WO2016093399A1

WO2016093399A1 - Lithium sulfonyl imide salt containing fluorine and purification method for the same

Info

Publication number: WO2016093399A1
Application number: PCT/KR2014/012203
Authority: WO
Inventors: Ltd Chun Bo.; Sang Ryul Lee; Kyoung Chol Kim; Kyoung Hwan Kim; Sung Hong Lee; Gang Woo Lee; Ja Young Park; Ji Ung Jeon; Yoon Sung Jung; Soo Jin Kim; Seok Hee JO; Young Tae Jeon
Original assignee: Chun Bo Ltd
Priority date: 2014-12-11
Filing date: 2014-12-11
Publication date: 2016-06-16

Abstract

The present invention is directed to a lithium sulfonyl imide salt containing fluorine and its purification method and, more particularly to, a lithium sulfonyl imide salt containing fluorine and its purification method that includes recrystal 1 izing the lithium sulfonyl imide salt containing fluorine using a solvent containing a heterocyclic compound and using a carbon substance to make the lithium sulfonyl imide salt containing fluorine useful in an electrolyte for non-aqueous electrolyte batteries.

Description

[DESCRIPTION]

[Invention Title]

LITHIUM SULFONYL IMIDE SALT CONTAINING FLUORINE AND PURIFICATION METHOD FOR THE SAME

[Technical Field]

The present invention relates to alithium sulfonyl imide salt containing fluorine and a purification method for the same and, more particularly to, a lithium sulfonyl imide salt containing fluorine and a purification method for the same, where the lithium sulfonyl imide salt containing fluorine is recrystal 1 ized with a solvent containing a heterocyclic compound and used in the electrolyte of a non-aqueous electrolyte cell using a carbon substance. [Background Art]

Recent years, electric condensers for small-sized high-energy density purposes, such as data-related devices, communication devices, video cameras, digital still cameras, portable devices, etc., and electric condensers for large-sized power purposes, such as electric cars, hybrid cars, auxiliary power for fuel battery car, electric power storage, etc., have been under spotlight. As one of the promising electric condensers, non-aqueous electrolyte batteries, such as lithium ion battery, lithium battery, lithium ion capacitor, etc., are currently in active research and development. In general, the non-aqueous electrolyte batteries use, as an ion conductor, a non-aqueous electrolyte or a non-aqueous electrolyte pseudo-sol idi fied with a gelling agent. As for the constitution of the non-aqueous electrolyte, the solvent is a mixed solvent including at least one solvent selected from non- proton solvents, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.; and the solute is a 1 ithium salt .

Battery capacity is one of the characteristics of the battery. In order to improve the battery capacity, it is necessary to minimize the content of impurities in the electrolyte and suppress the chemical reaction during the charging/discharging of the battery. Generally, the solvent and the solute constituting the electrolyte use materials with high purity of at least 99.0 wt .%.

In particular, a variety of lithium salts have been used as a solute in the non-aqueous electrolyte. Specific examples of the lithium salts includel ithium hexaf luorophosphate (LiPFe), lithium fluoroborate (L1BF4), lithium perchlorate (L1CIO4), lithium bis(tri f luoromethane sulfonyl) imide (LiN(CFsS02)2) , lithium tri f luoromethane sulfonate (L1CF3SO3), lithium tris(tr if luoromethane sulfonyl) methide, etc.

Generally, most of the perchlorates are highly explosive, so the lithium perchlorate is also very explosive. Lithium hexaf luorophosphate is unstable to the heat and susceptible to decomposition in the presence of water. Lithium salts of organic acids, such as lithium bisCtrif luoromethane sulfonyl) imide (LiNCCFsSC^) , lithium tri f luoromethane sulfonate (L1CF3SO3), lithium tr is(tri f luoromethane sulfonyl) methide, etc., are solutes that are excellent in thermal resistance but contains a high quantity of impurities, in which case the use of the solutes possibly has an adverse effect on the battery performance .

