ES2986008T3 - Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolytic solution for a lithium secondary battery and a lithium secondary battery, and in particular, to a non-aqueous electrolytic solution for a lithium secondary battery, which includes an additive having metal ion adsorption capacity and capable of forming a stable ion conductive film on the surface of an electrode, and to a lithium secondary battery in which an abnormal voltage drop phenomenon is improved by the inclusion thereof. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery including the same

Technical field

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery and to a lithium secondary battery including the same.

Background of the technique

In line with the trends of miniaturization, light weight, thin profile and portable in electronic devices as per the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased.

Lithium secondary batteries, specifically lithium-ion batteries (LIBs), as batteries that can best meet the need, have been adopted as power sources for many portable devices due to their high energy density and ease of design.

Recently, a lithium secondary battery, which can maintain excellent performance not only at room temperature but also in a harsher outdoor environment such as high temperature or low temperature environment, is required as the scope of lithium secondary batteries used has been expanded from conventional small electronic devices to large electronic devices, cars or smart grids.

A currently used lithium secondary battery consists of a carbon-based negative electrode capable of intercalation and deintercalation of lithium ions, a positive electrode formed by a lithium-containing oxide, and a non-aqueous electrolyte solution in which an appropriate amount of a lithium salt is dissolved in a carbonate-based mixed organic solvent, in which charging and discharging may be possible, because lithium ions, which are deintercalated from the positive electrode by charging, transfer energy while a phenomenon is repeated in which lithium ions are intercalated into the negative electrode, e.g., carbon particles, and deintercalated during discharge.

Metal ions dissolve from the surface of the positive electrode while the active material of the positive electrode structurally collapses as the charging and discharging of the secondary lithium battery proceeds. The dissolved metal ions are electrodeposited on the negative electrode to degrade the negative electrode. The degradation phenomenon tends to be further accelerated when the potential of the positive electrode is increased or the battery is exposed to high temperatures.

To address this limitation, a method has been suggested to add compounds capable of forming a protective layer such as a solid-electrolyte interface (SEI) on the negative electrode surface in the non-aqueous electrolyte solution.

However, there may be a case where the overall performance of the secondary battery is degraded due to the additives in the electrolyte solution causing other side effects.

Therefore, there is a continuing need to develop a non-aqueous electrolyte solution containing an additive that can improve battery performance and stability while minimizing side effects.

JP 2011 238373 A describes an electrolytic solution containing at least one of dicarbonate ester compound, dicarboxylic acid compound, lithium monofluorophosphate and lithium difluorophosphate and at least one of unsaturated oxalic acid compound and unsaturated sulfonic acid compound. EP 2830 142 A1 describes a non-aqueous electrolytic solution prepared by dissolving an electrolyte salt in a non-aqueous solvent, wherein the non-aqueous electrolytic solution includes LiPF2(-OC(=O)-C(=O)O-)2 and at least one kind of a compound having a carbon-carbon triple bond represented by the following general formula (I):

wherein R1 and R2 each independently represent a hydrogen atom or an alkyl group having from 1 to 6 carbon atoms and optionally substituted with a halogen atom; and R3 represents a methyl group or an ethyl group, and X represents a hydrogen atom or -CR1R2-OS(=O)2-R3. US 6479 191 B1 describes an electrolyte for a lithium secondary battery comprising (i) a non-aqueous solvent, (ii) an electrolyte salt, and (iii) an alkyne derivative or an alkyne carbonate derivative. EP 2768 064 A1 relates to an electrolyte composition containing (i) at least one aprotic organic solvent, (ii) at least one conductive salt, (iii) at least one alkyne compound of a specific formula, and (iv) optionally at least one additional additive. JP 2000 195545 A describes an electrolyte solution containing at least one of alkyne derivatives represented by three different formulae. US 2018/301758 A1 describes a non-aqueous electrolyte solution obtained by dissolving an electrolyte salt in a non-aqueous solvent, and characterized by containing 0.1-4% by mass of 1,3-dioxane in the non-aqueous electrolyte solution, while additionally containing 0.1-4% by mass of a compound having a carbon-carbon triple bond represented by a specific formula.

Prior art document

Japanese Patent Application Laid-Open Publication No. 2007-066864

Disclosure of the invention

Technical problem

One aspect of the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery that includes an additive having metal ion adsorption capacity and capable of forming a stable ion-conducting film on the surface of an electrode.

Another aspect of the present invention provides a lithium secondary battery in which an abnormal voltage drop phenomenon is improved by including the dissolution of non-aqueous electrolyte for a lithium secondary battery.

Technical solution

In accordance with one aspect of the present invention, there is provided a non-aqueous electrolyte solution for a lithium secondary battery including:

a lithium salt;

an organic solvent;

a compound represented by formula 1 as the first additive;

lithium difluorophosphate (LiPO2F2, hereinafter referred to as “LiDFP”) as a second additive, and

tetravinylsilane as a third additive,

wherein the first additive and the second additive are each independently included in an amount of 0.01% by weight to 8.5% by weight based on the total amount of the non-aqueous electrolyte solution.

(Formula 1)

Ri to R3 are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, and

A is,

wherein R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, or -O-R5; and

R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms.

Specifically, the substituted alkyl group having 1 to 6 carbon atoms is an alkyl group having 1 to 6 carbon atoms that is substituted with at least one halogen element or an alkyl group having 1 to 6 carbon atoms is substituted with an alkyl group having 1 to 3 carbon atoms, wherein the halogen element is preferably fluorine.

Furthermore, the substituted aryl group having 6 to 12 carbon atoms is a phenyl group substituted with at least one halogen element or a phenyl group substituted with an alkyl group having 1 to 3 carbon atoms, wherein the halogen element is preferably fluorine. The unsubstituted aryl group having 6 to 12 carbon atoms is a phenyl group.

Furthermore, the compound represented by formula 1, as a first additive, may include at least one selected from the group consisting of the compounds represented by formulas 1j to 1p. According to the disclosure, the non-aqueous electrolyte solution may also include at least one additional additive selected from the group consisting of the compounds represented by formulas 1a to 1i.

