KR101297786B1 - Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

PURPOSE: A non-aqueous electrolyte solution is provided to improve ion conductivity, to improve the charging and discharging performance of a battery and to reduce irreversible capacity by forming a stable solid electrolyte interface on the surface of an anode. CONSTITUTION: A non-aqueous electrolyte solution includes an imidazolium-based zwitterion, an inorganic solvent, and a lithium salt. In the chemical formula 1, R1 is a C1-6 linear or branched alkyl group; n is an integer from 3 or 4, and m is an integer of 2 or 3. The amount of the imidazolium-based zwitterion included is 0.5-3.0 wt% per the total weight of the non-aqueous electrolyte solution. A lithium secondary battery includes an anode, a cathode, and the non-aqueous electrolyte. [Reference numerals] (AA,CC) Current (mA); (BB) Example 1; (DD) Comparative example 2; (EE) Voltage vs. Li/Li^+(V)

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery including the same}

The present invention relates to a nonaqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the same, and more particularly, to a nonaqueous electrolyte for lithium secondary batteries having improved ion conductivity, initial capacity, and cycle characteristics, and a lithium secondary battery comprising the same. .

Recently, interest in electrochemical devices is increasing. In addition to mobile phones, camcorders, and notebook PCs, the field of application of electrochemical devices is expanding to power sources of electric vehicles or hybrid electric vehicles, and as development of alternative energy such as solar energy and wind energy increases, There is a growing interest in energy storage devices for storing energy.

Among the electrochemical devices currently applied, lithium secondary batteries, developed in the early 1990s, having excellent energy density, rapid charge / discharge characteristics, and cycle performance, are the most suitable electrochemical devices that can satisfy these requirements. And an anode containing graphite capable of inserting and desorption, a cathode containing a lithium-containing oxide, and the like, a separator for preventing a short circuit between the two electrodes, and a nonaqueous electrolyte solution in which lithium salt is dissolved in an appropriate amount in an organic solvent.

The average discharge voltage of the lithium secondary battery is about 3.6V to 3.7V, and one of the advantages is that the discharge voltage is higher than that of an alkaline battery, a nickel-cadmium battery, or the like. In order to produce such a high driving voltage, an electrochemically stable nonaqueous electrolyte is required in the charge and discharge voltage range of 0 to 4.2V. The nonaqueous electrolyte is generally composed of an organic solvent and a lithium salt, but in some cases, an additive may be added to supplement the mechanical strength of the nonaqueous electrolyte and the interface with the electrode.

In the lithium secondary battery, during initial charging, lithium ions in the nonaqueous electrolyte are reduced to be inserted between the graphite constituting the negative electrode, and the lithium metal oxide constituting the positive electrode is dissolved in the nonaqueous electrolyte to maintain the lithium ion concentration of the nonaqueous electrolyte. In this process, lithium ions and anions of organic solvents or lithium salts are partially decomposed to form a thin solid electrolyte interface (SEI) on the electrode surface.

SEI acts as a barrier to prevent the breakdown of the electrode structure by inserting organic solvents having a high molecular weight into the graphite constituting the negative electrode, and also serves as a passage to help smooth movement of lithium ions. Therefore, the composition and structure of the SEI formed on the surface of the negative electrode during the initial charging of the battery has a great influence on the battery performance. Therefore, in order to realize a high performance secondary battery, development of a non-aqueous electrolyte capable of forming a stable SEI for minimizing degradation of battery performance due to reduction and decomposition of an organic solvent has been urgently required.

To date, sulfide-based, vinyl ester-based, perfluorinated sulfone, divinylsulfone, vinyl silane, and borate-based compounds have been reported as additives in nonaqueous electrolytes forming SEI on the anode surface. In recent years, studies have been actively conducted to use ionic liquids having excellent properties such as non-volatile properties, non-flammability, and ionic conductivity as nonaqueous electrolytes for lithium secondary batteries. In particular, research on imidazolium-based or pyridine-based ionic liquids is most widely conducted.

However, due to the high price and high viscosity of the ionic liquid, it is used as an additive of a conventional non-aqueous electrolyte containing a lithium salt and an organic solvent, rather than using only the non-aqueous electrolyte itself. In this case, however, the cations of the ionic liquid move with the lithium ions to the electrode according to the potential difference, thereby decreasing the mobility of the lithium ions, and the ions of the ionic liquid transferred to the electrode are inserted into the electrodes and There is a problem in that deterioration of battery performance is impaired.