In the synthesis of the lithium sulfonyl imide salt, the raw materials and the target product, that is, lithium sulfonyl imide containing fluorine are highly acidic and adversely tend to yield a halogen hydride as a by-product. Therefore, when a general reaction container is used, the by-product is ready to corrode the reaction container and metals e luted from the reaction container are incorporated as impurities into the target product. In order to prevent the corrosion of the reaction container and the peripheral equipment caused by the by-product, it is necessary to do the frequent maintenance of the reaction container or the equipment, which possibly becomes an obstacle to the continuous process. Further, the by-product remaining in the product can corrode the peripheral equipment when the product is used for various purposes . On the other hand, the product can contain impurities derived from the starting materials in addition to the by-products or impurities from the by^¬ products, and the existence of the impurities is not ignorable in the aspect of the purity of the product. In particular, when the sulfonyl imides containing impurities are used in batteries of different kinds, the batteries may not have good characteristics in regards to withstand voltage, conductive properties, battery characteristics, etc.

Japanese Registration Patent No. 3874585 (January 31, 2007) discloses a method of reacting [ H(C2H₅)₃] ⁺ [CF₃-S02-N-S02-CF3]^' and alkali metal hydroxide such as sodium hydroxide, etc. to form an alkali metal salt and then performing purification.

However, the compound produced using sodium hydroxide is a sodium salt, and a cation exchange process is needed to obtain a lithium salt. To obtain a lithium salt as the product, lithium hydroxide can be used in place of sodium hydroxide, in which case the solvent is coordinated with the purified lithium salt and an additional step of eliminating the solvent is required. Further, the impurities to be removed can react with the alkali metal hydroxide to produce alkali metal salts of the impurities, which are more difficult to el iminate.

Accordingly, there is a need to study the method of reducing impurities that cause performance deterioration in order to use the sulfonyl imides containing fluorine as an additive for the electrolyte in the non-aqueous electrolyte batteries.

[Prior Documents]

[Patent Documents]

Japanese Registration Patent No. 3874585 (January 31, 2007)

[Summary of Invention]

[Technical Problem]

It is an object of the present invention to provide a lithium sulfonyl imide salt containing fluorine and its purification method and solve the problems possibly occurring when the lithium sulfonyl imide salt containing fluorine is used for a variety of purposes, such as producing hydrogen halides such as hydrogen fluoride (HF), etc. as by-products from the synthesis of a lithium sulfonyl imide salt containing fluorine, or impurities derived from the starting materials that can remain in the product to corrode the peripheral materials, or the problems in association with the characteristics peculiar to the sulfonyl imides, such as withstand voltage, electrically conductive properties, and battery properties.

It is another object of the present invention to provide an high-purity lithium sulfonyl imide salt containing fluorine that has such a low content of impurities that it does not cause a drop of battery capacity when used as an additive for a non-aqueous electrolyte battery.

[Technical Solution]

To achieve the objects of the present invention, there is provided a method for purifying a lithium sulfonyl imide salt containing fluorine that includes: (a) reacting a sulfonic acid containing chlorine as represented by the following chemical formula 1 and a sulfonyl isocyanate containing chloride as represented by the following chemical formula 2 to prepare a chlorosul fonyl imide represented by the following chemical formula 3;(b) reacting the chlorosul fonyl imide represented by the following formula 3 and a fluorinated ammonium to prepare a f luorosul fonyl imide ammonium salt represented by the following chemical formula 4;(c) reacting the f luorosul fonyl imide ammonium salt represented by the following chemical formula 4 and a lithium compound to prepare a lithium sulfonyl imide salt represented by the following chemical formula 5; and(d) dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then eliminating impurities through the contact with a carbon substance,

Li (5)

In the chemical formulas 1 to 5, R₁ and R2 are the same as or different from each other and independently represent a chloro groupor a linear or branched perchloroalkyl group having 1 to 4 carbon atoms; andl¾ and R are the same as or different from each other and independently represent a fluoro group or a linear or branched per f luoroalkyl group having 1 to 4 carbon atoms.

