WO2019093853A1 - Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same and, specifically, to a non-aqueous electrolyte for a lithium secondary battery, the non-aqueous electrolyte comprising: a lithium salt; an organic solvent; and an additive, the additive being a mixture additive comprising lithium difluorophosphate, fluorobenzene, tetravinyl silane, and a compound containing one sulfonate group or sulfate group at a weight ratio of 1 : 2-8 : 0.05-0.3 : 0.5-2, and to a lithium secondary battery comprising the same.

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same

Cross-reference with related application (s)

This application claims the benefit of priority based on Korean Patent Application No. 2017-0150920, dated November 13, 2017, and Korean Patent Application No. 2018-0138408, dated November 12, 2018, all of which are incorporated herein by reference in their entirety The contents of which are incorporated herein by reference.

Technical field

The present invention relates to a nonaqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

In recent years, interest in energy storage technology has been increasing, and efforts for research and development of electrochemical devices are becoming more and more specific as the applications of cell phones, camcorders, notebook PCs, and electric vehicles are expanded.

Among the electrochemical devices, there is a growing interest in the development of a rechargeable secondary battery. In particular, the lithium secondary battery developed in the early 1990s is attracting attention because of its high operating voltage and energy density.

The currently used lithium secondary battery is composed of a carbonaceous anode capable of intercalating and deintercalating lithium ions, a cathode made of a lithium-containing transition metal oxide or the like, and a non-aqueous electrolyte solution in which an appropriate amount of a lithium salt is dissolved in a carbonate-based organic solvent.

The lithium secondary battery is charged and discharged by transferring energy while repeating the phenomenon that lithium ions discharged from the positive electrode are inserted into the negative electrode, for example, carbon particles and discharged again when discharged by charging.

In the lithium secondary battery, a part of the electrolyte additive components and organic solvents are decomposed in the range of 0.5 V to 3.5 V during the initial charging to form a film on the surface of the negative electrode, and lithium ions generated from the positive electrode move to the negative electrode, And reacts with the electrolytic solution to produce compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a passivation layer on the surface of the negative electrode, which is referred to as a solid electrolyte interface (SEI) film.

The SEI film formed during the initial charge prevents the reaction between the lithium ion and the carbonaceous anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. This ion tunnel serves to prevent the organic solvent of the electrolyte having a large molecular weight, which is solvated by lithium ion, to co-intercalate with the carbon-based anode to collapse the structure of the carbon-based cathode. Therefore, in order to improve the high-temperature cycle characteristics and the low-temperature output of the lithium secondary battery, a solid SEI film must always be formed on the cathode of the lithium secondary battery.

On the other hand, when the organic solvent used for the non-aqueous electrolyte of the lithium secondary battery is stored for a long time at a high temperature, it is generally oxidized by a side reaction with the transition metal oxide released from the anode to generate gas, Deformation of the electrode assembly occurs.

In particular, when the battery is stored in a fully charged state at a high temperature (for example, stored at 60 ° C after being charged at 100% at 4.2 V), the SEI film is gradually collapsed to expose the negative electrode and the exposed negative electrode reacts with the electrolyte to continuously generate a side reaction Therefore, gases such as CO, CO ₂ , CH ₄ and C ₂ H ₆ are generated. As a result, the internal pressure of the battery is increased to cause deformation such as cell swelling. Further, when such an internal short circuit of the battery is caused by the battery deformation, the battery deteriorates and the battery may be ignited or exploded.

In order to solve this problem recently, a method has been proposed which includes an additive capable of forming an SEI film in a non-aqueous electrolyte. However, another side effect is caused by such an electrolyte additive, thereby causing another problem that the performance of the secondary battery is reduced.

Accordingly, there is a continuing need to develop a non-aqueous electrolyte having a novel structure capable of improving the high-temperature and overcharge stability of a lithium secondary battery while minimizing adverse effects.

Prior art literature

Japanese Laid-Open Patent Application No. 2017-117684

Disclosed is a non-aqueous electrolyte solution for a lithium secondary battery, which comprises an additive capable of forming a stable film on an electrode surface.

The present invention also provides a lithium secondary battery including the nonaqueous electrolyte solution for the lithium secondary battery, which has improved high temperature and overcharge stability and low temperature output characteristics.

In order to achieve the above object, in one embodiment of the present invention

Lithium salts; Organic solvent; And an additive,

The additive is selected from the group consisting of lithium difluorophosphate (LiPO ₂ F ₂ ): LiDFP, fluorobenzene (FB), tetravinyl silane (TVS) and one sulfonate group or sulfate group Which is a mixed additive containing a compound in a weight ratio of 1: 2 to 8: 0.05 to 0.3: 0.5 to 2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1,

Specifically, the weight ratio of the lithium difluorophosphate, the fluorobenzene, the tetravinylsilane, and the compound containing one sulfonate group or the sulfate group may be 1: 2 to 6: 0.05 to 0.3: 0.5 to 1.5.

The one sulfonate group or the compound containing a sulfate group may be selected from the group consisting of ethylene sulfate, trimethylene sulfate, methyl trimethylene sulfate, 1,3-propane sultone, 1 At least one selected from the group consisting of 4-butane sultone, ethene sultone, 1,4-butene sultone, 1-methyl-1,3-propane sultone and 1,3- And may specifically be at least one selected from the group consisting of ethylene sulfate, trimethylene sulfate, 1,3-propane sultone and 1,3-propenesultone.

In the nonaqueous electrolyte solution for a lithium secondary battery of the present invention, the additive may be included in an amount of 1 to 18% by weight based on the total weight of the nonaqueous electrolyte solution for a lithium secondary battery.

Meanwhile, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention can be used for forming at least one SEI film selected from the group consisting of a halogen-substituted carbonate compound, a nitrile compound, a cyclic carbonate compound, a phosphate compound, a borate compound and a lithium salt compound The first additive may further comprise a first additive.

The nonaqueous electrolyte solution for a lithium secondary battery of the present invention may further comprise at least one second additive for forming an SEI film selected from the group consisting of diphenyl disulfide, di-p-tolyl disulfide and bis (4-methoxyphenyl) disulfide (BMPDS) May be further included.

In an embodiment of the present invention,

A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte,

The nonaqueous electrolyte solution provides a lithium secondary battery comprising the nonaqueous electrolyte solution for a lithium secondary battery of the present invention.

The lithium-nickel-manganese-cobalt-based oxide may be Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ , Li (Ni _0.35 Mn _0.28 Co _0.37 ) O ₂ , Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , And at least one selected from the group consisting of Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, and Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ .

According to the present invention, it is possible to produce a nonaqueous electrolyte solution for a lithium secondary battery capable of forming a stable SEI film on the surface of a negative electrode by including an additive in which four kinds of compounds are mixed in a specific ratio. Also, by including it, it is possible to manufacture a lithium secondary battery having improved performance such as high temperature, overcharge stability, and low temperature output characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, It is not limited.

1 is a graph showing a result of evaluation of low-temperature output characteristics of a lithium secondary battery according to Experimental Example 1 of the present invention.

2 is a graph showing the overcharge stability evaluation result of the lithium secondary battery of Example 1 according to Experimental Example 6 of the present invention.

