METHOD FOR PRODUCING BIS(FLUOROSULFONYL)IMIDE LITHIUM SALT (LIFSI) WITH REDUCED FLUORINE ANION CONTENT BY USING ALKOXY TRIALKYL SILANE

Abstract

A method for producing a bis(fluorosulfonyl)imide lithium salt is disclosed. The method includes the steps of: (a) reacting bis(chlorosulfonyl)imide with NH.sub.4F(HF)n (n=0-10) to prepare ammonium bis(fluorosulfonyl)imide; and (b) reacting the ammonium bis(fluorosulfonyl)imide with a lithium base, wherein in at least one of steps (a) and (b), after the reaction, a process of adding an alkoxy trialkyl silane to the reaction solution to remove a fluorine anion is performed.

Claims

1. A method for producing a bis(fluorosulfonyl)imide lithium salt, comprising the steps of: (a) reacting bis(chlorosulfonyl)imide with NH.sub.4F(HF)n (n=0-10) to prepare ammonium bis(fluorosulfonyl)imide; and (b) reacting the ammonium bis(fluorosulfonyl)imide with a lithium base, wherein in at least one of steps (a) and (b), after the reaction, a process of adding an alkoxy trialkyl silane to the reaction solution to remove a fluorine anion is performed.

2. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 1, wherein the alkoxy trialkyl silane is added in an amount of 0.01 to 10 equivalents per 1 equivalent of fluorine anions (F.sup.−) generated after the reaction.

3. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 1, wherein (1) after the reaction in step (a), a step of adding and stirring alkoxy trialkyl silane to the reaction solution is performed; (2) after the reaction in step (b), a step of adding and stirring alkoxy trialkyl silane to the reaction solution is performed; or both of steps (1) and (2) above are performed.

4. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 3, wherein in the case of performing step (1), after the reaction is terminated, a process of bubbling is further performed by supplying nitrogen gas to the reactant until the pH of the flowing gas becomes 6 to 8.

5. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 3, wherein step (2) is carried out after a first concentration of the reaction product of step (b).

6. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 5, wherein after the reaction in step (2) is terminated, a secondary concentration process is further performed while supplying nitrogen gas to the reactant.

7. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 1, wherein the alkoxy trialkyl silane is at least one selected from methoxytrimethylsilane and ethoxytriethylsilane.

8. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 1, wherein the reactions in steps (a) and (b) are carried out in a solution, and the solvents are each independently at least one selected from the group consisting of diethyl ether, diisopropyl ether, methyl-t-butyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentane, hexane, and heptane.

9. The method for producing the bis(fluorosulfonyl)imide lithium salt according to claim 1, wherein the lithium base in step (c) is at least one selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH.H.sub.2O), lithium carbonate (Li.sub.2CO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), lithium chloride (LiCl), lithium acetate (LiCH.sub.3COO), and lithium oxalate (Li.sub.2C.sub.2O.sub.4).

Description

BEST MODE

[0030] Hereinafter, the present invention will be described in detail.

[0031] The present invention relates to a method for producing a bis(fluorosulfonyl)imide lithium salt, comprising the steps of:

[0032] (a) reacting bis(chlorosulfonyl)imide with NH.sub.4F(HF)n (n=0-10) to prepare ammonium bis(fluorosulfonyl)imide; and

[0033] (b) reacting the ammonium bis(fluorosulfonyl)imide with a lithium base, wherein in at least one of steps (a) and (b), after the reaction, a process of adding an alkoxy trialkyl silane to the reaction solution to remove a fluorine anion is performed.

[0034] In the process of producing bis(fluorosulfonyl)imide lithium salt, various adsorbents are used to remove fluorine anions (F.sup.−), and most of them are adsorbents in solid form. However, the adsorbents in the solid form increase the number of processes in the actual use process, and generate other impurities, and thus they have the disadvantage of being inefficient. In addition, known liquid adsorbents have an inefficient effect of removing fluorine anions, and there was a problem that it was not easy to separate them from the reaction solution.

[0035] The alkoxy trialkyl silane used in the present invention can very efficiently remove fluorine anion in the preparation process of bis(fluorosulfonyl)imide lithium salt, by forming a strong bond with fluorine anion and thus easily removing fluorine anion by a chemical method, as shown in Reaction Scheme 1 below.

[0036] Chemically, since the adsorptive power between Si and F is much greater than that between Si and O, alkoxy trialkyl silane is used for the deprotection reaction of silyl ether. Therefore, as shown in the following Reaction Scheme, if a reagent such as methoxytrimethylsilane is used, the concentration of fluorine anions generated in the preparation process of LiFSI can be significantly reduced.

