KR20200041171A - Non-aqueous electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte additive, a non-aqueous electrolyte for a lithium ion battery containing the same, and a lithium ion battery. Specifically, the present invention relates to a non-aqueous electrolyte containing a lithium salt, an organic solvent, and a Lewis base-based compound represented by chemical formula 1 as an additive. The present invention also relates to a lithium secondary battery having improved high-temperature storage performance by containing the same.

Description

Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries containing the same {NON-AQUEOUS ELECTROLYTE SOLUTION AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery containing an additive capable of removing a decomposition product of a lithium salt and forming a stable film on an electrode surface, and a lithium secondary battery having improved high temperature storage characteristics by including the same.

With the development of the information society, personal IT devices and computer networks have been developed, and as a result, the overall dependence of society on electrical energy has increased, and technology development for efficiently storing and utilizing electrical energy is required.

For this purpose, the technology most suitable for various uses is a secondary battery-based technology. In the case of a secondary battery, it can be miniaturized to a degree that can be applied to personal IT devices, etc., and it can be applied to electric vehicles, electric power storage devices, etc. Among these secondary battery technologies, lithium ion batteries, which are theoretically the most energy-dense battery systems, are in the spotlight and are currently applied to various devices.

In the case of the lithium ion battery system, unlike the early days when lithium metal was directly applied to the system, a transition metal oxide containing lithium is used as a positive electrode material, and carbon-based materials such as graphite and silicon alloy-based materials are used as a negative electrode material. A system in which lithium metal is not directly used inside a battery, such as application as a negative electrode, has been implemented.

That is, the lithium ion battery system is largely composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte solution as a medium for transferring lithium ions, and a separator.

In the case of the double electrolyte, it is known as a component having a great influence on the stability and safety of the battery, and many studies have been conducted on this. In the case of the electrolyte solution for a lithium ion battery, it is composed of a lithium salt, an organic solvent dissolving it, and a functional additive, and it is important to properly select these components in order to improve the electrochemical properties of the battery.

LiPF ₆ , LiBF ₄ , LiFSI (lithium fluorosulfonyl imide, LiN (SO ₂ F) ₂ ), LiTFSI (lithium (bis) trifluoromethanesulfonyl imide, LiN (SO ₂ CF ₃ ) ₂ ) or LiBOB ( Lithium bis (oxalate) borate, LiB (C ₂ O ₄ ) ₂ ), etc. are used, and in the case of an organic solvent, a carbonate-based organic solvent or an ester-based organic solvent is used.

In the case of such a lithium ion battery, deterioration in performance, such as an increase in resistance during charging and discharging at a high temperature or storage at a high temperature, and a decrease in capacity, has become a major problem.

One of the causes of this phenomenon is a side reaction caused by the deterioration of the electrolyte at high temperature, and among them, decomposition of the lithium salt is known as a cause. That is, by-products are generated by decomposition of the lithium salt at high temperature, and these by-products degrade the passivation film formed on the surfaces of the positive electrode and the negative electrode after activation, causing further decomposition of the electrolyte solution and self-discharge of the negative electrode accompanying it.

Accordingly, recently, in order to secure the passivation ability of the coating on the surface of the electrode at a high temperature, not only does the decomposition decomposition well in the electrolytic solution, but also the new composition of the non-aqueous electrolyte containing an additive capable of effectively removing the decomposition products of the lithium salt. Development is on the rise.

Korea Patent Publication No. 2015-0135278

The present invention is to provide a non-aqueous electrolyte solution for a lithium secondary battery including an additive capable of removing a decomposition product of a lithium salt and forming a stable film on the electrode surface.

In addition, the present invention is to provide a lithium secondary battery having improved high-temperature storage performance by including the non-aqueous electrolyte for the lithium secondary battery.

In one embodiment of the present invention for achieving the above object,

Lithium salt; Organic solvents; And additives,

The additive provides a non-aqueous electrolyte solution for a lithium secondary battery comprising a compound represented by the following Chemical Formula 1.

[Formula 1]

In Chemical Formula 1,

R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,

R ₁ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element or -OR ₂ , wherein R ₂ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element, and a is 0 or 1 It is an integer.

In Formula 1, R is an alkylene group having 1 to 3 carbon atoms, R ₁ is an alkyl group having 1 to 3 carbon atoms or -OR ₂ substituted with at least one fluorine element, wherein R ₂ is at least one fluorine element It may be a substituted C 1-3 alkyl group.

Specifically, the compound represented by Formula 1 may be at least one of the following Formula 1a to Formula 1d.

[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

More specifically, the compound represented by Formula 1 may be a compound represented by Formula 1a.

The compound represented by Formula 1 may be included in 0.07% to 5.5% by weight, specifically 0.1% to 5% by weight, and more specifically 0.5% to 3% by weight based on the total weight of the non-aqueous electrolyte.

In addition, the non-aqueous electrolyte for the lithium secondary battery may further include at least one additional additive selected from the group consisting of sultone-based compounds, halogen-substituted carbonate-based compounds, nitrile-based compounds, cyclic sulfite-based compounds, and cyclic carbonate-based compounds. You can. Specifically, the non-aqueous electrolyte solution for the lithium secondary battery may include a cyclic carbonate-based compound as an additional additive.

In addition, in another embodiment of the present invention

A negative electrode comprising a negative electrode active material; A positive electrode comprising a positive electrode active material; A separator interposed between the cathode and the anode; And an electrolyte,

The electrolyte solution provides a lithium secondary battery that is a non-aqueous electrolyte solution of the present invention.

In this case, the negative active material may include a silicon-based active material.

