KR20160079620A - Rechargeable lithium battery - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; and an electrolyte including a solvent and additives, wherein the positive electrode active material includes a transition metal oxide containing lithium, and the solvent includes hydrofluoroether. In addition, the additives include at least one selected from the group consisting of first additives represented by chemical formula 1, second additives represented by chemical formula 2, third additives represented by chemical formula 3, and forth additives represented by chemical formula 4. The lithium secondary battery of the present invention is capable of simultaneously improving cycle life characteristics and high temperature storage characteristics.

Description

[0002] Lithium secondary batteries {RECHARGEABLE LITHIUM BATTERY}

To a lithium secondary battery.

The lithium secondary battery includes a positive electrode active material layer and a negative electrode active material layer that electrochemically intercalates and deintercalates lithium ions, and an electrolyte solution in which lithium ions are dissolved, as disclosed in Japanese Laid-Open Patent Application No. 2013-37905 (Patent Document 1) do. The electrolytic solution is impregnated with a porous separator.

The technique disclosed in Patent Document 1 aims at improving the cycle life of a lithium secondary battery. In order to achieve this object, the lithium secondary battery has two types of pores having different characteristics and includes fluorinated ether in the electrolytic solution.

However, cost competition is intensifying in battery applications suitable for portable electronic devices (mobile devices) such as smart phones and tablet PCs. Under such circumstances, the use of a solid solution oxide described in Patent Document 1, for example, as a cathode material increases the cost, so that a transition metal oxide including lithium, such as lithium cobalt oxide, .

In recent years, electrolytes containing hydrofluoroether have been proposed in Japanese Patent Laid-Open Nos. 2014-112526, 2013-211095, and 2011-129352. When such an electrolytic solution is used in a lithium secondary battery using a transition metal oxide containing lithium as a cathode material, there is a problem that the cycle life and the storage characteristics at the time of high temperature storage are lowered.

One embodiment is to provide a lithium secondary battery that simultaneously improves cycle life characteristics and high temperature storage characteristics.

One embodiment includes a positive electrode comprising a positive electrode active material; And an electrolyte solution containing a solvent and an additive, wherein the cathode active material comprises a transition metal oxide containing lithium, the solvent includes hydrofluoroether, and the additive is a first additive represented by the following general formula And at least one selected from the group consisting of a second additive represented by the following general formula (2), a third additive represented by the following general formula (3), and a fourth additive represented by the following general formula (4).

[Chemical Formula 1]

(In the formula 1,

R ¹ to R ³ are each independently a substituted or unsubstituted C1 to C8 alkyl group, a vinyl group or a C1 to C5 alkyl group, which is unsubstituted or substituted with a vinyl group or a C1 to C5 alkyl group, A C5-C8 cycloalkyl group, a C6-C8 aryl group, or a fluorine atom;

R ⁴ is a C 1 to C 8 alkylene group, a C 2 to C 8 alkynylene group, a C ⁴ to C 8 alkylene group having an ether group, a C 1 to C 8 alkylene group having a plurality of -CF ₂ -bonding groups, or an 'ether group and a sulfide group'Lt; RTI ID = 0.0 > C4-C10 < / RTI >

(2)

(In the formula (2)

R ⁵ is a C 2 to C 6 alkylene group not containing a double bond, a C 2 to C 6 alkylene group having a double bond, a C 2 to C 6 alkenylene group, or a C 6 to C 12 arylene group,

R ⁶ to R ¹¹ are each independently a C 1 to C 6 alkyl group or a C 2 to C 6 alkenyl group.

(3)

(3)

R ¹² and R ¹³ are each independently a hydrogen atom or a C 1 to C 8 alkyl group,

R ¹⁴ is a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group substituted or unsubstituted with a vinyl group.

[Chemical Formula 4]

(In the formula 4,

R ¹⁵ and R ¹⁶ are each independently a hydrogen atom or a C1 to C8 alkyl group,

R ¹⁷ is a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group,

n is 1 or 2.)

The hydro-fluoro-ether (HFE) is 2,2,2-trifluoroethyl ether (CF ₃ CH ₂ OCH _3), 2,2,2-trifluoro-methyl-ethyl difluoromethyl ether (CF ₃ CH ₂ OCHF ₂ ), 2,2,3,3,3-pentafluoropropyl methyl ether (CF ₃ CF ₂ CH ₂ OCH ₃ ), 2,2,3,3,3-pentafluoropropyl difluoromethyl ether _{(CF 3 CF 2 CH 2 OCHF} 2), 2,2,3,3,3- pentamethyl to a profile -1,1,2,2- tetrahydro-fluoro-trifluoroethyl ether _{(CF 3 CF 2 CH 2 OCF} 2 CF 2 H), 1,1,2,2-tetrafluoroethyl methyl ether (HCF ₂ CF ₂ OCH ₃ ), 1,1,2,2-tetrafluoroethyl ethyl ether (HCF ₂ CF ₂ OCH ₂ CH ₃ ) , 1,1,2,2-tetrafluoroethyl propyl ether (HCF ₂ CF ₂ OC ₃ H ₇ ), 1,1,2,2-tetrafluoroethyl butyl ether (HCF ₂ CF ₂ OC ₄ H ₉ ) , 2,2,3,3-tetrafluoro-ethyl difluoromethyl ether _{(H (CF 2) 2 CH} 2 O (CF 2) H), 1,1,2,2- tetrafluoro-ethyl isobutyl ether (HCF ₂ CF ₂ OCH ₂ CH (CH ₃ ) ₂ ), 1,1,2,2-tetrafluoroethyl iso Pentyl ether (HCF ₂ CF ₂ OCH ₂ C (CH ₃ ) ₃ ), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HCF ₂ CF ₂ OCH ₂ CF ₃ ), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H), hexafluoroisopropyl methyl ether ( (CF ₃ ) ₂ CHOCH ₃ ), 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether ((CF ₃ ) ₂ CHCF ₂ OCH ₃ ) 3,3,3-hexafluoro-methyl ether _{(CF 3 CHFCF 2 OCH 3)} , a 1,1,2,3,3,3- hexafluoro-propyl ether _{(CF 3 CHFCF 2 OCH 2 CH} 3), 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether (CF ₃ CHFCF ₂ CH ₂ OCHF ₂ ), or a combination thereof.

The content of the hydrofluoroether may be 10 to 60% by volume based on the total volume of the solvent.

The first additive may be included in an amount of 0.01 to 1.5% by weight based on the total weight of the electrolytic solution.

The additive may include the first additive and the second additive. In this case, the second additive may be included in an amount of 0.05 to 1.00 wt% based on the total weight of the electrolyte solution.

The additive may include the first additive and the third additive. In this case, the third additive may be included in an amount of 0.04 to 1.00 wt% based on the total weight of the electrolyte solution.

The additive may include the first additive and the fourth additive. In this case, the fourth additive may be included in an amount of 0.01 to 1.00 wt% based on the total weight of the electrolyte solution.

The first additive may include at least one of the disilane compounds represented by the following general formulas (1-1) to (1-9).

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

[Chemical Formula 1-8]

[Chemical Formula 1-9]

The second additive may include a compound represented by the following formula (2-1), a compound represented by the formula (2-2), or a combination thereof.

[Formula 2-1]

[Formula 2-2]

The third additive may include at least one of unsaturated phosphoric acid ester compounds represented by the following formulas (3-1) to (3-8).

[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

[Chemical Formula 3-4]

[Formula 3-5]

[Chemical Formula 3-6]

[Chemical Formula 3-7]

[Chemical Formula 3-8]

The fourth additive may include at least one of unsaturated phosphoric acid ester compounds represented by the following general formulas (4-1) to (4-4).

[Formula 4-1]

[Formula 4-2]

[Formula 4-3]

[Formula 4-4]

The lithium-containing transition metal oxide may be a lithium-cobalt-based complex oxide.

The lithium secondary battery may further include a negative electrode including a negative electrode active material. The negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, a lithium metal oxide, .

The solvent may further comprise fluoroethylene carbonate.

The content of the fluoroethylene carbonate may be 10 to 30% by volume based on the total volume of the solvent.

The redox potential of the lithium secondary battery may be 4.3 V (vs. Li / Li ⁺ ) to 5.0 V or less.

The details of other embodiments are included in the detailed description below.

A lithium secondary battery having improved cycle life characteristics and high temperature storage characteristics can be realized.

