Patent Grant
11697589
The present invention relates to a composition based on the lithium salt of bis(fluorosulfonyl)imide.
By virtue of their very low basicity, anions of sulfonylimide type are increasingly used in the field of energy storage in the form of inorganic salts in batteries, or of organic salts in supercapacitors or in the field of ionic liquids. Since the battery market is in full expansion and reduction of battery manufacturing costs has become a major challenge, an inexpensive large-scale process for synthesizing anions of this type is necessary.
In the specific field of Li-ion batteries, the salt that is currently the most widely used is LiPF6, but this salt has many drawbacks such as limited thermal stability, sensitivity to hydrolysis and thus lower safety of the battery. Recently, novel salts bearing the group FSO2− have been studied and have demonstrated many advantages such as better ion conductivity and resistance to hydrolysis. One of these salts, LiFSI (LiN(FSO2)2), has shown highly advantageous properties which make it a good candidate for replacing LiPF6.
The identification and quantification of impurities in salts and/or electrolytes and the understanding of their impacts on battery performance have become paramount. For example, on account of their interference with electrochemical reactions, impurities bearing a labile proton lead to reduced overall performance qualities and stability for Li-ion batteries. The application of Li-ion batteries makes it necessary to have high-purity products (minimum amount of impurities).
There is a need for novel compositions based on lithium bis(fluorosulfonyl)imide salt, for use thereof in batteries.
The present invention relates to a composition comprising:
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(FSO2)2”, “lithium bis(sulfonyl)imide” and “lithium bis(fluorosulfonyl)imide” are used equivalently.
In the context of the invention, the term “ppm” or “parts per million” is intended to mean ppm by weight.
Preferably, the abovementioned composition comprises at least 99.78%, preferentially at least 99.80%, advantageously at least 99.85% and more advantageously at least 99.90% by weight of lithium salt of bis(fluorosulfonyl)imide relative to the total weight of said composition. Preferably, the composition comprises at least 99.95%, preferentially at least 99.97%, advantageously at least 99.98% and more advantageously at least 99.99% by weight of lithium salt of bis(fluorosulfonyl)imide 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, preferentially 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, for example less than or equal to 150 ppm. Even more preferably, the content of acetic acid 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, preferentially 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 abovementioned composition may also comprise:
According to one embodiment, the composition comprises:
According to one embodiment, the composition comprises:
The composition may also comprise a content of butyl acetate of less than or equal to 2000 ppm, preferably less than or equal to 1500 ppm, preferentially less than or equal to 1000 ppm, advantageously less than or equal to 500 ppm, even more advantageously less than 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 2200 ppm, preferably less than or equal to 1700 ppm, advantageously less than or equal to 1200 ppm, relative to 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 content of butanol of less than or equal to 500 ppm, preferably less than or equal to 300 ppm, preferentially less than or equal to 200 ppm, advantageously less than or equal to 100 ppm, in particular less than or equal to 50 ppm, 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, of less than or equal to 1000 ppm, preferably less than or equal to 800 ppm, preferentially 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” means the solvent which may be 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 of 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, 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 of butyl acetate and/or of butanol and/or of crystallization solvent is determined by proton NMR with an internal standard: trifluorotoluene.
The composition according to the invention may be obtained via a process comprising the following steps:
The lithium salt of bis(fluorosulfonyl)imide of composition C1 may be obtained via any known process for preparing said salt, for example as described in WO 2015/158979 or WO 2009/1233328.
Composition C1 may be obtained via any known process for preparing the lithium salt of bis(fluorosulfonyl)imide.
Composition C1 may also be obtained via a process comprising the following steps:
Preferably, composition C1 comprises:
The abovementioned organic solvent OS2 may be chosen from the group constituted of esters, nitriles, ethers, chlorinated solvents and aromatic solvents, and mixtures thereof. Preferably, the solvent OS2 is chosen from dichloromethane, ethyl acetate, butyl acetate, tetrahydrofuran, acetonitrile and diethyl ether, and mixtures thereof. Preferably, the organic solvent OS2 is butyl acetate.
According to the invention, the abovementioned step iii) may be repeated at least once.
According to one embodiment, the organic solvent OS1 is chosen from the group constituted of esters, nitriles, ethers, chlorinated solvents and aromatic solvents, and mixtures thereof. Preferably, the solvent OS1 is chosen from ethers and 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 mixtures thereof. Preferably, the solvent OS1 is chosen from methyl t-butyl ether, cyclopentyl methyl ether, ethyl acetate, propyl acetate and butyl acetate, and mixtures thereof, the organic solvent OS2 preferentially being butyl acetate.
The preconcentration step a) is preferably performed at a temperature ranging from 25° C. to 45° C., preferably from 30° C. to 40° C.
