KR102633561B1 - Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. Specifically, the non-aqueous electrolyte for lithium secondary batteries of the present invention includes lithium salt; Non-aqueous organic solvent; and an oligomer comprising a repeating unit derived from a monomer represented by Formula 1 below, a repeating unit derived from a monomer represented by Formula 2 below, and a repeating unit derived from a monomer represented by Formula 3 below. . In addition, the lithium secondary battery of the present invention can improve cycle characteristics and high-temperature storage characteristics by including the non-aqueous electrolyte for lithium secondary batteries.

Description

Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries containing the same

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery containing an additive capable of suppressing the elution of transition metals and stabilizing anions generated from lithium salts, and a lithium secondary battery containing the same.

Recently, due to the development of the information society, personal IT devices and computer networks have developed, and as the overall society's dependence on electric energy has increased, there is a need to develop technology to efficiently store and utilize electric energy.

Lithium secondary batteries are the most suitable technology for many purposes. Compared to lead batteries or nickel cadmium batteries, they can be miniaturized to the point where they can be applied to personal IT devices, have high energy density and operating voltage, and can be manufactured with high capacity, such as laptop computers, etc. It is used not only as a power source for mobile phones, but also as an electric vehicle and power storage device.

Lithium-ion batteries are largely composed of a positive electrode made of transition metal oxide containing lithium, a negative electrode that can store lithium, a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and a separator. Among these, lithium salts such as LiPF ₆ are used. Non-aqueous electrolytes that use dissolved non-aqueous organic solvents as their main ingredient are known to be a factor that greatly affects the stability and safety of the battery.

Meanwhile, when LiPF ₆ , a lithium salt in the non-aqueous electrolyte, decomposes during battery operation, LiF and PF ₅ are generated, and when it reacts with the non-aqueous organic solvent, it accelerates the depletion of the non-aqueous organic solvent or generates a large amount of gas. This results in deterioration of high temperature performance and vulnerability to safety. In addition, lithium ion batteries have a problem in which side reactions are promoted, such as transition metals being eluted and the eluted transition metals being reduced at the cathode, as the deterioration of the anode gradually worsens due to battery operation.

Therefore, there is a need for the development of a non-aqueous electrolyte that can form a stable film on the surface of the electrode, prevent side reactions between the non-aqueous electrolyte and the electrode, and suppress the elution of transition metals.

Korean Patent Publication No. 10-2152304

The present invention is intended to solve the above problems, and includes an oligomer obtained from a monomer based on an acrylate structure containing a nitrile group (-CN) and a monomer based on an acrylate structure containing a lactam group, thereby suppressing the elution of transition metals. and to provide a non-aqueous electrolyte for lithium secondary batteries that can realize stabilization of anions generated from lithium salts.

In addition, the present invention seeks to provide a lithium secondary battery with improved cycle characteristics and high-temperature storage characteristics by including the non-aqueous electrolyte for lithium secondary batteries.

According to one embodiment, the present invention

lithium salt;

Non-aqueous organic solvent; and

For a lithium secondary battery comprising; an oligomer comprising a repeating unit derived from a monomer represented by the following Formula 1, a repeating unit derived from a monomer represented by the following Formula 2, and a repeating unit derived from a monomer represented by the following Formula 3: Non-aqueous electrolyte:

[Formula 1]

In Formula 1,

R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms.

[Formula 2]

In Formula 2,

R ₃ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₄ and R ₅ are each independently an alkylene group having 1 to 10 carbon atoms.

[Formula 3]

In Formula 3 above,

R ₆ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₇ is an alkylene group having 1 to 10 carbon atoms.

According to another embodiment, the present invention provides a positive electrode including a positive electrode active material; A negative electrode containing a negative electrode active material; a separator interposed between the cathode and the anode; And it provides a lithium secondary battery comprising a non-aqueous electrolyte for a lithium secondary battery according to the present invention.

The non-aqueous electrolyte for lithium secondary batteries of the present invention contains an oligomer obtained from a monomer based on an acrylate structure containing a nitrile group (-CN) and a monomer based on an acrylate structure containing a lactam group, thereby forming a stable film on the surfaces of the cathode and anode. At the same time as forming, it is possible to chelate the eluted metal ion and form a complex with the anion dissociated from the lithium salt to suppress side reactions caused by the anion.

Therefore, by using the non-aqueous electrolyte for lithium secondary batteries of the present invention, it is possible to implement a lithium secondary battery with improved high-temperature storage performance and cycle capacity maintenance rate when driven at high voltage.

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

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

Meanwhile, in the present specification, “*” refers to a site connected to the main chain in an oligomer or to a binding site such as another monomer, substituent, or terminal group in a chemical formula.

Non-aqueous electrolyte for lithium secondary batteries

According to one embodiment, the present invention provides a non-aqueous electrolyte for lithium secondary batteries.

The non-aqueous electrolyte for the lithium secondary battery is

lithium salt;

Non-aqueous organic solvent; and

For a lithium secondary battery comprising; an oligomer comprising a repeating unit derived from a monomer represented by the following Formula 1, a repeating unit derived from a monomer represented by the following Formula 2, and a repeating unit derived from a monomer represented by the following Formula 3: Non-aqueous electrolyte:

[Formula 1]

In Formula 1,

R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms.

