KR20140147478A - Electrolyte comprising amide compound and electrochemical device containing the same - Google Patents

Abstract

The present invention relates to electrolyte including an amide compound and an electrochemical device including the electrolyte, and more particularly, discloses electrolyte, which includes an amide compound having a specific structure, ionizable lithium salt, a carbonate-based organic solvent, and halogenated cyclic carbonate, and an electrochemical device including the electrolyte. Electrolyte according to the present invention has excellent thermal and chemical stability and excellent charging and discharging performance and is thus useful for an electrochemical device.

Description

ELECTROLYTE COMPRISING AMIDE COMPOUND AND ELECTROCHEMICAL DEVICE CONTAINING THE SAME Technical Field The present invention relates to an electrolyte comprising an amide compound,

The present invention relates to an electrolyte comprising an amide compound and a linear ester compound, and an electrochemical device having the same.

2. Description of the Related Art [0002] Recently, electrochemical devices such as lithium secondary batteries, electrolytic capacitors, electric double layer capacitors, electrochromic display devices, and dye-sensitized solar cells Various kinds of electrolytes are used in the electrolyte, and their importance is increasing day by day.

Particularly, lithium secondary batteries are attracting the most attention as batteries having high energy density and long life. Typically, a lithium secondary battery includes a cathode made of a carbon material or a lithium metal alloy, a cathode made of a lithium metal oxide, and an electrolyte in which a lithium salt is dissolved in an organic solvent.

The electrolyte is a medium for transferring ions between electrodes. The electrolyte should have sufficient ion conductivity and low viscosity, and should be electrochemically stable in the operating temperature and pressure range of the battery. Currently, organic solvents widely used in the electrolyte of lithium secondary batteries include ethylene carbonate, propylene carbonate, dimethoxy ethane, g-butyrolactone (GBL), N, N-dimethyl Dimethyl formamide, tetrahydrofurane or acetonitrile, and the like. However, since the organic solvents generally have high volatility and flammability, the lithium secondary battery employing the lithium secondary batteries has problems in overcharge, overdischarge, short circuit, and high-temperature safety.

To solve this problem, a method of using an imidazolium series and an ammonium series ionic liquid as an electrolyte of a lithium secondary battery has been proposed. However, such an ionic liquid has a problem that the ionic liquid is reduced at a higher voltage than the lithium ion in the cathode, or imidazolium and ammonium cations are added together with the lithium ion into the cathode, which deteriorates the battery performance.

Japanese Patent Application Laid-Open No. 1997-259925 discloses a method of adding an incombustible gas having a boiling point of 25 캜 or less at the time of assembling an electrolyte. Japanese Patent Laid-Open Publication No. 2006-179458 and Japanese Patent Laid-Open Publication No. 2005-190873 disclose that a phosphoric acid ester is added to a carbonate-based electrolyte to ensure the nonflammability of the electrolyte, or US Patent Publication No. 6797437 discloses a method for producing a perfluoroalkyl or perfluoroester in a non- Is added in an amount of 30% or more.

However, the injection of the incombustible gas involves a volumetric expansion of the battery and a complicated cell assembly process, and the phosphoric acid ester additive causes a deterioration of battery performance due to a high reduction potential. Further, the addition of the exemplified perfluoroalkyl phase-separated upon mixing with the organic solvent electrolyte precipitates the lithium salt.

On the other hand, Korean Patent Registration No. 10-751203 and Korean Patent Laid-open Publication No. 10-2007-85575 disclose that an electrolyte is used as an electrolyte such as acetamide, urea, methylurea, caprolactam, valerlactam, trifluoroacetamide, carbamate, Eutectic mixture of an amide compound represented by a predetermined formula and a lithium salt is disclosed. Since such a eutectic mixture exhibits high thermal and chemical stability in addition to a relatively wide electrochemical window, problems such as evaporation and ignition of an electrolyte due to the use of conventional organic solvents are solved.

Accordingly, studies on electrolytes containing various amide compounds useful as electrolytes have been conducted in various fields.