1 is a cross-sectional view illustrating a lithium secondary battery according to one embodiment.
FIG. 2 is a scanning electron microscope (SEM) photograph showing the state of coating of the surface of LiCoO ₂ particles after storing the lithium secondary battery according to Example 1 and Comparative Example 1 at 60 ° C. for 24 hours.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

It is to be understood that where a layer, film, region, plate, or the like is referred to as being "on" another portion, unless stated otherwise in this specification, .

Hereinafter, a lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a cross-sectional view illustrating a lithium secondary battery according to one embodiment.

Referring to FIG. 1, the lithium secondary battery 10 may include an anode 20, a cathode 30, and a separator layer 40.

Li / Li ⁺ ) of not less than 5.0 V, specifically not less than 4.4 V and not more than 5.0 V, more specifically, May be 4.4 V or more and 4.6 V or less.

The shape of the lithium secondary battery 10 is not particularly limited, and may be cylindrical, angular, laminate, button, or the like.

The anode 20 may include a current collector 21 and a cathode active material layer 22 formed on the current collector.

The current collector 21 may be any conductive material such as aluminum, stainless steel, nickel coated steel, or the like.

The cathode active material layer 22 includes a cathode active material, and may further include a conductive material and a binder.

The positive electrode active material according to one embodiment may use a transition metal oxide containing lithium.

Examples of the transition metal oxide containing lithium include LiCoO ₂ , A lithium nickel cobalt manganese composite oxide such as LiNi _x Co _y Mn _z O ₂ , a lithium nickel composite oxide such as LiNiO ₂ , or a lithium manganese composite oxide such as LiMn ₂ O ₄ , . The cathode active material may be used alone or in combination of two or more thereof. Among them, when the lithium-cobalt composite oxide is used, the degradation of cycle life characteristics and high-temperature storage characteristics may be larger. According to one embodiment, by using the electrolyte additive described below together, the cycle life characteristics and the high-temperature storage characteristics can be greatly improved.

The content of the cathode active material is not particularly limited and may be a content applicable to the cathode active material layer of the lithium secondary battery.

The conductive material may be, for example, carbon black such as Ketjen black or acetylene black, natural graphite, artificial graphite or the like, but is not particularly limited as long as it enhances the conductivity of the anode.

The content of the conductive material is not particularly limited and may be a content applicable to the positive electrode active material layer of the lithium secondary battery.

The binder may be, for example, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, a polyvinyl acetate, a polymethyl methacrylate, a polyethylene, a nitrocellulose and the like can be cited. However, when the positive electrode active material and the conductive material are placed on the current collector 21 And is not particularly limited as long as it has oxidation resistance and electrolyte stability to withstand the high potential of the anode at the same time.

The content of the binder is not particularly limited and may be a content applicable to the positive electrode active material layer of the lithium secondary battery.

The density of the positive electrode active material layer 22 is not particularly limited. The density of the cathode active material layer 22 can be calculated by dividing the area density after the rolling of the cathode active material layer 22 by the thickness of the cathode active material layer 22 after rolling.

The cathode active material layer 22 can be produced, for example, in the following manner. First, a positive electrode active material, a conductive material, and a binder are dry-mixed to prepare a positive electrode mixture. Subsequently, the positive electrode material mixture is dispersed in a suitable organic solvent such as N-methyl-2-pyrrolidone to prepare a positive electrode material mixture slurry, the positive electrode material mixture slurry is coated on the current collector 21, To thereby produce a positive electrode active material layer.

The cathode 30 may include a current collector 31 and a negative electrode active material layer 32 formed on the current collector 31.

The current collector 31 may be any conductor, and may be, for example, copper (Cu), copper alloy, aluminum, stainless steel, nickel-plated steel, or the like.

The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder.

The negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, a lithium metal oxide, a metal lithium, or the like, or a mixture of two or more thereof. The carbon-based material may be, for example, graphite based materials such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite. The silicon-based material may be, for example, silicon, a silicon oxide, a silicon-containing alloy, or a mixture of these with a graphite-based material. The silicon oxide may be represented by SiOx (0 < x? 2). The tin-based material may be, for example, tin, tin oxide, a tin-containing alloy, a mixture thereof with a graphite-based material, or the like. The lithium metal oxide includes, for example, a titanium oxide-based compound such as Li ₄ Ti ₅ O ₁₂ .

For example, the negative electrode active material may be a mixture of a carbon-based material such as a graphite-based material and a silicon-based material such as a silicon-containing alloy. In this case, the carbon-based material and the silicon-based material may be mixed in a weight ratio of 50:50 to 90:10, such as 60:40 to 80:20. The content of silicon in the silicon-containing alloy may be 50% by weight or more based on the total amount of the silicon-containing alloy. According to one embodiment, when the negative electrode active material includes a silicon-based material, the cycle life characteristics and the high-temperature storage characteristics can be significantly improved at the same time as compared with the case where the negative active material contains no silicon-based material.

The binder may be of the same kind as the binder constituting the positive electrode active material layer (22).

The content of the binder is not particularly limited and may be any amount as long as it is applied to the negative electrode active material layer of the lithium secondary battery.

The negative electrode active material layer 32 may further include a thickener such as carboxymethyl cellulose (CMC). The content of the thickener may be 1/10 to 10/10 of the weight of the binder.

The density of the negative electrode active material layer 32 is not particularly limited. The density of the negative electrode active material layer 32 can be calculated by dividing the area density of the negative electrode active material layer 32 after rolling by the thickness of the negative electrode active material layer 32 after rolling.

The cathode 30 may be manufactured as follows. First, the negative electrode active material and the binder are dispersed in a solvent such as water and N-methyl-pyrrolidone to prepare a slurry, and the slurry is coated on the current collector 31 and dried.

The separator layer 40 includes a separator and an electrolytic solution.

The separator is not particularly limited and any separator can be used as long as it is used as a separator of a lithium secondary battery.

As the separator, a porous film or nonwoven fabric exhibiting excellent high rate discharge performance can be used singly or in combination.

Examples of the material constituting the separator include a polyolefin resin, a polyester resin, polyvinylidene fluoride (PVDF), a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-perfluoro Vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride- Copolymers, vinylidene fluoride-ethylene copolymers, vinylidene fluoride-propylene copolymers, vinylidene fluoride-trifluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers, Vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like Can. Examples of the polyolefin-based resin include polyethylene and polypropylene. Examples of the polyester-based resin include polyethylene terephthalate and polybutylene terephthalate.

The thickness of the separator is not particularly limited.

The electrolytic solution may include a lithium salt, a solvent, and an additive.

The lithium salt may be an electrolyte of an electrolytic solution. The lithium salt is, for _{example, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, LiSbF 6, LiSO 3 CF 3, LiN (SO 2 CF 3), LiN (SO 2 CF 2 CF 3), LiC (SO 2 (CF ₂ CF ₃ ) ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiI, LiCl, LiF, LiPF ₅ (SO ₂ CF ₃ ), and LiPF ₄ (SO ₂ CF ₃ ) ₂ . One or more of these lithium salts may be dissolved.

When the lithium salt is dissolved in the electrolytic solution, battery characteristics can be improved.

The concentration of the lithium salt is not particularly limited and may be, for example, 0.85 to 1.6 mol / L, and may be used at a concentration of, for example, 0.9 to 1.40 mol / L. When the concentration of the lithium salt is within the above range, battery characteristics can be improved.

The solvent according to one embodiment may comprise hydrofluoroether (HFE).

The hydrofluoroether (HFE) is obtained by replacing some hydrogen atoms of the ether with fluorine, and when used as a solvent, the oxidation resistance can be improved.

