KR20150072188A - Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery Containing the Same - Google Patents

Abstract

The present invention is to provide an electrolyte for a lithium secondary battery, and a lithium secondary battery containing the same. The electrolyte for a lithium secondary battery of the present invention has excellent high temperature stability, low temperature discharge capacity, and lifespan property. Also, the lithium secondary battery comprises: lithium salt; a non-aqueous organic solvent; and an oxalate derivative.

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 OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery containing the same. More particularly, the present invention relates to a lithium secondary battery electrolyte containing an oxalate derivative and a lithium secondary battery comprising the same.

2. Description of the Related Art [0002] In recent years, portable electronic devices have been widely used. As a result, with the rapid miniaturization, light weight, and thinness of portable electronic devices, batteries as a power source thereof are small, lightweight and can be charged / discharged for a long time. Development is strongly required.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium secondary battery has a safety problem such as ignition and explosion due to the use of a non-aqueous electrolyte, and such a problem becomes more serious as the capacity density of the battery is increased.

The nonaqueous electrolyte secondary battery has a serious problem in that the safety of the battery generated during continuous charging is lowered. One of the possible causes of this is fever due to structural collapse of the anode. The working principle of this is as follows. That is, the positive electrode active material of the nonaqueous electrolyte battery is composed of a lithium-containing metal oxide capable of intercalating and deintercalating lithium and / or lithium ions, etc. Such a positive electrode active material is deformed into a thermally unstable structure do. When the battery temperature reaches a critical temperature due to an external physical impact such as high temperature exposure in the overcharged state, oxygen is released from the cathode active material having an unstable structure, and the released oxygen causes an exothermic decomposition reaction with the electrolyte solvent or the like. Particularly, since the combustion of the electrolytic solution is further accelerated by the oxygen released from the anode, such a series exothermic reaction causes ignition and rupture of the battery due to thermal runaway.

In order to control the ignition or explosion due to the temperature rise inside the battery, a method of adding an aromatic compound as a redox shuttle additive in the electrolyte is used. For example, Japanese Patent Publication JP2002-260725 discloses a non-aqueous lithium ion battery capable of preventing an overcharge current and a thermal runaway phenomenon by using an aromatic compound such as biphenyl. In addition, U.S. Patent No. 5,879,834 discloses that aromatic compounds such as biphenyl and 3-chlorothiophene are added in a small amount to electrochemically polymerize in an abnormal overvoltage state to increase the internal resistance to improve the safety of the battery Is described.

However, when using an additive such as biphenyl, the amount of biphenyl is gradually reduced when the battery is decomposed gradually in the charge / discharge process or when the battery is discharged at a high temperature for a long period of time at a relatively high voltage locally at a normal operating voltage There is a problem that safety can not be guaranteed after 300 cycles of charging / discharging, and problems of storage characteristics.

Therefore, there is a need for research for improving safety at high temperature and low temperature while still maintaining a high capacity retention rate.

Japanese Patent JP2002-260725 U.S. Patent 5,879,834

The present invention provides a lithium secondary battery electrolyte having excellent high-temperature and low-temperature characteristics while maintaining good basic performance such as high rate charge / discharge characteristics and life characteristics, and a lithium secondary battery comprising the lithium secondary battery.

The present invention provides an electrolyte for a lithium secondary battery,

Lithium salts;

Non-aqueous organic solvent; And

An oxalate derivative represented by the following formula (1).

[Chemical Formula 1]

(In the formula 1,

R ¹ or R ² independently from each other are (C 2 -C 10) alkenyl, (C 2 -C 10) alkynyl or (C 6 -C 12) aryl;

n or m are each independently an integer of 0 to 5;

The alkenyl, alkynyl or aryl of R ¹ or R ² may be further substituted with cyano, hydroxy, halogen, halo (C 1 -C 10) alkyl, (C 1 -C 10) alkyl, or .)

The formula (1) according to an embodiment of the present invention may be represented by the following formula (2) or (3).

(2)

(3)

(In the above formula (2) or (3)

또는

이며,A or B independently of one another

or

Lt;

R ³ or R ⁴ independently from each other are hydrogen or (C 1 -C 10) alkyl;

R ¹¹ or R ¹² independently from each other are hydrogen, cyano, hydroxy, trifluoromethyl, (C 1 -C 10) alkyl, or (C 6 -C 12) aryl;

n or m are each independently an integer of 0 to 5;

o or p independently of one another is an integer of 1 to 5.)

