EP3802415A1

EP3802415A1 - Composition of bis(fluorosulfonyl)imide lithium salt

Info

Publication number: EP3802415A1
Application number: EP19736420.1A
Authority: EP
Inventors: Grégory Schmidt; Rémy Teissier; Jean-Luc Couturier
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2018-06-01
Filing date: 2019-05-28
Publication date: 2021-04-14
Also published as: FR3081857B1; FR3081857A1; KR20210015804A; WO2019229366A1; JP2021525700A; US20210221685A1; CN112272651A; US20230312344A1

Abstract

The invention relates to a composition containing: at least 99.75% by weight of bis(fluorosulfonyl)imide lithium salt; and acetic acid in a content by mass strictly greater than 0 and less than or equal to 400 ppm.

Description

COMPOSITION OF BIS LITHIUM SALT (FLUOROSULFONYL) IMIDE

FIELD OF THE INVENTION

The present invention relates to a bis (fluorosulfonyl) imide lithium salt composition.

TECHNICAL BACKGROUND

Anions of sulfonylimide type, by their very low basicity, are increasingly used in the field of energy storage in the form of inorganic salts in batteries, or organic salts in supercapacitors or in the field of liquids ionic. As the battery market is booming and the reduction of battery manufacturing costs becomes a major issue, a large-scale and low-cost synthesis process for this type of anion is necessary.

In the specific field of Li-ion batteries, the salt currently most used is LiPF ₆ but this salt shows numerous disadvantages such as limited thermal stability, sensitivity to hydrolysis and therefore lower battery safety. . Recently, new salts having the FSO ₂ group have been studied and have demonstrated many advantages such as better ionic conductivity and resistance to hydrolysis. One of these salts, LiFSI (LiN (FSO ₂ ) ₂ ) has shown very interesting properties that make it a good candidate to replace LiPF ₆ .

The identification and quantification of impurities in salts and / or electrolytes, and the understanding of their impacts on battery performance become paramount. For example, impurities having a mobile proton, due to their interference with electrochemical reactions, lead to lower overall performance and stability of the Li-ion batteries. The application of Li-ion batteries requires having products of high purity (minimum of impurities).

There is a need for novel bis (fluorosulfonyl) imide lithium salt compositions for use in batteries.

DESCRIPTION OF THE INVENTION

The present invention relates to a composition comprising:

at least 99.75% by weight of bis (fluorosulfonyl) imide lithium salt; and

- Acetic acid in a mass content strictly greater than 0 and less than or equal to 400 ppm. The mass contents mentioned above are relative to the total weight of the composition.

In the context of the invention, the terms "lithium salt of bis (fluorosulfonyl) imide", "lithium bis (sulfonyl) imide", "LiFSI", "LiN (FSO ₂ ) _2" are used in an equivalent manner, " bis (sulfonyl) imide lithium, or lithium bis (fluorosulfonyl) imide.

In the context of the invention, the term "ppm" or "part per million" means ppm by weight.

Preferably, the above-mentioned composition comprises at least 99.78%, preferably at least 99.80%, advantageously at least 99.85%, even more preferably at least 99.90% by weight of bis (fluorosulfonyl) lithium salt. imide, relative to the total weight of said composition. Preferably, the composition comprises at least 99.95%, preferably at least 99.97%, advantageously at least 99.98%, even more preferably at least 99.99% by weight of bis (fluorosulfonyl) imide lithium salt. relative to the total weight of said composition.

According to one embodiment, the mass content of acetic acid in the composition is less than or equal to 350 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 250 ppm, even more advantageously less than or equal to 200 ppm, example less than or equal to 150 ppm. Even more preferably, the acetic acid content in the composition is less than or equal to 100 ppm, and in particular less than or equal to 50 ppm, relative to the total weight of the composition.

According to one embodiment, the mass content of acetic acid in the composition is greater than or equal to 0.1 ppm, preferably greater than or equal to 1 ppm, advantageously greater than or equal to 10 ppm relative to the total weight of the composition. .

According to one embodiment, the mass content of acetic acid in the composition ranges from 0.1 ppm to 300 ppm, preferably from 0.1 ppm to 200 ppm, advantageously from 0.1 ppm to 150 ppm, even more advantageously from 0.1 ppm to 100 ppm relative to the total weight of the composition.