However, when an electrolyte solution comprising only an amide compound and a lithium salt is used, the ionic conductivity is lowered due to a high viscosity, which causes a problem that the charge / discharge capacity decreases at a high charge / discharge time.

Accordingly, an object of the present invention is to provide an electrolyte exhibiting high thermal and chemical stability and an electrochemical device having the same.

Another object of the present invention is to provide an electrolyte having a high ion conductivity and excellent charge / discharge performance, and an electrochemical device having the electrolyte, in addition to the above-mentioned objects.

In order to achieve the above object, an electrolyte comprising an ionizable lithium salt and an organic solvent according to the present invention is characterized in that the organic solvent comprises an amide compound represented by Chemical Formula 1 or 2 and a carbonate-based organic solvent, The electrolyte contains, as an additive, a linear ester compound represented by the following formula (3)

In Formula 1,

R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each independently selected from the group consisting of hydrogen, halogen, an alkyl group, an alkylamine group, an alkenyl group and an aryl group having 1 to 20 carbon atoms, At least one of R ₁ and R ₂ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,

X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) where X is oxygen or sulfur, R ₄ and R ₅ is not present, ii) X is a is nitrogen or phosphorus R ₅ is present However,

In Formula 2,

R ₆ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,

R ₇ and R ₈ are each independently selected from the group consisting of an alkyl group, an alkylamine group, an alkenyl group and an aryl group, each of which is substituted or unsubstituted with hydrogen, halogen, halogen,

X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) X is not is oxygen or sulfur, R ₇ and R ₈ are present, iii) X a is nitrogen or phosphorus R ₈ are present However,

In Formula 3,

R ₉ and R ₁₀ are independently of each other a linear or branched alkyl group having 1 to 6 carbon atoms, each of which is substituted or unsubstituted with at least one halogen.

In the electrolyte of the present invention, the amide compound may be at least one selected from the group consisting of N-methoxymethyl carbamate, N-methoxyethyl carbamate, N-methoxy-N-methyl methyl carbamate, N-methoxy- , N-methoxy-N-methylpropylcarbamate, N-methoxy-N-methylbutylcarbamate, N-methoxy N-methyl 2,2,2-trifluoroethylcarbamate, N-methoxy N -Methyl 2-fluoroethylcarbamate, N-methoxy N-methylpentafluoropropyl carbamate, N-methoxy-N-methyl 2- (perfluorohexyl) ethyl carbamate and N- -Methyl 6- (perfluorobutyl) hexylcarbamate, N-methoxyoxazolidinone, and the like.

In the electrolyte of the present invention, the anion of the lithium salt may be 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 ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- and the like.

In the electrolyte of the present invention, examples of the linear ester include methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

In the electrolyte of the present invention, the carbonate-based organic solvent may be any of carbonates used as an organic solvent for the electrolyte, and examples thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC) But are not limited to, dimethyl carbonate (DMC), dipropyl carbonate (DPC), butylene carbonate, methyl propyl carbonate, ethyl propyl carbonate and ethyl methyl carbonate (EMC).

In addition, the electrolyte of the present invention may be a liquid electrolyte and may be a polymer electrolyte such as a solid or gelled polymer itself, and the polymer electrolyte may contain a monomer capable of forming a polymer by the electrolyte and a polymerization reaction Or a polymer electrolyte in the form of a polymer impregnated with the electrolyte.

The electrolyte of the present invention can be applied to an electrochemical device such as a lithium secondary battery.

The electrolyte according to the present invention exhibits the following effects.

First, since the electrolyte of the present invention exhibits excellent thermal stability and chemical stability, problems such as evaporation, ignition, and side reaction of the electrolyte according to the conventional organic solvent are greatly improved, and the room temperature performance and the low temperature performance Can be improved.

Second, the electrolyte of the present invention facilitates dissociation of lithium cations by the linear ester compound having the specific structure, thereby lowering the viscosity of the electrolyte and increasing the ionic conductivity, thereby reducing the impedance of the battery and improving the initial capacity and charge / discharge performance .