(Formula 1a)

(Formula 1d)

(Formula 1i)

(Formula 1j)

(Formula 1)

The compound represented by formula 1, as a first additive, may be included in an amount of 0.1% by weight to 7% by weight, for example, 0.1% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.

Lithium difluorophosphate, as a second additive, is included in an amount of 0.1% by weight to 7% by weight, for example, 0.1% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte solution for a lithium secondary battery.

The non-aqueous electrolyte solution also includes tetravinylsilane as a third additive.

In accordance with another aspect of the present invention, there is provided a lithium secondary battery including the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

Beneficial effects

According to the present invention, a non-aqueous electrolyte solution, which can form a film having excellent stability on a surface of an electrode and can suppress a side effect in a battery caused by metal ions from the positive electrode or metallic foreign matter that can be included in the preparation process, can be prepared by including a propargyl group-containing compound having metal ion adsorption capability, as a first additive, and a second additive in the form of a salt, such as lithium difluorophosphate (LiDFP). Furthermore, a lithium secondary battery in which an abnormal voltage drop phenomenon during high temperature storage is improved and cycle life duration characteristics and high temperature storage performance are improved even during high voltage charging can be prepared by including the non-aqueous electrolyte solution.

Mode for carrying out the invention

Hereinafter, the present invention will be described in more detail.

It will be understood that expressions or terms used in the specification and claims are not to be construed as having the meaning defined in commonly used dictionaries. It will further be understood that expressions or terms are to be construed as having a meaning which is consistent with their meaning in the context of the relevant art and the technical idea of the invention, based on the principle that an inventor may appropriately define the meaning of expressions or terms to best explain the invention. It will further be understood that the terms “include,” “comprises,” or “has,” when used in this specification, specify the presence of mentioned features, numerals, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numerals, steps, elements, or combinations thereof.

Before describing the present invention, the terms “a” and “b” in the description of “a to b carbon atoms” in the specification each indicate the number of carbon atoms included in a specific functional group. That is, the functional group may include “a” to “b” carbon atoms. For example, the term “alkyl group having 1 to 5 carbon atoms” indicates an alkyl group including 1 to 5 carbon atoms, that is, -CH3, -CH2CH3, -CH2CH2CH3, -CH2(CH2)CH3, -CH(CH2)C H and -CH(CH2)CH2CH3.

Furthermore, in the present specification, the term “aryl group” indicates a functional group in which a hydrogen atom is abstracted from an aromatic hydrocarbon group, wherein the aryl group includes a phenyl group, a tolyl group, a xylene group or a naphthyl group.

Furthermore, unless otherwise defined in the specification, the term “substitution” indicates that at least one hydrogen bonded to the carbon is replaced by an element other than hydrogen, for example, an alkyl group having 1 to 5 carbon atoms or at least one fluorine atom.

Furthermore, in this specification, the expression “%” indicates % by weight unless explicitly stated otherwise.

In general, when overcharging of a secondary battery occurs, the structure of a positive electrode active material becomes unstable while an excessive amount of lithium ions is discharged from a positive electrode. As a result, oxygen is released from the positive electrode active material, and the released oxygen causes a decomposition reaction of an electrolyte solution. The dissolution of metallic foreign matter, such as cobalt (Co), manganese (Mn), and nickel (Ni), from the positive electrode active material is increased by the structural collapse of the positive electrode active material and a secondary reaction with the electrolyte solution, and the dissolved metallic foreign matter moves to a negative electrode and precipitates as dendrites on a surface of the negative electrode to cause a micro short circuit between the positive electrode and the negative electrode. The overall performance of the battery is degraded while an abnormal voltage drop phenomenon, in which the battery voltage is reduced, occurs due to the short circuit. In this case, the low voltage phenomenon may also be caused by metallic foreign matter that is included in the raw materials of the lithium battery or incorporated in a preparation process.

In the present invention, to improve these limitations, there is provided a non-aqueous electrolyte solution which includes a compound, which performs a passivation function to prevent dissolved metallic foreign matter from growing on the surface of the negative electrode as dendrites by adsorbing metal ions, as a first additive, and a compound capable of forming a film having improved thermal stability on the surface of the electrode as a second additive.

Furthermore, in the present invention, there is provided a lithium secondary battery in which the abnormal voltage drop phenomenon during high temperature storage is improved and the cycle life duration characteristics and high temperature storage performance are improved even during high voltage charging including non-aqueous electrolyte dissolution.

Non-aqueous electrolyte solution

Specifically, a non-aqueous electrolyte solution for a lithium secondary battery is provided including:

a lithium salt;

an organic solvent;

a compound represented by formula 1 as the first additive;

lithium difluorophosphate (LiDFP) as a second additive, and

tetravinylsilane as a third additive,

wherein the first additive and the second additive are each independently included in an amount of 0.01% by weight to 8.5% by weight based on the total amount of the non-aqueous electrolyte solution.

(Formula 1)

R1 to R3 are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, and

A is,

wherein R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, or -O-R5; and R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms.

Specifically, the substituted alkyl group having 1 to 6 carbon atoms is an alkyl group having 1 to 6 carbon atoms that is substituted with at least one halogen element or an alkyl group having 1 to 6 carbon atoms that is substituted with an alkyl group having 1 to 3 carbon atoms, wherein the halogen element is preferably fluorine.

Furthermore, the substituted aryl group having 6 to 12 carbon atoms is a phenyl group substituted with at least one halogen element or a phenyl group substituted with an alkyl group having 1 to 3 carbon atoms, wherein the halogen element is preferably fluorine. The unsubstituted aryl group having 6 to 12 carbon atoms is a phenyl group.