The aforementioned composition may also include:

a content of Cl ions less than or equal to 20 ppm by weight, preferably less than or equal to 15 ppm, advantageously less than or equal to 10 ppm, by weight relative to the total weight of said composition; and or

an F-content of less than or equal to 200 ppm, preferably less than or equal to 50 ppm, advantageously less than or equal to 30 ppm by weight relative to the total weight of said composition; and or

an H ₂ O content less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, still more preferably less than or equal to 30 ppm by weight relative to the total weight of said composition; and or

a content of S0 ₄ ² less than or equal to 300 ppm, preferably less than or equal to 200 ppm, advantageously less than or equal to 100 ppm, still more advantageously less than or equal to 50 ppm by weight relative to the total weight of said composition ; and or

a Na ⁺ content less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, still more advantageously less than or equal to 20 ppm by weight relative to the total weight of said composition; and or

a content of FSO ₃ Li less than or equal to 500 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 200 ppm, even more advantageously less than or equal to 100 ppm, and in particular less than or equal to 20 ppm by weight relative to the total weight of said composition; and or

a content of FSO2NH2 less than or equal to 200 ppm, preferably less than or equal to 100 ppm, advantageously less than or equal to 50 ppm, even more advantageously less than or equal to 20 ppm, and in particular less than or equal to 10 ppm by weight relative to the total weight of said composition.

According to one embodiment, the composition comprises:

C1 ions in a content ranging from 0 to 20 ppm by weight, preferably from 0 to 15 ppm, and still more advantageously from 0 to 10 ppm by weight relative to the total weight of said composition; and or

an F content ranging from 0 to 200 ppm, preferably ranging from 0 to 50 ppm, advantageously ranging from 0 to 30 ppm by weight relative to the total weight of said composition; and or

an H ₂ O content ranging from 0 to 200 ppm, preferably ranging from 0 to 100 ppm, advantageously ranging from 0 to 50 ppm, still more advantageously ranging from 0 to 30 ppm by weight relative to the total weight of said composition; ; and or

a content of SO ₄ ² ranging from 0 to 300 ppm, preferably ranging from 0 to 200 ppm, advantageously ranging from 0 to 100 ppm, still more advantageously ranging from 0 to 50 ppm by weight relative to the total weight of said composition; ; and or

a Na ⁺ content ranging from 0 to 200 ppm, preferably ranging from 0 to 100 ppm, advantageously ranging from 0 to 50 ppm, even more advantageously ranging from 0 to 20 ppm by weight relative to the total weight of said composition; and or

a content of FSO ₃ Li ranging from 0 to 500 ppm, preferably ranging from 0 to 300 ppm, advantageously ranging from 0 to 200 ppm, still more advantageously ranging from 0 to 100 ppm, and in particular ranging from 0 to 20 ppm; by weight relative to the total weight of said composition; and or

a content of FSO ₂ NH ₂ ranging from 0 to 200 ppm, preferably ranging from 0 to 100 ppm, advantageously ranging from 0 to 50 ppm, still more advantageously ranging from 0 to 20 ppm, and in particular ranging from 0 to 10 ppm; ppm by weight relative to the total weight of said composition.

According to one embodiment, the composition comprises:

C1 ions in a content ranging from 0.1 to 20 ppm by weight, preferably from 0.1 to 15 ppm, and still more advantageously from 0.1 to 10 ppm by weight relative to the total weight of said composition; and or

an F-content ranging from 0.1 to 200 ppm, preferably ranging from 0.1 to 50 ppm, advantageously ranging from 0.1 to 30 ppm by weight relative to the total weight of said composition; and or

a content of H ₂ O ranging from 0.1 to 200 ppm, preferably ranging from 0.1 to 100 ppm, advantageously ranging from 0.1 to 50 ppm, still more advantageously from 0.1 to 30 ppm by weight; relative to the total weight of said composition; and or

a content of SO ₄ ² ranging from 0.1 to 300 ppm, preferably ranging from 0.1 to 200 ppm, advantageously ranging from 0.1 to 100 ppm, still more advantageously ranging from 0.1 to 50 ppm by weight; relative to the total weight of said composition C; and or

a Na ⁺ content ranging from 0.1 to 200 ppm, preferably ranging from 0.1 to 100 ppm, advantageously ranging from 0.1 to 50 ppm, still more advantageously ranging from 0.1 to 20 ppm by weight; relative to the total weight of said composition; and or

