KR20160002314A - Electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte and to a lithium secondary battery comprising the same. The electrolyte comprises a compound represented by chemical formula 1, and a compound represented by chemical formula 2. In the chemical formula 1 and 2, R^1 to R^5 are the same as defined in the specification. The lithium secondary battery using the electrolyte has excellent charge/discharge efficiency at high temperature, and low resistance, especially has improved long life efficiency at high temperature, and reducing increase rate of internal resistance.

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 and a lithium secondary battery including the same, and more particularly to a lithium secondary battery having excellent charge / discharge efficiency and low resistance at high temperature when applied to a lithium secondary battery, And to a lithium secondary battery comprising the electrolyte.

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. 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.

On the other hand, interest in environment-friendly vehicles has been increasing worldwide due to environmental concerns, and domestic / foreign battery companies are making efforts to develop lithium secondary batteries for automobiles. In automotive lithium secondary batteries, charge / discharge efficiency and low resistance characteristics (DC-IR reduction) at high temperatures are important characteristics. The present invention relates to a high temperature charge / discharge efficiency enhancement and low resistance additive which can be applied to an automotive lithium secondary battery.

U.S. Publication No. 2013-0244122 (published on September 19, 2013)

An object of the present invention is to provide a lithium secondary battery using an electrolyte according to the present invention, which is excellent in charge / discharge efficiency and low resistance characteristics at high temperatures, and particularly has a high long-term lifetime efficiency and a reduction effect of internal resistance rise rate.

Still 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 a compound represented by the following formula (1) and a compound represented by the following formula (2).

[Chemical Formula 1]

(2)

(Wherein R ¹ to R ⁵ are each independently selected from the group consisting of a hydrogen atom, a methyl group and an ethyl group, and n is 0 or 1)

The compound represented by Formula 1 may be any one selected from the group consisting of compounds represented by Formulas 1-1 to 1-4 and mixtures thereof.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

The compound represented by the formula (2) may be any one selected from the group consisting of compounds represented by the following formulas (2-1) to (2-5) and mixtures thereof.

[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Chemical Formula 2-4]

[Chemical Formula 2-5]

The electrolyte may contain 0.1 to 10% by weight of the compound represented by the general formulas (1) and (2) for the whole electrolyte.

The electrolyte may be any one selected from the group consisting of fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ), a compound represented by the following formula (3) As shown in FIG.

(3)

(Wherein R ²¹ is selected from the group consisting of functional groups having the structures represented by the following formulas (3-1) to (3-3), R ²² represents a halogen group, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms A halogenated alkyl group, an aryl group having 6 to 30 carbon atoms and a halogenated aryl group having 6 to 30 carbon atoms, and X < ^{1 >} And X ² will be each independently selected from oxygen (O) or sulfur (S), and wherein M ₁ is selected from the group consisting of transition metal elements, 3B group elements, 4B group elements and 5B group elements, wherein M ₂ is 1A (A), wherein a is an integer of 1 to 4, b is an integer of 0 to 8, and c, d, e and f are each an integer of 1 to 4, Lt; / RTI >

[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

(Wherein R ³¹ represents an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 30 carbon atoms, and a halogenated arylene group having 6 to 30 carbon atoms) And R ³² and R ³³ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 30 carbon atoms, and a halogenated aryl group having 6 to 30 carbon atoms Lt; / RTI >

The compound represented by Formula 3 is a compound wherein R ²² is a halogen group, X ¹ And X ² are each oxygen (O), M ₁ is phosphorus (P), M ₂ is an element of Group 1A or Group 2A, a is an integer of 1 to 3, and b is 2 or 4 And c, d, e, and f may be an integer of 1 to 3, respectively.

The compound represented by Formula 3 may be lithium difluorobis (oxalato) phosphate.

The compound represented by Formula 1 and the compound represented by Formula 2 are reacted with fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ), the compound represented by Formula 3, May be contained in the electrolyte in a weight ratio of 1:10 to 10: 1.

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 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.

A lithium secondary battery according to another 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 to face the positive electrode, and a negative electrode including a positive electrode active material interposed between the positive electrode and the negative electrode. And an electrolyte according to the example.

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

The lithium secondary battery using the electrolyte according to the present invention is excellent in charging / discharging efficiency and low-resistance characteristics at high temperatures, and particularly has a high long-term lifetime efficiency and a reduction effect of internal resistance (DC-IR) rising rate.

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.

