Salt compositions for low acetamide content electrolytes

Abstract

The present invention relates to a composition comprising a salt consisting of a sodium cation and an anion of the following formula (II): [Chemical 7] # imgabs0 # wherein R1 and R2 independently represent a fluorine atom or a perfluorinated group, the composition having an acetamide content of 0.1 to 1000 ppm by weight. The invention also relates to a process for preparing the composition and to an electrolyte comprising the composition.

Description

Technical Field

[0001] The present invention relates to a salt composition for an electrolyte intended for use in a sodium ion battery, a process for preparing the same, and an electrochemical cell incorporating an electrolyte containing the composition. Background Art

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

[0003] Sodium-ion (Na-ion) batteries are a more environmentally friendly alternative to Li-ion batteries.

[0004] Na-ion batteries include at least a negative electrode (anode), a positive electrode (cathode), an electrolyte and preferably a separator. The electrolyte is generally formed by a sodium salt dissolved in a solvent, which can be a mixture of organic solvents to achieve a good compromise between the viscosity and dielectric constant of the electrolyte.

[0005] The passivation layer formed during the first charge / discharge cycle of the battery is critical to the battery life. The passivation layer specifically includes the passivation of aluminum (aluminum is generally used for the current collector at the cathode) and the solid electrolyte interface (SEI), which is an inorganic and polymer layer formed at the anode / electrolyte and cathode / electrolyte interfaces. The stability of these interfaces is a major challenge to improve battery life.

[0006] Regarding the existing technology of Na-ion batteries, please refer to the following review articles:

[0007] -Hwang et al., Sodium-ion batteries: present and future, in Chem.Soc.Rev., 46:3529-2614(2017);

[0008] -Chen et al., Readiness Level of Sodium-Ion Battery Technology: AMaterialsReview, in Adv.Sus.Sys., DOI: 10.1002 / adsu.201700153 (2018);

[0009] -Eshetu et al., Electrolytes and Interphases in Sodium-Based Rechargeable Batteries: Recent Advances and Perspectives, in Adv. Energy Mater., 10:2000093 (2020).

[0010] In the latter, various electrolytes for Na-ion batteries are proposed. NaFSI (sodium bis(fluorosulfonyl imide)) is mentioned as a possible electrolyte salt.

[0011] Document EP 2578533 describes alkali metal salts (preferably lithium salts) of the fluorosulfonyl imide type having a sulfate ion content of less than 3000 ppm.

[0012] Document US Pat. No. 9,440,852 describes NaFSI (sodium bis(fluorosulfonyl imide)) salts having a purity greater than or equal to 99.5% by weight, free of moisture, and in which NaCl, NaF and NaFSO3 impurities are present in a content less than or equal to 1000 ppm.

[0013] Document JP 6592380 discloses an electrolyte for Na-ion batteries, which contains NaFSI and propylene carbonate (PC), wherein the ratio between PC and sodium is specified.

[0014] Document EP 3985775 teaches an electrolyte comprising a sodium salt, a carbonate-type solvent and an additive (alkylene carbonate or nitrile). NaFSI is mentioned in the list of possible sodium salts.

[0015] Document WO 2019 / 229359 describes a process for preparing salts such as lithium bis(fluorosulfonyl)imide (LiFSI) from bis(fluorosulfonyl)imide (HFSI).

[0016] There is a need to provide compositions that can be used to prepare electrolytes for Na-ion batteries, which compositions have advantageous properties in terms of non-flammability, performance and in particular battery life, and which can be manufactured by simple and inexpensive processes. Summary of the invention

[0017] The present invention firstly relates to a composition comprising a salt consisting of a sodium cation and an anion of the following formula (II): [Chemistry 1]

[0018]

[0019] Where R 1 and R 2 independently represents a fluorine atom or a perfluorinated group, the composition having an acetamide content of 0.1 to 1000 ppm by weight.

[0020] In some embodiments, the anion of formula (II) is a bis(fluorosulfonyl)imide anion or a bis(trifluoromethylsulfonyl)imide anion, preferably a bis(fluorosulfonyl)imide anion.

[0021] In some embodiments, the acetamide content is 1 to 5000 ppm, preferably 2 to 100 ppm by weight.

[0022] In some embodiments, the salt is present in a weight content greater than or equal to 99.5 weight %, preferably greater than or equal to 99.8 weight %, more preferably greater than or equal to 99.9 weight %.

[0023] In some embodiments, the composition further comprises, by weight:

[0024] - 0 to 500 ppm of water, preferably 0.5 to 100 ppm and more preferably 1 to 50 ppm;

[0025] -0 to 50 ppm Cl - ions, preferably 0.5 to 20 ppm, more preferably 1 to 10 ppm;

[0026] - 0 to 100 ppm of F- ions, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm;

[0027] -0 to 3000 ppm SO4 2- ions, preferably 0.5 to 500 ppm, more preferably 1 to 20 ppm;

[0028] -0 to 100 ppm FSO3 - ions, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm.

[0029] The present invention also relates to a process for preparing the above-mentioned composition, which comprises:

[0030] -Providing a compound of the following formula (I):

[0031] [Chemistry 2]

[0032]

[0033] Where R 1 and R 2 independently represent a fluorine atom or a perfluorinated group,

[0034] - reacting a compound of formula (I) with a sodium compound.

[0035] In some embodiments, the sodium compound is NaCl or a sodium base, which is preferably selected from NaH, NaOH, NaHCO3, Na2CO3 and Na(OAc), and preferably Na2CO3.

