Method for manufacturing sodium bis(fluorosulfonyl)imide salt

Abstract

The present invention relates to a method for preparing the sodium salt of bis(fluorosulfonyl)imide (NaFSI).

Description

DescriptionMethod for manufacturing sodium bis(fluorosulfonyl)imide saltCross reference to related patent application(s)

[0001] The present application claims priority filed in Europe on 7 August 2023 with No.23306343.7, the whole content of this patent application being incorporated herein by reference for all purposes.Technical field

[0002] The present invention relates to a method for preparing the sodium salt of bis(fluorosulfonyl)imide (NaFSI).Background

[0003] Lithium-ion batteries are one of the most important energy storage products in the field of consumer electronics, electric vehicles, and so on.

[0004] However, lithium metal resources are limited, unevenly distributed, it is difficult to meet the huge energy storage market demand in the future, so finding lithium alternatives is an important way to solve this problem.

[0005] Sodium-ion batteries and lithium-ion batteries have a similar working principle, and have received much attention in recent years.

[0006] Several types of sodium salts have been studied as electrolytes for sodium-ion batteries, among which sodium bis(fluorosulfonyl)imide is considered of interest for its high conductivity, excellent stability and high and low temperature performance.

[0007] Methods for manufacturing sodium bis(fluorosulfonyl)imide and its use in sodium-ion batteries have been disclosed, for example, in CN116143087 (in the name of ZHEJIANG YANYI NEW ENERGY TECHNOLOGY CO., LTD.), CN115692827 (in the name of SHENZHEN CAPCHEM TECHNOLOGY CO., LTD.).

[0008] CN 114572945 discloses in Example 8, a method for preparing sodium salt of bis(fluorosulfonyl)imide (FSI) as follows :(1) charging a flask with chloroform solvent and sodium bicarbonate (with a mass concentration of water of 0.2 ppm) under the protection of highly pure argon. The temperature of the mixture was brought to 25 °C, then 1 mol of the FSI placed in a dry constant pressure dropping funnel was added dropwise to the flask containing chloroform and sodium bicarbonate, and the drop acceleration was controlled by keeping the mixture at 25 °C. After the addition was complete, the reaction was stirred at 50 °C for 20 hours and then slowly warmed to 130 °C for 3 hours. (2) After completion of the reaction, the mixture obtained after the reaction is filtered, and the solid material obtained is dried under reduced pressure at a temperature of 80 °C and a vacuum of 100 Pa. When the product becomes a paste, the vacuum is adjusted to 2 Pa to give crude sodium bisfluorosulfonimide. This document dislcoses that the reactants are put at 25°C but it is then necessary to increase the temperature up to 50°C and then up to 130°C for the reaction to proceed.

[0009] CN 116354319 discloses a method comprising the steps of: (1) reacting a bisfluorosulfonimide acid with an alkali metal source, which is a carbonate or an alkali metal hydroxide, in a poor solvent for the bisfluorosulfonimide salt to form the bisfluorosulfonimide salt; (2) when the alkali metal source in step (1) is an alkali metal hydroxide, or the alkali metal source in step (1) is carbonate and the molar ratio of carbonate to bisfluorosulfonimide acid < 1:1, carbonate is added to the reacted system, and then the reaction is carried out by passing carbon dioxide gas, when the lithium source in step (1) is carbonate and the molar ratio of carbonate to bisfluorosulfonimide acid is greater than or equal to 1:1, the solid-liquid separation yields the crude bisfluorosulfonimide salt. The reaction is carried out by passing carbon dioxide gas directly into the reaction system and separating the solid and liquid to obtain the crude difluorosulfonimide salt; the carbonate is lithium carbonate or sodium carbonate; and the hydroxide of the alkali metal is lithium hydroxide or sodium hydroxide.

[0010] The poor solvent in step (1) - when the alkali metal source is lithium carbonate or lithium hydroxide - is one or both of dichloromethane, dichloroethane, which comply with the requirements of not dissolving lithium carbonate and lithium bisfluorosulfonimideSummary of the invention

[0011] The Applicant faced the problem of providing a stable NaFSI solution, in a suitable solvent, which can be directly used in the manufacture of an electrolyte formulation.

[0012] More in particular, the Applicant faced the problem of developing a method for the manufacture of a solution of a high purity sodium bis(fluorosulfonyl)imide, wherein the formation of FSI side-products is limited or even avoided, such that a high purity salt of bis(fluorosulfonyl)imide is obtained and the need for post-purification step(s) is limited.

[0013] Surprisingly, the Applicant developed a method for the manufacture of a solution of a high purity sodium bis(fluorosulfonyl)imide, wherein certain FSI side-products are in the solid form, such that they can be easily removed via filtration or any other solid / liquid separation method.