Preferably, in Formula 2 or 3 according to an embodiment of the present invention, R ³ or R ⁴ are independently of each other hydrogen; n or m may be an integer of 0 to 1 independently of each other.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the formula 1 may be selected from the following structures, but is not limited thereto.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the oxalate derivative represented by Formula 1 may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolytic solution.

In the electrolytic solution of the lithium secondary battery according to an embodiment of the present invention, the electrolyte may contain one or two selected from the group consisting of an oxalate borate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound, and a sulfinyl group- Or more of the above additives.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the electrolyte is selected from the group consisting of lithium difluoroarsalate borate (LiFOB), lithium bis oxalate borate (LiB (C ₂ O ₄ ) ₂ , LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate, , Ethane sultone, propane sultone (PS), butane sultone, ethene sultone, butene sultone and propensulfone (PRS).

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the additive may be included in an amount of 0.1% to 5.0% by weight based on the total weight of the electrolyte solution.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may be selected from a cyclic carbonate solvent, a linear carbonate solvent, and a mixed solvent thereof. The cyclic carbonate may be ethylene carbonate, propylene carbonate , Butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and mixtures thereof. The linear carbonate may be selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl Carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof.

In the electrolyte of the lithium secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may have a mixing volume ratio of linear carbonate solvent: cyclic carbonate solvent of 1 to 9: 1.

In the lithium secondary battery electrolyte according to one embodiment of the invention, the lithium salt is _{LiPF 6, LiBF 4, LiClO 4} , LiSbF 6, LiAsF 6, LiN (SO 2 C 2 F 5) 2, LiN (CF 3 SO 2 _{) 2, LiN (SO 3 C} 2 F 5) 2, LiN (SO 2 F) 2, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiC 6 H 5 SO 3, LiSCN, LiAlO 2, LiAlCl 4, LiN _{(C x F 2x + 1 SO} 2) (C y F 2y + 1 SO 2) ( where, x and y are natural numbers), LiCl, LiI, and LiB (C ₂ O ₄₎ one selected from the group consisting of ₂ Or two or more.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the lithium salt may be present at a concentration of 0.1 to 2.0 M.

The present invention also provides a lithium secondary battery comprising the lithium secondary battery electrolyte.

The electrolyte of the lithium secondary battery according to the present invention has an excellent high temperature storage characteristic because swell of the battery at a high temperature is remarkably improved by including an oxalate derivative.

Also, the lithium secondary battery electrolyte according to the present invention contains an oxalate derivative having an aromatic ring, an alkenyl or an alkynyl functional group in the oxalate skeleton and has a very high capacity recovery rate at a high temperature as well as a discharge capacity at a low temperature.

The electrolyte for a lithium secondary battery according to the present invention may further comprise at least one compound selected from the group consisting of oxalate derivatives represented by the formula (1) of the present invention, oxalate borate compounds, fluorine-substituted carbonate compounds, vinylidene carbonate compounds and sulfinyl- And further has one or more additives selected to have better life characteristics, high temperature stability and low temperature characteristics.

Also, the lithium secondary battery of the present invention employs the lithium secondary battery electrolytic solution of the present invention including an oxalate derivative, so that it has excellent high-temperature storage stability and low-temperature characteristics while maintaining good performance such as high efficiency charge / discharge characteristics and life characteristics.

Hereinafter, the present invention will be described in more detail. Unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the following description, And a description of the known function and configuration will be omitted.

The present invention relates to a lithium secondary battery electrolyte for providing a battery having a high discharge capacity at a low temperature while having a high temperature storage characteristic and a long life characteristic.

The present invention relates to a lithium salt; Non-aqueous organic solvent; And an oxalate derivative represented by the following formula (1): < EMI ID = 1.0 >

 [Chemical Formula 1]

(In the formula 1,

R ¹ or R ² independently from each other are (C 2 -C 10) alkenyl, (C 2 -C 10) alkynyl or (C 6 -C 12) aryl;

n or m are each independently an integer of 0 to 5;

The alkenyl, alkynyl or aryl of R ¹ or R ² may be further substituted with cyano, hydroxy, halogen, halo (C 1 -C 10) alkyl, (C 1 -C 10) alkyl, or .)

