KR20150056430A - Electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte and a lithium secondary battery including the electrolyte, wherein the electrolyte comprises alkyl acetate having 1 to 4 carbon atoms and alkoxy substituted nitrile having 3 to 7 carbon atoms. The electrolyte can improve lifetime properties at a low temperature without a lifetime deterioration of a lithium secondary battery at a room temperature.

Description

ELECTROLYTE AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to an electrolyte capable of improving lifetime characteristics at a low temperature without deterioration of the normal temperature service life of the lithium secondary battery, and a lithium secondary battery comprising the electrolyte.

Lithium secondary batteries are used not only as portable power sources for 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. In the lithium ion secondary battery, Electricity is generated or consumed by the redox reaction due to desorption.

Various non-aqueous solvents and additives have been studied as electrolyte-containing components in order to improve battery characteristics such as output characteristics, cycle characteristics, and storage characteristics of lithium ion batteries. In addition, even when a specific compound is added to an electrolyte as an additive for improving battery performance, performance of some items of most battery performance can be expected to be improved, but the performance of other items is rather reduced.

Korean Patent Registration No. 0546781 (Registered Date: Jan. 19, 2006) Japanese Patent Registration No. 4158412 (registered on July 25, 2008)

An object of the present invention is to provide an electrolyte capable of improving lifetime characteristics at a low temperature without deterioration of the normal temperature service life of the lithium secondary battery.

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

In order to achieve the above object, an electrolyte according to an embodiment of the present invention includes an alkyl acetate having 1 to 4 carbon atoms and an alkoxy substituted nitrile having 3 to 7 carbon atoms.

The alkyl acetate may be any one selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert- .

The alkoxy-substituted nitrile may be any one selected from the group consisting of alkoxyacetonitrile, alkoxypropionitrile, and combinations thereof.

The alkyl acetate and the alkoxy substituted nitrile may be contained in an amount of 5 to 75% by volume based on the total volume of the electrolyte.

The electrolyte may include the alkyl acetate and the alkoxy substituted nitrile in a ratio of 2: 1 to 15: 1 by volume.

The electrolyte may further include an organic solvent and a lithium salt.

The organic solvent may be selected from the group consisting of an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, and a mixture thereof. The organic solvent may be ethylene carbonate.

The organic solvent may include an organic solvent having a high dielectric constant and a low viscosity organic solvent at a volume ratio of 2: 8 to 8: 2.

The organic solvent having a high dielectric constant is selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof. The low viscosity organic solvent includes methylethylcarbonate, dimethylcarbonate, Diethylcarbonate, and mixtures thereof.

Wherein the organic solvent is selected from the group consisting of ethylene carbonate and propylene carbonate; Ethyl methyl carbonate; And one of dimethyl carbonate and diethyl carbonate in a volume ratio of 5: 1: 1 to 2: 5: 3.

The lithium salt is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAl0 4, LiAlCl 4, LiCF 3 SO 3, 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 (C a F 2a + 1} SO 2) (C b F 2b + 1 SO 2) ( However, a and b are natural numbers), may be selected from LiCl, LiI, and mixtures thereof.

According to another embodiment of the present invention, there is provided a lithium secondary battery comprising a cathode disposed opposite to the anode, including a cathode active material, and an electrolyte interposed between the anode and the cathode, wherein the electrolyte has a carbon number of 1 to 4 Alkyl acetates and alkoxy substituted nitriles having 3 to 7 carbon atoms.

Other details of the embodiments of the present invention are included in the following detailed description.

The electrolyte according to the present invention can improve the lifetime characteristics at low temperatures without deterioration of the normal temperature service life of the lithium secondary battery.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention.

The present invention is capable of various modifications and various embodiments and is intended to illustrate and describe the specific embodiments in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

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 "comprises" or "having" are used to designate the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In the present specification, all the compounds or functional groups may be substituted or unsubstituted, unless otherwise specified. Herein, the term "substituted" means that at least one hydrogen contained in the compound or the functional group is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group, a cycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, Substituted with a substituent selected from the group consisting of an alkoxy group having 1 to 10 carbon atoms, a carboxylic acid group, an aldehyde group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group and derivatives thereof.