[0036] In some embodiments, the reaction is carried out as follows:

[0037] - in the presence of an organic solvent, preferably selected from nitriles, esters, ethers, ketones, alcohols, carbonates and combinations thereof; and / or

[0038] - in the case where the molar ratio of sodium compound / compound of formula (I) is from 0.9 to 1.1, preferably from 1 to 1.05; and / or

[0039] - at a temperature of -5°C to 40°C, preferably 15°C to 25°C.

[0040] In some embodiments, the reaction is carried out in the presence of acetonitrile as an organic solvent.

[0041] In some embodiments, the process comprises the following steps:

[0042] - Synthesis of compounds of formula (I), preferably by fluorination of chlorinated compounds and optionally distillation.

[0043] In some embodiments, the process further comprises the following steps:

[0044] - Purification of the reaction mixture after the reaction, preferably by filtration and crystallization.

[0045] In some embodiments, the crystallization is carried out in the presence of a non-solvent for the compound of formula (II), preferably selected from the group consisting of chlorinated solvents, aromatic solvents, alkanes, and combinations thereof.

[0046] The invention also relates to an electrolyte comprising the above composition, mixed with one or more solvents and optionally one or more additives.

[0047] In some embodiments, the electrolyte further comprises an ionic liquid, which preferably comprises a FSI or TFSI anion combined with an onium cation.

[0048] The present invention also relates to an electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte, wherein the electrolyte comprises the above-mentioned composition.

[0049] In some embodiments, the negative electrode includes hard carbon and / or soft carbon as an electrochemically active material, and wherein the positive electrode includes a poly(anionic) compound containing sodium.

[0050] The invention also relates to a battery comprising at least one electrochemical cell as described above.

[0051] The present invention makes it possible to meet the above needs.

[0052] Advantageously, the composition of the invention makes it possible to improve the quality of the SEI in Na-ion batteries.

[0053] Advantageously, the composition of the invention makes it possible to improve the coulombic efficiency after formation of the SEI and to increase the lifetime of the battery (ie to increase the number of cycles allowing to maintain at least 80% of the initial capacity of the battery).

[0054] Advantageously, batteries incorporating the compositions of the present invention exhibit good performance even at high charge and discharge rates.

[0055] Advantageously, the composition of the invention can be produced at moderate cost and in particular without using expensive raw materials such as LiFSI or KFSI.

[0056] Advantageously, purification of the composition is simplified.

[0057] Advantageously, a raw material such as HFSI is used, which has specific qualities making it easy to obtain a composition with high performance. DETAILED DESCRIPTION

[0058] The invention will now be described in more detail and in a non-limiting manner in the following description.

[0059] Unless otherwise indicated, all percentages and ratios are by weight and all ratios between two quantities are by weight ratios.

[0060] Compositions including salt

[0061] The present invention firstly relates to a composition comprising at least one salt consisting of an anion of the following formula (II):

[0062] [Chemistry 3]

[0063]

[0064] and sodium cations.

[0065] In formula (II), R 1 and R 2 Independently represents a fluorine atom or a perfluorinated group, which preferably contains 1 to 8 carbon atoms, more preferably 1 to 3 carbon atoms, and which is more preferably a trifluoromethyl group.

[0066] In some embodiments, there may be multiple anions of formula (II), but preferably only one anion of formula (II) is present. Preferably, the anion of formula (II) is a bis(fluorosulfonyl)imide anion, also known as an FSI anion; and / or a bis(trifluoromethylsulfonyl)imide anion, also known as a TFSI anion. Even more preferably, it is a FSI anion, in which case the salt is NaFSI.

[0067] Throughout the following, it is understood that a reference to an anion of formula (II) in the singular may be a reference to a plurality of anions of formula (II).

[0068] The composition according to the invention may comprise salt (anions of formula (II) and sodium cations) in a content preferably greater than or equal to 99% by weight, more preferably greater than or equal to 99.5% by weight, still more preferably greater than or equal to 99.8% by weight, or even 99.9% by weight relative to the total weight of the composition. The salt content represents the sum of the content of anions of formula (II) and the content of sodium cations.

[0069] The composition of the present invention may include acetamide in an amount by weight of: less than or equal to 1000 ppm; less than or equal to 500 ppm; less than or equal to 200 ppm; less than or equal to 100 ppm; less than or equal to 50 ppm; less than or equal to 20 ppm; less than or equal to 10 ppm.

[0070] In particular, the composition according to the invention may comprise an acetamide content by weight ranging from 0.1 to 1000 ppm, preferably from 1 to 500 ppm, more preferably from 2 to 100 ppm.

[0071] In particular, the composition according to the invention may comprise an acetamide content by weight of: 0.1 to 10 ppm; 10 to 50 ppm; 50 to 100 ppm; 100 to 200 ppm; 200 to 300 ppm; 300 to 500 ppm; 500 to 1000 ppm.

[0072] The acetamide content indicated above makes it possible to obtain the best performance of the composition, especially when it is used in a Na-ion battery electrolyte.

[0073] In particular, the composition of the invention may comprise one or more other anions and / or one or more other cations.

[0074] In some embodiments, the composition optionally includes sulfamate ions (NH2SO3 - ): less than or equal to 3000ppm, preferably less than or equal to 1000ppm, more preferably less than or equal to 300ppm. The aminosulfonate ion may be substantially absent or present in an amount greater than or equal to 0.1ppm by weight, or 1ppm by weight, or 10ppm by weight. For example, the content of the aminosulfonate ion may be 0 to 3000ppm by weight, preferably 1 to 1000ppm, more preferably 10 to 300ppm.