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 discharge capacities of a battery manufactured according to Example 4, Example 5, and Comparative Example 3 for a cycle.
FIG. 2 is a graph showing impedance of a secondary battery manufactured according to Example 4 and Comparative Example 3. FIG.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

The electrolyte comprising an ionizable lithium salt and an organic solvent according to the present invention is characterized in that the organic solvent comprises an amide compound represented by the following formula 1 or 2 and a carbonate organic solvent, Lt; RTI ID = 0.0 > of: < / RTI &

[Chemical Formula 1]

In Formula 1,

R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each independently selected from the group consisting of hydrogen, halogen, an alkyl group, an alkylamine group, an alkenyl group and an aryl group having 1 to 20 carbon atoms, At least one of R ₁ and R ₂ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,

X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) where X is oxygen or sulfur, R ₄ and R ₅ is not present, ii) X is a is nitrogen or phosphorus R ₅ is present However,

(2)

In Formula 2,

R ₆ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,

R ₇ and R ₈ are each independently selected from the group consisting of an alkyl group, an alkylamine group, an alkenyl group and an aryl group, each of which is substituted or unsubstituted with hydrogen, halogen, halogen,

X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) X is not is oxygen or sulfur, R ₇ and R ₈ are present, iii) X a is nitrogen or phosphorus R ₈ are present However,

(3)

In Formula 3,

R ₉ and R ₁₀ are independently of each other a linear or branched alkyl group having 1 to 6 carbon atoms, each of which is substituted or unsubstituted with at least one halogen.

The electrolyte of the present invention includes the amide compound represented by the above formula (1) or (2), and can exhibit high thermal and chemical stability. Specifically, the vapor pressure of the organic solvent is higher than that of a conventional organic solvent, thereby solving the problems such as evaporation and ignition of the electrolyte due to use, thereby improving the charge / discharge performance of the battery. In addition, the electrolyte of the present invention has characteristics such as a wide electrochemical window, a liquid-phase region in a wide temperature range, a high solvation ability, and a non-coordination bond, thereby exhibiting battery performance and safety, particularly excellent high temperature stability.

Furthermore, the carbonyl group (C = O) and the amine group (-NR ₂ ) in the amide compound according to the present invention can weaken the bond between the cation and the anion of the ionizable lithium salt or weaken the bond in the other amide compound . Therefore, the electrolyte of the present invention can maintain a high ionic conductivity even at room temperature, preferably -20 占 폚 or lower, more preferably -40 占 폚 or lower, thereby improving the room temperature performance and the low temperature performance of the battery.

In the electrolyte of the present invention, specific examples of the aforementioned amide compound include N-methoxymethyl carbamate, N-methoxyethyl carbamate, N-methoxy-N-methyl methyl carbamate, N- -Methyl ethyl carbamate, N-methoxy N-methyl propyl carbamate, N-methoxy-N-methyl butyl carbamate, N-methoxy N-methyl 2,2,2-trifluoroethyl carbamate, Methoxy N-methyl 2- (perfluorohexyl) ethyl carbamate, N-methoxy N-methylpentafluoropropyl carbamate, N-methoxy- -Methoxy-N-methyl 6- (perfluorobutyl) hexylcarbamate, N-methoxyoxazolidinone, and the like, but are not limited thereto.

Further, in the electrolyte of the present invention, the above-mentioned lithium salt can be expressed as Li ⁺ X ^- as an ionizable lithium salt. In this lithium salt anion is not particularly ^{limited, 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 ^- , and the like.

On the other hand, the electrolyte of the present invention includes a carbonate-based organic solvent.

Since ionic conductivity is generally determined by the mobility of ions moving within the electrolyte solution, the factors affecting ionic conductivity are the viscosity of the electrolyte solution and the concentration of ions in the solution. The lower the viscosity of the solution, the more the ions move in the solution and the ionic conductivity increases. The higher the concentration of ions in the solution, the higher the ionic conductivity of the charge transport chain. The amide compound has a relatively high viscosity, but the electrolyte of the present invention uses a carbonate-based organic solvent in combination to lower the viscosity and increase the ionic conductivity to improve the charge-discharge performance.

