阅读说明：本技术 锂二次电池用非水性电解液和包含其的锂二次电池 (Nonaqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same ) 是由 金铉承 安俞贺 李哲行 吴正友 于 2020-08-11 设计创作，主要内容包括：本发明涉及一种锂二次电池用非水性电解液和包含其的锂二次电池,特别地,本发明涉及一种锂二次电池用非水性电解液,其包含作为第一添加剂的由式1表示的化合物和作为第二添加剂的二氟磷酸锂,所述由式1表示的化合物具有优异的清除由电解液中的锂盐生成的分解产物的效果,并且本发明涉及通过包含该电解液而提高了高温耐久性的改善效果的锂二次电池。(The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, and more particularly, to a non-aqueous electrolyte for a lithium secondary battery comprising a compound represented by formula 1 as a first additive and lithium difluorophosphate as a second additive, the compound represented by formula 1 having an excellent effect of scavenging decomposition products generated from a lithium salt in the electrolyte, and a lithium secondary battery having an improved effect of high-temperature durability by comprising the electrolyte.)

1. A non-aqueous electrolyte for a lithium secondary battery, comprising:

a lithium salt;

an organic solvent;

a compound represented by formula 1 as a first additive; and

lithium difluorophosphate (LiDFP) as a second additive:

[ formula 1]

Wherein, in the formula 1,

r is an alkyl group having 1 to 5 carbon atoms which may or may not have a substituent.

2. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein R is an alkyl group having 1 to 3 carbon atoms which may or may not have a substituent in formula 1.

3. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the compound represented by formula 1 comprises a compound represented by formula 1 a:

[ formula 1a ]

4. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the content of the compound represented by formula 1 is 0.1 to 5% by weight, based on the total weight of the non-aqueous electrolyte.

5. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein the content of the second additive is 0.1 to 5% by weight based on the total weight of the non-aqueous electrolyte.

6. The non-aqueous electrolyte for a lithium secondary battery according to claim 1, wherein a weight ratio of the first additive to the second additive is 1:1 to 1: 10.

7. The non-aqueous electrolyte for a lithium secondary battery according to claim 6, wherein the weight ratio of the first additive to the second additive is 1:1 to 1: 5.

8. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1, further comprising at least one third additive selected from the group consisting of cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate ester/salt compounds, phosphate ester/salt compounds, borate ester/salt compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

9. A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery according to claim 1.

Technical Field

The present application claims priority from korean patent application No. 10-2019-0102520, filed on 8/21/2019, the disclosure of which is incorporated herein by reference.

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery, which contains an additive having an excellent effect of scavenging decomposition products generated from a lithium salt, and a lithium secondary battery having improved high-temperature durability by containing the electrolyte.

Background

As the information society develops, personal IT devices and computer networks have developed, and the society as a whole has increased dependence on electric energy, there is a need to develop technologies for efficiently storing and utilizing electric energy.

Among the technologies developed for this purpose, the technology based on the secondary battery is the technology most suitable for various applications. Interest in secondary batteries has been generated because they can be miniaturized to be suitable for personal IT devices and can be applied to electric vehicles and electric power storage devices. Among these secondary battery technologies, lithium ion batteries have attracted attention as a battery system having the theoretically highest energy density, and are currently used for various devices.

A lithium ion battery is composed of a positive electrode formed of a lithium-containing transition metal oxide, a negative electrode formed of a carbon-based material capable of storing lithium (e.g., graphite), an electrolyte solution that becomes a medium for transporting lithium ions, and a separator, and it is important to appropriately select these components to improve the electrochemical properties of the battery.

The lithium ion battery has a disadvantage in that an increase in resistance and a decrease in capacity occur during charge and discharge or storage at high temperatures, thereby deteriorating performance. One of the reasons for such a problem has been revealed to be side reactions due to deterioration of the electrolytic solution at high temperatures, particularly deterioration due to decomposition of lithium salts.

LiPF₆Has been mainly used as a lithium salt to obtain suitable secondary battery characteristics, wherein PF due to the lithium salt₆ ^-Anions are very weak to heat and are known to produce, for example, PF from pyrolysis when the cell is exposed to high temperatures₅And the like.

PF so formed₅Not only causes decomposition reaction of an organic solvent such as ethylene carbonate, but also destroys a Solid Electrolyte Interphase (SEI) formed on the surface of an active material (e.g., graphite) outside an electrochemical stability window of the electrolyte at an operating voltage, thereby causing additional decomposition of the electrolyte and resulting in an increase in resistance and a decrease in battery life.

Therefore, various methods have been proposed to remove the LiPF by scavenging₆PF formed by pyrolysis of a salt-like compound₅To preserve the passivating ability of the SEI upon exposure to heat and to inhibit the degradation behavior of the battery.

Disclosure of Invention

[ problem ] to

An aspect of the present invention provides a non-aqueous electrolyte for a lithium secondary battery, which includes an additive having an excellent effect of removing decomposition products generated from a lithium salt in the electrolyte.

Another aspect of the present invention provides a lithium secondary battery in which the effect of improving high-temperature durability is enhanced by including the non-aqueous electrolyte for a lithium secondary battery.

[ solution ]

According to an aspect of the present invention, there is provided a non-aqueous electrolyte for a lithium secondary battery, including:

a lithium salt;

an organic solvent;

a compound represented by formula 1 as a first additive; and

lithium difluorophosphate (LiDFP) as a second additive.

[ formula 1]

Wherein, in the formula 1,

r is an alkyl group having 1 to 5 carbon atoms which may or may not have a substituent.

According to another aspect of the present invention, there is provided a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of the present invention.