The method further includes, prior to the step (d), dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then performing recrystal 1 izat ion.

The lithium compound is a lithium alkoxy compound represented by the following chemical formula 6:

Li OR_{5 (6)}

In the chemical formula 6, R5 represents a carbon atom or an alkyl or aryl group having 1 to 10 carbon atoms.

The heterocyclic compound is at least one selected from the group consisting of a heterocyclic alkyl group and/or a heteroaryl group. The heterocyclic alkyl group is a monocyclic or condensed cyclic group of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S.

The heteroaryl group is an aromatic ring of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S.

The step (d) includes having the solvent containing the heterocyclic compound with the dissolved lithium sulfonyl imide salt pass through the pores of multi-layered porous panels containing carbon nanotubes to eliminate impurities. The multi-layered porous panels are formed to have an asymmetric arrangement of pores so that the pores of one porous panel are not vertically in accord with the pores of adjacent porous panels. The step (d) includes having the solvent containing the heterocyclic compound with the dissolved lithium sulfonyl imide salt pass through a filter medium type block containing carbon nanotubes to eliminate impurities.

In accordance with another embodiment of the present invention, there are provided a lithium sulfonyl imide salt containing fluorine as purified by the purification method as described above, and a crystalline solid type lithium sulfonyl imide salt purified by the purification method as described above and having a bond between the heterocyclic compound and the lithium sulfonyl imide sal t .

In accordance with further another embodiment of the present invention, there are provided a non-aqueous electrolyte containing a lithium sulfonyl imide salt containing fluorine as purified by the method as described above.

[Advantageous Effects]

The present invention is directed to a lithium sulfonyl imide salt containing fluorine and its purification method that can remarkably reduce the content of impurities and thus provide high performance when used in the electrolyte for a non-aqueous electrolyte battery.

Further, the present invention makes it easy to control the water content by reducing the use of water in purification of the lithium sulfonyl imide salt containing fluorine and secures a low content of impurities in the lithium sulfonyl imide salt containing fluorine so that the non-aqueous electrolyte battery using the lithium sulfonyl imide salt containing fluorine in the electrolyte can acquire high stability and enhanced performance.

[Mode for Invention]

Hereinafter, a detailed description will be given as to the preferred embodiment of the present invention. The terms or words used in the specification and claims of the present invention are not to be confined to the general or dictionary meanings but to have meaning coinciding with those of terms in the related technology.

If not stated otherwise, it will be further understood that the terms "comprises" and/or "includes" throughout the specification of the present invention specify the presence of stated components but do not preclude the presence of addition of one or more other components.

Although ordinal numbers such as "first", "second", and so forth will be used to describe various components, those components are not limited by the terms. The terms are used only for distinguishing one component from another component. For example, a first component may be referred to as a second component and likewise, a second component may also be referred to as a first component .

In the individual steps, the identification symbols are used for the convenience of the explanation and the identification numbers are not given to indicate the order of the individual steps, which may be performed in the different order from the indicated order unless stated in a specific order. In other words, the individual steps may be performed in the specified order, or substantially at the same time, or in the reverse order.

In the present invention, the fluorosul fonyl imide includes di(fluorosul fonyl) imide having two fluorosul fonyl groups or N-( fluorosul fonyl )-N- (f luoroalkylsul fonyl ) imide having a f luorosul fonyl group and a fluorinated alkyl group. In the same manner, the chlorosul fonyl imide includes di (chlorosul fonyl ) imide having two chlorosul fonyl groups or N- ( chlorosul fonyl )-N-(chloroalkylsul fonyl) imide having a chlorosul fonyl group and a chlorinated alkyl group. The term "f luoroalkyl " as used herein means an alkyl group having 1 to 4 carbon atoms with at least one hydrogen atom substituted by a fluorine atom and includes a fluoromethyl group, a cli f luoromethyl group, a tri fluoromethyl group, a fluoroethyl group, a di f luoroethyl group, a tri fluoroethyl group, a pentaf luoroethyl group, etc. Hereinafter, the lithium sulfonyl imide salt containing fluorine and its purification method according to the present invention will be described in further detai 1.