Preferably, the preconcentration step a) is performed 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 preconcentration step a) may be performed by any concentrating means, for example using an evaporator.
Preferably, the abovementioned step b) is performed in a short-path thin-film evaporator, under the following conditions:
In the context of the invention, and unless otherwise mentioned, the term “residence time” means the time which elapses between the entry of the solution of lithium bis(fluorosulfonyl)imide salt (in particular obtained on conclusion of the abovementioned step b)) into the evaporator and the exit 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° C. and 5° C., preferably between −35° C. and 5° C. In particular, the condenser temperature is −5° C.
The short-path thin-film evaporators according to the invention are also known as “wiped-film short-path” (WFSP) evaporators. They are typically referred to as such since the vapors generated during the evaporation cover a short path (travel a short distance) before being condensed in the condenser.
Among the short-path thin-film evaporators, mention may notably be made of the evaporators sold by the companies Buss SMS Ganzler ex Luwa AG, UIC GmbH or VTA Process.
Typically, the short-path thin-film evaporators may comprise a condenser for the solvent vapors placed inside the machine itself (in particular at the center of the machine), unlike other types of thin-film evaporator (which are not short-path evaporators) in which the condenser is outside the machine.
In this type of machine, the formation of a thin film, of product to be distilled, on the hot inner wall of the evaporator may typically be ensured by continuous spreading over the evaporation surface with the aid of mechanical means specified below.
The evaporator may notably be equipped, at its center, with 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 vanes, lobed rotors with three or four vanes made of flexible or rigid materials, distributed over the entire height of the rotor, or rotors equipped with mobile vanes, paddles, doctor blades or guided scrapers. In this case, the rotor may be constituted by a succession of pivot-articulated paddles mounted on a shaft or axle by means of radial supports. Other rotors may be equipped with mobile rollers mounted on secondary axles and said rollers are held tight against the wall by centrifugation. The spin speed of the rotor, which depends on the size of the machine, may be readily determined by a person skilled in the art. The various spindles may be made of various materials: metallic, for example steel, steel alloy (stainless steel), aluminum, or polymeric, 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 an evaporation area of 0.04 m2.
According to one embodiment, the abovementioned process also comprises a step c) of crystallization of the lithium bis(fluorosulfonyl)imide salt obtained on conclusion of the abovementioned step b).
The crystallization step may be performed in an organic solvent (“crystallization solvent”) chosen from chlorinated solvents, for instance dichloromethane, and aromatic solvents, for instance toluene.
Preferably, the LiFSI composition obtained on conclusion of step c) is recovered by filtration.
Preferably, the crystallization is performed at a temperature of less than or equal to 25° C., preferentially less than or equal to 15° C.
The solvents of ester type used for preparing the lithium salt of bis(fluorosulfonyl)imide may be hydrolyzed (in the presence of water) to decomposition products: acid and alcohol. Butyl acetate may notably be hydrolyzed to acetic acid and butanol. The inventors have discovered that a high content of acetic acid may harm the performance of the battery. Thus, the process according to the invention advantageously makes it possible to reduce, or even to prevent, the partial decomposition of the organic solvents used, for instance butyl acetate to acetic acid and/or butanol.
The composition according to the invention advantageously gives improved performance in batteries. In particular, the composition according to the invention has at least one of the following advantages:
The present invention also relates to the use of the composition according to the invention in batteries, notably in Li-ion batteries.
In particular, the composition according to the invention may be used in Li-ion batteries of mobile devices (for example cellphones, cameras, tablets or laptop computers), or electric vehicles, or for storing renewable energy (such as photovoltaic or wind energy).
In the context of the invention, the term “between x and y” or “ranging from x to y” means a range in which the limits x and y are included. For example, the temperature “between 30 and 100° C.” notably includes the values 30° C. and 100° C.
All the embodiments described above may be combined with each other.
The present invention is illustrated by the example which follows, to which it is not, however, limited.
Content of Residual Solvents: Headspace Method
Equipment: Agilent 6890
Chromatographic headspace system: Agilent 6890
HP-5 column length: 30 m, inside diameter 0.32 mm, active phase thickness: 0.25 μm Chromatographic conditions: oven at 60° C. for 2 minutes then ramp of 30° C./minute up to 300° C. and then maintenance at 300° C. for 2 minutes.
Injector: 250° C.
FID detector at 300° C.
Headspace conditions: 80° C. for 30 minutes
Sampling: 0.05 g of LiFSI dissolved in 200 ml of aqueous dimethyl sulfoxide DMSO solution: DMSO/ultra-pure water: 20/80 by volume. 2 ml of aqueous NaCl solution (20% by mass) are then added. The solution obtained is then transferred into a vial, which is sealed.