The hydro-fluoro-ether (HFE) is given and the like resistant to the charge voltage and current density of the cathode material, 2,2,2-trifluoroethyl ether _{(CF 3 CH 2 OCH 3)} , 2,2, 2-trifluoromethyl methyl ether in ethyl difluoro _{(CF 3 CH 2 OCHF 2)} , 2,2,3,3,3-pentafluoro-propyl ether _{(CF 3 CF 2 CH 2 OCH} 3), 2,2 , methyl 3,3,3-pentafluoroethyl profile difluoromethyl ether _{(CF 3 CF 2 CH 2 OCHF} 2), 2,2,3,3,3- pentafluoropropyl -1,1,2,2- Tetrafluoroethyl ether (CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H), 1,1,2,2-tetrafluoroethyl methyl ether (HCF ₂ CF ₂ OCH ₃ ), 1,1,2,2- Tetrafluoroethyl ethyl ether (HCF ₂ CF ₂ OCH ₂ CH ₃ ), 1,1,2,2-tetrafluoroethyl propyl ether (HCF ₂ CF ₂ OC ₃ H ₇ ), 1,1,2,2- Tetrafluoroethyl butyl ether (HCF ₂ CF ₂ OC ₄ H ₉ ), 2,2,3,3-tetrafluoroethyl difluoromethyl ether (H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) H) , 1,1,2,2-tetrafluoroethyl iso Butyl ether _{(HCF 2 CF 2 OCH 2 CH} (CH 3) 2), 1,1,2,2- tetrafluoro-ethyl isopentyl ether _{(HCF 2 CF 2 OCH 2 C} (CH 3) 3), 1,1 , 2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HCF ₂ CF ₂ OCH ₂ CF ₃ ), 1,1,2,2-tetrafluoroethyl-2,2,3 , 3-tetrafluoropropyl ether (HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H), hexafluoroisopropyl methyl ether ((CF ₃ ) ₂ CHOCH ₃ ), 1,1,3,3,3-penta Fluoro-2-trifluoromethylpropyl methyl ether ((CF ₃ ) ₂ CHCF ₂ OCH ₃ ), 1,1,2,3,3,3-hexafluoropropyl methyl ether (CF ₃ CHFCF ₂ OCH ₃ ) , a 1,1,2,3,3,3- hexafluoro-propyl ether _{(CF 3 CHFCF 2 OCH 2 CH} 3) and methyl-2,2,3,4,4,4- hexafluoro-butyl-di-fluoro Ether (CF ₃ CHFCF ₂ CH ₂ OCHF ₂ ) and the like. Any one or a mixture of two or more of them may be used.

The content of the hydrofluoroether is not particularly limited, but it may be 10 to 60% by volume, for example, 30 to 50% by volume, for example, 35 to 50% by volume based on the total volume of the solvent . When the content of the hydrofluoroether is within the above range, the battery characteristics can be improved.

In addition to the hydrofluoroether, the solvent may be a non-aqueous solvent used in a conventional lithium secondary battery without any particular limitation.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic esters such as? -butyrolactone and? -valerolactone; Chain esters such as methyl formate, methyl acetate and butyric acid methyl; Tetrahydrofuran or a derivative thereof; Ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyl diglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone, ethyl methyl sulfone, or a derivative thereof; May be used alone or as a mixture of two or more thereof, but the present invention is not limited thereto. When a mixture of two or more nonaqueous solvents is used, the mixing ratio of each solvent can be applied at a mixing ratio that can be used in a conventional lithium secondary battery. Of these, the above chain carbonates may be specifically used.

The content of the chain carbonate may be 5 to 60% by volume, for example, 20 to 50% by volume based on the total volume of the solvent. When the content of the chain carbonate is within the above range, the battery characteristics can be improved.

The solvent may further use fluoroethylene carbonate.

The content of the fluoroethylene carbonate may be 10 to 30% by volume based on the total volume of the solvent, for example, 15 to 20% by volume. When the content of the fluoroethylene carbonate is within the above range, the cycle life characteristics can be improved.

The additive may include a first additive represented by the following general formula (1), a second additive represented by the following general formula (2), a third additive represented by the following general formula (3), and a fourth additive represented by the following general formula As shown in FIG. For example, the additive includes a first additive represented by the following general formula (1), and further includes a second additive represented by the following general formula (2), a third additive represented by the following general formula (3), and a fourth additive represented by the following general formula And at least one selected from the group consisting of

Hereinafter, each of the first to fourth additives will be described in detail.

The first additive

The first additive may be a disilane compound represented by the following general formula (1). The first additives may be used alone or in combination of two or more.

[Chemical Formula 1]

In Formula 1, R ¹ to R ³ each independently represent a C1 to C8 alkyl group, a vinyl group or a C1 to C5 alkyl group, which is unsubstituted or substituted with a vinyl group or a C1 to C5 alkyl group, A substituted or unsubstituted C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C5 to C8 cycloalkyl group, a C6 to C8 aryl group, or a fluorine atom. The C1 to C8 alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a pentyl group, an isopentyl group, pentyl group, hexyl group, secondary hexyl group, heptyl group, secondary heptyl group, octyl group, secondary octyl group, 2-methylpentyl group and 2-ethylhexyl group. The C2 to C8 alkenyl group includes, for example, 1,3-butadienyl, 1,2-propanediyl, 1,4-pentadienyl, Propenylene group, butynylene group, pentynylene group, and hexynylene group, and the like can be given as examples of the phenylene group. Examples of the C5 to C8 cycloalkyl group include a cyclopentyl group, a cyclohexyl group, and a cyclohexylmethyl group. Examples of the C6 to C8 aryl group include a phenyl group, a tolyl group, and a xylyl group. Some of the hydrogen atoms of the substituents may be substituted with a halogen atom, a vinyl group, a C1 to C5 alkyl group, or the like. For example, the C1 to C8 alkyl group may include a double bond or may not include a double bond.

A C1 to C8 alkyl group including a double bond such as a propyl group including a double bond can be represented by the following formula (A).

(A)

In the above formula (1), R ⁴ is a C 1 to C 8 alkylene group, a C 2 to C 8 alkynylene group, a C ⁴ to C 8 alkylene group having an ether group, a C 1 to C 8 alkylene group having a plurality of -CF ₂ -connecting groups, And a C4 to C10 alkylene group having a sulfide group. Group is the C1 to C8 alkylene group one or more of -CF ₂ - may include a linking group, it may not be included. For example, four -CF ₂ - groups to C5 to C8 alkyl containing alkylene linkage can be represented by the following general formula B) to (E and the like.

[Chemical Formula B]

&Lt; RTI ID = 0.0 &

[Chemical Formula D]

(E)

Examples of the C1 to C8 alkylene group include methylene, ethylene, propylene, butylene, pentamethylene, hexamethylene, heptamethylene, octamethylene and 2-methylbutylene. The C2 to C8 alkynylene group includes, for example, ethynylene, propynylene, butynylene, pentynylene, hexynylene, heptynylene, Diary, and the like. The C4 to C8 alkylene group having an ether group may be, for example, a C4 to C8 alkylene group having an ether group containing at least one of an oxygen atom and a sulfur atom including a thioether group. Specifically, 4-oxaheptylene group, 5-oxanonylene group and the like can be given. The ether group may be represented by -O-, and the sulfide group may be represented by -S-. Some hydrogen atoms of the substituent may be substituted with a halogen atom.

Specific examples of the first additive include 1,2-bis (difluoromethoxysilyl) ethane, 1,3-bis (difluoromethylsilyl) propane, 1,2-bis (difluoromethylsilyl) , 1,2-bis (difluoroethylsilyl) ethane, 1-difluoromethylsilyl-2-difluoroethylsilylethane, 1-difluoromethylsilyl-2-difluoropropylsilylethane, 1 , 3,3-tetraethyldisiloxane, 1,3-difluoro-1,1,3,3-tetrapropyldisiloxane, 1,3-difluoro-1,1,3,3-tetrabutyl di Siloxane, 1,3-difluoro-1,1,3,3-tetrapentyldisiloxane, 1,3-difluoro-1,1,3,3-tetrahexyldisiloxane, 1,2-bis ( (Fluorodiethylsilyl) ethane, 1,2-bis (fluorodibutylsilyl) ethane, 1-fluoro Dimethylsilyl-2-fluoroethylsilylethane, 1,3-bis (fluorodimethylsilyl) propane, 1,3-bis (fluorodiethylsilyl) (Fluorodipropylsilyl) propane, 1,3-divinyl-1,1,3,3-tetraethyldisiloxane, 1,3-bis (fluorodipropylsilyl) Divinyl-1,1,3,3-tetrapropyldisiloxane, 1,3-divinyl-1,1,3,3-tetrabutyldisiloxane, 1,3-divinyl-1,1,3,3 - tetrapentyldisiloxane, 1,3-divinyl-1,1,3,3-tetrahexyldisiloxane, 1,3-diethynyl-1,1,3,3-tetramethyldisiloxane, 1,3- Diethynyl-1,1,3,3-tetraethyldisiloxane, 1,3-diethynyl-1,1,3,3-tetrapropyldisiloxane, 1,3-diethynyl-1,1,3,3 (2-ethoxydifluorosilyl) ethyl) thio) propiodifluorosilane, 2,2 '- (ethylene dithio) bis (difluoroethylsilane) and the like .

Specifically, the first additive may include at least one of the disilane compounds represented by the following general formulas (1-1) to (1-9). Among them, among the disilane compounds represented by the following general formulas At least one of which may be more specifically included.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

[Chemical Formula 1-8]

[Chemical Formula 1-9]

Second additive

The second additive may be a disilane compound represented by the following formula (2). The second additives may be used alone or in combination of two or more.