(1) Lithium salt

First, in the non-aqueous electrolyte solution for a secondary battery according to the embodiment of the present invention, any lithium salt normally used in an electrolyte solution for a lithium secondary battery can be used as the above lithium salt without limitation, and, for example, the lithium salt may include Li+ as a cation, and may include at least one selected from the group consisting of F-, Cl-, Br-, I-, NO3", N(CN)2-, BF4-, ClO4-, B1cCl1c-, AlO4-, AlCl4-, PF6-, SbF6-, AsF6-, BF2C2O4-, BC4O8-, PF4C2O4-, PF2C4O8-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-, CF3SO3-, C4F9SO3-, CF3CF2SO3-, ^ S O ^ N -, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN- and (CF3CF2SO2)2N- as anion. Specifically, the lithium salt may include a single material selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB10Cl10, L iA O LiAlCU, LiPF6, LiSbF6, LiAsF6, UCF3SO3, UCF3CO2, UCH3CO2, lithium bisperfluoroethanesulfonimide (LiBETI, LiN(SO2CF2CF3)2), lithium fluorosulfonylimide (LiFSI, LiN(SO2F)2) and lithium (bis)trifluoromethanesulfonimide (LiTFSI, LiN(SO2CF3)2) or a mixture of two or more thereof. Furthermore, the lithium salt may specifically include a single material selected from the group consisting of LiPF6, LiBF4, UCH3CO2, LiCF3CO2, LiFSI, LiTFSI and LiBETI, or a mixture of two or more thereof. However, the lithium salt does not include LiDFP, as the lithium salt of the second additive.

Lithium salt can be appropriately changed within a normally usable range, but can be included in a concentration of 0.1M to 3M, for example, 0.8M to 2.5M in the electrolyte solution. In a case where the concentration of lithium salt is 0.1M or less, the cycle life characteristics and capacity characteristics of the secondary lithium battery may be degraded, and in a case where the concentration of lithium salt is more than 3M, the film-forming effect may be relatively reduced. (2) Organic solvent

The organic solvent is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the secondary battery and can exhibit desired characteristics with the additive. For example, an ether-based solvent, an ester-based solvent, or an amide-based solvent can be used alone or as a mixture of two or more of them.

As the ether-based solvent among the organic solvents, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or a mixture of two or more thereof can be used, but the present invention is not limited thereto.

Furthermore, the ester-based solvent may include at least one compound selected from the group consisting of a cyclic carbonate compound, a linear carbonate compound, a linear ester compound, and a cyclic ester compound.

Among these compounds, specific examples of the cyclic carbonate compound may be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene carbonate (FEC), or a mixture of two or more thereof.

Furthermore, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, or a mixture of two or more thereof, but the present invention is not limited thereto.

Specific examples of the linear ester compound may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, or a mixture of two or more thereof, but the present invention is not limited thereto.

Specific examples of the cyclic ester compound may be any one selected from the group consisting of y-butyrolactone, y-valerolactone, y-caprolactone, a-valerolactone and s-caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

Particularly, among the ester-based solvents, since the cyclic carbonate-based compound dissociates lithium salt well in the electrolyte due to the high permittivity as a highly viscous organic solvent. Therefore, an electrolyte solution having high electrical conductivity can be prepared when the above cyclic carbonate-based compound is mixed with the low-viscosity and low-permittivity linear carbonate-based compound such as dimethyl carbonate and diethyl carbonate in an appropriate ratio and used.

(3) First additive

Furthermore, the non-aqueous electrolyte solution of the present invention includes a compound represented by formula 1 as a first additive.

That is, since the compound represented by Formula 1, which is included as the first additive, includes both (i) a propargyl group having a triple bond known to have metal ion adsorption capability and (ii) an oxygen atom in its structure, the compound represented by Formula 1 can be easily adsorbed on metallic foreign matter such as iron (Fe), Co, Mn and Ni dissolved from the positive electrode or metallic foreign matter such as copper (Cu) dissolved from the negative electrode during charging and discharging, or metallic foreign matter incorporated from raw materials or in the preparation process. As a result, since the compound represented by Formula 1 can suppress the growth of dissolved metallic foreign matter to give dendrites at the negative electrode, the anomalous phenomenon of voltage drop during high temperature storage due to dissolved metallic foreign matter can be improved.

Furthermore, since the compound represented by Formula 1 containing the propargyl group can be reduced on the surface of the negative electrode to form a stable ionic conductive film on the surface of the negative electrode when a predetermined voltage is reached during charging and discharging, a further decomposition reaction of the electrolyte solution can be suppressed, and furthermore, the anomalous voltage drop phenomenon of the secondary battery, the cycle life duration characteristics and the high temperature storage performance can be improved by facilitating the intercalation and deintercalation of lithium ions into and from the negative electrode even during overcharging or high temperature storage.

The compound represented by formula 1, which is included as a first additive, may be at least one selected from the group consisting of the compounds represented by formulas 1j to 1p. According to the disclosure, the non-aqueous electrolyte solution may also include at least one additional additive selected from the group consisting of the compounds represented by formulas 1a to 1i.

(Formula 1a)

(Formula 1f)

(Formula 1m)

Specifically, the compound represented by formula 1 may be at least one selected from the group consisting of the compounds represented by formulas 1a to 1f (which are not part of the claimed subject matter).

That is, since the compounds represented by formulas 1a to 1f contain a “-OCO2R4” group having a smaller size than that of a sulfonate anion contained in the compounds represented by formulas 1j to 1l, the reactivity with a carbonate-based organic solvent such as ethylene carbonate is improved while the aggressiveness of the anions is increased. Therefore, the compounds represented by formulas 1a to 1f can form a passivation film having higher stability on the electrode surface compared with the compounds represented by formulas 1j to 1l. Furthermore, with respect to the compounds represented by formulas 1m to 1p containing an -OSO2-OR5 group in which an oxygen-containing alkoxide group (-OR5), as an electron-withdrawing group, is bonded to an “-OSO2-” group, since the reduction decomposition is simpler, the compounds represented by formulas 1m to 1p can form a film having higher stability compared with the compounds represented by formulas 1j to 1l in which ‘W, which is a functional group providing a delocalized negative charge not containing oxygen, is directly bonded to the “OSO2” group.

The compound represented by formula 1, as a first additive, is included in an amount of 0.01% by weight to 8.5% by weight, and may be particularly included in an amount of 0.1% by weight to 7% by weight, more particularly 0.1% by weight to 5% by weight, and most particularly 0.5% by weight to 3% by weight based on the total amount of the non-aqueous electrolyte solution.