a content of FS0 ₃ Li ranging from 0.1 to 500 ppm, preferably ranging from 0.1 to 300 ppm, advantageously ranging from 0.1 to 200 ppm, more advantageously from 0.1 to 100 ppm, and in particular ranging from 0.1 to 20 ppm by weight relative to the total weight of said composition; and or

a content of FSO ₂ NH ₂ ranging from 0.1 to 200 ppm, preferably ranging from 0.1 to 100 ppm, advantageously ranging from 0.1 to 50 ppm, more advantageously from 0.1 to 20 ppm, and in particular ranging from 0.1 to 10 ppm by weight relative to the total weight of said composition. The composition may also comprise a butyl acetate content less than or equal to 2000 ppm, preferably less than or equal to 1500 ppm, preferably less than or equal to 1000 ppm, advantageously less than or equal to 500 ppm, even more advantageously lower or equal to 250 ppm, for example less than or equal to 150 ppm.

Preferably, the composition according to the invention is characterized in that the sum of the total contents of acetic acid and of butyl acetate is less than or equal to 2 200 ppm, preferably less than or equal to 1 700 ppm, advantageously less than or equal to at 1200 ppm based on the total weight of the composition. In particular, the composition is such that:

0.1 ppm <[acetic acid] + [butyl acetate] <1500 ppm, and preferentially:

0.1 ppm <[acetic acid] + [butyl acetate] <1000 ppm.

The composition may also comprise a butanol content less than or equal to 500 ppm, preferably less than or equal to 300 ppm, preferably less than or equal to 200 ppm, advantageously less than or equal to 100 ppm, in particular less than or equal to 50 ppm by relative to the total weight of the composition.

The composition may also comprise a content of crystallization solvent, preferably chosen from chlorinated solvents and aromatic solvents, less than or equal to 1000 ppm, preferably less than or equal to 800 ppm, preferably less than or equal to 500 ppm, advantageously less than or equal to 200 ppm, in particular less than or equal to 100 ppm relative to the total weight of the composition.

In the context of the invention, the term "crystallization solvent", the solvent optionally used to crystallize the lithium salt of bis (fluorosulfonyl) imide. This solvent is preferably dichloromethane or toluene.

Preferably, the composition according to the invention is characterized in that the sum of the total contents of acetic acid and water is less than or equal to 400 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 250 ppm by relative to the total weight of the composition. In particular, the composition is such that:

0.1 ppm <[acetic acid] + [water] <150 ppm, and preferentially:

0.1 ppm <[acetic acid] + [water] <100 ppm

The amount of acetic acid and / or butyl acetate and / or butanol and / or crystallization solvent is determined by proton NMR with an internal standard: trifluorotoluene. The composition according to the invention can be obtained by a process comprising the following steps:

a) a step of pre-concentration of a composition C1 comprising an organic solvent SOI, water and bis (fluorosulfonyl) imide salt, to produce a composition C2 comprising:

o the lithium salt of bis (fluorosulfonyl) imide in a content ranging from 35% to 50%, preferably from 40% to 45% by weight relative to the total weight of the composition C2;

water at a mass content less than or equal to 500 ppm, preferably less than or equal to 300 ppm, advantageously less than or equal to 100 ppm relative to the total mass of the composition C2;

said pre-concentration step being carried out at a temperature of less than or equal to 50 ° C;

b) a step of concentration of the composition C2;

- c) a possible crystallization step of the composition obtained in step b).

The bis (fluorosulfonyl) imide lithium salt of the composition C1 can be obtained by any known method for preparing said salt, for example as described in WO2015 / 158979 or WO2009 / 1233328.

The composition C1 may be obtained by any known method for preparing bis (fluorosulfonyl) imide lithium salt.

The composition C1 can also be obtained according to a process comprising the following steps:

i) a process for preparing the lithium salt of bis (fluorosulfonyl) imide, said salt possibly being solid or in solution in an organic solvent SO 2;

ii) a step of contacting with an organic solvent SO 2 in the case where the LiFSI salt obtained in step i) is solid;

iii) liquid-liquid extraction of said salt from the solution containing the organic solvent SO 2 and the salt, with deionized water to form an aqueous solution of said bis (fluorosulfonyl) imide salt;

iv) optionally step of concentration of said aqueous solution;

v) liquid-liquid extraction of the bis (fluorosulfonyl) imide salt from the aqueous solution with an organic solvent SOI, to recover the composition C1.

