KR102240799B1 - Imidazolium functionalized imide based lithium salt, process for preparing the same and electrolyte composition for Li-ion battery comprising the same - Google Patents

Abstract

The present invention provides a newly prepared imidazolium functionalized imide-based lithium salt, a method for preparing the same, and an electrolyte composition for a lithium ion battery comprising the same.
The imidazolium functionalized imide-based lithium salt of the present invention, a method for preparing the same, an electrolyte composition comprising the same, and a lithium ion battery comprising the same are used as high-performance electrolytes in the field of lithium ion batteries based on the functionalization of the imidazolium IL-based ionic salt. It can be usefully used.

Description

[Imidazolium functionalized imide based lithium salt, process for preparing the same and electrolyte composition for Li-ion battery comprising the same}

The present invention relates to an imide-based lithium salt, a method for preparing the same, and an electrolyte composition for a lithium ion battery comprising the same, and more particularly, a novel imide type lithium salt obtained by functionalizing 1-methylimidazole, and It relates to a manufacturing method and an electrolyte composition for a lithium ion battery comprising the same.

Rechargeable lithium-ion batteries (LIBs) are the most common electrochemical energy storage devices, and are an attractive power source for portable electronic devices and hybrid electric vehicles. This is due to high specific capacity (C _sp ), high energy density (150-200 WhKg ^-1 ), acceptable cycle life and low self-discharge. The performance of LIB is highly dependent on the chemical and electrochemical properties of the electrolyte, which significantly affects the charge transport kinetics within the cell, and at the same time affects the amount of energy that can be transferred and the lifetime of the LIB. The composition of a new electrolyte with high safety, excellent ionic conductivity (σ), and high electrochemical and thermal stability is one of the main issues for developing high-performance LIB. Electrolytes used in LIB can exist in a variety of forms, including molten salts, ionic liquids, solid ionic conductors, and salts dissolved in solvents.

To date, most commercial LIBs have used inorganic lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte, which is ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). It was in a dissolved form in a mixture of organic solvents. LiPF ₆ salt-based electrolyte has relatively high anode stability (about 4.5 V in EC/DEC mixed solvent) and high σ (10.7 mS/cm in EC/DMC mixed solvent), and Al current collector passivation. Show. Nevertheless, LiPF ₆ is easily decomposed into _{PF 5} and LiF above 60 ℃. The PF ₅ induces a series of irreversible reactions at both the anode and the cathode to degrade battery performance. Lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (perfluoroethylsulfonyl) imide, nonafluorobutylsulfonyl tri Lithium sulfonyl imide salt based electrolytes such as fluoromethyl sulfonylimide and lithium bis(pentafluoroethylsulfonyl)imide have attracted much attention as an alternative to overcome the limitations _{of LiPF 6.} This is due to their high thermal, chemical and electrochemical stability, good sigma and safety. In particular, LiFSI and LiTFSI have high oxidative stability, thermal stability, low viscosity, and excellent performance of forming a stable solid-electrolyte interface (SEI) on the anode surface, and _{σ corresponding to LiPF 6} (9.73 each). And 7.57 mS/cm), which is the most widely used imide type electrolyte salt in LIB applications. However, all of them exhibit high reaction with the Al current collector above 3.7 V, which is the operating voltage, thereby extending the life of the LIB. Thus, these salts are generally used as co-salts or additives with other salts to improve the electrochemical performance of LIB without compromising its extended life. Moreover, LiFSI and LiTFSI have excellent ability to form LiF as an SEI layer on the anode surface, ^{creating an environment favorable for Li +} diffusion and at the same time increasing the life of the battery.

Taking into account the above main issues of LiFSI and LiTFSI, FSI and TFSI anions have recently been used to obtain high voltage, longevity and safer LIB, and both imidazolium, pyrrolidinium and piperidinium type ionic liquids (IL) and both. It is widely used to design and formulate zwitterionic liquid (ZIL) based electrolytes. For this, an optimal amount of LiFSI or LiTFSI salt was added to IL and ZIL with or without extra solvent. For example, 1-ethyl-3-methylimidazolium FSI and 1-ethyl-3-methylimidazolium TFSI IL based electrolytes were developed by mixing with appropriate amounts of LiFSI and LiTFSI, respectively. Similarly, 1-(2-methoxyethyl)-3-methylimidazolium TFSI and 3-(2-(2-methoxyethoxy)ethyl)-1-methylimidazolium TFSI, N-propyl-N- Other reported IL-based electrolytes including methylpyrrolidinium FSI and N-butyl-N-methylpyrrolidinium TFSI also showed long cycle life in LIB. These electrolytes showed excellent stability and safety when LIB was applied because there was no combustible organic solvent, but showed relatively low σ and high viscosity at room temperature. Therefore, the electrochemical performance of these IL-based electrolytes is generally low at room temperature. In addition, the presence of a small amount of Li salt in such an IL electrolyte may be another reason for the low σ, which cannot be overcome simply by increasing the concentration of the Li salt above the optimum concentration. The reason is that high concentrations of Li-salt can ^{increase the interaction between FSI or TFSI anions and IL+,} ultimately increasing the viscosity of the electrolyte and reducing σ as well as electrochemical performance. Therefore, the preparation of ionic salts based on these imidazolium, pyrrolidinium and piperidinium ILs with ^{Li + ions is an attractive way to develop high performance LIBs.}

Korean Patent Publication No. 10-2017-0030116 (2017.03.17.)

Journal of Fluorine Chemistry 164 (2014) 38-43.

The inventors of the present invention were studying to develop a LIB electrolyte having excellent ionic conductivity and chemical and thermal stability, while functionalizing 1-methylimidazole to form a novel imide-type salt, lithium (fluorosulfonyl) ((3 -(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl)imide) bis(trifluorosulfonyl)imide [LiFSMIPTFSI] is mixed with EC and dimethylsulfoxide (DMSO) As a solvent-based electrolyte salt for LIB, it exhibits low viscosity, high Li ⁺ conductivity and high anode stability at _{room temperature, shows excellent C sp} in LIB, and further improves electrochemical performance by adding a small amount of additives LiFSI and LiTFSI. I found it to be.

Accordingly, an object of the present invention is to provide an imidazolium-functionalized imide-based lithium salt, a method for preparing the same, and an electrolyte composition for a lithium ion battery comprising the same.

According to an aspect of the present invention, there is provided a lithium salt of Formula 1 below.

[Formula 1]

(In the above formula, n is an integer of 1 to 5).

In one embodiment, the lithium salt may be a lithium salt represented by Formula 1a below.