In the present invention, by including a Lewis base material containing a triple bond and a non-covalent electron pair in the structure as an electrolyte additive, the Lewis acid, a decomposition product generated by decomposition of a lithium salt, is simultaneously removed, and is stable on the electrode surface. A non-aqueous electrolyte solution capable of suppressing the elution of the transition metal from the anode by forming a coating film can be provided. In addition, by including this, it is possible to manufacture a lithium secondary battery with improved high temperature storage performance by improving the self-discharge phenomenon due to the destruction of the SEI film.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor appropriately defines the concept of terms in order to explain his or her invention in the best way. Based on the principle that it can be done, it should be interpreted as a meaning and a concept consistent with the technical idea of the present invention.

Meanwhile, the terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms "include", "have" or "have" are intended to indicate the presence of implemented features, numbers, steps, elements or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

In this specification, "%" means weight percent unless otherwise indicated.

Before describing the present invention, in the description of "carbon numbers a to b" in the specification, "a" and "b" mean 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, "an alkylene group having 1 to 5 carbon atoms" means an alkylene group containing 1 to 5 carbon atoms, ie -CH _2- , -CH ₂ CH _2- , -CH ₂ CH ₂ CH ₂ -,- CH ₂ (CH ₂ ) CH-, -CH (CH ₂ ) CH ₂ -and -CH (CH ₂ ) CH ₂ CH _2- .

At this time, the term "alkylene group" refers to a functional group in the form of a branched or unbranched aliphatic hydrocarbon group or a hydrogen atom missing one by one from carbon atoms located at both ends of the aliphatic hydrocarbon group.

In addition, in the present specification, "substitution" means that at least one hydrogen bonded to carbon is substituted with an element other than hydrogen, unless otherwise defined, for example, an alkyl group having 1 to 5 carbon atoms or a fluorine element. Means substituted with.

In addition, unless otherwise specified in the present invention, "*" means the same or different atoms or connected parts between the ends of chemical formulas.

The passivation film formed on the surface of a conventional positive / negative electrode is formed by decomposition of an electrolytic solution, and is a factor having a great influence on securing high temperature storage performance.

Meanwhile, Lewis acid materials such as HF and PF ₅ produced by thermal decomposition of LiPF ₆ , a lithium salt widely used in lithium ion batteries, are known to be one of the factors that deteriorate the coating. That is, when the surface of the anode is deteriorated by the attack of the acid, transition metal elution occurs, and the surface resistance of the anode increases due to the change in the local structure of the surface, and the theoretical capacity decreases due to the loss of the redox center. The expression dose can be reduced. In addition, in the case of eluted metal ions, it is electrodeposited on the negative electrode reacting in a strong reduction potential band, thereby exposing the negative electrode surface while destroying the film, thereby increasing the irreversible capacity due to the consumption of electrons due to additional electrolyte decomposition and resisting the negative electrode By increasing the, there is a problem of continuously lowering the cell capacity.

Therefore, in order to maintain the passivation ability of the electrode surface, the main solution is to suppress the damage of the coating by removing Lewis acid, which is a decomposition product of the lithium salt.

Accordingly, the present invention is to provide a non-aqueous electrolyte solution containing a Lewis base material capable of removing decomposition products of lithium salt generated during high temperature storage as an additive, and a lithium secondary battery having improved high temperature storage stability by including the same.

Non-aqueous electrolyte

Specifically, in one embodiment of the present invention

Lithium salt; Organic solvents; And additives,

The additive provides a non-aqueous electrolyte solution for a lithium secondary battery comprising a compound represented by the following Chemical Formula 1.

[Formula 1]

In Chemical Formula 1,

R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,

R ₁ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element or -OR ₂ , wherein R ₂ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element, and a is 0 or 1 It is an integer.

(1) lithium salt

First, the lithium salt is in can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example comprising a Li ⁺ as the cation, the anion is ^{F -, Cl -, Br -} , I -, NO 3 _{^{-, N (CN) 2 -}} , BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, B 10 Cl 10 -, BF 2 C 2 O 4 - _{, B (C 2 O 4)} 2 -, 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 -, (CF 3) 6 P -, CF 3 SO 3 -, 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 -, CH 3 SO 3 -, CF 3 (CF 2) 7 SO 3 -, CF _{^{3 CO 2 -, CH 3 CO}} 2 -, SCN - may be at least one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N. Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiCF ₃ CO _2, LiBOB (LiB (C ₂ O ₄ ) ₂ ), LiTFSI (LiN (SO ₂ CF ₃ ) ₂ ), LiFSI (LiN (SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , and LiCH ₃ CO ₂ Or a mixture of two or more.

The lithium salt may be appropriately changed within a range that can be normally used, and may be included in an electrolytic solution at a concentration of 0.8M to 4.0M in order to obtain an optimal passivation film forming effect on the electrode surface.

(2) Organic solvent

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

Specifically, the organic solvent may include a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent.

Examples of the cyclic carbonate-based organic solvent include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3- And any one or a mixture of two or more selected from the group consisting of pentylene carbonate and vinylene carbonate. Among them, as a high-viscosity organic solvent, the dielectric constant is high and ethylene carbonate that dissociates lithium salt in the electrolyte well is included. You can.

In addition, specific examples of the linear viscosity-based organic solvent having low viscosity and low dielectric constant are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl Any one selected from the group consisting of propyl carbonate and ethylpropyl carbonate or a mixture of two or more of them may be used, but is not limited thereto.

Further, the organic solvent may further include the linear ester-based organic solvent and / or the cyclic ester-based organic solvent in order to prepare an electrolyte having high electrical conductivity.

Examples of the linear ester-based organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate. Can be lifted. In addition, the cyclic ester-based organic solvent includes at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. You can.

The organic solvent may be used by adding, without limitation, an organic solvent that is conventionally used in an electrolyte for a lithium secondary battery. For example, at least one organic solvent of an ether-based organic solvent and a nitrile-based organic solvent may be further included.

As the ether-based organic solvent, 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 of them may be used. It is not limited.