On the other hand, in order to overcome this problem, a method of adding zwitter ions (zwitterions) in which the anion portion and the cationic portion exist in the same molecular structure to the nonaqueous electrolyte of a lithium secondary battery has been proposed. To this end, there is a need for improvement of the molecular structure.

Accordingly, the problem to be solved by the present invention is to improve the ion conductivity, to form a stable SEI on the anode surface, a non-aqueous electrolyte that can reduce the irreversible capacity and improve the charge and discharge characteristics of the battery and a lithium secondary battery comprising the same To provide.

In addition, another object of the present invention is to provide an electrochemical and thermally stable nonaqueous electrolyte and a lithium secondary battery comprising the same.

In order to solve the above problems, according to an aspect of the present invention, the imidazolium-based zwitter ion represented by the following formula (1); Organic solvent; And a lithium salt; a nonaqueous electrolyte solution for a lithium secondary battery is provided.

[Formula 1]

In Formula 1,

R ₁ is a linear or branched alkyl group having 1 to 6 carbon atoms, n is an integer of 3 or 4, and m is an integer of 2 or 3.

Here, R ₁ is methyl, ethyl or butyl, n is 3, m may be 2.

The imidazolium-based zwitter ions may be included in an amount of 0.5 wt% to 3.0 wt% based on the total weight of the nonaqueous electrolyte.

In addition, the lithium salt ^{anion, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 _{^{-, (CF 3) 3 PF}} 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, _{(CF 3 SO 2) 2 N} -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF ^{_{3 SO 2) 3 C -,}} CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN ^- may be at least one or two kinds selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N.

The lithium salt concentration of the electrolyte solution may be 0.8 M to 1.5 M.

In addition, the organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2 3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), Methylpropyl carbonate, ethylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and It may be any one selected from the group consisting of ε-caprolactone or a mixture of two or more thereof.

The nonaqueous electrolyte solution for lithium secondary batteries may further include an ionic liquid.

Here, the ionic liquid may be any one selected from the group consisting of imidazolium, pyridinium, ammonium, morpholinium, and pyrrolidinium, or a mixture of two or more thereof.

On the other hand, according to another aspect of the present invention, there is provided a lithium secondary battery comprising an anode, a cathode, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is a nonaqueous electrolyte described above.

According to one embodiment of the present invention, during the initial aging of a lithium secondary battery, imidazolium-based zwitter ions are adsorbed on the electrode by nitrile groups and contribute to the formation of stable SEI, thereby causing electrochemical stability and thermal stability of the lithium secondary battery. And ionic conductivity, and in particular, reduction of irreversible capacity and improvement of charge / discharge characteristics of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a graph showing the measurement of the circulating voltage current of the three-electrode cell using the nonaqueous electrolyte prepared according to Example 1 and Comparative Example 2 of the present invention.
Figure 2 is a graph showing the initial discharge capacity, measured through a charge and discharge test for the lithium secondary battery prepared according to Examples 1 to 3 and Comparative Example 1 of the present invention.
FIG. 3 shows capacity retention rates measured through charge and discharge tests over 0.5 C, 1.0 C, 1.5 C, and 2.0 C for lithium secondary batteries manufactured according to Examples 1 to 3 and Comparative Example 1 of the present invention. The graph shown.
Figure 4 is a graph showing the cycle characteristics measured by repeated charge and discharge tests for 100 times at 1 C lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Example 1 of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention various equivalents that can be substituted for them at the time of the present application It should be understood that there may be water and variations.

Non-aqueous electrolyte solution for lithium secondary batteries according to the present invention, the imidazolium-based zwitter ion represented by the formula (1); Organic solvent; And lithium salts.

In Formula 1, R ₁ is a substituted or unsubstituted linear or branched alkyl group having 1 to 6 carbon atoms, n is an integer of 3 or 4, m is an integer of 2 or 3.

The imidazolium-based zwitter ion represented by Formula 1 may be prepared by reacting imidazolium substituted with a nitrile group with 1,4-butanesultone or 1,3-propanesultone as in Scheme 1 below. .