Since the compound represented by Formula 1 is included in an amount within the above range, a secondary battery having a more improved overall performance can be prepared. For example, when the amount of the first additive is less than 0.01% by weight, the effect of improving the anomalous voltage drop phenomenon may be negligible. Specifically, when the amount of the first additive is 0.1% by weight or more, for example, 0.5% by weight or more, a stabilizing effect or a dissolution suppression effect during the formation of an electrolyte-solid interface (SEI) can be obtained while suppressing an increase in resistance as much as possible, and when the amount of the additive is 7% by weight or less, for example, 5% by weight or less, the maximum dissolution suppression effect can be obtained within the increase in resistance that can be accommodated.

Normally, in a lithium secondary battery, a kind of passivation layer is formed at a position where surface bonding exists on a positive electrode of the battery or an activated position during charging and discharging by an electrochemical oxidation decomposition reaction of an electrolyte solution. The passivation layer increases the impedance for the co-intercalation of lithium ions into a positive electrode active material. In addition, during repeated charge and discharge cycles, structural collapse of LiCoO2, LiMn2O4 or LiNiO2, as a positive electrode active material, or a chemical dissolution reaction by electrolyte dissolution occurs so that foreign matters of cobalt (Co), manganese (Mn), nickel (Ni), iron (Fe) and aluminum (Al) are dissolved from the positive electrode active material. These reactions not only lead to a degradation of the performance of the positive electrode itself, but also cause a phenomenon in which dissolved metallic foreign matters are precipitated and electrodeposited on the surface of a negative electrode. Furthermore, since the metallic foreign matter electrodeposited on the negative electrode reduces the mobility of lithium ions while exhibiting high reactivity toward electrolyte dissolution, an irreversible reaction is enhanced upon charge and discharge due to a reduction in the amount of lithium, and as a result, the capacity and charge and discharge efficiency of the battery are reduced.

Typically, a method has been proposed in which the dissolution of metallic foreign matter present in the battery is suppressed by including an additive in the electrolyte solution. However, it is not known how long the suppression reaction by the additive will last, and furthermore, since the suppression effect is reduced over time, the low voltage phenomenon may occur when the dissolution of metallic foreign matter is no longer suppressed. Therefore, in the present invention, the dissolution of metal ions from the positive electrode or the metallic foreign matter, which may be included in the preparation process, can be suppressed, and a stable film can be formed on the surfaces of the negative electrode and the positive electrode by including the compound including a propargyl group having metal ion adsorption capacity, a non-aqueous electrolyte dissolution additive component, as the first additive.

(4) Second additive

An organic film formed on the surface of the positive electrode by the compound represented by formula 1 has a limitation that it is thermally unstable. Therefore, to improve such limitation in the present invention, a film, in which thermal stability is improved by including an inorganic component on the surface of the positive electrode, can be formed by additionally using the second additive in the form of a salt, such as LiDFP, as the second additive component together in the non-aqueous electrolyte solution.

In this case, in the non-aqueous electrolyte solution for a secondary lithium battery according to the present invention, lithium difluorophosphate, as a second additive, is included in an amount of 0.01% by weight to 8.5% by weight, and may be included in an amount particularly of 0.1% by weight to 7% by weight, more particularly of 0.1% by weight to 5% by weight, and most particularly of 0.5% by weight to 3% by weight based on the total weight of the non-aqueous electrolyte solution.

Since the second additive is included in an amount within the above range, since a film having excellent thermal stability can be formed on the electrode surface, the output of the secondary battery can be improved.

If the amount of the second additive is less than 0.01% by weight, the SEI forming effect may be negligible. Specifically, in a case where the second additive is included in an amount of 0.01% by weight or more, for example, 0.1% by weight or more, the electrode surface can be stabilized by an SEI forming process in a lithium ion battery, and the cycle characteristics and capacity characteristics after high temperature storage can be improved. In addition, if the second additive is included in an amount of 7% by weight or less, for example, 5% by weight or less, a side reaction due to the excessive amount of the additive can be suppressed.

(5) Third additive

Furthermore, since the non-aqueous electrolyte solution for a lithium secondary battery according to the present invention further includes tetravinylsilane as a third additive, the tetravinylsilane is bonded with the compound represented by formula 1, as a first additive, to be able to form a stronger double or triple film on the surface of the negative electrode.

The third additive may be included in an amount of 0.01% by weight to 5% by weight, particularly 0.01% by weight to 3% by weight, and more particularly 0.1% by weight to 3% by weight based on the total weight of the non-aqueous electrolyte solution.

In a case where the third additive is included in an amount within the above range, a secondary battery having a more improved overall performance can be prepared. For example, in a case where the third additive is included in an amount of 0.01% by weight or more, there is an effect of improving the durability of the SEI while suppressing the increase in resistance as much as possible, and, in a case where the third additive is included in an amount of 5% by weight or less, there is an effect of long-term maintenance and repair of the SEI within the increase in resistance that can be accommodated.

(6) Fourth additive to form the SEI

Furthermore, to further improve the characteristics of high rate discharge at low temperature, high temperature stability, overcharge protection and a swelling enhancing effect during high temperature storage, the non-aqueous electrolyte solution of the present invention may further include an additive for forming an SEI which can form a more stable ionic conductive film on the electrode surface, if necessary.

Specifically, as a representative example, the additional additive may include at least one additive for forming an SEI that is selected from the group consisting of a sultone-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, a cyclic sulfite-based compound, and a cyclic carbonate-based compound.

The sultone-based compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethane sultone, 1,3-propene sultone (PRS), 1,4-butene sultone and 1-methyl-1,3-propene sultone. The sultone-based compound may be included in an amount of 0.3% by weight to 5% by weight, for example, 1% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte solution. In a case where the amount of the sultone-based compound in the non-aqueous electrolyte solution is more than 5% by weight, since a thick film is formed due to the excessive amount of the additive, degradation of the output and an increase in resistance may occur.

In addition, the halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and may be included in an amount of 5% by weight or less based on the total weight of the non-aqueous electrolyte solution. In a case where the amount of the halogen-substituted carbonate-based compound is more than 5% by weight, the swelling performance of the cell may be deteriorated.

Furthermore, the nitrile-based compound may include at least one compound selected from the group consisting of succinonitrile (NA), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

The nitrile-based compound may be included in an amount of 5% by weight to 8% by weight, for example, 6% by weight to 8% by weight based on the total weight of the non-aqueous electrolyte solution. In a case where the total amount of the nitrile-based compound in the non-aqueous electrolyte solution is more than 8% by weight, since the resistance increases due to an increase in the film formed on the electrode surface, the battery performance may be deteriorated.