The nitrile organic solvent is, for example, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4 It may be one or more selected from the group consisting of -fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

(3) Additive

In addition, the non-aqueous electrolyte solution for a lithium secondary battery of the present invention may include a compound represented by the following Chemical Formula 1 as an additive.

[Formula 1]

In Formula 1, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, R ₁ is an alkyl group having 1 to 5 carbon atoms or -OR ₂ substituted with at least one fluorine element, wherein R ₂ is at least It is an alkyl group of 1 to 5 carbon atoms substituted with one or more fluorine elements, and a is an integer of 0 or 1.

Preferably, in the formula (1), R is an alkylene group having 1 to 3 carbon atoms, R ₁ is an alkyl group having 1 to 3 carbon atoms or -OR ₂ substituted with at least one fluorine element, wherein R ₂ is at least one or more It may be an alkyl group having 1 to 3 carbon atoms substituted with a fluorine element.

In the present invention, the compound represented by Chemical Formula 1, which is included as an electrolyte additive, is a Lewis base material, and removes a Lewis acid such as HF and PF _{5 to} decompose products of lithium salts that cause deterioration at a high temperature of the battery, Deterioration of the SEI film can be prevented, and further disadvantages such as elution of a transition metal from the anode can be improved.

That is, in the case of the compound represented by Chemical Formula 1, since it contains a nitrogen element having a non-covalent electron pair in the structure, it cannot function to suppress the decomposition of the lithium salt by functioning as a Lewis base, but HF is a decomposition product generated by decomposition of anions. And Lewis acids such as PF ₅ can be removed from the electrolyte solution, and thus, the deterioration behavior due to the chemical reaction of the SEI film on the anode or cathode surface resulting from these Lewis acids can be suppressed. As a result, deterioration of the SEI film can be suppressed, and further decomposition of the electrolyte solution of the battery due to destruction of the SEI film can be prevented, thereby finally preventing self-discharge of the battery.

In addition, since the compound represented by Chemical Formula 1 contains a triple-linked propargyl functional group and a fluorine (F) element, the functional group undergoes reductive decomposition to form an SEI film having a high passivation ability on the negative electrode surface, thereby providing high temperature durability of the negative electrode itself. Not only can it be improved, but also the amount of the transition metal deposited on the cathode itself can be reduced. Further, by the propargyl group, adsorption of impurities on the surface of the metallic impurities contained in the anode may be difficult, and thus it is possible to suppress precipitation of the eluted metal ions from the cathode surface. Moreover, since the propargyl group is easily reduced on the surface of the cathode, it is possible to form a stable film on the surface of the cathode, and thus a graphite-based or silicon-based negative electrode by additional reduction and decomposition reaction of the electrolyte solution generated by instability of the SEI film Self-discharge reaction can be prevented.

Therefore, in the case of the non-aqueous electrolyte solution of the present invention containing such a compound as an additive, it is possible to suppress the elution of metal ions by forming a stable SEI film on the cathode and anode surfaces, and attack the anode and cathode surfaces to self-discharge the battery Since it is possible to remove the Lewis acid that can cause the self-discharge of the secondary battery, it is possible to improve the high-temperature storage performance. In particular, even when a non-carbon-based material such as SiO is used as the negative electrode active material, a more stable SEI film can be formed even during volume expansion due to charging and discharging of the electrode, so that a secondary battery with improved high temperature durability can be manufactured.

Meanwhile, the compound represented by Chemical Formula 1 may be at least one of the following Chemical Formulas 1a to 1d.

[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

More specifically, the compound represented by Formula 1 may be a compound represented by Formula 1a.

That is, in the case of the compound represented by Formula 1a, compared to the compound represented by Formula 1d, because of the relatively low molecular weight, the highest proportion of the non-covalent electron pair of nitrile in the compound, the most effective Lewis base. Can play a role. In addition, in the case of the compound of Formula 1a having -SO ₂ -OCF ₃ -at the terminal, the desorption of the fluorine (F) element is easier than the compounds of Formulas 1b and 1c having the -SO ₂ -CF ₃ -group at the terminal Therefore, it has a more advantageous structure to form a negative electrode film such as element LiF. Therefore, in the case of the compound represented by the formula (1a), compared to the compounds represented by the formula (1b to 1d), since the effect of forming a negative electrode film is excellent, when using a non-carbon-based negative electrode such as Si to form a relatively dense and excellent film can do.

Meanwhile, the compound represented by Chemical Formula 1 may be included in an amount of 0.07% to 5.5% by weight, specifically 0.1% to 5% by weight, and more specifically 0.5% to 3% by weight based on the total weight of the non-aqueous electrolyte.

When the compound represented by Chemical Formula 1 is included in the above range, the metal elution suppression effect is improved by the stabilizing effect of the SEI film, and the effect of removing decomposition products of the lithium salt and controlling the increase in resistance of the SEI film are excellent. If the content of the additive is 0.07% by weight, specifically less than 0.1% by weight, HF or PF ₅ may be removed, but the continuous removal effect may be negligible, and when it exceeds 5.5% by weight, decomposition of the excess additive Due to this, the resistance of the electrode may be increased.

Therefore, when the content of the compound represented by Formula 1 is 0.07% by weight to 5.5% by weight, specifically 0.1% by weight to 5% by weight, decomposition products of lithium salts while maximally suppressing a decrease in capacity and an increase in resistance due to side reactions, etc. Can be removed more effectively.

In addition, the non-aqueous electrolyte solution for lithium secondary batteries of the present invention prevents the non-aqueous electrolyte solution from being decomposed and decomposes in the high-power environment, further improves low-temperature high-rate discharge characteristics, high temperature stability, overcharge prevention, and swelling improvement effect during high temperature storage. In order to improve, in addition to the compound of Formula 1, it may further include additional additives capable of forming a more stable ion conductive film on the electrode surface.

