KR20160063186A - Electrolyte for lithium second battery and lithium second battery having the electrolyte - Google Patents

Abstract

Disclosed is an electrolyte for a lithium secondary battery which can improve lifespan properties of the lithium secondary battery by having a phenyl group and a sulfate group and thus rapidly forming thin films having low resistance on a negative electrode of the lithium secondary battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, which can improve the lifetime performance of the lithium secondary battery.

Lithium secondary batteries can be used not only as portable power sources such as mobile phones, notebook computers, digital cameras and camcorders but also as power tools, electric bicycles, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles HEV, PHEV), and the like. As the application field is expanded and demand is increased, the external shape and size of the battery are variously changed, and performance and stability are demanded more than the characteristics required in the conventional small batteries. In order to meet such a demand, the performance of the battery should be stabilized in a condition where battery components are flowing in a large current.

The lithium secondary battery is manufactured by using a material capable of inserting and desorbing lithium ions as a cathode and an anode, providing a porous separator between the two electrodes, and injecting a liquid electrolyte. The insertion and extraction of lithium ions in the cathode and the anode, Electricity is generated or consumed by the redox reaction due to desorption.

Various non-aqueous solvents and additives as an electrolyte-containing component have been studied in order to improve the battery characteristics such as the output characteristics, cycle characteristics, and storage characteristics of the lithium secondary battery. Particularly, various studies have been made on additives for improving the lifetime performance of lithium secondary batteries.

An object of the present invention is to provide an electrolyte for a lithium secondary battery capable of rapidly forming a low resistance film on a negative electrode of a lithium secondary battery to improve the life performance of the lithium secondary battery.

Another object of the present invention is to provide a lithium secondary battery comprising the electrolyte.

An electrolyte for a lithium secondary battery according to an embodiment of the present invention includes a life improving additive having a structure represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ to R ₅ independently represent hydrogen (H), fluorine (F), a hydrocarbon group having 1 to 6 carbon atoms, a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and a fluorocarbon Lt; / RTI > For example, R ₁ to R ₅ may be independently selected from hydrogen (H), fluorine (F), CH ₃ , CH ₂ F, and CF ₃ . And R ₆ may be alkoxy of 1 to 6 carbon atoms date.

In one embodiment, the lifetime enhancing additive may comprise a compound having the structure of Formula 2:

(2)

In one embodiment, the lifetime enhancing additive may be included in an amount of about 0.5 wt% to 3 wt% based on the total weight of the electrolyte. In this case, the electrolyte for the lithium secondary battery may further include an organic solvent and a lithium salt.

A lithium secondary battery according to an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material disposed opposite to the positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode, And a life improving additive having the structure of Formula 1 above.

In one embodiment, the electrolyte comprises the lifetime enhancing additive in an amount of 0.5 wt% to 3 wt% with respect to the total weight of the electrolyte.

Since the electrolyte for a lithium secondary battery according to an embodiment of the present invention includes a lifetime enhancing additive having a phenyl group and a sulfate group, it is possible to rapidly form a low resistance film on a negative electrode of a lithium secondary battery, .

1 is a graph showing discharge capacity measurement results of lithium secondary batteries of Examples 1, 2 and 3 and lithium secondary batteries of Comparative Examples 1 and 2.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as comprise, having, or the like are intended to designate the presence of stated features, integers, steps, operations, elements, parts or combinations thereof, and may include one or more other features, , But do not preclude the presence or addition of one or more other features, elements, components, components, or combinations thereof.

As used herein, the combination thereof means that two or more substituents are bonded to each other through a single bond or a linking group, or two or more substituents are condensed and connected unless otherwise specified.

In the present specification, unless otherwise specified, all the compounds or substituents may be substituted or unsubstituted. The term "substituted" as used herein means that hydrogen is substituted with at least one substituent selected from the group consisting of a halogen atom, a hydroxyl group, a carboxyl group, a cyano group, a nitro group, an amino group, a thio group, a methylthio group, an alkoxy group, a nitryl group, an aldehyde group, Substituted with any one selected from the group consisting of acetal, ketone, alkyl, perfluoroalkyl, cycloalkyl, heterocycloalkyl, allyl, benzyl, aryl, heteroaryl, .

The lithium secondary special-purpose electrolyte according to an embodiment of the present invention may include a non-aqueous organic solvent, a lithium salt, and a life improving additive.

The non-aqueous organic solvent may be used without particular limitation as long as it can act as a medium through which ions involved in an electrochemical reaction of a battery can move. For example, the organic solvent may be an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, etc. These solvents may be used alone or in combination of two or more Can be used.