[Formula 1a]

According to another aspect of the present invention, there is provided an electrolyte composition comprising the lithium salt.

In one embodiment, the electrolyte composition may further include an additive selected from the group consisting of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, and mixtures thereof, and the The additive may be included in a lithium salt: additive = 1:0.1 to 0.3 molar ratio.

In one embodiment, the solvent of the electrolyte composition may be one selected from the group consisting of ethylene carbonate, dimethyl sulfoxide, and mixtures thereof.

According to another aspect of the present invention, there is provided a lithium ion battery comprising the electrolyte composition.

According to another aspect of the present invention, (a) preparing a compound of formula (3) by chlorination reaction of a compound of formula _{(2) with thionyl chloride (SOCl 2 );} (b) reacting the compound of formula 3 obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4; And (c) reacting the compound of Formula 4 obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare the compound of Formula 1; do.

[Formula 1]

(In the above formula, n is an integer from 1 to 5)

[Formula 2]

(In the above formula, n is an integer from 1 to 5)

[Formula 3]

(In the above formula, n is an integer from 1 to 5)

[Formula 4]

(In the above formula, n is an integer from 1 to 5)

In one embodiment, the method of preparing the lithium salt comprises the steps of: (a) chlorinating a compound of the following formula 2a with thionyl chloride (SOCl ₂ ) to prepare a compound of the following formula 3a; (b) reacting the compound of formula 3a obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4a; And (c) reacting the compound of Formula 4a obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare the compound of Formula 1a. have.

[Formula 1a]

[Formula 2a]

[Formula 3a]

[Formula 4a]

In one embodiment, the compound of Formula 2a in step (a) of the method for preparing a lithium salt of Formula 1a may be prepared by an addition reaction of 1-methylimidazole and 1,3-propane sultone.

The newly prepared imidazolium functionalized imide-based lithium salt of the present invention exhibits a wide range of electrochemical stability, high thermal stability, excellent Li ⁺ conductivity and low intrinsic viscosity when used as an electrolyte for LIB, and at 0.1 C in LIB. denotes a non-discharge capacity of about 141 mAhg ^-1, lithium bis (fluoro-sulfonyl) imide [LiFSI] or lithium bis (methylsulfonyl-trifluoromethyl) if already used with additives such as de [LiTFSI] The performance of the electrolyte is further enhanced, showing ^{a specific discharge capacity of about 160 and 150 mAhg -1} at 0.1 C, respectively, and excellent cycling stability (capacity retention about 98.50%) after a charge-discharge cycle, resulting in high performance for lithium ion batteries. It has been found that it can be used as an electrolyte.

Therefore, the imidazolium functionalized imide-based lithium salt of the present invention, a method for preparing the same, an electrolyte composition containing the same, and a lithium ion battery including the same are high performance in the field of lithium ion batteries based on functionalization of the imidazolium IL-based ionic salt It can be usefully used as an electrolyte.

1 ^{is a 1} H NMR spectrum of (a) MSIC and (b) FSSPMIC.
Figure 2 is (a) ¹⁹ F NMR, (b) ¹ H NMR and (c) FTIR spectra of LiFSMIPTFSI.
3 is (a) a TGA plot of LiFSMIPTFSI, LiFSI and LiTFSI, (b) LiFSMIPTFSI with and without LiFSI (0.2M) and LiTFSI (0.2M) additives in an EC and DMSO mixed solvent (75:25 v/v) ( 1 M) is a viscosity plot.
4 is a (a) LSV plot (scan rate 10 mV/s) of LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes, (b) ionic conductivity versus temperature plot, (c) Arrhenius of measured ionic conductivity. ) Plot, (d) a graph showing the change in ion conductivity according to the number of EIS scans at 30°C.
5 is a CD plot of a LIB coin cell at (a) 0.1 C, (b) 0.2 C and (c) 0.3 C at 30° C., and (d) specific capacity and coulomb as a function of CD cycle. It is a change in efficiency.
6 is an FE-SEM image of a graphite anode based on (ab) LiFSMIPTFSI, (cd) LiFSMIPTFSI+LiFSI, and (ef) LiFSMIPTFSI+LiTFSI electrolyte contained in LIB, respectively. The anode was recovered after 500 CD cycles of the corresponding electrolyte-based LIB at 0.1 C.
7 is a ¹⁹ F NMR spectrum of _{FSO 2 NCO.}
8 is a (a) ¹ H NMR, (b) ¹⁹ F NMR and (c) FTIR spectra of _{FSO 2} NH _2.
9 is a ¹ H NMR spectrum of CSPMIC.
10 is an LSV plot of LiFSI and LiTFSI electrolytes (1 M each) at a scan rate of 25 mV/s.
11 is a schematic diagram of an asymmetric (a) dummy cell and (b) a coin cell.
12 is an EIS spectrum according to the temperature change of (a) LiFSMIPTFSI, (b) LiFSMIPTFSI + LiFSI and (c) LiFSMIPTFSI + LiTFSI electrolyte-based dummy cell, all EIS spectra of 0.1 Hz to 0.1 MHz with an AC amplitude of 5 mV. It was measured under open circuit conditions in the frequency range.
13 shows an equivalent circuit model that fits the EIS spectrum of a dummy cell.
14 is a schematic diagram showing negative charge delocalization in an FSMIPTFSI anion.
Figure 15 is a continuous EIS spectrum of (a) LiFSMIPTFSI, (b) LiFSMIPTFSI + LiFSI and (c) LiFSMIPTFSI + LiTFSI electrolyte-based dummy cell at 30 °C, the EIS measurement sequence is as follows: 10 × CV scan (0 ~ Potential range between +6 V, scan rate 25 mV/s); Relaxation at 0 V (1 min). This series of electrochemical stability tests was repeated 10 times.
16 is a CD plot of LIB coin cells of different electrolytes at 1 C and 30°C.
17 is (a) an FE-SEM image of a graphite anode and (b) an enlarged photograph of the surface thereof.
Figure 18 is (a) selected regions of the graphite anode of the LiFSMIPTFSI electrolyte-based LIB (insertion diagram shows the wt% of C, N, O, F and S elements), and (bf) C, O, F, S and respectively EDS element mapping of N is shown. The graphite anode was recovered after 500 CD cycles.
Figure 19 is (a) selected regions of the graphite anode of the LiFSMIPTFSI + LiFSI electrolyte-based LIB (inset diagram shows the wt% of C, N, O, F and S elements), and (bf) C, O, F, respectively. EDS element mapping of S and N is shown. The graphite anode was recovered after 500 CD cycles.
Figure 20 is (a) selected regions of the graphite anode of the LiFSMIPTFSI + LiTFSI electrolyte-based LIB (inset diagram shows the wt% of C, N, O, F and S elements), and (bf) C, O, F, respectively. EDS element mapping of S and N is shown. The graphite anode was recovered after 500 CD cycles.