Such additional additives may include at least one selected from the group consisting of sultone compounds, halogen substituted carbonate compounds, nitrile compounds, cyclic sulfite compounds, and cyclic carbonate compounds.

The sultone compounds include 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1, And at least one compound selected from the group consisting of 3-propene sultone. The sultone-based compound may be included in 5% by weight or less based on the total weight of the non-aqueous electrolyte. When the content of the sultone-based compound in the non-aqueous electrolyte exceeds 5% by weight, a thick film formed by excess additives may be formed, resulting in an increase in resistance and output deterioration.

In addition, the halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC), and may contain 5% by weight or less based on the total weight of the non-aqueous electrolyte. When the content of the halogen-substituted carbonate-based compound exceeds 5% by weight, cell swelling performance may be deteriorated.

In addition, the nitrile-based compound is succinonitrile (NA), adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane With carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile And at least one compound selected from the group consisting of.

The nitrile-based compound may be included in an amount of 8% by weight or less based on the total weight of the non-aqueous electrolyte. When the total content of the nitrile-based compound in the non-aqueous electrolyte exceeds 8% by weight, resistance increases due to an increase in the coating formed on the electrode surface, and battery performance may be deteriorated.

In addition, the cyclic sulfite-based compounds include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5 -Dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like. It may contain 5% by weight or less based on the total weight of the non-aqueous electrolyte. When the content of the cyclic sulfite-based compound exceeds 5% by weight, a thick film formed by excess additives may be formed, resulting in increased resistance and output deterioration.

In addition, the cyclic carbonate-based compound may include vinylene carbonate (VC) or vinyl ethylene carbonate, and may include 3% by weight or less based on the total weight of the non-aqueous electrolyte. When the content of the cyclic carbonate-based compound in the non-aqueous electrolyte exceeds 3% by weight, cell swelling inhibiting performance may be deteriorated.

More specifically, the additional additive may be a cyclic carbonate-based compound.

The additional additives may be used in combination of two or more, and may be included in an amount of 20% by weight or less, specifically 0.01% by weight to 20% by weight, preferably 0.1 to 10% by weight based on the total amount of the electrolyte solution. When the content of the additive is less than 0.01% by weight, the effect of improving the low temperature output of the battery and improving the high temperature storage characteristic and the high temperature life characteristic is negligible, and when the content of the additional additive exceeds 20% by weight, charge and discharge of the battery There is a possibility that side reactions in the electrolytic solution may occur excessively. Particularly, when the additives for forming the SEI film are added in an excessive amount, they cannot be sufficiently decomposed at a high temperature, and may remain unreacted or precipitated in an electrolyte at room temperature. Accordingly, a side reaction may occur in which the life or resistance characteristics of the secondary battery are deteriorated.

Secondary battery

In addition, it provides a lithium secondary battery comprising the non-aqueous electrolyte of the present invention. Specifically, the lithium secondary battery according to the present invention includes a negative electrode comprising a negative electrode active material; A positive electrode comprising a positive electrode active material; A separator interposed between the cathode and the anode; And a non-aqueous electrolyte solution according to the present invention.

The lithium secondary battery may be prepared by storing an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially stacked in a secondary battery exterior material and then injecting a non-aqueous electrolyte solution of the present invention.

(1) anode

At this time, the positive electrode may be prepared by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Surface treatment with nickel, titanium, silver, or the like can be used.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), a lithium-cobalt oxide (eg, LiCoO _2, etc.), a lithium-nickel oxide (Eg, LiNiO _2, etc.), lithium-nickel-manganese oxide (eg, LiNi _1-Y Mn _Y O ₂ (here, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( Here, 0 <Z <2), etc.), lithium-nickel-cobalt oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1), etc.), lithium-manganese-cobalt System oxides (for example, LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn _2-z1 Co _z1 O ₄ (here, 0 <Z1 <2), etc.), lithium-nickel -Manganese-cobalt oxide (for example, Li (Ni _p Co _q Mn _r1 ) O ₂ (where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2), etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, respectively, 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc.) and the like, and any one or more of these compounds may be included. Among them, the lithium composite metal oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ in that the capacity and stability of the battery can be improved. , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.8 Mn _0.1 Co _0.1 ) O _2, etc.), or lithium nickel cobalt aluminum oxide (for example, Li (Ni _0.8 Co _0.15 Al _0.05 ) O _2, etc.) ), And considering the remarkable improvement effect according to the control of the type and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide is 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 or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O _2, etc., any one or a mixture of two or more of them can be used. have.

The positive electrode active material may be included in 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of solids in the positive electrode slurry. At this time, when the content of the positive electrode active material is 80% by weight or less, the energy density may be lowered and the capacity may be lowered.

In addition, the binder is a component that assists in the bonding of the active material and the conductive material and the like to the current collector, and is usually added at 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, And polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.

In addition, the conductive material is a material that imparts conductivity without causing a chemical change in the battery, and may be added in an amount of 1 to 20% by weight based on the total weight of solids in the positive electrode slurry.

Examples of the conductive material include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; Graphite powder such as natural graphite, artificial graphite, or graphite, which has a very developed crystal structure; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 can be used. Currently, acetylene black-based conductive materials (manufactured by Chevron Chemical Company, manufactured by Denka Singapore Private Limited, or Gulf Oil Company), Ketjen Black EC series (manufactured by Armak Company), Vulcan It is also possible to use commercially available products such as XC-72 (manufactured by Cabot Company) and Super-P (manufactured by Timcal), which are furnace blacks.

In addition, the solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), it may be used in an amount that becomes a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. For example, the solid content concentration in the slurry containing the positive electrode active material and optionally the binder and the conductive material may be included to be 10% to 60% by weight, preferably 20% to 50% by weight.