In one embodiment of the present invention, there is provided a method for purifying a lithium sulfonyl imide salt containing fluorine that includes: (a) reacting a sulfonic acid containing chlorine as represented by the following chemical formula 1 and a sulfonyl isocyanate containing chloride as represented by the following chemical formula 2 to prepare a chlorosul fonyl imide represented by the following chemical formula 3; (b) reacting the chlorosul fonyl imide represented by the following formula 3 and a fluorinated ammonium to prepare a f luorosul fonyl imide ammonium salt represented by the following chemical formula 4; (c) reacting the f luorosulfonyl imide ammonium salt represented by the following chemical formula 4 and a lithium compound to prepare a lithium sulfonyl imide salt represented by the following chemical formula 5; and (d) dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then eliminating impurities through the contact with a carbon substance,

In the chemical formulas 1 to 5, Ri and R2 are the same as or different from each other and independently represent a chloro group or a linear or branched perchloroalkyl group having 1 to 4 carbon atoms! and R3 and R4 are the same as or different from each other and independently represent a fluoro group or a linear or branched perf luoroalkyl group having 1 to 4 carbon atoms.

The lithium sulfonyl imide salt containing fluorine as represented by the chemical formula 5 includes not just di (f luorosul fonyl ) imide having two f luorosulfonyl groups, but also (f luorosul fonyl )-N-(f luoroalkylsul fonyl ) having a f luorosul fonyl group and a f luoroalkylsul fonyl group, such as (f luorosulfonyl )-N-(f iLioroethylsulfonyl ) having a f luorosul fonyl group and a f luoroethylsulfonyl group, etc.

The term "f luoroalkyl " as used herein refers to an alkyl having 1 to 4 carbon atoms with at least one hydrogen atom substituted by a fluorine atom and includes a fluoromethyl group, a di f luoromethyl group, a tr i f luoromethyl group, a fluoroethyl group, a di f luoroethyl group, a tr i f luoroethyl group, a pentaf luoroethyl group, etc.

The step (a), a step of preparing a sulfonyl imide salt represented by the chemical formula 3, includes reacting a sulfonic acid containing chlorine as represented by the following chemical formula 1 and a sulfonyl isocyanate containing chloride as represented by the following chemical formula 2 under the nitrogen atmosphere. The supply of nitrogen is terminated when the nitrogen atmosphere is provided in the reaction container. The reason is that the nitrogen can react with the sulfonyl isocyanate containing chlorine to form a white solid compound.

The step (a) is carried out while the reactants are heated slowly. An abrupt increase in the temperature during the reaction can increase the formation of carbon dioxide (CO₂) to raise the inner pressure of the reaction container. It is therefore preferable to slowly heat the reaction container up to an inner temperature of 120 ^° C and reflux the carbon dioxide (CO2) produced at the same time. As by-products form when the inner temperature of the reaction container exceeds 130 ^° C, the heat is raised up to 120 ^° C and, when the carbon dioxide to be refluxed is not produced, the reaction is terminated to prepare the sulfonyl imide salt.

The step (b) includes adding the sulfonyl imide salt of the chemical formula 3 and a fluorinated ammonium to an organic solvent to form a sulfonyl imide ammonium salt represented by the chemical formula 4.

The step (b) is preferably performed at 200 ^° C or below for 5 minutes to 48 hours, more preferably at 1 ^° C to 100 ^° C for 1 to 24 hours.

The organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butyl carbonate, γ -butylolactone, γ -valerolactone, dimethoxy methane, 1,2-dimethoxy ethane, tetrahydrofuran, 4-methyl-l,3-dioxorane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulforane, 3- methyl sulforane, dimethyl sulfoxide, Ν,Ν-dimethyl form amide, N-methyl oxazol idinone, valeronitr i le, benzonitri le, ethyl acetate, isopropyl acetate, butyl acetate, nitro methane, and benzene. Among these non-proton solvents are preferred.

The termination of the step (b) can be determined by, for example, ¹⁹F-NMR, etc. In other words, the progress of the reaction is shown as a peak for the chemical shift to the fluoro group, where the relative intensity of the peak (integral) is increased. It is therefore possible to determine the termination of the reaction by checking on the progress of the reaction through the ¹⁹F-NMR analysis. As the yield of the by-products increases when the reaction time is exceedingly long, it is desirable to terminate the reaction of the step (b) at the point of time that the peak for the target product has the greatest relative intensity.

The step (c) is a step of reacting the f luorosul fonyl imide ammonium salt represented by the following chemical formula 4 and a lithium compound to prepare a lithium sulfonyl imide salt represented by the following chemical formula 5. The step (c) may use a method of reacting a salt containing a lithium cation and the sulfonyl imide ammonium salt of the chemical formula 4 or a method of having the sulfonyl imide ammonium salt of the chemical formula 4 in contact with a cation exchange resin. The lithium compound is preferably used at a molar ratio of 4 to 10 moles with respect to one mole of the sulfonyl imide ammonium salt of the chemical formula 4. When the molar ratio of the lithium compound to one mole of the sulfonyl imide ammonium salt of the chemical formula 4 is less than 4 moles, the substitution reaction between the ammonium cation and the lithium cation tends to occur insufficiently. When the molar ratio of the lithium compound to one mole of the sulfonyl imide ammonium salt of the chemical formula 4 is greater than 10 moles, it tends to increase the content of the lithium compound in the lithium sulfonyl imide salt of the chemical formula 5.

It is advantageous in the step (c) that the purification process can be carried out without an additional step of removing water because the reaction of the sulfonyl imide ammonium salt and the lithium compound does not use water. A high water content can cause the reduction of the electrolyte to occur and produce a passive film on the electrodes when using the electrolyte as a non-aqueous electrolyte. This reaction accompanies the production of gas to make the battery unstable.

The step (d) is a step of dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then eliminating impurities through the contact with a carbon substance. The heterocyclic compound is at least one selected from the group consisting of a heterocyclic alkyl group and/or a heteroaryl group. The heterocyclic alkyl group is a monocyclic or condensed cyclic group of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S. And, the heteroaryl group is an aromatic ring of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S. Preferably, the heterocyclic compound is at least one selected from the group consisting of imidazole, 1- methyl imidazole, oxazole, 1,4-oxazole, 1,4-dioxane 1,3-dioxane, 1 , 3-d ioxo lane , oxathiole, oxathiane, fur an, tetrahydrofuran, tetrahydropyran, tetrahydrozol ine, 2-methyltetrahydrofuran, and methyl N-methylanthrani late and not specifically limited so long as it is an organic solvent that can be used to crystallize the lithium sulfonyl imide salt.

The dissolved amount of the lithium sulfonyl imide salt in the solvent is preferably 10 to 40 wt.%. When the dissolved amount of the lithium sulfonyl imide salt in the solvent is less than 10 wt.%, the lithium sulfonyl imide salt is completely dissolved and hard to crystal ize, making it difficult to purify the lithium sulfonyl imide salt. When the dissolved amount of the lithium sulfonyl imide salt in the solvent is greater than 40 wt.%, the lithium sulfonyl imide salt is hard to dissolve completely, causing deterioration in the efficiency of purification.