Further, unless otherwise specified is "a combination thereof" in the present specification, two or more functional groups, for a single bond, double bond, triple bond, an alkylene group having 1 to 10 carbon atoms (for example, methylene (-CH ₂ -), (-CH ₂ CH ₂ -), etc.), a fluoroalkylene group having 1 to 10 carbon atoms (for example, fluoromethylene (-CF ₂ -), perfluoroethylene (-CF ₂ CF ₂ -), etc.) ), A hetero atom such as N, O, P, S, or Si or a functional group containing the same (specifically, a carbonyl group (-C═O-), an ether group (-O-), an ester group -), -S-, -NH- or -N = N-), or two or more functional groups are condensed and connected.

An electrolyte according to an embodiment of the present invention includes a compound represented by the following formula (1) and a compound represented by the following formula (2).

The compound represented by the formula (1) is excellent in charge / discharge efficiency and low resistance at high temperature, and is expected to be used as an electrolyte additive for automotive lithium secondary batteries. . However, when the compound represented by the above formula (2) is used together with the compound represented by the above formula (1), the high temperature performance and the internal resistance increase rate reduction effect are excellent.

[Chemical Formula 1]

In Formula 1, R ¹ and R ² are each independently selected from the group consisting of a hydrogen atom, a methyl group, and an ethyl group.

(2)

In Formula 2, each of R ³ to R ⁵ is independently selected from the group consisting of a hydrogen atom, a methyl group, and an ethyl group, and n is 0 or 1.

Specifically, the compound represented by the formula (1) is the same as the compound represented by the following formulas (1-1) to (1-4).

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

Specifically, the compound represented by the formula (2) is the same as the compound represented by the following formulas (2-1) to (2-5).

[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Chemical Formula 2-4]

[Chemical Formula 2-5]

The electrolyte may contain 0.1 to 10% by weight of the compound represented by Formula 1 and the compound represented by Formula 2 with respect to the entire electrolyte. If the content of the compound is less than 0.1% by weight, the effect of using the compound is insignificant, and if it exceeds 10% by weight, the initial capacity may decrease. Preferably, each of the compounds represented by the above formulas (1) and (2) is independently contained in an amount of 0.5 to 3% by weight based on the total weight of the electrolyte.

Meanwhile, the electrolyte may be any one selected from the group consisting of fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ), a compound represented by the following general formula (3) ≪ / RTI >

Usually, in the case of high-voltage electrolyte additives, it is adsorbed at the defect points or activation points of the surface of the anode of the electrochemical device to inhibit the oxidative decomposition reaction of the nonaqueous electrolyte or form a complex with the metal ions eluted from the anode, . However, the FEC, LiPO ₂ F ₂ and the compound represented by the formula 3 stabilize the battery by forming a solid electrolyte interface (SEI) on the surfaces of the negative electrode and the positive electrode to improve the battery characteristics of the lithium secondary battery, The performance can be improved, gas generation can be suppressed, and the overcharge preventing characteristic can be improved. In particular, the FEC, LiPO ₂ F ₂ and the compound represented by the general formula (3) are selected so as to maximize the above effects in the electrolyte containing the compounds represented by the general formulas (1) and (2).

(3)

In Formula 3, R < ²¹ > is selected from the group consisting of functional groups having the structures represented by the following Formulas 3-1 to 3-3.

[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

In the formulas (3-1) to (3-3), R ³¹ is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 30 carbon atoms, and a halogenated arylene group having 6 to 30 carbon atoms And R ³² and R ³³ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 30 carbon atoms and a halogenated aryl group having 6 to 30 carbon atoms Is selected.

In Formula 3, R ²² is selected from the group consisting of a halogen group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 30 carbon atoms, and a halogenated aryl group having 6 to 30 carbon atoms And X ¹ And X ² are each independently oxygen (O) or sulfur (S), and M ¹ is a transition metal element, or a group selected from the group consisting of Group 3B elements, Group 4B elements and Group 5B elements in the monoclinic periodic table M ² is selected from the group consisting of Group 1A element, Group 2A element and aluminum (Al) in the monoclinic periodic table, and a is an integer of 1 to 4, and b is an integer of 0 to 8 And c, d, e, and f are integers of 1 to 3, respectively.

Preferably, in Formula 3, R ²¹ is selected from the group consisting of functional groups having the structures of Formulas 3 to 5, and R ²² is a halogen group, preferably a fluoro group. Further, the X ¹ And X < ² > may all be oxygen (O). The M ₁ may be phosphorus (P), and the M ₂ may be a group 1A element or a group 2A element in the monoclinic periodic table, more preferably lithium. And a is an integer of 1 to 3, b is an integer of 2 or 4, and c, d, e, and f may each be an integer of 1 to 3.