The secondary battery electrolyte of the present invention is an oxalate derivative, specifically, an oxalate derivative having an allyl, alkenyl or alkynyl functional group, more specifically, an oxalate derivative having an allyl, alkenyl or alkynyl functional group on both sides of the oxalate skeleton Has an oxalate derivative represented by the above formula (1) having a specific structure, has a high capacity recovery rate and stability at a high temperature, and has a very excellent discharge capacity at a low temperature.

Preferably, the oxalate derivative of the present invention may have the same substituent on both sides of the oxalate skeleton.

The formula (1) according to an embodiment of the present invention may be represented by the following formula (2) or (3).

(2)

(3)

(In the above formula (2) or (3)

또는

이며,A or B independently of one another

or

Lt;

R ³ or R ⁴ independently from each other are hydrogen or (C 1 -C 10) alkyl;

R ¹¹ or R ¹² independently from each other are hydrogen, cyano, hydroxy, trifluoromethyl, (C 1 -C 10) alkyl, or (C 6 -C 12) aryl;

n or m are each independently an integer of 0 to 5;

o or p independently of one another is an integer of 1 to 5.)

From the viewpoint of achieving a higher high-temperature stability, R ³ or R ⁴ in the general formula (2) or (3) is independently from each other hydrogen; n or m may be an integer of 0 to 1 independently of each other.

More specifically, the oxalate derivatives of the present invention can be selected in the following structure, but are not limited thereto:

The substituents comprising the "alkyl", "alkoxy" and other "alkyl" moieties described in the present invention include both straight-chain or branched forms and have 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 Lt; / RTI > to 4 carbon atoms.

The term " aryl " in the present invention means an organic radical derived from an aromatic hydrocarbon by the removal of one hydrogen, and may be a single or fused ring containing 4 to 7, preferably 5 or 6 ring atoms, A ring system, and a form in which a plurality of aryls are connected by a single bond. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, indenyl, fluorenyl, and the like.

"Heteroaryl" in the present invention includes 1 to 4 heteroatoms selected from B, N, O, S, P (= O), Si and P as aromatic ring skeletal atoms and the remaining aromatic ring skeletal atoms are carbon Means a 5 to 6 membered monocyclic heteroaryl and a polycyclic heteroaryl condensed with at least one benzene ring and may be partially saturated. The heteroaryl in the present invention also includes a form in which one or more heteroaryl is connected to a single bond.

The term " alkenyl ", alone or as part of another group described in the present invention, means a straight, branched or cyclic hydrocarbon radical containing from 2 to 10 carbon atoms and at least one carbon to carbon double bond. More preferred alkenyl radicals are lower alkenyl radicals having from 2 to about 6 carbon atoms. The most preferred lower alkenyl radical is a radical having from 2 to about 4 carbon atoms. The alkenyl group may also be substituted at any available point of attachment. Examples of alkenyl radicals include ethenyl, propenyl, allyl, propenyl, butenyl, and 4-methylbutenyl. The terms alkenyl and lower alkenyl include cis and trans orientation, or alternatively, radicals having an E and Z orientation.

The term " alkynyl ", alone or as part of another group described herein, means a straight, branched or cyclic hydrocarbon radical containing from 2 to 10 carbon atoms and at least one carbon to carbon triple bond. More preferred alkynyl radicals are lower alkynyl radicals having from 2 to about 6 carbon atoms. Most preferred is a lower alkynyl radical having from 2 to about 4 carbon atoms. Examples of such radicals include propargyl, butynyl, and the like. The alkynyl group may also be substituted at any available attachment point.

The halogen-substituted alkyl or haloalkyl described in this invention means that at least one of the hydrogens present on the alkyl is substituted with a halogen.

In the electrolyte of the lithium secondary battery according to an embodiment of the present invention, the oxalate derivative of Formula 1 may be contained in an amount of 0.1 to 5% by weight based on the total weight of the secondary battery electrolyte, 3% by weight. If the oxalate derivative of Formula 1 is contained in an amount of less than 0.1 wt%, the effect of addition such as low stability at a high temperature or improvement of the capacity retention rate is insignificant and the effect of improving the discharge capacity or output of the lithium secondary battery is insignificant, If it is contained in an amount exceeding 5% by weight, rapid deterioration of the life span occurs, and the characteristics of the lithium secondary battery deteriorate.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the electrolyte is a lifetime improving additive for improving the life of the battery. The electrolyte is an oxalate borate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound, Containing compound, and at least one additive selected from the group consisting of a metal-containing compound.