The carbonate compound contained in the electrolyte of the present invention can be used as long as it is a carbonate compound conventionally used in a non-aqueous electrolyte of a lithium secondary battery. Examples of the carbonate compound include propylene carbonate (PC), ethylene carbonate (EC) Diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), butylene carbonate, methyl propyl carbonate, ethyl propyl carbonate and ethyl methyl carbonate (EMC) Can be used.

In addition, the electrolyte of the present invention includes a linear ester compound represented by the above formula (3) as an additive.

Although the carbonate-based solvent according to the present invention plays a role of lowering the high viscosity of the amide compound, it is used as an organic solvent of a conventional electrolyte and has a relatively low viscosity as compared with the amide compound, When mixed with a compound, it may have a somewhat higher viscosity than a conventional electrolyte. Further, since the carbonate solvent has high reactivity with the negative electrode, it has a problem of increasing the thickness of the battery by decomposing during the charging / discharging process.

Accordingly, the present invention solves the above problems by using a linear ester compound as an additive. Since the linear ester compound has lower viscosity than the carbonate organic solvent, the viscosity is lowered and the ionic conductivity is improved, and the reactivity with the cathode is lower than that of the carbonate organic solvent, thereby suppressing the increase of the cell thickness and solving the problem of disappearance of the electrolyte. And exhibits a remarkable effect in improving discharge characteristics.

It will be apparent to those skilled in the art that the electrolyte of the present invention may further contain various kinds of additives or organic solvents to the extent that the object of the present invention is not impaired.

The electrolyte of the present invention can be applied to any type of electrolyte, regardless of the type of electrolyte, and can be used, for example, as a liquid electrolyte or a polymer electrolyte such as a solid phase or a gel phase of the polymer itself.

When the electrolyte of the present invention is a polymer electrolyte, it is preferable to use a gel polymer electrolyte formed by polymerization of the above-described electrolyte and a precursor solution containing a monomer capable of forming a polymer by a polymerization reaction, Or a polymer electrolyte impregnated into a polymer such as a gel.

First, the gel polymer electrolyte prepared by the polymerization reaction of the precursor solution will be described.

A gel polymer electrolyte according to one aspect of the present invention comprises (i) an electrolyte comprising the above-mentioned amide compound, a lithium salt, a carbonate-based organic solvent and a linear ester compound; And (ii) polymerizing a precursor solution containing a monomer capable of forming a polymer by a polymerization reaction.

The monomer may be any kind of monomers capable of forming a gel polymer together with the electrolyte as the polymerization proceeds, and examples thereof include vinyl monomers and the like. The vinyl monomer is advantageous in that polymerization is very simple when it is mixed with the electrolyte to form a gel polymer.

Non-limiting examples of usable vinyl monomers include acrylonitrile, methyl methacrylate, methyl acrylate, methacrylonitrile, methyl styrene, vinyl esters, vinyl chloride, vinylidene chloride, acrylamide, tetrafluoroethylene , Vinyl acetate, vinyl chloride, methyl vinyl ketone, ethylene, styrene, paramethoxystyrene, and p-cyanostyrene. These may be used alone or in combination of two or more thereof.

The precursor solution may additionally comprise conventional polymerization initiators or photoinitiators wherein the initiator is decomposed by heat or ultraviolet rays to form radicals and reacts with the monomers by free radical polymerization to form gel polymer electrolytes do. Further, polymerization of the monomer may be carried out without using an initiator. In general, free radical polymerization is a kind of reaction that initiates transient molecules or active sites with high reactivity, a growth reaction in which monomers are added at the active chain ends to form active sites at the chain ends, a chain transfer reaction , And the active chain center is destroyed.