The present invention provides a lithium salt of the following formula (1).

[Formula 1]

(In the above formula, n is an integer of 1 to 5).

The lithium salt of the present invention is an imidazolium functionalized imide-based lithium salt prepared by functionalizing 1-methylimidazole with lithium bis(trifluoromethylsulfonyl)imide. In Formula 1, the length of the alkyl chain connected to the imidazolium ring may be adjusted according to the integer size of n.

In one embodiment, the lithium salt of Formula 1 is a lithium salt of Formula 1a when n=3.

[Formula 1a]

The lithium salt of Formula 1a functionalizes 1-methylimidazole to 3-(3-(N-(fluorosulfonyl)sulfamoyl)propyl)-1-methyl-1H-imidazol-3-lium chloride[ FSSPMIC] was obtained and then reacted with lithium bis(trifluoromethylsulfonyl)imide [LiTFSI], and the ionic salt synthesized as a corresponding salt, lithium (fluorosulfonyl) ((3-(1-methyl-1H) -Imidazol-3-ium-3-yl)propyl)sulfonyl)imide) bis(trifluorosulfonyl)imide [LiFSMIPTFSI].

Imidazolium-functionalized imide-based lithium salt of the present invention comprises the steps of (a) chlorinating a compound of formula 2 with thionyl chloride (SOCl ₂ ) to prepare a compound of formula 3; (b) reacting the compound of formula 3 obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4; And (c) reacting the compound of Formula 4 obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare the compound of Formula 1 Can be manufactured.

[Formula 1]

(In the above formula, n is an integer from 1 to 5)

[Formula 2]

(In the above formula, n is an integer from 1 to 5)

[Formula 3]

(In the above formula, n is an integer from 1 to 5)

[Formula 4]

(In the above formula, n is an integer from 1 to 5)

In one embodiment, when the lithium salt of Formula 1 is n=3, (a) preparing a compound of Formula 3a by chlorinating _{a compound of Formula 2a with thionyl chloride (SOCl 2 );} (b) reacting the compound of formula 3a obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4a; And (c) reacting the compound of Formula 4a obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare the compound of Formula 1a. It can be prepared (see Scheme 1 below).

[Formula 1a]

[Formula 2a]

[Formula 3a]

[Formula 4a]

[Scheme 1]

In the method for preparing the lithium salt of Formula 1a, 1-methyl-3-(3-sulfopropyl)-1H-imidazol-3-lium chloride [MSIC, Formula 2a] is 1-methylimidazole and 1,3- It can be prepared through an addition reaction between propane sultones (see Scheme 1). _{Thereafter, thionyl chloride (SOCl 2} ) was added dropwise to the prepared MSIC [Chemical Formula 2a] in a nitrogen atmosphere at -10 °C to 10 °C (for example, 0 °C), followed by a chlorination reaction to 3-(3-(chlorosulfuryl). Phonyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [CSPMIC, formula 3a] is prepared [ie, step (a)].

The prepared CSPMIC [Chemical Formula 3a] is reacted with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of Formula 4a [ie, step (b)]. _{Specifically, sulfamoyl fluoride (FSO 2} NH ₂ ) was added to a solution of CSPMIC [Formula 3a] in a suitable solvent (eg, tetrahydrofuran, THF) and stirred at an appropriate reaction temperature (eg, 25° C.) To prepare 3-(3-(N-(fluorosulfonyl)sulfamoyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [FSSPMIC, Formula 4a]. Thereafter, THF was evaporated from the reaction solution, and FSSPMIC [Chemical Formula 4a] was extracted with ethyl acetate (EA) and water to obtain.

The FSSPMIC [Chemical Formula 4a] obtained in the above step is reacted with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to prepare a compound of Formula 1a [ie, step (c)]. Specifically, LiTFSI was added to the FSSPMIC solution dissolved in an appropriate solvent (eg, acetone) and stirred under a nitrogen atmosphere for an appropriate reaction time (eg, 3 hours) at an appropriate reaction temperature (eg, 25° C.). Lithium(fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl)imide) bis(trifluorosulfonyl)imide [LiFSMIPTFSI , Formula 1a] is prepared. Thereafter, the product was extracted with water and butyl acetate, the water was evaporated, and the gel-like LiFSMIPTFSI was collected from the aqueous layer, which was further recrystallized with acetonitrile to obtain a final product, LiFSMIPTFSI [Formula 1a].

According to another aspect of the present invention, there is provided an electrolyte composition comprising the lithium salt. The imidazolium-based lithium salt of the present invention is used as an electrolyte for application to a lithium-ion battery (LIB), and when used as an electrolyte for LIB, a wide range of electrochemical stability and high thermal stability, excellent Li ⁺ conductivity and It has a low intrinsic viscosity. The electrolyte prepared with the imidazolium-based lithium salt of the present invention exhibits a specific discharge capacity of about 141 mAhg ^-1 at 0.1 C in LIB, and lithium bis(fluorosulfonyl)imide [LiFSI] or lithium bis When an additive such as (trifluoromethylsulfonyl)imide [LiTFSI] is further included, the performance of the electrolyte is further enhanced, and the specific discharge capacities of ^{about 160 and 150 mAhg -1 are respectively shown at 0.1 C.} The additive may be included in a lithium salt: additive = 1:0.1 ~ 0.3 molar ratio. LiFSMIPTFSI electrolyte used for LIB together with the additives exhibits high cycling stability among the electrolytes after 500 charge-discharge cycles, and in particular, when LiFSI additives are used, the highest cycling stability (capacity maintenance about 98.50%) is shown.

At this time, as the solvent of the electrolyte composition, a solvent composed of ethylene carbonate or dimethyl sulfoxide and a mixture thereof may be used, but as long as the electrolyte performance of the imidazolium-based lithium salt of the present invention is not impaired, it is limited to the solvent. no. The ethylene carbonate and dimethyl sulfoxide may be used as a mixed solvent, and ethylene carbonate: dimethyl sulfoxide may be mixed in a volume ratio of 90:10 to 60:40, preferably 80:20 to 70:30 by volume.