[0014] Also, the method developed by the Applicant is characterized by a low energy consumption, which makes it suitable for industrial application.

[0015] Thus, in a first embodiment, the present invention relates to a method for manufacturing a solution comprising at least one organic aprotic solvent and at least one sodium salt of bis(fluorosulfonyl)imide.Detailed description of the invention

[0016] In the present description and in the following claims:- the numerical ranges include the limits, unless otherwise specified;- any description, even though described in relation to a specific embodiment, is applicable to and interchangeable with other embodiments of the present invention;- where an element or component is said to be included in and / or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components; any element or component recited in a list of elements or components may be omitted from such list;- any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited ranges as well as the endpoints of the range and equivalents.

[0017] Thus, in a first embodiment, the present invention relates to a method for manufacturing a liquid composition [composition (S1)] comprising at least one organic aprotic solvent and sodium bis(fluorosulfonyl)imide salt (NaFSI) represented by the following formula (I):said method comprising the following steps:(A) contacting hydrogen bis(fluorosulfonyl)imide (HFSI), at least one aprotic organic solvent [solvent (S)] and at least one sodium-containing compound [compound (Na)], so as to provide a reaction mixture [mixture (M1)],(B) controlling the temperature of said mixture (M1) between 15°C and 35°C,(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) and at least one by-product in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

[0018] Surprisingly, the Applicant found that controlling the temperature of mixture (M1), in particular in the range between 15°C and 35°C, allows to hydrolyse certain byproducts as insoluble solid particles, which can be easily removed via step (D), while the NaFSI salt is stable and does not degrade into additional impurities.

[0019] Surprisingly, the Applicant found that by controlling the temperature of mixture (M1) during step (B) and step (C), it is possible to obtain the final composition without the need of raising the reaction temperature up to 50°C or even up to higher temeprature.

[0020] Advantageously, the method according to the present invention allows to avoid a step of removal of water, such as for example drying or azeotropic drying, whilesteps (B) and (C) proceed, or at the end of step (C), or after step (C) and before step (D). In other words, in the method according to the present invention, no step of water removal is performed after step (B) and / or after step (C) and / or before step (D).

[0021] Preferably, said compound (Na) is selected from inorganic compounds, and more preferably from the group comprising, even more preferably consisting of: NaOH, NaOH.H2O, Na2CO3 and NaHCCh. More preferably, said compound (Na) is selected from the group consisting of NaOH and NaOH.H2O. Even more preferably, said compound (Na) is NaOH.

[0022] Preferably, the amount of said compound (Na) is from about 1.0 mol to about 2.0 mol, more preferably of from 1.0 mol to 1.5 mol, even more preferably of from 1.0 mol to 1.4 mol, and still more preferably from 1.0 mol to 1.3 mol, per 1.0 mol of HFSI. Even more preferably, the amount of said compound (Na) is from about 1.10 to 1.3 per mol of HFSI.

[0023] Advantageously, said solvent (S) is a good solvent for the reactants.

[0024] Preferably, said solvent (S) is selected in the group comprising ethylene carbonate, propylene carbonate, butylene carbonate, y-butyrolactone, y-valerolactone, dimethoxymethane, 1 ,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1 ,3-dioxane, 4-methyl-1 ,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyl oxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane and nitrobenzene.

[0025] More preferably, said solvent (S) is selected from ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, valeronitrile, benzonitrile.

[0026] According to a preferred aspect, said solvent (S) has a water content of 500 ppm or less, preferably of 250 ppm or less, more preferably of 100 ppm or less, and even more preferably of 50 ppm or less.

[0027] Advantageously, said composition (S1) is in the form of a solution.

[0028] Preferably, step (A) is performed at room temperature, which is a temperature below 30°C, such as between 20°C and 27°C.

[0029] Preferably, step (B) is performed such that the temperature is brought and kept between 15°C and 35°C, more preferably between 15°C and 25°C.

[0030] Preferably, step (C) is performed such that the temperature is kept between 15°C and 35°C, more preferably between 15°C and 25°C.

[0031] Preferably, step (A) and step (B) are performed simultaneously.

[0032] According to this embodiment, step (A) is performed by contacting said compound (AM), said solvent (S) and the HFSI, while controlling the temperature in the range between 15°C and 35°C.

[0033] Preferably, step (A), step (B) and step (C) are performed simultaneously.

[0034] Preferably, step (A), step (B) and step (C) are performed at the same pressure.

[0035] Preferably, steps (A), (B) and (C) are performed at a pressure from 1 mbar to 1 bar.

