes place in an organic solvent. Preferably, this organic solvent is chosen from an ether selected from 1,4-dioxane, tetrahydrofuran (THF), methyl tert-butyl ether (MTBE), diisopropyl ether, or cyclopentyl methyl ether (CPME), most preferably cyclopentyl methyl ether. The weight concentration of DAMN in the solvent is between 5% and 50%, preferably between 10% and 30%, most preferably between 10% and 20% by weight relative to the total weight of the solvent. The molar ratio of the trifluoroacetic acid derivative to DAMN is between 0.9 and 2, preferably between 1 and 1.2.

[0117] In a particularly preferred embodiment, the reaction step between DAMN and the trifluoroacetic acid derivative is carried out in the absence of phosphorus pentoxide (P2O5).

[0118] The duration of the reaction step between DAMN and the trifluoroacetic acid derivative can be between 0.5 hours and 12 hours, preferably between 1 hour and 8 hours, more preferably between 1 hour and 3 hours.

[0119] The reaction between DAMN and the trifluoroacetic acid derivative yields the uncyclized compounds of formulas (1a) and (1b). Following the first reaction step, a cyclization step (b) is carried out at a temperature T2 higher than T1. The temperature T2 can be between 50°C and 150°C, preferably between 75°C and 130°C, and preferably between 80°C and 110°C. The duration of the cyclization step (b) can be between 0.5 hours and 12 hours, preferably between 1 hour and 8 hours, and more preferably between 1 hour and 3 hours. The cyclization step yields 4,5-dicyano-2-trifluoromethylimidazole (HTDI) of formula (1c).

[0120] 4,5-Dicyano-2-trifluoromethylimidazole can then be purified, preferably using activated carbon. Examples of activated carbons include Acticarbone® BGX or BGE (CalgonCarbon) or organosorb®10 (Desotec). The purification step is preferably carried out in the solvent used in the reaction between DAMN and the trifluoroacetic acid derivative.

[0121] A neutralization reaction of filtered HTDI with a sodium base in an organic solvent yields a sodium 4,5-dicyano-2-trifluoromethylimidazole salt. The organic solvent for the neutralization reaction may be a nitrile or an organic carbonate. The sodium base may be sodium carbonate, caustic soda, sodium fluoride, and preferably sodium carbonate. The molar ratio of the sodium base to the HTDI in the neutralization reaction is preferably between 1 and 2 (Na equivalents), and even more preferably between 1 and 1.1. When the base is sodium carbonate, the molar ratio of sodium carbonate to HTDI in the neutralization reaction is preferably between 0.50 and 0.55.The process according to the invention may further include, before the neutralization step, a titration step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) of formula (1 c) with sodium hydroxide in order to adjust the amount of base to be added during the neutralization step.

[0122] The neutralization step yields the sodium salt of 4,5-dicyano-2-trifluoromethylimidazole (HTDI). This neutralization step is preferably carried out at a temperature between 0°C and 30°C, and more preferably between 5°C and 15°C.

[0123] The salt can then be filtered through a filtration membrane. The pore size of the filtration membrane can be less than or equal to 10 µm, preferably less than or equal to 1 µm, preferably less than or equal to 0.5 µm. The filtration membrane can be selected from a microfiltration membrane, a nanofiltration membrane, or an ultrafiltration membrane.

[0124] The sodium salt of 4,5-dicyano-2-trifluoromethylimidazole (HTDI) can then be precipitated by concentrating the filtrate and then adding a non-solvent. The non-solvent can be a chlorinated solvent chosen from dichloromethane or dichloroethane, an aromatic solvent chosen from toluene, xylenes, chlorobenzene, or dichlorobenzenes, or a hydrocarbon chosen from pentane, hexane, heptane, or cyclohexane, and combinations thereof. Preferably, the non-solvent is a chlorinated solvent, and more preferably dichloromethane.

[0125] The sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt, after the precipitation step and before the recrystallization step, has a color of at least 3 units on the Gardner scale, i.e., the salt is pale yellow. The Gardner scale can be evaluated according to ISO 4630:2015.