According to another aspect of the present invention, there is provided a lithium ion battery comprising the electrolyte composition. The lithium ion battery may be manufactured by a commonly used lithium ion battery manufacturing method.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

<Example>

1. Experimental method

(1) description

Toluene, tetrahydrofuran (THF), acetone, sulfurisocyanatidic chloride, hexane, methylene chloride (MC), DMSO, ethyl acetate (EA), EC, LiFSI (99.9%), LiTFSI (99.95%) ), LiFePO ₄ , carbon black and poly(vinylidene difluoride, PVDF) were purchased from Sigma-Aldrich (St. Louis, MO, USA) and used without further purification. Trifluorostibine, 1,3-propane sultone, anhydrous formic acid, 1-methylimidazole, and hydrochloric acid (37%) are used in Alpha Eisa (Alfa). Aesar, Ward Hill, Massachusetts, USA). LiFePO ₄ coated aluminum foil, CMS graphite coated Cu foil and Celgard separator were purchased from MTI Corporation (MTI Corporation, CA, USA). A fluorine-doped tin oxide (FTO) electrode was purchased from Pilkington (8 Ω/sq., USA).

(2) Measurement and measurement

In order to analyze the chemical structure of the compound, ¹ H NMR (Bruker DRX, 400 MHz) and ¹⁹ F NMR (JEOL JNM-ECZ400 s/Li, 400 MHz) spectrometers were used. For the measurement of the NMR spectrum, DMSO- d ₆ , deuterated water (D ₂ O) and deuterated chloroform (CDCl ₃ ) were used as solvents, and tetramethylsilane (TMS) was used as an internal standard. Fourier-transform infrared spectra (FTIR) was measured with a spectrophotometer (Nicolet iS5, ASB1100426, ThermoFisher Scientific, Massachusetts, USA). Thermogravimetric analysis (TGA) was performed using a Scinco TGA-N 1000 analyzer at a heating rate of 5° C./min _{in N 2 atmospheric conditions in a temperature range of 30 to 600° C.} The dynamic viscosity of the electrolyte was measured with a viscometer (RheoSense, hts-VROCTM). For surface morphology and elemental analysis, field-emission scanning electron microscope (FE-SEM, JEOL 7401F) and energy dispersive X-ray spectroscopy (EDS, INCAx-sight7421, Oxford Instruments) were used, respectively.

All electrochemical measurements, including linear sweep voltammetry (LSV), cyclic voltammetry (CV) and galvanostatic charge-discharge (CD), are multi-channel potentiometer/galvanostat (Ivium-n-Stat, Ivium Technologies, The Netherlands). For LSV and CV measurements, conventional platinum (Pt), Ag/AgCl [ _{saturated with KCl (aq.)} ] and Pt wires were used as working electrodes, reference electrodes, and auxiliary electrodes, respectively. The CD cycling test of the coin cell was performed by applying a constant current (0.1, 0.2, 0.3 and 1 C) in the potential range of 0-4 V. The C ratio was calculated based on the weight of the active cathode material (about 12.80 mg/cm ^{2 ).} The electrochemical impedance spectrum (EIS) was measured with an impedance analyzer (IM6ex, Zahner-Elektrik GmbH & Co. KG instrument, Germany).

The frequency range, applied voltage and AC amplitude for EIS measurements were 0.1-10 ⁵ Hz, open circuit conditions, and 5 mV, respectively. Z-view software (version 3.1, Scribner Associates Inc., USA) was used to fit the EIS spectrum.

2. Synthesis of lithium salt

Scheme 1 below is a schematic diagram of a stepwise reaction for the synthesis of LiFSMIPTFSI.

[Scheme 1]

(1) 1-methyl-3-(3-sulfopropyl)-1H-imidazol-3-ium chloride [1-methyl-3-(3-sulfopropyl)-1H-imidazol-3-ium chloride, MSIC, chemical formula 2a]

As shown in Scheme 1 below, through an addition reaction between 1-methylimidazole and 1,3-propane sultone, 1-methyl-3-(3-sulfopropyl)-1H-imidazol-3-lium chloride ( MSIC) was synthesized. Briefly, methyl-1,3-propane sultone (65.0 mmol) was added dropwise to 1-methylimidazole (50.0 mmol) and stirred at 100° C. for 12 hours. After completion of the reaction, a white precipitate was collected and washed several times with toluene and diethyl ether. After that, the same amount of concentrated hydrochloric acid (37%) was added to the precipitate, followed by stirring at 60° C. for 12 hours. The resulting liquid of MSIC was washed with toluene and diethyl ether and vacuum dried at 120° C. for 12 hours.

(2) 3-(3-(chlorosulfonyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [3-(3-(chlorosulfonyl)propyl)-1-methyl-1H-imidazol-3 Synthesis of -ium chloride, CSPMIC, formula 3a]

3-(3-(chlorosulfonyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [CSPMIC] was prepared by chlorination of MSIC and thionyl chloride (SOCl _{2 ). Specifically, SOCl 2} (130.0 mmol) was added dropwise to MSIC (12.5 mmol) at 0 °C under a nitrogen atmosphere. After this, the reaction mixture was refluxed for 12 hours. Subsequently, unreacted SOCl ₂ was sequentially removed by evaporation and toluene washing (several times). ¹ H NMR of CSPMIC is shown in FIG. 9, and corresponding analysis data are as follows.

CSPMIC. ¹ H NMR (DMSO: 298K): δ= 9.2(s, H), 7.8(s, H), 7.7(s, H), 4.25-4.35(t, 2H), 3.85(s, 3H), 2.4- 2.6 (t, 2H), 2.0-2.2 (m, 2H) ppm.

(3) 3-(3-(N-(fluorosulfonyl) sulfamoyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [3-(3-(N-(fluorosulfonyl)sulfamoyl) Synthesis of propyl)-1-methyl-1H-imidazol-3-ium chloride, FSSPMIC, Formula 4a]

Prior to the synthesis of FSSMIC, precursors of sulfur isocyanate fluoride (FSO ₂ NCO) and sulfamoyl fluoride (FSO ₂ NH ₂ ) were synthesized with high purity as shown in Scheme 1, which was 3-(3-( It was reacted with chlorosulfonyl)propyl)-1-methyl-1H-imidazol-3-lium chloride [CSPMIC]. The synthesis and characterization of FSO ₂ NCO and FSO ₂ NH _{2 are described below.} For the synthesis of FSSMIC, FSO ₂ NH ₂ (15.0 mmol) was added to the prepared CSPMIC solution in THF and stirred at 25° C. for 24 hours. After completion of the reaction, THF was evaporated, and FSSPMIC was extracted using EA and water. Thereafter, yellowish FSSPMIC was collected in the EA layer.