Specifically, the compound represented by Formula 3 may be lithium tetrafluoro (oxalato) phosphate or lithium difluorobis (oxalato) phosphate, or the like. , And lithium difluorobis (oxalate) phosphate represented by the following formula (3a) may be more preferable in terms of improvement effect:

[Chemical Formula 3]

The FEC, LiPO ₂ F ₂ and the compound represented by the general formula (3) may be contained in an amount of 0.1 to 10 wt%, preferably 0.5 to 3 wt%, based on the total weight of the electrolyte. If the content of the compound is less than 0.1% by weight, the effect of the use of the compound is insignificant. If the content is more than 10% by weight, the lifetime retention rate may be lowered. If the content is excessively large, have.

Also, the compound represented by Formula 1 and the compound represented by Formula 2 may be combined with fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ) And a mixture thereof may be contained in the electrolyte in a weight ratio of 1:10 to 10: 1, and preferably in a weight ratio of 5: 1 to 5: 1. When the amount of the FEC, LiPO ₂ F ₂ and the compound represented by the formula (3) is too low in the content of the compound represented by the formula (1) and the compound represented by the formula (2), the FEC, LiPO ₂ F ₂ and the formula And the content of the compound represented by the general formula (3) is larger than the content of the compound represented by the general formula (1) and the compound represented by the general formula (2) in the content of the FEC, LiPO ₂ F ₂ , Excessively high temperatures may cause a reduction in the overall life-time maintenance rate.

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).

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 which can appropriately control the viscosity of the organic solvent having a high electrical conductivity. 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 , AgF 2, BaF 2, CaF 2, CdF 2, FeF 2, HF 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, ZrF4 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), 4-tolunitrile, 1,3,6-hexanetricarbonitrile (1,3,6-hexanetricarbonitrile) , Propylene sulfide (PS), 3,3'- (3,3'-thiodipropionitrile, TPN), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethyl carbonate fluoromethylcarbonate, fluorodimethylcarbonate, fluoroethylmethylcarbonate, lithium bis (trifluoromethylsulfonyl) imide, LiTFSI, lithium tetrafluoroborate (LiBF ₄ ), lithium tetrafluoroborate Lithium bis (oxalato) borate, LiBOB, Lithium difluoro (oxalate) borate, LiDFOB), lithium (malonate oxalate) borate malonato oxalato) borate, LiMOB), phosphates of lithium difluoro _{(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-propane sultone, 1,3-propene sultone, biphenayl, cyclohexyl benzene, 4-fluorotoluene, succinonohydride ( succinic anhydride, ethylene sulfate anhydride and tris (trimethylsilyl) borate). One of them may be used singly or two or more of them may be used in combination. have.

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 an 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. Although the pouch type lithium secondary battery is described as an example in the present embodiment, the present invention is not limited to the 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.

[ Example  And Comparative Example : Preparation of Electrolyte]

A mixed solvent in which 0.9 M LiPF ₆ as a lithium salt, ethylene carbonate (EC), ethylmethylcarbonate (EMC) and diethyl carbonate (DEC) as an organic solvent were mixed at a volume ratio of 30:50:20, , An electrolyte was prepared using the compound represented by Formula 1 and the compound represented by Formula 2 as shown in FIG.

Type 1 Formula 1 Content Type 2 The content of formula 2 FEC LiPO ₂ F ₂ Lithium difluorobis (oxalate) phosphate Comparative Example 1 (1-1) 0.8 - - - - - Comparative Example 2 - - 2-1 0.8 - - - Example 1 (1-1) 0.3 2-1 0.5 - - - Example 2 (1-1) 0.3 2-1 0.5 One 0.5 - Example 3 (1-1) 0.3 2-1 0.5 - - One Example 4 (1-1) 0.3 2-1 0.5 One - - Example 5 (1-1) 0.3 2-1 0.5 - - 1.3 Example 6 (1-1) 0.3 2-1 0.5 0.5 One Example 7 1-2 0.3 2-1 0.5 - - - Example 8 1-3 0.3 2-1 0.5 - - - Example 9 Formula 1-4 0.3 2-1 0.5 - - - Example 10 (1-1) 0.3 2-2 0.5 - - - Example 11 (1-1) 0.3 (2-3) 0.5 - - - Example 12 (1-1) 0.3 2-4 0.5 - - - Example 13 (1-1) 0.3 2-5 0.5 - - -

(Unit: wt%)

[ Manufacturing example : Production of lithium secondary battery]

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 Example and Comparative Example was injected and vacuum packed with an aluminum pouch to prepare a lithium secondary battery.

In order to evaluate the lifetime characteristics of the lithium secondary battery including the electrolyte according to the present invention, the electrolyte prepared in the above production example was injected into a 1Ah class pouch cell, and then CC (Constant current) / The battery was charged at a constant voltage (CV) condition of 4.2 V (0.5 C rate) and discharged to 2.7 V at a CC (0.5 C rate) condition after 10 minutes of resting. 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 Tables 2 and 3 below.