Non-limiting examples of usable thermal polymerization initiators include organic peroxides such as Benzoyl peroxide, Acetyl peroxide, Dilauryl peroxide, Di-tert-butyl peroxide, Cumyl hydroperoxide and Hydrogen peroxide, hydroperoxides such as 2,2-azobis -cyanobutane, 2,2-azobis (methylbutyronitrile), azobis (isobutyronitrile) and azobisdimethyl-valeronitrile (AMVN), and organic metals such as alkylated ones. Examples of the photoinitiator in which radicals are formed by the photo-initiator include, but are not limited to, chlo- roacetophenone, diethoxyacetophenone (DEAP), 1-phenyl-2-hydroxy-2-methyl propaneone (HMPP), 1 -hydroxy cyclrohexyl phenyl ketone, Benzoin Ether, Benzyl Dimethyl ketal, Benzophenone, Thioxanthone, 2-ethyle nthraquinone (2-ETAQ).

In addition to the components described above, the precursor solution of the gel polymer electrolyte according to the present invention may optionally contain other additives known in the art.

The above-described precursor solution is used to form a gel polymer electrolyte according to a conventional method known in the art. It is preferable to prepare a gel polymer electrolyte by an in-situ polymerization reaction in an electrochemical device. In-situ polymerization can be done by heat or ultraviolet irradiation. The weight ratio of the electrolyte and the monomer in the precursor solution is preferably 0.5 to 0.95: 0.05 to 0.5 in view of having a viscosity suitable for use as a gel polymer electrolyte. The degree of polymerization of the gel polymer can be controlled depending on the polymerization time, the polymerization temperature, or the light irradiation amount, which is a reaction factor, so that the polymer is over-polymerized without leakage of the electrolyte, so that the volume is not shrunk.

In another method for producing a polymer electrolyte according to the present invention, the electrolyte may be injected into an already formed solid polymer or gel polymer, and the electrolyte may be impregnated into the polymer.

Non-limiting examples of the usable polymer include polymethyl methacrylate, polyvinylidene difluoride, polyvinyl chloride, polyethylene oxide, polyhydroxyethyl methacrylate, etc. These may be used alone or as a mixture of two or more thereof have. This method can simplify the manufacturing process compared to the above - described In-Situ method.

As another method for producing the polymer electrolyte according to the present invention, a method of forming the polymer electrolyte by dissolving the electrolyte and the polymer in a solvent and removing the solvent may be used. At this time, the electrolyte becomes a form contained in the polymer matrix.

The solvent is not particularly limited, and examples thereof include toluene, acetone, acetonitrile, THF, and the like. There is no particular limitation on the method of removing the solvent, and conventional methods such as applying heat can be used.

The electrolyte according to the present invention is applicable to a conventional electrochemical device known in the art which requires various electrochemical characteristics depending on the purpose of use.

Non-limiting examples of the electrochemical device include all kinds of primary and secondary batteries, a fuel cell, a solar cell, an electrochromic device, an electrolytic capacitor or a capacitor. Lithium secondary batteries, electric double layer capacitors, dye-sensitized solar cells, and electrochromic devices.

For example, in the lithium secondary battery, the electrolyte of the present invention may be manufactured as a lithium secondary battery by injecting the positive electrode, the negative electrode, and the separator interposed between the positive and negative electrodes into an electrode structure. The positive electrode, the negative electrode and the separator constituting the electrode structure may be any of those conventionally used in the production of lithium secondary batteries.

For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < 1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-y Co _y O ₂ (0 <y <1), LiCo _1-y Mn _y O ₂ 0? _Y <1), LiNi _1-y Mn _y O ₂ (0? _Y <1), Li (Ni _a Co _b Mn _c ) O ₄ <a 2, a + b + c = 2), LiMn 2-z Ni z O 4 (0 <z <2), LiMn 2-z Co z O 4 (0 <z <2), LiCoPO 4 and LiFePO ₄ Or a mixture of two or more of them may be used. In addition to these oxides, sulfide, selenide and halide may also be used.