[0126] According to the invention, the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt is subjected to a recrystallization step in a solvent-non-solvent mixture. The solvent is an alcohol selected from methanol, ethanol, propanol, or isopropanol, and / or an organic carbonate selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). Preferably, the solvent is an alcohol, and more preferably ethanol. The non-solvent can be as described in connection with the precipitation step.The composition comprising the salt obtained at the end of the recrystallization step may further exhibit a color of less than 500 Hazen units, preferably a color of less than or equal to 400 Hazen units, preferably a color of less than or equal to 300 Hazen units, preferably a color of less than or equal to 200 Hazen units, preferably a color of less than or equal to 100 Hazen units, preferably less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units and even more preferably less than or equal to 20 Hazen units, on the APHA scale.

[0127] The process according to the invention may further include a vacuum drying step at a temperature between 20°C and 100°C after the recrystallization step.

[0128] In a particularly preferred embodiment, the process according to the invention comprises the following steps:

[0129] - a reaction step between diaminomaleonitrile (DAMN) and a derivative of trifluoroacetic acid at a temperature T1 in a solvent leading to the production of compounds of formula (1a) and (1b);

[0130] o

[0131]

[0132] (! a) (W)

[0133] - a cyclization step at a temperature T2 higher than T1 allowing the 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) of formula (1c);

[0134]

[0135] - a purification step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI);

[0136] - a neutralization step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) with a base to form the sodium salt of 4,5-dicyano-2-trifluoromethyl-imidazole of formula (1) NC X^N

[0137] T ^CF3

[0138] (1) NC' / Z ^ N N / A +

[0139]

[0140] - a filtration step of the sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt; - a precipitation step of the sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt; and

[0141] - a recrystallization step to obtain a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt.

[0142] The invention also relates to a composition comprising a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt obtained by the process according to the invention, comprising an amount of non-cyclized products of formula (1a) and (1b) less than or equal to 100 ppm by weight, and / or an amount of water less than or equal to 100 ppm by weight.

[0143] Electrolyte

[0144] The composition described above may be included in an electrolyte. The electrolyte may comprise the composition described above in a mass proportion of 1 to 70%, preferably 3 to 50%, and preferably 5 to 30%.

[0145] The electrolyte is preferably non-aqueous. It is therefore free of water or essentially free of water. The water content can be from 0 to 500 ppm, preferably from 0.5 to 100 ppm, and even more preferably from 1 to 50 ppm by weight.

[0146] The sulfamate ion content in the electrolyte can be from 0.1 to 3000 ppm, preferably from 1 to 1000 ppm and preferably still from 10 to 300 ppm, by weight.

[0147] The acetamide content in the electrolyte can be from 0 to 1000 ppm, preferably from 1 to 500 ppm, preferably still from 2 to 100 ppm by weight.

[0148] The content of Cl' ions in the electrolyte can be from 0 to 50 ppm, preferably from 0.5 to 20 ppm, preferably still from 1 to 10 ppm.

[0149] The F' ion content in the electrolyte can be from 0 to 100 ppm, preferably from 0.5 to 50 ppm, preferably still from 1 to 10 ppm.

[0150] SCk ion content 2 ' in the electrolyte can be from 0 to 3000 ppm, preferably from 0.5 to 500 ppm, preferably still from 1 to 20 ppm.

[0151] The FSOs' ion content in the electrolyte can be from 0 to 100 ppm, preferably from 0.5 to 50 ppm, preferably still from 1 to 10 ppm.

[0152] The electrolyte may include, in addition to the composition according to the invention, one or more other sodium salts, one or more solvents and one or more additives.

[0153] Other sodium salts may be selected from, in particular, NaPFe, NaCICk, NaBF4, NaOTf (sodium triflate), NaBOB (sodium bis(oxalato)borate), NaDFOB (sodium difluoro(oxalato)borate), NaTDI (sodium 4,5-dicyano-2-trifluoromethylimidazolide), and combinations thereof. When several sodium salts are used in combination, preferably the total content of all sodium salts is 1 to 70%, preferably 3 to 50%, and preferably 5 to 30% by weight. In some embodiments, the electrolyte consists essentially of, or even consists of, the composition described above (optionally in combination with one or more other sodium salts), the solvent(s), and the additive(s).