Battery life efficiency (45 ℃ Cycle Efficiency (%)) Initial Cycle 300cycle Comparative Example 1 100 77.9 Comparative Example 2 100 72.6 Example 1 100 83.4 Example 2 100 84.0 Example 7 100 82.1

After standing at 60 ° C, DC-IR (mΩ) 0 weeks 4 weeks Comparative Example 1 35.2 61.4 Comparative Example 2 33.7 62.9 Example 1 32.9 56.4 Example 2 31.3 54.3 Example 7 31.7 58.8

As a result of the battery life efficiency test and the low resistance property test, Examples 1 to 3, which are the batteries including the electrolyte including both the compound represented by the formula (1) and the compound represented by the formula (2), exhibited the charge / discharge efficiency And charging DC-IR, and compared with the battery of Comparative Example 2 containing only the compound of Comparative Example 1 and the compound of Formula 2 containing only the compound of Formula 1, the long-term lifetime efficiency and the internal resistance increase rate reduction effect were improved , And the same level of results were obtained for Examples 3 to 6 and 8 to 13.

In particular, the battery life efficiency and the DC-IR value of Example 2 including fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO ₂ F ₂ ) were higher than those of Examples 1 and 3 .

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 (15)

An electrolyte comprising a compound represented by the following formula (1) and a compound represented by the following formula (2).
[Chemical Formula 1]

(2)

(In the above formulas (1) and (2)
Wherein R ¹ to R ⁵ are each independently selected from the group consisting of a hydrogen atom, a methyl group, and an ethyl group, and n is 0 or 1)
The method according to claim 1,
Wherein the compound represented by Formula 1 is any one selected from the group consisting of compounds represented by Chemical Formulas 1-1 to 1-4 and mixtures thereof.
[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

The method according to claim 1,
Wherein the compound represented by Formula 2 is any one selected from the group consisting of compounds represented by the following Chemical Formulas 2-1 to 2-5 and mixtures thereof.
The compound represented by the formula (2) may be any one selected from the group consisting of compounds represented by the following formulas (2-1) to (2-5) and mixtures thereof.
[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Chemical Formula 2-4]

[Chemical Formula 2-5]

The method according to claim 1,
Wherein the electrolyte comprises 0.1 to 10% by weight of the compound represented by Formula 1 and the compound represented by Formula 2 with respect to the whole electrolyte. The method according to claim 1,
The electrolyte may be any one selected from the group consisting of fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO ₂ F ₂ ), a compound represented by the following formula (3) Further comprising an electrolyte.
(3)

(3)
Wherein R &lt; ²¹ &gt; is selected from the group consisting of functional groups having the structures of the following formulas (3-1) to (3-3)
Wherein R ²² is selected from the group consisting of a halogen group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 30 carbon atoms, and a halogenated aryl group having 6 to 30 carbon atoms,
The X ¹ And X &lt; ² &gt; are each independently oxygen (O) or sulfur (S)
Wherein M ₁ is selected from the group consisting of a transition metal element, a group 3B element, a group 4B element and a group 5B element,
M ₂ is selected from the group consisting of Group 1A elements, Group 2A elements and aluminum (Al), and
Wherein a is an integer of 1 to 4, b is an integer of 0 to 8, c, d, e and f are each an integer of 1 to 3,
[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

In the formulas (3-1) to (3-3), R ³¹ is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 30 carbon atoms, and a halogenated arylene group having 6 to 30 carbon atoms And R ³² and R ³³ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 30 carbon atoms and a halogenated aryl group having 6 to 30 carbon atoms Selected) 6. The method of claim 5,
The compound represented by Formula 3 is a compound wherein R ²² is a halogen group, X ¹ And X ² are each oxygen (O), M ₁ is phosphorus (P), M ₂ is an element of Group 1A or Group 2A, a is an integer of 1 to 3, and b is 2 or 4 And each of c, d, e and f is an integer of 1 to 3, respectively. 6. The method of claim 5,
Wherein the compound represented by Formula 3 is lithium difluorobis (oxalato) phosphate. 6. The method of claim 5,
(1), the compound represented by the general formula (2), the fluoroethylene carbonate (FEC), the lithium difluorophosphate (LiPO ₂ F ₂ ) The compound to be displayed, and the mixture thereof is contained in the electrolyte at a weight ratio of 1:10 to 10: 1. The method according to claim 1,
Wherein the electrolyte further comprises an organic solvent and a lithium salt. 10. The method of claim 9,
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. 10. The method of claim 9,
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. 12. The method of claim 11,
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. 12. The method of claim 11,
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. 10. The method of claim 9,
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
The lithium secondary battery according to claim 1, wherein the electrolyte is interposed between the positive electrode and the negative electrode.

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