[ advantageous effects ]

Since the non-aqueous electrolyte according to the present invention includes a lewis base material as a first additive capable of forming a Solid Electrolyte Interface (SEI), it can ensure the passivation ability of the SEI during high-temperature storage by removing decomposition products formed by pyrolysis of a lithium salt and enhancing the SEI. In addition, since the non-aqueous electrolyte of the present invention combines the second additive having an excellent film-forming effect with the first additive, it can suppress the initial resistance of the battery by forming a desired film on the surfaces of the positive and negative electrodes. Therefore, if the non-aqueous electrolyte of the present invention is used, a lithium secondary battery having an improved high-temperature durability improvement effect can be prepared.

Drawings

FIG. 1 is a graph showing the rate of increase in resistance after storage at high temperature (60 ℃ C.) in the secondary battery of example 1 and the secondary battery of comparative example 1;

fig. 2 is a graph showing the rate of increase in resistance of the secondary battery of example 1 and the secondary battery of comparative example 1 after 200 cycles at high temperature (45 ℃).

Detailed Description

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

It will be understood that the words or terms used in the specification and claims should not be construed as meanings defined in commonly used dictionaries, and will also be understood as having meanings consistent with their meanings in the context of the relevant art and the technical idea of the present invention based on the principle that the inventor can properly define the meanings of the words or terms to best explain the present invention.

For a lithium secondary battery, high-temperature storage characteristics are improved by forming a film having passivation ability on the surfaces of a positive electrode and a negative electrode while a non-aqueous electrolyte is decomposed during first charge and discharge. However, such a film may be widely used for a lithium salt (LiPF) of a lithium ion battery₆Etc.) acids formed by pyrolysis (e.g., HF and PF)₅) And (4) degrading. The elution of the transition metal element occurs in the positive electrode due to the corrosion by the acid, and at the same time, the surface resistance of the electrode increases due to the change in the surface structure, and the theoretical capacity decreases due to the loss of the metal element as the redox center, so that the capacity may decrease. Further, since the thus-eluted transition metal ions are electrodeposited on the negative electrode reacting in a strong reduction potential range, not only electrons are consumed, but also the film is broken at the time of electrodeposition to expose the surface of the negative electrode, thereby causing an additional electrolyte decomposition reaction. As a result, the negative electrode resistance increases, and the battery capacity may continuously decrease while the irreversible capacity increases.

Accordingly, the present invention has been made in an effort to provide a non-aqueous electrolyte solution that can enhance a Solid Electrolyte Interphase (SEI) on the surface of a negative electrode while preventing the dissolution of transition metals from a positive electrode or the degradation of the SEI during high-temperature storage by scavenging acids caused by the decomposition of lithium salts, by including an additive capable of forming the SEI as a component of the non-aqueous electrolyte solution, and a lithium secondary battery including the same.

Nonaqueous electrolyte for lithium secondary battery

First, the nonaqueous electrolytic solution for a lithium secondary battery of the present invention will be described.

The nonaqueous electrolyte for a lithium secondary battery of the present invention includes: (1) a lithium salt, (2) an organic solvent, (3) a compound represented by the following formula 1 as a first additive, and (4) lithium difluorophosphate (LiDFP) as a second additive:

[ formula 1]

Wherein, in the formula 1,

r is an alkyl group having 1 to 5 carbon atoms which may or may not have a substituent.

(1) Lithium salt

First, in the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, any lithium salt generally used in an electrolyte for a lithium secondary battery may be used as the lithium salt without limitation, and for example, the lithium salt may include Li⁺As a cation, and may include a cation selected from the group consisting of F^-、Cl^-、Br^-、I^-、NO₃ ^-、N(CN)₂ ^-、BF₄ ^-、ClO₄ ^-、AlO₄ ^-、AlCl₄ ^-、PF₆ ^-、SbF₆ ^-、AsF₆ ^-、B₁₀Cl₁₀ ^-、BF₂C₂O₄ ^-、BC₄O₈ ^-、PF₄C₂O₄ ^-、PF₂C₄O₈ ^-、(CF₃)₂PF₄ ^-、(CF₃)₃PF₃ ^-、(CF₃)₄PF₂ ^-、(CF₃)₅PF^-、(CF₃)₆P^-、CF₃SO₃ ^-、C₄F₉SO₃ ^-、CF₃CF₂SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、CF₃CF₂(CF₃)₂CO^-、(CF₃SO₂)₂CH^-、CH₃SO₃ ^-、CF₃(CF₂)₇SO₃ ^-、CF₃CO₂ ^-、CH₃CO₂ ^-、SCN^-And (CF)₃CF₂SO₂)₂N^-At least one of the group consisting of as an anion. Specifically, the lithium salt may include one selected from the group consisting of LiCl, LiBr, LiI, LiBF₄、LiClO₄、LiAlO₄、LiAlCl₄、LiPF₆、LiSbF₆、LiAsF₆、LiB₁₀Cl₁₀、LiBOB(LiB(C₂O₄)₂)、LiCF₃SO₃、LiTFSI(LiN(SO₂CF₃)₂)、LiFSI(LiN(SO₂F)₂)、LiCH₃SO₃、LiCF₃CO₂、LiCH₃CO₂And LiBETI (LiN (SO)₂CF₂CF₃)₂) At least one of the group consisting of. More specifically, the lithium salt may include a lithium salt selected from the group consisting of LiBF₄、LiClO₄、LiPF₆、LiBOB(LiB(C₂O₄)₂)、LiCF₃SO₃、LiTFSI(LiN(SO₂CF₃)₂)、LiFSI(LiN(SO₂F)₂) And LiBETI (LiN (SO)₂CF₂CF₃)₂) A single material of the group, or a mixture of two or more thereof.

The lithium salt may be appropriately changed within a generally usable range, but may be contained in the electrolytic solution at a concentration of 0.8M to 3.0M, for example, 1.0M to 3.0M, to obtain the best effect of forming a film for preventing corrosion of the electrode surface.

If the concentration of the lithium salt is less than 0.8M, the capacity characteristics may be reduced due to the reduction of the mobility of lithium ions, and if the concentration of the lithium salt is more than 3.0M, the wettability of the electrolyte may be reduced due to the excessive increase of the viscosity of the non-aqueous electrolyte solution, and the film forming effect may be reduced.