[0154] The solvent(s) may be chosen from among: ethers, including dimethoxyethane (DME), diethylene glycol dimethyl ether (DEGDME) or tetraethylene glycol dimethyl ether (TEGDME); esters, including ethyl acetate or methyl propionate; lactones, including gamma-butyrolactone; nitriles, including acetonitrile; sulfoxides, including dimethyl sulfoxide; sulfones, including sulfolane; carbonates; and combinations thereof.

[0155] Among carbonates, the solvent(s) may include C3-C6 alkylcarbonate solvents, particularly cyclic and / or linear ones.

[0156] In some embodiments, a mixture of at least two solvents is provided, namely a cyclic C3-C6 alkylcarbonate solvent and a linear C3-C6 alkylcarbonate solvent.

[0157] As a cyclic C3-C6 alkylcarbonate, ethylene carbonate (EC), butylene carbonate (BC) or propylene carbonate (PC) can be used in particular.

[0158] As a linear C3-C6 alkyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC) can be used in particular.

[0159] The additives may include a C2-C6 alkylene carbonate. The additives may include a C1-C8 nitrile.

[0160] The additives may include a C2-C6 alkylene carbonate and a C1-C8 nitrile.

[0161] C2-C6 alkylene carbonate can be cyclic or linear. For example, C2-C6 alkylene carbonate can be a vinylene carbonate.

[0162] The C1-C8 nitrile may comprise at least two nitrile units. Preferably, the C1-C8 nitrile may have the general formula NC-(CH) n-CN with n being an integer from 1 to 6, preferably 2, 3 or 4. The C1-C8 nitrile can be chosen from adiponitrile, succinonitrile or glutaronitrile, adiponitrile being preferred (n=4). The electrolyte may include from 2 to 10% by weight of C2-C6 alkylene carbonate(s).

[0163] The electrolyte may include, in particular, 0.2 to 5% by weight of C1-C8 nitrile(s).

[0164] As additives, the electrolyte may also include at least one fluorinated carbonate, such as FEC (fluoroethylene carbonate) or F2EC (difluoroethylene carbonate); or at least one phosphate such as TMP (trimethylphosphate) or phosphite such as TMSPI (tris(trimethylsilyl)phosphite).

[0165] The electrolyte may also include an ionic liquid (in addition to the solvents and additives described above). Ionic liquids are salts with a melting point below 100 °C and preferably below room temperature (i.e., between 15 and 35 °C). Thus, an "ionic liquid" is understood to mean a salt, that is, an ionic compound comprising at least one anion and one cation, present in liquid form at a temperature of 100 °C. The ionic liquids likely to be present are in particular those which include FSI or TFSI as an anion, associated with an onium cation, preferably chosen from the group consisting of quaternary ammonium ions, pyridinium ions, imidazolium ions, oxazolidinium ions, piperidinium ions, phosphonium ions, pyrrolidinium ions, sulfonium ions, oxonium ions and mixtures thereof.The onium cation can be in particular trimethylpropyl ammonium, trimethylbutyl ammonium, trimethylhexyl ammonium, tributylmethyl ammonium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, 1-propyl-3-methylpyrrolidinium, 1-butyl-1-methylpiperidinium, 1-methyl-1-propylpiperidinium and methyl(triethyl)phosphonium.

[0166] Use

[0167] The invention therefore also relates to an electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte comprising the composition according to the invention.

[0168] The invention also relates to a battery comprising at least one electrochemical cell according to the invention.

[0169] The electrochemical cell may also include a separator, in which the electrolyte is impregnated. The electrolyte wets the electrodes and the separator.

[0170] By "negative electrode" we mean the electrode which acts as an anode when the cell is delivering current (i.e. when it is in the process of discharging) and which acts as a cathode when the cell is in the process of charging.

[0171] The negative electrode typically comprises an electrochemically active material (negative material), possibly an electronically conductive material, and possibly a binder; preferably a negative material, an electronically conductive material, and a binder.

[0172] By "positive electrode" we mean the electrode which acts as the cathode when the cell is delivering current (i.e. when it is in the process of discharging) and which acts as the anode when the cell is in the process of charging.