Specific examples of the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl But are not limited to, ethyl propionate, propyl propionate, butyl propionate,? -Butyrolactone, decanolide,? -Valerolactone valerolactone, Mevalonolactone,? -caprolactone,? -valerolactone, or? -caprolactone may be used.

Specific examples of the ether solvent include dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

Specific examples of the ketone-based solvents include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

Specific examples of the carbonate solvent include dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC) ), Methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) And fluoroethylene carbonate (FEC).

In one embodiment, the non-aqueous organic solvent may be a mixture of a carbonate-based solvent and the ester-based solvent. For example, ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) can be mixed and used as the non-aqueous organic solvent. The ethylene carbonate (EC) and propylene carbonate (PC) can increase the charge / discharge performance of the battery as a high dielectric constant solvent having a high ionic conductivity, and the propyl propionate (PP) It is possible to appropriately control the viscosity of the organic solvent. The ethylene carbonate (EC), propylene carbonate (PC) and propyl propionate (PP) may be mixed in a weight ratio of about 3: 1: 6.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiC ₄ F ₉ SO ₃ , LiN _{(C 2 F 5 SO 3)} 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) 2, LiN (CaF 2a +1 SO 2) (CbF 2b +1 SO 2) ( however, a and b are natural numbers, preferably 1? a? 20 and 1? b? 20), LiCl, LiI, LiB (C ₂ O ₄ ) ₂ and the like can be used singly or in combination of two or more . For example, lithium hexafluorophosphate (LiPF ₆ ) can be used as the lithium salt.

When the lithium salt is dissolved in the electrolyte, the lithium salt functions as a source of lithium ions in the lithium secondary battery and can promote the movement of lithium ions between the anode and the cathode. Accordingly, it is preferable that the lithium salt is contained in the electrolyte at a concentration of about 0.6 M to 2M. If the concentration of the lithium salt is less than 0.6 M, the conductivity of the electrolyte may be lowered to deteriorate the performance of the electrolyte. If the concentration exceeds 2 M, the viscosity of the electrolyte may increase and the mobility of the lithium ion may be lowered. Considering the conductivity of the electrolyte and the mobility of lithium ions, it is more preferable that the lithium salt is contained in the electrolyte at a concentration of about 0.7 M to 1.6 M.

The life improving additive can quickly form a coating on the negative electrode with a low resistance, thereby improving the lifetime of the lithium secondary battery. In one embodiment, the lifetime enhancing additive may have the structure of Formula 1 below.

[Chemical Formula 1]

In Formula 1, R ₁ to R ₅ may independently be hydrogen (H), fluorine (F), or a hydrocarbon group having 1 to 6 carbon atoms, a fluorinated hydrocarbon group, a fluorinated carbon group, or the like. For example, R ₁ to R ₅ may independently be hydrogen (H), fluorine (F), CH ₃ , CH ₂ F, CF ₃ , and the like.

And R ₆ may be an alkoxy group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, for example, the alkoxy group may be CH ₂ OH, CH ₂ CH ₂ OH, and the fluorinated alkoxy group may be CF ₂ OH , CF ₂ CF ₂ OH, and the like.

The lifetime enhancing additive having the structure of Formula 1 has a sulfate group to form a coating having a low resistance in the anode of a lithium secondary battery and has a phenyl group to enable rapid film formation from a cathode of a lithium secondary battery, The lifetime of the lithium secondary battery can be remarkably improved.

In one embodiment, the lifetime enhancing additive may comprise from about 0.5% to about 3% by weight based on the total weight of the electrolyte. If the content of the lifetime enhancing additive is less than 0.5% by weight, the lifetime enhancing additive is too small to exhibit the above effect. When the content of the lifetime enhancing additive is more than 3% by weight, There is a problem that the resistance of the coating increases due to the reaction and the initial capacity of the lithium secondary battery is lowered.

In one embodiment, the lifetime enhancing additive having the structure of Formula 1 may include 2,2-dioxide-5-phenyl-1,3,2-dioxathiolane-4-methanol having the structure of Formula 2 have.

(2)

In addition to the above-mentioned components, the lithium secondary special-purpose electrolyte according to the embodiment of the present invention may further include other additives that can be generally used for the electrolyte for the purpose of improving lifetime characteristics of the lithium secondary battery, suppressing reduction in battery capacity, .