(2)

In Formula 2, R ⁵ may be a C 2 to C 6 alkylene group that does not include a double bond, a C 2 to C 6 alkylene group that contains a double bond, a C 2 to C 6 alkenylene group, or a C 6 to C 12 arylene group. Examples of the C2 to C6 alkylene group include an ethylene group, a propylene group, a butylene group, a pentamethylene group and a hexamethylene group. The C2 to C6 alkylene group may include a double bond. For example, a C3 alkylene group containing one double bond may be represented by the following formula (F).

[Chemical Formula F]

The C6 to C12 arylene group includes, for example, 1,2-phenylene group, 1,4-phenylene group, and (1,1'-biphenyl) -4,4'-diyl group. Some hydrogen atoms of the substituent may be substituted with a halogen atom.

In the general formula (2), R ⁶ to R ¹¹ may each independently be a C 1 to C 6 alkyl group or a C 2 to C 6 alkenyl group. The C 1 to C 6 alkyl group may be, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a 2-propyl group, a 3-fluoropropyl group, a 3-fluorobutyl group, Butyl group and the like. The C2 to C6 alkenyl group may be a 1,3-butadienyl group, a 1,2-propanediyl group, a 1,4-pentadienyl group, a vinylene group, a propenylene group, an isopropenylene group, , Hexenylene group and the like. Some hydrogen atoms of the substituent may be substituted with a halogen atom.

Specific examples of the second additive include bis (trimethylsilyl) acetylenedicarboxylate, bis (ethyldimethylsilyl) acetylenedicarboxylate, bis (dimethylpropylsilyl) acetylenedicarboxylate, bis (dimethylbutylsilyl) (Dimethylsilyl) acetylenicarboxylate, bis (trimethylsilyl) fumarate, bis (trimethylsilyl) maleate, bis (trimethylsilyl) phthalate, bis (trimethylsilyl) isophthalate, terephthalic acid bis Trimethylsilyl), itaconic acid bis (trimethylsilyl), and the like.

More specifically, the second additive may include the following formula (2-1), (2-2), or a combination thereof.

[Formula 2-1]

[Formula 2-2]

Third additive

The third additive may be an unsaturated phosphoric acid ester compound represented by the following general formula (3). The third additive may be used alone or in combination of two or more.

(3)

In Formula 3, R ¹² and R ¹³ each independently represent a hydrogen atom or a C1 to C8 alkyl group. The C1 to C8 alkyl group is preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a t- butyl group, a pentyl group, an isopentyl group, , A hexyl group, a secondary hexyl group, a heptyl group, a secondary heptyl group, an octyl group, a secondary octyl group, a 2-methylpentyl group and a 2-ethylhexyl group. Among them, a hydrogen atom, a methyl group, an ethyl group, a propyl group and the like can be used in view of a small adverse effect on the movement of lithium ions and good charging characteristics. Specifically, hydrogen atoms and methyl groups can be used. More specifically, A hydrogen atom can be used.

In Formula 3, R ¹⁴ may be a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group substituted or unsubstituted with a vinyl group. Examples of the C1 to C8 alkyl group and the C2 to C8 alkenyl group are the same as those described in the description of the substituents of R ¹ to R ³ in the formula (1). Examples of the C2 to C8 alkynyl group include an ethynyl group, a 2-propynyl group (also called "propargyl"), a 3-butynyl group, a 1-methyl- And the like. Examples of the C1 to C8 halogenated alkyl group include chloromethyl, trifluoromethyl, 2-fluoroethyl, 2-chloroethyl, 2,2,2-trifluoroethyl, 2,2,2- Chloropropyl group, 2-chloro-2-propyl group, 3,3,3-trifluoropropyl group, 3,3,3-trifluoropropyl group, 2-chlorobutyl group, 3-chlorobutyl group, 4-chlorobutyl group, 3-chloro- Chloro-2-methylpropyl group, 3-chloro-2-methylpropyl group, 3-chloro-2-methylpropyl group, , 3-chloro-2,2-dimethyl group, 6-chlorohexyl group and the like. Among them, the lithium secondary battery has a smaller internal resistance, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a 2-propyl group, A methyl group, an ethyl group, a propyl group, a 2-propynyl group and the like can be used. More specifically, an ethyl group, a 2-propynyl group and the like can be used.

Among the specific examples of the third additive, examples of the compound in which R ¹² and R ¹³ are hydrogen atoms include methyl bis (2-propynyl) phosphate, ethyl bis (2-propynyl) phosphate, Bis (2-propynyl) phosphate, allylbis (2-propynyl) phosphate, tris (2-propynyl) phosphate, 2-chloroethyl bis (Propyl) phosphate, 2,2,2-trifluoroethyl bis (2-propynyl) phosphate and 2,2,2-trichloroethyl bis (2-propynyl) phosphate.

Among specific examples of the third additive, R ¹² is a methyl group and R ¹³ is an example of a compound wherein the hydrogen atom, methyl bis (1-methyl-2-propynyl) phosphate, ethyl-bis (1-methyl-2 Propyl) phosphate, propyl bis (1-methyl-2-propyl) phosphate, butyl bis (1-methyl- Propyl) phosphate, tris (1-methyl-1-methyl-2-propynyl) phosphate, 2-chloropropylbis Propyl) phosphate, 2,2,2-trichloroethyl bis (1-methyl-2-propynyl) phosphate, -Propinyl) phosphate, and the like.

Among the specific examples of the third additive, examples of the compound in which R ¹² and R ¹³ are methyl groups include methyl bis (1,1-dimethyl-2-propynyl) phosphate, ethyl bis (1,1- Propyl) phosphate, propyl bis (1,1-dimethyl-2-propynyl) phosphate, butyl bis (1,1- ) Phosphate, allylbis (1,1-dimethyl-2-propynyl) phosphate, 2-propynyl bis (1,1- ) Phosphate, 2,2,2-trifluoroethyl bis (1,1-dimethyl-2-propynyl) phosphate, 2,2,2- , 2-trichloroethyl bis (1,1-dimethyl-2-propynyl) phosphate, and the like.

Specific examples of the third additive include methyl bis (2-propynyl) phosphate, ethyl bis (2-propynyl) phosphate, propyl bis (2-propynyl) phosphate, butyl bis (2-propynyl) phosphate, tris (2-propynyl) phosphate and 2-chloroethyl bis (2-propynyl) phosphate. Specific examples thereof include ethyl bis (2-propynyl) phosphate, butyl bis (2-propynyl) phosphate and tris (2-propynyl) phosphate. More specific examples thereof include ethyl bis -Propinyl) phosphate and the like can be used.

More specifically, the third additive may include at least one of unsaturated phosphoric acid ester compounds represented by the following general formulas (3-1) to (3-8), specifically, Unsaturated phosphoric acid ester compound represented by a combination thereof.

[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

[Chemical Formula 3-4]

[Formula 3-5]

[Chemical Formula 3-6]

[Chemical Formula 3-7]

[Chemical Formula 3-8]

Fourth additive

The fourth additive may be an unsaturated phosphoric acid ester compound represented by the following general formula (4). The fourth additives may be used alone or in combination of two or more.

[Chemical Formula 4]

In Formula 4, R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom or a C1 to C8 alkyl group. The C1 to C8 alkyl groups are the same as those exemplified in the description of the substituents of R ¹ to R ³ in the formula (1). Among them, a hydrogen atom, a methyl group, an ethyl group, a propyl group and the like can be used in view of a small adverse effect on the movement of lithium ions and good charging characteristics. Specifically, hydrogen atoms and methyl groups can be used. More specifically, A hydrogen atom can be used.

In Formula 4, R ¹⁷ may be a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group. Examples of the C1 to C8 alkyl group and the C2 to C8 alkenyl group are the same as those described in the description of the substituents of R ¹ to R ³ in the formula (1). The C 2 to C 8 alkynyl group and the C 1 to C 8 halogenated alkyl group are the same as those described in the description of the substituent of R ¹⁴ in Formula 3. Among them, the lithium secondary battery has a smaller internal resistance, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a 2-propyl group, A methyl group, an ethyl group, a propyl group, and a 2-propyl group can be used, and more specifically, a methyl group and an ethyl group can be used.

In Formula 4, n may be 1 or 2. Of these, n can be 2 in that phosphate ester reaction from alkene diol as a raw material is easy and a high yield can be obtained. When n is 2, it can be represented by the following formula (G).