[Formula 2]

In Formula 2,

R ₃ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₄ and R ₅ are each independently an alkylene group having 1 to 10 carbon atoms.

[Formula 3]

In Formula 3 above,

R ₆ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₇ is an alkylene group having 1 to 10 carbon atoms.

(1) Lithium salt

First, the lithium salt is explained as follows.

The lithium salt may be those commonly used in electrolytes for lithium secondary batteries without limitation, and for example, includes Li ⁺ as a cation, and F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , as an anion. N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , B ₁₀ Cl ₁₀ ^- , AlCl ₄ ^- , AlO ₄ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , CH ₃ SO ₃ ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , 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 ^- , (CF ₃ ) ₆ P ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and SCN ^- may include at least one selected from the group consisting of.

Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiB ₁₀ Cl ₁₀ , LiAlCl 4, LiAlO ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH _{3 CO 2 ,} LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiCH ₃ SO ₃ , LiN(SO ₂ F) ₂ (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO ₂ CF ₂ CF ₃ ) ₂ (lithium bis(pentafluoroethanesulfonyl) imide, LiBETI) and LiN( It may contain a single substance selected from the group consisting of SO ₂ CF ₃ ) ₂ (lithium bis(trifluoromethanesulfonyl) imide, LiTFSI) or a mixture of two or more types, and in addition to the above-mentioned lithium salt, it is a lithium salt commonly used in the electrolyte solution of lithium secondary batteries. It can be used without this limitation. Specifically, the lithium salt may include LiPF ₆ .

The lithium salt can be appropriately changed within the range commonly used, but in order to obtain the optimal effect of forming an anti-corrosion film on the surface of the electrode, it should be included in the electrolyte solution at a concentration of 0.8 M to 3.0 M, specifically at a concentration of 1.0 M to 3.0 M. You can. When the concentration of the lithium salt satisfies the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved to improve the capacity characteristics and cycle characteristics of the lithium secondary battery. there is.

(2) Non-aqueous organic solvent

Additionally, a description of the non-aqueous organic solvent is as follows.

As the non-aqueous organic solvent, various non-aqueous organic solvents commonly used in non-aqueous electrolytes can be used without limitation. Decomposition due to oxidation reactions, etc. during the charging and discharging process of secondary batteries can be minimized, and the desired characteristics can be maintained together with additives. There is no limit to the type as long as it can be performed.

Specifically, the non-aqueous organic solvent may include at least one of a cyclic carbonate-based compound with high viscosity that easily dissociates lithium salts due to a high dielectric constant, and a linear carbonate-based compound with low viscosity and low dielectric constant.

The cyclic carbonate-based compounds include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. And it may include at least one selected from the group consisting of vinylene carbonate, and among these, it may include ethylene carbonate.

The linear carbonate-based compound is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. It may include at least one, and specifically may include ethylmethyl carbonate (EMC).

In the present invention, the cyclic carbonate-based compound and the linear carbonate-based compound can be mixed and used. In this case, the mixing ratio of the cyclic carbonate-based compound and the linear carbonate-based compound is 10:90 to 80:20 by volume, specifically 30:70 to 30:70. It may be a 50:50 volume ratio.

When the mixing ratio of the cyclic carbonate-based compound and the linear carbonate-based compound satisfies the above range, a non-aqueous electrolyte solution having higher electrical conductivity can be produced.

Meanwhile, in the present invention, in order to improve the disadvantages of the carbonate-based compound and at the same time increase stability at high temperature and high voltage operation, a propionate compound can be further mixed with the non-aqueous organic solvent.

The propionate compound may include at least one selected from the group consisting of methyl propionate, ethyl propionate (EP), propyl propionate, and butyl propionate, specifically ethyl propionate and propyl propionate. It may contain at least one of propionate.

Meanwhile, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, all components other than the non-aqueous organic solvent, such as lithium salt, oligomer, and optionally included additives, may be non-aqueous organic solvents unless otherwise specified. there is.

(3) Oligomer

The non-aqueous electrolyte for a lithium secondary battery of the present invention contains an oligomer.

The oligomer may include a repeating unit derived from a monomer represented by Formula 1 below, a repeating unit derived from a monomer represented by Formula 2 below, and a repeating unit derived from a monomer represented by Formula 3 below.

[Formula 1]

In Formula 1,

R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms.

[Formula 2]

In Formula 2,

R ₃ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₄ and R ₅ are each independently an alkylene group having 1 to 10 carbon atoms.

[Formula 3]

In Formula 3 above,

R ₆ is hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₇ is an alkylene group having 1 to 10 carbon atoms.

The oligomer of the present invention contains a repeating unit structure derived from a monomer containing a terminal nitrile group based on an acrylate-based structure, thereby forming a stable film on the surface of the anode and forming a strong coordination bond with the metal ion eluted from the anode. By forming, metal ion elution can be controlled. Therefore, the high-temperature durability, high-temperature storage characteristics, and high-temperature stability of the battery can be improved.