(2) Organic solvent

Various organic solvents generally used in lithium electrolytes may be used as the organic solvent without limitation. For example, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

The cyclic carbonate-based organic solvent is an organic solvent that can well dissociate lithium salts in an electrolyte due to a high dielectric constant, as a high-viscosity organic solvent, wherein specific examples of the cyclic carbonate-based organic solvent may be at least one organic solvent selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, and vinylene carbonate, wherein the cyclic carbonate-based organic solvent may include ethylene carbonate.

Further, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, wherein typical examples of the linear carbonate-based organic solvent may be at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and the linear carbonate-based organic solvent may specifically include ethylmethyl carbonate (EMC).

In order to prepare an electrolyte having high ionic conductivity, the organic solvent may include a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent in a volume ratio of 1:9 to 5:5, for example, 2:8 to 4: 6.

In addition, if necessary, the organic solvent may further include a linear ester organic solvent and/or a cyclic ester organic solvent, which are generally used in the electrolyte of the lithium secondary battery, in addition to the cyclic carbonate organic solvent and/or the linear carbonate organic solvent.

As a specific example, the linear ester-based organic solvent may 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.

As a specific example, the cyclic ester-based organic solvent may include at least one organic solvent selected from the group consisting of γ -butyrolactone, γ -valerolactone, γ -caprolactone, δ -valerolactone and ∈ -caprolactone.

In addition to the carbonate organic solvent or the ester organic solvent, an ether organic solvent or a nitrile organic solvent may be further mixed and used as necessary.

As the ether 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 thereof may be used.

The nitrile solvent may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

(3) First additive

The non-aqueous electrolyte of the present invention includes a compound represented by the following formula 1 as a first additive.

[ formula 1]

In the formula 1, the first and second groups,

r is an alkyl group having 1 to 5 carbon atoms which may or may not have a substituent.

In formula 1, R may be a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms. In particular, the compound represented by formula 1 may be a compound represented by the following formula 1 a.

[ formula 1a ]

The content of the compound represented by formula 1 may be 0.1 to 5% by weight, particularly 0.1 to 4% by weight, and more particularly 1 to 3% by weight, based on the total weight of the non-aqueous electrolyte.

In the case where the amount of the compound represented by formula 1 satisfies the above range, since the effect of removing the decomposition product of the lithium salt is excellent while suppressing disadvantages such as side reactions, capacity decrease, and resistance increase caused by additives as much as possible, a secondary battery having further improved overall performance can be prepared.

If the first additionThe amount of agent is less than 0.1 wt%, and HF or PF can be eliminated₅But the cleaning effect may become insignificant over time. Also, if the amount of the first additive is greater than 5.0 wt%, rate performance or low-temperature lifespan characteristics may be deteriorated during high-temperature storage since the viscosity of the non-aqueous electrolyte may not only increase due to the excess of the additive, but also decrease ion conductivity due to the increase in viscosity, thereby adversely affecting ion mobility in the battery. In addition, the resistance of the battery may increase due to decomposition of the excessive additive.

As described above, by including a lewis base-based compound (e.g., a compound represented by formula 1) having a C ═ S functional group, the nonaqueous electrolyte of the present invention can easily remove by-products causing deterioration of the battery at high temperatures, such as lewis acids (e.g., HF) formed by decomposition of lithium salts^-Or PF₅ ^-). Therefore, since the deterioration behavior due to the chemical reaction of the film on the surface of the positive or negative electrode caused by the lewis acid can be suppressed, the additional decomposition of the battery electrolyte due to the destruction of the film can be prevented, and also, the high-temperature storage characteristics can be improved by reducing the self-discharge of the secondary battery.

In particular, since the compound represented by formula 1, which is included as a non-aqueous electrolyte additive, has a double bond and a C ═ S bond functional group, it may form a more firm SEI. In other words, since the compound represented by formula 1 of the present invention has C ═ S bond as an electron-rich functional group, not C ═ O bond, an interface containing sulfur (S) may be formed when the compound is reduced to form SEI. Therefore, the initial resistance can be further reduced as compared with the case where the compound represented by the following formula 3 is contained. Further, since the molecular weight of the compound represented by formula 1 is lower than that of the ionic bond (e.g., SO) having an ester bond represented by the following formula 4₃ ^-) The compound of (a) has therefore a high solubility in organic solvents used in lithium ion batteries, and therefore has the advantage that it functions more easily as an additive.

[ formula 3]

[ formula 4]

(4) Second additive

The nonaqueous electrolytic solution of the present invention contains lithium difluorophosphate (LiDFP) represented by the following formula 2 as a second additive.

[ formula 2]

Lithium difluorophosphate (LiDFP) is a component for obtaining an effect of improving long-term life characteristics of a secondary battery, in which lithium ion components formed by decomposition during first charge are electrochemically decomposed on the surface of the negative electrode, thereby forming stable SEI. The formation of SEI may not only improve lithium (Li) mobility towards the negative electrode, but also may reduce interface resistance. In addition, the difluorophosphate anion formed by decomposition during the first charge, when present on the surface of the positive electrode, can improve the stabilization and discharge characteristics of the positive electrode. Therefore, the effect of improving the long-term life characteristics of the secondary battery can be achieved.

The content of lithium difluorophosphate (LiDFP) as the second additive may be 0.1 to 5% by weight, specifically 0.5 to 3% by weight, more specifically 1 to 3% by weight, based on the total weight of the nonaqueous electrolyte solution.

When the amount of lithium difluorophosphate (LiDFP) satisfies the above range, a firm SEI forming effect and film forming effect can be obtained.

If the amount of lithium difluorophosphate (LiDFP) is more than 5.0 wt%, not only may an increase be caused by an excessive amount of the compound due to the viscosity of the electrolyte, but also an excessively thick film may be formed on the surface of the electrode, resulting in an increase in resistance and a decrease in capacity characteristics. If the amount of lithium difluorophosphate (LiDFP) is less than 0.1 wt%, the film-forming effect on the electrode surface may not be significant.