(3-a) sulfur isocyanate fluoride (sulfurisocyanatidic fluoride, FSO) ₂ Synthesis of NCO)

For the synthesis of sulfur isocyanate-based fluoride (FSO ₂ NCO), a mixture of sulfur isocyanate chloride (sulfurisocyanatidic chloride, 1 mol) and antimony trifluoride (0.33 mol) was stirred at 70° C. for 48 hours. Thereafter, the reaction mixture was distilled at 80° C. to obtain _{FSO 2 NCO, a pure colorless acidic liquid.} Fig. 7 shows a ¹⁹ _{F NMR spectrum of FSO 2} NCO, and the analysis data are as follows.

FSO ₂ NCO. Yield = 86%, ¹⁹ F NMR (CDCl3; 298K): δ = 62 (s, 1F) ppm.

(3-b) sulfamoyl fluoride (FSO) ₂ NH ₂ ) Of the synthesis

Protocols described in prior literature [RMS Alvarez, et al., J. Mol. Str. 657 (2003) 291-300.], sulfamoyl fluoride (FSO ₂ NH ₂ ) was synthesized. In summary, 400 mmol of dried formic acid _{was added dropwise to FSO 2} NCO (270 mmol) synthesized at 0° C. (Safety note: Formic acid reacts violently with _{FSO 2 NCO while generating CO 2} , CO and HF. ). Then, the reaction mixture was stirred at 25° C. for 24 hours. _{After the reaction was completed, FSO 2} NH ₂ was obtained by distillation at 70° C. using a vacuum pump and liquid nitrogen, which was repeatedly purified by a trap-to-trap distillation method under reduced pressure. Fig. 8 shows ¹ H NMR, ¹⁹ F NMR and FTIR spectra _{of FSO 2} NCO. The analysis data is summarized as follows.

FSO ₂ NH ₂ . Yield = 60%, ¹ H-NMR (DMSO- d ₆ ; 298 K): d = 8.12 (s, 2H) ppm, ¹⁹ F-NMR (DMSO- d ₆ ; 298 K): d = 59 (s, 1 F ) ppm. FTIR (KBr disc): n = 3585 (-NH ₂ asymmetric elongation), 3565 (-NH ₂ asymmetric elongation), 1761 (-NH ₂ def.), 1387 (SO ₂ symmetric elongation), 1201 (O=S=O Symmetrical height), 900 (SN height), 776 (SF height) cm ^-1 .

(4) Lithium(fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-lium-3-yl)propyl)sulfonyl)imide)(bistrifluorosulfonyl)imide Synthesis of [lithium (fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl)imide)(bistrifluorosulfonyl)imide, LiFSMIPTFSI, Formula 1a]

For the synthesis of LiFSMIPTFSI, LiTFSI (30 mmol) was added to a solution in which FSSPMIC (25 mmol) was dissolved in acetone (15 mL), and stirred at 25° C. for 3 hours under a nitrogen atmosphere (Scheme 1). After this time, the product was extracted with water and butyl acetate. After evaporation of water, a gel-like product was collected from the aqueous layer, and it was recrystallized in a powder form with acetonitrile to obtain LiFSMIPTFSI with a yield of about 50%. Finally, the synthesized LiFSMIPTFSI salt was dried in a vacuum oven at 80° C. for 30 hours and stored in a glove box under _{N 2 atmosphere.}

3. Electrolyte solution and cell fabrication and performance evaluation

(1) Preparation of electrolyte solution

A mixed solvent of EC and DMSO (75:25 v/v) was used to prepare the LiFSMIPTFSI (1 M) electrolyte solution. This is due to the very low solubility of LiFSMIPTFSI in conventional EC/DEC or EC/dimethyl carbonate (DMC) mixed solvents for LIB. LiFSI and LiTFSI 20% (0.2 M) were each added to the LiFSMIPTFSI (1M) electrolyte solution prepared as an additive (hereinafter, referred to as LiFSMIPTFSI + LiFSI and LiFSMIPTFSI + LiTFSI, respectively). All electrolyte solutions were prepared in a glove box under inert atmospheric conditions. Fabrication of the dummy and coin cell is as follows.

(2) Fabrication of asymmetric dummy cells and coin cells

Fig. 11(a) shows a schematic structure of a dummy cell. For the fabrication of the dummy cell, a _{fluorine-doped tin oxide (FTO) electrode coated with LiFePO 4} and carbon black was used as a spacer and a sealant. I made a sandwich. The LiFePO ₄ film was deposited on an FTO electrode (active area: 0.15 cm ² _{, thickness: about 10 μm) by a doctor blade method using a homemade paste of LiFePO 4} and dried at 90° C. in a vacuum state. In the paste, LiFePO ₄ , carbon black and poly(vinylidene difluoride) [poly(vinylidene difluoride), PVDF] were 86, 5 and 9% by weight, respectively. ^{Similar to the above, a graphite film was deposited on an FTO electrode (active area: 0.15 cm 2} , thickness: about 12 μm) using a paste containing 90% by weight and 10% by weight of graphite carbon and PVDF, respectively. Prior to sandwich formation, both electrodes were immersed in the electrolyte solution for 15 minutes. After assembling the dummy cell, the electrolyte solution was injected through a hole previously drilled on one side of the FTO and sealed with scotch tape as a temporary seal. A schematic structure of a coin cell is shown in FIG. 5B. To fabricate a coin cell, a graphite coated Cu foil, a LiFePO ₄ coated Al foil, and a cell guard film were used as an anode, a cathode, and a separator, respectively. Before assembling the cell, both the anode and the cathode were immersed in a 0.3 mL electrolyte solution for 15 minutes. The cells were assembled in a glove box under inert atmospheric conditions.

(3) ion conductivity measurement

Li ⁺ ion conductivity (σ) of the electrolyte was measured according to the following [Equation 1].

[Equation 1]

Where l is the distance between two asymmetric electrodes, R _s is the bulk resistance, and a is the area of the electrode.

(4) transmission number (t _Li+ ) Of the measurement

_{T Li+} of the electrolyte was measured using a dummy cell. Bipolar polarization of 10 mV was applied between the electrodes of the dummy cell, and steady-state current (I _ss ) and initial current (I _o ) were measured by chronoamperometry. In addition, the EIS spectrum of the dummy cell was measured before and after polarization to obtain the initial resistance (R _o ) and the steady state resistance (R _{ss ).} Finally, t _Li+ of the electrolyte was calculated according to the following [Equation 2].