[0075] In some embodiments, the composition optionally includes water in an amount of less than or equal to 500 ppm, preferably less than or equal to 200 ppm, preferably less than or equal to 100 ppm, and in some cases less than or equal to 50 ppm by weight. Water may be substantially absent or present in an amount greater than or equal to 0.1 ppm by weight, or 0.5 ppm by weight, or 1 ppm by weight. For example, the water content may be 0 to 500 ppm, or 0.5 to 100 ppm, or 1 to 50 ppm by weight.

[0076] In some embodiments, the composition optionally includes Cl- ions in an amount less than or equal to 50 ppm, preferably less than or equal to 20 ppm, preferably less than or equal to 10 ppm by weight. - The ions may be substantially absent or present in an amount greater than or equal to 0.1 ppm by weight, or 0.5 ppm by weight, or 1 ppm by weight. - The content of ions may be 0 to 50 ppm, or 0.5 to 20 ppm, or 1 to 10 ppm by weight.

[0077] In some embodiments, the composition optionally includes F- ions in an amount less than or equal to 100 ppm, preferably less than or equal to 50 ppm, preferably less than or equal to 10 ppm by weight. F- ions may be substantially absent or present in an amount greater than or equal to 0.1 ppm by weight, or 0.5 ppm by weight, or 1 ppm by weight. For example, the content of F- ions may be 0 to 100 ppm, or 0.5 to 50 ppm, or 1 to 10 ppm by weight.

[0078] In some embodiments, the composition optionally includes SO4 in an amount as follows: 2- Ions: less than or equal to 3000 ppm, preferably less than or equal to 500 ppm, preferably less than or equal to 100 ppm, or even less than or equal to 20 ppm by weight. SO4 2- The ions may be substantially absent or present in an amount greater than or equal to 0.1 ppm by weight, or 0.5 ppm by weight, or 1 ppm by weight. For example, SO4 2- The content of the ions may be 0 to 3000 ppm, or 0.5 to 500 ppm, or 1 to 20 ppm by weight.

[0079] In some embodiments, the composition optionally includes FSO3 in the following amounts: - Ions: less than or equal to 100 ppm, preferably less than or equal to 50 ppm, more preferably less than or equal to 10 ppm by weight. FSO3- The ions may be substantially absent or present in an amount greater than or equal to 0.1 ppm by weight, or 0.5 ppm by weight, or 1 ppm by weight. For example, FSO3 - The content of the ions may be 0 to 100 ppm, or 0.5 to 50 ppm, or 1 to 10 ppm by weight.

[0080] The ion content in the composition can be analyzed by ion chromatography and / or inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission spectrometry (ICP-AES) and / or X-ray fluorescence spectrometry (XRF).

[0081] The water content can be determined by Karl Fisher analysis.

[0082] Acetamide and FSO3 - The ion content can be determined by nuclear magnetic resonance (NMR). 19 F and 1 H) determination.

[0083] General Protocol for Preparing Compositions

[0084] The composition can be prepared by a process comprising the following steps:

[0085] - Optionally, synthesizing a compound of formula (I):

[0086] [Chemistry 4]

[0087]

[0088] - reacting a compound of formula (I) with a sodium compound;

[0089] - Optionally, purifying the reaction mixture.

[0090] In formula (I), R 1 and R 2 has the same meaning as in formula (II).

[0091] In particular, when R 1 =R 2 =F, the compound of formula (I) is bis(fluorosulfonyl)imide or HFSI (which makes it possible to obtain NaFSI).

[0092] In particular, when R 1 =R 2 =CF3, the compound of formula (I) is bis(trifluoromethylsulfonyl)imide (which makes it possible to obtain NaTFSI).

[0093] Synthesis of compounds of formula (I)

[0094] In particular, the compound of formula (I) can be synthesized by fluorination of a chlorinated compound. The chlorinated compound has the same structure as the compound of formula (I), except that R 1 and R 2 independently represents a halogen atom (F or Cl) or a perhalogenated group, which preferably contains 1 to 8 carbon atoms, more preferably 1 to 3 carbon atoms, and which is more preferably a trihalomethyl group, provided that the chlorinated compound includes at least one chlorine atom. Preferably, the chlorinated compound has formula (I), R 1 and R 2 R independently represents a chlorine atom or a perchloro group, which preferably contains 1 to 8 carbon atoms, more preferably 1 to 3 carbon atoms, and which is more preferably a trichloromethyl group.

[0095] In particular, the chlorinated compound may be (bis(chlorosulfonyl)imide), which makes it possible to obtain HFSI.

[0096] In particular, the chlorinated compound may be (bis(trichloromethylsulfonyl)imide), which makes it possible to obtain bis(trifluoromethylsulfonyl)imide.

[0097] Fluorination is carried out by contacting the chlorinated compound with a fluorinating agent, which is preferably selected from HF (preferably anhydrous HF), KF, AsF3, BiF3, ZnF2, SnF2, PbF2, CuF2 and mixtures thereof, and the fluorinating agent is preferably HF, and even more preferably anhydrous HF. "Anhydrous HF" is understood to mean HF containing less than 500 ppm of water, preferably less than 300 ppm of water, preferably less than 200 ppm of water.

[0098] The fluorination is preferably carried out in at least one organic solvent SO1. The organic solvent SO1 preferably has a donor number between 1 and 70 and advantageously between 5 and 65. The donor index of the solvent represents the -ΔH value, ΔH being the enthalpy of interaction between the solvent and antimony pentachloride (according to the method described in Journal of Solution Chemistry, vol. 13, no. 9, 1984). As organic solvent SO1, mention may be made in particular of esters, nitriles, dinitriles, ethers, diethers, amines, phosphines and mixtures thereof.