Furthermore, the cyclic sulfite-based compound may include ethylene sulfite, methylethylene sulfite, ethylethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethylethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite and 1,3-butylene glycol sulfite, and may be included in an amount of 5% by weight or less based on the total weight of the non-aqueous electrolyte solution. In a case where the amount of the cyclic sulfite-based compound is more than 5% by weight, since a thick film is formed due to the excessive amount of the additive, degradation of output and increase of resistance may occur.

The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the non-aqueous electrolyte solution. In a case where the amount of the cyclic carbonate-based compound in the non-aqueous electrolyte solution is more than 3% by weight, the cell swelling inhibition performance may be deteriorated. Secondary battery

A lithium secondary battery is also provided including the electrolyte solution of the present invention.

The lithium secondary battery of the present invention can be prepared by injecting the non-aqueous electrolyte solution of the present invention into an electrode assembly composed of a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode.

In this case, any positive electrode, negative electrode and separator, which have been commonly used in the preparation of a secondary lithium battery, can be used as the positive electrode, negative electrode and separator constituting the electrode assembly.

(1) Positive electrode

First, the positive electrode can be prepared by forming a positive electrode material mixture layer on a positive electrode collector. The positive electrode material mixture layer can be formed by coating the positive electrode collector with a positive electrode slurry including a positive electrode active material, a binder, a conductive agent and a solvent, and then drying and laminating the coated positive electrode collector.

The positive electrode collector is not particularly limited as long as it has conductivity without causing adverse chemical changes to the battery, and, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel that is surface treated with one of carbon, nickel, titanium, silver, or the like can be used.

The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, wherein the positive electrode active material may specifically include a lithium metal composite oxide including lithium and at least one metal such as cobalt, manganese, nickel or aluminum. Specifically, the lithium-metal composite oxide may include lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxide (e.g., LiCoO2, etc.), lithium-nickel-based oxide (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxide (e.g., LiNh_YMnYO2 (where 0<Y<1), LiMn2-ZNizO4 (where 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (e.g., LiNi-mCoY-^ (where 0<Y1<1), lithium-manganesecobalt-based oxide (e.g., LiCo-i_Y2MnY2O2 (where 0<Y2<1), LiMn2-Z1Coz1O4 (where 0<Z1<2), etc.), lithium-nickel-manganese-cobalt-based oxide (e.g., Li(NipCoqMnri)O2 (where 0<p<1, 0<q<1, 0<r1<1, and p+q+r1=1) or Li(Nip1Coq1Mnr2)O4 (where 0<p1<2, 0<q1<2, 0<r2<2, and p1+q1+r2=2), etc.) or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Nip2Coq2Mnr3MS2)O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and s2 are atomic fractions of each of the independent elements, where 0<p2<1, 0<q2<1, 0<r3<1, 0<S2<1 and p2+q2+r3+S2=1), etc.), and any one of them or two or more compounds thereof may be included. Among these materials, in terms of improving the capacity and stability characteristics of the battery, the lithium-metal composite oxide can include LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (e.g., Li(Nh/3Mn1/3Co1/3)O2, Li(Ni0.6Mn0.2Co0.2)O2, Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2, or Li(Ni0.8Mn0,-iCo0.1)O2), or lithium-nickel-cobalt-aluminum oxide (e.g., LiNi0.8Co0.15Al0.05O2, etc.). The positive electrode active material may be included in an amount of 40% by weight to 90% by weight, for example, 40% by weight to 75% by weight based on the total weight of the solid content in the positive electrode suspension. The binder is a component which aids in bonding between the active material and the conductive agent and in bonding with the current collector, wherein the binder is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the positive electrode suspension. Examples of the binder may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber, a fluorinated rubber, various copolymers, and the like.

The conductive agent is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the positive electrode suspension.

Any conductive agent may be used without particular limitation as long as it has a suitable conductivity without causing adverse chemical changes in the battery, and, for example, a conductive material such as: graphite; a carbon-based material such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powder such as fluorocarbon powder, aluminum powder and nickel powder; conductive single-crystalline short fibers such as zinc oxide single-crystalline short fibers and potassium titanate single-crystalline short fibers; conductive metal oxide such as titanium oxide; or polyphenylene derivatives may be used.

The solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount such that the desirable viscosity is obtained when the positive electrode active material, as well as selectively the binder and the conductive agent are included. For example, the solvent may be included in an amount such that the concentration of the solids content in the suspension including the positive electrode active material, as well as selectively the binder and the conductive agent is in a range of 10% by weight to 70% by weight, for example, 20% by weight to 60% by weight.

(2) Negative electrode

Furthermore, the negative electrode may be prepared by forming a negative electrode material mixture layer on a negative electrode collector. The negative electrode material mixture layer may be formed by coating the negative electrode collector with a slurry including a negative electrode active material, a binder, a conductive agent, and a solvent, and then drying and laminating the coated negative electrode collector.

The negative electrode collector generally has a thickness of 3 μm to 500 μm. The negative electrode collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes to the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel that is surface treated with one of carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. Furthermore, similarly to the positive electrode collector, the negative electrode collector may have fine surface roughness to improve the adhesion force with the negative electrode active material, and the negative electrode collector may be used in various forms such as a film, a foil, a sheet, a net, a porous body, a foam body, a nonwoven textile body, and the like.

Furthermore, the negative electrode active material may include a single material selected from the group consisting of a lithium-containing titanium composite oxide (LTO); a carbon-based material such as non-graphitizable carbon and graphite-based carbon; a complex metal oxide such as LixFe2O3 (0<x<1), LixWO2 (0<x<1), and SnxMe-i-xMe'yOz (Me: manganese (Mn), iron (Fe), lead (Pb), or germanium (Ge); Me': aluminum (Al), boron (B), phosphorus (P), silicon (Si), elements of groups I, II, and III of the periodic table, or halogen; 0<x<1; 1<y<3; 1<z<8); a lithium metal; a lithium alloy; a silicon-based alloy; a tin-based alloy; a metal oxide such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and BhOs; and a conducting polymer, such as polyacetylene, or a mixture of two or more thereof.