[Equation 2]

(5) Measurement of EIS spectrum

The EIS spectra of the LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolyte-based dummy cells according to different temperatures are shown in FIG. 12. All EIS spectra showed a concave semicircle in the high frequency region corresponding to the resistance to ^{Li +} migration through the electrode material _{(R SEI ).} The second semicircle in the mid-frequency region _{represents the charge transfer resistance (R CT} ) during the electrochemical reaction, and the third semi-circle in the low-frequency region _{corresponds to Warburg diffusion resistance (Z w} ) at the electrode. R _s is the bulk resistance induced by the movement of ^{Li +} ions through the electrolyte.

4. Results

(1) NMR and FTIR characterization

¹ H NMR spectra of MSIC and FSSPMIC are shown. _{From the presence of the -SO 3} H proton peak at about 4.7 ppm, along with other characteristic proton peaks in the spectrum of MSIC, the addition reaction between 1-methylimidazole and 1,3-propanesultone proceeded successfully, resulting in MSIC. It can be seen that it was formed. In FSSPMIC, a broad peak of NH protons at 9.9-10.5 ppm appeared along with other characteristic proton peaks, indicating that FSSPMIC was successfully synthesized by a reaction between _{FSO 2} NH _{2 and CSPMIC.} Analysis data obtained from ¹ H NMR spectra for MSIC and FSSPMIC are as follows.

For MSIC, ¹ H-NMR (D ₂ O; 298 K): d = 8.65 (s, H), 7.4 (s, H), 7.3 (s, H), 4.7 (s, SO ₃ H), 4.2 -4.3 (t, 2H), 3.79 (s, 3H), 2.79-2.81 (t, 2H), 2.15-2.22 (m, 2H) ppm.

For FSSPMIC, ¹ H-NMR (DMSO; 298 K): d = 9.9-10.5 (s, NH), 9.2 (s, H), 7.8 (s, H), 7.7 (s, H), 4.25-4.35 (t, 2H), 3.85 (s, 3H), 2.4-2.6 (t, 2H), 2.0-2.2 (m, 2H) ppm.

2A and 2B show ¹⁹ F NMR and ¹ H NMR spectra of LiFSMIPTFSI, respectively. ^{The 19} F NMR spectra showed two peaks at about 78.04 and -126.47 ppm for two different electronic environments of the F atom. The first peak with high intensity represents the F atom in the TFSI anion, and the second peak with low intensity is lithium(fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-ium-3-yl) Represents the F atom of )propyl)sulfonyl)imide. ^{The disappearance of the broad peak of the NH proton in the 1} H NMR spectrum and the presence of another proton peak similar to FSSPMIC indicate successful lithiation of FSSPMIC and formation of LiFSMIPTFSI. Analytical data obtained from ¹ H and ¹⁹ F NMR for LiFSMIPTFSI are as follows.

¹ H-NMR (DMSO- d ₆ ; 298 K): d = 9.2 (s, H), 7.8 (s, H), 7.7 (s, H), 4.25-4.35 (t, 2H), 3.85 (s, 3H), 2.4-2.6 (t, 2H), 2.0-2.2 (m, 2H) ppm. ¹⁹ F-NMR (DMSO; 298 K): d = 52.04 (s, 2F), -126.47 (s, F) ppm.

Figure 2c shows the FTIR spectrum of LiFSMIPTFSI, LiFSI and LiTFSI. All compounds exhibited SN overtone and O=S=O (symmetric) peaks at about 1640 and 1190 cm ^{-1, respectively.} LiFSMIPTFSI showed C=C, C=N, and C=H elongation peaks at about 1472, 1580 and 3104 cm ^{−1, respectively, suggesting the successful synthesis of LiFSMIPTFSI.}

(2) Physical and chemical properties

Figure 3a shows the TGA plot of LiFSMIPTFSI, LiFSI and LiTFSI. Both LiFSI and LiFSMIPTFSI exhibited a two-step digestion process. The first step weight loss in the temperature range of 200 to 340 °C for LiFSI was about 6%, and for LiFSMIPTFSI was about 50% at 210 to 390 °C. Thereafter, for LiFSI, a rapid weight reduction of about 80% occurred up to 475°C, but for LiFSMIPTFSI, a weight reduction of about 20% occurred up to 600°C. This two-step weight reduction for LiFSI and LiFSMIPTFSI can be attributed to the slow reaction rate of their particular digestion process. The decomposition of LiTFSI follows a single step weight loss occurring at 320 °C, which is in good agreement with the prior literature [M. Kerner, N. Plylahan, J. Scheers, P. Johansson, Phys. Chem. Chem. Phys. 17 (2015) 19569-19581]. The weight loss of LiTFSI was about 88% at 430°C. This indicates that LiFSMIPTFSI has similar thermal stability to LiFSI, and is slightly lower than LiTFSI. Therefore, considering the normal operating temperature (-40 ~ 85 ℃) of LIB, LiFSMIPTFSI is promising for the development of heat resistant electrolyte. The remaining amounts (%) of LiFSI, LiTFSI and LiFSMIPTFSI were about 11, 12 and 40% at 600°C, respectively. This is presumed to be due to the formation of residual carbon species induced by decomposition. The high residual ratio for LiFSMIPTFSI compared to LiFSI and LiTFSI may be due to the presence of a high ratio of atomic carbon in the structure of LiFSMIPTFSI compared to LiFSI and LiTFSI. In addition, the melting temperature of LiFMIPTFSI (165-169 °C) was measured, which was slightly higher than LiFSI (132-145 °C) and much lower than LiTFSI (234 °C).

3B shows a plot of the viscosity versus temperature of the electrolyte in the temperature range of 30 to 80°C. The viscosity of LiFSMIPTFSI (1 M) decreased with increasing temperature, and was about 2.90 and 1.0 cP at 30 and 80° C., respectively. The decrease in viscosity with increasing temperature can be attributed to the decrease in intermolecular force between LiFSMIPTFSI molecules. The viscosity of the LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes was higher than that of LiFSMIPTFSI alone electrolyte at 30° C., about 3.30 and 4.80 cP, respectively, and about 1.70 and 2.20 cP at 80° C., respectively. The low viscosity over a wide temperature range of all electrolytes indicates a high ability to conduct ^{Li + ions in the LIB.}