3 is a graph showing the overcharge stability evaluation result of the lithium secondary battery of Comparative Example 7 according to Experimental Example 6 of the present invention.

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

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

 Moreover, the terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, the terms " comprising, " " comprising, " or " having ", and the like are intended to specify the presence of stated features, But do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

Non-aqueous electrolyte for lithium secondary battery

Specifically, in one embodiment of the present invention

Lithium salts; Organic solvent; And an additive,

The additive may be selected from the group consisting of lithium difluorophosphate (LiDFP), fluorobenzene (FB), tert-vinylsilane (TVS) and a compound containing one sulfonate group or sulfate group in a ratio of 1: To 8: 0.05 to 0.3: 0.5 to 2 by weight, based on the total weight of the non-aqueous electrolyte.

(1) Lithium salt

In the nonaqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention, the lithium salt may be any of those conventionally used in an electrolyte for a lithium secondary battery, and may include, for example, Li ⁺ as a cation of the lithium salt, The anions include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , B ₁₀ Cl ₁₀ ^- , PF ₆ ^- , CF ₃ SO ₃ ^{- _{CH 3 CO 2 -, CF 3}} CO 2 -, AsF 6 -, SbF 6 -, AlCl 4 -, AlO 4 -, CH 3 SO 3 -, BF 2 C 2 O 4 -, BC 4 O 8 -, PF 4 _{^{C 2 O 4 -, PF 2}} C 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, C ^{_{4 F 9 SO 3 -, CF}} 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2 _{^{) 2 CH -, (SF 5}} ) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - consisting of And at least one selected from the group consisting of

Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlO ₄ , LiCH ₃ SO ₃ , LiFSI (lithium fluorosulfonyl imide, LiN (SO ₂ F) ₂ ), LiTFSI (lithium bis) trifluoromethanesulfonimide, LiN (SO ₂ CF ₃ ) ₂ and LiBETI (lithium bisperfluoroethanesulfonimide, ₂ C ₂ F ₅ ) ₂ ), or a mixture of two or more thereof.

Specifically, the lithium salt is _{LiPF 6, LiBF 4, LiCH 3} CO 2, LiCF 3 CO 2, LiCH 3 SO 3, LiFSI, LiTFSI and _{LiN (C 2 F 5 SO 2} ) or more danilmul selected from the group consisting of ₂ or two And mixtures thereof. However, the lithium salt does not include LiDFP, which is a lithium salt contained in the mixed additive.

The lithium salt may be appropriately changed within a range that is generally usable, but specifically, it may be contained in the electrolyte in an amount of 0.1M to 3M, specifically 0.8M to 2.5M. If the concentration of the lithium salt exceeds 3M, the viscosity of the non-aqueous electrolyte increases to lower the lithium ion transporting effect, and the wettability of the non-aqueous electrolyte deteriorates, making it difficult to form a uniform SEI film.

(2) Organic solvent

In the non-aqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention, the organic solvent may minimize decomposition due to an oxidation reaction or the like during charging and discharging of the secondary battery, There is no limit to its kind. For example, a carbonate-based organic solvent, an ether-based organic solvent or an ester-based organic solvent may be used alone or in combination of two or more.

The carbonate-based organic solvent in the organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, (Ethylene carbonate), ethylene carbonate (ethylene carbonate) having a high dielectric constant and ethylene carbonate (ethylene carbonate) having a dielectric constant higher than that of ethylene carbonate, And a mixed solvent of propylene carbonate having a low melting point.

The linear carbonate-based organic solvent may be a solvent having a low viscosity and a low dielectric constant, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC) And at least one selected from the group consisting of propyl carbonate, ethyl carbonate, propyl carbonate, and ethyl propyl carbonate, and more specifically, dimethyl carbonate.

The ether organic solvent may be 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. It is not.

The ester-based organic solvent may include at least one selected from the group consisting of a linear ester organic solvent and a cyclic ester organic solvent.

The linear ester organic solvent 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. A mixture of two or more thereof, and the like may be used, but the present invention is not limited thereto.

Specific examples of the cyclic ester organic solvent include any one selected from the group consisting of? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or 2 Mixtures of two or more species may be used, but are not limited thereto.

The organic solvent may be a high-viscosity cyclic carbonate-based organic solvent having high permittivity and dissociating the lithium salt in the electrolyte. Further, in order to produce an electrolyte having a higher electrical conductivity, the organic solvent may be used together with the above-mentioned environmental carbonate-based organic solvent to prepare a low viscosity, low dielectric constant linear carbonate compound and linear ester compound such as dimethyl carbonate and diethyl carbonate They can be mixed and used in an appropriate ratio.

More specifically, the organic solvent may be a mixture of a cyclic carbonate compound and a linear carbonate compound. The weight ratio of the cyclic carbonate compound to the linear carbonate compound in the organic solvent may be 10:90 to 70:30.

(3) Mixed additives

On the other hand, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention may include an additive which is a mixture of lithium difluorophosphate, fluorobenzene, tetravinylsilane, and one sulfonate group or a compound containing a sulfate group.

Here, lithium difluorophosphate (LiDFP) represented by the following formula (1), which is one of the components of the mixed additive, is a component for realizing long-term lifetime improvement effect of a secondary battery, and is electrochemically decomposed The SEI film can be formed to prevent exposure to the non-aqueous electrolyte. As a result, it is possible to suppress the generation of O ₂ from the anode and the side reaction between the anode and the electrolyte, thereby improving the durability of the battery. Further, since the di-fluorophosphate structure is reduced when the battery is driven, a stable and stable SEI film can be formed on the surface of the negative electrode, thereby improving durability and high-temperature storage characteristics of the battery.

[Chemical Formula 1]

The fluorobenzene represented by the following formula (2), which is one of the components of the mixed additive, is a component for improving the stability during overcharging. The product decomposed at a specific potential forms a polymer layer on the surface of the positive electrode and the negative electrode, By preventing the side reaction of the electrode, the high temperature storage stability of the lithium secondary battery can be improved.

(2)

Tetravinyl silane (TVS) represented by the following chemical formula (3), which is one of the mixed additive components, forms a solid SEI film through physical adsorption and electrochemical reaction on the surfaces of the positive and negative electrodes, It is possible to prevent exposure of the cathode. As a result, it is possible to suppress the side reaction of the non-aqueous electrolyte at high temperature and the electrode, and to prevent the increase in resistance, so that the high temperature storage stability of the lithium secondary battery can be improved.

 (3)

In addition, one sulfonate group or a compound containing a sulfate group, which is one of the above-mentioned mixed additive components, can form a stable coating film that is not cracked even when stored at high temperature on the surface of the negative electrode. The negative electrode coated with such a coating suppresses the decomposition of the non-aqueous solvent by the negative active material during storage at a high temperature even when a carbon material highly crystallized by the activity of natural graphite or artificial graphite is used for the negative electrode, have. Therefore, high temperature stability of the lithium secondary battery and cycle life and capacity characteristics at high temperature storage can be improved, and resistance reduction can be suppressed.