The weight ratio of the first additive to the second additive in the non-aqueous electrolyte of the present invention may be 1:1 to 1:10, particularly 1:1 to 1:5, more particularly 1:1 to 1: 3.

In the case where the first additive and the second additive are mixed in the above ratio, the wetting of the electrolyte can be improved by reducing the surface tension. In addition, since a stable SEI is formed without increasing resistance, side reactions between an electrode and an electrolyte during charging at high temperatures may be suppressed.

If the weight ratio of the second additive to the first additive is greater than 10, the output may be reduced because the initial interface resistance increases when an excessively thick film is formed on the surface of the electrode. In addition, in the case where the weight ratio of the second additive to the first additive is less than 1, since the effect of forming the SEI is insignificant, the effect of inhibiting side reactions between the electrode and the electrolyte may be reduced.

(5) Additional additives

In addition, in order to prevent the decomposition of the non-aqueous electrolyte to cause the collapse of the negative electrode under a high output environment, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and cell swelling suppression effect at high temperature, the non-aqueous electrolyte for a lithium secondary battery of the present invention may further include an additional third additive in the non-aqueous electrolyte, as necessary.

As typical examples, these third additives may include at least one additive selected from the group consisting of cyclic carbonate-based compounds, halogenated carbonate-based compounds, sultone-based compounds, sulfate ester-based compounds, phosphate ester-based compounds, borate ester-based compounds, nitrile-based compounds, benzene-based compounds, amine-based compounds, silane-based compounds, and lithium salt-based compounds.

The cyclic carbonate-based compound may include Vinylene Carbonate (VC) or vinyl ethylene carbonate.

The halogenated carbonate compound may include fluoroethylene carbonate (FEC).

The sultone-based compound may include at least one compound selected from the group consisting of 1, 3-Propane Sultone (PS), 1, 4-butane sultone, ethane sultone, 1, 3-propene sultone (PRS), 1, 4-butene sultone, and 1-methyl-1, 3-propene sultone.

The sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).

The phosphate ester/salt-type compound may include at least one compound selected from lithium difluorobis (oxalyl) phosphate, tris (trimethylsilyl) phosphite, tris (2,2, 2-trifluoroethyl) phosphate, and tris (trifluoroethyl) phosphite compounds, in addition to lithium difluorophosphate contained as the second additive.

The borate/salt compounds may include tetraphenyl borate and lithium oxalyldifluoroborate.

The nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

The benzene-based compound may include fluorobenzene, the amine-based compound may include triethanolamine or ethylenediamine, and the silane-based compound may include tetravinylsilane.

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, wherein the lithium salt-based compound may include a compound selected from the group consisting of LiPO₂F₂LiODFB, LiBOB (lithium bis (oxalyl) borate) (LiB (C)₂O₄)₂) And LiBF₄At least one compound of the group consisting of.

In the case of including vinylene carbonate, vinyl ethylene carbonate, or succinonitrile among these additional additives, a more robust SEI may be formed on the surface of the anode during initial activation of the secondary battery.

In the presence of LiBF₄In the case of (2), the secondary can be improved by suppressing gas generation which may occur due to decomposition of the electrolytic solution at high temperatureHigh temperature stability of the battery.

The third additive may be used as a mixture of two or more, and may be contained in an amount of 0.01 to 50% by weight, particularly 0.01 to 10% by weight, and preferably 0.05 to 5% by weight, based on the total weight of the non-aqueous electrolyte. If the amount of the additive is less than 0.01 wt%, the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature lifespan characteristics is insignificant, and if the amount of the additive is greater than 50 wt%, side reactions in the electrolyte may excessively occur during the charge and discharge of the battery. In particular, since the third additive may not be sufficiently decomposed at high temperature when an excessive amount of the third additive is added, the third additive may be present in the electrolyte in the form of an unreacted material or a precipitate at room temperature. Therefore, a side reaction may occur that degrades the life or resistance characteristics of the secondary battery.

Lithium secondary battery

In another embodiment of the present invention, there is provided a lithium secondary battery comprising the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

The lithium secondary battery of the present invention may be prepared by: an electrode assembly in which a cathode, an anode, and a separator disposed between the cathode and the anode are sequentially stacked is formed, the electrode assembly is received in a battery case, and then the non-aqueous electrolyte of the present invention is injected.

Conventional methods known in the art may be used as the method for manufacturing the lithium secondary battery of the present invention, and specifically, the method for manufacturing the lithium secondary battery of the present invention is as follows.

(1) Positive electrode

The positive electrode may be prepared by: a positive electrode current collector is coated with a positive electrode slurry including a positive electrode active material, a binder, a conductive agent, and a solvent, and then the coated positive electrode current collector is dried and roll-pressed.

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

The positive active material is a compound capable of reversibly intercalating and deintercalating lithium, wherein the positive active material may include a lithium transition metal oxide containing lithium and at least one metal selected from cobalt, manganese, nickel or aluminum, and may specifically include a compound selected from lithium manganese-based oxides, lithium iron phosphate and lithium nickel manganese cobalt-based oxides (e.g., Li (Ni) having high stability and capacity characteristics of a battery_pCo_qMn_r1)O₂(wherein 0)<p<1，0<q<1，0<r1<1，p+q+r1＝1)。

Specifically, the lithium manganese-based oxide may include LiMn₂O₄And the lithium iron phosphate may, for example, comprise LiFePO₄。

In addition, the lithium nickel manganese cobalt oxide may include oxides selected from Li (Ni)_1/3Mn_1/3Co_1/3)O₂、Li(Ni_0.6Mn_0.2Co_0.2)O₂、Li(Ni_0.5Mn_0.3Co_0.2)O₂、Li(Ni_0.7Mn_0.15Co_0.15)O₂And Li (Ni)_0.8Mn_0.1Co_0.1)O₂Wherein it is preferable that the lithium nickel manganese cobalt-based oxide includes a lithium transition metal oxide in which nickel is present in an amount of 60 atomic% or more in the transition metal. That is, since the higher the amount of nickel in the transition metal, the higher the capacity that can be achieved, it is more advantageous to use a lithium transition metal oxide having a nickel content of 60 atomic% or more to achieve a high capacity. That is, the lithium transition metal oxide may include Li (Ni)_0.6Mn_0.2Co_0.2)O₂、Li(Ni_0.7Mn_0.15Co_0.15)O₂And Li (Ni)_0.8Mn_0.1Co_0.1)O₂At least one of (1).