[0099] The organic solvent SO1 is preferably selected from methyl acetate, ethyl acetate, butyl acetate, acetonitrile, propionitrile, isobutyronitrile, glutaronitrile, dioxane, tetrahydrofuran, triethylamine, tripropylamine, diethylisopropylamine, pyridine, trimethylphosphine, triethylphosphine, diethylisopropylphosphine and mixtures thereof. In particular, the organic solvent SO1 is dioxane.

[0100] Fluorination can be carried out at a temperature between 0°C and the boiling point of the organic solvent SO1 (or a mixture of organic solvents SO1). Preferably, step b) is carried out at a temperature between 5°C and the boiling point of the organic solvent SO1 (or a mixture of organic solvents SO1), preferably at a temperature between 20°C and the boiling point of the organic solvent SO1 (or a mixture of organic solvents SO1).

[0101] Fluorination, preferably using anhydrous hydrofluoric acid, can be carried out at a pressure between 0 and 16 bar absolute.

[0102] Fluorination is preferably carried out by dissolving the chlorinated compound in an organic solvent SO1 or a mixture of organic solvents SO1 before reaction with the fluorinating agent, preferably anhydrous HF.

[0103] The weight ratio of the chlorinated compound to the organic solvent SO1 or the mixture of organic solvents SO1 is preferably between 0.001 and 10, and advantageously between 0.005 and 5.

[0104] According to one embodiment, anhydrous HF is introduced into the reaction medium, preferably in gaseous form.

[0105] The molar ratio of fluorinating agent (preferably anhydrous hydrogen fluoride) to chlorinated compound is preferably between 1 and 10, and advantageously between 1 and 5.

[0106] The reaction with the fluorinating agent, preferably anhydrous hydrogen fluoride, can be carried out in a closed medium or in an open medium, preferably in an open medium, wherein HCl is released, in particular in gaseous form.

[0107] The fluorination reaction typically results in the formation of HCl, which can be largely degassed from the reaction medium (like an excess of HF if the fluorinating agent is HF), for example by stripping with a neutral gas such as nitrogen, helium or argon.

[0108] However, residual HF and / or HCl may be dissolved in the reaction medium. In the case of HCl, the amount is very low since it is mainly in gaseous form at the operating pressure and temperature.

[0109] The product obtained at the end of the fluorination reaction can be stored in a container resistant to HF.

[0110] The products obtained at the end of the fluorination reaction may include HF (especially unreacted HF), chlorinated compounds, solvent SO1 (such as dioxane), and optionally HCl, and / or optionally heavy compounds.

[0111] After the reaction, the compound of formula (I) can be purified, in particular by one or more distillation steps.

[0112] According to one embodiment, the distillation step makes it possible to form and recover:

[0113] a first stream F1 comprising HF, optionally an organic solvent SO1 and / or optionally HCl, preferably at the top of a distillation column, said stream F1 being gaseous or liquid;

[0114] a second stream F2 comprising compounds of formula (I) and optionally heavy compounds, preferably at the bottom of the distillation column, said stream F2 preferably being in liquid state.

[0115] When the stream F2 comprises heavy compounds, it may be subjected to an additional distillation step in a second distillation column to form and recover:

[0116] a stream F2-1 comprising compounds of formula (I), free of heavy compounds, preferably at the top of a distillation column, said stream F2-1 preferably being in liquid state,

[0117] a stream F2-2 comprising heavy compounds and compounds of formula (I), preferably at the bottom of the distillation column, said stream F2-2 containing less than 10% by weight, preferably less than 7% by weight and preferably less than 5% by weight of compounds of formula (I) contained in the composition obtained in step b), said stream F2-2 being preferably in liquid state.

[0118] "Heavy compounds" are understood to mean organic compounds having a boiling point higher than that of the compounds of formula (I). They may be produced by cleavage reactions of chlorinated compounds, leading to the formation of, for example, compounds such as FSO2NH2, and / or by solvent degradation reactions, leading to the formation of oligomers.

[0119] According to one embodiment, the distillation step makes it possible to form and recover:

[0120] a first stream F'1 comprising HF, optionally an organic solvent SO1 and / or optionally HCl, preferably at the top of a distillation column, said stream F'1 being gaseous or liquid;

[0121] a second stream F'2 comprising compounds of formula (I), preferably recovered by side stream withdrawal, said stream F'2 preferably being in liquid state;

[0122] a third stream F'3 comprising heavy compounds and compounds of formula (I), preferably at the bottom of the distillation column, said stream F'3 containing less than 10% by weight, preferably less than 7% by weight and preferably less than 5% by weight of compounds of formula (II) contained in the composition obtained in step b), said stream F'3 being preferably in liquid state.

[0123] For the side stream withdrawal, the distillation column can contain at least one tray.

[0124] The distillation step may be carried out at a pressure ranging from 0 to 5 absolute pressures, preferably from 0 to 3 absolute pressures, preferably from 0 to 2 absolute pressures, and advantageously from 0 to 1 absolute pressure.

[0125] The distillation step can be carried out in any conventional apparatus. This can be a distillation apparatus comprising a distillation column, a boiler and a condenser. The distillation column can comprise at least one packing, such as a random packing and / or a structured packing, and / or trays, such as perforated trays, fixed valve trays, moving valve trays, bubble cap trays, or a combination thereof.

[0126] At the end of the purification, the compound of formula (I) can be recovered with high purity. The use of a compound of formula (I) of high purity advantageously allows the preparation of a composition comprising a high purity salt, avoiding complex subsequent purification steps.

[0127] Thus, the product collected (and / or used for reaction with the sodium compound) preferably comprises at least 95% by weight of the compound of formula (I), more preferably at least 98% by weight, at least 99% by weight, at least 99.5% by weight or even at least 99.8% by weight of the compound of formula (I).