The lithium sulfonyl imide salt is dissolved in a solvent containing the heterocyclic compound and put in contact with a carbon substance. The carbon substance is an adsorbent material capable of adsorbing impurities dissolved in the solvent and may be replaced by zeolite, alumina, silica gel, ordiatomite. But, the carbon substance that has a high adsorption capacity is preferred as the adsorbent material. The carbon substance may be selected from activated carbon, graphene, carbon nanotube, and fullerene. Among these, carbon nanotube is more preferable as the carbon substance in the aspect of adsorption efficiency. The contact method is not specifically limited so long as it includes a step of performing an adsorptive filtration of impurities by passing the solvent through a porous panel containing carbon nanotubes or a block containing carbon nanotubes.

Preferably, a plurality of porous panels containing carbon nanotubes are laminated, where the porous panels have a plurality of pores and are asymmetrically laminated so that the pores of one porous panel are not vertically in accord with the pores of adjacent porous panels. The impurities are eliminated while the solvent in which the lithium sulfonyl imide salt is dissolved passes through the pores of the porous panels. Alternatively, the solvent is passed through the blocks containing filter medium type carbon nanotubes so that the impurities contained in the solvent are adsorbed by the carbon nanotubes and eliminated.

The method may further include, prior to the step (d), dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then performing recrystal 1 ization.

Li OR_{5 (6)} In the chemical formula 6, R₅ represents a carbon atom or an alkyl or aryl group having 1 to 10 carbon atoms.

The heterocyclic compound is at least one selected from the group consisting of a heterocyclic alkyl groupand/or a heteroaryl group.

The step (d) includes having the solvent containing the heterocyclic compound with the dissolved lithium sulfonyl imide salt pass through a filter medium type block containing carbon nanotubes to eliminate impurities. The efficiency of purification is increased due to the effect of such a multi^¬ stage purification process.

The step (d) and the recrystal 1 izat ion step, each of which has an effect of removing impurities, may be performed repeatedly without a fixed order. In other words, the same effect of removing impurities can be achieved in either case the recrystal 1 izat ion step is subsequent to the step (cl) or the step (d) is carried out after the recrystal 1 i zat ion step.

The heterocyclic compound does not bond with impurities but with the lithium sulfonyl imide salt only to form a solvate complex crystal, so the crystal obtained after recrystal 1 izat ion is subjected to purification and filtration to yield a lithium sulfonyl imide salt with high purity.

The solvate complex crystal used in the present invention is a compound formed by an equivalent bonding between a solute and at least one solvent molecule through chemical interactions. The solvate complex crystal varies in chemical stability. For example, the solvate complex crystal such as hydrate may be a crystalline solid having a bonding between the solute and the solvent not readily breakable; or a solid very unstable so that the bonding between the solute and the solvent is too loose to form a salt; or a solid with medium stability that is capable of forming a salt and readily dissolved without many steps.

The molar ratio of the heterocyclic compound to the lithium sulfonyl imide salt is preferably 10:1 to 1:10, more preferably 5:1 to 1:5.

In order to obtain a lithium sulfonyl imide salt purified from the solvate complex crystal of the heterocyclic compound and the lithium sulfonyl imide salt, the solvate complex crystal is heated under vacuum at a temperature lower than the melting temperature of the solvate complex crystal. The temperature is preferably the melting temperature of the solvate complex crystal minus 35 ^° C, more preferably the melting temperature of the solvent complex crystal minus 20 ^° C.

The type and quantity of the impurities in the lithium sulfonyl imide salt containing fluorine according to the present invention can be analyzed by the ICP emission spectrochemical analysis or NMR measurement. Preferably, the NMR (Nuclear Magnetic Resonance) method is used. In the MR method, the nuclide is preferably ¾, ¹⁹F, ¹³C, etc. and more preferably ¹⁹F.