In addition, the oligomer of the present invention contains a repeating unit structure derived from a monomer containing a terminal lactam group based on an acrylate-based structure, so that it can form a complex by coordinating with the thermal decomposition product of lithium salt or an anion dissociated from lithium salt. , As a result, the thermal decomposition products of the lithium salt or the anions dissociated from the lithium salt are stabilized, thereby suppressing side reactions between them and the electrolyte for a lithium secondary battery.

The non-aqueous electrolyte containing the oligomer of the present invention can suppress side reactions of the electrolyte and form a strong SEI film with low resistance, thereby preventing side reactions between the electrode and the electrolyte and suppressing gas generation. Additionally, the cycle characteristics of a lithium secondary battery can be improved by significantly lowering the defect occurrence rate by reducing the internal resistance of the battery.

The oligomer of the present invention may be an oligomer represented by the following formula (4).

[Formula 4]

In Formula 4 above,

R ₁ , R ₃ and R ₆ are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,

R ₂ is an alkyl group having 1 to 20 carbon atoms,

R ₄ , R ₅ and R ₇ are each independently an alkylene group having 1 to 10 carbon atoms,

m is 0.1 to 30 moles,

n is 0.1 to 80 moles,

o is from 0.1 to 80 moles.

Specifically, in Formula 4, R ₂ may be an alkyl group having 1 to 10 carbon atoms, and preferably an alkyl group having 1 to 7 carbon atoms.

Additionally, in Formula 4, R ₄ and R ₅ may each independently be an alkylene group having 1 to 7 carbon atoms, and preferably each independently may be an alkylene group having 1 to 5 carbon atoms.

Additionally, in Formula 4, R ₇ may be an alkylene group having 1 to 7 carbon atoms, and preferably an alkylene group having 1 to 5 carbon atoms.

Preferably, the oligomer may be at least one selected from the group consisting of oligomers represented by the following formulas 4-1 and 4-2.

[Formula 4-1]

In Formula 4-1,

m1 is 0.1 to 30 moles,

n1 is 0.1 to 80 moles,

o1 is from 0.1 to 80 moles.

[Formula 4-2]

In Formula 4-2,

m2 is 0.1 to 30 moles,

n2 is 0.1 to 80 moles,

o2 is from 0.1 to 80 moles.

The weight average molecular weight (Mw) of the oligomer of the present invention can be adjusted by the number of repeating units and may be about 3,000 g/mol to 300,000 g/mol, specifically 5,000 g/mol to 50,000 g/mol. When the weight average molecular weight of the oligomer is within the above range, the physical properties of the oligomer itself are prevented from becoming rigid, and the affinity for the non-aqueous electrolyte solvent increases so that it can be easily dissolved, so the formation of a uniform and excellent electrolyte can be expected.

The weight average molecular weight can be measured using a gel permeation chromatography (GPC) device, and unless otherwise specified, molecular weight may refer to the weight average molecular weight. For example, in the present invention, measurement is performed using the Agilent 1200 series under GPC conditions, and the column used at this time can be an Agilent PL mixed B column, and the solvent can be THF or DMF.

Additionally, the oligomer may be included in an amount of 0.1% to 25% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery. When the oligomer is included in the above content range, the effect of improving anion stabilization and forming a stable film can be realized.

When the oligomer content is 0.1% by weight or more, anion stabilization can be maintained more stably due to the formation of a complex with anions during the battery operation time, and metal ion elution is prevented by forming a film and complex with metal ions due to adsorption on the anode surface. It can be suppressed. In addition, when the content of the oligomer is 25% by weight or less, an increase in the viscosity of the electrolyte due to excess compounds can be prevented, the mobility of ions in the battery can be improved, and the cell swelling inhibition effect can be greatly improved, By suppressing excessive film formation, an increase in battery resistance can be effectively prevented, thereby preventing a decrease in capacity and cycle characteristics.

Specifically, the oligomer may be included in an amount of 0.5 to 20% by weight, preferably 0.5 to 15% by weight, and more preferably 0.5 to 7.0% by weight, based on the total weight of the non-aqueous electrolyte for lithium secondary batteries.

(4) Other additives

In addition, the non-aqueous electrolyte for lithium secondary batteries of the present invention prevents the non-aqueous electrolyte from decomposing in a high-power environment, causing cathode collapse, and has low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion suppression effects at high temperatures. In order to improve, other additional additives may be added in addition to the above two types of nitrile-based additives, if necessary.

Examples of such other additives include cyclic carbonate-based compounds, halogen-substituted carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphate-based or phosphite-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, At least one selected from the group consisting of silane-based compounds and lithium salt-based compounds may be mentioned.

Examples of the cyclic carbonate-based compound include vinylene carbonate (VC), vinylethylene carbonate (VEC), and the like.

Examples of the halogen-substituted carbonate-based compound include fluoroethylene carbonate (FEC).

The sultone-based compounds include, for example, 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1- It may be at least one compound selected from the group consisting of methyl-1,3-propene sultone.

The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), etc.

The phosphate-based or phosphite-based compounds include, for example, lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and tris(2). It may be at least one selected from the group consisting of ,2,2,-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphite.

The borate-based compounds include, for example, tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), which can form a film on the surface of the cathode, lithium bisoxalate borate (LiB(C ₂ O ₄ ) ₂ , LiBOB ), etc.