The oxalate borate compound may be a compound represented by the following formula (11) or lithium bis oxalate borate (LiB (C ₂ O ₄ ) ₂ , LiBOB).

(11)

(Wherein R ₁₁ and R ₁₂ are each independently a halogen atom or a halogenated C 1 to C 10 alkyl group).

Specific examples of the oxalate borate type additive include LiB (C ₂ O ₄ ) F ₂ (lithium difluoroarsalate borate, LiFOB) or LiB (C ₂ O ₄ ) ₂ (lithium bis oxalate borate, LiBOB) .

The fluorine-substituted carbonate compound may be fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluorodimethyl carbonate (FDMC), fluoroethylmethyl carbonate (FEMC) or a combination thereof.

The vinylidene carbonate-based compound may be vinylene carbonate (VC), vinylethylene carbonate (VEC), or a mixture thereof.

The sulfinyl group (S = O) -containing compound may be sulfone, sulfite, sulfonate and sulphonate (cyclic sulfonate), which may be used singly or in combination. Specifically, the sulfone may be represented by the following general formula (12), and may be divinyl sulfone. The sulfite may be represented by the following general formula (13), and may be ethylene sulfite or propylene sulfite. The sulfonate may be represented by the following formula (14) and may be a diallyl sulfonate. Also, non-limiting examples of sulphon include ethane sulphone, propane sulphone, butane sulphone, ethene sulphone, buten sulphone, propene sultone, and the like.

[Chemical Formula 12]

[Chemical Formula 13]

[Chemical Formula 14]

(Wherein R ₁₃ and R ₁₄ each independently represent a hydrogen atom, a halogen atom, a C 1 -C 10 alkyl group, a C 2 -C 10 alkenyl group, a halogen-substituted C 1 -C 10 alkyl group, or a halogen A substituted C2-C10 alkenyl group).

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the electrolyte is preferably lithium difluoroarsalate borate (LiFOB), lithium bis oxalate borate (LiB (C ₂ O ₄ ) ₂ , LiBOB) (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallylsulfonate the composition may further comprise an additive selected from the group consisting of diallyl sulfonate, ethane sultone, propane sultone (PS), butane sultone, ethene sultone, butene sultone and propensulfone (PRS) (LiB (C ₂ O ₄ ) ₂ , LiBOB), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfite, ethane sulphone, propane s ultor, PS). < / RTI >

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the content of the additive is not particularly limited, but is preferably 0.1 to 5% by weight based on the total weight of the electrolyte to improve battery life in the electrolyte of the secondary battery 0.1 to 3% by weight.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may include a carbonate, an ester, an ether, or a ketone, or a mixed solvent thereof, but may include a cyclic carbonate solvent, a linear carbonate solvent, And a mixed solvent thereof. It is most preferable to use a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent. The cyclic carbonate solvent has a large polarity, which can sufficiently dissociate lithium ions, but has a disadvantage in that the ion conductivity is low due to the high viscosity. Therefore, by using a linear carbonate solvent having a low polarity but a low viscosity in the cyclic carbonate solvent, the characteristics of the lithium secondary battery can be optimized.

The cyclic carbonate solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluorethylene carbonate, and mixtures thereof. The linear carbonate solvent may be selected from the group consisting of dimethyl carbonate, Diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof.

In the electrolyte for a lithium secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a cyclic carbonate solvent and a linear carbonate solvent, wherein the volume ratio of the linear carbonate solvent: cyclic carbonate solvent is 1 to 9: , Preferably in a volume ratio of 1.5 to 4: 1.