The electrolyte according to an embodiment of the present invention includes an alkyl acetate having 1 to 4 carbon atoms and an alkoxy substituted nitrile having 3 to 7 carbon atoms. By including the alkyl acetate and the alkoxy substituted nitrile together in the electrolyte, the electrolyte can improve lifetime characteristics at low temperature without deterioration of the normal temperature service life of the lithium secondary battery.

The alkyl acetate is specifically selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert- And may be isopropyl acetate or isobutyl acetate.

The alkoxy-substituted nitrile may specifically be any one selected from the group consisting of alkoxyacetonitrile, alkoxypropionitrile, and combinations thereof, and may be preferably methoxyacetonitrile or 3-methoxypropionitrile.

The alkyl acetate and the alkoxy substituted nitrile may be contained in an amount of 5 to 75% by weight, preferably 5 to 40% by volume, more preferably 5 to 20% by volume based on the total volume of the electrolyte. When the content of the alkyl acetate and the alkoxy substituted nitrile is less than 5 vol%, the lifetime may be deteriorated at room temperature, and when it exceeds 75 vol%, the lifetime may be deteriorated.

The electrolyte may contain the alkyl acetate and the alkoxy substituted nitrile in a ratio of 2: 1 to 15: 1 by volume, preferably in a ratio of 5: 1 to 7: 1, more preferably 6: 1 to 6.5 : 1 volume ratio. If the volume ratio of the alkyl acetate is less than 2, the life may be deteriorated at low temperature, and if it is more than 7, the normal temperature life may be deteriorated.

The electrolyte may further include an organic solvent and a lithium salt in addition to the electrolyte additive.

The organic solvent may be any organic solvent that can act as a medium through which ions involved in an electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include 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 singly or in combination of two or more.

Specific examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, But are not limited to, ethyl propionate,? -Butyrolactone, decanolide,? -Valerolactone, mevalonolactone,? -Caprolactone (? -caprolactone, 隆 -valerolactone, 竜 -caprolactone, and the like.

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) , Methyl ethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) And fluoroethylene carbonate (FEC).

Particularly, when ethylene carbonate is used as the organic solvent, the compatibility of the alkyl acetate and the alkoxy substituted nitrile is excellent and the effect of the present invention for improving lifetime characteristics at low temperatures without deterioration of the normal temperature service life of the lithium secondary battery Can be further improved. The ethylene carbonate, the alkyl acetate, and the alkoxy substituted nitrile may be included in a volume ratio of 2: 7: 1 to 3: 6: 1, and preferably in a volume ratio of 3: 5: 2 to 3: 6: And more preferably in a volume ratio of 2.5: 6.5: 1 to 3: 6: 1. If the volume ratio of the ethylene carbonate is less than 2, the life may be deteriorated, and if it is more than 3, the life may be deteriorated at a low temperature.

Among them, a carbonate-based solvent is preferably used as the organic solvent. Among the carbonate-based solvents, a carbonate-based organic solvent having a high ionic conductivity, which can increase the charge / discharge performance of the battery, It may be preferable to use a mixture of a carbonate-based organic solvent having a low viscosity that can appropriately control the viscosity of the high-dielectric constant organic solvent. Specifically, an organic solvent having a high dielectric constant selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof, and an organic solvent having a low viscosity selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, Can be mixed and used. More preferably, the organic solvent having a high dielectric constant and the organic solvent having a low viscosity are mixed at a volume ratio of 2: 8 to 8: 2, and more specifically, ethylene carbonate or propylene carbonate; Ethyl methyl carbonate; And dimethyl carbonate or diethyl carbonate in a volume ratio of 5: 1: 1 to 2: 5: 3, preferably 3: 5: 2.