[Formula G]

Among the specific examples of the fourth additive, examples of the compound wherein n is 1 include 2-butyne-1,4-diol tetramethyldiphosphate, 2-butene-1,4-diol tetraethyldiphosphate, 1,4-diol tetrabutyl diphosphate, 2-butene-1,4-diol tetrabutyl diphosphate, 2-butene-1,4-diol tetrabutyl diphosphate, 1,4-diol tetrakis (2-propynyl) diphosphate, 2-butyne-1,4-diol tetrakis (3- chloropropyl) diphosphate, 2-butyne- Diol tetrakis (3-chlorobutyl) diphosphate, 2-butene-1,4-diol tetrakis (4-chlorobutyl) diphosphate and the like. Of these, 2-butyne- Butene-1,4-diol tetraethyl di- phosphate, 2-butene-1,4-diol tetrapropyl diphosphate, 2-butene- Can be used to scan sulfate or the like, it can be specifically used such as 2-butyne-1,4-diol tetramethyldisiloxane phosphate, 2-butyne-1,4-diol-tetrakis (2-propynyl) diphosphate.

Among the specific examples of the fourth additive, examples of the compound wherein n is 2 include 2,4-hexadiyne-1,6-diol tetramethyldiphosphate, 2,4-hexadiyne-1,6-diol tetra Ethyl diphosphate, 2,4-hexadiene-1,6-diol tetrapropyldiphosphate, 2,4-hexadiene-1,6-diol tetraisopropyldiphosphate, 2,4-hexadiene- , 6-diol tetrabutyl diphosphate, 2,4-hexadiene-1,6-diol tetrapentyl diphosphate, 2,4-hexadiene-1,6-diol tetrakis (2-propynyl) (3-chloropropyl) diphosphate, 2,4-hexadienyl-1,6-diol tetrakis (3-chlorobutyl) diphosphate, 2 , 4-hexadiene-1,6-diol tetrakis (4-chlorobutyl) diphosphate, etc. Among them, 2,4-hexadiene-1,6-diol tetramethyldiphosphate, 4-hexadiene-1,6-diol tetraethyl diphosphate, 2,4-hexadiene-1 Diol tetrapropyl diphosphate, 2,4-hexadiene-1,6-diol tetrakis (2-propynyl) diphosphate and the like. Specific examples thereof include 2,4- , 6-diol tetramethyl diphosphate, 2,4-hexadiene-1,6-diol tetrakis (2-propynyl) diphosphate, and the like.

More specifically, the fourth additive may include at least one of unsaturated phosphoric acid ester compounds represented by the following general formulas (4-1) to (4-4), specifically, Unsaturated phosphoric acid ester compound represented by a combination thereof.

[Formula 4-1]

[Formula 4-2]

[Formula 4-3]

[Formula 4-4]

By adding at least one of the first additive and the second to fourth additives to the electrolyte, cycle life characteristics and high temperature storage characteristics can be improved. For example, the electrolytic solution may include the first additive and the second additive, or may include the first additive and the third additive, or may include the first additive and the fourth additive. For example, the electrolyte may include the first additive, the second additive, and the third additive, or may include the first additive, the second additive, and the fourth additive, or may contain the first additive, 3 additive, and the fourth additive. For example, the transfer liquid may include both the first additive, the second additive, the third additive, and the fourth additive.

Specifically, the first to fourth additives are preferentially decomposed to a lower potential than the solvent, for example, hydrofluoroether (HFE) contained in the electrolytic solution, or the additive is adsorbed on the surface of the cathode active material. The first to fourth additives or their decomposition products cover the cathode active material to inhibit decomposition of the hydrofluoroether. For example, the first to fourth additives themselves or decomposition products thereof cover the cathode active material, thereby suppressing contact between the hydrofluoroether and the cathode active material. As a result, formation of a high-resistance film derived from the decomposition products of the solvent, particularly hydrofluoroether, on the cathode active material is suppressed and the generation of the decomposition gas of the electrolytic solution (HFE) during storage is suppressed.

The effect of addition of the first to fourth additives will be described in more detail as follows.

The terminal silyl group of the first additive tends to interact with a part of the LiPF ₆ electrolyte or the hydrofluoric acid which is slightly liberated in the electrolytic solution. The terminal silyl group of the first additive is decomposed before the second to fourth additives To form a film. An unsaturated group (such as an alkynyl group) between the two silyl groups also contributes to the film formation. Next, the second additive appears to decompose, and the carbonyl group in the structure appears to confer ionic conductivity of the coating. The third and fourth additives are more stable in chemical structure than the first and second additives and have relatively withstand voltage characteristics. The third and fourth additives are adsorbed to the cathode active material by the phosphonic acid moiety while being adhered to the coating derived from the first additive. As a result, it appears that a dense, low-resistance film is formed which suppresses the contact of the hydrofluoroether.

The first additive may be included in an amount of 0.01 to 1.5% by weight, for example, 0.1 to 1.4% by weight, 0.2 to 1.4% by weight and 0.4 to 1.3% by weight based on the total weight of the electrolytic solution. When the content of the first additive is within the above range, cycle life characteristics and storage characteristics can be greatly improved.

The second additive may be included in an amount of 0.05 to 1.00 wt%, for example, 0.07 to 1.00 wt%, 0.07 to 0.6 wt%, and 0.1 to 0.6 wt% based on the total weight of the electrolytic solution. When the content of the second additive is within the above range, the cycle life characteristics and storage characteristics can be greatly improved.

The third additive may be contained in an amount of 0.04 to 1.00 wt%, for example 0.05 to 1.00 wt%, 0.07 to 1.00 wt%, 0.07 to 0.6 wt%, and 0.1 to 0.6 wt%, based on the total weight of the electrolytic solution . When the content of the third additive is within the above range, cycle life characteristics and storage characteristics can be greatly improved.

The fourth additive may be contained in an amount of 0.01 to 1.0% by weight based on the total weight of the electrolytic solution and may be 0.05 to 1.0% by weight, 0.07 to 1.0% by weight, 0.1 to 0.7% by weight, 0.1 to 0.6% 0.1 to 0.4% by weight. When the content of the fourth additive is within the above range, cycle life characteristics and storage characteristics can be greatly improved.

The electrolytic solution may further include various additives other than the first to fourth additives. Examples of such an additive include a negative electrode active additive, an anionic additive, an ester additive, a carbonic ester additive, a sulfuric acid ester additive, a phosphate ester additive, a borate ester additive, an acid anhydride additive, Additives, and the like. Any one of them may be added to the electrolytic solution, or a plurality of kinds of additives may be added to the electrolytic solution.

As described above, the electrolytic solution according to one embodiment includes at least one of the first additive and the second to fourth additives, so that a positive electrode containing a lithium-containing transition metal oxide as a positive electrode active material, a hydrofluoro The cycle life characteristics and the storage characteristics of a lithium secondary battery using an electrolyte containing an ether can be greatly improved.

Hereinafter, a method for producing a lithium secondary battery will be described.

The anode 20 can be manufactured as follows. First, a mixture obtained by mixing a cathode active material, a conductive material and a binder is dispersed in a solvent, for example, N-methyl-2-pyrrolidone to prepare a slurry. Then, the slurry is coated on the current collector 21 and dried to form the positive electrode active material layer 22. The coating method is not particularly limited, and examples thereof include a knife coater method and a gravure coater method. The following application process can be carried out in the same way. Subsequently, the cathode 20 is formed by compressing the cathode active material layer 22 to a density within the above range by a compressor.

The cathode (3) can be manufactured in the same manner as the anode (20). For example, first, a mixture of an anode active material and a binder is dispersed in a solvent such as N-methyl-2-pyrrolidone or water to prepare a slurry, and then the slurry is coated on the current collector 31 and dried Thereby forming the anode active material layer 32. Subsequently, the negative electrode 30 is formed by compressing the negative electrode active material layer 32 to a density within the above range by a compressor.

The separator 40a may be manufactured as follows. First, the resin constituting the porous layer 42 and the water-soluble organic solvent are mixed at a weight ratio of 5 to 10: 90 to 95 to prepare a coating liquid. Examples of the water-soluble organic solvent include N-methyl-2-pyrrolidone, dimethylacetamido (DMAc) and tripropylene glycol (TPG). Subsequently, the coating liquid is applied on both sides or one side of the substrate 41 to a thickness of 1 to 5 mu m. Subsequently, the base material 41 coated with the coating liquid is treated with a coagulating liquid to solidify the resin in the coating liquid. Examples of the method of treating the base material 41 coated with the coating liquid with the coagulating liquid include a method of impregnating the coagulating liquid with the base material 41 coated with the coating liquid, ), And a method in which the coagulating solution is sharply poured. Thus, the separator 40a can be formed. Here, the coagulating solution is, for example, water mixed with the water-soluble organic solvent. The mixing amount of water may be 40 to 80% by volume based on the total volume of the coagulating solution. Subsequently, the separator 40a is washed with water and dried to remove water and a water-soluble organic solvent from the separator 40a.