The negative electrode active material may be included in an amount of 80% by weight to 99% by weight based on the total weight of the solids content in the negative electrode suspension.

The binder is a component which assists in the bonding between the conductive agent, the active material and the current collector, wherein the binder is usually added in an amount of 1% by weight to 30% by weight based on the total weight of the solid content in the negative electrode suspension. Examples of the binder may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene polymer (EPDM), a sulfonated EPDM, a styrene-butadiene rubber, a fluorinated rubber, and various copolymers thereof.

The conductive agent is a component for further improving the conductivity of the negative electrode active material, wherein the conductive agent may be added in an amount of 1% by weight to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Any conductive agent may be used without particular limitation as long as it has conductivity without causing adverse chemical changes to the battery, and for example, a conductive material such as: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powder such as fluorocarbon powder, aluminum powder, and nickel powder; conductive single-crystalline short fibers such as zinc oxide single-crystalline short fibers and potassium titanate single-crystalline short fibers; conductive metal oxide such as titanium oxide; or polyphenylene derivatives may be used.

The solvent may include water or an organic solvent such as NMP and alcohol, and may be used in such an amount that the desirable viscosity is obtained when the negative electrode active material as well as selectively the binder and the conductive agent are included. For example, the solvent may be included in such an amount that a concentration of the solid content in the suspension including the negative electrode active material as well as selectively the binder and the conductive agent is in a range of 50% by weight to 75% by weight, for example, 50% by weight to 65% by weight.

In addition, the separator plays a role in blocking an internal short circuit between both electrodes and in impregnating the electrolyte, in which, after mixing a polymer resin, a filler and a solvent to prepare a separator composition, the separator composition is directly coated on the electrode and dried to form a separator film, or, after the separator composition is cast on a support and dried, the separator can be prepared by laminating a separator film peeled from the support onto the electrode.

A commonly used porous polymer film, for example, a porous polymer film prepared from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, may be used alone or in a lamination therewith as a spacer. In addition, a typical porous nonwoven textile material, for example, a nonwoven textile material formed of glass fibers or high-melting point polyethylene terephthalate fibers, may be used, but the present invention is not limited thereto.

In this case, the porous separator may generally have a pore diameter of 0.01 |im to 50 |im and a porosity of 5% to 95%. In addition, the porous separator may generally have a thickness of 5 |im to 300 |im. The shape of the secondary lithium battery of the present invention is not particularly limited, but a cylindrical type using a can, a prismatic type, a bag type or a button type may be used.

Hereinafter, the present invention will be described in more detail by way of examples. However, the invention may be implemented in many different ways and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

Examples

Reference example 1 (not part of the claimed content)

(Preparation of non-aqueous electrolyte solution)

A non-aqueous electrolyte solution was prepared by adding 1 g of the compound of formula 1a, as the first additive, and 1 g of LiDFP, as the second additive, to 98 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70) in which 61.0 M LiPF was dissolved.

(Preparation of positive electrode)

Lithium cobalt composite oxide (LiCoO2) as positive electrode active material particles, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a ratio of 90:5:5 (wt%) to prepare a positive electrode active material slurry (solid content of 50 wt%). A 100 μm positive electrode collector (Al thin film) was coated with the positive electrode active material slurry, dried, and roll-pressed to prepare a positive electrode.

(Preparation of negative electrode)

Natural graphite as a negative electrode active material, PVDF as a binder, and carbon black as a conductive agent were added to NMP as a solvent in a ratio of 95:2:3 (wt%) to prepare a negative electrode active material slurry (solid content of 60 wt%). A 90 μm thick negative electrode collector (Cu thin film) was coated with the negative electrode active material slurry, dried, and roll-pressed to prepare a negative electrode.

(Secondary battery preparation)

After an electrode array was prepared by stacking a porous polyethylene film as a separator with the positive electrode and the negative electrode prepared by the methods described above, the electrode array was placed in a battery case, the non-aqueous electrolyte solution was injected into it, and the battery case was sealed to prepare a lithium secondary battery (battery capacity of 5.5 mAh). In this case, Fe particles having a diameter of 280 |im to 330 |im were arranged between the positive electrode and the separator.

Reference example 2 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1b, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 3 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1c, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 4 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1d, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 5 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1e, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 6 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1f, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 7 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1g, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 8 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1h, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 9 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1i, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 10 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1j, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 11 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1k, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 12 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1l, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 13 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1m, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 14 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1n, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 15 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1o, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 16 (not part of the claimed content)

A non-aqueous electrolyte solution and a secondary battery including it were prepared in the same manner as in Reference Example 1 except that the compound of formula 1p, instead of the compound of formula 1a, was added during the preparation of the non-aqueous electrolyte solution.

Reference example 17 (not part of the claimed content)

A non-aqueous electrolyte solution of the present invention was prepared by adding 1 g of the compound of formula 1a, as the first additive, 1 g of LiDFP, as the second additive, and 0.2 g of tetravinylsilane, as the third additive, to 97.8 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M LiPF was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Example 1

A non-aqueous electrolyte solution of the present invention was prepared by adding 1 g of the compound of formula 1k, as the first additive, 1 g of LiDFP, as the second additive, and 0.2 g of tetravinylsilane, as the third additive, to 97.8 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M LiPF was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Reference example 18 (not part of the claimed content)

A non-aqueous electrolyte solution was prepared by adding 7 g of the compound of formula 1a, as the first additive, and 7 g of LiDFP, as the second additive, to 86 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 1.0 M LiPF6 was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Reference example 19 (not part of the claimed content)

A non-aqueous electrolyte solution was prepared by adding 5 g of the compound of formula 1a, as the first additive, and 5 g of LiDFP, as the second additive, to 90 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 1.0 M LiPF6 was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Comparative example 1

A non-aqueous electrolyte solution and a lithium secondary battery including it were prepared in the same manner as in Reference Example 1 except that neither the first nor the second additive were included during the preparation of the non-aqueous electrolyte solution in Reference Example 1.

Comparative example 2

A non-aqueous electrolyte solution was prepared by including 1 g of the compound of formula 1a, as a first additive, in 99 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M LiPF was dissolved, and not including a second additive during the preparation of the non-aqueous electrolyte solution.