 Specifically, the one sulfonate group or the compound containing a sulfate group may be selected from the group consisting of ethylene sulfate (Esa) represented by the following formula (4a), trimethylene sulfate (TMS) represented by the following formula (4b) Methyl trimethylene sulfate (MTMS), 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,4-butene sultone And 1-methyl-1,3-propenesultone and 1,3-propenesultone (PRS) represented by the following formula (4e).

 [Chemical Formula 4a]

(4b)

[Chemical Formula 4c]

[Chemical formula 4d]

[Chemical Formula 4e]

Specifically, the one sulfonate group or the compound containing a sulfate group may be at least one or more of ethylene sulfate, trimethylene sulfate, 1,3-propane sultone and 1,3-propene sultone.

Such a sulfonate group or a compound containing a sulfate group may be used in an amount of up to 6.5% by weight, specifically 0.1% by weight to 6.5% by weight, more specifically 0.5% by weight to 4.0% by weight, based on the total weight of the nonaqueous electrolyte solution for a lithium secondary battery .

At this time, if the total content of one sulfonate group or sulfate group-containing compound in the non-aqueous electrolyte solution for the lithium secondary battery is more than 6.5% by weight, an excessively thick film may be formed and resistance increase and output deterioration may occur.

On the other hand, in the case of a compound containing both of two or more sulfonate groups and / or sulfate groups as in the case of the compound represented by the following general formula (5), there is a high possibility that denaturation of the nonaqueous electrolyte itself occurs due to high reduction reactivity. Furthermore, as the composition ratio of S and O in the film formed on the surface of the anode or the cathode increases, the ionic conductivity increases and the output characteristic improves, while the side reaction with the electrolyte increases, The durability of the secondary battery is relatively reduced at a high temperature, and the use thereof is avoided.

[Chemical Formula 5]

On the other hand, the compound containing lithium difluorophosphate, fluorobenzene, tetravinylsilane and one sulfonate group or sulfate group may be used in a ratio of 1: 2 to 8: 0.05 to 0.3: 0.5 to 2, particularly 1: 2 to 6 : 0.05 to 0.3: 0.5 to 1.5 by weight.

That is, when the respective components of the additive are mixed in the nonaqueous electrolyte of the present invention in the above ratio, a secondary battery having improved performance can be manufactured.

For example, when the weight ratio of fluorobenzene to lithium difluorophosphate is 8 or less, an increase in internal resistance of the battery due to excessive use of the additive can be prevented. Further, when the weight ratio of the fluorobenzene is 2 or more, stability at the time of overcharging can be improved.

When the weight ratio of the tetravinylsilane to the lithium difluorophosphate is 0.3 or less, side reactions due to surplus tetravinylsilane are caused to prevent the resistance of the battery from increasing and the cycle life characteristics are lowered Can be prevented. When the weight ratio of tetravinylsilane is 0.05 or more, the gas generation reduction effect and the SEI film formation stabilization effect can be obtained.

When the weight ratio of the compound containing one sulfonate group or sulfate group to the lithium difluorophosphate is 2 or less, a stabilizing effect upon formation of the SEI film can be ensured and high-temperature storage characteristics and cycle life characteristics can be improved . In addition, when the weight ratio of the one sulfonate group or the sulfate group-containing compound is 0.5 or more, it is possible to improve the stability of the SEI film and suppress the electrolyte side reaction without increasing the resistance.

In the non-aqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention, the additive is contained in an amount of 1 to 18 wt%, specifically 8 to 10 wt% based on the total weight of the nonaqueous electrolyte solution for a lithium secondary battery .

At this time, when the content of the additive is 18% by weight or less, not only the gas generating effect and the like due to the use of additives can be improved but also the components are prevented from remaining excessively, A stable SEI film can be formed on the surface, and the high-temperature stability of the lithium secondary battery can be improved.

In addition, when the content of the additive is 1 wt% or more, it is possible to form a stable (SEI) coating on the surface of the negative electrode, and to prevent decomposition of the electrolyte due to reaction between the electrolyte and the negative electrode, The expected effect can be met.

If the content of the mixed additive exceeds 18% by weight, the solubility and wettability may deteriorate as the viscosity of the non-aqueous electrolyte increases due to the excess amount of the additive, resulting in degradation of output characteristics and cycle life characteristics. ,

During the initial charging of the lithium ion battery, lithium ions from the lithium metal oxide used as an anode migrate to a carbon (crystalline or amorphous) electrode used as a cathode and are intercalated into the carbon of the cathode. At this time, Therefore, an organic material and Li ₂ CO ₃ , Li ₂ O, LiOH, etc. are formed by reacting with the carbon-based anode, and these form an SEI film on the surface of the cathode. Once the SEI film is formed at the time of initial charging, it will prevent the reaction between the lithium ion and the carbon-based anode or other materials during repeated charging and discharging by the use of the battery, and serves as an ion tunnel through which only lithium ions pass between the electrolyte and the cathode . Due to the ion tunneling effect, the SEI film prevents the migration of organic solvents, such as EC, DMC, DEC, PP, etc., having a large molecular weight to the carbonaceous cathode, co-decomposition of the structure of the carbon-based anode. That is, once the film is formed, the lithium ions do not react with the carbonaceous anode or other materials, and thereby the amount of lithium ions can be reversibly maintained at the time of charge / discharge by the use of the battery.

In other words, the carbon material of the negative electrode reacts with the electrolytic solution at the time of initial charging to form a passivation layer on the surface of the negative electrode so as to maintain stable charging / discharging without further decomposition of the electrolytic solution. At this time, The amount of charge consumed in the layer formation is irreversible capacity, which is characterized in that it does not react reversibly during discharging. For this reason, the lithium ion battery can maintain a stable life cycle without any irreversible reaction after the initial charging reaction .

However, when the lithium ion battery is stored at a high temperature (for example, at a temperature of 60 ° C after being charged at a temperature of 4.15 V or more at 100%) in a fully charged state, the SEI film gradually degrades due to increased electrochemical energy and thermal energy over time .

Such SEI film breakdown exposes the surface of the negative electrode, and the exposed negative electrode surface is decomposed while the carbonate-based solvent in the electrolyte is reacted to cause continuous side reaction.

These side reactions generate gas continuously. The main gases produced are CO, CO ₂ , CH ₄ , C ₂ H _6, etc., depending on the type of carbonate used and the kind of negative active material used. Regardless of the type, continuous gas evolution at high temperatures causes the cell internal pressure of the lithium ion battery to rise, causing the cell thickness to expand.

Accordingly, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention includes a mixed additive in which lithium difluorophosphate, fluorobenzene, tetravinylsilane and one sulfonate group or a compound containing a sulfate group are mixed in a specific ratio, It is possible to improve the overall performance such as high-temperature storage characteristics and lifetime characteristics of the lithium secondary battery by suppressing the electrolyte side reaction during high-temperature storage as well as improving the low-temperature output characteristics by forming a more stable and solid SEI film on the surface of the negative electrode .

(4) Additive for forming SEI film

Meanwhile, the non-aqueous electrolyte according to an embodiment of the present invention may be used together with the above-mentioned mixed additive to form a stable coating on the surface of the negative electrode and the positive electrode, An additional additive capable of suppressing the decomposition of the solvent in the electrolyte solution and serving as a complementary agent for improving the mobility of the lithium ion may be further included.