(3) Electrochemical oxidation stability and ionic conductivity

The electrochemical oxidation stability of all electrolytes was measured by LSV. Figure 4a shows the LSV plots of all electrolytes in the Pt working electrode in the potential range of 1.5 to 7.0 V (Li/Li ^{+ vs.).} In addition, for comparison, LSV plots of LiFSI and LiTFSI electrolytes (1M each) are shown in FIG. 10. The electrochemical oxidation stability of the LiFSMIPTFSI electrolyte was about 5.3 V, and about 6.0, 5.60, 4.75 and 4.65 V for the LiFSMIPTFSI+LiFSI, LiFSMIPTFSI+LiTFSI, LiFSI and LiTFSI electrolytes, respectively. Compared with LiFSMIPTFSI, the improvement of oxidation stability in LiFSMIPTFSI + LiFSI and LiFSMIPTFSI + LiTFSI electrolytes can be attributed to the enlargement of the band gap promoted by the synergistic effect of LiFSMIPTFSI and additives (LiFSI or LiTFSI). It also indicates that both LiFSI and LiTFSI are effective inhibitors of the electrochemical degradation of LiFSMIPTFSI. The oxidation stability voltage of this electrolyte is much higher than that _{of the conventional LiCoO 2} and LiFePO ₄ cathodes (about 4 and 3.5 V compared to Li/Li ^{+, respectively).} Therefore, all electrolytes will be usefully used in the development of LIBs having high voltage and stability.

By applying the EIS method, σ of the electrolyte was measured using an asymmetric dummy cell (FIG. 11) in a temperature range of 30 to 80°C. The information on the measurement of σ and EIS spectrum is as described above. The σ value of the electrolyte is shown in Fig. 4b, and the similar EIS spectrum is shown in Fig. 12, and an appropriate equivalent circuit model is applied as in Fig. 13. Σ of LiFSMIPTFSI electrolyte was about 6.10 mS/cm at 30° C., Li ⁺ transition number (t _Li+ ) was about 0.55, which was reported LiBF ₄ (4.9 mS/cm), LiClO ₄ (8.4 mS/cm) and IL-based Higher than or similar to electrolytes. Measurement of t _Li+ is as described above. Σ of the LiFSMIPTFSI electrolyte increased with increasing temperature, and was about 7.50 mS/cm at 80°C. This is in good agreement with the change of the dynamic viscosity of the LiFSMIPTFSI electrolyte with temperature. The high σ of the LiFSMIPTFSI electrolyte can be further explained by the charge delocalization of the FSMIPTFSI anion, as shown in FIG. 14. The delocalization of the negative charge of the FSMIPTFSI anion can lead to stabilization, and at the same time, can reduce the association constant of ion pairing and increase σ.

LiFSI and LiTFSI additives both improved the σ of LiFSMIPTFSI electrolyte, LiFMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes were about 8.5 and 7.90 mS/cm at 30° C., respectively, and t _Li+ was 0.64 and 0.60, respectively. At 80° C., they were about 9.65 and 9.10 mS/cm. This also coincides with the change in viscosity with temperature. The σ enhancement of the LiFSMIPTFSI electrolyte by the additive can be attributed to the net enhancement of ^{the Li + concentration to the corresponding electrolyte.} The LiFSMIPTFSI+LiFSI electrolyte showed the most improved improvement of σ compared to the LiFSMIPTFSI+LiTFSI electrolyte, which can be attributed to the _{low viscosity and high t Li+ compared to the LiFSMIPTFSI+LiTFSI electrolyte.} In addition, the smaller FSI anion compared to the TFSI anion enables faster ion migration and at the same time improves the σ of LiFSMIPTFSI+LiFSI electrolyte. Figure 4c shows the Arrhenius plot of the measured σ of all electrolytes. _{The activation energies (E a} ) for the LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes were about 2.80, 2.35 and 2.50 kJ/mol, respectively. This low E _a value of ^{all electrolytes indicates a weak binding energy between Li +} and the corresponding anion of the electrolyte, which is advantageous in obtaining high σ and electrochemical performance in LIB.

The electrochemical stability of all electrolytes was investigated by measuring the change in σ value by continuous EIS (10 times) measurement at 30°C. Each EIS spectrum was measured after CV sweeping (10 cycles) of dummy cells in a potential range of 0 to 7 V (relative to Li/Li ^{+) at a scan rate of 25 mV/s.} 4D summarizes the change in σ value according to the number of EIS scans, and the corresponding EIS spectrum is shown in FIG. 15. σ decreased by only about 6.56, 7.10 and 8.0% in the case of LiFSMIPTFSI, LiFSMIPTFSI+LiFSI, and LiFSMIPTFSI+LiTFSI electrolytes, respectively. These small changes in σ values of all electrolytes show excellent electrochemical stability promising for the development of stable LIBs.

(4) Electrochemical performance of electrolyte

5(ac) shows _{the device structure of LiFePO 4} /electrolyte/graphite, showing the CD profiles of all LIBs at 0.1, 0.2 and 0.3 C, respectively. LiFSMIPTFSI electrolyte-based LIB showed the highest overvoltage, but the overvoltage decreased with the addition of additives and the lowest for LiFSMIPTFSI+LiFSI at all C rates. This indicates that LiFSI and LiTFSI are effective additives for obtaining high energy efficiency with excellent reversibility to LiFSMIPTFSI electrolyte. The C _sp of these LIBs was calculated based on the cathode material LiFePO _{4. The C sp} of the LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolyte-based LIB was 141, 160, and 150 mAhg ⁻¹ at 0.1 C, respectively. At 0.2 C, it was about 130, 150, and 141 mAhg ^-1 , respectively, and at 0.3 C, it was about 121, 138 and 129 mAhg ^-1, respectively. _{The C sp} of all electrolyte-based LIBs was measured to be about 95, 115 and 105 mAhg ⁻¹ at 1 C, respectively (FIG. 16). For comparison, EC / DMSO solvent at the same device structure (75:25 v / v) in LiFSI (1 M) and the electrochemical performance of LiTFSI (1 M) was also measured, each about 126 at 0.1 C and 123 mAhg ^{- It} represents the C _{sp of 1.} This indicates that the LiFSMIPTFSI electrolyte can outperform the electrochemical performance of LiFSI and LiTFSI electrolyte-based batteries and may be a promising alternative. _{The C sp} of pure LiFSMIPTFSI electrolyte based LIB is higher or similar to other reported LIBs as listed in Table 1. _{The C sp} of the LiFSMIPTFSI electrolyte-based LIB was improved by the addition of LiFSI and LiTFSI additives, and the LiFSI additive was more effective. The results so far agree well with the changes in _{σ, t Li+ and viscosity of the corresponding electrolyte.}

Table 1 is a table comparing the specific capacity of the electrolyte developed in the present invention and the recently reported electrolyte for LIB.