[Reaction Scheme 1]

On the other hand, examples of the unsubstituted alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isoamyl, hexyl and the like. One or more hydrogen atoms included in the alkyl group include a halogen atom, a hydroxyl group, a hydrosulfide group, a nitro group, a cyano group, a substituted or unsubstituted amino group (-NH ₂ , -NH (R), -N (R ')). (R "), R 'and R" are independently of each other an alkyl group having 1 to 10 carbon atoms), amidino group, hydrazine, or hydrazone group carboxyl group, sulfonic acid group, phosphoric acid group, C1-C20 alkyl group, C1-C20 halogenation Alkyl group, C1-C20 alkenyl group, C1-C20 alkynyl group, C1-C20 heteroalkyl group, C6-C20 aryl group, C6-C20 arylalkyl group, C6-C20 heteroaryl group, or C6-C20 It may be substituted with a heteroarylalkyl group.

Imidazolium-based zwitter ions represented by the formula (1) according to the invention is characterized in that it includes both nitrile group and sulfonate group. By including the imidazolium-based zwitter ions, during the initial aging of the lithium secondary battery, imidazolium-based zwitter ions are adsorbed to the electrode by the nitrile group to form a stable SEI.

The imidazolium-based zwitter ion, the appropriate content may be selected according to the specific type of the organic solvent, lithium salt, electrode active material. For example, the composition may be included in an amount of 0.5 wt% to 3.0 wt%, more preferably 0.5 wt% to 1.5 wt% based on the total weight of the nonaqueous electrolyte. When the numerical range is satisfied, a stable SEI is formed and the electrochemical stability, thermal stability, and ion conductivity of the lithium secondary battery are further improved.

And, as an anion wherein the lithium salt is included in the non-aqueous liquid electrolyte of the present ^{invention, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF _{^{6 -, (CF 3) 2}} PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 _{^{-, CF 3 CF 2 SO 3}} -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, ^{_{(SF 5) 3 C -,}} (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, It may include any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof. Non-limiting examples of the lithium salt herein include LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carbonate and lithium tetraphenyl borate may be used, but is not limited thereto.

The lithium salt concentration of the nonaqueous electrolyte may be 0.8 M to 1.5 M. When the concentration of the lithium salt satisfies the numerical range, the performance of the lithium secondary battery is prevented from deteriorating.

As the organic solvent included in the nonaqueous electrolyte solution described above, those conventionally used in the nonaqueous electrolyte solution for a lithium secondary battery may be used without limitation, and for example, ethers, esters, amides, linear carbonates, and cyclic carbonates may be used alone or in combination. It can mix and use the above.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Mixtures of two or more of them may be representatively used, but are not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have high dielectric constants and can dissociate lithium salts in non-aqueous electrolytes more efficiently as cyclic carbonates. By mixing the same low viscosity, low dielectric constant linear carbonate in an appropriate ratio, a nonaqueous electrolyte having a higher electrical conductivity can be made.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used. However, the present invention is not limited thereto.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and One or a mixture of two or more selected from the group consisting of ε-caprolactone may be used, but is not limited thereto.

The nonaqueous electrolyte solution for lithium secondary batteries of the present invention may further include an ionic liquid within a range not departing from the object of the present invention.

Here, the ionic liquid is any one or two or more selected from the group consisting of imidazolium, pyridinium, ammonium, morpholinium, and pyrrolidinium, which are ionic liquids commonly used in lithium secondary batteries. It may be a mixture, but is not limited thereto. The content of the ionic liquid may be 10 wt% to 50 wt%, more preferably 10 wt% to 30 wt%, based on the total weight of the nonaqueous electrolyte, but is not limited thereto.

In addition, the nonaqueous electrolyte of the present invention may further include various additives such as an adhesion improving agent, a filler, and the like in order to improve the mechanical strength of the nonaqueous electrolyte and the interface performance with the electrode.

Meanwhile, the lithium secondary battery according to the present invention is a lithium secondary battery including an anode, a cathode, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is a nonaqueous electrolyte according to the present invention.

The lithium secondary battery of the present invention can be produced by a conventional method known in the art. For example, a porous separator may be inserted between the cathode and the anode, and the nonaqueous electrolyte solution according to the present invention may be added to the separator.