Such an additive is not particularly limited as long as it is an additive for forming an SEI film capable of forming a stable film on the surfaces of the anode and the cathode.

Specifically, the SEI film forming additive includes at least one SEI film selected from the group consisting of a halogen-substituted carbonate compound, a nitrile compound, a cyclic carbonate compound, a phosphate compound, a borate compound and a lithium salt compound And a second additive for forming the first additive.

Specifically, the halogen-substituted carbonate compound is fluoroethylene carbonate (FEC)), and may be contained in an amount of 5% by weight or less based on the total weight of the non-aqueous electrolyte. If the content of the halogen-substituted carbonate compound exceeds 5% by weight, the cell swelling performance may deteriorate.

The nitrile compound may be at least one selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, In the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile At least one compound selected.

At this time, when the nitrile compound is used together with the above-mentioned mixed additive, effects such as improvement in high-temperature characteristics can be expected by stabilizing the positive / negative electrode coating. In other words, it can serve as a complement in forming the negative electrode SEI coating, can play a role of inhibiting the decomposition of the solvent in the electrolyte, and can improve the mobility of lithium ions. Such a nitrile compound may be contained in an amount of 8% by weight or less based on the total weight of the nonaqueous electrolyte solution. If the total content of the nitrile compound in the nonaqueous electrolyte exceeds 8 wt%, resistance increases due to an increase in the film formed on the surface of the electrode, and battery performance may be deteriorated.

The carbonate-based compound forms a stable SEI film mainly on the surface of the negative electrode at the time of battery activation, thereby improving the durability of the battery. The cyclic carbonate-based compound may be vinylene carbonate (VC) or vinylethylene carbonate. The cyclic carbonate-based compound may include up to 3% by weight based on the total weight of the non-aqueous electrolyte. When the content of the cyclic carbonate compound in the nonaqueous electrolyte solution exceeds 3% by weight, the cell swelling inhibition performance and initial resistance may be deteriorated.

In addition, since the phosphate compound stabilizes the PF ₆ anion and the like in the electrolytic solution and assists in the formation of the anode and cathode coatings, the durability of the battery can be improved. Such phosphate-based compounds include, but are not limited to, difluoro (bisoxalato) phosphate (LiDFOP), tetramethyltrimethylsilyl phosphate (LiTFOP), trimethylsilylphosphite (TMSPi), tris (2,2,2-trifluoroethyl) phosphate (TFEPa) and tris (trifluoroethyl) phosphite (TFEPi), and may be contained in an amount of 3% by weight or less based on the total weight of the nonaqueous electrolyte solution.

The borate compound promotes ion-pair separation of the lithium salt, improves the mobility of lithium ions, can lower the interfacial resistance of the SEI film, and can be used for a material such as LiF By dissociation, problems such as generation of hydrofluoric acid gas can be solved. Examples of such a borate compound include lithium foroxylate borate (LiBOB, LiB (C ₂ O ₄ ) ₂ ), lithium oxalyl difluoroborate or tetramethyltrimethylsilylborate (TMSB), and based on the total weight of the non- 3% by weight or less.

The lithium salt compound may be at least one compound selected from the group consisting of LiODFB and LiBF ₄ , which is different from the lithium salt contained in the non-aqueous electrolyte. The lithium salt compound may be contained in an amount of not more than 3% by weight based on the total weight of the non- .

The first additives for forming the SEI film may be used in combination of two or more, and may be contained in an amount of 10 wt% or less, specifically 0.01 wt% to 10 wt%, preferably 0.1 wt% to 5.0 wt% based on the total amount of the electrolytic solution .

 If the content of the first additive for SEI film formation is less than 0.01% by weight, the high-temperature storage characteristics and gas reduction effect to be realized from the additive are insignificant. If the content of the first additive for SEI film formation exceeds 10% by weight There is a possibility that a side reaction in the electrolytic solution occurs excessively during charging and discharging of the battery. In particular, when the first additive for SEI film formation is added in an excessive amount, it can not be decomposed sufficiently and may be present in the electrolyte solution at room temperature without being reacted or precipitated. As a result, the resistance increases and the lifetime characteristics of the secondary battery may be deteriorated.

The nonaqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention may include diphenyl disulfide (DPDS), di-p-tolyl disulfide (DTDS), and bis (4- Methoxyphenyl) disulfide (BMPDS) as a second additive for forming at least one SEI film.

The second additive for forming the SEI film contributes to the formation of a stable protective film on the surface of the negative electrode carbon material. This protective film maintains a stable state even if charge and discharge are repeated. By the action of the protective film, the non-aqueous solvent in the electrolytic solution is electrochemically reduced and gas generation is suppressed. As a result, peeling of the negative electrode carbon material from the negative electrode can be suppressed and the cycle characteristics can be improved.

In addition, DPDS, DTDS, and BMPDS act on the polar terminal end of PVDF and P (VDF-HFP), which are the binders, of the reaction product of the nonaqueous solvent and the carbonaceous anode at the time of forming the protective film, and the swelling of the binder by the non- And the adhesion between the electrode materials is maintained. As a result, it is possible to suppress the rise of the impedance of the electrode and further improve the cycle characteristics.

The second additive for forming the SEI film may be contained in an amount of 0.6 wt% or less, specifically 0.1 wt% to 0.6 wt%, based on the total weight of the nonaqueous electrolyte solution for a lithium secondary battery. If the content of the additive is 0.1% by weight or more, the effect to be achieved from the additive can be obtained. When the additive is 0.6% by weight or less, a side reaction due to a surplus additive can be prevented.

Lithium secondary battery

In an embodiment of the present invention,

A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte,

The nonaqueous electrolyte solution provides a lithium secondary battery comprising the nonaqueous electrolyte solution of the present invention.

At this time, the anode may include a lithium-nickel-manganese-cobalt oxide as a cathode active material.

Meanwhile, in the lithium secondary battery of the present invention, the positive electrode, the negative electrode, and the separator interposed between the positive electrode and the negative electrode are sequentially laminated to form an electrode assembly. At this time, the positive electrode, negative electrode, And those used in the production of lithium secondary batteries can all be used.

(1) anode

The positive electrode may be produced by forming a positive electrode mixture layer on the positive electrode collector. The positive electrode mixture layer may be formed by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode collector, followed by drying and rolling.

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the positive electrode collector may be formed of a metal such as carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used.

The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and may specifically include a lithium composite metal oxide including lithium and at least one metal such as cobalt, manganese, nickel, or aluminum have. More specifically, the lithium composite metal oxide is a lithium-nickel-manganese-cobalt oxide (for example, Li (Ni _p Co _q Mn _{r 1} ) O ₂ , 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) , or _{Li (Ni p1 Co q1 Mn r2} ) O 4 ( here, 0 <p1 <2, 0 (Q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2)).

The positive electrode active material that is a typical example _{Li (Ni 1/3 Mn 1/3 Co 1/3} ) O 2, Li (Ni 0.35 Mn 0.28 Co 0.37) O 2, Li (Ni 0.6 Mn 0.2 Co 0.2) O 2, Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, and Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ .

(For example, LiMnO ₂ , LiMn ₂ O _4, etc.), a lithium-cobalt oxide (for example, LiCoO _2, etc.) in addition to the lithium-nickel-manganese-cobalt oxide, Lithium-nickel-based oxides such as LiNiO ₂ , lithium-nickel-manganese-based oxides such as LiNi _{1 -Y} Mn _Y O ₂ (where 0 <Y <1), LiMn _2-z Ni _z O ₄ (where, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1), etc.), lithium-manganese-cobalt oxide (e. g., LiCo (here _{1-Y2 Mn Y2 O 2,} 0 <Y2 <1), LiMn 2-z1 Co z1 O 4 ( here, 0 <Z1 <2), etc. ), or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni _p2 Co _q2 Mn _r3 M _S2) O ₂ (here, M is Al, Fe, V, Cr, Ti, Ta , Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 < 1, p2 + q2 + r3 + s2 = 1))), and the like, and any one or two or more of these compounds may be included.

Such a cathode active material may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or lithium nickel cobalt aluminum oxide (for example, Li (Ni _0.8 Co _0.15 Al _0.05 ) O _2, etc.).

The positive electrode active material may include 90 wt% to 99 wt%, specifically 93 wt% to 98 wt%, based on the total weight of the solid content in the positive electrode slurry.

The binder is a component that assists in bonding of the active material to the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene (Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, the conductive material may be carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, Carbon powder; Graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

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

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a preferable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the solid content in the slurry containing the cathode active material, and optionally the binder and the conductive material may be 10 wt% to 70 wt%, preferably 20 wt% to 60 wt%.

(2) cathode

The negative electrode may be manufactured by forming a negative electrode mixture layer on the negative electrode collector. The negative electrode material mixture layer may be formed by coating a negative electrode current collector with a slurry containing a negative electrode active material, a binder, a conductive material, a solvent, and the like, followed by drying and rolling.

The anode current collector generally has a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may be a lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal complex oxide, lithium capable of doping and dedoping lithium Materials, and transition metal oxide transition metal oxides.

The carbonaceous material capable of reversibly intercalating / deintercalating lithium ions is not particularly limited as long as it is a carbonaceous anode active material generally used in a lithium ion secondary battery. Examples of the carbonaceous material include crystalline carbon, Amorphous carbon or any combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in the form of amorphous, plate-like, flake, spherical or fiber, and examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, fired coke, and the like.

The metal or an alloy of these metals and lithium may be selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, And Sn, or an alloy of these metals and lithium may be used.

In the metal composite oxide is _{PbO, PbO 2, Pb 2 O} 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4 , Bi ₂ O ₅ , Li _x Fe ₂ O ₃ (0? _X? 1), Li _x WO ₂ (0? _X? 1), and Sn _x Me _1-x Me _{y y z} , Pb, Ge, Me ': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen: 0 <x? 1; 1? Y? May be used.

As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x? 2), Si-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, Rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is at least one element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Element and an element selected from the group consisting of combinations thereof, and not Sn), and at least one of them may be mixed with SiO ₂ . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, and combinations thereof.

Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, and the like.

The negative active material may be contained in an amount of 80% by weight to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 1 to 20 wt% based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The solvent may include water or an organic solvent such as NMP, alcohol, etc., and may be used in an amount in which the negative electrode active material and, optionally, a binder, a conductive material, and the like are contained in a desired viscosity. For example, the slurry containing the negative electrode active material and, optionally, the binder and the conductive material may be contained in such a manner that the solid concentration of the slurry is 50% by weight to 75% by weight, preferably 50% by weight to 65% by weight.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example 1.

(Preparation of non-aqueous electrolyte)

Lithium difluorophosphate (LiDFP): Fluorobenzene (FB): tetravinylsilane (TVS) as an additive: 96.4 g of an organic solvent in which 1.0 M LiPF ₆ is dissolved (ethylene carbonate: ethyl methyl carbonate = 30:70 by volume) And 3.6 g of a mixed additive in which 1,3-propane sultone (PS) was mixed at a weight ratio of 1: 2: 0.1: 0.5 was added to prepare a non-aqueous electrolyte of the present invention (see Table 1 below).

(Electrode manufacturing)

A negative active material (Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ ), a conductive material (carbon black) and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 90: (NMP) to prepare a positive electrode active material slurry (solid content concentration: 50% by weight). The positive electrode active material slurry was applied to a positive electrode current collector (Al thin film) having a thickness of 100 m, dried, and roll pressed to produce a positive electrode.

A negative electrode active material slurry (solid concentration: 60% by weight) was prepared by adding a negative electrode active material (artificial graphite), a binder (PVDF), and a conductive material (carbon black) to NMP as a solvent at a weight ratio of 95: 2: 3. The negative electrode active material slurry was coated on a negative electrode current collector (Cu thin film) having a thickness of 90 탆, dried, and rolled to produce a negative electrode.

(Secondary Battery Manufacturing)

The positive electrode and the negative electrode prepared by the above-mentioned method were sequentially laminated together with a polyethylene porous film to prepare an electrode assembly, which was then placed in a battery case, the nonaqueous electrolyte was injected, and the battery was sealed to manufacture a lithium secondary battery.

Example 2.

Except that 2.16 g of a mixed additive prepared by mixing 97.84 g of an organic solvent with LiDFP: FB: TVS: PS in an amount of 1: 2: 0.1: 0.5 by weight as an additive was added during the preparation of the non-aqueous electrolyte. The non-aqueous electrolyte of the present invention and a secondary battery containing the same were prepared (see Table 1 below).

Example 3.

In the same manner as in Example 1 except that 5.4 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS in an amount of 1: 2: 0.1: 1.5 by weight as an additive was added to 94.6 g of a solvent during the preparation of the non- To prepare a nonaqueous electrolyte of the present invention and a secondary battery comprising the same (see Table 1 below).

Example 4.

In the same manner as in Example 1 except that 11.3 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS in an amount of 1: 8: 0.3: 2 by weight as an additive was added to 88.7 g of a solvent during the preparation of the non- To prepare a nonaqueous electrolyte of the present invention and a secondary battery comprising the same (see Table 1 below).

Example 5.

Except that 4 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS in an amount of 1: 8: 0.3: 2 by weight as an additive was added to 96 g of the solvent in the preparation of the non-aqueous electrolyte. The nonaqueous electrolytic solution of the invention and the secondary battery comprising the same were prepared (see Table 1 below).

Example 6.

In the same manner as in Example 1 except for adding, to the 83.05 g of the solvent, 16.95 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS in a weight ratio of 1: 8: 0.3: To prepare a nonaqueous electrolyte of the present invention and a secondary battery comprising the same (see Table 1 below).

Example 7.

Except that 8.7 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 6: 0.2: 1.5 as an additive was added to 91.3 g of a solvent in the preparation of the non-aqueous electrolyte, To prepare a nonaqueous electrolyte of the present invention and a secondary battery comprising the same (see Table 1 below).

Example 8.