_{Figure 5d shows the change in C sp} and Coulomb efficiency (η) for the number of CD cycles of all electrolyte-based LIBs at 0.1°C and 30°C. _{The C sp} for LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolyte-based LIB decreased ^{by about 12.2 (130.80 mAhg -1} ), 4.52 (169 mAhg ^-1 ) and 9.90% (145.10 mAhg ^-1 ), respectively, after 500 CD cycles. This indicates that LiFSI is a better additive than LiTFSI for LiFSMIPTFSI electrolyte to obtain improved electrochemical performance. For LiFSMIPTFSI, LiFSMIPTFSI+LiFSI, and LiFSMIPTFSI+LiTFSI electrolyte-based batteries, η in one CD cycle was about 90, 92 and 91%, respectively, which increased monotonically to about 95.90, 98.50 and 97.40%, respectively, after 500 CD cycles. The monotonic increase in η with increasing the number of CD cycles may be due to the formation of a stable SEI layer on the anode surface induced by the electrolyte. The η of LiFSMIPTFSI electrolyte based batteries was slightly lower than those based on LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes. This may be due to the low ability to form an SEI layer on the graphite anode.

In order to further investigate the LIB stability and η, the cell interface stability of the electrolyte-based LIB was investigated by analyzing the surface morphology of the graphite anode. Fig. 6 shows an FE-SEM image of a graphite anode of LIB based on LiFSMIPTFSI, LiFSMIPTFSI+LiFSI and LiFSMIPTFSI+LiTFSI electrolytes recovered after 500 CD cycles at 0.1 C. For comparison, an FE-SEM image (FIG. 17) of pure graphite was also measured, which showed a very smooth surface. It was shown that a dense and stable SEI layer _{of LiF, Li 2} S and Li _y C ₂ F _x compounds was formed on the surface of the graphite anode of this electrolyte-based LIB. The density of the SEI layer formed on the graphite anode induced by LiFSMIPTFSI+LiFSI electrolyte was much higher than that of the SEI layer formed by LiFSMIPTFSI, LiFSMIPTFSI+LiTFSI electrolyte. This SEI layer can increase the stability of the electrode/electrolyte interface, and at the same time improve the stability and η of LIB. This appears to be very consistent with the stability of this electrolyte-based LIB and η. Formation of the SEI layer on the surface of the graphite anode implemented by these electrolytes was further verified by the EDS elemental map, and the results are shown in FIGS. 18 to 20. The EDS elemental map clearly indicated the presence of elements C, O, S, F and N on the graphite anode surface, and the proportion of these elements was found to be higher in LiFSMIPTFSI+LiFSI.

5. Conclusion

In the present invention, an electrolyte salt LiFSMIPTFSI was prepared for application in LIB. LiFSMIPTFSI electrolyte showed excellent σ, t _Li+ , high electrochemical and thermal stability, and low viscosity, and at the same time conducted C _sp ^{of about 141 mAhg -1} at 0.1 C in the LIB of the device structure of _{LiFePO 4 /electrolyte/graphite.} The physicochemical properties of LiFSMIPTFSI, σ, t _Li+, and electrochemical oxidation stability were further improved by adding LiFSI and LiTFSI additives. As a result of the measurement, it was confirmed that LiFSI is an additive superior to LiTFSI in LiFSMIPTFSI, and C _sp ^{of about 160 mAhg -1} was conducted at 0.1 C with maximum capacity maintenance and η. The electrochemical performance of the electrolyte was found to be higher or comparable to that of many other electrolyte-based LIBs reported. However, the safety of these electrolyte-based LIBs is still of great interest due to the use of organic solvents and further studies are required. The present invention will provide an idea in developing high performance electrolyte salts based on other electrolyte solutions.

6. Summary

In the present invention, as an electrolyte for the development of a lithium-ion battery (LIB), an imide-based electrolyte salt functionalized with imidazolium, lithium (fluorosulfonyl) ((3-(1-methyl-1H-imidazole) -3-Rium-3-yl)propyl)sulfonyl)imide) bis(trifluorosulfonyl)imide (LiFSMIPTFSI) was synthesized. LiFSMIPTFSI electrolyte shows high electrochemical oxidation stability and good Li ⁺ conductivity, and at the same time provides a specific discharge capacity of ^{141 mAhg -1 at 0.1 C.} The electrochemical performance of the LiFSMIPTFSI electrolyte is about each by adding lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)), which are conventional imide salts, as additives. An additional 20% improvement. LiFSMIPTFSI electrolyte-based LIB with LiFSI additive shows maximum capacity retention (about 95.50%) with the highest Coulomb efficiency (98.50%) after 500 charge-discharge cycles.

Claims (10)

Lithium salt of formula 1:
[Formula 1]

(In the above formula, n is an integer of 1 to 5). The lithium salt of claim 1, wherein the lithium salt is of formula 1a:
[Formula 1a]

. An electrolyte composition comprising the lithium salt of claim 1 or 2. The electrolyte composition of claim 3, further comprising an additive selected from the group consisting of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, and mixtures thereof. . The electrolyte composition according to claim 4, wherein the additive is contained in a lithium salt: additive = 1:0.1 to 0.3 molar ratio. The electrolyte composition according to claim 3, wherein the solvent is one selected from the group consisting of ethylene carbonate, dimethyl sulfoxide, and mixtures thereof. A lithium ion battery comprising the electrolyte composition of claim 3. (a) preparing a compound of formula 3 by chlorination reaction of the compound of formula 2 with thionyl chloride (SOCl _{2 );}
(b) reacting the compound of formula 3 obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4; And
(c) reacting the compound of formula 4 obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare a compound of formula 1
The method for preparing the lithium salt of claim 1 comprising:
[Formula 1]

(In the above formula, n is an integer from 1 to 5)
[Formula 2]

(In the above formula, n is an integer from 1 to 5)
[Formula 3]

(In the above formula, n is an integer from 1 to 5)
[Formula 4]

(In the above formula, n is an integer of 1 to 5). The method of claim 8,
(a) preparing a compound of formula 3a by chlorinating the compound of formula 2a with thionyl chloride (SOCl _{2 );}
(b) reacting the compound of formula 3a obtained in step (a) with sulfamoyl fluoride (FSO ₂ NH ₂ ) to prepare a compound of formula 4a; And
(c) reacting the compound of formula 4a obtained in step (b) with lithium bis(trifluoromethylsulfonyl)imide to prepare a compound of formula 1a
Method for preparing a lithium salt of Formula 1a comprising:
[Formula 1a]

[Formula 2a]

[Formula 3a]

[Formula 4a]

. The method of claim 9, wherein the compound of formula 2a in step (a) is prepared by addition reaction of 1-methylimidazole and 1,3-propane sultone.

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