Preferably, the composition C1 comprises:

a mass content of water ranging from 0.1% to 10%, preferably from 1% to 10%, advantageously from 1.5% to 10% by weight relative to the total weight of said composition C1; and or a mass content of bis (fluorosulfonyl) imide salt ranging from 5% to 30%, preferably from 5% to 20% by weight relative to the total mass of the composition.

The above-mentioned organic solvent SO 2 may be selected from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. Preferably, the solvent SO 2 is chosen from dichloromethane, ethyl acetate, butyl acetate, tetrahydrofuran, acetonitrile, diethyl ether, and mixtures thereof. Preferably, the organic solvent SO 2 is butyl acetate.

According to the invention, the above-mentioned step iii) can be repeated at least once.

According to one embodiment, the organic solvent SOI is selected from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. Preferably, the SOI solvent is chosen from ethers, esters, and mixtures thereof. For example, mention may be made of methyl t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, butyl acetate, dichloromethane, tetrahydrofuran, acetonitrile and diethyl ether, and their mixtures. Preferably, the solvent SOI is chosen from methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate and butyl acetate, and mixtures thereof, the organic solvent SO 2 being preferentially butyl acetate.

Pre-concentration step a) is preferably carried out at a temperature of 25 ° C to 45 ° C, preferably 30 ° C to 40 ° C.

Preferably, the pre-concentration step a) is carried out under reduced pressure, for example at a pressure of less than or equal to 50 mbar abs, in particular at a pressure of less than or equal to 30 mbar abs.

The pre-concentration step a) can be carried out by any means allowing the concentration, for example using an evaporator.

Preferably, the above-mentioned step b) is carried out in a short-path thin-film evaporator under the following conditions:

temperature between 30 ° C and 95 ° C, preferably between 30 ° C and 90 ° C, preferably between 40 ° C and 85 ° C, in particular between 60 ° C and 80 ° C,

pressure between 10 ³ mbar abs and 5 mbar abs, and in particular between

5.10 ¹ and 2 mbar abs;

- residence time less than or equal to 5 min, preferably less than or equal to 3 min.

In the context of the invention, and unless otherwise stated, the term "residence time" means the time elapsing between the entry of the lithium salt solution of bis (fluorosulfonyl) imide (in particular obtained at the end of step b) above) in the evaporator and the outlet of the first drop of the solution.

According to a preferred embodiment, the temperature of the condenser of the short-path thin-film evaporator is between -50 ° to 5 ° C., preferably between -35 ° C. and 5 ° C. In particular, the temperature of the condenser is -5 ° C.

Short-path thin-film evaporators according to the invention are also known under the name "Wiped film short path" (WFSP). They are typically so called because the vapors generated during evaporation make a "short trip" (short distance) before being condensed to the condenser.

Among the short-path thin film evaporators, there may be mentioned evaporators marketed by the companies Buss SMS Ganzler ex Luwa AG, UIC Gmbh or VTA Process.

Typically, short-path thin-film evaporators may include a solvent vapor condenser positioned within the apparatus itself (particularly in the center of the apparatus), unlike other types of film evaporators. thin (which are not short path) in which the condenser is located outside the device.

In this type of apparatus, the formation of a thin film of product to be distilled on the internal hot wall of the evaporator can typically be provided by continuously spreading on the evaporation surface by mechanical means. specified below.

The evaporator may in particular be provided at its center, an axial rotor on which are mounted the mechanical means that allow the formation of the film on the wall. They may be rotors equipped with fixed blades: three-blade or four-blade lobed rotors in flexible or rigid materials, distributed over the entire height of the rotor or rotors equipped with moving blades, pallets, scrapers, guided rubbers. In this case, the rotor may be constituted by a succession of articulated pallets on pivot mounted on a shaft or axis via radial supports. Other rotors may be equipped with mobile rollers mounted on secondary axes and said rollers are pressed on the wall by centrifugation. The rotational speed of the rotor which depends on the size of the apparatus can be readily determined by those skilled in the art. The various mobiles can be made of various materials, for example metal, steel, alloy steel (stainless steel), aluminum, or polymers, for example polytetrafluoroethylene PTFE or glass materials (enamel); metallic materials coated with polymeric materials.

According to one embodiment, the solution is introduced into the short-path thin film evaporator with a flow rate of between 700 g / h and 1200 g / h, preferably between 900 g / h and 1100 g / h for a evaporation surface of 0.04 m ² . According to one embodiment, the aforementioned method further comprises a step c) of crystallization of the lithium salt of bis (fluorosulfonyl) imide obtained at the end of step b) mentioned above.