Specific examples of the other additives include vinylene carbonate (VC), metal fluoride, glutaronitrile (GN), succinonitrile (SN), adiponitrile adiponitrile, AN), 4-tolunitrile, 1,3,6-hexanetricarbonitrile, propylene sulfide (PS), 3,3'- (3,3'-thiodipropionitrile, TPN), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethyl carbonate (fluoromethylsulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium bis (fluorosulfonyl) imide fluorosu _{lfonyl) imide, LiN (FSO 2} ) 2), lithium tetrafluoroborate (LiBF _4), lithium bis (oxalate reyito) borate (Lithium bis (oxalato) borate, LiBOB), lithium difluoro (oxalate reyito) borate ( Lithium difluoro (oxalate) borate, LiDFOB), lithium malonate oxalato borate (LiMOB), lithium difluorophosphate (LiPO ₂ F ₂ ), LiPF ₂ C ₄ O _{8, LiSO 3 CF 3, LiPF} 4 (C 2 O 4), LiP (C 2 O 4) 3, LiC (SO 2 CF 3) 3, LiBF 3 (CF 3 CF 2), LiPF 3 (CF 3 CF 2 ) ₃ , Li ₂ B ₁₂ F ₁₂ , 1,3-propane sultone, 1,3-propene sultone, biphenayl, cyclohexylbenzene cyclohexyl benzene, 4-fluorotoluene, succinic anhydride, ethylene sulfate anhydride, tris (methylsilyl) borate, And the like. 1 kinds may also include, alone or in combination. Wherein methyl fluoride is, for example, LiF, RbF, TiF, AgF , AgF 2, BaF 2, CaF 2, CdF 2, FeF 2, HgF 2, Hg 2 F 2, MnF 2, NiF 2, PbF 2, _{SnF 2, SrF 2, XeF 2} , ZnF 2, AlF 3, BF 3, BiF 3, CeF 3, CrF 3, DyF 3, EuF 3, GaF 3, GdF 3, FeF 3, HoF 3, InF 3, LaF 3 , LuF ₃ , MnF ₃ , NdF ₃ , PrF ₃ , SbF ₃ , ScF ₃ , SmF ₃ , TbF ₃ , TiF ₃ , TmF ₃ , YF ₃ , YbF ₃ , TIF ₃ , CeF ₄ , GeF ₄ , HfF ₄ , SiF _{4, SnF 4, TiF 4,} VF 4, ZrF 44, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6, WF 6, CoF 2, CoF 3, CrF 2, CsF, ErF ₃ , PF ₃ , PbF ₃ , PbF ₄ , ThF ₄ , TaF ₅ , SeF ₆ , and the like.

The other additives may be contained in an amount of 0.1 to 20% by weight, preferably 0.2 to 5% by weight, based on the total weight of the electrolyte.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the electrolyte.

The lithium secondary battery includes a negative electrode including a negative electrode active material, a positive electrode including a positive electrode active material, a separator interposed between the negative electrode and the positive electrode, and an electrolyte impregnated in the separator.

As the negative electrode active material of the negative electrode, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon. Further, in addition to the carbonaceous material, a compound including a metallic compound capable of alloying with lithium or a metallic compound and a carbonaceous material may be used as the negative electrode active material.

At least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys and Al alloys may be used as the metal capable of being alloyed with lithium. Further, a metal lithium thin film may be used as the negative electrode active material. As the negative electrode active material, any one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, lithium metal, lithium-containing alloy, and mixtures thereof may be used in view of high stability.

The cathode may further include a binder, a conductive agent, or a current collector.

The binder serves to attach the electrode active material particles to each other and to adhere the electrode active material to the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC) , Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber , Fluorine rubber, various copolymers thereof, and the like.

The current collector may be any metal selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be carbon, nickel, The aluminum alloy may be an aluminum-cadmium alloy. Alternatively, a non-conductive polymer surface-treated with a conductive material, a conductive polymer, or the like may be used.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

As the positive electrode active material of the positive electrode, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Specifically, a lithium-containing transition metal oxide may be preferably used. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < 0 <b <1, 0 < c <1, a + b + c = 1), LiNi 1 - y Co y O 2, LiCo 1 - y Mn y O 2, LiNi 1 -y Mn y O 2 (O≤ y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O ₄ , LiMn _{2 -z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition to these oxides, sulfide, selenide and halide may be used.

The anode may further include a binder, a conductive agent, or a current collector. The contents of the binder, the conductive agent, and the collector are the same as those described in the cathode, and a detailed description thereof will be omitted.