In addition to the above-described lithium transition metal oxide, the positive electrode active material of the present invention may further include: lithium manganese oxides, e.g. LiMnO₂、LiMn₂O₄Etc.; oxides of the lithium cobalt type, e.g. LiCoO₂Etc.; lithium nickel oxides, e.g. LiNiO₂Etc.; lithium nickel manganese oxides, e.g. LiNi_1-YMn_YO₂(wherein 0)<Y<1)、LiMn_2-ZNi_zO₄(wherein 0)<Z<2) (ii) a Lithium nickel cobalt oxides, e.g. LiNi_1-Y1Co_Y1O₂(wherein 0)<Y1<1) (ii) a Oxides of the lithium manganese cobalt type, e.g. LiCo_1-Y2Mn_Y2O₂(wherein 0)<Y2<1)、LiMn_2-Z1Co_z1O₄(wherein 0)<Z1<2) (ii) a Lithium nickel manganese cobalt oxides, e.g. Li (Ni)_pCo_qMn_r1)O₂(wherein 0)<p<1，0<q<1，0<r1<1, p + q + r1 ═ 1) or Li (Ni)_p1Co_q1Mn_r2)O₄(wherein 0)<p1<2，0<q1<2，0<r2<2, p1+ q1+ r2 ═ 2); or lithium nickel cobalt transition metal (M) oxides, e.g. Li (Ni)_p2Co_q2Mn_r3M_S2)O₂(wherein M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and s2 are atomic fractions of respective independent elements, wherein 0 is<p2<1，0<q2<1，0<r3<1，0<S2<1, and p2+ q2+ r3+ S2 ═ 1), and may further include any one or two or more compounds thereof.

The positive electrode active material may be contained in an amount of 80 to 99 wt%, for example, 90 to 99 wt%, based on the total weight of solids in the positive electrode slurry. In the case where the content of the positive electrode active material is 80 wt% or less, the capacity may be reduced because the energy density is reduced.

The binder is a component contributing to adhesion between the active material and the conductive agent and adhesion to the current collector, wherein the binder is generally added in an amount of 1 to 30 wt% based on the total weight of solids in the positive electrode slurry. Examples of the binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, fluororubber, various copolymers thereof, and the like.

Also, the conductive agent is a material that provides conductivity without causing adverse chemical changes in the battery, and may be added in an amount of 1 to 20 wt% based on the total weight of solids in the positive electrode slurry.

As typical examples of the conductive agent, the following conductive materials can be used, for example: carbon powder 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 whose crystal structure is sufficiently developed; conductive fibers, such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a polyphenylene derivative.

In addition, the solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount such that a desired viscosity is obtained when the cathode active material and optionally the binder and the conductive agent are included. For example, the solvent may be contained in an amount such that the concentration of solids in the slurry including the cathode active material and optional binder and conductive agent is in the range of 10 to 60 wt%, for example 20 to 50 wt%.

(2) Negative electrode

The negative electrode may be prepared by: the negative electrode current collector is coated with a negative electrode slurry including a negative electrode active material, a binder, a conductive agent, and a solvent, and then the coated negative electrode current collector is dried and roll-pressed.

The thickness of the negative electrode current collector is generally 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium or silver, and aluminum-cadmium alloy, etc. may be used. Further, the negative electrode current collector may have fine surface roughness to improve the bonding strength with the negative electrode active material, similar to the positive electrode current collector, and the negative electrode current collector may be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, and the like.

In addition, the anode active material may include at least one selected from the group consisting of: lithium metal, a carbon material capable of reversibly intercalating/deintercalating lithium ions, a metal or an alloy of lithium and the metal, a metal composite oxide, a material that can dope and deddope lithium, and a transition metal oxide.

As the carbon material capable of reversibly intercalating/deintercalating lithium ions, a carbon-based negative electrode active material generally used in a lithium ion secondary battery may be used without particular limitation, and as a typical example, crystalline carbon and/or amorphous carbon may be used. Examples of crystalline carbon may be graphite such as irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon may be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide and fired coke.

As the metal or the alloy of lithium and the metal, a metal selected from the group consisting of copper (Cu), nickel (Ni), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), and tin (Sn), or an alloy of lithium and the metal may Be used.

As the metal composite oxide, one selected from the group consisting of PbO and PbO can be used₂、Pb₂O₃、Pb₃O₄、Sb₂O₃、Sb₂O₄、Sb₂O₅、GeO、GeO₂、Bi₂O₃、Bi₂O₄、Bi₂O₅、Li_xFe₂O₃(0≤x≤1)、Li_xWO₂(x is more than or equal to 0 and less than or equal to 1) and Sn_xMe_1-xMe'_yO_z(Me: manganese (Mn), Fe, Pb or Ge; Me': Al, boron (B), phosphorus (P), Si, elements of groups I, II and III of the periodic Table or halogen, 0<x is less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8).