A lithium secondary battery including non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Comparative example 3

A non-aqueous electrolyte solution was prepared by including 1 g of a second additive in 99 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 1.0 M LiPF6 was dissolved, and by not including a first additive during the preparation of the non-aqueous electrolyte solution.

A lithium secondary battery including non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Comparative example 4

A non-aqueous electrolyte solution and a lithium secondary battery including it were prepared in the same manner as in Reference Example 1 except that a compound of the following formula 2 was included, instead of the first additive, during the preparation of the non-aqueous electrolyte solution.

Formula 2

Comparative example 5

A non-aqueous electrolyte solution was prepared by adding 13 g of the compound of formula 1a, as the first additive, and 7 g of LiDFP, as the second additive, to 80 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M LiPF was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Comparative example 6

A non-aqueous electrolyte solution was prepared by adding 7 g of the compound of formula 1a, as the first additive, and 13 g of LiDFP, as the second additive, to 80 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M LiPF was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Comparative example 7

A non-aqueous electrolyte solution was prepared by adding 10 g of the compound of formula 1a, as the first additive, and 10 g of LiDFP, as the second additive, to 80 g of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC)=volume ratio of 30:70), in which 61.0 M L<í>P<f> was dissolved, during the preparation of the non-aqueous electrolyte solution.

Subsequently, a secondary battery including the non-aqueous electrolyte dissolution was prepared in the same manner as in Reference Example 1.

Experimental examples

Experimental example 1.

After eight samples were prepared for each of the lithium secondary batteries prepared in Reference Examples 1 to 19, Example 1, and Comparative Examples 1 to 7, each secondary battery was charged at a constant current of 0.1 C to a voltage of 4.2 V at 25 °C. After that, each secondary battery was charged at a constant voltage of 4.2 V, and charging was terminated when the charging current became 0.275 mA. After that, after each battery was allowed to stand for 10 minutes, each battery was discharged at a constant current of 0.5 C to a voltage of 3.0 V. The number of chargeable and dischargeable secondary batteries among the eight secondary batteries prepared in each Example and Comparative Example was checked and indicated in the following Table 1.

[Table 1]

Referring to Table 1, with respect to the secondary batteries of Reference Examples 1 to 19 and Example 1, since the first additive removed dissolved metal by complexing with metallic foreign matter and simultaneously formed a film on the positive electrode surface, and LiDFP, as the second additive, improved thermal stability by increasing an inorganic component on the film, it can be understood that 60% or more of the prepared batteries were chargeable and dischargeable.

In contrast, with respect to the secondary battery of Comparative Example 1 which included the non-aqueous electrolyte solution which included neither the first additive nor the second additive, the number of chargeable and dischargeable cells was 1, and with respect to the secondary battery of Comparative Example 3 which included the non-aqueous electrolyte solution which included only the second additive, it can be understood that the number of chargeable and dischargeable cells was 2.

Furthermore, since the secondary battery of Comparative Example 4, which included the non-aqueous electrolyte solution including the compound of formula 2, instead of the compound of formula 1, as the first additive, did not include an additive capable of adsorbing the metallic foreign matter (Fe), it can be understood that the number of chargeable and dischargeable cells was 1.

With respect to the secondary battery of Comparative Example 2, which included the non-aqueous electrolyte solution including only the first additive, and the secondary batteries of Comparative Examples 5 to 7 which respectively included the non-aqueous electrolyte solutions including the excessive amount of the first additive and/or the second additive, it can be understood that 80% or more of the prepared batteries were chargeable and dischargeable. Experimental Example 2.

After each of the secondary batteries prepared in Reference Examples 1 to 19, Example 1, and Comparative Examples 1 to 7 was charged at a rate of 0.8 C to 4.2 V under a constant current/constant voltage condition and stored at 45 °C for 6 days, the voltages at 45 °C were measured, and an average value thereof is shown in the following Table 2.

[Table 2]

Referring to Table 2, with respect to the secondary batteries of Reference Examples 1 to 19 and Example 1 that included both the first additive and the second additive, since the first additive compound removed the dissolved metal by complexing with the metallic foreign matter and simultaneously formed a film on the positive electrode surface and the LiDFP, as the second additive, improved the thermal stability by increasing an inorganic component on the film, low voltage was prevented even after high temperature storage, and thus, it can be understood that the voltage was maintained at about 3.85 V or more.

In contrast, with respect to the secondary battery of Comparative Example 1 which included the non-aqueous electrolyte solution which included neither the first additive nor the second additive and the secondary battery of Comparative Example 3 which included the non-aqueous electrolyte solution which included only the second additive, it can be understood that the voltages after high-temperature storage were significantly low at 2.55 V and 2.63 V, respectively. Furthermore, since the secondary battery of Comparative Example 4 which included the non-aqueous electrolyte solution which included the compound of formula 2 instead of the compound of formula 1 as the first additive did not include an additive capable of adsorbing metallic foreign matter (Fe), it can be understood that the voltage after high-temperature storage was significantly low at 2.24 V.

With respect to the secondary batteries of Comparative Examples 5 to 7 respectively including the non-aqueous electrolyte solutions including the excessive amount of the first additive and/or the second additive, the voltages after high-temperature storage were 3.83 V, 3.78 V and 3.72 V, respectively, due to the secondary reaction of the additive and the increase in resistance in the secondary battery, where it can be understood that the voltages were lower than those of the secondary batteries of Reference Examples 1 to 19 and Example 1.

Regarding the secondary battery of Comparative Example 2 which included the non-aqueous electrolyte solution that only included the first additive effective in improving the low voltage, the voltage after high temperature storage was 4.03 V, where it can be understood that the voltage was slightly reduced compared with that of the secondary batteries of Reference Examples 1 to 19 and Example 1.

Experimental example 3.