As the negative electrode active material, a carbon material, lithium metal, silicon, or tin, in which lithium ions can be occluded and released, can be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can 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 negative electrode may include a binder. Examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, Various kinds of binder polymers such as polymethylmethacrylate may be used.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

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

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

1. Preparation of electrolyte

Example 1

A 1.2 M LiPF ₆ electrolyte solution having a composition of N-methoxy-N-methyl 2,2,2-trifluoroethyl carbamate (MMTFEC): ethylene carbonate (EC): ethyl propionate (EP) = 40: 30: .

Example 2

An electrolytic solution was prepared in the same manner as in Example 1, except that the composition had a composition of MMTFEC: EC: EP = 40: 20: 40.

Example 3

An electrolytic solution was prepared in the same manner as in Example 1, except that the composition had a composition of MMTFEC: EC: EP = 55: 30: 15.

Comparative Example 1

A 1.2 M LiPF ₆ electrolyte solution having a composition of N-methoxy-N-methyl 2,2,2-trifluoroethyl carbamate (MMTFEC): ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 40: 30: .

Comparative Example 2

An electrolytic solution was prepared in the same manner as in Comparative Example 1, except that the composition was changed to MMTFEC: EC: EMC = 40: 20: 40.

EXPERIMENTAL EXAMPLE 1 Evaluation of Physical Properties of Electrolyte

In order to evaluate the electrolytic solution produced according to the above-described Examples and Comparative Examples, the following properties evaluation tests were carried out.

As the samples, electrolytes of Examples 1 to 3 and Comparative Examples 1 and 2 were used. Viscosity was measured using an RS150 viscometer at 25 ° C, and conductivity was measured using an Inolab 740 instrument. The results are shown in Table 1 below.

Viscosity (cP) Conductivity (mS / cm) Example 1 6.1 6.4 Example 2 4.9 6.5 Example 3 9.3 4.6 Comparative Example 1 5.8 5.1 Comparative Example 2 5.3 5.7

Referring to Table 1, the electrolytes of Examples 1 to 3 have a viscosity and an ion conductivity higher than the electrolytes of Comparative Examples 1 and 2.

<Manufacture of Battery>

Example 4

A lithium polymer secondary battery was fabricated by a conventional method using LiCoO ₂ as a cathode active material, artificial graphite as an anode active material, the electrolyte prepared in Example 1, and an aluminum laminate packing material as a packaging material.

Example 5

A secondary battery was produced in the same manner as in Example 4, except that the electrolyte solution of Example 2 was used as the electrolyte solution.

Comparative Example 3

A secondary battery was produced in the same manner as in Example 4, except that the electrolyte solution of Comparative Example 1 was used as the electrolyte solution.

Experimental Example 2: Evaluation of charge / discharge performance of secondary battery

Charging and discharging of the batteries of Examples 4 to 5 and Comparative Example 3 were carried out at 1 C / 1 C, and the charging / discharging capacity according to the cycle was measured. The results are shown in FIG.

As shown in FIG. 1, it can be seen that the batteries of Examples had an initial capacity and a discharge capacity after 50 cycles of the battery increased by about 20% as compared with the battery of Comparative Example 3. FIG.

Experimental Example 3: Impedance Measurement of Secondary Battery

The batteries of Example 4 and Comparative Example 3 were measured for impedance using Potentiostat, and the results are shown in Fig. Impedance measurements were made by applying a small voltage (10 mV) from a frequency of 3 kHz to 100 mHz after charging the cell to 4.2 V and measuring the resulting current response.

As shown in FIG. 2, it can be seen that the battery of Example 4 has a significantly reduced impedance than that of Comparative Example 3. From this, it can be confirmed that when the linear ester compound is used in the electrolyte of the present invention, the impedance is decreased by improving the viscosity and conductivity.