The nitrile-based compounds include compounds other than 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile, such as succinonitrile, pimelonitrile, adiponitrile, acetonitrile, and pro Phionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluoride It may include at least one compound selected from the group consisting of robenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

The benzene-based compound may be fluorobenzene or the like.

The amine-based compound may be triethanolamine, ethylenediamine, etc., and the silane-based compound may be tetravinylsilane.

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution and includes LiPO ₂ F ₂ , LiBF ₄ , and the like.

Among these other additives, in order to form a more robust SEI film on the cathode surface, other additives with excellent film forming effect on the cathode surface, specifically VC, 1,3-PS, Esa, vinylethylene carbonate, and fluoroethylene carbonate (FEC) , lithium oxalyldifluoroborate (LiODFB), 1,4-dicyano-2-butene, and 1,3,5-cyclohexanetricarbonitrile.

The other additives may be used in combination of two or more types of compounds, and may be included in the non-aqueous electrolyte in an amount of 0.01 to 50% by weight, specifically 0.01 to 10% by weight, and preferably 0.05 to 5% by weight. When it is within the above range, it is desirable because it is possible to sufficiently realize the effect of improving cycle characteristics by other additives, while preventing the remaining unreacted substances of other additives and the occurrence of excessive side reactions due to excessive addition.

Lithium secondary battery

In addition, another embodiment of the present invention provides a lithium secondary battery containing the non-aqueous electrolyte for lithium secondary batteries of the present invention. Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and the non-aqueous electrolyte solution for lithium secondary batteries described above.

Meanwhile, the lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially stacked between the positive electrode and the negative electrode, storing it in a battery case, and then adding the non-aqueous electrolyte of the present invention.

The method of manufacturing the lithium secondary battery of the present invention can be manufactured and applied according to a common method known in the art, and will be described in detail later.

(1) anode

The positive electrode according to the present invention may include a positive electrode active material layer containing a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive material and/or a binder.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and is specifically composed of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), and aluminum (Al). It may include a lithium composite metal oxide represented by the following formula (5) containing lithium and at least one metal selected from the group.

[Formula 5]

Li _1+a Ni _x Co _y M ¹ _z M ² _w O ₂

In Formula 5 above,

M ¹ is Mn, Al or a combination thereof,

M ² is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, 0≤a≤0.5, 0<x≤1.0, 0<y≤0.4, 0<z≤0.4, 0 ≤w≤0.1.

The 1+a represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0≤a≤0.5, preferably 0≤a≤0.2, and more preferably 0≤a≤0.1.

The x represents the atomic fraction of nickel among all transition metal elements in lithium transition metal oxide, 0<x≤1.0, specifically 0.55<x<1.0, more specifically 0.6≤x≤0.98, and even more specifically 0.6. It may be ≤x≤0.95.

The y represents the atomic fraction of cobalt among all transition metal elements in the lithium transition metal oxide, and may be 0<y≤0.4, specifically 0<y≤0.3, and more specifically 0.05≤y≤0.3.

The z represents the atomic fraction of the M ¹ element among all transition metal elements in the lithium transition metal oxide, and may be 0<z≤0.4, preferably 0<z≤0.3, and more preferably 0.01≤z≤0.3.

The w represents the atomic fraction of the M ² element among all transition metal elements in the lithium transition metal oxide, and is 0<w≤0.1, preferably 0<w≤0.05, and more preferably 0<w≤0.02.

Specifically, in order to implement a high-capacity battery, the positive electrode active material is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ with a Ni content of 0.55 atm% or more, Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ , Li(Ni _0.7 Mn _0.2 Co _0.1 )O ₂ , Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , Li( _{It may include a lithium complex transition metal oxide such as Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 ) O 2 or Li ( Ni 0.90 Mn 0.05 Co 0.05 ) O 2} .

On the other hand, when high-content nickel (Hi-Ni) with a Ni content exceeding 0.55 is applied as the lithium transition metal oxide, the size of the Li ⁺¹ ion and Ni ⁺² ion are similar, so the positive electrode active material is used during the charge and discharge process. A cation mixing phenomenon occurs in which the positions of Li ⁺¹ ions and Ni ⁺² ions change within the layered structure. In other words, depending on the variation in the oxidation number of Ni contained in the positive electrode active material, the nickel transition metal with d orbitals must have a regular octahedral structure when coordinated in environments such as high temperatures, but the order of energy levels may be reversed due to external energy supply. A distorted octahedron is formed due to a non-uniformization reaction in which the oxidation number changes, resulting in deformation and collapse of the crystal structure of the positive electrode active material. Moreover, during high-temperature storage, the side reaction between the cathode active material and the electrolyte causes another side reaction in which transition metals, especially nickel metal, are eluted from the cathode active material, resulting in depletion of the electrolyte and deterioration of overall performance of the secondary battery due to structural collapse of the cathode active material. do.