(2) Cathode

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

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

The negative electrode active material may include a carbon-based active material capable of reversibly intercalating / deintercalating lithium ions, or a silicon-based active material capable of doping and dedoping lithium with the carbon-based active material. .

As the carbon-based active material capable of reversibly intercalating / deintercalating the lithium ions, a carbon-based negative electrode active material generally used in lithium-ion secondary batteries can be used without particular limitation, and typical examples thereof include crystalline carbon, Amorphous carbon or these can be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). Or hard carbon, mesophase pitch carbide, calcined coke, and the like.

In addition, Si, SiO _x (0 <x≤2) and Si-Y alloys (where Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element) as a silicon-based active material capable of doping and dedoping the lithium. It is an element selected from the group consisting of transition metals, rare earth elements, and combinations thereof, and may include at least one selected from the group consisting of not Si), specifically SiO _x (0 <x≤2). have. At this time, the elements Y are Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

In addition, the negative electrode active material is selected from the group consisting of a tin-based active material capable of doping and de-doping lithium, lithium metal, metal or an alloy of these metals and lithium, a metal composite oxide and a transition metal oxide in addition to the carbon-based active material and silicon-based active material. You can also use at least one.

The tin-based active material is Sn, SnO ₂ , Sn-Y (the Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, Sn).

Examples of the metal or alloys of these metals and lithium include Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al And a metal selected from the group consisting of Sn or an alloy of these metals and lithium.

The metal composite oxide includes 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 O _z (Me: Mn, Fe, Pb, Ge; Me ': Al, B, P, Si, Group 1, 2, 3 elements of the periodic table, halogen; group consisting of 0 <x≤1;1≤y≤3; 1≤z≤8) The one selected from can be used.

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

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of solids 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 at 1% to 30% by weight based on the total weight of solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, 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 at 1 to 20% by weight based on the total weight of solids in the negative electrode slurry. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, for example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black. Carbon powder; Graphite powder such as natural graphite, artificial graphite, or graphite, which has a very developed crystal structure; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The solvent may include water or an organic solvent such as NMP and alcohol, and may be used in an amount that becomes a desirable viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, the solid content concentration in the slurry containing the negative electrode active material and optionally the binder and the conductive material may be included to be 50% to 90% by weight, preferably 50% to 85% by weight.

(3) separator

In addition, the separator included in the lithium secondary battery of the present invention is a commonly used conventional porous polymer film, for example, ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / meta Porous polymer films made of polyolefin-based polymers, such as acrylate copolymers, may be used alone or by laminating them, or conventional porous nonwoven fabrics, such as non-woven fabrics of high melting point glass fibers, polyethylene terephthalate fibers, etc. It can be used, but is not limited thereto.

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 or a coin shape using a can.

Hereinafter, examples will be described in detail to specifically describe the present invention. However, the embodiments according to the present invention can be modified in many different 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 more fully describe the present invention to those skilled in the art.

Example

Example 1

(Manufacture of non-aqueous electrolyte)

0.1 g of the compound represented by Formula 1a in 99.4 g of a non-aqueous organic solvent in which 1.0 M LiPF ₆ is dissolved (ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3: 7 volume ratio) and vinylene carbonate as an additive 0.5 g was added to prepare a non-aqueous electrolyte solution of the present invention (see Table 1 below).

(Anode production)

Lithium nickel-manganese-cobalt oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ; NCM) as the positive electrode active material particles, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) 90 as the binder: A positive electrode active material slurry (48% by weight of a solid content) was prepared by adding to the solvent N-methyl-2-pyrrolidone (NMP) at a weight ratio of 5: 5. The positive electrode active material slurry was coated on a positive electrode current collector (Al thin film) having a thickness of 100 μm, dried, and subjected to roll press to prepare a positive electrode.

(Cathode production)

Cathode active material slurry (solid content: 70 wt%) by adding anode active material (artificial graphite: SiO = 95: 5 weight ratio), PVDF as a binder, and carbon black as a conductive material in a weight ratio of 95: 2: 3 to NMP as a solvent. The negative electrode active material slurry was coated on a negative electrode current collector (Cu thin film) having a thickness of 90 µm, dried, and roll-pressed to prepare a negative electrode.

(Secondary battery manufacturing)

The positive electrode and the negative electrode prepared by the above-described method were stacked together with a polyethylene porous film as a separator to prepare an electrode assembly, and then put it in a battery case, poured the non-aqueous electrolyte solution, and sealed to seal the pouch type lithium secondary battery (battery capacity 5.5 mAh ).

Example 2

When preparing the non-aqueous electrolyte, the non-aqueous electrolyte and the same were used in the same manner as in Example 1, except that 5g of the compound represented by Formula 1a and 0.5g of vinylene carbonate as an additive were added to 94.5g of the non-aqueous organic solvent. A lithium secondary battery was prepared (see Table 1 below).

Example 3

When preparing the non-aqueous electrolyte, the non-aqueous electrolyte and the non-aqueous electrolyte were prepared in the same manner as in Example 1, except that 36.5 g of the compound represented by Chemical Formula 1a and 0.5 g of an additional additive, vinylene carbonate, were added to 96.5 g of the non-aqueous organic solvent. A lithium secondary battery including the same was prepared (see Table 1 below).

Example 4

When preparing the non-aqueous electrolyte, the non-aqueous electrolyte and the non-aqueous electrolyte were prepared in the same manner as in Example 1, except that 18.5 g of the compound represented by Chemical Formula 1a and 0.5 g of an additional additive, vinylene carbonate, were added to 98.5 g of the non-aqueous organic solvent. A lithium secondary battery including the same was prepared (see Table 1 below).