Subsequently, the separator 40a is sandwiched between the positive electrode 20 and the negative electrode 30 to manufacture an electrode structure. When the porous layer 42 is formed on only one side of the base material 41, the cathode 30 is opposed to the porous layer 42. Then, the produced electrode structure is processed into a desired shape, for example, a cylindrical shape, a square shape, a laminate shape, a button shape, or the like, and inserted into the container of the above-described shape. Further, by injecting the desired electrolyte into the vessel, the electrolyte is impregnated into each pore in the separator 40a. Thus, a lithium secondary battery is manufactured.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto. In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

Example  One

98% by weight of LiCoO ₂ , 1% by weight of polyvinylidene fluoride and 1% by weight of Ketjenblack were dispersed in N-methyl-2-pyrrolidone to prepare a slurry. Then, the slurry was cast on an aluminum current collector Followed by coating and drying to form a positive electrode active material layer. Subsequently, the positive electrode active material layer was pressed by a press machine to obtain a positive electrode active material layer having a density of 4.0 g / cm ³ .

A slurry was prepared by dispersing 90 wt% of an anode active material, 7 wt% of polyacrylic acid, and 2 wt% of conductive carbon mixed in a mixture of silicon alloy (containing 70 atom% of silicon) and artificial graphite in a weight ratio of 30:70 , The slurry was applied onto an aluminum current collecting foil as a current collector and dried to form a negative electrode active material layer. Subsequently, the negative electrode active material layer was pressed by a press machine to obtain a negative electrode active material layer having a density of 1.45 g / cm &lt; ^{3 &} gt ;.

Subsequently, a separator (separator made by Mitsubishi Plastics, Ltd., thickness 20 μm) was disposed between the positive electrode and the negative electrode to prepare an electrode structure.

Then, the electrode structure was inserted into a test container.

(CF ₂ ) ₂ CH ₂ O (CF ₂ ) H as a fluoroethylene carbonate (FEC), ethylmethylsulfone (EMS), dimethyl carbonate (DMC), and hydrofluoroether (HFE) 40, LiPF ₆ was dissolved at a concentration of 1.3 mol / L to prepare a basic electrolytic solution. Next, the first additive represented by Formula 1-1 and the third additive represented by Formula 3-1 were added to the basic electrolyte solution to prepare an experimental electrolytic solution. The first additive was added in an amount of 0.2 wt% based on the total weight of the test electrolytic solution, and the third additive was added in an amount of 0.2 wt% based on the total weight of the test electrolytic solution.

Then, the above-described experimental electrolytic solution was injected into the test container, and the opening was sealed to prepare the lithium secondary battery of Example 1. [

Example  2 to 18 and Comparative Example  1 to 10

A lithium secondary battery was produced in the same manner as in Example 1, except that the kind and the amount of the additive in Example 1 were changed as shown in Tables 1 and 2 below.

(evaluation)

Rating 1: SEM  Picture

FIG. 2 is a scanning electron microscope (SEM) photograph showing the state of coating of the surface of LiCoO ₂ particles after storing the lithium secondary battery according to Example 1 and Comparative Example 1 at 60 ° C. for 24 hours.

FIG beam traces, that is, the SEM image portion surrounded by a square in Fig. Comparative Example 1-2 at the time of referring to Figure 2, the case of Comparative Example 1 on the surface of LiCoO ₂ particles SEM image taken was observed. This shows that, on the surface of the LiCoO ₂ particles, a decomposition product of a film derived from hydrofluoroether (HFE), for example, HFE is formed.

Evaluation 2: Cycle life test

Cycle tests were conducted on the lithium secondary batteries according to Examples 1 to 18 and Comparative Examples 1 to 10.

Specifically, the battery was charged at a constant current and a constant voltage at 0.2 mA / cm ² until the battery voltage reached 4.4 V at a temperature of 25 캜 for the first time, and discharge was performed until the battery voltage reached 3.0 V. This charging and discharging was carried out twice.

Then, at a temperature of 45 캜, a constant current and constant voltage charging was carried out at a rate of 2 mA / cm ² until the battery voltage reached 4.4 V, and a charging / discharging cycle of 2 mA / cm ² until the battery voltage reached 3.0 V Was performed 300 times.

Then, the discharge capacity (mAh) in each cycle was measured. The discharge capacity was measured by TOSCAT3000 (Toyo system co., Ltd.).

In the following Tables 3 and 4, the capacity retention rate after 300 cycles when the initial discharge capacity at 45 占 폚 was 100 was shown as a result of the cycle test.

Rating 3: Storage test

Storage tests were conducted on the lithium secondary batteries of Examples 1 to 18 and Comparative Examples 1 to 10.

Specifically, the battery was charged at 0.2 mA / cm ² at a constant current and a constant voltage until the battery voltage reached 4.4 V at a temperature of 25 캜 for the first time, and discharge was performed until the battery voltage reached 3.0 V. This charging and discharging was carried out twice, and the discharge capacity of the second time was set to an initial value of 100.

Subsequently, the battery was charged at a constant current and a constant voltage of 0.2 mA / cm ² at a temperature of 25 캜 until the battery voltage reached 4.4 V, transferred to a constant temperature bath at a temperature of 60 캜, and allowed to stand for 30 days.

Further, after left to stand 12 hours transferred to a constant temperature bath at temperature 25 jonae ℃, the cell voltage was subjected to discharging at a current density of 0.2 mA / cm ² until the 3.0V. The discharge capacity at this time is taken as the remaining capacity and the remaining capacity is set as the capacity ratio before storage in the thermostatic chamber at 60 캜, that is, the initial value 100 of the second discharging capacity at 25 캜, Respectively.

The increase in the volume of the battery before the measurement of the remaining capacity with respect to the volume of the battery before storage in the thermostatic chamber at 60 占 폚 is shown in Tables 3 and 4 as the volume increase rate when the battery volume before storage is 100.

Electrolyte composition Basic electrolyte (solvent) additive LiPF ₆
(mol / L) FEC
(volume%) EMS
(volume%) DMC
(volume%) HFE
(volume%) The first additive
(weight%) Second additive
(weight%) Third additive
(weight%) Fourth additive
(weight%) Other additives
(weight%) Example 1 1.3 15 0 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 2 1.3 12 3 45 40 0.20 (Formula 1-1) 0.20 (Formula 2-1) - - - Example 3 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.40 (Formula 3-1) - - Example 4 1.3 12 3 45 40 0.20 (Formula 1-1) - - 0.20 (Formula 4-1) - Example 5 1.3 12 3 45 40 0.20 (Formula 1-1) 0.20 (Formula 2-1) 0.20 (Formula 3-1) - - Example 6 1.3 12 3 45 40 0.20 (Formula 1-1) - - 0.20 (Formula 4-1) - Example 7 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) 0.20 (Formula 4-1) - Example 8 1.3 12 3 45 40 0.40 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 9 1.3 12 3 45 40 0.80 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 10 1.3 12 3 45 40 1.00 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 11 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) - 1 (SN) Example 12 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) - 1 (SN),
1 (VC) Example 13 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) - 1 (SN),
0.3 (LiFOB) Example 14 1.3 12 3 45 40 0.20 (Formula 1-1) - 0.20 (Formula 3-1) - 1 (SN),
0.5 (LiBOB) Example 15 1.3 12 3 45 40 0.05 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 16 1.3 12 3 45 40 0.10 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 17 1.3 12 3 45 40 0.14 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 18 1.3 12 3 45 40 1.30 (1-1) - 0.20 (Formula 3-1) - -

Electrolyte composition Basic electrolyte (solvent) additive LiPF ₆
(mol / L) FEC
(volume%) EMS
(volume%) DMC
(volume%) HFE
(volume%) The first additive
(weight%) Second additive
(weight%) Third additive
(weight%) Fourth additive
(weight%) Other additives
(weight%) Comparative Example 1 1.3 12 3 45 40 - - - - - Comparative Example 2 1.3 12 3 45 40 - - - - 3 (SN) Comparative Example 3 1.3 12 3 45 40 - - - - 3 (PS) Comparative Example 4 1.3 12 3 45 40 0.20 (Formula 1-1) - - - - Comparative Example 5 1.3 12 3 45 40 - 0.20 (Formula 2-1) - - - Comparative Example 6 1.3 12 3 45 40 - - 0.20 (Formula 3-1) - - Comparative Example 7 1.3 12 3 45 40 - - - 0.20 (Formula 4-1) - Comparative Example 8 1.3 12 3 45 40 - 0.20 (Formula 2-1) 0.20 (Formula 3-1) - - Comparative Example 9 1.3 12 3 45 40 - 0.20 (Formula 2-1) - 0.20 (Formula 4-1) - Comparative Example 10 1.3 12 3 45 40 - - 0.20 (Formula 3-1) 0.20 (Formula 4-1) -