[0128] The collected (and / or used to react with the sodium compound) product preferably has a sulfamic acid content of less than or equal to 5000ppm, preferably less than or equal to 4000ppm, less than or equal to 3000ppm, less than or equal to 2500ppm, or even less than or equal to 2000ppm by weight. In some cases, sulfamic acid may be substantially absent or present in a content of at least 1ppm by weight. In particular, the content of sulfamic acid may be 1 to 5000ppm, 10 to 4000ppm, 100 to 3000ppm, or 500 to 2500ppm by weight. For example, it may be: 1 to 10 ppm, 10 to 50 ppm, 50 to 100 ppm, 100 to 200 ppm, 200 to 500 ppm, 500 to 1000 ppm, 1000 to 2000 ppm, 2000 to 3000 ppm, 3000 to 4000 ppm or 4000 to 5000 ppm by weight. The aminosulfonic acid content can be determined by ion chromatography (expressed as NH2SO3 - ).

[0129] For ion chromatography measurements, in particular the THERMO brand ICS-5000 device can be used. It has two analysis channels, one of which is dedicated to anion analysis and consists of:

[0130] -Ultrapure water (18.2Mohm) supplied via a double piston pump;

[0131] -Automatic eluent generator (EGC);

[0132] - Valve with injection loop (volume = 25 μl);

[0133] - Guard column (AG19, T = 35 ° C) and separation column (AS19, T = 20 ° C);

[0134] - Suppressor (AERS 62mA);

[0135] - Conductivity meter for detection of peaks.

[0136] The eluent used may be a KOH solution at a concentration of 25 mmol / L and may have a flow rate of 1 mL / min.

[0137] Reaction of the compound of formula (I) with a sodium compound

[0138] The term "sodium compound" is understood to mean a compound comprising sodium.

[0139] The reaction with the sodium compound may be an ion exchange reaction. In this case, the sodium compound may in particular be sodium chloride.

[0140] Alternatively, the reaction may be an acid-base reaction, in which case the sodium compound is a sodium base.

[0141] The term "sodium base" is understood to mean a basic compound comprising sodium.

[0142] In particular, the sodium base may be selected from NaH, NaOH, NaHCO3, Na2CO3, Na(OAc) (sodium acetate) and mixtures thereof. Preferably, Na2CO3 is used.

[0143] The reaction can be carried out in the presence of an organic solvent, which makes it possible to particularly promote the recovery of the compound of formula (II). Preferably, the solvent in which the compound of formula (II) is soluble is selected. In particular, the organic solvent can be selected from nitriles (in particular acetonitrile, propionitrile or butyronitrile), esters (in particular methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate or butyl acetate), ethers (in particular ether or methyl tert-butyl ether), ketones (in particular acetone or methyl ethyl ketone), alcohols (in particular methanol, ethanol or isopropanol), carbonates (in particular dimethyl carbonate, diethyl carbonate or methyl ethyl carbonate), and mixtures thereof.

[0144] Preferably, the reaction is carried out in the presence of acetonitrile as an organic solvent.

[0145] The reaction can be carried out by pouring the compound of formula (I) onto a dispersion of a sodium compound (e.g., sodium base) in an organic solvent. The weight ratio of the solvent to the compound of formula (I) can be between 0.5 and 10, preferably between 1 and 4. The molar ratio between the sodium compound (Na equivalent) and the compound of formula (I) can be between 0.9 and 1.1, preferably between 1 and 1.05. The reaction temperature can be between -5°C and 40°C, preferably between 15°C and 25°C.

[0146] At the end of the reaction, the reaction mixture may be purified. The purification may include filtration, crystallization and one or more washings; or preferably filtration followed by crystallization and optionally one or more washings.

[0147] The crystallization can be carried out by evaporating the solvent, in particular under vacuum or atmospheric pressure, for example by batch evaporation, by continuous evaporation with a falling film evaporator, or a thin film evaporator, or alternatively a short-path wiped film evaporator.

[0148] Preferably, crystallization is carried out by adding an organic solvent that is a non-solvent for the compound of formula (II). The compound of formula (II) can be present at a solid content greater than or equal to 50%, preferably greater than or equal to 70%. In particular, the organic solvent can be selected from: chlorinated solvents such as methylene chloride or ethylene dichloride, aromatic solvents such as toluene or xylene, or alkanes (linear, branched or cyclic) such as pentane, cyclohexane or heptane, and also selected from mixtures thereof. In particular, crystallization can be carried out at a temperature between -15°C and 25°C.

[0149] Optionally, the product may be washed one or more times, in particular with an organic solvent as described above for the crystallization. Preferably, the organic solvent used for washing is the same as the organic solvent used for the crystallization.

[0150] Finally, the product can be dried, for example in a vacuum oven.

[0151] The yield of the compound of formula (II) obtained relative to the reactant of formula (I) may be greater than 70 mol%, or greater than 80 mol%, or greater than 90 mol%, or even greater than 95 mol%.

[0152] The product obtained can be characterized by nuclear magnetic resonance, by Karl Fischer analysis for its water content and by ion chromatography for its anion and cation content.

[0153] Electrolytes

[0154] The above composition may be included in an electrolyte. The electrolyte may include the above salt in the following weight proportions: 1% to 70%, preferably 3% to 50%, more preferably 5% to 30%.

[0155] The electrolyte is preferably non-aqueous. Thus, it contains no water or substantially no water. The water content may be 0 to 500 ppm, preferably 0.5 to 100 ppm, and more preferably 1 to 50 ppm by weight.