In the present invention, this problem can be improved by using a non-aqueous electrolyte containing an additive of a specific composition and a positive electrode containing a high content nickel (Hi-Ni) transition metal oxide as a positive electrode active material. That is, the non-aqueous electrolyte of the present invention forms a strong ion conductive film on the surface of the anode, suppressing the mixing of positive ions between Li ⁺¹ ions and Ni ⁺² ions, and effectively suppressing side reactions between the anode and the electrolyte and metal elution. This can alleviate the structural instability of the high-capacity electrode. Therefore, a sufficient amount of nickel transition metal can be secured to secure the capacity of the lithium secondary battery, and the output characteristics can be improved by increasing the energy density.

On the other hand, the positive electrode active material of the present invention may include a lithium composite metal oxide represented by Chemical Formula 5, a lithium-manganese-based oxide (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), and a lithium-cobalt-based oxide, depending on the secondary battery use. (e.g., LiCoO _2, etc.), lithium-nickel-based oxide (e.g., LiNiO ₂ , etc.), lithium-nickel-manganese oxide (e.g., LiNi _1-Y Mn _Y O ₂ (0<Y< 1), LiMn _2-z Ni _z O ₄ (0＜Z＜2), lithium-nickel-cobalt-based oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (0<Y1<1), lithium-manganese -Cobalt-based oxides (e.g., LiCo _1-Y2 Mn _Y2 O ₂ (0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (0<Z1<2), or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (0＜p1＜2, 0＜q1＜2, 0＜r2＜2, p1+q1+r2=2) etc. can also be used in combination.

The positive electrode active material may be included in an amount of 80 to 98% by weight, more specifically, 85 to 98% by weight, based on the total weight of the positive electrode active material layer. When the positive electrode active material is contained within the above range, excellent capacity characteristics can be exhibited.

Next, the conductive material is used to provide conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. Specific examples include carbon powders such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; 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; Conductive powders such as fluorinated carbon powder, aluminum powder, or 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, and one type of these may be used alone or a mixture of two or more types may be used.

The conductive material may be included in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the positive electrode active material layer.

Next, the binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive active material and the current collector.

Examples of such binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; And one type alone or a mixture of two or more types of silane-based binders may be used.

The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the positive electrode active material layer.

The positive electrode of the present invention can be manufactured according to a positive electrode manufacturing method known in the art. For example, the positive electrode is prepared by dissolving or dispersing the positive electrode active material, binder, and/or conductive material in a solvent, applying a positive electrode slurry onto the positive electrode current collector, followed by drying and rolling to form an active material layer, or It can be manufactured by casting the positive electrode active material layer on a separate support and then laminating the film obtained by peeling off the support on the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , surface treated with silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. and the like, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used can be adjusted so that the positive electrode mixture has an appropriate viscosity in consideration of the application thickness, manufacturing yield, workability, etc. of the positive electrode mixture, and is not particularly limited.

(2) cathode

Next, the cathode will be explained.

The negative electrode according to the present invention includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material layer may further include a conductive material and/or binder, if necessary.

The negative electrode active material may be various types of negative electrode active materials used in the art, such as carbon-based negative electrode active materials, silicon-based negative electrode active materials, or mixtures thereof.

According to one embodiment, the negative electrode active material may include a carbon-based negative electrode active material, and the carbon-based negative electrode active material may include various carbon-based negative electrode active materials used in the industry, such as natural graphite, artificial graphite, and kishimen. Graphite-based materials such as graphite (Kish graphite); Pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes. High-temperature calcined carbon, soft carbon, hard carbon, etc. may be used. The shape of the carbon-based negative active material is not particularly limited, and materials of various shapes such as amorphous, plate-shaped, flaky, spherical, or fibrous may be used.

Preferably, the negative electrode active material may be at least one of natural graphite and artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion to the current collector and suppress detachment of the active material.

According to another embodiment, the negative electrode active material may include a silicon-based negative electrode active material together with the carbon-based negative electrode active material.

The silicon-based negative electrode active material is, for example, metallic silicon (Si ₎ , silicon oxide (SiO It is an element selected from the group consisting of elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, but may include one or more types selected from the group consisting of Si. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), 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.

Since the silicon-based negative electrode active material exhibits higher capacity characteristics than the carbon-based negative electrode active material, better capacity characteristics can be obtained when the silicon-based negative electrode active material is additionally included. However, in the case of an anode containing a silicon-based anode active material, the SEI film contains more oxygen (O)-rich components than a graphite anode, and the SEI film containing O-rich components is electrolyte solution. If a Lewis acid such as HF or PF ₅ is present, it tends to decompose more easily. Therefore, in the case of a negative electrode containing a silicon-based negative electrode active material, it is necessary to suppress the generation of Lewis acids such as HF and PF ₅ in the electrolyte solution or to remove (or scavenge) the generated Lewis acids in order to maintain a stable SEI film. Since the non-aqueous electrolyte according to the present invention contains an electrolyte additive that forms a stable film on the positive and negative electrodes and has an excellent Lewis acid removal effect, it can effectively suppress SEI film decomposition when using a negative electrode containing a silicon-based active material.

Meanwhile, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 3:97 to 99:1, preferably 5:95 to 15:85, in weight ratio. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, capacity characteristics are improved and volume expansion of the silicon-based negative electrode active material is suppressed, thereby ensuring excellent cycle performance.

The negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent capacity characteristics and electrochemical properties can be obtained.