In the electrolyte for a high-voltage lithium secondary battery according to an embodiment of the present invention, the lithium salt is not limited to LiPF ₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , _{LiN (CF 3 SO 2) 2} , LiN (SO 3 C 2 F 5) 2, LiN (SO 2 F) 2, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiC 6 H 5 SO 3, LiSCN, LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) wherein x and y are natural numbers, LiCl, LiI and LiB (C ₂ O ₄ ) ₂ Or one or more selected from the group consisting of

The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M, and more preferably in the range of 0.7 to 1.6 M. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte is lowered to deteriorate the performance of the electrolyte. If the concentration exceeds 2.0 M, the viscosity of the electrolyte increases and the lithium ion mobility decreases. The lithium salt acts as a source of lithium ions in the battery, thereby enabling operation of a basic lithium secondary battery.

The lithium secondary battery electrolyte of the present invention is stable in a temperature range of -20 ° C to 60 ° C and maintains electrochemically stable characteristics even in a voltage range of 4.4V, so that it is applicable to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries .

The present invention also provides a lithium secondary battery comprising the lithium secondary battery electrolyte.

Non-limiting examples of the secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

The lithium secondary battery produced from the lithium secondary battery according to the present invention exhibits a high temperature storage efficiency of 75% or more and at the same time, when the battery is allowed to stand at a high temperature for a long time, the thickness increase rate of the battery is 1 to 20%, preferably 1 to 15% .

The lithium secondary battery of the present invention includes a positive electrode and a negative electrode.

The positive electrode includes a positive electrode active material capable of intercalating and deintercalating lithium ions, and the positive electrode active material is preferably a composite metal oxide of lithium and at least one selected from cobalt, manganese, and nickel. In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Sr, V, and a rare earth element. Specific examples of the positive electrode active material may include a compound represented by any one of the following formulas:

Li _a A _1-b B _b D ₂ wherein, in the formula, 0.90? A? 1.8, and 0? B? 0.5; Li _a E _1-b B _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The negative electrode includes a negative electrode active material capable of intercalating and deintercalating lithium ions. Examples of the negative electrode active material include carbon materials such as crystalline carbon, amorphous carbon, carbon composite and carbon fiber, lithium metal, an alloy of lithium and other elements . Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 ° C. or lower, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an interplanar distance of 3.35 to 3.38 angstroms and a crystallite size (Lc) of at least 20 nm by X-ray diffraction. Other elements constituting the alloy with lithium may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The anode or the cathode can be produced by dispersing an electrode active material, a binder and a conductive material, and if necessary, a thickening agent in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and copper or a copper alloy may be used as the negative electrode current collector. The anode current collector and the anode current collector may be in the form of a foil or a mesh.

The binder is a substance that acts as a paste for the active material, mutual adhesion of the active material, adhesion to the current collector, buffering effect on the expansion and contraction of the active material, and the like. Examples of the binder include polyvinylidene fluoride (PVdF), polyhexafluoro (PVdF / HFP)), poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methyl methacrylate) Acrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesive force between the electrode active material and the current collector is insufficient. If the content of the binder is too large, the adhesive force is improved but the content of the electrode active material is reduced accordingly.

The conductive material is used for imparting conductivity to the electrode. Any conductive material may be used without causing any chemical change in the battery. Examples of the conductive material include a graphite conductive agent, a carbon black conductive agent, a metal or metal compound system And at least one selected from the group consisting of a conductive agent may be used. Examples of the graphite based conductive agent include artificial graphite and natural graphite. Examples of the carbon black conductive agent include acetylene black, ketjen black, denkablack, thermal black, channel black and the like. Examples of metal or metal compound conductive agents include perovskite such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , LaSrMnO ₃ , There is material. However, the present invention is not limited to the conductive agents listed above.

The content of the conductive agent is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive agent is less than 0.1% by weight, the electrochemical characteristics are deteriorated, and when it exceeds 10% by weight, the energy density per weight is decreased.

The thickening agent is not particularly limited as long as it can serve to control the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and the like can be used.

As the solvent in which the electrode active material, the binder, the conductive material and the like are dispersed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The lithium secondary battery of the present invention may include a separator for preventing a short circuit between the positive electrode and the negative electrode and providing a passage for lithium ion. Examples of the separator include a polypropylene, a polyethylene, a polyethylene / polypropylene, a polyethylene / polypropylene / Polyolefin-based polymer membranes such as polyethylene, polypropylene / polyethylene / polypropylene, or multi-membranes thereof, microporous films, woven fabrics and nonwoven fabrics can be used. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The lithium secondary battery of the present invention may have other shapes such as a cylindrical shape, a pouch shape, and the like.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples. The electrolyte solution can be formed by dissolving the lithium salt in the basic solvent so that the lithium salt such as LiPF ₆ becomes 1 mole (1M) concentration in order to obtain the lithium ion concentration of 1 mole (1M) .