[0173] The positive electrode typically comprises an electrochemically active material (positive material), possibly an electronically conductive material, and possibly a binder; preferably a negative material, an electronically conductive material, and a binder.

[0174] An "electrochemically active material" is defined as a material capable of reversibly inserting ions.

[0175] An "electronic conductive material" is defined as a material capable of conducting electrons.

[0176] In each electrode independently, the electronically conductive material is preferably conductive carbon.

[0177] Conductive carbon provides electronic conductivity and can be essentially any carbon exhibiting electronic conductivity behavior such as, in particular, carbon nanoparticles, carbon black, graphite, Ketjen® carbon, Shawinigan carbon, graphene, carbon nanotubes, carbon fibers (e.g., gas-formed carbon fibers or VGCF), non-powdery carbon obtained by carbonization of an organic precursor, or a combination of two or more of these.

[0178] In each electrode independently, the binder can be any polymer that ensures the mechanical integrity of the electrode.

[0179] 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 a mixture of the two (or an EO / PO copolymer), and possibly including crosslinkable units), water-soluble binders (such as polyacrylic acid, CMC (carboxymethylcellulose), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber)), or fluorinated polymer binders (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene)), and combinations thereof.

[0180] Preferably, it can be polyacrylic acid, CMC (for example in combination with SBR), or PVDF.

[0181] The negative material can be any carbon containing amorphous and graphitic domains in varying ratios. It includes both hard and soft carbons. Hard carbon is a solid form of carbon that cannot be converted into graphite by heat treatment, unlike soft carbon. Therefore, the amorphous domains of soft carbons reorganize into graphitic planes upon appropriate heat treatment. Soft carbon thus represents non-graphitizable carbon with high electronic conductivity, whose degree of graphitization and interlayer spacing can be adjusted by heat treatment.

[0182] Soft carbon can, for example, include soft carbon derived from pitch, carbon black, spherical carbon derived from mesitylene, or partially carbonized aromatic hydrocarbons doped with heteroatoms.

[0183] The negative material can be any mixture of hard and soft carbons and can be post-treated either with heat treatment or with chemical treatment using acidic or alkaline media.

[0184] The positive material can be a polyanionic compound, preferably comprising sodium. This includes, in particular, layered oxides. In some embodiments, the polyanionic compound can have the formula NaMxOy, with x preferably ranging from 1 to 2 and y preferably ranging from 2 to 3, for example, NaMC. In these two formulas, as well as all those below, M represents a metal or a mixture of metals.

[0185] Optionally, oxygen can be partially or totally substituted, preferably partially, by any other element, for example a halogen and preferably fluorine: for example the corresponding materials may have the formula NaMxOy-zFz, with z ranging from 0 to y, and x and y preferably being in the ranges above.

[0186] Optionally, the oxygen may be partially or totally substituted, preferably totally, by a sulfate, phosphate, or silicate and, optionally, by another element, particularly a halogen, preferably fluorine. This may, in particular, be a compound with the formula Na₂O. q Mx(PO4)yF z preferably with q = 1 to 4, x = 2 to 4, y = 2 to 4 and z = 0 to 3, for example Na3V2(PO4)2F3. It can also be a compound with the formula Na q Mx(SO4)y with preferably q = 1 to 4, x = 1 to 4, y = 1 to 4, for example Na2Fe(SO4)2. It can also be a Na compound q M x(SiO4)y with preferably q = 1 to 4, x = 1 to 2 and y = 1 to 4, like Na2FeSiO4 for example.

[0187] The negative electrode can be supported, for example, on a sheet of aluminum.

[0188] The positive electrode can be supported, for example, on a sheet of aluminum.

[0189] In both cases, the aluminum sheet can have a thickness of approximately 5 to 40 µm.

[0190] The aluminum may have been chemically treated or coated with a specific coating such as a carbon coating.

[0191] The support (e.g. aluminum foil) can be coated with an ink or dispersion comprising the active material (positive or negative), the electronically conductive material (e.g. conductive carbon), the binder and a solvent.