##STR00003##

[0037] As used herein, the term “alkyl” may be an alkyl group having 1 to 5 carbon atoms, and may be, for example, methyl, ethyl, propyl, or butyl.

[0038] As used herein, the term “alkoxy” may be an alkoxy group having 1 to 4 carbon atoms, and may be, for example, methoxy, ethoxy, propoxy, butoxy, or the like.

[0039] In the present invention, the alkoxy trialkyl silane may be added in an amount of 0.01 to 10 equivalents per 1 equivalent of fluorine anion (F.sup.−) generated after the reaction, more preferably in an amount of 0.05 to 10 equivalents. If the alkoxy trialkyl silane is contained in the range as described above, it is preferable because it can sufficiently remove fluorine anions.

[0040] In one embodiment of the present invention, the process of removing the fluorine anions may be achieved by performing,

[0041] (1) a step of adding and stirring alkoxy trialkyl silane to the reaction solution, after the reaction in step (a);

[0042] (2) a step of adding and stirring alkoxy trialkyl silane to the reaction solution, after the reaction in step (b); or

[0043] both of steps (1) and (2) above.

[0044] In the case of performing step (1) or step (2) above, after the reaction is terminated, a bubbling process may be further performed by supplying nitrogen gas to the reactant until the pH of the flowing gas is 6 to 8.

[0045] The bubbling of the nitrogen gas should be carried out by supplying nitrogen gas to the reactant until the pH of the flowing gas is 6 to 8, so that the desired effect can be obtained.

[0046] That is, when the pH of the flowing gas is less than 6, when the bubbling of the nitrogen gas is stopped, the HF removal rate is in a low state. If the pH of the flowing gas exceeds 8, the amount of HF in the reactant may increase even more than when the nitrogen gas is not bubbled.

[0047] It is more preferable to stop the bubbling of the nitrogen gas when the pH becomes 6.5 to 7.5, and even more preferably to stop the bubbling of the nitrogen gas when the pH becomes 6.8 to 7.2.

[0048] In step (b), the pH of the flowing gas can be measured using a pH paper, but is not limited to this method, and may also be measured by a method known in the art.

[0049] Step (2) is preferably carried out after the first concentration of the reaction product of step (b) in order to efficiently remove the fluorine anions (F.sup.−) generated during the reaction.

[0050] After the reaction in step (2) is terminated, a second concentration process may be further performed while supplying nitrogen gas to the reactant.

[0051] In the production method of the present invention, the alkoxy trialkyl silane may be at least one selected from methoxytrimethylsilane and ethoxytriethylsilane.

[0052] The processes of steps (a) and (b) are not particularly limited in the present invention, and may be performed by methods known in the art.

[0053] Step (a) is a step of reacting bis(chlorosulfonyl)imide with NH.sub.4F(HF)n (n=0˜10) to prepare bis(fluorosulfonyl)imide, which can be represented by Reaction Scheme 2 below:

##STR00004##

[0054] In the above reaction, the solvent may comprise diethyl ether, diisopropyl ether, methyl-t-butyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentane, hexane, heptane and the like, and these may be used alone or in combination of two or more. Among these, butyl acetate can be more preferably used.

[0055] The reaction may be carried out under a nitrogen atmosphere.

[0056] In step (a), after bubbling nitrogen gas, filtration and concentration may be performed to obtain a crude compound. At this time, recrystallization may be performed by adding methylene chloride and the like together with a solvent to the crude compound.

[0057] Step (b) may be carried out as shown in Reaction Scheme 3 below:

##STR00005##

[0058] In the above reaction of step (b), the solvent may comprise diethyl ether, diisopropyl ether, methyl-t-butyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentane, hexane, heptane and the like, and these may be used alone or in combination of two or more. Among these, butyl acetate can be more preferably used.

[0059] In step (b), the lithium base may be at least one selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide hydrate (LiOH.H.sub.2O), lithium carbonate (Li.sub.2CO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), lithium chloride (LiCl), lithium acetate (LiCH.sub.3COO), and lithium oxalate (Li.sub.2C.sub.2O.sub.4). Among these, lithium hydroxide hydrate can be preferably used.

[0060] In step (b), after mixing the reactant, bubbling of nitrogen gas may be further performed.

[0061] In step (b), washing, filtration concentration, recrystallization, and the like of the obtained compound may be further carried out by a conventional method.

[0062] Hereinafter, preferred examples are presented to aid in the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims.