[0036] The reaction time required for step (C) is not limited. Preferably, the reaction time for step (C) is from about 10 minutes to 48 hours, more preferably between 30 minutes and 24 hours and even more preferably between 1 hour and 10 hours.

[0037] Preferably, step (A) comprises:(Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S), and(Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1).

[0038] According to an embodiment, the method of the present invention comprises:(Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S), (Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1);(B) controlling the temperature of said mixture (M1) in the range between 15°C and 35°C,(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) as defined above and at least one byproduct in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

[0039] Preferably, step (Ai) is performed at room temperature, which is below 30°C, preferably between 20°C and 27°C.

[0040] Preferably, step (Aii) and step (B) are performed simultaneously, after step (Ai). Thus, step (Aii) is performed by controlling the temperature in the range between 15°C and 35°C.

[0041] According to another embodiment, the method of the present invention comprises: (Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S), (B*) controlling the temperature of said mixture (M-i) in the range between 15°C and 35°C,(Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1),(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) as defined above and at least one byproduct in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

[0042] According to this embodiment, step (B*) corresponds to step (B) disclosed above.

[0043] Preferably, step (Ai) and step (B*) are performed simultaneously, followed by step (Aii).

[0044] Preferably, step (Ai) is performed at a temperature in the range between 15°C and 35°C.

[0045] According to this embodiment, step (Aii) is performed at the same temperature of step (Ai).

[0046] Advantageously, composition (S1) obtained at the end of step (C) comprises between 5 and 70 wt.% of said salt of formula (I), based on the total weight of the solution.

[0047] Preferably, said composition (S1) comprises between 2 and 60 wt.% of said salt of formula (I), more preferably between 5 and 50 wt.% and even more preferably between 10 and 40 wt.%.

[0048] Preferably, step (D) is performed by filtration or centrifugation.

[0049] Preferably, the filtration is performed with a polymeric filter, such as polytetrafluoroethylene (PTFE) filter.

[0050] Step (D) can be performed via other solid / liquid separation methods, depending on the circumstances.

[0051] Advantageously, the at least one by-product in the form of solid particles contains sulfate anions and / or fluoride anions.

[0052] Without being bound by any theory, the Applicant surprisingly found that by controlling the temperature under step (B), the FSOs" anions decompose into insoluble species, notably sulfate anions and / or fluoride anions, which are easily separated from composition (S) under step (D).

[0053] The method of the present invention is advantageously performed in a reaction vessel, which is preferably made from a material selected from glass, a fluororesin or a polyethylene resin.

[0054] The reaction vessel is preferably suitable for being heated at the temperature selected under step (B).

[0055] The method of the present invention may be carried out in a continuous or semi- continuous mode.

[0056] Advantageously, the ratio between the amount of FSOs" in composition (S1) obtained according to the present invention and the amount of FSOs" in the HFSI is preferably 0.30:1 or less, more preferably 0.10:1 or less and even more preferably 0.05:1, as measured by ion chromatography (IC).

[0057] A second object of the present invention is a liquid composition [composition (S1)] comprising at least one organic aprotic solvent, sodium salt of bis(fluorosulfonyl)imide (NaFSI), and at least one of the following:- fluoride anions in an amount of less than 5 ppm as measured by ion chromatography (IC), and / or- chloride anions in an amount of less than 15 ppm as measured by ion chromatography (IC), and / or- sulfate anions in an amount of less than 7 ppm as measured by ion chromatography (IC), and / or- fluorosulfonate anions in an amount of less than 5 ppm as measured by ion chromatography (IC).

[0058] Advantageously, composition (COMP) corresponds to composition (S1) as obtained after step (D) of the method according to the present invention.

[0059] A further object of the present invention is the use of said composition (S1) as electrolyte in a non-aqueous battery electrolyte solution.

[0060] Alternatively, if required by the final use or other circumstances, solid NaFSi can be obtained by properly processing said composition (S1).

[0061] Preferably, said processing is performed via known methods, such as concentration, precipitation, washing and drying.

[0062] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0063] The disclosure will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the disclosure.

[0064] Experimental Section

[0065] Example 1 - Preparation of NaFSI solution

[0066] A glass flask equipped with a mechanical stirring, a thermostated bath, a temperature probe, a syringe pump and a condenser was placed inside a glovebag, fed with dry argon flow.

[0067] The flask was loaded with acetonitrile (ACN) and NaOH (NaOH:HFSI 1.20:1 mol). The temperature setpoint of the condenser was set at 20°C, and the reaction medium at 20°C.

[0068] HFSI was added to the reaction mixture over 1 hour.This starting HFSI contained the following impurities (ppm): F = 100.0 Cl = 43.0 SO42’ = 105.0 FSO3’ = 112.0

[0069] The NaFSI concentration in the mixture at the end of the 1 hour addition was in the range 20-40 wt%. The reaction medium was maintained for 3 hours at the same temperature.