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. Specifically, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , 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 (C a F 2a +1 SO} 2) (C b F 2b +1 SO 2) ( However, a and b is a natural number, preferably 1≤a≤20, 1≤b≤20 and Im), LiCl, LiI, and mixtures thereof. It is preferable to use lithium hexafluorophosphate (LiPF ₆ ).

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, the lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%. If the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If the concentration exceeds 2 mol%, 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 controlled to be approximately 0.7 mol% to 1.6 mol% in the electrolyte.

The electrolyte further includes an additive (hereinafter, referred to as "other additive") which can be generally used for an electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing the decrease of battery capacity, and improving the discharge capacity of the battery in addition to the electrolyte components can do.

Examples of the other additives include vinylene carbonate (vinylenecarbonate, VC), metal fluoride (metal fluoride, for example, LiF, RbF, TiF, AgF , AgF2, 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 4, 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 and SeF ₆ ), glutaronitrile Succinonitrile (SN), adiponitrile (AN), 3,3'-thiodipropionitrile (TPN), vinylethylene carbonate (VEC) Fluoroethylene carbone Fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethylcarbonate, and fluoroethylmethylcarbonate. Of these, one kind or two or more kinds of them may be used. And may be mixed.

The other additives may be included in an amount of 0.1 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 according to the embodiment of the present invention can be classified into a lithium ion battery, a lithium ion polymer battery and a lithium polymer battery depending on the type of the separator and the electrolyte used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, Etc., and can be divided into a bulk type and a thin film type depending on the size. The electrolyte according to the embodiment of the present invention may be particularly excellent for application to a lithium ion battery, an aluminum laminated battery and a lithium polymer battery.

Specifically, the lithium secondary battery includes a cathode including a cathode active material disposed opposite to each other, a cathode including a cathode active material, and the electrolyte interposed between the anode and the cathode.

1 is an exploded perspective view of a lithium secondary battery 1 according to an embodiment of the present invention. 1, a lithium secondary battery 1 according to another embodiment of the present invention includes a separator 7 between a cathode 3, an anode 5, the cathode 3, and an anode 5, (5) and the separator (7) are impregnated into the electrolyte (15) by injecting a non-aqueous electrolyte into the electrode assembly (9) have.

Conductive lead members 10 and 13 for collecting a current generated during a battery operation can be attached to the cathode 3 and the anode 5 respectively and the lead members 10 and 13 are respectively connected to the anode 5, And the current generated in the cathode (3) can be led to the positive electrode and the negative electrode terminal.

The anode 5 is prepared by mixing a cathode active material, a conductive agent and a binder to prepare a composition for forming a cathode active material layer, applying the composition for forming a cathode active material layer to a cathode current collector such as aluminum foil, can do.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Specifically, an olivine-type lithium metal compound represented by the following formula (6) can be used.

[Chemical Formula 6]

Li _x M _y M ' _z XO _{4 - w} Y _w

M and M 'are each independently Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, And X is an element selected from the group consisting of P, As, Bi, Sb, Mo, and combinations thereof, and Y is selected from the group consisting of F, S, and combinations thereof 0 <x? 1, 0 <y? 1, 0 <z? 1, 0 <x + y + z? 2, and 0? W?

Among these compounds, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Mn _(1-x) O ₂ (where 0 <x <1) and LiM _lx M _2y O ₂ (However, 0≤x≤1, 0≤y≤1, 0≤x + y≤1 , M 1 and M ₂ is one selected from the group consisting of Al, Sr, Mg and La are each independently One), and a mixture thereof.

The negative electrode 3 is prepared by mixing a negative electrode active material, a binder and an optional conductive agent in the same manner as the positive electrode 5 to prepare a composition for forming a negative electrode active material layer and then applying the composition to a negative electrode current collector such as a copper foil .

As the negative electrode active material, 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.