Example 5

When preparing the non-aqueous electrolyte, the non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 0.05 g of the compound represented by Chemical Formula 1a and 0.5 g of an additional additive, vinylene carbonate, were added to 99.45 g of the non-aqueous organic solvent. And a lithium secondary battery including the same (see Table 1 below).

Example 6

When preparing the non-aqueous electrolyte, the non-aqueous electrolyte and the non-aqueous electrolyte were prepared in the same manner as in Example 1, except that 63.5 g of the compound represented by Chemical Formula 1a and 0.5 g of an additional additive were added to 93.5 g of the non-aqueous organic solvent. A lithium secondary battery including the same was prepared (see Table 1 below).

Comparative Example 1

A non-aqueous electrolyte and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the additive did not contain an additive and only an additive was added during the production of the non-aqueous electrolyte (see Table 1 below).

Comparative Example 2

A non-aqueous electrolyte and a lithium secondary battery comprising the same were prepared in the same manner as in Example 4, except that instead of the compound of Formula 1a as an additive in the preparation of the non-aqueous electrolyte, the method of Example 4 was used (Table 1 below). Reference).

[Formula 2]

Example Lithium salt Organic solvent additive Additional additives Configuration Amount added
(g) Chemical formula Amount added
(g) Kinds Addition amount (g) Example 1 1.0 M
LiPF ₆ EC: EMC
= 30: 70
(vol%) 99.4 1a 0.1 VC 0.5 Example 2 94.5 1a 5 VC 0.5 Example 3 96.5 1a 3 VC 0.5 Example 4 98.5 1a One VC 0.5 Example 5 99.45 1a 0.05 VC 0.5 Example 6 93.5 1a 6 VC 0.5 Comparative Example 1 99.5 - - VC 0.5 Comparative Example 2 98.5 2 One VC 0.5

Experimental example

Experimental Example 1. Metal (Mn) elution inhibition evaluation experiment

Lithium-manganese-based active material (LiMn ₂ O ₄ ) as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder at a weight ratio of 90: 7.5: 2.5 and a positive electrode current collector having a thickness of 20 μm ( Al foil), dried and roll-pressed to prepare an anode.

Subsequently, the positive electrode was introduced into the non-aqueous electrolyte prepared in Examples 1 to 6 and the respective non-aqueous electrolyte prepared in Comparative Examples 1 and 2 (5 mL), and the electrode was charged for 2 weeks with 0% SOC at 60 ° C. After storage, the concentration of the metal (Mn) eluted in the electrolytic solution was measured using an inductively coupled plasma optical emission spectrophotometer (ICP-OES, inductively coupled plasma optical emission spectrophotometer). The amounts are shown in Table 2 below.

Example Mn elution amount (ppm) Example 1 32 Example 2 15 Example 3 21 Example 4 25 Example 5 40 Example 6 11 Comparative Example 1 78 Comparative Example 2 72

Referring to Table 2, in the case of the non-aqueous electrolytes of Examples 1 to 4 and Example 6 of the present invention, the metal elution was inhibited from the positive electrode containing lithium-manganese oxide by the compound of Formula 1a included as an additive. The effect is remarkably improved, and it can be seen that the concentration of the eluted metal (Mn) is as low as 32 ppm or less.

On the other hand, in the case of the non-aqueous electrolyte solution of Example 5 containing a small amount of additive, the concentration of the eluted metal (Mn) is 40 ppm, it can be seen that increased compared to the non-aqueous electrolyte solution of Examples 1 to 4 and Example 6. .

On the other hand, in the case of the non-aqueous electrolyte of Comparative Example 1, which does not contain an additive, and the non-aqueous electrolyte of Comparative Example 2, which contains an additive that does not contain a -C≡N group, the concentration of the eluted metal (Mn) is 72 ppm or more. , It can be seen that, compared to the non-aqueous electrolytes of Examples 1 to 6, the effect of suppressing metal elution from the anode was significantly reduced.

Experimental Example 2. Performance evaluation experiment after storage at high temperature (60 ℃)

After the high temperature storage of the secondary batteries prepared in Examples 1 to 6 and the secondary batteries prepared in Comparative Examples 1 and 2, the volume change rate and the increase rate of resistance were measured in the following manner.

1) Volume change rate (%):

The secondary batteries prepared in Examples 1 to 6 and the secondary batteries prepared in Comparative Examples 1 and 2 were fully charged with 0.33 C / 4.2 V constant current-constant voltage at room temperature (25 ° C.), respectively, and SOC 50% to 5 C. Initial charging and discharging was performed by discharging for 10 seconds. Then, using the Two-pls, TWD-150DM equipment, the initial volume was measured by putting the initially charged and discharged lithium secondary battery in a bowl filled with ethanol at 25 ° C.

Then, the initially charged and discharged lithium secondary battery is charged to 4.2V each, stored at 60 ° C for 10 weeks (SOC; state of charge 100%), and then used by Two-pls, TWD-150DM equipment. The lithium secondary battery was put in a bowl filled with ethanol at 25 ° C to measure the volume after high temperature storage.

The volume change rate was measured by substituting the initial volume measured as described above and the volume after high temperature storage into the following formula (1), and the results are shown in Table 3 below.

Equation (1): volume change rate (%) = {(volume after high temperature storage-initial volume) / initial volume} × 100

2) Resistance increase rate (%)

The secondary batteries prepared in Examples 1 to 6 and the secondary batteries prepared in Comparative Examples 1 and 2 were fully charged with 0.33 C / 4.2 V constant current-constant voltage at room temperature (25 ° C.), respectively, and 2.5 C at SOC 50%. The discharge was conducted for 10 seconds to perform initial charge and discharge.

At this time, the initial voltage was measured using a PNE-0506 charge / discharger (manufacturer: PNE solution, 5V, 6A). Then, the initial voltage was divided by the current (2.5C) to calculate the resistance value.