The crystallization step may be carried out in an organic solvent ("crystallization solvent") chosen from chlorinated solvents, such as, for example, dichloromethane, and aromatic solvents, such as, for example, toluene.

Preferably, the LiFSI composition obtained at the end of step c) is recovered by filtration.

Preferably, the crystallization is carried out at a temperature of less than or equal to 25 ° C., preferably less than or equal to 15 ° C.

The ester solvents used to prepare the bis (fluorosulfonyl) imide lithium salt can be hydrolyzed (in the presence of water) to the decomposition products: acid and alcohol. Butyl acetate can in particular be hydrolyzed to acetic acid and butanol. The inventors have discovered that a high content of acetic acid can adversely affect the performance of the battery. Thus, the process according to the invention advantageously makes it possible to reduce or even avoid the partial decomposition of the organic solvents used, such as, for example, butyl acetate and acetic acid and / or butanol.

The composition according to the invention advantageously leads to improved performance in the batteries. In particular, the composition according to the invention has at least one of the following advantages:

the corrosion of the aluminum current collector is advantageously reduced and / or zero;

- improved battery life;

- improved battery performance.

The present invention also relates to the use of the composition according to the invention in batteries, in particular in Li-ion batteries.

In particular, the composition according to the invention can be used in Li-ion batteries of mobile devices (for example mobile phones, cameras, tablets or laptops), or electric vehicles, or storage vehicles. renewable energy (such as photovoltaic or wind energy).

In the context of the invention, "between x and y" or "ranging from x to y" means an interval in which the terminals x and y are included. For example, the temperature "between 30 and 100 ° C" includes in particular the values 30 ° C and 100 ° C. All the embodiments described above can be combined with each other.

The present invention is illustrated by the following example, to which it is however not limited.

EXPERIMENTAL PART

Residual solvent content: Head space method or head space

Equipment: Agilent 6890

Head-space chromatographic system: Agilent 6890

Column HP-5 length: 30m, internal diameter 0.32mm, active phase thickness: 0.25pm Chromatographic conditions: oven 60 ° C for 2minute then ramp from 30 ° C / min to 300 ° C and maintained at 300 ° C for 2 minutes.

Injector: 250 ° C

FID detector at 300 ° C

Head-space conditions 80 ° C for 30minutes

Sampling: 0.05 g of LiFSI dissolved in 200 ml of an aqueous solution of dimethylsulfoxide, DMSO: DMSO / ultra pure water: 20/80 by volume. 2 ml of an aqueous solution of NaCl (20% by weight) are then added. The solution obtained is then transferred to a vial which is sealed.

Quantification:

A calibration was carried out from the pure products. The detection limits were evaluated:

Butyl acetate = 0.01% by weight

Butanol-1 = 0.01% by weight

Dichloromethane = 0.01% by weight

Toluene = 0.05% by weight

Acetic acid = 5% by weight

The limit of detection of acetic acid is particularly high.

Residual solvent content: NMR method

The H1 NMR analysis conditions are as follows:

Equipment: NMR spectra and quantification were performed on a Bruker AV 400 spectrometer, at 376.47 MHz for ¹⁹ F, on a 5 mm BBFO ⁺ probe.

Sampling:

The LiFSI samples are dissolved in DMSO-d6 (about 30 mg in 0.6 ml). Quantification:

Absolute quantification by ¹⁹ F NMR and proton NMR is done by metered addition of α, α, α-trifluorotoluene (TFT), Aldrich into the tube containing the sample. The signals of the fluorinated species to be assayed are integrated in comparison with that of the CF _3s of this internal standard, according to a method well known to those skilled in the art. In proton NMR the quantification is done similarly to the aromatic proton signal of trifluorotoluene. The limit of quantification of a species is of the order of fifty ppm.

Example 1

Either a solution of 134 g of LiFSI in 823 g of butyl acetate (which can for example be obtained according to the method described in WO2015158979). The concentration of LiFSI is about 10% by weight and the water content of this solution is 3% by weight. The water content of this solution is greater than the solubility of water in butyl acetate due to the combination of lithium salt with water. A first concentration by evaporation of the solvent is carried out with a rotary evaporator at 40 ° C under reduced pressure (P <30mbars). A solution is obtained whose dry extract is 42% and the water content measured by titration is 430 pppm. The last concentration is carried out on a film evaporation apparatus WFSP (Wiped Film Short Path) at the temperature of 80 ° C scus a vacuum of 0.5 mbar. This concentrate is taken up in dichloromethane. LiFSI crystallizes rapidly. After one hour of contact time, solid LiFSI is obtained which is recovered by filtration and which is dried under vacuum for at least 24 hours. The mass of solid LiFSI is 1 10 g, a yield of 82%.