Next, the conductive material is an ingredient to further improve the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. These conductive materials are not particularly limited as long as they are conductive without causing chemical changes in the battery. For example, carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or carbon powder such as thermal black; 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; Conductive powders such as fluorinated carbon 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 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 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of binders include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); Rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; A polyalcohol-based binder containing polyvinyl alcohol; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binder; polyester-based binder; and silane-based binders.

The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the negative electrode active material layer.

The cathode can be manufactured according to a cathode manufacturing method known in the art. For example, the negative electrode may be prepared by applying a negative electrode slurry prepared by dissolving or dispersing the negative electrode active material and optionally a binder and a conductive material in a solvent onto the negative electrode current collector, followed by rolling and drying to form an active material layer, or using the negative electrode active material. It can be manufactured by casting the layer on a separate support and then peeling off the support and lamination of the obtained film onto the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, it may be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector may typically have a thickness of 3㎛ to 500㎛, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. and the like, and one type of these may be used alone or a mixture of two or more types may be used. The amount of the solvent used can be adjusted so that the anode slurry has an appropriate viscosity in consideration of the application thickness of the anode mixture, manufacturing yield, workability, etc., and is not particularly limited.

(3) Separator

The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

The separator separates the negative electrode from the positive electrode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. In particular, it has low resistance to ion movement of lithium salts and moisturizes the electrolyte. It is desirable to have excellent abilities.

Specifically, a porous polymer film as a separator, for example, a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Alternatively, a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing a ceramic component or polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

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

The lithium secondary battery according to the present invention can not only be used in battery cells used as a power source for small devices, but can also be preferably used as a unit cell in medium to large-sized battery modules containing a plurality of battery cells.

Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. Examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

Example

Example One.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

LiPF ₆ was dissolved to 1.0M in a non-aqueous organic solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at a volume ratio of 30:70, and then dissolved in an oligomer represented by Chemical Formula 4-1 (m1: 20, n1: 70, o1:10, weight average molecular weight: 12,000 g/mol) and other additives such as 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate for lithium secondary batteries. A non-aqueous electrolyte was prepared (see Table 1 below).

(Lithium secondary battery manufacturing)

The positive electrode active material (Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ ), conductive material (carbon black), and binder (polyvinylidene fluoride) were mixed with the solvent N-methyl-2-pyrrolidone in a weight ratio of 97.5:1:1.5. (NMP) was added to prepare a positive electrode slurry (solid content: 50% by weight). The positive electrode slurry was applied to a 12㎛ thick aluminum (Al) thin film, which is a positive electrode current collector, and dried and roll pressed to prepare a positive electrode.

The negative electrode active material (artificial graphite:SiO=88:12 weight ratio), binder (SBR-CMC), and conductive material (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to create a negative electrode slurry (solid content: 60% by weight). ) was prepared. The negative electrode slurry was applied to a 6㎛ thick copper (Cu) thin film, which is a negative electrode current collector, and dried and roll pressed to prepare a positive electrode.

An electrode assembly is manufactured by interposing a porous polymer separator made of polyolefin polymer between the manufactured positive electrode and the negative electrode in a dry room, then the assembled electrode assembly is stored in a pouch-type battery case, and the non-aqueous electrolyte for a lithium secondary battery is added. A pouch-type lithium secondary battery was manufactured by injecting the solution.

An electrode assembly is manufactured in a dry room using a polyolefin-based porous separator coated with inorganic particles (Al ₂ O ₃ ) between the manufactured positive electrode and the negative electrode, and then the assembled electrode assembly is stored in a pouch-type battery case, A pouch-type lithium secondary battery was manufactured by injecting the non-aqueous electrolyte for a lithium secondary battery.

Example 2.

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, then 5.0% by weight of the oligomer represented by Chemical Formula 4-1 (m1: 20, n1: 70, o1:10, weight average molecular weight: 12,000 g/mol) and other Lithium was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was prepared by adding 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate as additives. A non-aqueous electrolyte for secondary batteries and a lithium secondary battery containing the same were manufactured (see Table 1 below).

Example 3.

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, and then 10.0% by weight of the oligomer represented by Chemical Formula 4-1 (m1: 20, n1: 70, o1:10 / weight average molecular weight: 12,000 g/mol) and other Lithium was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was prepared by adding 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate as additives. A non-aqueous electrolyte for secondary batteries and a lithium secondary battery containing the same were manufactured (see Table 1 below).

Example 4.

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, then 30.0% by weight of the oligomer represented by Chemical Formula 4-1 (m1: 20, n1: 70, o1:10 / weight average molecular weight: 12,000 g/mol) and other Lithium was prepared in the same manner as in Example 1, except that a non-aqueous electrolyte for a lithium secondary battery was prepared by adding 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate as additives. A non-aqueous electrolyte for secondary batteries and a lithium secondary battery containing the same were manufactured (see Table 1 below).

Comparative Example 1.

LiPF ₆ is dissolved in a non-aqueous organic solvent to a concentration of 1.0M, and then other additives such as 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate are added to prepare a non-aqueous electrolyte solution. A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the same were manufactured in the same manner as in Example 1, except that (see Table 1 below).