The use of the lithium sulfonyl imide salt containing fluorine purified by the above-described purification method as a non-aqueous electrolyte can provide high ion conductivity from low temperature to high temperature, dramatically reduce the content of impurities to enhance the performance of the electrolyte and properly maintain the viscosity of the electrolyte to improve the mobility of lithium ions.

Hereinafter, a detailed description will be given as to the preferred embodiments of the present invention, which are not limited to the specific examples or disclosure of the present invention but susceptible to many changes and modifications without departing from the scope and spirit of the present invention. Such modifications and variations which may be apparent to a person skilled in the art are intended to be included within the scope of this invention.

[Experimental Example 1]

Preparation of Lithium Bi s(Fluorosul fonyl ) Imide

250 g of chlorosulfonic acid and 313 g of chlorosulfonyl isocyanate are added into a 1L reaction container (flask) under the nitrogen atmosphere and mixed under agitation. The reaction container is slowly heated and agitated. When the inner temperature of the reaction container reaches 120 ^° C, the reaction container is cooled down with a stop of the agitation to obtain 413 g of bisCchlorosulfonyl ) imide.

71.36 g of ammonium fluoride and 200 g of acetonitrile are added into a reaction container, which is stirred at an average temperature of 50 ^° C and cooled down to 3 ^° C. 50 g of the bisCchlorosulfonyl ) imide is slowly added to the reaction container and a two-hour reflux is performed. After the completion of the reflux, the solid yielded is filtered out and eliminated. 10 g of lithium methoxide is added to the resultant filtrate, which is then stirred for one hour and filtered. The organic layer thus obtained after the filtration is dried out to obtain 42 g of a solid (Comparative Example 1).

[Experimental Example 2]

Purification of Lithium Bi s(Fluorosul fonyl ) Imide

37 g of the solid (Comparative Example 1) prepared in Experimental Example 1 is added to 100 g of 1-methyl imidazole, and the mixture is stirred at an average temperature of 70 ^° C for 12 hours.

After the completion of the agitation, the reaction container is heated up to 200 ^° C for 6 hours and the mixture is subjected to filtration and recrystal 1 izat ion to obtain a product (Example 1).

1-methyl imidazole containing the dissolved lithium bis(f luorosul fonyl ) imide after the agitation is passed through a filter filled with a filter medium type block containing carbon nanotubes at a linear speed of 35 m/hr to accomplish absorption filtration of impurities.

The solution containing the filtered bis(f luorosul fonyl ) imide dissolved in is kept at the room temperature for 10 hours for cooling down and filtered out to yield 55 g of a solvate complex crystal of lithium bis(f luorosulfonyl) imide. In this regard, the solvate complex crystal contains bis(f luorosulfonyl imide and 1-methyl imidazole at a molar ratio of 1:1.

55 g of the solvate complex crystal is heated up to 100 C for 6 hours and further to 120 ^° C for 12 hours and then heated up to 140 ^° C for 12 hours in a vacuum oven. After the heating, 30 g of the product (Example 2) is obtained. The product (Example 2) is added to 100 g of 1-methyl imidazole, and the mixture is stirred at an average temperature of 70 ^° C for 10 hours, heated up to 200 C for 6 hours and then filtered out to yield 27 g of the recrystal 1 ized product (Example 3).

[Experimental Example 3]

Measurement of Impurity Content The impurity content of each product (Comparative Example 1 and Examples 1 and 3) is analyzed through the ¹⁹F-NMR (CD₃CN).

Measurement instrument: JNM-GSX400 type NMR instrument (JEOL Ltd.)

Solvent: Dichloroform

Reference material : Freon-11 (CFCI3)

¹⁹F-NMR (CD₃CN): δ 56.0

In the following Table 1, "< 1" indicates the_, weight limit that is 0.1 and greater and less than 1 ppm.