Subsequently, the initially charged and discharged lithium secondary battery is charged to 4.2V each, stored at 60 ° C for 10 weeks (SOC; state of charge) 100%), and then discharged again at SOC 50% to 2.5C for 10 seconds. The voltage after high temperature storage was measured. At this time, the voltage was measured using a PNE-0506 charge / discharger (manufacturer: PNE solution, 5V, 6A). Then, the voltage after the high temperature storage was divided by the current (2.5C) to calculate a resistance value.

The resistance increase rate was measured by substituting the initial resistance value measured as described above and the resistance value after high temperature storage into Equation (2) below, and the results are shown in Table 3 below.

Equation (2): Resistance increase rate (%) = {(resistance value after high temperature storage-initial resistance value) / initial resistance value} × 100

Example Volume conversion rate (%) Resistance increase rate (%) Example 1 15 7 Example 2 7 15 Example 3 9 13 Example 4 10 10 Example 5 18 18 Example 6 6 22 Comparative Example 1 35 45 Comparative Example 2 36 41

Looking at Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 4 of the present invention have a volume conversion rate of 15% or less and a resistance increase rate of 15% or less after high temperature storage.

On the other hand, it can be seen that the secondary battery of Example 5 with a non-aqueous electrolyte containing a small amount of additives showed a small increase in volume conversion rate and resistance increase rate after storage at high temperature, both of which were 18%, compared to the secondary batteries of Examples 1 to 4.

In addition, the secondary battery of Example 6 with a non-aqueous electrolyte containing an excessive amount of additives had a volume conversion ratio of 6% after high temperature storage, which was lower than that of the secondary batteries of Examples 1 to 4, but increased in resistance by 22%. It can be seen that the increase from the secondary battery of Examples 1 to 4.

On the other hand, in the case of the lithium secondary battery of Comparative Example 1 with a non-aqueous electrolyte solution containing no additives and the secondary battery of Comparative Example 2 with a non-aqueous electrolyte solution containing an additive not containing -C≡N groups, the volume conversion rate is It can be seen that the secondary battery of Examples 1 to 6 increased significantly to 35% and 36%, respectively.

In addition, in the case of the lithium secondary battery of Comparative Example 1 with a non-aqueous electrolyte solution containing no additives and the secondary battery of Comparative Example 2 with a non-aqueous electrolyte solution containing additives not containing -C≡N groups, the resistance increase rate was respectively It can be seen that the secondary battery of Examples 1 to 6 was significantly increased at 45% and 41%.

Experimental Example 3. Evaluation of anion stabilization

After storing the non-aqueous electrolyte prepared in Examples 1 to 6 and the non-aqueous electrolyte prepared in Comparative Examples 1 and 2 at 60 ° C for 2 weeks, NMR analyzer ( ^1H Bruker 700MHz NMR, solvent tetramethylsilane (TMS) )) To determine the PF ₆ ^- peak value in the electrolyte to evaluate the anion stability. The results are shown in Table 4 below. In this case, the integration value of the PF ₆ ^- peak may be determined to be stabilized as the higher the value, the less the PF ₆ ^- anion is decomposed.

Example PF ₆ ^- integration value of the peak Example 1 99.81 Example 2 99.92 Example 3 99.85 Example 4 99.81 Example 5 99.05 Example 6 99.95 Comparative Example 1 78.58 Comparative Example 2 79.31

Looking at Table 4, in the case of the non-aqueous electrolytes of Examples 1 to 6 of the present invention, the integral value of PF ₆ ^- peak appears at 99 ppm or more, whereas Comparative Examples 1 and 2 containing no additives of the non-aqueous electrolyte PF ₆ ^- it can be seen that the integral of the peak appears in the lower area of less than 80 ppm.

That is, when a lithium salt included in the non-aqueous electrolyte solution, such as LiPF ₆ , is exposed to high temperature, an anion by-product (Lewis acid) of a lithium salt such as PF ₅ is produced. In the case of the non-aqueous electrolyte solution of the present invention, a Lewis base type additive is included. By doing so, it can be determined that the formation of byproducts of the lithium salt is suppressed, resulting in stabilization of PF ₆ ^- ions.

Experimental Example 4. Evaluation of cycle performance at 45 ° C

The secondary batteries prepared in Examples 1 to 6 and the secondary batteries prepared in Comparative Examples 1 and 2, respectively, would be 4.2V at a constant current at 0.33C under a voltage driving range of 3.0V to 4.2V, respectively, at 45 ° C. Charging until then, charging with a constant voltage of 4.2V, the charging was terminated when the charging current became 0.275 mA. Then, it was left for 10 minutes, and then discharged at a constant current of 0.33C until 3.0V. 500 cycles of charging and discharging were performed using the above-mentioned charging and discharging as one cycle.

At this time, the capacity after the first cycle and the capacity after the 500th cycle were measured using a PNE-0506 charge / discharger (manufacturer: PNE Solution Co., Ltd., 5V, 6A), and the capacity was substituted by the following equation (3) to maintain capacity. Was measured. The results are shown in Table 5 below.

Equation (3): Capacity retention rate (%) = (capacity after 500 cycles / capacity after 1 cycle) × 100

Meanwhile, after performing one cycle, the initial voltage was measured by discharging at 50C at 50C for 10 seconds. At this time, the initial voltage was measured using a PNE-0506 charge / discharger (manufacturer: PNE solution, 5V, 6A). Then, the initial resistance value was calculated by dividing the initial voltage by the current (2.5C).

Subsequently, 500 cycles were performed, and then discharge was performed at 50C at 50C for 10 seconds to measure the voltage after 500 cycles. At this time, the voltage was measured using a PNE-0506 charge / discharger (manufacturer: PNE solution, 5V, 6A). Then, the voltage after 500 cycles was divided by the current (2.5C) to calculate a resistance value after 500 cycles.