Comparative Example 2.

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, and then 0.5% by weight of the compound represented by the following formula (6) (a: 30, b: 70, weight average molecular weight: 12,000 g/mol) and other additives, vinylene carbonate. A non-aqueous electrolyte for a lithium secondary battery and a non-aqueous electrolyte containing the same were prepared in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 1% by weight, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate. A lithium secondary battery was manufactured (see Table 1 below).

[Formula 6]

Comparative Example 3.

LiPF ₆ was dissolved in a non-aqueous organic solvent to a concentration of 1.0M, and then 5.0% by weight of the oligomer represented by Chemical Formula 6 and other additives such as 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone, and 1.0% by weight of ethylene sulfate were added. A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery containing the same were prepared in the same manner as in Example 2, except that the non-aqueous electrolyte for a lithium secondary battery was prepared by adding % (see Table 1 below).

Example additive oligomer Total content of other additives (% by weight) chemical formula Content (% by weight) Example 1 4-1 0.5 2.5 Example 2 4-1 5.0 2.5 Example 3 4-1 10.0 2.5 Example 4 4-1 30.0 2.5 Comparative Example 1 - - 2.5 Comparative Example 2 6 0.5 2.5 Comparative Example 3 6 5.0 2.5

Experiment example

Experimental Example 1. Evaluation of high temperature cycle characteristics (1)

The lithium secondary batteries prepared in Examples 1 to 3 and the lithium secondary batteries prepared in Comparative Examples 1 to 3 were each charged to 4.2V at 45°C at a 0.33C rate under constant current/constant voltage conditions, and then charged under constant current conditions at a 0.33C rate. One cycle of discharging to 3V was performed, and then the discharge capacity and resistance after one cycle were measured.

Then, after 100 cycles of charging and discharging under the 1 cycle conditions, the capacity maintenance rate (%) and resistance increase rate (%) were measured. Capacity retention rate (%) was calculated according to [Equation 1] below, and resistance increase rate (%) was calculated according to [Equation 2] below. The measurement results are listed in Table 2 below.

[Equation 1]

Capacity maintenance rate (%) = (discharge capacity after 100 cycles/discharge capacity after 1 cycle) × 100

[Equation 2]

Resistance increase rate (%) = {(resistance after 100 cycles - resistance after 1 cycle)/resistance after 1 cycle}×100

Experimental Example 2. Evaluation of high temperature cycle characteristics (2)

The lithium secondary batteries prepared in Examples 1 to 3 and the lithium secondary batteries prepared in Comparative Examples 1 to 3 were each charged to 4.2V at 45°C at a 0.33C rate under constant current/constant voltage conditions, and then charged under constant current conditions at a 0.33C rate. After one cycle of discharging to 3V under low temperature, the initial thickness was measured. Then, after 100 cycles of charging and discharging under the above 1 cycle conditions, the thickness was measured, the volume increase rate was calculated, and the results are listed in Table 2 below.

After 100 cycles
Capacity maintenance rate (%) After 100 cycles
Resistance increase rate (%) After 100 cycles
Volume increase rate (%) Example 1 98.0 1.9 2.9 Example 2 98.8 1.5 2.6 Example 3 97.6 2.2 3.2 Comparative Example 1 87.6 6.0 8.5 Comparative Example 2 91.3 4.3 5.4 Comparative Example 3 92.2 3.6 5.1

Looking at Table 2, in the case of the secondary batteries of Examples 1 to 3 of the present invention, the capacity retention rate (%), resistance increase rate (%), and volume increase rate (%) after 100 cycles at high temperature (45°C) were compared to Comparative Example 1. It can be seen that there is an improvement compared to the secondary battery of 3 to 3.

Experimental Example 3. Evaluation of volume increase rate after high temperature storage

The lithium secondary batteries manufactured in Examples 1 to 3 and the lithium secondary batteries manufactured in Comparative Examples 1 to 3 were each charged to 4.2V under constant current/constant voltage conditions at a rate of 0.33C at room temperature (25°C), and then charged to 4.2V under constant current/constant voltage conditions. of discharge) was discharged to 50% to set the SOC to 50%, then discharged for 10 seconds at a 2.5C rate, and then the initial volume was measured.

Then, after storing at 60°C for 8 weeks, the volume of each lithium secondary battery was measured after high temperature storage to confirm the volume increase rate, and the results are listed in Table 3 below.

Volume increase rate (%) after high temperature storage Example 1 1.2 Example 2 0.9 Example 3 1.8 Comparative Example 1 3.7 Comparative Example 2 3.0 Comparative Example 3 2.7

Looking at Table 3, it can be seen that in the case of the secondary batteries of Examples 1 to 3 of the present invention, the volume increase rate (%) after high temperature storage was suppressed compared to the secondary batteries of Comparative Examples 1 to 3.

Experimental Example 4. Evaluation of recovery capacity

The lithium secondary batteries manufactured in Examples 1 to 4 and the lithium secondary batteries manufactured in Comparative Examples 1 to 3 were fully charged to SOC 100% (4356 mAh) under voltage conditions of 4.45 V, respectively. Afterwards, the temperature was raised from 25℃ to 60℃ at a heating temperature of 0.7℃/min, stored at 60℃ for 8 weeks, then charged at 0.33C and discharged at 0.33C to measure the recovery capacity, and the results were reported. It is shown in Table 4 below.