45 ° C cycle test 60 ℃ * 30 days storage test Capacity retention rate
(% @ 300 ^th ) Volume increase rate
∇V (%) Remaining capacity
(%) Example 1 73 10 70 Example 2 78 5 73 Example 3 81 2 81 Example 4 71 5 74 Example 5 77 6 76 Example 6 70 3 76 Example 7 74 3 74 Example 8 83 One 73 Example 9 83 One 80 Example 10 73 5 74 Example 11 78 One 84 Example 12 85 One 80 Example 13 88 One 90 Example 14 89 One 88 Example 15 46 44 43 Example 16 69 16 61 Example 17 70 13 66 Example 18 48 2 69

45 ° C cycle test 60 ℃ * 30 days storage test Capacity retention rate
(% @ 300th) Volume increase rate
∇V (%) Remaining capacity
(%) Comparative Example 1 35 94 10 Comparative Example 2 42 64 15 Comparative Example 3 30 36 33 Comparative Example 4 53 25 51 Comparative Example 5 42 31 40 Comparative Example 6 38 60 41 Comparative Example 7 42 35 45 Comparative Example 8 39 45 48 Comparative Example 9 44 30 42 Comparative Example 10 40 35 39

In Table 1 and Table 2, SN denotes succinonitrile, VC denotes vinylene carbonate, PS denotes 1,3-propane sultone, LiFOB denotes lithium difluoro (oxalate) borate, LiBOB denotes lithium bis (oxalate) borate . The addition amount of the additive represents the weight% with respect to the total weight of the experimental electrolytic solution (basic electrolyte (solvent) + additive). Also, "-" indicates that no additive is added.

Referring to Tables 3 and 4, in the case of Examples 1 to 18 in which at least one of the first additive and the second to fourth additives were added, the capacity retention rate after 300 cycles was increased, and the capacity increase rate of the battery And the remaining capacity after storage is also increased. From this, it can be seen that cycle life characteristics and storage characteristics are greatly improved by adding at least one of the first additive and the second to fourth additives to the basic electrolytic solution.

It can also be seen that as the range of the addition amount of the first additive is narrowed to 0.1 to 1 wt%, 0.2 to 0.8 wt% and 0.4 to 0.8 wt%, the effect of improving cycle life characteristics and storage characteristics is further enhanced .

Example  19

A lithium secondary battery was fabricated in the same manner as in Example 1, except that the composition of the basic electrolyte solution, the kind of the additive to be added to the basic electrolyte solution, and the amount thereof were changed as shown in Table 5 below.

Example  20 to 44 and Comparative Example  11

A lithium secondary battery was produced in the same manner as in Example 19, except that the kind and the amount of the additive in Example 19 were changed as shown in Table 5 below.

(evaluation)

Evaluation 4: Cycle life test

Cycle tests were conducted on the lithium secondary batteries of Examples 19 to 44 and Comparative Example 11.

Specifically, the battery was charged at a constant current and a constant voltage at 0.2 mA / cm ² until the battery voltage reached 4.4 V at a temperature of 25 캜 for the first time, and discharge was performed until the battery voltage reached 3.0 V. This charging and discharging was carried out twice.

Then, at a temperature of 45 캜, a constant current and constant voltage charging was carried out at a rate of 2 mA / cm ² until the battery voltage reached 4.4 V, and a charging / discharging cycle of 2 mA / cm ² until the battery voltage reached 3.0 V Was performed 200 times.

Then, the discharge capacity (mAh) in each cycle was measured. The discharge capacity was measured by TOSCAT3000 (Toyo system co., Ltd.).

In Table 6, the capacity retention ratio after 200 cycles when the initial discharge capacity at 45 占 폚 was 100 was shown as a result of the cycle test.

Rating 5: Storage test

Storage tests were conducted on the lithium secondary batteries of Examples 19 to 44 and Comparative Example 11.

Specifically, the battery was charged at 0.2 mA / cm ² at a constant current and a constant voltage until the battery voltage reached 4.4 V at a temperature of 25 캜 for the first time, and discharge was performed until the battery voltage reached 3.0 V. This charging and discharging was carried out twice, and the discharge capacity of the second time was set to an initial value of 100.

Subsequently, the battery was charged at a constant current and a constant voltage at 0.2 mA / cm ² at a temperature of 25 캜 until the battery voltage reached 4.4 V, transferred to a constant temperature bath at a temperature of 60 캜, and allowed to stand for 15 days.

Further, after left to stand 12 hours transferred to a constant temperature bath at temperature 25 jonae ℃, the cell voltage was subjected to discharging at a current density of 0.2 mA / cm ² until the 3.0V. The discharge capacity at this time is taken as the remaining capacity, and the remaining capacity is shown in Table 6 below as the capacity ratio before storage in a thermostatic chamber at 60 캜, that is, the initial value 100 of the second discharging capacity at 25 캜 .

The increase in the volume of the battery before the measurement of the remaining capacity with respect to the volume of the battery before storage in the thermostatic chamber at 60 占 폚 is shown in Table 6 below as the volume increase rate when the cell volume before storage is 100.

Electrolyte composition Basic electrolyte (solvent) additive LiPF ₆
(mol / L) FEC
(volume%) EMS
(volume%) DMC
(volume%) HFE
(volume%) The first additive
(weight%) Second additive
(weight%) Third additive
(weight%) Fourth additive
(weight%) Other additives
(weight%) Comparative Example 11 1.3 12 3 45 40 0.80 (Formula 1-1) - - - - Example 19 1.3 12 3 45 40 0.80 (Formula 1-1) - 0.20 (Formula 3-1) - - Example 20 1.3 12 3 45 40 0.80 (Formula 1-2) - 0.20 (Formula 3-1) - - Example 21 1.3 12 3 45 40 0.80 (Formula 1-3) - 0.20 (Formula 3-1) - - Example 22 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.20 (Formula 3-1) - - Example 23 1.3 12 3 45 40 0.80 (Formula 1-4) 0.20 (Formula 2-1) - - - Example 24 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.20 (Formula 3-1) - - Example 25 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.20 (Formula 4-2) - Example 26 1.3 12 3 45 40 0.80 (Formula 1-4) 0.05 (Formula 2-1) - - - Example 27 1.3 12 3 45 40 0.80 (Formula 1-4) 0.07 (Formula 2-1) - - - Example 28 1.3 12 3 45 40 0.80 (Formula 1-4) 0.10 (Formula 2-1) - - - Example 29 1.3 12 3 45 40 0.80 (Formula 1-4) 0.38 (Formula 2-1) - - - Example 30 1.3 12 3 45 40 0.80 (Formula 1-4) 0.60 (Formula 2-1) - - - Example 31 1.3 12 3 45 40 0.80 (Formula 1-4) 1.00 (Formula 2-1) - - - Example 32 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.04 (Formula 3-1) - - Example 33 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.07 (Formula 3-1) - - Example 34 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.10 (Formula 3-1) - - Example 35 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.40 (Formula 3-1) - - Example 36 1.3 12 3 45 40 0.80 (Formula 1-4) - 0.60 (Formula 3-1) - - Example 37 1.3 12 3 45 40 0.80 (Formula 1-4) - 1.00 (Formula 3-1) - - Example 38 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.05 (Formula 4-2) - Example 39 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.07 (Formula 4-2) - Example 40 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.10 (Formula 4-2) - Example 41 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.40 (Formula 4-2) - Example 42 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.60 (Formula 4-2) - Example 43 1.3 12 3 45 40 0.80 (Formula 1-4) - - 0.66 (Formula 4-2) - Example 44 1.3 12 3 45 40 0.80 (Formula 1-4) - - 1.00 (Formula 4-2) -

45 ° C cycle test 60 ℃ * 15 days storage test Capacity retention rate
(% @ 200 ^th ) Volume increase rate
∇V (%) Remaining capacity
(%) Comparative Example 11 65 15 60 Example 19 84 3 84 Example 20 82 4 79 Example 21 85 2 72 Example 22 86 2 88 Example 23 77 2 78 Example 24 85 2 81 Example 25 81 2 79 Example 26 62 12 62 Example 27 70 7 68 Example 28 74 3 77 Example 29 83 2 85 Example 30 73 One 84 Example 31 66 0 75 Example 32 62 9 62 Example 33 68 8 68 Example 34 73 5 68 Example 35 80 2 85 Example 36 73 0 84 Example 37 68 0 72 Example 38 58 16 53 Example 39 63 11 63 Example 40 76 6 74 Example 41 71 2 73 Example 42 69 One 66 Example 43 57 One 41 Example 44 47 One 41

The content in the above Table 5 represents the weight% with respect to the total weight of the test electrolytic solution (basic electrolyte + additive). "-" indicates that no additive is added.