Each of the secondary batteries prepared in Reference Examples 1 to 19, Example 1, and Comparative Examples 1 to 7 was charged at a rate of 0.8 C to 4.35 V under a constant current/constant voltage condition, charged to the cut-off point at 0.05 C, and discharged at 0.5 C to a voltage of 3.0 V (initial discharge capacity). Subsequently, each of the secondary batteries was charged at a rate of 0.8 C to 4.35 V under a constant current/constant voltage condition, charged to the cut-off point at 0.05 C, and stored at 60 °C for 2 weeks. Thereafter, each battery was discharged at 0.5 C to a voltage of 3.0 V at room temperature, and the discharge capacity (residual discharge capacity) was measured. Again, each battery was charged at a rate of 0.8 C to 4.35 V under a constant current/constant voltage condition, charged to the cut-off point at 0.05 C, and discharged at 0.5 C to a voltage of 3.0 V to measure the discharge capacity (recovery discharge capacity). The residual discharge capacity and recovery discharge capacity were expressed as a percentage (%) relative to the initial discharge capacity, and the results of these are presented in the following Table 3.

After that, discharging at 0.5 C to a voltage of 3.0 V at room temperature was set as one cycle, and the capacity after 100 cycles was expressed as a percentage (%) relative to the capacity of the first cycle and was given in Table 3 below.

[Table 3]

As illustrated in Table 3, with respect to the secondary batteries of Reference Examples 1 to 19 and Example 1 respectively including the non-aqueous electrolyte solutions including both the first additive and the second additive, the residual discharge capacities during high-temperature storage were about 78% or more, the recovery discharge capacities were about 86% or more, and the cycle capacity retentions were about 79% or more, from which it can be understood that the residual capacities, recovery capacities, and cycle capacity retentions were all excellent.

In contrast, with respect to the secondary battery of Comparative Example 1 including the non-aqueous electrolyte solution including neither the first additive nor the second additive, the residual discharge capacity during high-temperature storage was about 71%, the recovery discharge capacity was about 82%, and the cycle capacity retention was about 63%, in which it can be confirmed that the overall performance was degraded compared with that of the secondary batteries of Reference Examples 1 to 19 and Example 1.

Furthermore, with respect to the secondary battery of Comparative Example 2 including the non-aqueous electrolyte solution including only the compound of Formula 1a, the first additive, as a non-aqueous electrolyte solution additive, the residual discharge capacity during high temperature storage was about 86%, the recovery discharge capacity was about 92%, and the cycle capacity retention was about 73%, whereby it can be understood that the residual capacity, recovery capacity, and cycle capacity retention were significantly reduced compared with those of the secondary battery of Reference Example 1.

Furthermore, with respect to the secondary battery of Comparative Example 3 including the non-aqueous electrolyte solution including only the second additive as the non-aqueous electrolyte solution additive, since it did not include an additive capable of adsorbing the metallic foreign matter (Fe), the cycle capacity retention was about 74%, where it can be understood that the cycle capacity retention was reduced compared with that of the secondary batteries of Reference Examples 1 to 19 and Example 1.

Furthermore, since the secondary battery of Comparative Example 4, which included the non-aqueous electrolyte solution including the compound of Formula 2 instead of the compound of Formula 1 as the first additive, did not include an additive capable of adsorbing the metallic foreign matter (Fe), the residual discharge capacity during high-temperature storage was 66%, the recovery discharge capacity was 77%, and the cycle capacity retention was 69%, from which it can be understood that the residual capacity, recovery capacity, and cycle capacity retention were significantly lower than those of the secondary batteries of Reference Examples 1 to 19 and Example 1.

With respect to the secondary batteries of Comparative Examples 5 to 7 respectively including the non-aqueous electrolyte solutions including the excessive amount of the first additive and/or the second additive, the residual discharge capacities during high-temperature storage were respectively 76%, 80% and 73%, the recovery discharge capacities were respectively 87%, 85% and 77% and the cycle capacity retentions were respectively 77%, 75% and 67% due to the secondary reaction of the additive and the increase in resistance in the secondary battery, in which it can be understood that the residual capacities, the recovery capacities and the cycle capacity retentions were significantly reduced compared with those of the secondary batteries of Reference Examples 1 to 19 and Example 1.

Claims (10)

CLAIMS Non-aqueous electrolyte solution for a lithium secondary battery, the non-aqueous electrolyte solution comprising: a lithium salt; an organic solvent; a compound represented by formula 1 as a first additive; lithium difluorophosphate (LiDFP) as a second additive; and tetravinylsilane as a third additive, wherein the first additive and the second additive are each independently included in an amount of 0.01% by weight to 8.5% by weight based on the total amount of the non-aqueous electrolyte solution: (Formula 1) Ri to R3 are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, and A is, where R6 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, or -OR5; and wherein R5 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms, wherein the substituted alkyl group having 1 to 6 carbon atoms is an alkyl group having 1 to 6 carbon atoms that is substituted with at least one halogen element or an alkyl group having 1 to 6 carbon atoms that is substituted with an alkyl group having 1 to 3 carbon atoms; and wherein the substituted aryl group having 6 to 12 carbon atoms is a phenyl group substituted with at least one halogen element or a phenyl group substituted with an alkyl group having 1 to 3 carbon atoms, and wherein the unsubstituted aryl group having 6 to 12 carbon atoms is a phenyl group. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the halogen element as a substituent in the substituted alkyl group having 1 to 6 carbon atoms is fluorine. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the halogen element as a substituent in the substituted phenyl group is fluorine. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by formula 1 comprises at least one selected from the group consisting of the compounds represented by formulas 1j to 1p: (Formula 1j) (Formula 1) 5. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein the compound represented by formula 1, as a first additive, is included in an amount of 0.1% by weight to 7% by weight based on the total amount of the non-aqueous electrolyte solution. 6. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 5, wherein the compound represented by formula 1, as a first additive, is included in an amount of 0.1% by weight to 5% by weight based on the total amount of the non-aqueous electrolyte solution. 7. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein lithium difluorophosphate, as a second additive, is included in an amount of 0.1% by weight to 7% by weight based on the total weight of the non-aqueous electrolyte solution. 8. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 7, wherein lithium difluorophosphate, as a second additive, is included in an amount of 0.1% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte solution. 9. Non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein tetravinylsilane, as a third additive, is included in an amount of 0.01% by weight to 5% by weight based on the total weight of the non-aqueous electrolyte solution. 10. A lithium secondary battery comprising the non-aqueous electrolyte solution for a lithium secondary battery according to claim 1.