Since the electrolyte is the same as described above in connection with the electrolyte, the description thereof will be omitted.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer The porous polymer film made of a polymer may be used alone or in a laminated form, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, polyethylene terephthalate fiber or the like may be used. no.

As described above, the lithium secondary battery including the electrolyte according to the embodiment of the present invention can exhibit an improved lifetime performance and can be used in portable devices such as mobile phones, notebook computers, digital cameras, camcorders, and hybrid electric vehicles vehicle, HEV), plug-in hybrid electric vehicle (HEV, PHEV), and medium and large-sized energy storage systems.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[ Manufacturing example ]

( Manufacturing example  1: manufacture of positive electrode)

LiCoO ₂ was prepared the positive electrode active material. Thereafter, a slurry was prepared by mixing the cathode active material: conductive material: binder in a weight ratio of 96: 2: 2, coating the aluminum (Al) foil current collector by a conventional method, and drying to prepare a cathode.

( Manufacturing example  2: manufacture of cathode)

An anode active material slurry was prepared by mixing an artificial graphite: SBR binder: a thickener in a weight ratio of 98: 1: 1, and then coated on a collector of a copper (Cu) foil by a conventional method to prepare a negative electrode.

( Manufacturing example  3: Production of lithium secondary battery)

A pouch type lithium secondary battery was prepared by injecting the non-aqueous electrolyte prepared in Table 1 into a pouch-shaped battery case made of the stacked electrode assembly formed by interposing a polyethylene porous film between the prepared positive electrode and negative electrode.

[ Example  One]

(EC), propylene carbonate (PC) and propyl propionate (PP) were mixed in a weight ratio of 3: 1: 6 as a non-aqueous organic solvent, and lithium hexafluorophosphate (LiPF ₆ (2,2-dioxide-5-phenyl-1,3,2-dioxathiolane-4-methanol) and vinylene carbonate (VC) as an additive were added to prepare an electrolyte . Lithium hexafluorophosphate (LiPF ₆ ) was added so as to be 1 M, and the lifetime enhancing additive having the structure of formula (2) and vinylene carbonate (VC) were added by 2 wt% and 0.5 wt%, respectively, relative to the total weight of the electrolyte.

Next, the lithium secondary battery of Example 1 was prepared using the prepared electrolyte, a nickel / manganese / cobalt trivalent (NMC) cathode active material, and a crystalline graphite anode active material.

[ Example  2]

(EC), propylene carbonate (PC) and propyl propionate (PP) were mixed in a weight ratio of 3: 1: 6 as a non-aqueous organic solvent, and lithium hexafluorophosphate (LiPF ₆ (2,2-dioxide-5-phenyl-1,3,2-dioxathiolane-4-methanol) and vinylene carbonate (VC) as an additive were added to prepare an electrolyte . Lithium hexafluorophosphate (LiPF ₆ ) was added so as to be 1 M, and the life improving additive having the structure of formula (2) and vinylene carbonate (VC) were added by 1.0 wt% and 0.5 wt%, respectively, relative to the total weight of the electrolyte.

Next, the lithium secondary battery of Example 2 was prepared using the prepared electrolyte, a nickel / manganese / cobalt trivalent (NMC) cathode active material, and a crystalline graphite anode active material.

[ Example  3]

(EC), propylene carbonate (PC) and propyl propionate (PP) were mixed in a weight ratio of 3: 1: 6 as a non-aqueous organic solvent, and lithium hexafluorophosphate (LiPF ₆ (2,2-dioxide-5-phenyl-1,3,2-dioxathiolane-4-methanol) and vinylene carbonate (VC) as an additive were added to prepare an electrolyte . Lithium hexafluorophosphate (LiPF ₆ ) was added to make 1 M, and the life improving additive having the structure of formula (2) and vinylene carbonate (VC) were added by 0.5 wt% and 0.5 wt%, respectively, with respect to the total weight of the electrolyte.

Next, a lithium secondary battery of Example 3 was prepared using the prepared electrolyte, a nickel / manganese / cobalt trivalent (NMC) cathode active material, and a crystalline graphite anode active material.

[ Comparative Example  One]

(EC), propylene carbonate (PC) and propyl propionate (PP) were mixed in a weight ratio of 3: 1: 6 as a non-aqueous organic solvent, and lithium hexafluorophosphate (LiPF ₆ ) And vinylene carbonate (VC) as an additive were added to prepare an electrolyte. That is, the above-described life improving additive was not added. Lithium hexafluorophosphate (LiPF ₆ ) was added so as to be 1 M, and vinylene carbonate (VC) was added by 0.5 wt% with respect to the total weight of the electrolyte.