Claims (15)

In an electrolyte comprising an ionizable lithium salt and an organic solvent,
Wherein the organic solvent comprises an amide compound represented by Chemical Formula 1 or Chemical Formula 2 and a carbonate-based organic solvent,
Wherein the electrolyte comprises a linear ester compound represented by the following formula (3) as an additive:
[Chemical Formula 1]

In Formula 1,
R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each independently selected from the group consisting of hydrogen, halogen, an alkyl group, an alkylamine group, an alkenyl group and an aryl group having 1 to 20 carbon atoms, At least one of R ₁ and R ₂ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,
X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) where X is oxygen or sulfur, R ₄ and R ₅ is not present, ii) X is a is nitrogen or phosphorus R ₅ is present However,
(2)

In Formula 2,
R ₆ is an alkoxy group represented by -O (CH ₂ ) p CH ₃ , p is an integer of 0 to 8,
R ₇ and R ₈ are each independently selected from the group consisting of an alkyl group, an alkylamine group, an alkenyl group and an aryl group, each of which is substituted or unsubstituted with hydrogen, halogen, halogen,
X is a least one selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus and silicon, i) X is not is oxygen or sulfur, R ₇ and R ₈ are present, iii) X a is nitrogen or phosphorus R ₈ are present However,
(3)

In Formula 3,
R ₉ and R ₁₀ are independently of each other a linear or branched alkyl group having 1 to 6 carbon atoms, each of which is substituted or unsubstituted with at least one halogen. The method according to claim 1,
The amide compound may be selected from the group consisting of N-methoxymethylcarbamate, N-methoxyethylcarbamate, N-methoxy-N-methylmethylcarbamate, N-methoxy- Methylpropylcarbamate, N-methoxy-N-methylbutylcarbamate, N-methoxy N-methyl 2,2,2-trifluoroethylcarbamate, N-methoxy N-methyl 2-fluoroethyl (Perfluorohexyl) ethylcarbamate and N-methoxy-N-methyl 6- (perfluoro (meth) acrylate), N-methoxy N-methylpentafluoropropyl carbamate, N- Hexylcarbamate, and N-methoxyoxazolidinone. &Lt; RTI ID = 0.0 &gt; 18. &lt; / RTI &gt; The method according to claim 1,
The anion of the lithium salt is selected from the group consisting of 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 ^- . The method according to claim 1,
Wherein the linear ester is selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate and butyl propionate. The method according to claim 1,
The carbonate-based organic solvent may be at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), butylene carbonate, methylpropyl carbonate, Ethyl methyl carbonate (EMC), or a mixture of two or more thereof. The method according to claim 1,
Wherein the electrolyte is a polymer electrolyte. The method according to claim 6,
The polymer electrolyte comprises (i) the electrolyte of claim 1; And (ii) a polymerization product of a precursor solution containing a monomer capable of forming a polymer by a polymerization reaction. 8. The method of claim 7,
Wherein the monomer is a vinyl monomer. 9. The method of claim 8,
The vinyl monomer may be selected from the group consisting of acrylonitrile, methyl methacrylate, methyl acrylate, methacrylonitrile, methyl styrene, vinyl esters, vinyl chloride, vinylidene chloride, acrylamide, tetrafluoroethylene, vinyl acetate, vinyl chloride , Methyl vinyl ketone, ethylene, styrene, para-methoxystyrene, and paraxanostyrene, or a mixture of two or more thereof. 10. The method of claim 9,
Wherein the weight ratio of the electrolyte and the monomer of claim 1 in the precursor solution is 0.5 to 0.95: 0.05 to 0.5. 8. The method of claim 7,
Wherein the gel polymer electrolyte is produced by in-situ polymerization in an electrochemical device. The method according to claim 6,
Wherein the polymer electrolyte is impregnated with a polymer of the electrolyte of claim 1. 13. The method of claim 12,
Wherein the polymer is any one selected from the group consisting of polymethyl methacrylate, polyvinylidene difluoride, polyvinyl chloride, polyethylene oxide and polyhydroxyethyl methacrylate, or a mixture of two or more thereof. . 1. An electrochemical device comprising an anode, a cathode, and an electrolyte,
The electrochemical device according to any one of claims 1 to 13, wherein the electrolyte is an electrolyte. 15. The method of claim 14,
Wherein the electrochemical device is a lithium secondary battery.

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