The analysis of the residual solvents in the LiFSI obtained is as follows:

Example 2 (comparative):

Either a solution containing 53 g of LiFSI in 640 g of butyl acetate (for example obtained according to the process described in WO2015158979). The water content is 3.2% by weight. Evaporated under vacuum at 70 ° C. A solution is obtained when the solids content is 40% and the water content is 1050 ppm by weight. The last concentration is carried out on a film evaporation apparatus WFSP (Wiped Film Short Path) at a temperature of 80 ° C. under a vacuum of 0.5 mbar. The concentrate is taken up in dichloromethane. LiFSI crystallizes rapidly. After one hour of contact time, 44 g LiFSI is obtained which is recovered by filtration and which is dried under vacuum for at least 24 hours. Residual solvent analysis is given below.

The "head-space" measurement method by gas chromatography introduces a bias in the quantification of organic species because the measurement is directly related to the liquid / vapor equilibrium of the system (underestimated results). The NMR assay method is more reliable because it is a direct measurement of the composition, and has a lower detection limit than the head-space method.

Example 3: chronoamperometry and cyclic voltammetry tests

The electrolyte solutions No. 1 and No. 2 are made by dissolving the LiFSIs prepared according to Examples 1 and 2 above in a mixture of ethylene carbonate / ethylmethylcarbonate 3/7 by volume. The concentration of LiFSI is 0.8 mol / l. In addition, 2% by weight of fluroethylene carbonate is added to each electrolyte.

Cyclic voltammetry test: The cyclic volumetric tests are performed on button cells with a lithium metal anode and an aluminum cathode with the prepared electrolyte. The voltage is varied between 0 and 6V with a scanning speed of 1 mV / s over 3 cycles. The current obtained in the third cycle is noted, therefore, after formation of the optional passivation layer. The table below presents the results:

It is observed that the electrolyte # 2 led to a running having a higher intensity than that obtained with the electrolyte ⁰ n 1. The current with a higher intensity (electrolyte No. 2) indicates a higher corrosion of the aluminum.

This test consists in imposing a constant voltage on a battery of the same type as that described for the cyclic voltametry test and for monitoring the intensity of current through the cell. The objective is to measure the leakage current, residual current of constant intensity, which accounts for the polarization of the battery and its lifetime. The higher the leakage current, the shorter the life of the battery. The test was performed at 4V.

For the cell made with the LiFSI of the exemplel, the leakage current is 3.1 mA. The leakage current for the cell manufactured with the LiFSI of Example 2 is 15 mA.

These two tests show that electrolyte No. 2 prepared with a LiFSI containing 550 ppm of acetic acid has degraded performance relative to the electrolyte No. 1 prepared with the LiFSI of Example 1.

Claims

1. Composition comprising:

at least 99.75% by weight of bis (fluorosulfonyl) imide lithium salt; and

- Acetic acid in a mass content strictly greater than 0 and less than or equal to 400 ppm.

2. Composition according to claim 1, comprising at least 99.78%, preferably at least 99.80%, advantageously at least 99.85%, even more preferably at least 99.90% by weight of bis (fluorosulfonyl) lithium salt. imide, based on the total weight of said composition.

3. Composition according to any one of claims 1 or 2, comprising at least 99.95%, preferably at least 99.97%, advantageously at least 99.98%, even more preferably at least 99.99% by weight of lithium salt of bis (fluorosulfonyl) imide relative to the total weight of said composition.

4. Composition according to any one of claims 1 to 3, wherein the mass content of acetic acid is less than or equal to 350 ppm, preferably less than or equal to 300 ppm, preferably less than or equal to 250 ppm, still more advantageously lower or equal to 200 ppm, for example less than or equal to 150 ppm relative to the total weight of the composition.

5. A composition according to any one of claims 1 to 4, wherein the mass content of acetic acid ranges from 0.1 ppm to 300 ppm, preferably from 0.1 ppm to 200 ppm, preferably from 0.1 ppm to 150 ppm, more preferably from 0.1 ppm to 100 ppm relative to the total weight of the composition.