Except that 14 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 8: 0.05: 0.5 as an additive was added to 86 g of a solvent in the preparation of the non-aqueous electrolyte, The nonaqueous electrolytic solution of the invention and the secondary battery comprising the same were prepared (see Table 1 below).

Example 9.

Except that 4 g of a mixed additive prepared by mixing 96 g of a solvent with LiDFP: FB: TVS: PRS in a weight ratio of 1: 8: 0.3: 2 as an additive agent was added in the same manner as in Example 1 The nonaqueous electrolytic solution of the invention and the secondary battery comprising the same were prepared (see Table 1 below).

Example 10.

Except that 4 g of a mixed additive in which 96 g of a solvent was mixed with LiDFP: FB: TVS: TMS in a weight ratio of 1: 8: 0.3: 2 as an additive agent was added at the time of preparing the non-aqueous electrolyte. The nonaqueous electrolytic solution of the invention and the secondary battery comprising the same were prepared (see Table 1 below).

Example 11.

The procedure of Example 1 was repeated except for adding 16.95 g of a mixed additive obtained by mixing 83.05 g of a solvent with LiDFP: FB: TVS: PS: TMS in a weight ratio of 1: 8: 0.3: The non-aqueous electrolyte of the present invention and a secondary battery containing the same were prepared (see Table 1 below).

Example 12.

Except that 8.7 g of a mixed additive prepared by mixing 91.3 g of a solvent with LiDFP: FB: TVS: PS: Esa in a weight ratio of 1: 6: 0.2: 0.5: The non-aqueous electrolyte of the present invention and a secondary battery containing the same were prepared (see Table 1 below).

Example 13.

Except that 10.05 g of a mixed additive in which LiDFP: FB: TVS: Esa was mixed at a weight ratio of 1: 4: 0.2: 1.5 as an additive was added to 89.95 g of the solvent at the time of preparing the non-aqueous electrolyte, To prepare a nonaqueous electrolyte of the present invention and a secondary battery comprising the same (see Table 1 below).

Example 14.

Except that 18 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS: Esa in an amount of 1: 8: 0.3: 1: 1 by weight as an additive was added to 92 g of an organic solvent at the time of preparing the non-aqueous electrolyte. In the same manner, the nonaqueous electrolyte of the present invention and a secondary battery containing the same were prepared (see Table 1 below).

Example 15.

Except that 22 g of a mixed additive obtained by mixing LiDFP: FB: TVS: PS: ESa in an amount of 1: 4: 0.2: 0.5: 1 by weight as an additive was added to 78 g of an organic solvent during the preparation of the non-aqueous electrolyte. In the same manner, the nonaqueous electrolyte of the present invention and a secondary battery containing the same were prepared (see Table 1 below).

Comparative Example 1

A nonaqueous electrolytic solution and a secondary battery including the nonaqueous electrolytic solution were prepared in the same manner as in Example 1 except that only 3 g of vinylene carbonate was added as an additive to 97 g of a solvent in the preparation of the nonaqueous electrolyte (see Table 2 below).

Comparative Example 2

A non-aqueous electrolyte and a secondary battery containing the non-aqueous electrolyte were prepared in the same manner as in Example 1 except that only 2 g of LiBF ₄ was added as an additive to 98 g of a solvent in the preparation of the non-aqueous electrolyte (see Table 2 below).

Comparative Example 3

Except that 12.7 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 15: 0.2: 1.5 as an additive was added to 87.3 g of a solvent at the time of preparing the non-aqueous electrolyte, To prepare a nonaqueous electrolyte and a secondary battery containing the same (see Table 2 below).

Comparative Example 4

In the same manner as in Example 1, except that 9 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 6: 0.5: 1.5 as an additive was added to 91 g of a solvent at the time of preparing the non-aqueous electrolyte, To prepare an electrolytic solution and a secondary battery containing the electrolytic solution (see Table 2 below).

Comparative Example 5

Except that 10.2 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 6: 0.2: 5 as an additive was added to 89.8 g of a solvent in the preparation of the non-aqueous electrolyte, To prepare a nonaqueous electrolyte and a secondary battery containing the same (see Table 2 below).

Comparative Example 6

Aqueous electrolyte solution was prepared in the same manner as in Example 1, except that 8.2 g of a mixed additive obtained by mixing FB: TVS: PS at a weight ratio of 6: 0.2: 2 as an additive in 91.8 g of a solvent was added. And a secondary battery containing the same was prepared (see Table 2 below).

Comparative Example 7

Aqueous electrolyte solution was prepared in the same manner as in Example 1, except that 5.2 g of a mixed additive obtained by mixing 94.8 g of a solvent with LiDFP: TVS: PS at a weight ratio of 2: 0.2: 3 as an additive was added. And a secondary battery containing the same was prepared (see Table 2 below).

Comparative Example 8

Aqueous electrolyte solution was prepared in the same manner as in Example 1, except that 8.5 g of a mixed additive in which LiDFP: FB: PS was mixed at a weight ratio of 1: 6: 1.5 as an additive was added to 91.5 g of a solvent at the time of preparing the non- And a secondary battery containing the same was prepared (see Table 2 below).

Comparative Example 9

Aqueous electrolyte solution was prepared in the same manner as in Example 1, except that 7.2 g of a mixed additive obtained by mixing LiDFP: FB: TVS in an amount of 1: 6: 0.2 by weight as an additive in 92.8 g of a solvent was added. And a secondary battery containing the same was prepared (see Table 2 below).

Comparative Example 10.

Except that 9.2 g of a mixed additive obtained by mixing LiDFP: FB: TVS: MMDS (methylene methane disulfonate) as an additive in a weight ratio of 1: 6: 0.2: 2 was added to 90.8 g of a solvent in the preparation of the non- A nonaqueous electrolyte and a secondary battery containing the same were prepared in the same manner as in Example 1 (see Table 2 below).

Comparative Example 11.

The procedure of Example 1 was repeated except that 2.15 g of a mixed additive prepared by mixing 97.85 g of a solvent with LiDFP: FB: TVS: TMS in a weight ratio of 0.9: 8: 0.3: 2 as an additive was added during the preparation of the non- To prepare a nonaqueous electrolyte and a secondary battery containing the same (see Table 2 below).

Comparative Example 12.

Except that 9.04 g of a mixed additive obtained by mixing 90.96 g of a solvent with LiDFP: FB: TVS: ESa in a weight ratio of 1: 6: 0.04: 2 as an additive was added to the nonaqueous electrolyte solution in the same manner as in Example 1 To prepare a nonaqueous electrolyte and a secondary battery containing the same (see Table 2 below).

Comparative Example 13.

In the same manner as in Example 1 except that 3.5 g of a mixed additive in which LiDFP: FB: TVS: PS was mixed at a weight ratio of 1: 6: 0.2: 0.4 as an additive was added to 96.5 g of a solvent at the time of preparing the non- To prepare a nonaqueous electrolyte and a secondary battery containing the same (see Table 2 below).

Experimental Example

Experimental Example 1. Evaluation of low-temperature output characteristics

Each of the lithium secondary batteries prepared in Examples 1 and 4 and Comparative Example 1 and Comparative Example 4 was charged at a constant voltage of 0.33 C / 4.25 V constant current-constant voltage 4.25 V / 0.05 C condition and discharging SOC 50% at a constant current of 0.33C to adjust the charged state of the battery.