The resistance increase rate was measured by substituting the initial resistance value measured as described above and the resistance value after 500 cycles into the following equation (4). The results are shown in Table 5 below.

Equation (4): Resistance increase rate (%) = {(resistance value after 500 cycles-initial resistance value) / initial resistance value} × 100

500 ^th capacity retention rate (%) 500 ^th resistance increase rate (%) Example 1 85 8 Example 2 91 19 Example 3 88 16 Example 4 87 12 Example 5 82 15 Example 6 90 21 Comparative Example 1 74 52 Comparative Example 2 75 56

Looking at Table 5, it can be seen that the lithium secondary batteries prepared in Examples 1 to 6 with the non-aqueous electrolyte containing additives had a capacity retention rate of 85% or more after 500 cycles.

On the other hand, after 500 cycles of the lithium secondary battery of Comparative Example 1 with the non-aqueous electrolyte solution containing no additive and the lithium secondary battery of Comparative Example 2 with the non-aqueous electrolyte solution containing the additive containing no -C≡N group It can be seen that the capacity retention rates were significantly reduced to 74% and 75%, respectively.

In addition, it can be seen that the lithium secondary batteries prepared in Examples 1 to 5 with the non-aqueous electrolyte solution containing the additive had a resistance increase rate of 19% or less after 500 cycles.

On the other hand, after 500 cycles of the lithium secondary battery of Comparative Example 1 with the non-aqueous electrolyte solution containing no additive and the lithium secondary battery of Comparative Example 2 with the non-aqueous electrolyte solution containing the additive containing no -C≡N group It can be seen that the rate of increase in resistance increased significantly to 52% and 56%, respectively.

On the other hand, in the case of the secondary battery of Example 6 with a non-aqueous electrolyte containing an excessive amount of additives, the resistance increase rate was 21%, which is inferior to that of the lithium secondary battery with the non-aqueous electrolyte of Examples 1 to 5 You can.

As described above, in the case of a lithium secondary battery having a non-aqueous electrolyte solution containing the additive of the present invention, it can be confirmed that the capacity retention rate and the resistance increase rate, etc., are improved during high temperature storage or charge / discharge at 45 ° C. It can be seen that when the content of the displayed compound satisfies 0.1 to 5% by weight, it exhibits particularly excellent effects.

This is presumed to be due to the fact that if the content of the additive is too low, the effect of removing the decomposition products of the lithium salt and the effect of forming the SEI film on the surface of the negative electrode are insignificant, and if the content of the additive is too large, the capacity retention rate is equal to or higher, but the rate of increase in resistance increases.

On the other hand, since the negative electrode containing a silicon-based active material (for example, SiO) is relatively vulnerable to a Lewis acid-type material, in the case of a secondary battery containing the same, the performance of the electrolyte is accelerated during decomposition of the electrolyte during high temperature storage or high temperature charge / discharge. This tends to deteriorate. However, when using the non-aqueous electrolyte of the present invention containing the compound of Formula 1, it can be seen that the high temperature storage and high temperature charge and discharge performance of the secondary battery having a negative electrode containing a silicon-based active material is improved.

Claims (11)

Lithium salt; Organic solvents; Contains additives,
The additive is a non-aqueous electrolyte solution for a lithium secondary battery comprising a compound represented by Formula 1:
[Formula 1]

In Chemical Formula 1,
R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,
R ₁ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element or -OR ₂ , wherein R ₂ is an alkyl group of 1 to 5 carbon atoms substituted with at least one fluorine element, and a is 0 or 1 It is an integer.
The method according to claim 1,
In Formula 1, R is an alkylene group having 1 to 3 carbon atoms, R ₁ is an alkyl group having 1 to 3 carbon atoms or -OR ₂ substituted with at least one fluorine element, wherein R ₂ is at least one fluorine element A non-aqueous electrolyte solution for a lithium secondary battery, which is a substituted C 1-3 alkyl group.
The method according to claim 1,
The compound represented by Formula 1 is a non-aqueous electrolyte solution for a lithium secondary battery that is at least one of those represented by the following Formulas 1a to 1d.
[Formula 1a]

[Formula 1b]

[Formula 1c]

[Formula 1d]

The method according to claim 3,
The compound represented by Formula 1 is a non-aqueous electrolyte solution for a lithium secondary battery, which is a compound represented by Formula 1a.
The method according to claim 1,
The compound represented by Chemical Formula 1 is a non-aqueous electrolyte solution for a lithium secondary battery that is included in 0.07% to 5.5% by weight based on the total weight of the non-aqueous electrolyte.
The method according to claim 1,
The compound represented by the formula (1) is a non-aqueous electrolyte solution for a lithium secondary battery that is included in 0.1% to 5% by weight based on the total weight of the non-aqueous electrolyte.
The method according to claim 1,
The compound represented by the formula (1) is a non-aqueous electrolyte solution for a lithium secondary battery that is included in 0.5% to 3% by weight based on the total weight of the non-aqueous electrolyte.
The method according to claim 1,
The non-aqueous electrolyte solution for the lithium secondary battery further includes at least one additional additive selected from the group consisting of sultone-based compounds, halogen-substituted carbonate-based compounds, nitrile-based compounds, cyclic sulfite-based compounds, and cyclic carbonate-based compounds. Non-aqueous electrolyte for lithium secondary batteries.
The method according to claim 8,
The additive is a non-aqueous electrolyte for a lithium secondary battery that is a cyclic carbonate-based compound.
A negative electrode comprising a negative electrode active material;
A positive electrode comprising a positive electrode active material;
A separator interposed between the cathode and the anode; And a non-aqueous electrolyte,
The non-aqueous electrolyte is a lithium secondary battery that is the non-aqueous electrolyte of claim 1.
The method according to claim 10,
The negative active material is a lithium secondary battery comprising a silicon-based active material.