[0192] The solvent can be water or an aqueous solution, or an organic solvent (e.g., ethanol, N-methylpyrrolidone) that ensures homogeneous mixing of the components and the possibility of coating the ink using a coating method, for example, with a slotted matrix or a Comma Coater® device. The viscosity of the solution can be adjusted by the dry mass ratio, defined as the mass of all solids divided by the total mass (solids and liquids). When the binder is carboxymethylcellulose or polyacrylic acid, water or an aqueous solution is preferred. When the binder is polyvinylidene fluoride, an organic solvent is preferred.

[0193] The separator can be a porous membrane, which acts as a barrier between the negative and positive electrodes and is electronically insulating but ionically conductive.

[0194] The separator may comprise or be based on a polyolefin or cellulose. As a polyolefin, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a multilayer structure of the above-mentioned polymers may be used. Alternatively, the separator may be made of glass fibers. The invention also relates to a battery comprising at least one, and preferably several, electrochemical cells as described above. The electrochemical cells may be assembled in series and / or in parallel within the battery.

[0195]

[0196] The following example illustrates the invention without limiting it.

[0197] In a 1 L glass reactor, 51 g of diaminomaleonitrile (0.47 mol, 1 equivalent) and 330 g of cyclopentyl methyl ether are added. Maintaining the temperature between 5°C and 10°C, 107 g of trifluoroacetic anhydride (0.51 mol, 1.1 equivalents) are poured over a period of 1 hour. At the end of the pour, a mixture containing coproducts of formulas (1a) and (1b) is obtained. The mixture is heated in the reactor to a temperature between 90°C and 100°C and, under a pressure of 850 mbar, the water and trifluoroacetic acid produced by the cyclization reaction are removed using a Dean-Stark apparatus over a period of 2.5 hours.

[0198] At the end of this step, the HTDI solution in cyclopentyl methyl ether is contacted with 20 g of BGX activated carbon (source: CalgonCarbon) for purification. After 15 minutes of stirring, the dispersion is filtered through a 0.45-micron Milipore filter, and the filtrate is evaporated under vacuum (60°C, 0.1 mbar) to remove the cyclopentyl methyl ether. Dried HTDI is recovered by dissolution in 250 g of acetonitrile. The HTDI yield, determined by dry extract, is 97%, yielding 85.2 g of HTDI.

[0199] In a 1 L glass reactor, 250 g of acetonitrile and 26.7 g of Na₂CO₃ (0.25 mol, 0.53 equivalent) are loaded for a neutralization step. Maintaining the temperature between 5°C and 10°C, the HTDI solution is added to the previously prepared acetonitrile solution over a period of 1 hour. After the addition, the reaction is allowed to proceed for 6 hours at room temperature. The resulting pH is 8. The reaction mixture is filtered through a 0.45 micron filter.

[0200] The filtrate is concentrated under vacuum to remove 60% of the acetonitrile, then 400 g of dichloromethane is added and the mixture is cooled to 2°C. The resulting suspension is filtered, and the precipitate is washed with 200 g of dichloromethane and then dried under vacuum. 74.6 g of off-white solid is obtained (yield = 76%).

[0201] The product is analyzed by NMR 1 H and 19 F (DMSO-de solvent):

[0202] [Table 1] Product % weight

[0203] NaTDI 99.07

[0204] Non-cycled impurities (1a) and (1b) 0.3

[0205]

[0206] Other 0.63

[0207] At this stage, the uncycled impurity content is too high for use in a battery.

[0208] The NaTDI produced is then redissolved in 75g of ethanol, to which 250g of dichloromethane is added before cooling to 5°C. After drying under vacuum (0.1 mbar) at 30°C, 66.8 g of NaTDI is obtained in the form of a white powder (overall yield=68%).

[0209] The product is analyzed by NMR 1 H and 19 F (DMSO-de solvent):

[0210] [Table 2] _ _

[0211] Product % weight

[0212] NaTDI 99.77

[0213] Non-cycled impurities (1a) and (1b) 0.0

[0214]

[0215] Other 0.23

[0216] The water content analysis using the Karl Fischer method is 25 ppm. Water content analysis using the Karl Fischer method can be performed according to ISO 760:1978.