Metals that can be doped and dedoped with lithium can include: si, SiO_x(0<x is less than or equal to 2), Si-Y alloy (whereinY 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, and is not Si), Sn, SnO₂And Sn-Y (wherein 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, and is not Sn), and SiO may also be used₂And mixtures with at least one thereof. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, scandium (Sc), yttrium (Y), Ti, zirconium (Zr), hafnium (Hf),(Rf), V, niobium (Nb), Ta,(Db), Cr, Mo, tungsten (W),(Sg), technetium (Tc), rhenium (Re),(Bh), Fe, Pb, ruthenium (Ru), osmium (Os),(Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, gallium (Ga), Sn, In, Ge, P, arsenic (As), Sb, bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

The transition metal oxide may include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

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

The binder is an ingredient contributing to adhesion between the conductive agent, the active material, and the current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of solids in the anode slurry. Examples of the binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber.

The conductive agent is an ingredient for further improving the conductivity of the anode active material, wherein the conductive agent may be added in an amount of 1 to 20 wt% based on the total weight of solid matters in the anode slurry. Any conductive agent may be used without particular limitation so long as it has conductivity without causing adverse chemical changes in the battery, and for example, the following conductive materials may be used: carbon powder 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 whose crystal structure is sufficiently developed; conductive fibers, such as carbon fibers or metal fibers; metal powders such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or a polyphenylene derivative.

The solvent may include water or an organic solvent, such as NMP and alcohol, and may be used in such an amount that a desired viscosity is obtained when the anode active material and optionally the binder and the conductive agent are included. For example, the solvent may be contained in an amount such that the concentration of solids in the slurry including the negative electrode active material and optional binder and conductive agent is in the range of 50 to 75 wt%, for example 50 to 65 wt%.

(3) Diaphragm

As the separator included in the lithium secondary battery of the present invention, a typical porous polymer film generally used, for example, a porous polymer film made of polyolefin-based polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer) may be used alone or in a stack, and a typical porous non-woven fabric, for example, a non-woven fabric formed of high-melting glass fibers or polyethylene terephthalate fibers, may be used, but the present invention is not limited thereto.

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

Hereinafter, the present invention will be described in more detail based on examples. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Examples

Example 1

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

0.5g of the compound represented by formula 1a as a first additive, 1.0g of lithium difluorophosphate as a second additive, and 0.1g of tetravinylsilane, 1.0g of ethylene sulfonate, 0.5g of 1, 3-propanesultone, 0.2g of LiBF as a third additive₄And 6.0g of fluorobenzene was added to a solution of 0.7M LiPF₆And 0.3M LiFSI in 90.7g of an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume), thereby preparing a nonaqueous electrolyte for a lithium secondary battery.

(Secondary Battery production)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂:Li(Ni_0.6Co_0.2Mn_0.2)O₂At a weight ratio of 7: 3), carbon black as a conductive agent, and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried and then rolled to prepare a positive electrode.

A negative electrode active material (graphite: SiO 95:5 weight ratio), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 weight%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and a nonaqueous electrolyte for a lithium secondary battery was injected thereto to prepare a lithium secondary battery.

Example 2

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

0.2g of the compound represented by the formula 1a as a first additive, 1.0g of lithium difluorophosphate as a second additive, and 1.0g of ethylene sulfonate, 0.5g of 1, 3-propane sultone and 0.2g of LiBF as a third additive were added₄And 6.0g of fluorobenzene was added to a solution of 0.7M LiPF₆And 91.1g of 0.3M LiFSI in an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume), thereby preparing a nonaqueous electrolyte for a lithium secondary battery.

(Secondary Battery production)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂) Carbon black as a conductive agent and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried and then rolled to prepare a positive electrode.

A negative electrode active material (graphite: SiO 95:5 weight ratio), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 weight%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and a nonaqueous electrolyte for a lithium secondary battery was injected thereto to prepare a lithium secondary battery.

Example 3

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

0.3g of the compound represented by formula 1a as a first additive, 1.0g of lithium difluorophosphate as a second additive, and 1.0g of ethylene sulfonate, 0.5g of 1, 3-propane sultone, and 0.2g of LiBF as a third additive were added₄And 6.0g of fluorobenzene was added to a solution of 1.2M LiPF₆91.0g of an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume) was added to prepare a nonaqueous electrolyte solution for a lithium secondary battery.

(Secondary Battery production)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂) Carbon black as a conductive agent and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried and then rolled to prepare a positive electrode.

A negative electrode active material (graphite), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 wt%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and a nonaqueous electrolyte for a lithium secondary battery was injected thereto to prepare a lithium secondary battery.

Example 4

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

0.3g of the compound represented by formula 1a as a first additive, 1.5g of lithium difluorophosphate as a second additive, and 1.0g of ethylene sulfonate and 0.5g of 1, 3-propane sultone as a third additive were added to a solution in which 1.2M LiPF was dissolved₆96.7g of organic solvent (ethylene carbonate)Ethyl methyl carbonate at a 3:7 volume ratio) was added to the mixture to prepare a nonaqueous electrolyte for a lithium secondary battery.

(Secondary Battery production)

A lithium secondary battery was prepared in the same manner as in example 3, except that the non-aqueous electrolyte solution for a lithium secondary battery prepared as described above was injected instead of the non-aqueous electrolyte solution for a lithium secondary battery of example 3.

Comparative example 1

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

1.0g of lithium difluorophosphate as a second additive, 0.1g of tetravinylsilane as a third additive, 1.0g of ethylene sulfonate, 0.5g of 1, 3-propanesultone, 0.2g of LiBF were added₄And 6.0g of fluorobenzene was added to a solution of 0.7M LiPF₆And 0.3M LiFSI in 91.2g of an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume) to prepare a nonaqueous electrolyte for a lithium secondary battery.

(Secondary Battery production)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂:Li(Ni_0.6Co_0.2Mn_0.2)O₂At a weight ratio of 7: 3), carbon black as a conductive agent, and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried and then rolled to prepare a positive electrode.

A negative electrode active material (graphite: SiO 95:5 weight ratio), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 weight%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and a nonaqueous electrolyte for a lithium secondary battery was injected thereto to prepare a lithium secondary battery.