[Preparation Example 1] Synthesis of diphenyl oxalate (hereinafter referred to as 'PEA36')

Phenol (9.88 g) and triethylamine (10.6 g) were added to dichloromethane (100 mL) under a nitrogen atmosphere, and the mixture was stirred at 0 ^° C for 30 minutes. Oxalyl chloride (6.35 g) was slowly added dropwise to the cooled solution for 30 minutes, and the reaction solution was stirred at room temperature for 2 hours. The organic solution was washed twice with a 1N aqueous hydrochloric acid solution (50 mL), and the organic solution was washed twice with a saturated aqueous solution of sodium hydrogencarbonate (50 mL). The washed layer was dried over anhydrous magnesium sulfate, and then filtered to remove magnesium sulfate. The filtrate was distilled under reduced pressure to remove the solvent, and recrystallized from hexane and ethyl acetate to obtain diphenyl oxalate (8.48 g).

_{^{1 H NMR (CDCl 3, 500}} MHz): δ 7.44 (t, J = 8.0 Hz, 4H), 7.31 (t, J = 7.6 Hz, 2H), 7.26 (d, J = 8.0 Hz, 4H)

[Preparation Example 2] Synthesis of diallyl oxalate (hereinafter referred to as 'PEA47')

Allyl alcohol (6.10 g) and triethylamine (10.6 g) were added to dichloromethane (100 mL) under a nitrogen atmosphere, and the mixture was stirred at 0 ^° C for 30 minutes. Oxalyl chloride (6.35 g) was slowly added dropwise to the cooled solution for 30 minutes, and the reaction solution was stirred at room temperature for 2 hours. The organic solution was washed twice with a 1N aqueous hydrochloric acid solution (50 mL), and the organic solution was washed twice with a saturated aqueous solution of sodium hydrogencarbonate (50 mL). The washed layer was dried over anhydrous magnesium sulfate, and then dried to remove magnesium sulfate. The filtrate was distilled under reduced pressure to obtain diallyl oxalate (5.53 g).

_{^{1 H NMR (CDCl 3, 500}} MHz): δ 4.78 (ddd, J = 1.2, 1.3, 6.1 Hz, 4H), 5.32-5.35 (m, 2H), 5.42 (ddt, J = 1.3, 1.4, 17.0 Hz, 2H), 5.97 (ddt, J = 6.1, 10.5, 17.0 Hz, 2H).

[Production Example 3] Synthesis of dibenzyl oxalate (hereinafter referred to as 'PEA55')

Benzyl alcohol (11.4 g) and triethylamine (10.6 g) were added to dichloromethane (100 mL) under a nitrogen atmosphere, and the mixture was stirred at 0 ^° C for 30 minutes. To the cooled solution oxalyl chloride (6.35 g) was slowly added dropwise over 30 minutes and the reaction solution was stirred at ambient temperature for 2 hours. The organic solution was washed twice with a 1N aqueous hydrochloric acid solution (50 mL), and the organic solution was washed twice with a saturated aqueous solution of sodium hydrogencarbonate (50 mL). The washed organic layer was dried over anhydrous magnesium sulfate, and then filtered to remove magnesium sulfate. The filtered solution was distilled under reduced pressure to remove the solvent, and recrystallized from hexane and ethyl acetate to obtain dibenzyl oxalate (9.73 g).

¹ H NMR (CDCl ₃ , 500 MHz):? 7.46-7.36 (m, 10H), 5.32 (s, 4H).