In the separator, as the porous substrate on which the porous coating layer is formed, any porous substrate commonly used in an electrochemical device may be used. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used. It is not limited.

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene and ultra high molecular weight polyethylene, One membrane can be mentioned.

The nonwoven fabric may be, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, or polycarbonate. ), Polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene, etc. Or the nonwoven fabric formed from the polymer which mixed these is mentioned. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

The anode has a structure in which the anode layer including the anode active material and the binder is supported on one or both surfaces of the current collector. At this time, the anode layer may further include a cellulose-based thickener such as carboxymethyl cellulose (CMC) to further increase the viscosity of the anode active material slurry.

As the anode active material, a lithium metal, a carbon material, a metal compound, or a mixture thereof, which may normally occlude and release lithium ions, may be used.

Concretely, as the carbon material, low-crystallinity carbon and high-crystallinity carbon may be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The cathode has a structure in which a cathode layer including a cathode active material, a conductive material and a binder is supported on one or both surfaces of the current collector.

The cathode active material may include a lithium-containing oxide, and the lithium-containing oxide may be a lithium-containing transition metal oxide. The lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition to the lithium-containing transition metal oxides, sulfides, selenides, and halides may also be used.

The conductive material is not particularly limited as long as it is an electron conductive material that does not cause chemical change in the electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material and the like can be used. Commercially available products as the conductive material include acetylene black series (manufactured by Chevron Chemical Co., (Chevron Chemical Company or Gulf Oil Company products), Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (MM (MMM)). For example, acetylene black, carbon black and graphite.

The binder used for the cathode and the anode has a function of holding the cathode active material and the anode active material in the current collector and also connecting the active materials, and a commonly used binder may be used without limitation.

For example, it is possible to use vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, styrene Various types of binder polymers such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

The current collector used for the cathode and the anode may be any metal having a high conductivity and a metal which can easily adhere to the slurry of the active material and is not reactive in the voltage range of the battery. Specifically, examples of the current collector for a cathode include aluminum, nickel, or a combination thereof. Examples of the current collector for an anode include copper, gold, nickel, or a copper alloy or a combination thereof And the like. In addition, the current collector may be used by laminating the substrates made of the above materials.

The cathode and the anode were kneaded using an active material, a conductive material, a binder, a thickener, and a high boiling point solvent to form an electrode mixture, and then the mixture was applied to a copper foil of a current collector, dried, and press-molded. It may be produced by heat treatment under vacuum at about 2 hours to a temperature of about ℃ to 250 ℃.

The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be cylindrical, square, pouch type or coin type using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, embodiments according to the present invention can be modified in various other forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

(1) Preparation of imidazolium-based zwitter ions

In a 250 ml three-necked flask, 50 ml of dimethylformamide and 50 mmol of 1- (2-nitrileethyl) -2-methylimidazole were exchanged in a vacuum state for 1 hour, followed by 1 using a syringe. , 3-propanesultone was added and refluxed at 80 ° C. for 12 hours. The reaction mixture was then filtered, washed several times with dimethylformamide and dried for 24 hours, yielding 1-propanenitrile-2-methylimidazolium-3-propanesulfonate as a white solid, the yield of which was Was measured at 93%. On the other hand, the structure was confirmed by ¹ H NMR measurement.

Elemental analysis calculations: C 46.98%; N 16.34%; H 6.04%; S 12.36%; Degree of substitution 0.98.

¹ H NMR (sol, D ₂ O): δ (ppm) = 7.56 ppm (d, 2H, NCH ₂ ), 7.55 ppm (d, 2H, NCH ₂ ), 2.39 ppm (s, 3H, NCCH ₃ ), 4.34 ppm (t, 2H, NCH ₂ ), 2.73 ppm (q, 2H, CH ₂ ), 2.97 ppm (t, 2H, CH ₂ S), 4.54 ppm (t, 2H, NCH ₂ ) and 3.13 ppm (t, 2H , CH ₂ CN).

FAB-MS: 258 m / z: ([M + H] ⁺ ).

(2) Preparation of non-aqueous electrolyte

0.39 mmol of the 1-propanenitrile-2-methylimidazolium-3-propanesulfonate prepared above was added to 20 g of a 3: 7 mixed solution of ethylene carbonate: diethyl carbonate in which 1M LiPF ₆ was dissolved. Prepared by stirring for 24 hours.