Each of the secondary batteries was allowed to stand for 4 hours or more at -30 ° C for temperature equilibrium, and then the voltage drop was measured in a state where a discharge pulse was applied for 30 seconds at a power of 3W to 7W. The SOC setting and the evaluation of the output power at low temperature were conducted using a PNE-0506 charge / discharge device (PNE solution, 5V, 6A, manufactured by the company).

The output characteristics at low temperature for each secondary battery are calculated using the obtained falling voltage value, and are shown in Fig.

Referring to FIG. 1, it can be seen that the voltage drop of the lithium secondary battery including the non-aqueous electrolyte according to the first and fourth embodiments of the present invention is smaller than that of the lithium secondary batteries of Comparative Examples 1 and 4 . From these results, it can be confirmed that the low-temperature output characteristics are excellent.

Experimental Example 2. Evaluation of Capacity Retention after High Temperature Storage

The lithium secondary batteries prepared in Examples 1 to 15 and the lithium secondary batteries prepared in Comparative Examples 1 to 13 were respectively charged at a constant current / constant voltage (CC / CV) of 4.25 V / 0.05 C And discharged at a constant current of 0.33C / 3.0V. At this time, the initial discharge capacity was defined as the discharge capacity measured by using a PNE-0506 charge / discharge device (manufactured by PNE Co., Ltd., 5V, 6A) prior to cell assembly / high temperature storage.

Each lithium secondary battery was set to a SOC 100% charged state and stored at 60 占 폚 for 16 weeks.

Then, the battery was charged at a constant current / constant voltage (CC / CV) of 4.25 V / 0.05 C at 25 ° C and discharged at a constant current of 0.33 C / 3.0 V, and charged in a PNE-0506 charge / discharge device Solution, 5V, 6A) was used to measure the discharge capacity. At this time, the measured discharge capacity was defined as discharge capacity after high temperature storage.

The capacity retention was measured by substituting it into the following formula (1), and the results are shown in Tables 1 and 2 below.

(1): Capacity retention rate (%) = (discharge capacity after high-temperature storage / initial discharge capacity) x 100

Experimental Example 3. Evaluation of Output Characteristics after Storage at High Temperature

The lithium secondary batteries prepared in Examples 1 to 15 and the lithium secondary batteries prepared in Comparative Examples 1 to 13 were respectively discharged at a constant current of 0.33 C at 25 DEG C for an SOC of 50%

Then, the output of each lithium secondary battery was measured through a voltage drop at a constant current (CC) condition of 2.5 V and a discharge pulse for 30 seconds at 2.5C. At this time, the discharge output value measured using a PNE-0506 charge / discharge device (manufacturer: PNE solution, 5V, 6A) was defined as an initial discharge output after cell assembly / high temperature storage.

Each lithium secondary battery was set to a SOC 100% charged state and stored at 60 占 폚 for 16 weeks.

Then, the battery was charged at a constant current / constant voltage (CC / CV) of 4.25 V / 0.05 C at 25 ° C and discharged at a constant current of 0.33 C / 3.0 V, and charged in a PNE-0506 charge / discharge device Solution, 5V, 6A) was used to measure the discharge output value. At this time, the measured discharge output value was defined as discharge output value after storing at high temperature.

The cell measured output was substituted into the following equation (2) to calculate the output retention ratio (%). The results are shown in Tables 1 and 2 below.

(2): Output characteristic (%) = (discharge output (W) / initial discharge output (W) after high temperature storage) × 100

Experimental Example 4. Evaluation of Cell Thickness Growth Rate After High Temperature Storage

The lithium secondary batteries manufactured in Examples 1 to 15 and the lithium secondary batteries prepared in Comparative Examples 1 to 13 were respectively driven at a voltage of 3.0 V to 4.25 V at 25 캜 in a voltage driving range of 0.33 C / 4.25 V constant current - constant voltage 4.25 V / 0.05C, and the thickness of each secondary cell was measured with a plate thickness meter (Mitutoyo (Japan)) under SOC 100% condition. The initial thickness measured after cell assembly is defined as the initial thickness

Then, the initial charge and discharge of the rechargeable lithium secondary batteries were charged to 4.2 V of SOC up to 100%, stored at 60 DEG C for 16 weeks, cooled at room temperature, and then stored at a high temperature using a plate thickness meter (Mitutoyo, The thickness was measured.

The initial thickness and the thickness after high-temperature storage as described above were substituted into the following equation (3) to calculate the thickness increase rate, and the results are shown in Tables 1 and 2 below.

(3): Thickness increase rate (%) = {(thickness after high temperature storage - initial thickness) / initial thickness} x 100

EXPERIMENTAL EXAMPLE 5. Evaluation of cycle life characteristics after storage at high temperature

The lithium secondary batteries prepared in Examples 1 to 15 and the lithium secondary batteries prepared in Comparative Examples 1 to 13 were respectively charged at 25 DEG C at 45 DEG C and at a constant current / constant voltage (CC / CV) of 4.25 V /0.05C and discharged at a constant current of 0.33C / 3.0V. The charging and discharging was performed in one cycle, and the charging and discharging was repeated 500 times.

At this time, the capacity after the first cycle and the capacity after the 500th cycle were measured using a PNE-0506 charge / discharge machine (manufacturer: PNE solution, 5V, 6A by the manufacturer), and the capacity was substituted into the following expression (4) The properties were evaluated. The results are shown in Tables 1 and 2 below.

(4): cycle life characteristic (%) = (500 cycle capacity / one cycle capacity) x 100

In Table 1 and Table 2, PS means 1,3-propane sultone, PRS means 1,3-propanesultone, TMS means trimethylene sulfate, and ESa means ethylene sulfate. Also, MMDS means methylene methane disulfonate.

As shown in Tables 1 and 2, the lithium secondary battery having the non-aqueous electrolyte containing the mixed additives of Examples 1 to 14 had a capacity retention rate of 79.1% or more after high temperature storage, an output characteristic of 81.9% The capacity retention ratio, the output characteristics, the cell thickness increase rate, and the battery capacity increase rate after storage at a high temperature compared to the lithium secondary batteries of Comparative Example 1 and Comparative Example 2 having a non-aqueous electrolyte containing no mixed additive at 29.5% or less and a cycle life characteristic of 80.2% And the cycle life characteristics are all significantly improved.

On the other hand, in the case of the lithium secondary battery of Example 15 in which an excessive amount of the mixed additive was contained, the capacity retention ratio was improved as compared with Comparative Example 2, while the electrolyte wettability was decreased due to the increase of the non-aqueous electrolyte viscosity, Is reduced in comparison with the lithium secondary batteries of Examples 1 to 14.

On the other hand, in the case of the lithium secondary batteries of Comparative Examples 3 to 5 having the nonaqueous electrolyte solution containing at least one component of the mixed additive component in an excessive amount, in Examples 1 to 14 with the nonaqueous electrolyte solution of the present invention The capacity retention rate, the output characteristics, and the cycle life characteristics are all degraded, except for the cell thickness increase rate after high temperature storage, as compared with the lithium secondary battery.