[Production Example 4] Dimethyl oxalate (hereinafter referred to as &quot; &Quot; PEA35 &quot;)

Methanol (3.36 g) and triethylamine (10.6 g) were added to dichloromethane (100 mL) under a nitrogen atmosphere, and the mixture was stirred at 0 ^° C for 30 minutes. Oxalyl chloride (6.35 g) was slowly added dropwise to the cooled solution for 30 minutes, and the reaction solution was stirred at room temperature for 2 hours. The organic solution was washed twice with a 1N aqueous hydrochloric acid solution (50 mL), and the organic solution was washed twice with a saturated aqueous solution of sodium hydrogencarbonate (50 mL). The washed layer was dried over anhydrous magnesium sulfate, and then filtered to remove magnesium sulfate. The filtered solution was distilled under reduced pressure to remove the solvent, and recrystallized from diethyl ether and petroleum ether to obtain dimethyl oxalate (4.13 g).

_{^{1 H NMR (CDCl 3, 500}} MHz): δ 3.58 (s, 6H)

[Examples 1-7 and Comparative Example 1-3]

The electrolyte solution was prepared by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a volume ratio of 3: 7 to prepare a 1.0 M solution. The resulting solution was dissolved in a basic electrolyte (1M LiPF ₆ , EC / EMC = 3 : 7) were further added with the components listed in Table 1 below.

A battery to which the non-aqueous electrolytic solution was applied was prepared as follows.

LiNiCoMnO ₂ and LiMn ₂ O ₄ were mixed as a cathode active material at a weight ratio of 1: 1, and polyvinylidene fluoride (PVdF) as a binder and carbon as a conductive agent were mixed at a weight ratio of 92: 4: 4, Methyl-2-pyrrolidone to prepare a positive electrode slurry. This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode. Styrene-butadiene rubber as a binder and carboxymethylcellulose as a thickener were mixed in a weight ratio of 96: 2: 2 and then dispersed in water to prepare a negative electrode active material slurry. This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode.

A film separator made of polyethylene (PE) having a thickness of 25 탆 was stacked between the prepared electrodes to form a cell using a pouch having a size of 8 mm × 270 mm × 185 mm in size , And the above non-aqueous electrolyte solution was injected to prepare a 25Ah-class lithium secondary battery for EV.

The performance of the 25Ah battery for EV thus manufactured was evaluated as follows. The evaluation items are as follows.

* Evaluation Items *

1. -20 ℃ 1C Discharge Capacity: 25A at room temperature, 4.2V CC-CV for 3 hours, then left at -20 ℃ for 4 hours, then 25A current, (%) Were measured.

2. Recovery rate at 60 ° C for 30 days: 4.2V at room temperature, 3 hours at 25A CC-CV, after 60 days at 30 ° C, 25% recovery, Were measured.

3. Thickness increase rate after 60 days at 60 ° C: 4.2 V at room temperature and 3 hours at 25 A CC-CV. The thickness of the battery was defined as A, and the battery was sealed at 60 ° C. and atmospheric pressure for 30 days When the thickness of the neglected cell is denoted by B, the increase rate of the thickness is calculated as follows.

[Formula 1]

(B-A) / A x 100 (%)

4. Normal-temperature life: After charging for 3 hours at 4.2V and 50A CC-CV at room temperature, discharge is repeated 500 times up to 2.7V with current of 2.7V and 25A. At this time, the first discharge capacity was denoted by C, and the 300th discharge capacity was divided by the first discharge capacity to calculate the capacity retention rate during the lifetime.

As shown in Table 1, the lithium secondary battery including the lithium secondary battery according to the present invention exhibited a capacity recovery rate of 75% or more even after 30 days at 60 ° C, and the rate of thickness increase was as low as 3 to 18% have.

On the other hand, Comparative Example 1, which did not include the oxalate derivative of the present invention, showed a low capacity recovery rate of 37% and a high cell growth rate of 30%, indicating a very low stability at high temperatures.

In addition, the secondary battery employing the secondary battery electrolyte containing PEA 35, which is an oxalate derivative different in structure from the present invention, had a high temperature capacity recovery rate of 27% and a low temperature discharge capacity, and even when further additives were added thereto, High temperature and low temperature characteristics.

For example, oxalate derivatives of PEA36, PEA47 and PEA55 of the present invention may be prepared by reacting oxalate derivatives substituted with oxalate derivatives upon reduction and decomposition on the surface of the anode, It is considered that the fluorine functional group forms a stable SEI layer in a solid form, thereby greatly reducing the internal resistance of the cell, thereby greatly improving the low temperature and high temperature performance of the cell.