(3) Production of lithium secondary battery

As a pouch-type lithium secondary battery, LiCoO ₂ was used as the cathode active material, graphite was used as the anode active material, polypropylene was used as the separator, and 0.5 g of the prepared nonaqueous electrolyte was injected as the electrolyte, followed by A lithium secondary battery was prepared by aging for 2 hours under conditions.

Example  2

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.78 mmol of 1-propanenitrile-2-methylimidazolium-3-propanesulfonate was added.

Example  3

A nonaqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 1.18 mmol of 1-propanenitrile-2-methylimidazolium-3-propanesulfonate was added.

Comparative example  One

A nonaqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 1-propanenitrile-2-methylimidazolium-3-propanesulfonate was not added.

Comparative example  2

(1) Preparation of imidazolium-based zwitter ions

In a 250 ml three-necked flask, 50 ml of acetone and 50 mmol of 1,2-dimethylimidazole were added and exchanged under vacuum for 1 hour. Then, 1,3-propanesultone was added using a syringe at 28 ° C. It was refluxed for 8 hours. The reaction mixture was then filtered, washed several times with acetone and dried for 24 hours to give 1,2-dimethylimidazolium-3-propanesulfonate as a white solid, the yield being determined to be 87%. On the other hand, the structure was confirmed by ¹ H NMR measurement.

Elemental analysis calculations: C 43.89%; N 12.83%; H 6.66%; S 14.65%; Degree of substitution 0.98.

¹ H NMR (sol, D ₂ O): δ (ppm) = 7.41 ppm (d, 2H, NCH ₂ ), 7.34 ppm (d, 2H, NCH ₂ ), 2.61 ppm (s, 3H, NCCH ₃ ), 4.29 ppm (t, 2H, NCH ₂ ), 2.26 ppm (q, 2H, CH ₂ ), 2.95 ppm (t, 2H, CH ₂ S) and 3.77 ppm (t, 3H, CNCH ₃ ).

FAB-MS: 219 m / z ([M + H] ⁺ ).

(2) Preparation of non-aqueous electrolyte

0.39 mmol of the prepared 1,2-dimethylimidazolium-3-propanesulfonate was added to 20 g of a 3: 7 mixed solution of ethylene carbonate: diethyl carbonate in which 1 M LiPF ₆ was dissolved, and then, for 24 hours. Prepared by stirring.

(3) Production of lithium secondary battery

As a pouch-type lithium secondary battery, LiCoO ₂ was used as the cathode active material, graphite was used as the anode active material, polypropylene was used as the separator, and 0.5 g of the prepared nonaqueous electrolyte was injected as the electrolyte, followed by A lithium secondary battery was prepared by aging for 2 hours under conditions.

Comparative example  3

A nonaqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Comparative Example 2, except that 0.78 mmol of 1,2-dimethylimidazolium-3-propanesulfonate was added.

Comparative example  4

A nonaqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Comparative Example 2 except that 1.18 mmol of 1,2-dimethylimidazolium-3-propanesulfonate was added.

Comparative example  5

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Comparative Example 2, except that 1.58 mmol of 1,2-dimethylimidazolium-3-propanesulfonate was added.

Test Example  1: Ion Conductivity Measurement

The resistance values of the nonaqueous electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were measured using an electrochemical impedance analyzer (Solartron 1255) at 20 ° C. And a lithium secondary battery was prepared using a stainless electrode and injecting 0.5 g of each nonaqueous electrolyte. The cross-sectional area of the electrode was 0.283 cm ² , the distance between the two electrodes was measured to be 0.022 cm, the calculated ion conductivity value based on this is shown in Table 1 below.

Zwitter ion content (mmol) Ionic Conductivity (mS / cm) Example 1 0.39 6.27 Example 2 0.78 7.64 Example 3 1.18 6.80 Comparative Example 1 0.00 5.64 Comparative Example 2 0.39 5.42 Comparative Example 3 0.78 5.20 Comparative Example 4 1.18 4.49 Comparative Example 5 1.58 3.16

As shown in Table 1, when the non-aqueous electrolyte solution containing the imidazolium-based zwitter ions substituted with the nitrile group was used, it was confirmed that the ionic conductivity was increased compared to Comparative Example 1 without adding anything. It was confirmed that Example 2 shows the highest value, whereas in Comparative Examples 2 to 5, it was confirmed that the ionic conductivity is reduced than Comparative Example 1.