[0156] The content of acetamide in the electrolyte may be 0 to 1000 ppm, preferably 1 to 500 ppm, more preferably 2 to 100 ppm by weight.

[0157] The sulfamate ion content in the electrolyte may be 0 to 3000 ppm by weight, preferably 1 to 1000 ppm, and more preferably 10 to 300 ppm.

[0158] Cl in electrolyte - The content of the ions may be 0 to 50 ppm, preferably 0.5 to 20 ppm, more preferably 1 to 10 ppm.

[0159] F in electrolyte - The content of the ions may be 0 to 100 ppm, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm.

[0160] SO4 in electrolyte 2- The content of the ions may be 0 to 3000 ppm, preferably 0.5 to 500 ppm, more preferably 1 to 20 ppm.

[0161] FSO3 in electrolyte - The content of the ions may be 0 to 100 ppm, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm.

[0162] Besides the composition according to the invention, the electrolyte may comprise one or more other sodium salts, one or more solvents and one or more additives.

[0163] In particular, other sodium salts may be selected from NaPF6, NaClO4, NaBF4, NaOTf (sodium trifluoromethanesulfonate), NaBOB (sodium bis(oxalate)borate), NaDFOB (sodium difluoro(oxalate)borate), NaTDI (sodium 4,5-dicyano-2-trifluoromethylimidazolium), and combinations thereof. When several sodium salts are used in combination, the total content of all sodium salts is preferably 1 wt % to 70 wt %, more preferably 3 wt % to 50 wt %, more preferably 5 wt % to 30 wt %. In some embodiments, the electrolyte is substantially composed of or even composed of the above composition (optionally in combination with one or more other sodium salts), (one or more) solvents, and (one or more) additives.

[0164] In particular, the solvent can be selected from the following: ethers, in particular dimethoxyethane (DME), diethylene glycol dimethyl ether (DEGDME) or tetraethylene glycol dimethyl ether (TEGDME); esters, in particular ethyl acetate or methyl propionate; lactones, in particular γ-butyrolactone; nitriles, in particular acetonitrile; sulfoxides, in particular dimethyl sulfoxide; sulfones, in particular cyclopentane sulfone; carbonates; and combinations thereof.

[0165] Among the carbonates, the solvent may especially be a C3-C6 alkyl carbonate solvent, the C3-C6 alkyl carbonate being in particular cyclic and / or linear.

[0166] In some embodiments, a mixture of at least two solvents is provided, namely a cyclic C3-C6 alkyl carbonate solvent and a linear C3-C6 alkyl carbonate solvent.

[0167] As the cyclic C3-C6 alkyl carbonate, ethylene carbonate (EC), butylene carbonate (BC), or propylene carbonate (PC) can be used in particular.

[0168] As linear C3-C6 alkyl carbonates, use may be made, inter alia, of dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC).

[0169] The additive may include a C2-C6 alkylene carbonate.

[0170] The additive may include C1-C8 nitrile.

[0171] The additives may include C2-C6 alkylene carbonates and C1-C8 nitriles.

[0172] The C2-C6 alkylene carbonate may be cyclic or linear. For example, the C2-C6 alkylene carbonate may be ethylene carbonate.

[0173] 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, wherein n is an integer between 1 and 6, preferably 2, 3 or 4. The C1-C8 nitrile may be selected from adiponitrile, succinonitrile, or glutaronitrile, preferably adiponitrile (n=4).

[0174] In particular, the electrolyte may include 2 to 10 wt % of the C2-C6 alkylene carbonate(s).

[0175] In particular, the electrolyte may include 0.2 wt % to 5 wt % of the C1-C8 nitrile(s).

[0176] As additives, the electrolyte may also include at least one fluorocarbonate such as FEC (fluoroethylene carbonate) or F2EC (difluoroethylene carbonate); or at least one phosphate such as TMP (trimethyl phosphate) or a phosphite such as TMSPI (tris(trimethylsilyl) phosphite).

[0177] The electrolyte may also include an ionic liquid (in addition to the above-mentioned solvents and additives). An ionic liquid is a salt having a melting point below 100° C. and preferably below room temperature (i.e. below a temperature in the range of 15° C. to 35° C.). Thus, "ionic liquid" is understood to mean a salt, i.e. an ionic compound comprising at least one anion and one cation, present in liquid form at a temperature of 100° C. In particular, the ionic liquids that may be present are those that include FSI or TFSI as anions in combination with onium cations, the onium cations being preferably selected from quaternary ammonium ions, pyridinium ions, imidazolium ions, oxazolidinium ions, piperidinium ions, phosphonium ions, pyrrolidinium ions, sulfonium ions, oxonium ions, and mixtures thereof. In particular, the onium cation may be trimethylpropylammonium, trimethylbutylammonium, trimethylhexylammonium, tributylmethylammonium, 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.

[0178] Electrochemical cells and batteries

[0179] The invention also relates to an electrochemical cell comprising an electrolyte as described above. The electrochemical cell also comprises a negative electrode (or anode) and a positive electrode (or cathode).

[0180] The electrochemical cell may also include a separator in which the electrolyte is impregnated. The electrolyte wets the electrodes and the separator.

[0181] “Negative electrode” means an electrode that functions as an anode when the unit cell outputs current (ie, when it is in the process of discharging), and an electrode that functions as a cathode when the unit cell is in the process of charging.

[0182] The negative electrode typically comprises an electrochemically active material (negative electrode material), optionally an electronically conductive material, and optionally a binder; preferably a negative electrode material, an electronically conductive material, and a binder.

[0183] “Positive electrode” means an electrode that functions as a cathode when a unit cell outputs current (ie, when it is in the process of discharging), and an electrode that functions as an anode when the unit cell is in the process of charging.