6. Composition according to any one of claims 1 to 5, comprising:

C1 ions in a content ranging from 0 to 20 ppm by weight, preferably from 0 to 15 ppm, from 0 to 10 ppm relative to the total weight of said composition; and or

an F-content ranging from 0 to 200 ppm, preferably ranging from 0 to 50 ppm, advantageously ranging from 0 to 30 ppm by weight relative to the total weight of said composition; and or an H ₂ O content ranging from 0 to 200 ppm, preferably ranging from 0 to 100 ppm, advantageously ranging from 0 to 50 ppm, still more advantageously ranging from 0 to 30 ppm by weight relative to the total weight of said composition; ; and or

a Na ⁺ content ranging from 0 to 200 ppm, preferably ranging from 0 to 100 ppm, advantageously ranging from 0 to 50 ppm, still more advantageously ranging from 0 to 20 ppm by weight relative to the total weight of said composition; and or

a content of FS0 ₃ Li ranging from 0 to 500 ppm, preferably from 0 to

300 ppm, advantageously ranging from 0 to 200 ppm, more advantageously from 0 to 100 ppm, and in particular ranging from 0 to 20 ppm by weight relative to the total weight of said composition; and or

a content of FSO ₂ NH ₂ ranging from 0 to 200 ppm, preferably from 0 to

100 ppm, advantageously ranging from 0 to 50 ppm, more advantageously from 0 to 20 ppm, and in particular ranging from 0 to 10 ppm by weight relative to the total weight of said composition.

7. Composition according to any one of claims 1 to 6, comprising a content of butyl acetate less than or equal to 2000 ppm, preferably less than or equal to 1500 ppm, preferably less than or equal to 1000 ppm, advantageously less than or equal to 500 ppm, still more preferably less than or equal to 250 ppm, for example less than or equal to 150 ppm.

8. Composition according to any one of claims 1 to 7, characterized in that the sum of the total contents of acetic acid and butyl acetate is less than or equal to 2200 ppm, preferably less than or equal to 1700 ppm, advantageously less than or equal to 1,200 ppm relative to the total weight of the composition.

9. Composition according to any one of claims 1 to 8, comprising a butanol content less than or equal to 500 ppm, preferably less than or equal to 300 ppm, preferably less than or equal to 200 ppm, advantageously less than or equal to at 100 ppm, in particular less than or equal to 50 ppm by weight relative to the total weight of the composition.

10. Composition according to any one of claims 1 to 9, comprising a content of crystallization solvent, preferably selected from chlorinated solvents and aromatic solvents, less than or equal to 1000 ppm, preferably less than or equal to 800 ppm, preferably less than or equal to 500 ppm, advantageously less than or equal to 200 ppm, in particular less than or equal to 100 ppm relative to the total weight of the composition.

1. Composition according to any one of claims 1 to 10, characterized in that the sum of the total contents of acetic acid and water is less than or equal to 400 ppm, preferably less than or equal to 300 ppm, advantageously lower or equal to 250 ppm relative to the total weight of the composition.

Process for the preparation of a composition according to any one of Claims 1 to 11, comprising the following steps:

b) a step of concentration of the composition C2;

- c) a possible crystallization step of the composition obtained in step b).

13. Process according to claim 12, characterized in that the composition C1 comprises:

a mass content of water ranging from 0.1% to 10%, preferably from 1% to 10%, advantageously from 1.5% to 10% by weight relative to the total weight of said composition C1; and or

a mass content of bis (fluorosulfonyl) imide salt ranging from 5% to 30%, preferably from 5% to 20% by weight relative to the total mass of the composition.

14. Process according to any one of claims 12 or 13, characterized in that the organic solvent SOI is chosen from the group consisting of esters, nitriles, ethers, chlorinated solvents, aromatic solvents, and mixtures thereof. preferably being selected from methyl-t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate, butyl acetate, and mixtures thereof, the organic solvent SO 2 being preferentially ethyl acetate. butyl.

15. A process according to any one of claims 12 to 14, wherein the pre-concentration step a) is carried out under reduced pressure, for example at a pressure of less than or equal to 50 mbar abs, in particular at a lower pressure. or equal to 30 mbar abs.

The process according to any of claims 12 to 15, wherein step b) is carried out in a short-path thin-film evaporator under the following conditions:

- pressure between 10 ^-3 mbar abs and 5 mbar abs, and in particular at between 5.10 ¹ and 2 mbar abs;