On the other hand, when comparing the lithium secondary batteries of Example 7 and Comparative Example 6 in which the addition of lithium difluorophosphate was different among the additive components, the lithium secondary battery of Comparative Example 6 was incapable of cell operation, 7 lithium secondary batteries exhibited excellent capacity retention, output characteristics, cell thickness increase rate, and high temperature cycle life characteristics after high-temperature storage.

Comparing the lithium secondary batteries of Example 7 and Comparative Example 7 in which addition of fluorobenzene was different among the additive components, the battery of Comparative Example 7 was ignited during overcharging, whereas in Example 7 Of the lithium secondary battery can not be ignited during overcharging while maintaining the capacity retention rate, output characteristics, cell thickness increase rate, and high temperature cycle life characteristics after high temperature storage.

Comparing the lithium secondary batteries of Example 7 and Comparative Example 8 in which addition of tetravinylsilane is different among the additive components, the lithium secondary battery of Example 7 is superior to the lithium secondary battery of Comparative Example 8 by addition of tetravinylsilane It can be seen that exceptionally good capacity retention, output characteristics and cycle life characteristics are realized except for the cell thickness increase rate after high temperature storage.

Further, when comparing the lithium secondary batteries of Example 7 and Comparative Example 9 in which the addition of one sulfonate group or sulfate group-containing compound among the additive components is different, The lithium secondary battery exhibits excellent capacity and output characteristics and cycle life characteristics at a high temperature, which is superior to that of the lithium secondary battery, and exhibits an excellent effect of suppressing the cell thickness increase.

On the other hand, in the case of the secondary battery of Comparative Example 10 having the non-aqueous electrolyte containing methylene methadylsulfonate containing two sulfonate groups, the output characteristics were similar to those of Examples 1 to 14 The capacity retention rate, the output characteristics, and the cycle life characteristics are all degraded compared to the lithium secondary batteries of Examples 1 to 14 having the non-aqueous electrolyte of the present invention.

On the other hand, in the case of the secondary batteries of Comparative Examples 11 to 13 having a non-aqueous electrolyte containing a small amount of at least one component of the mixed additive component, the lithium secondary batteries of Examples 1 to 14 having the non- The capacity retention rate, the output characteristics, and the cycle life characteristics are all degraded.

Experimental Example 6 Overcharge Safety Evaluation Experiment

The lithium secondary battery manufactured in Example 1 and the lithium secondary battery manufactured in Comparative Example 7 were each subjected to a SOC 100% state at 25 占 폚 using a PNE-0506 charge / discharge device (PNE solution, 5V, 6A, 0.33C / 4.25V constant current / constant voltage (CC / CV) conditions. Thereafter, overcharging was carried out with a correct current of 0.33C up to 6.4 V, and the change of temperature and voltage of the battery was measured to confirm whether or not the battery was ignited. The results of the lithium secondary battery of Example 1 are shown in FIG. 2, and the results of the lithium secondary battery of Comparative Example 7 are shown in FIG.

In the case of the lithium secondary battery of Example 1 (see FIG. 2), the voltage was found to be 5.0 V or less in the range of 7 to 22 minutes, while fluorobenzene It is found that the voltage of the lithium secondary battery of Comparative Example 7 (see FIG. 3) provided with the nonaqueous electrolyte solution which does not react with the nonaqueous electrolyte solution rose to 5.2 V around 25 minutes.

That is, in the case of the lithium secondary battery of the present invention, the fluorobenzene reacts with the corresponding voltage band to decompose, thereby suppressing the additional reaction between the battery and the electrolyte, thereby preventing overcharge of the battery. At this time, it can be confirmed that ignition is suppressed by significantly preventing the electrolyte depletion and lithium precipitation due to the temperature increase of the battery and the additional overcharge.

In the case of the lithium secondary battery of Example 1 (see FIG. 2) equipped with a non-aqueous electrolyte containing fluorobenzene as an essential additive component, the temperature rises rapidly to 100 DEG C for 40 minutes, Minute, CID is short-circuited. As a result, the temperature gradually decreases and it is found that the temperature does not reach the ignition temperature. On the other hand, in the case of the secondary battery of Comparative Example 7 (see FIG. 3) provided with the non-aqueous electrolyte containing no fluorobenzene as an additive, the temperature rises rapidly to about 33 minutes, As a result, it can be confirmed that the battery is finally ignited.

These results show that the lithium secondary battery of Example 1 has improved stability upon overcharging.

Claims (10)

1. A lithium salt, an organic solvent and an additive,

   The additive is a mixed additive comprising lithium difluorophosphate, fluorobenzene, tetravinylsilane and one sulfonate group or a compound containing a sulfate group in a weight ratio of 1: 2 to 8: 0.05 to 0.3: 0.5 to 2 A non-aqueous electrolyte for a lithium secondary battery.
2. The method according to claim 1,

   Wherein the weight ratio of the lithium difluorophosphate, the fluorobenzene, the tetravinylsilane and the compound containing one sulfonate group or the sulfate group is 1: 2 to 6: 0.05 to 0.3: 0.5 to 1.5. .
3. The method according to claim 1,

   The one sulfonate group or the compound containing a sulfate group is selected from the group consisting of ethylene sulfate, trimethylene sulfate, methyltrimethylene sulfate, 1,3-propane sultone, 1,4-butane sultone, ethenesulfone, 1-methyl-1,3-propanesultone and 1,3-propanesultone. 2. A non-aqueous electrolyte solution for a lithium secondary battery, comprising:
4. The method according to claim 1,

   Wherein the one sulfonate group or the compound containing a sulfate group is at least one or more selected from the group consisting of ethylene sulfate, trimethylene sulfate, 1,3-propane sultone and 1,3-propanesultone. .
5. The method according to claim 1,

   Wherein the additive is contained in an amount of 1 wt% to 18 wt% based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
6. The method according to claim 1,

   Wherein the nonaqueous electrolyte solution for a lithium secondary battery comprises at least one SEI film forming first additive selected from the group consisting of a halogen-substituted carbonate compound, a nitrile compound, a cyclic carbonate compound, a phosphate compound, a borate compound and a lithium salt compound Further comprising a non-aqueous electrolyte solution for a lithium secondary battery.
7. The method according to claim 1,

   Wherein the nonaqueous electrolyte solution for lithium secondary batteries further comprises a second additive for forming at least one SEI film selected from the group consisting of diphenyl disulfide, di-p-tolyl disulfide and bis (4-methoxyphenyl) disulfide (BMPDS) A non-aqueous electrolyte for a lithium secondary battery.
8. A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte,

   And the nonaqueous electrolyte solution comprises the nonaqueous electrolyte solution for a lithium secondary battery according to claim 1.
9. In claim 8,

   Wherein the positive electrode comprises a lithium-nickel-manganese-cobalt oxide as a positive electrode active material.
10. In claim 9,

    Wherein the lithium-nickel-manganese-cobalt oxide is Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ , Li (Ni _0.35 Mn _0.28 Co _0.37 ) O ₂ , Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Wherein the lithium secondary battery is at least one selected from the group consisting of Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, and Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ .

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