Comparative example 2

(Secondary Battery production)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂) Carbon black as a conductive agent and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried and then rolled to prepare a positive electrode.

A negative electrode active material (graphite: SiO 95:5 weight ratio), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 weight%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and the nonaqueous electrolyte solution for a lithium secondary battery prepared in comparative example 1 was injected thereto to prepare a lithium secondary battery.

Comparative example 3

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

1.0g of lithium difluorophosphate as a second additive, and 0.1g of Tetravinylsilane (TVS), 1.0g of ethylene sulfonate, 0.5g of 1, 3-propanesultone, 0.2g of LiBF as a third additive₄And 6.0g of fluorobenzene was added to a solution of 1.2M LiPF₆91.2g of an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume) was added to prepare a nonaqueous electrolyte solution for a lithium secondary battery.

(preparation of Secondary Battery)

A positive electrode active material (Li (Ni))_0.8Co_0.1Mn_0.1)O₂) Carbon black as a conductive agent and polyvinylidene fluoride as a binderN-methyl-2-pyrrolidone (NMP) as a solvent was added in a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A positive electrode current collector (Al thin film) 15 μm thick was coated with the positive electrode slurry, dried, and then rolled to prepare a positive electrode.

A negative electrode active material (graphite), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 wt%). A 6 μm thick copper (Cu) thin film as a negative electrode current collector was coated with the negative electrode slurry, dried, and then rolled to prepare a negative electrode.

Stacking the positive electrode in sequence, coated with inorganic particles (Al)₂O₃) The polyolefin-based porous separator and the negative electrode to prepare an electrode assembly.

The prepared electrode assembly was received in a battery case, and a nonaqueous electrolyte for a lithium secondary battery was injected thereto to prepare a lithium secondary battery.

Comparative example 4

(preparation of non-aqueous electrolyte for lithium Secondary Battery)

1.5g of lithium difluorophosphate as a second additive, and 1.0g of ethylene sulfonate and 0.5g of 1, 3-propane sultone as a third additive were added to a solution of 1.2M LiPF₆In 97g of an organic solvent (ethylene carbonate: ethylmethyl carbonate: 3:7 by volume), to prepare a nonaqueous electrolyte solution for a lithium secondary battery.

(preparation of Secondary Battery)

A secondary battery was prepared in the same manner as in example 3, except that the non-aqueous electrolyte solution for a lithium secondary battery prepared above was injected instead of the non-aqueous electrolyte solution for a lithium secondary battery of example 3.

Examples of the experiments

Experimental example 1-1 evaluation of high temperature (60 ℃ C.) storage durability (1)

After the lithium secondary batteries prepared in example 1 and comparative example 1 were each activated at CC of 0.1C, degassing was performed.

Subsequently, each secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. After setting the above charge and discharge to 1 cycle and performing 3 cycles, each lithium secondary battery was charged to a state of charge (SOC) of 50%, and then the initial resistance was calculated from the voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. The voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A).

Subsequently, each lithium secondary battery was recharged to a state of charge (SOC) of 100% at a CC of 0.33C, and then stored at a high temperature (60 ℃) for 13 weeks.

After every 2 weeks, 4 weeks, 8 weeks, 10 weeks, and 13 weeks, each lithium secondary battery was charged to a state of charge (SOC) of 50%, and then the resistance after storage (DC-iR) was calculated from the voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. The voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A).

The calculated initial resistance and the resistance measured every week after high-temperature storage were substituted into the following [ equation 1] to calculate a resistance increase rate (%), and the results thereof are presented in fig. 1.

[ equation 1]

Resistance increase rate (%) { (resistance after high-temperature storage-initial resistance)/initial resistance } × 100

Referring to fig. 1, it can be understood that the resistance increase rate of the secondary battery of example 1 after high-temperature storage is significantly improved as compared to comparative example 1.

Experimental examples 1-2: evaluation of high temperature (60 ℃ C.) storage durability (2)

After the lithium secondary battery prepared in example 2 and the lithium secondary battery prepared in comparative example 2 were each activated at CC of 0.1C, degassing was performed.

Subsequently, each secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. After the charge and discharge were set to 1 cycle and performed for 3 cycles, the initial discharge capacity was measured using a PNE-0506 charge/discharge device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A). Then, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the initial resistance was calculated by a voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. The voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A).

Subsequently, each lithium secondary battery was recharged to a state of charge (SOC) of 100% at a CC of 0.33C, and then stored at a high temperature (60 ℃) for 2 weeks.

After two weeks, CC-CV charging and discharging were performed at CC of 0.33C, and then the discharge capacity after high-temperature storage was measured using PNE-0506 charging/discharging equipment (manufacturer: PNE SOLUTION co., ltd., 5V, 6A). Further, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the resistance after high-temperature storage (DC-iR) was calculated from the voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

The calculated initial resistance and the resistance after storage at high temperature for 2 weeks were substituted into [ equation 1] to calculate a resistance increase rate (%), and the results thereof are presented in table 1 below.

In addition, the initial discharge capacity and the discharge capacity after 2 weeks of high-temperature storage were substituted into the following [ equation 2], and the capacity retention rate (%) was calculated, and the results thereof are presented in table 1 below.

[ equation 2]

Discharge capacity retention (%) (discharge capacity after high-temperature storage/initial discharge capacity) × 100

[ Table 1]

Referring to table 1, it can be understood that the resistance increase rate and the capacity retention rate after high-temperature storage of the secondary battery of example 2 are improved as compared to comparative example 2.

Experimental examples 1 to 3: evaluation of high temperature (60 ℃ C.) storage durability (3)

After the lithium secondary battery prepared in example 3 and the lithium secondary battery prepared in comparative example 3 were each activated at CC of 0.1C, degassing was performed.