Example 1: Preparation of bis(fluorosulfonyl)imide lithium salt

[0063] 58.83 g of anhydrous ammonium fluoride from which water was purified and 300 g of butyl acetate were charged into a reactor equipped with a stirring device, a condenser, and a thermometer at room temperature under a nitrogen atmosphere. 100 g of bis(dichlorosulfonyl)imide was slowly added thereto, while stirring the mixture, and then reacted for 2 hours while raising the temperature to 80° C. After completion of the reaction, the temperature of the reactant was lowered to room temperature, filtered, and concentrated to obtain 83.32 g of a crude compound.

[0064] After 111.10 g of butyl acetate was added to the crude compound and stirred, 583.26 g of methylene chloride was added, recrystallized, and filtered, and then the solid was vacuum-dried for at least 2 hours to obtain 74.06 g of ammonium bis(fluorosulfonyl)imide (yield: 80%).

[0065] 74.06 g of ammonium bis(fluorosulfonyl)imide and 444.39 g of butyl acetate were added to reactor 1 and stirred. 41.96 g of LiOH.H.sub.2O and 220.63 g of butyl acetate were added to reactor 2 and stirred. The solution of reactor 1 was slowly added dropwise to reactor 2. After completion of the reaction, the temperature of the reactant was lowered to room temperature, filtered, and first concentrated.

[0066] 50.0 g of the first concentrate was added to a 500 mL 3-neck RBF, 0.51 mL (384 mg) of methoxytrimethylsilane was added, and the mixture was stirred at room temperature for 1 hour. The reaction mixture was kept at an internal temperature of 50 to 60° C., and concentrated under reduced pressure while blowing nitrogen (secondary concentration).

[0067] 200 g of toluene was added to the secondary concentrate, followed by stirring at room temperature for 20 minutes. The resulting solid was filtered and dried under vacuum to obtain 17.5 g of bis(fluorosulfonyl)imide lithium salt (yield: 62%).

Example 2: Preparation of bis(fluorosulfonyl)imide lithium salt

[0068] 17.0 g of bis(fluorosulfonyl)imide lithium salt was obtained by performing the same method as in Example 1, except that 1.01 mL (760 mg) of methoxytrimethylsilane was used instead of 0.51 mL (384 mg) of methoxytrimethylsilane (yield: 60%).

Example 3: Preparation of bis(fluorosulfonyl)imide lithium salt

[0069] 18.0 g of bis(fluorosulfonyl)imide lithium salt was obtained by performing the same method as in Example 1, except that 5.07 mL (3.84 g) of methoxytrimethylsilane was used instead of 0.51 mL (384 mg) of methoxytrimethylsilane (yield: 64%).

Comparative Example 1: Preparation of bis(fluorosulfonyl)imide lithium salt

[0070] 17.7 g of bis(fluorosulfonyl)imide lithium salt was obtained by performing the same method as in Example 1, except that methoxytrimethylsilane was not used (yield: 63%).

Experimental Example 1: Measurement of the Concentration of Fluorine Anions (F.SUP.−.) Contained in bis(fluorosulfonyl)imide lithium salt

[0071] The concentration of fluorine anions (F−) from the bis(fluorosulfonyl)imide lithium salt prepared in Examples 1 to 3 and Comparative Example 1 was measured using an F ion meter of Metrohm company. The measurement results of the concentration of the fluorine anions (F.sup.−) are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Concentration Concentration Whether and Amount of of the of fluorine how much sample measured anions Remarks Measured methoxytrimethyl Measurement injected sample (F.sup.−) (fluorine sample silane is used mV (g) (ppm) (ppm) anions) Experimental Methoxytrimethyl 88.1 1.0332 87.4 87.4 — Example 1 silane was not used Example 1 Use of 384 mg of 88.9 1.1682 74.9 74.9 14.3% methoxytrimethyl reduction silane in step (b) Example 2 Use of 760 mg of 154.8 1.2000 5.1 5.1 94.2% methoxytrimethyl reduction silane in step (b) Example 3 Use of 3.84 g of 161.7 1.2363 3.7 3.7 95.8% methoxytrimethyl reduction silane in step (b)

[0072] As shown in Table 1, in the case of the bis(fluorosulfonyl)imide lithium salt of Examples 1 to 3 in which fluorine anions were removed using methoxytrimethylsilane, the concentration of fluorine anions was significantly reduced as compared with Experimental Example 1 without treatment with methoxytrimethylsilane. In particular, it was confirmed that the content of fluorine anions is inversely proportional to the amount of methoxytrimethylsilane used and Examples 2 and 3, which increased the amount of methoxytrimethylsilane used, showed more remarkable effects.

[0073] Therefore, this fact indicates that the alkoxy trialkyl silane of the present invention can very effectively remove fluorine anions.