On the other hand, since the electrolyte is the same as described above with respect to the electrolyte, the description thereof will be omitted. Since the lithium secondary battery can be manufactured by a conventional method, a detailed description thereof will be omitted herein. In the present embodiment, pouch type lithium secondary battery is taken as an example, but the technology of the present invention is not limited to a pouch type lithium secondary battery, and any shape can be used as long as it can operate as a battery.

As described above, the lithium secondary battery including the electrolyte according to the embodiment of the present invention can exhibit low DC-IR characteristics, high-temperature storage characteristics, and improved output characteristics, It can be useful for portable devices such as computers, digital cameras, camcorders, electric vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (HEV, PHEV) have.

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  1: Preparation of electrolyte]

( Comparative Example  One)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), ethylmethylcarbonate (EMC) and diethyl carbonate (DEC) as an organic solvent were mixed in a volume ratio of 3: 5: 2 to prepare an electrolyte.

( Comparative Example  2)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC) and isobutyl acetate (IBA) as an organic solvent were mixed at a volume ratio of 2.5: 7.5 to prepare an electrolyte.

( Comparative Example  3)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC) and methoxyacetonitrile (MAN) as an organic solvent were mixed at a volume ratio of 2.5: 7.5 to prepare an electrolyte.

( Example  One)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), isobutyl acetate and methoxy acetonitrile as organic solvents were mixed at a volume ratio of 2.5: 6.5: 1 to prepare an electrolyte.

( Example  2)

0.9 M LiPF ₆ as a lithium salt, ethylene carbonate (EC) as an organic solvent, isobutyl acetate and methoxy acetonitrile were mixed at a volume ratio of 2: 6: 1 to prepare an electrolyte.

( Example  3)

0.9 M LiPF ₆ as a lithium salt, ethylene carbonate (EC), isobutyl acetate and methoxy acetonitrile as organic solvents were mixed at a volume ratio of 4: 6.5: 1 to prepare an electrolyte.

( Example  4)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), isobutyl acetate and methoxy acetonitrile as organic solvents were mixed at a volume ratio of 2: 7.5: 0.5 to prepare an electrolyte.

( Example  5)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), isobutyl acetate and methoxy acetonitrile as organic solvents were mixed at a volume ratio of 3: 5.5: 1.5 to prepare an electrolyte.

( Example  6)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), isobutyl acetate and methoxyacetonitrile as organic solvents were mixed at a volume ratio of 3: 6: 1 to prepare an electrolyte.

( Example  7)

0.9 M LiPF ₆ as a lithium salt, and ethylene carbonate (EC), isobutyl acetate and methoxy acetonitrile as organic solvents were mixed at a volume ratio of 4: 5: 1 to prepare an electrolyte.

[ Manufacturing example  2: The lithium secondary battery  Produce]

A composition for forming a positive electrode active material layer containing 85 wt% of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 7.5 wt% of polyvinylidene fluoride as a binder and 7.5 wt% of super-P carbon as a conductive material, And dried to prepare a positive electrode. A composition for forming a negative electrode active material layer containing 88 weight% of artificial graphite as a negative electrode active material, 4 weight% of super-P carbon as a conductive material and 8 weight% of polyvinylidene fluoride as a binder was coated on a copper foil as a current collector And dried to prepare a negative electrode. The separator was placed on the positive electrode prepared above, and the carbon negative electrode was placed thereon. Then, the electrolyte prepared in the above examples and comparative examples were injected and vacuum packed with an aluminum pouch to prepare a lithium secondary battery.

[ Test Example  1: Evaluation of battery life characteristics at normal temperature and low temperature]

In order to evaluate the life characteristics of the charge and discharge of the rechargeable lithium battery including the electrolyte according to the present invention, Battronix ^® cell in (Battronix Co., Ltd.) Examples and Comparative after each injection of the electrolyte produced in Example, 60 ℃ in (0.5 C rate) under constant current (CC) / constant voltage (CV) conditions and discharged to 2.7 V under CC (0.5 C rate) conditions after 10 minutes of dormancy. At this time, the normal capacity was 1000 mAh. The charging and discharging were repeated for one cycle for 300 cycles, and the change in capacity due to charging and discharging was measured. The results are shown in Table 1 below.