Quantification:
Calibration was performed using pure products. The detection limits were evaluated:
Butyl acetate=0.01% by weight
1-Butanol=0.01% by weight
Dichloromethane=0.01% by weight
Toluene=0.05% by weight
Acetic acid=5% by weight
The acetic acid detection limit is particularly high.
Content of residual solvents: NMR method:
The 1H NMR analysis conditions are as follows:
Equipment: The NMR spectra and quantifications were performed on a Brüker AV 400 spectrometer, at t 376.47 MHz for 19F, on a 5 mm probe of BBFO+ type.
Sampling:
The LiFSI samples are dissolved in DMSO-d6 (about 30 mg in 0.6 ml).
Quantification:
The absolute quantification in 19F NMR and proton NMR is performed by dosed addition of α,α,α-trifluorotoluene (TFT, Aldrich) to the tube containing the sample. The signals for the fluorinated species to be assayed are integrated in comparison with that of the CF3 of this internal standard, according to the method that is well known to those skilled in the art. In proton NMR, the quantification is performed in a similar manner relative to the signal for the aromatic protons of the trifluorotoluene. The quantification limit of a species is of the order of a 50th of a ppm.
A solution of 134 g of LiFSI in 823 g of butyl acetate (which may be obtained, for example, according to the process described in WO 2015/158979). The LiFSI concentration is approximately 10% by weight and the water content of this solution is 3% by weight. The water content of this solution is higher than the solubility of water in butyl acetate due to the association of the lithium salt with water. A first concentration by evaporation of the solvent is performed with a rotary evaporator at 40° C. under reduced pressure (P<30 mbar). A solution with a solids content of 42% and a water content, measured by titration, of 430 ppm by weight is obtained. The final concentration is performed in a WFSP (wiped-film short-path) evaporation machine at a temperature of 80° C. under a vacuum of 0.5 mbar. This concentrate is taken up in dichloromethane. The LiFSI crystallizes rapidly. After a contact time of 1 hour, solid LiFSI is obtained and is recovered by filtration and dried under vacuum for at least 24 hours. The mass of solid LiFSI is 110 g, i.e. a yield of 82%.
The analysis of the residual solvents in the LiFSI obtained is as follows:
A solution of 53 g of LiFSI in 640 g of butyl acetate (obtained, for example, according to the process described in WO 2015/158979). The water content is 3.2% by weight. The solution is evaporated under vacuum at 70° C. A solution with a solids content of 40% and a water content of 1050 ppm by weight is obtained. The final concentration is performed in a WFSP (wiped-film short-path) evaporation machine at a temperature of 80° C. under a vacuum of 0.5 mbar. The concentrate is taken up in dichloromethane. The LiFSI crystallizes rapidly. After a contact time of 1 hour, 44 g of LiFSI are obtained and are recovered by filtration and dried under vacuum for at least 24 hours.
The residual solvent analysis is given below:
The headspace measurement method by gas chromatography introduces a bias in the quantification of the organic species since the measurement is directly linked to the liquid/vapor equilibria of the system (underestimated results). The NMR assay method is more reliable since it is a direct measurement of the composition, and it has a lower detection limit than the headspace method.
The electrolyte solutions No. 1 and No. 2 are prepared by dissolving the LiFSI prepared according to the preceding Examples 1 and 2 in a 3/7 by volume ethylene carbonate/ethyl methyl carbonate mixture. The LiFSI concentration is 0.8 mol/l. Furthermore, 2% by weight of fluoroethylene carbonate is added to each electrolyte.
Cyclic voltammetry test: The cyclic voltammetry 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 6 V with a sweep speed of 1 mV/s over three cycles. The current obtained on the third cycle, thus after the possible formation of the passivation layer, is noted.
The table below presents the results:
It is observed that electrolyte No. 2 leads to a current having a higher intensity than that obtained with electrolyte No. 1. The current with a higher intensity (electrolyte No. 2) indicates greater corrosion of the aluminum.
Chronoamperometry:
This test consists in imposing a constant voltage to a battery of the same type as that described for the cyclic voltammetry test and in monitoring the current intensity across the cell. The objective is to measure the leakage current, residual current of constant intensity, which reflects the polarization of the battery and thus its service life. The greater the leakage current, the shorter will be the service life of the battery. The test was performed at 4 V.
For the cell prepared with the LiFSI of Example 1, the leakage current is 3.1 pA. The leakage current for the cell manufactured with the LiFSI of Example 2 is 15 pA.
These two tests show that electrolyte No. 2 prepared with an LiFSI containing 550 ppm of acetic acid has degraded performance relative to electrolyte No. 1 prepared with the LiFSI of Example 1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1854788 | Jun 2018 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2019/051244 | 5/28/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2019/229366 | 12/5/2019 | WO | A |
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| 20210221685 A1 | Jul 2021 | US |