Subsequently, each secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. After the charge and discharge were set to 1 cycle and performed for 3 cycles, the initial discharge capacity was measured using a PNE-0506 charge/discharge device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A). Then, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the initial resistance was calculated by a voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

Next, each lithium secondary battery was recharged to a state of charge (SOC) of 100% at a CC of 0.33C, and then stored at a high temperature (60 ℃) for 4 weeks.

After 4 weeks, CC-CV charging and discharging were performed at CC of 0.33C, and then the discharge capacity after high-temperature storage was measured using PNE-0506 charging/discharging equipment (manufacturer: PNE SOLUTION co., ltd., 5V, 6A). In addition, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the resistance after high-temperature storage (DC-iR) was calculated from the voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

The calculated initial resistance and the resistance after 4 weeks of high-temperature storage were substituted into [ equation 1] to calculate a resistance increase rate (%), and the results thereof are presented in table 2 below.

In addition, the measured initial discharge capacity and the discharge capacity after 4 weeks of high-temperature storage were substituted into [ equation 2], and the capacity retention rate (%) was calculated, and the results thereof are presented in table 2 below.

[ Table 2]

Referring to table 2, it can be understood that the resistance increase rate and the capacity retention rate after high-temperature storage of the secondary battery of example 3 are significantly improved as compared to comparative example 3, respectively.

Experimental examples 1 to 4: evaluation of high temperature (60 ℃ C.) storage durability (4)

After the secondary battery prepared in example 4 and the lithium secondary battery prepared in comparative example 4 were each activated at CC of 0.1C, degassing was performed.

Subsequently, the discharge capacity retention ratio (%) after storage at high temperature for 2 weeks and the resistance increase ratio (%) after storage at high temperature for 2 weeks were calculated by the same method as the high temperature (60 ℃) storage durability evaluation method of experimental example 1-2, and the results thereof are presented in table 3 below.

[ Table 3]

Referring to table 3, it can be understood that the capacity retention rate and the resistance increase rate after high-temperature storage of the secondary battery of example 4 are respectively improved as compared with comparative example 4.

Experimental example 2-1: evaluation of high temperature (45 ℃ C.) Life characteristics (1)

After the lithium secondary battery prepared in example 1 and the secondary battery prepared in comparative example 1 were each activated at CC of 0.1C, degassing was performed.

Subsequently, each secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. After the charge and discharge were set to 1 cycle and performed for 3 cycles, the initial discharge capacity was measured using a PNE-0506 charge/discharge device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A). Then, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the initial resistance was calculated by a voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

Thereafter, each lithium secondary battery was charged to 4.20V at a rate of 0.33C under a constant current-constant voltage (CC-CV) condition at 45 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. The above charge and discharge were defined as one cycle, and the resistance increase (%) was measured when 200 charge and discharge cycles were performed at high temperature (45 ℃).

In this case, the resistance increase rate (%) was measured at intervals of 50 cycles, in which each lithium secondary battery was charged to a 50% state of charge (SOC) after performing charge-discharge cycles, after which the direct-current internal resistance (hereinafter, referred to as "DC-iR") was calculated by the voltage drop obtained in a state in which each lithium secondary battery was subjected to a discharge pulse at 2.5C for 10 seconds, and was substituted into the following [ equation 3] to calculate the resistance increase rate (%). The measurement results are presented in fig. 2. In this case, the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A).

[ equation 3]

Resistance increase rate (%) { (resistance after cycle-initial resistance)/initial resistance } × 100

Referring to fig. 2, with the secondary battery of example 1, since a stable film was formed on the surface of the positive/negative electrode, it was confirmed that the resistance increase rate was improved compared to comparative example 1 due to the suppression of additional electrolyte decomposition when long-term charge and discharge were performed at high temperature.

Experimental example 2-2: evaluation of high temperature (45 ℃ C.) Life characteristics (2)

After the lithium secondary battery prepared in example 2 and the secondary battery prepared in comparative example 2 were each activated at CC of 0.1C, degassing was performed.

Subsequently, each secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. After the charge and discharge were set to 1 cycle and performed for 3 cycles, the initial discharge capacity was measured using a PNE-0506 charge/discharge device (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A). Then, after each lithium secondary battery was charged to a state of charge (SOC) of 50%, the initial resistance was calculated by a voltage drop obtained in a state where a discharge pulse was applied to each lithium secondary battery at 2.5C for 10 seconds. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

Thereafter, each lithium secondary battery was charged to 4.20V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition of 45 ℃, then was cut off at a current of 0.05C, and was discharged to 2.5V at a rate of 0.33C under a constant current condition. The charge and discharge were defined as 1 cycle, and 50 charge and discharge cycles were performed at a high temperature (45 ℃ C.).

After 50 cycles, each lithium secondary battery was charged to 4.2V at a rate of 0.33C under a constant current and constant voltage (CC-CV) condition at 25 ℃, and then discharged to 2.5V at a rate of 0.33C under a constant current condition, and the discharge capacity was measured using a PNE-0506 charge/discharge device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A), and was substituted into [ equation 4] to measure the capacity retention rate, and the results thereof are presented in table 4 below.

Subsequently, the direct current internal resistance (hereinafter, referred to as "DC-iR") was calculated from the voltage drop obtained in the state where a discharge pulse of 10 seconds was applied to each lithium secondary battery at 2.5C at an SOC of 50%, and was substituted into [ equation 3] to calculate the resistance increase rate (%), and the results thereof were then presented in table 4 below. In which the voltage drop was measured using a PNE-0506 charging/discharging device (manufacturer: PNE SOLUTION co., ltd., 5V, 6A).

[ equation 4]

Capacity retention (%) (discharge capacity after cycle/initial discharge capacity) × 100

[ Table 4]

Referring to table 4, with the secondary battery of example 2, since a stable film was formed on the surface of the cathode/anode, it was confirmed that the resistance increase rate was improved compared to comparative example 2 due to the inhibition of additional electrolyte decomposition when long-term charge and discharge were performed at high temperature.