Electrolyte composition (volume ratio) Life characteristics Low temperature (-25 degrees) Room temperature Comparative Example 1 EC: EMC: DEC = 3: 5: 2 5.2% 92.1% Comparative Example 2 EC: IBA = 2.5: 7.5 49.8% 85.2% Comparative Example 3 EC: MAN = 2.5: 7.5 2.8% 42.1% Example 1 EC: IBA: MAN = 2.5: 6.5: 1 53.1% 92.2% Example 2 EC: IBA: MAN = 2: 6: 1 18.2% 90.2% Example 3 EC: IBA: MAN = 4: 6.5: 1 38.2% 88.9% Example 4 EC: IBA: MAN = 2: 7.5: 0.5 42.5% 87.2% Example 5 EC: IBA: MAN = 3: 5.5: 1.5 21.5% 89.1% Example 6 EC: IBA: MAN = 3: 6: 1 48.2% 90.2% Example 7 EC: IBA: MAN = 4: 5: 1 40.2% 84.2%

Table 1 shows that the comparative example 1 exhibits a life efficiency of 40% or less at a low temperature, whereas the comparative example 2 has an excellent low temperature longevity efficiency compared to the comparative example 1, It can be seen that it is lowered. However, in the case of the examples, it can be seen that the low-temperature lifetime efficiency is excellent and the room temperature lifetime efficiency is not lowered.

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 of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

1: Lithium secondary battery
3: cathode 5: anode
7: separator 9: electrode assembly
10, 13: lead member 15: case

Claims (13)

An alkyl acetate having 1 to 4 carbon atoms and an alkoxy substituted nitrile having 3 to 7 carbon atoms. The method according to claim 1,
Wherein the alkyl acetate is any one selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert- Electrolytes that will be. The method according to claim 1,
Wherein the alkoxy-substituted nitrile is any one selected from the group consisting of alkoxyacetonitrile, alkoxypropionitrile, and combinations thereof. The method according to claim 1,
Wherein the alkyl acetate and the alkoxy substituted nitrile are contained in an amount of 5 to 75% by volume based on the total volume of the electrolyte. The method according to claim 1,
Wherein the electrolyte comprises the alkyl acetate and the alkoxy substituted nitrile in a volume ratio of 2: 1 to 15: 1. The method according to claim 1,
Wherein the electrolyte further comprises an organic solvent and a lithium salt. The method according to claim 6,
Wherein the organic solvent is selected from the group consisting of an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, and mixtures thereof. The method according to claim 6,
Wherein the organic solvent is ethylene carbonate. The method according to claim 6,
Wherein the organic solvent comprises an organic solvent having a high dielectric constant and a low viscosity organic solvent in a volume ratio of 2: 8 to 8: 2. 10. The method of claim 9,
The high-k organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof,
Wherein the low-viscosity organic solvent is selected from the group consisting of methylethylcarbonate, dimethylcarbonate, diethylcarbonate, and mixtures thereof. The method according to claim 6,
Wherein the organic solvent is selected from the group consisting of ethylene carbonate and propylene carbonate; Ethyl methyl carbonate; And one of dimethyl carbonate and diethyl carbonate in a volume ratio of 5: 1: 1 to 2: 5: 3. The method according to claim 6,
The lithium salt is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAl0 4, LiAlCl 4, LiCF 3 SO 3, 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 (C a F 2a + 1} SO 2) (C b F 2b + 1 SO 2) ( However, a and b are natural numbers), the electrolyte is selected from LiCl, LiI, and mixtures thereof. An anode including a cathode active material,
A negative electrode disposed opposite to the positive electrode and including a negative electrode active material, and
And an electrolyte interposed between the anode and the cathode,
Wherein the electrolyte comprises an alkyl acetate having 1 to 4 carbon atoms and an alkoxy substituted nitrile having 3 to 7 carbon atoms.

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