On the other hand, in the case of PEA35, which is a comparative example of the present invention, a compound in which oxalate structure is not substituted with fluorine, and the methyl functional group substituted with an oxalate derivative is decomposed into gas components such as CO and CO ₂ So that a stable polymer film can not be formed on the surface of the cathode.

Accordingly, the oxalate derivative in which at least one fluoro group of the present invention is substituted has at least one fluoro group, and more preferably at least one trifluoro group, to the oxalate derivative, so that the oxalate derivative has better high temperature and low temperature characteristics.

In addition, the electrolytic solution of the secondary battery of the present invention can be prepared by mixing the oxalate derivative represented by the formula (1) of the present invention with lithium bis oxalate borate (LiB (C ₂ O ₄ ) ₂ , LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate VEC), ethylene sulfite, ethane sultone, and propane sultone (PS), it is possible to further improve the high temperature storage stability, the low temperature discharge capacity and the life characteristics, A lithium secondary battery including a battery electrolyte has extremely high efficiency, stability, and lifetime characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. And various modifications may be made to the invention. Therefore, modifications of the embodiments of the present invention will not depart from the scope of the present invention.

Claims (14)

Lithium salts;
Non-aqueous organic solvent; And
An oxalate derivative represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]

(In the formula 1,
R ¹ or R ² independently from each other are (C 2 -C 10) alkenyl, (C 2 -C 10) alkynyl or (C 6 -C 12) aryl;
n or m are each independently an integer of 0 to 5;
The alkenyl, alkynyl or aryl of R ¹ or R ² may be further substituted with cyano, hydroxy, trifluoromethyl, (C 1 -C 10) alkyl, or (C 6 -C 12) aryl. The method according to claim 1,
Wherein the formula (1) is represented by the following formula (2) or (3).
(2)

(3)

(In the above formula (2) or (3)
A or B independently of one another

or

Lt;
R ³ or R ⁴ independently from each other are hydrogen or (C 1 -C 10) alkyl;
R ¹¹ or R ¹² independently from each other are hydrogen, cyano, hydroxy, trifluoromethyl, (C 1 -C 10) alkyl, or (C 6 -C 12) aryl;
n or m are each independently an integer of 0 to 5;
o or p independently of one another is an integer of 1 to 5.) 3. The method of claim 2,
R ³ or R ⁴ independently from each other are hydrogen;
and n or m are independently an integer of 0 to 1. The method according to claim 1,
Wherein the formula (1) is selected from the following structures.
The method according to claim 1,
Wherein the oxalate derivative is contained in an amount of 1 to 5% by weight based on the total weight of the electrolytic solution. The method according to claim 1,
Wherein the electrolytic solution further comprises at least one additive selected from the group consisting of an oxalate borate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound, and a sulfinyl group-containing compound. The method according to claim 6,
The electrolytic solution may be at least one selected from the group consisting of lithium difluoroarsalate borate (LiFOB), lithium bis oxalate borate (LiB (C ₂ O ₄ ) ₂ , LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate, ethane sultone, propane sultone (PS), butane Wherein the electrolyte further comprises an additive selected from the group consisting of butane sultone, ethene sultone, butene sultone, and propene sultone (PS). The method according to claim 6,
Wherein the additive is contained in an amount of 0.1 to 5.0% by weight based on the total weight of the electrolytic solution. The method according to claim 1,
The non-aqueous organic solvent is selected from cyclic carbonate-based solvents, linear carbonate-based solvents, and mixed solvents thereof. 10. The method of claim 9,
Wherein the cyclic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluorethylene carbonate and mixtures thereof, and the linear carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, A secondary battery electrolyte selected from the group consisting of carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof. 10. The method of claim 9,
Wherein the non-aqueous organic solvent has a mixing volume ratio of linear carbonate solvent: cyclic carbonate solvent of 1 to 9: 1. The method according to claim 1,
Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₃ C ₂ F ₅ ) ₂ , _{LiN (SO 2 F) 2,} LiCF 3 SO 3, LiC 4 F 9 SO 3, LiC 6 H 5 SO 3, LiSCN, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, and LiB (C ₂ O ₄ ) ₂ . The method according to claim 1,
Wherein the lithium salt is present in a concentration of from 0.1 to 2.0 M. A lithium secondary battery comprising a secondary battery electrolyte according to any one of claims 1 to 13.