With reference to Table 6, the first additive is improved in the cycle life characteristics and the storage properties in the order of the chemical formulas 1-4, 1-3, 1-1, and 1-2, .

It can also be seen that as the range of the added amount of the second additive is narrowed to 0.07 to 1 wt%, 0.07 to 0.4 wt% and 0.1 to 0.4 wt%, the effect of improving cycle life characteristics and storage characteristics is further enhanced .

It can also be seen that as the range of the amount of the third additive is narrowed from 0.07 to 1% by weight, from 0.07 to 0.6% by weight and from 0.1 to 0.6% by weight, the effect of improving cycle life characteristics and storage properties is further enhanced .

It is also seen that as the range of the amount of the fourth additive is narrowed to 0.1 to 0.6% by weight and 0.1 to 0.4% by weight, the effect of improving cycle life characteristics and storage characteristics is further enhanced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

10 lithium secondary battery
20 anode
21 Home
22 cathode active material layer
30 cathode
31 Home Full
32 Anode active material layer
40 Separator layer

Claims (16)

A cathode comprising a cathode active material; And
A solvent, and an additive,
Wherein the cathode active material comprises a lithium-containing transition metal oxide,
Wherein the solvent comprises hydrofluoroether,
The additive
A first additive represented by Formula 1 below, and
At least one selected from the group consisting of a second additive represented by the following general formula (2), a third additive represented by the following general formula (3) and a fourth additive represented by the following general formula (4)
And a lithium secondary battery.
[Chemical Formula 1]

(In the formula 1,
R ¹ to R ³ are each independently a substituted or unsubstituted C1 to C8 alkyl group, a vinyl group or a C1 to C5 alkyl group, which is unsubstituted or substituted with a vinyl group or a C1 to C5 alkyl group, A C5-C8 cycloalkyl group, a C6-C8 aryl group, or a fluorine atom;
R ⁴ is a C 1 to C 8 alkylene group, a C 2 to C 8 alkynylene group, a C ⁴ to C 8 alkylene group having an ether group, a C 1 to C 8 alkylene group having a plurality of -CF ₂ -bonding groups, or an 'ether group and a sulfide group'Lt; RTI ID = 0.0 &gt; C4-C10 &lt; / RTI &
(2)

(In the formula (2)
R ⁵ is a C 2 to C 6 alkylene group not containing a double bond, a C 2 to C 6 alkylene group having a double bond, a C 2 to C 6 alkenylene group, or a C 6 to C 12 arylene group,
R ⁶ to R ¹¹ are each independently a C 1 to C 6 alkyl group or a C 2 to C 6 alkenyl group)
(3)

(3)
R ¹² and R ¹³ are each independently a hydrogen atom or a C 1 to C 8 alkyl group,
R ¹⁴ is a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group substituted or unsubstituted with a vinyl group;
[Chemical Formula 4]

(In the formula 4,
R ¹⁵ and R ¹⁶ are each independently a hydrogen atom or a C1 to C8 alkyl group,
R ¹⁷ is a C1 to C8 alkyl group, a C2 to C8 alkenyl group, a C2 to C8 alkynyl group, or a C1 to C8 halogenated alkyl group,
n is 1 or 2)
The method of claim 1,
The hydro-fluoro-ether (HFE) is 2,2,2-trifluoroethyl ether (CF ₃ CH ₂ OCH _3), 2,2,2-trifluoro-methyl-ethyl difluoromethyl ether (CF ₃ CH ₂ OCHF ₂ ), 2,2,3,3,3-pentafluoropropyl methyl ether (CF ₃ CF ₂ CH ₂ OCH ₃ ), 2,2,3,3,3-pentafluoropropyl difluoromethyl ether _{(CF 3 CF 2 CH 2 OCHF} 2), 2,2,3,3,3- pentamethyl to a profile -1,1,2,2- tetrahydro-fluoro-trifluoroethyl ether _{(CF 3 CF 2 CH 2 OCF} 2 CF 2 H), 1,1,2,2-tetrafluoroethyl methyl ether (HCF ₂ CF ₂ OCH ₃ ), 1,1,2,2-tetrafluoroethyl ethyl ether (HCF ₂ CF ₂ OCH ₂ CH ₃ ) , 1,1,2,2-tetrafluoroethyl propyl ether (HCF ₂ CF ₂ OC ₃ H ₇ ), 1,1,2,2-tetrafluoroethyl butyl ether (HCF ₂ CF ₂ OC ₄ H ₉ ) , 2,2,3,3-tetrafluoro-ethyl difluoromethyl ether _{(H (CF 2) 2 CH} 2 O (CF 2) H), 1,1,2,2- tetrafluoro-ethyl isobutyl ether (HCF ₂ CF ₂ OCH ₂ CH (CH ₃ ) ₂ ), 1,1,2,2-tetrafluoroethyl iso Pentyl ether (HCF ₂ CF ₂ OCH ₂ C (CH ₃ ) ₃ ), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HCF ₂ CF ₂ OCH ₂ CF ₃ ), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H), hexafluoroisopropyl methyl ether ( (CF ₃ ) ₂ CHOCH ₃ ), 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether ((CF ₃ ) ₂ CHCF ₂ OCH ₃ ) 3,3,3-hexafluoro-methyl ether _{(CF 3 CHFCF 2 OCH 3)} , a 1,1,2,3,3,3- hexafluoro-propyl ether _{(CF 3 CHFCF 2 OCH 2 CH} 3), 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether (CF ₃ CHFCF ₂ CH ₂ OCHF ₂ ), or a combination thereof.
The method of claim 1,
And the content of the hydrofluoroether is 10 to 60% by volume based on the total volume of the solvent.
The method of claim 1,
Wherein the first additive is contained in an amount of 0.01 to 1.5% by weight based on the total weight of the electrolyte solution.
5. The method of claim 4,
Wherein the additive comprises the first additive and the second additive,
And the second additive is contained in an amount of 0.05 to 1.00 wt% based on the total weight of the electrolyte solution.
5. The method of claim 4,
Wherein the additive comprises the first additive and the third additive,
And the third additive is contained in an amount of 0.04 to 1.00 wt% based on the total weight of the electrolyte solution.
5. The method of claim 4,
Wherein the additive comprises the first additive and the fourth additive,
Wherein the fourth additive is contained in an amount of 0.01 to 1.00 wt% based on the total weight of the electrolyte solution.
The method of claim 1,
Wherein the first additive comprises at least one of the disilane compounds represented by the following general formulas 1-1 to 1-9.
[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

[Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

[Chemical Formula 1-8]

[Chemical Formula 1-9]

The method of claim 1,
Wherein the second additive comprises the following formula (2-1), (2-2), or a combination thereof.
[Formula 2-1]

[Formula 2-2]

The method of claim 1,
And the third additive comprises at least one of unsaturated phosphoric acid ester compounds represented by the following general formulas (3-1) to (3-8).
[Formula 3-1]

[Formula 3-2]

[Formula 3-3]

[Chemical Formula 3-4]

[Formula 3-5]

[Chemical Formula 3-6]

[Chemical Formula 3-7]

[Chemical Formula 3-8]

The method of claim 1,
And the fourth additive comprises at least one of unsaturated phosphoric acid ester compounds represented by the following general formulas (4-1) to (4-4).
[Formula 4-1]

[Formula 4-2]

[Formula 4-3]

[Formula 4-4]

The method of claim 1,
Wherein the lithium-containing transition metal oxide is a lithium-cobalt composite oxide.
The method of claim 1,
The lithium secondary battery further includes a negative electrode including a negative electrode active material,
Wherein the negative electrode active material is a carbon-based material, a silicon-based material, a tin-based material, a lithium metal oxide, or a metal lithium, alone or in a mixture of two or more.
The method of claim 1,
Wherein the solvent further comprises fluoroethylene carbonate.
The method of claim 14,
And the content of the fluoroethylene carbonate is 10 to 30% by volume based on the total volume of the solvent.
The method of claim 1,
Wherein the redox potential of the lithium secondary battery is 4.3 V (vs. Li / Li ⁺ ) to 5.0 V.

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