Test Example 2 : Electrochemical Performance Measurement

After the three-electrode cells were prepared using the nonaqueous electrolytes prepared in Example 1 and Comparative Example 2, cyclic voltammetry was measured for each cell. As a measuring instrument, CHI900B SECM manufactured by CH Instruments was used. At this time, a graphite electrode was used as an electrode, and lithium metal was used as a counter electrode and a reference electrode, respectively. And the measurement speed was 0.5 mVS ^{- 1} .

As a result, in Example 1 including imidazolium-based zwitter ions substituted with a nitrile group, as shown in FIG. 1, SEI was well formed at the interface of the graphite electrode so that insertion and desorption of lithium ions occurred smoothly. Could confirm. On the other hand, in the case of Comparative Example 2 containing an imidazolium-based zwitter ion unsubstituted nitrile group, it was confirmed that the stable SEI was not formed, the insertion and desorption of lithium ions did not occur smoothly.

Test Example 3 : Charge / discharge performance measurement

The charging and discharging characteristics of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Example 1 were measured using a charger / discharger (WBCS 3000: Wonatech).

The initial charge and discharge up to three times were performed at 0.2C, and the performance measurement for each charge and discharge rate was performed at 0.5C up to 4.2V, and the discharge was 0.5C, 1.0C, 1.5C and 2.0C. Each was carried out. In addition, repeated charge and discharge performance measurements were performed 100 times at 1C.

As a result, as shown in FIG. 2, in the case of Examples 1 to 3, which are lithium secondary batteries containing imidazolium-based zwitter ions substituted with nitrile groups, it was confirmed that the initial discharge capacity was improved compared to Comparative Example 1. . In addition, as shown in FIG. 3 and FIG. 4, the lithium secondary battery including the imidazolium-based zwitter ion in which the nitrile group is substituted has the performance according to the charge / discharge rate and the repetitive charge / discharge performance than those not included. It was confirmed that high.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (9)

Imidazolium-based Zwitter ions represented by Formula 1 below;
Organic solvent; And
Non-aqueous electrolyte solution for lithium secondary batteries comprising a lithium salt;
[Formula 1]

In Chemical Formula 1,
R ₁ is a linear or branched alkyl group having 1 to 6 carbon atoms, n is an integer of 3 or 4, and m is an integer of 2 or 3. The method of claim 1,
R ₁ is methyl, ethyl or butyl,
N is 3, and m is 2, the nonaqueous electrolyte solution for a lithium secondary battery. The method of claim 1,
The imidazolium-based zwitter ions, the non-aqueous electrolyte for lithium secondary battery, characterized in that contained in 0.5% to 3.0% by weight based on the total weight of the nonaqueous electrolyte. The method of claim 1,
The lithium salt ^{anion, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ^{_{(CF 3) 3 PF 3 -}} , (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF ^{_{3 SO 2) 2 N -,}} (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO ^{_{2) 3 C -, CF 3}} (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN ^- and _{(CF 3 CF 2 SO 2)} 2 N - non-aqueous electrolyte lithium secondary battery, characterized in that any one or two or more species selected from the group consisting of. The method of claim 1,
The lithium salt concentration of the said nonaqueous electrolyte is 0.8 M-1.5 M, The nonaqueous electrolyte solution for lithium secondary batteries characterized by the above-mentioned. The method of claim 1,
The organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3 Pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl Carbonate, ethylpropyl carbonate, dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethyl propyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ- Selected from the group consisting of butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone The one or a non-aqueous electrolyte lithium secondary battery, characterized in that a mixture of two or more of these. The method of claim 1,
The nonaqueous electrolyte solution for lithium secondary batteries further comprises an ionic liquid. The method of claim 7, wherein
The ionic liquid is any one selected from the group consisting of imidazolium, pyridinium, ammonium, morpholinium, and pyrrolidinium, or a mixture of two or more thereof. A lithium secondary battery comprising an anode, a cathode, and a non-aqueous electrolyte,
The nonaqueous electrolyte is a nonaqueous electrolyte for lithium secondary batteries according to any one of claims 1 to 8, characterized in that the lithium secondary battery.

Images