Recovery Capacity (%) Example 1 96.4 Example 2 97.2 Example 3 95.9 Example 4 83.1 Comparative Example 1 86.0 Comparative Example 2 91.9 Comparative Example 3 93.2

Looking at Table 4, it can be seen that in the case of the secondary batteries of Examples 1 to 4 of the present invention, the recovery capacity (%) was improved compared to the secondary batteries of Comparative Examples 1 to 3. Meanwhile, in the case of the secondary battery of Example 4 containing a somewhat large amount of additives, it can be seen that the recovery capacity (%) decreased compared to the secondary battery of Examples 1 to 3 due to an increase in the internal resistance of the battery.

Experimental Example 5. Evaluation of metal elution amount

The lithium secondary batteries manufactured in Examples 1 to 4 and the lithium secondary batteries manufactured in Comparative Examples 1 to 3 were each fully charged to SOC 100% (4356 mAh) under voltage conditions of 4.45 V. Afterwards, the temperature was raised from 25℃ to 60℃ at a heating temperature of 0.7℃/min, stored at 60℃ for 8 weeks, then charged at 0.33C and discharged at 0.33C, and decomposed in a fully discharged state to the cathode. The amounts of precipitated Ni, Co, and Mn were analyzed (ICP-OES, Perkin Elmer, AVIO 500), and the results are shown in Table 5 below.

Metals (Ni, Co, Mn) total elution amount (ppm) Example 1 176 Example 2 134 Example 3 87 Example 4 74 Comparative Example 1 303 Comparative Example 2 105 Comparative Example 3 98

Looking at Table 5, it can be seen that in the case of the secondary batteries of Examples 1 to 4 of the present invention, the volume increase rate (%) of the amount of metal ions eluted after high temperature storage decreased compared to the secondary batteries of Comparative Examples 1 to 3. From these results, it can be seen that the lithium secondary battery using the non-aqueous electrolyte of the present invention has an improved effect of suppressing metal elution.

Claims (10)

lithium salt;
Non-aqueous organic solvent; and
A non-aqueous electrolyte solution for a lithium secondary battery containing an oligomer represented by the following formula (4):
[Formula 4]

(In Formula 4 above,
R ₁ , R ₃ and R ₆ are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms,
R ₂ is an alkyl group having 1 to 20 carbon atoms,
R ₄ , R ₅ and R ₇ are each independently an alkylene group having 1 to 10 carbon atoms,
m is 0.1 to 30 moles,
n is 0.1 to 80 moles,
o is from 0.1 to 80 moles).
delete In claim 1,
R ₂ is an alkyl group having 1 to 10 carbon atoms,
R ₄ and R ₅ are each independently an alkylene group having 1 to 7 carbon atoms,
Wherein R ₇ is an alkylene group having 1 to 7 carbon atoms.
In claim 1,
R ₂ is an alkyl group having 1 to 7 carbon atoms,
R ₄ and R ₅ are each independently an alkylene group having 1 to 5 carbon atoms,
Wherein R ₇ is an alkylene group having 1 to 5 carbon atoms.
In claim 1,
A non-aqueous electrolyte for a lithium secondary battery, wherein the oligomer is at least one selected from the group consisting of oligomers represented by the following formulas 4-1 and 4-2:
[Formula 4-1]


(In Formula 4-1 above,
m1 is 0.1 to 30 moles,
n1 is 0.1 to 80 moles,
o1 is from 0.1 to 80 moles);

[Formula 4-2]

(In Formula 4-2 above,
m2 is 0.1 to 30 moles,
n2 is 0.1 to 80 moles,
o2 is from 0.1 to 80 moles).
In claim 1,
The oligomer is a non-aqueous electrolyte for a lithium secondary battery, wherein the oligomer is contained in an amount of 0.1% to 25% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
In claim 1,
A non-aqueous electrolyte for a lithium secondary battery, wherein the oligomer is contained in an amount of 0.5% by weight to 20% by weight based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
In claim 1,
The non-aqueous electrolyte solution for a lithium secondary battery includes a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a sultone-based compound, a sulfate-based compound, a phosphate-based or phosphite-based compound, a borate-based compound, a nitrile-based compound, a benzene-based compound, and an amine-based compound. , a non-aqueous electrolyte solution for a lithium secondary battery, which further comprises at least one additive selected from the group consisting of a silane-based compound and a lithium salt-based compound.
A positive electrode containing a positive electrode active material;
A negative electrode containing a negative electrode active material;
a separator interposed between the cathode and the anode; and
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of claim 1.
In claim 9,
A lithium secondary battery in which the positive electrode active material includes a lithium composite metal oxide represented by the following formula (5):
[Formula 5]
Li _{1 + a} Ni _x Co _y M ¹ _z M ² _w O ₂
(In Formula 5 above,
M ¹ is Mn, Al or a combination thereof,
M ² is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca and Sr, 0≤a≤0.5, 0<x≤1.0, 0<y≤0.4, 0<z≤0.4, 0 ≤w≤0.1).