[0217] Conclusion

[0218] The process according to the invention makes it possible to improve the purity of the 4,5-dicyano-2-trifluoromethylimidazole sodium salt to obtain salts directly usable for the manufacture of electrolytes, electrochemical cells and Na-ion batteries.

Claims

Demands 1. Composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) of formula (1) comprising an amount of non-cyclized products of formula (1a) and (1b) less than or equal to 100 ppm by weight. o Ua) (ib) 2. Composition according to claim 1 wherein the quantity of non-cyclized products of formula (1a) and (1b) is less than or equal to 50 ppm by weight.

3. Composition according to any one of the preceding claims wherein the water content is less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight.

4. Composition according to any one of the preceding claims wherein the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt is present in an amount greater than or equal to 99.5% by weight relative to the total weight of the composition.

5. Composition according to any one of the preceding claims having a color less than 500 Hazen units, preferably a color less than or equal to 400 Hazen units, preferably a color less than or equal to 300 Hazen units, preferably a color less than or equal to 200 Hazen units, preferably a color less than or equal to 100 Hazen units, preferably less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units and even more preferably less than or equal to 20 Hazen units, on the APHA scale.

6. A process for preparing a composition comprising a sodium salt of 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI) comprising the following steps: - a reaction step between diaminomaleonitrile (DAMN) and a derivative of trifluoroacetic acid at a temperature T1 in a solvent leading to the production of compounds of formula (1a) and (1b); o U a) (1b) - a cyclization step at a temperature T2 higher than T1 allowing the 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) of formula (1c); NC X "N X / ^ CFs / '''■'N NC \ H (1c) - a neutralization step of 4,5-dicyano-2-trifluoromethyl-imidazole (HTDI) with a sodium base to form the sodium salt of 4,5-dicyano-2-trifluoromethyl-imidazole of formula (1) - a recrystallization step to obtain a sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt comprising an amount of uncyclized products of formula (1a) and (1b) less than or equal to 100 ppm by weight.

7. A process according to claim 6 wherein the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt at the end of the recrystallization step further has an amount of water less than or equal to 100 ppm, preferably less than or equal to 50 ppm by weight. 8.A process according to claim 6 or 7 wherein the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt at the end of the recrystallization step further exhibits a color of less than 500 Hazen units, preferably a color of less than or equal to 400 Hazen units, preferably a color of less than or equal to 300 Hazen units, preferably a color of less than or equal to 200 Hazen units, preferably a color of less than or equal to 100 Hazen units, preferably a color of less than or equal to 75 Hazen units, more preferably less than or equal to 50 Hazen units, even more preferably less than or equal to 25 Hazen units and even more preferably less than or equal to 20 Hazen units, on the APHA scale.

9. A process according to claims 6 to 8 wherein the recrystallization step of sodium 4,5-dicyano-2-trifluoromethyl-imidazole salt is carried out in a solvent and non-solvent mixture.

10. A process according to claim 9 wherein the solvent is an alcohol selected from methanol, ethanol, propanol or Tisopropanol, and / or an organic carbonate selected from dimethyl carbonate (DMC), diethyl carbonate (DEC) or Tethyl methyl carbonate (EMC).

11. A process according to claim 9 or 10 wherein the non-solvent is a chlorinated solvent selected from dichloromethane or dichloroethane, an aromatic solvent selected from toluene, xylenes, chlorobenzene or dichlorobenzenes, or a hydrocarbon selected from pentane, Thexane, Theptane or cyclohexane, and combinations thereof.

12. A process according to claims 6 to 11 in which the recrystallization step is followed by a vacuum drying step at a temperature between 20°C and 100°C.

13. A process according to one of claims 6 to 12 further comprising a step of precipitation of the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt preceding the recrystallization step.

14. A process according to claim 13 wherein the sodium 4,5-dicyano-2-(trifluoromethyl)imidazole salt at the end of the precipitation step and before the recrystallization step has a color of at least 3 units on the Gardner scale.

15. Electrolyte comprising the composition according to any one of claims 1 to 5.

16. Electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte comprising the composition according to any one of claims 1 to 5.

17. Battery comprising at least one electrochemical cell according to claim 16.

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