[0070] The setup was then filtered on a 0.22 micron PTFE membrane obtaining a filtrate of ACN containing NaFSI, which was analyzed by ion chromatography. The results are in Table 1 below and are compared to the initial impurities measured in the starting material (HFSI)Table 1

Claims

Claims1. A method for manufacturing a liquid composition [composition (S1)] comprising at least one organic aprotic solvent and sodium bis(fluorosulfonyl)imide salt (NaFSI) represented by the following formula (I):said method comprising the following steps:(A) contacting hydrogen bis(fluorosulfonyl)imide (HFSI), at least one aprotic organic solvent [solvent (S)] and at least one sodium-containing compound [compound (Na)], so as to provide a reaction mixture [mixture (M1)],(B) controlling the temperature of said mixture (M1) between 15°C and 35°C,(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) and at least one by-product in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

2. The method according to Claim 1 , wherein said at least one compound (Na) is selected from inorganic compounds, preferably selected from the group comprising: NaOH, NaOH.H2O, Na2CO3and NaHCO3.

3. The method according to Claim 1 or 2, wherein the amount of said compound (Na) is from 1.0 mol to 2.0 mol, per 1.0 mol of HFSI.

4. The method according to any one of Claims 1 to 3, wherein said solvent (S) is selected in the group comprising ethylene carbonate, propylene carbonate, butylene carbonate, y-butyrolactone, y-valerolactone, dimethoxymethane, 1 ,2- dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1 ,3-dioxane, 4-methyl- 1 ,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, 3-methylsulfolane, dimethylsulfoxide, N,N-dimethylformamide, N-methyl oxazolidinone, acetonitrile, valeronitrile, benzonitrile, ethyl acetate, isopropyl acetate, n-butyl acetate, nitromethane and nitrobenzene.

5. The method according to any one of Claims 1 to 4, wherein step (A) and step (B) are performed simultaneously.

6. The method according to any one of Claims 1 to 5, wherein step (A) comprises: (Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S),and(Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1).

7. The method according to any one of Claims 1 to 6, said method comprising:(Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S), (Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1);(B) controlling the temperature of said mixture (M1) in the range between 15°C and 35°C,(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) as defined in Claim 1 and at least one by-product in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

8. The method according to Claim 7, wherein step (Aii) and step (B) are performed simultaneously, after step (Ai).

9. The method according to any one of Claims 1 to 6, said method comprising:(Ai) providing a mixture (M-i) comprising said compound (Na) and said solvent (S), (B*) controlling the temperature of said mixture (M-i) in the range between 15°C and 35°C,(Aii) contacting said HFSI with said mixture (M-i), so as to provide mixture (M1),(C) letting said mixture (M1) to react, thus obtaining a composition (S) comprising at least one aprotic solvent, NaFSI of formula (I) as defined in Claim 1 and at least one by-product in the form of solid particles, and(D) separating at least a part of said at least one by-product in the form of solid particles, thus obtaining said composition (S1).

10. The method according to Claim 9, wherein step (Ai) and step (B*) are performed simultaneously, followed by step (Aii).

11. The method according to any one of Claims 1 to 10, wherein:- step (C) is performed by keeping the temperature between 15°C and 35°C, more preferably between 15°C and 25°C; and / or- step (D) is performed by filtration or centrifugation.

12. The method according to any one of Claims 1 to 11 , wherein said at least one byproduct in the form of solid particles contains sulfate anions and / or fluoride anions.

13. The method according to any one of Claims 1 to 12, wherein the ratio between the amount of FSOs" in composition (S1) and the amount of FSCh' in the HFSI is preferably 0.30:1 or less, more preferably 0.10:1 or less and even more preferably 0.05:1, as measured by ion chromatography (IC).

14. A liquid composition [composition (S1 )] comprising at least one organic aprotic solvent, sodium salt of bis(fluorosulfonyl)imide (NaFSI), and at least one of the following:- fluoride anions in an amount of less than 5 ppm as measured by ion chromatography (IC), and / or- chloride anions in an amount of less than 15 ppm as measured by ion chromatography (IC), and / or- sulfate anions in an amount of less than 7 ppm as measured by ion chromatography (IC), and / or- fluorosulfonate anions in an amount of less than 5 ppm as measured by ion chromatography (IC).

15. The composition (S1) according to Claim 14, which is obtained at the end of step (D) of the method according to any one of Claims 1 to 13.

16. Use of composition (S1) according to Claim 14 and 15, as electrolyte in a nonaqueous battery electrolyte solution.

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