[0184] The positive electrode typically includes an electrochemically active material (positive electrode material), optionally an electronically conductive material, and optionally a binder; preferably a negative electrode material, an electronically conductive material, and a binder.

[0185] The term "electrochemically active material" is understood to mean a material which is able to reversibly insert ions.

[0186] The term "electron conducting material" is understood to mean a material which is able to conduct electrons.

[0187] Independently in each electrode, the electron conducting material is preferably conductive carbon.

[0188] The conductive carbon ensures the electronic conductivity and can be essentially any carbon that exhibits electronically conductive behavior, such as in particular carbon nanoparticles, carbon black, graphite, Carbon, Shawinigan carbon, graphene, carbon nanotubes, carbon fibers (such as vapor grown carbon fibers or VGCF), non-powdered carbon obtained by carbonization of an organic precursor, or a combination of two or more of these.

[0189] Independently in each electrode, the binder may be any polymer that ensures the mechanical integrity of the electrode.

[0190] The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched and / or cross-linked polyether polymer binders (e.g., based on polyethylene oxide (PEO), or polypropylene oxide (PPO), or a mixture of the two (or EO / PO copolymers), and optionally a polymer including a cross-linkable unit), a water-soluble binder (such as polyacrylic acid, CMC (carboxymethyl cellulose), SBR (styrene / butadiene rubber), NBR (acrylonitrile / butadiene rubber)), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylate rubber), or a fluorine-containing polymer binder (such as PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene)), and combinations thereof.

[0191] Preferably, it may be polyacrylic acid, CMC (for example used in combination with SBR), or PVDF.

[0192] The negative electrode material can be any carbon having amorphous domains and graphite domains in different ratios. It includes hard carbon and soft carbon. Hard carbon is carbon in solid form, which, unlike soft carbon, cannot be converted into graphite by heat treatment. Therefore, during appropriate heat treatment, the amorphous domains of soft carbon are reorganized into graphite planes. Therefore, soft carbon refers to non-graphite carbon with high electronic conductivity, which graphitization degree and interlayer distance can be adjusted by heat treatment.

[0193] For example, the soft carbon may include soft carbon derived from pitch, carbon black, spherical carbon derived from mesitylene, or partially carbonized aromatic hydrocarbon doped with heteroatoms.

[0194] The negative electrode material may be any mixture of hard and soft carbon and may be post-treated by heat treatment or by chemical treatment using acidic or alkaline media.

[0195] The positive electrode material may be a polyanionic compound, which preferably includes sodium. In particular, this includes layered oxides. In some embodiments, the polyanionic compound may be NaM x O y Formulae wherein x is preferably 1 to 2 and y is preferably 2 to 3, for example NaMO2. In these two formulae and also in all the following formulae, M represents a metal or a mixture of metals.

[0196] Optionally, oxygen may be partially or fully, preferably partially, substituted by any other element such as halogen and preferably fluorine: for example, the corresponding material may have the formula NaM x O y-z F z , wherein z is 0 to y, and x and y are preferably within the above range.

[0197] Optionally, the oxygen may be partially or completely, preferably completely, replaced by sulfate, phosphate or silicate, and optionally by another element, in particular a halogen, preferably fluorine.

[0198] In particular, it may be of the formula Na q M x (PO4) y F z A compound of the formula Na q M x (SO4) y A compound, preferably wherein q=1 to 4, x=1 to 4, y=1 to 4, such as Na2Fe(SO4)2. It may also be a compound Na q M x (SiO4) y , preferably wherein q=1 to 4, x=1 to 2, and y=1 to 4, such as Na2FeSiO4.

[0199] The negative electrode may be supported on, for example, aluminum foil.

[0200] The positive electrode can be supported on, for example, aluminum foil.

[0201] In both cases, the aluminum foil may have a thickness of approximately 5 to 40 μm.

[0202] The aluminum may have been chemically treated or have a special coating such as a carbon coating.

[0203] A support (eg, aluminum foil) may be coated with an ink or dispersion that includes an active material (positive or negative electrode), an electron conducting material (eg, conductive carbon), a binder, and a solvent.

[0204] The solvent may be water or an aqueous solution, or an organic solvent (e.g. ethanol, N-methylpyrrolidone, etc.), which ensures a uniform mixing of the components and allows for the coating to be carried out by a coating method such as by slot die or Comma. The device can be coated with ink. The viscosity of the solution can be adjusted by the dry mass ratio, which is defined as the mass of all solids to the total mass (solids and liquids). When the binder is carboxymethylcellulose or polyacrylic acid, water or an aqueous solution is preferably used. When the binder is polyvinylidene fluoride, an organic solvent is preferably used.

[0205] The separator may be a porous membrane that acts as a barrier between the negative electrode and the positive electrode and is electronically insulating but ionically conductive.

[0206] The separator may comprise or be based on a polyolefin or cellulose. As 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 polymers may be used. Alternatively, the separator may be made of glass fiber.

[0207] The invention also relates to a battery comprising at least one, and preferably a plurality of, electrochemical cells as described above. The electrochemical cells can be assembled in the battery in series and / or in parallel.

[0208] Example

[0209] The following examples illustrate the invention without limiting the invention.

[0210] Example 1

[0211] 175.7g of sodium carbonate (1.66mol) and 2100g of acetonitrile are loaded into a 4-liter reactor. While stirring and maintaining the temperature between 15°C and 20°C, 600g of molten HFSI (3.31mol) is poured over a period of 2 hours. At the end of the addition, the mixture is reacted at 20°C for 4 hours. The pH of the solution is then 6. The solution is filtered and then evaporated on a rotary evaporator at 40°C under vacuum. Drying is completed in a vacuum oven. 652g of NaFSI in the form of a white powder is obtained. The yield is 97%.