Next, a lithium secondary battery of Comparative Example 1 was fabricated using the prepared electrolyte, a nickel / manganese / cobalt ternary system (NMC) cathode active material, and a crystalline graphite anode active material.

[ Comparative Example  2]

(EC), propylene carbonate (PC) and propyl propionate (PP) were mixed in a weight ratio of 3: 1: 6 as a non-aqueous organic solvent, and lithium hexafluorophosphate (LiPF ₆ (2,2-dioxide-4-methyl-5-phenyl-1,3,2-dioxathiolane) and vinylene carbonate (VC) as an additive. Lithium hexafluorophosphate (LiPF ₆ ) was added so as to be 1 M, and the life enhancing additive (2,2-dioxide-4-methyl-5-phenyl-1,3,2-dioxathiolane) RenCarbonate (VC) was added in amounts of 4 wt% and 0.5 wt%, respectively, relative to the total weight of the electrolyte.

Next, a lithium secondary battery of Comparative Example 2 was prepared using the prepared electrolyte, a nickel / manganese / cobalt ternary system (NMC) cathode active material, and a crystalline graphite anode active material.

[ Experimental Example : Evaluation of Discharge Capacity of Lithium Secondary Battery]

2 is a graph showing discharge capacity measurement results of the lithium secondary batteries of Examples 1, 2 and 3 and the lithium secondary batteries of Comparative Examples 1 and 2. The graph of FIG. 2 shows that the lithium secondary batteries of Examples 1-3 and 1-2 were charged under the condition of 4.2 V CC / CV (0.7 C) at 45 ° C. and discharged at the condition of CC (0.5 C) And the measurement was repeated 400 times.

Referring to FIG. 2, the lithium secondary batteries of Examples 1, 2 and 3 and the lithium secondary batteries of Comparative Examples 1 and 2 exhibit almost the same discharge capacity until the charging / discharging process reaches about 250 times . However, in the lithium secondary batteries of Comparative Examples 1 and 2, the discharge capacity rapidly decreased while the charging / discharging process exceeded about 250 times, whereas the lithium secondary batteries of Examples 1, 2, and 3 exhibited a substantially constant discharge capacity And it decreases gradually. That is, it can be seen that the lithium secondary batteries of Examples 1, 2, and 3 have remarkably improved lifetime performance as compared with the lithium secondary batteries of Comparative Examples 1 and 2.

Since the electrolyte for a lithium secondary battery according to an embodiment of the present invention includes a lifetime enhancing additive having a phenyl group and a sulfate group, it is possible to rapidly form a low resistance film on a negative electrode of a lithium secondary battery, .

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

Claims (8)

An electrolyte for a lithium secondary battery comprising a life improving additive having a structure represented by the following formula
[Chemical Formula 1]

In Formula 1, R ₁ to R ₅ are each independently selected from the group consisting of hydrogen (H), a halogen, a hydrocarbon group having 1 to 6 carbon atoms, a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and a fluorinated carbon group having 1 to 6 carbon atoms one and, R ₆ is an alkoxy group having 1 to 6 carbon atoms. The method according to claim 1,
Wherein R ₁ to R ₅ are independently selected from hydrogen (H), fluorine (F), CH ₃ , CH ₂ F, and CF ₃ . In the first aspect,
Wherein the lifetime enhancing additive comprises a compound having the structure of Formula 2:
(2)

The method according to claim 1,
Wherein the life improving additive is contained in an amount of 0.5 wt% to 3 wt% based on the total weight of the electrolyte. The method according to claim 1,
An electrolyte for a lithium secondary battery, further comprising an organic solvent and a lithium salt. A cathode comprising a cathode active material;
A negative electrode disposed opposite to the positive electrode and including a negative active material; And
And an electrolyte interposed between the anode and the cathode,
Wherein the electrolyte comprises a life improving additive having a structure represented by the following Formula 1:
[Chemical Formula 1]

In Formula 1, R ₁ to R ₅ are each independently selected from the group consisting of hydrogen (H), a halogen, a hydrocarbon group having 1 to 6 carbon atoms, a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and a fluorinated carbon group having 1 to 6 carbon atoms one and, R ₆ is an alkoxy group having 1 to 6 carbon atoms. The method according to claim 6,
Wherein the lifetime enhancing additive comprises a compound having a structure of Formula 2:
(2)

The method according to claim 6,
Wherein the electrolyte comprises the life improving additive in an amount of 0.5 wt% to 3 wt% based on the total weight of the electrolyte.

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