[Table 1]

As can be seen from the results of Table 1, the products of Examples 1, 2 and 3 has a lower impurity content than the product of Comparative Example 1. In particular, the recrystal 1 izat ion of the lithium f luorosul fonyl imide with a solvent is not enough to reduce the content of impurities, but the recrystal 1 i zat ion in combination with adsorption filtration in contact with the carbon substance can effectively reduce the content of impurities. As a result, the purification method of the present invention can yield a lithium sulfonyl imide containing fluorine with reduced impurity content.

[Industrial Applicability]

The present invention has an industrial applicability since it can remarkably reduce the content of impurities and thus provide high performance when used in the electrolyte for non-aqueous electrolyte batteries.

Claims

[CLAIMS]

[Claim 1]

A method for purifying a lithium sulfonyl imide salt containing fluorine, comprising:

(a) reacting a sulfonic acid containing chlorine as represented by the following chemical formula 1 and a sulfonyl isocyanate containing chloride as represented by the following chemical formula 2 to prepare a chlorosul fonyl imide represented by the following chemical formula 3;

(b) reacting the chlorosul fonyl imide represented by the following formula 3 and a fluorinated ammonium to prepare a f luorosul fonyl imide ammonium salt represented by the following chemical formula 4;

(c) reacting the f luorosul fonyl imide ammonium salt represented by the following chemical formula 4 and a lithium compound to prepare a lithium sulfonyl imide salt represented by the following chemical formula 5; and

(d) dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then eliminating impurities through the contact with a carbon substance,

wherein Ri and R2 are the same as or different from each other and independently represent a chloro group or a linear or branched perchloroalkyl group having 1 to 4 carbon atoms; and

R3 and R4 are the same as or different from each other and independently represent a fluoro group or a linear or branched perf luoroalkyl group having 1 to 4 carbon atoms.

[Claim 2] The method as claimed in claim 1, further comprising:

prior to the step (d), dissolving the lithium sulfonyl imide salt in a solvent containing a heterocyclic compound and then performing recrystal 1 izat ion.

[Claim 3]

The method as claimed in claim 1, wherein the lithium compound is a lithium alkoxy compound represented by the following chemical formula 6:

Li OR 5, (6) wherein F¾ represents a carbon atom or an alkyl or aryl group having 1 to 10 carbon atoms.

[Claim 4]

The method as claimed in claim 1, wherein the heterocyclic compound is at least one selected from the group consisting of a heterocyclic alkyl group and/or a heteroaryl group.

[Claim 5]

The method as claimed in claim 4, wherein the heterocyclic alkyl group is a monocyclic or condensed cyclic group of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S.

[Claim 6]

The method as claimed in claim 4, wherein the heteroaryl group is an aromatic ring of 5 to 15 cyclic atoms containing at least one or two heteroatoms selected from N, 0 and S.

[Claim 7]

The method as claimed in claim 1, wherein the step (d) includes having the solvent containing the heterocyclic compound with the lithium sulfonyl imide salt dissolved therein pass through the pores of mul t i -layered porous panels containing carbon nano tubes to eliminate impurities.

[Claim 8]

The method as claimed in claim 7, wherein the multi-layered porous panels are formed to have an asymmetric arrangement of pores so that the pores of one porous panel are not vertically in accord with the pores of adjacent porous panels .

[Claim 9]

The method as claimed in claim 1, wherein the step (d) includes having the solvent containing the heterocyclic compound with the lithium sulfonyl imide salt dissolved therein pass through a filter medium type block containing carbon nano tubes to eliminate impurities.

[Claim 10] A lithium sulfonyl imide salt containing fluorine as purified by the method as claimed in any one of claims 1 to 9.

[Claim 11]

A crystalline solid type lithium sulfonyl imide salt purified by the method as claimed in any one of claims 1 to 9 and having a bond between the heterocyclic compound and the lithium sulfonyl imide salt.

[Claim 12]

A non-aqueous electrolyte containing a lithium sulfonyl imide salt containing fluorine as purified by the method as claimed in any one of claims 1 to 9.