[0212] 19 F NMR analysis showed the presence of a peak corresponding to NaFSI.

[0213] 1 H NMR analysis showed the presence of acetamide at a level of 300 ppm.

[0214] Karl Fischer analysis showed a water content of 10 ppm.

[0215] The analysis by ion chromatography is as follows:

[0216] -NH2SO3 - =540ppm

[0217] -Cl - <5ppm

[0218] -F - =80ppm

[0219] -SO4 2- =1680ppm

[0220] -FSO3 - <5ppm

[0221] Example 2

[0222] 215.4g of sodium carbonate (2.03mol) and 5600g of acetonitrile are loaded into a 10-liter reactor. While stirring and maintaining the temperature between 15°C and 20°C, 700g of molten HFSI (3.87mol) is poured over during 2 hours. At the end of the addition, the reaction lasts for 2 hours at 20°C. The solution is filtered and then concentrated to a concentration of 75% with a short-path wiped film evaporator under vacuum. The concentrated solution thus obtained is poured into 2250g of dichloromethane and placed overnight at 5°C. The solution is then filtered, and the precipitate is washed with dichloromethane and then dried on a filter at 40°C under nitrogen. 715g of NaFSI in the form of white powder is obtained. The yield is 91%.

[0223] 19 F NMR analysis showed the presence of a peak corresponding to NaFSI.

[0224] 1 H NMR analysis showed the presence of acetamide at a level of 40 ppm.

[0225] Karl Fischer analysis showed a water content of 50 ppm.

[0226] The analysis by ion chromatography is as follows:

[0227] -NH2SO3 - =20ppm

[0228] -Cl - <5ppm

[0229] -F - <5ppm

[0230] -SO4 2- <5ppm

[0231] -FSO3 - <5ppm

Claims

1. A composition comprising a salt consisting of a sodium cation and an anion of the following formula (II): [Chemistry 5] Where R 1 and R 2 independently represents a fluorine atom or a perfluorinated group, the composition having an acetamide content of 0.1 to 1000 ppm by weight.

2. The composition of claim 1, wherein the anion of formula (II) is a bis(fluorosulfonyl)imide anion or a bis(trifluoromethylsulfonyl)imide anion, preferably a bis(fluorosulfonyl)imide anion.

3. The composition according to claim 1, wherein the acetamide content is from 1 to 500 ppm by weight, preferably from 2 to 100 ppm by weight.

4. The composition according to any one of claims 1 to 3, wherein the salt is present in a weight content greater than or equal to 99.5% by weight, preferably greater than or equal to 99.8% by weight, more preferably greater than or equal to 99.9% by weight.

5. A composition according to any one of claims 1 to 4, further comprising by weight: - 0 to 500 ppm of water, preferably 0.5 to 100 ppm and more preferably 1 to 50 ppm; - 0 to 50 ppm of Cl- ions, preferably 0.5 to 20 ppm, more preferably 1 to 10 ppm; - 0 to 100 ppm of F- ions, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm; -0 to 3000 ppm SO4 2- ions, preferably 0.5 to 500 ppm, more preferably 1 to 20 ppm; -0 to 100 ppm FSO3 - ions, preferably 0.5 to 50 ppm, more preferably 1 to 10 ppm.

6. A process for preparing a composition according to any one of claims 1 to 5, comprising: -Providing a compound of the following formula (I): [Chemistry 6] Where R 1 and R 2 independently represent a fluorine atom or a perfluorinated group, - reacting a compound of formula (I) with a sodium compound.

7. The process of claim 6, wherein the sodium compound is NaCl or a sodium base, preferably selected from the group consisting of NaH, NaOH, NaHCO3, Na2CO3 and Na(OAc), and preferably is Na2CO3.

8. The process as claimed in one of claims 6 and 7, wherein the reaction is carried out as follows: - in the presence of an organic solvent, preferably selected from nitriles, esters, ethers, ketones, alcohols, carbonates and combinations thereof; and / or - in the case where the molar ratio of sodium compound / compound of formula (I) is from 0.9 to 1.1, preferably from 1 to 1.05; and / or - at a temperature of -5°C to 40°C, preferably 15°C to 25°C.

9. The process as claimed in claim 6, wherein the reaction is carried out in the presence of acetonitrile as organic solvent.

10. The process according to any one of claims 6 to 9, comprising the following steps: - Synthesis of compounds of formula (I), preferably by fluorination of chlorinated compounds and optionally distillation.

11. The process according to any one of claims 6 to 10, further comprising the following steps: - Purification of the reaction mixture after the reaction, preferably by filtration and crystallization.

12. The process of claim 11, wherein the crystallization is carried out in the presence of a non-solvent for the compound of formula (II), preferably selected from the group consisting of chlorinated solvents, aromatic solvents, alkanes and combinations thereof.

13. An electrolyte comprising a composition as claimed in any one of claims 1 to 5, mixed with one or more solvents and optionally one or more additives.

14. The electrolyte of claim 13, further comprising an ionic liquid, preferably comprising FSI or TFSI anions in combination with onium cations.

15. An electrochemical cell comprising a negative electrode, a positive electrode and an electrolyte, wherein the electrolyte comprises a composition according to any one of claims 1 to 5.

16. The unit cell according to claim 15, wherein the negative electrode comprises hard carbon and / or soft carbon as an electrochemically active material, and wherein the positive electrode comprises a polyanionic compound containing sodium.

17. Battery comprising at least one electrochemical cell according to claim 15 or 16.

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