WO2024219896A1 - Non-aqueous electrolyte and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte comprising lithium salt, an organic solvent, and an additive, wherein the additive comprises a cyclic siloxane compound represented by a specific chemical formula.

Description

Non-aqueous electrolyte and lithium secondary battery containing the same

Cross-citation with related applications

This application claims the benefit of priority to Korean Patent Application No. 10-2023-0052976, filed April 21, 2023, the entire contents of which are incorporated herein by reference.

Technical field

The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same.

As personal IT devices and computer networks have developed due to the development of the information society, and as a result, the overall dependence of society on electric energy has increased, there is a demand for technology development to efficiently store and utilize electric energy.

Among the developed technologies, secondary batteries are the most suitable for various applications, and among these secondary batteries, lithium secondary batteries are attracting attention as they can be miniaturized to the point where they can be applied to personal IT devices and have the highest energy density.

Typically, lithium secondary batteries are manufactured by injecting or impregnating a non-aqueous electrolyte into an electrode assembly consisting of a cathode, an anode, and a porous separator.

The positive active materials of these lithium secondary batteries are being considered to include lithium-containing cobalt oxide, LiMnO ₂ with a layered crystal structure, LiMn ₂ O ₄ with a spinel crystal structure, lithium-containing nickel oxide (LiNiO ₂ ), and lithium nickel-cobalt-manganese transition metal oxides.

Meanwhile, carbon-based active materials such as graphite have been used as negative active materials, but recently, silicon-based active materials are also being considered because they have higher capacity than carbon-based active materials. The silicon-based active material has the advantage of having a high capacity, but has the problem of very large volume expansion/contraction during the charge/discharge process. This large volume expansion/contraction greatly reduces the conductivity of the negative electrode, which causes a decrease in life performance. In addition, a solid electrolyte interface layer (hereinafter referred to as SEI film) is formed on the negative electrode surface during initial activation, but silicon-based active materials have a large volume expansion, which causes problems such as SEI film breakage and continuous generation of new negative electrode surfaces. Accordingly, SEI film formation reactions continuously occur, which accelerates electrolyte side reactions, and the thickness of the SEI film increases, which increases resistance.

One object of the present invention is to solve the above problems, and to provide a non-aqueous electrolyte capable of forming an SEI film having excellent resilience and improved durability on a negative electrode, thereby implementing a lithium secondary battery having improved life performance and storage performance.

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent and an additive, wherein the additive comprises a compound represented by the following chemical formula 1.

[Chemical Formula 1]

In the chemical formula 1, R ₁ and R ₂ independently represent F, Br, Cl, I, a nitrile group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, a substituent represented by the following chemical formula 2, or a combination of two or more thereof, at least one of the R ₁ and R ₂ comprises a substituent represented by the following chemical formula 2, and n is an integer of 3 to 8.

[Chemical formula 2]

In the above chemical formula 2, L ₁ is an alkylene group, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof having 1 to 10 carbon atoms, R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

In addition, the present invention provides a lithium secondary battery including a cathode; a cathode opposite to the cathode; a separator interposed between the cathode and the cathode; and the non-aqueous electrolyte described above.

The non-aqueous electrolyte of the present invention is characterized by including a cyclic siloxane compound having a specific structure including an alkoxy group in which at least one F is substituted as an additive. The compound is capable of forming a polymer-type siloxane SEI film upon reduction at an anode, and such a polymer-type siloxane SEI film has a high shear modulus and can contribute to the formation of an SEI film having excellent thermal stability and chemical and electrochemical safety. In addition, the alkoxy group in which at least one F is substituted included in the cyclic siloxane compound enables the formation of an inorganic SEI film such as LiF upon reduction at an anode, thereby improving the durability of the SEI film, and in particular, since the alkoxy group is a good leaving group, it can strongly induce an SEI film formation reaction. Accordingly, a lithium secondary battery including the non-aqueous electrolyte according to the present invention can have improved cycle performance and storage performance, particularly improved cycle performance and storage performance at high temperatures.

The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner.

It should be understood that the terms “comprise,” “include,” or “have,” as used herein, are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

Meanwhile, before explaining the present invention, unless otherwise specifically stated, "*" in the present invention means a connected portion (bonding site) between terminals of identical or different atoms or chemical formulas.

In addition, in the description of "carbon atoms a to b" in the present specification, "a" and "b" mean the number of carbon atoms included in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "an alkyl group having 1 to 5 carbon atoms" means an alkyl group including 1 to ₅ carbon atoms, that is, CH ₃ -, CH ₃ CH ₂ -, CH ₃ CH ₂ CH ₂ -, (CH ₃ ) ₂ CH-, CH ₃ CH ₂ CH ₂ CH ₂ -, (CH ₃ ) 2 CHCH ₂ -, CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ -, (CH ₃ ) ₂ CHCH ₂ CH ₂ -, etc.

Additionally, in the present specification, both the alkyl group and the aryl group may be substituted or unsubstituted. The above "substitution" means, unless otherwise defined, that at least one hydrogen bonded to carbon is replaced with an element other than hydrogen, for example, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkynyl group having 2 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a halogen atom, an aryl group having 2 to 20 carbon atoms, a cycloalkyl ... It means substituted with a heteroaryl group having 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc.

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

Electrolyte of the dagger

The present invention relates to a non-aqueous electrolyte.

Specifically, the non-aqueous electrolyte according to the present invention comprises a lithium salt, an organic solvent and an additive, and is characterized in that the additive comprises a compound represented by the following chemical formula 1.

[Chemical Formula 1]

In the chemical formula 1, R ₁ and R ₂ independently represent F, Br, Cl, I, a nitrile group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, a substituent represented by the following chemical formula 2, or a combination of two or more thereof, at least one of the R ₁ and R ₂ comprises a substituent represented by the following chemical formula 2, and n is an integer of 3 to 8.

[Chemical formula 2]

In the above chemical formula 2, L ₁ is an alkylene group, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof having 1 to 10 carbon atoms, R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

(1) Lithium salt

As the lithium salt used in the present invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. _{For example} ^, _{the lithium} ^salt _{contains Li} ^{+ as} a cation and _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- ^, _C It may include at least one selected from the group consisting of ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CH ₃ SO ₃ ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Specifically, the lithium salt may include at least one selected from the group consisting of LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiBOB (LiB(C ₂ O ₄ ) ₂ ), LiCF ₃ SO ₃ , LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF ₄ , LiClO ₄ , LiPF ₆ , LiBOB (LiB(C ₂ O ₄ ) ₂ ), LiCF ₃ SO ₃ , LiTFSI (LiN(SO ₂ CF ₃ ) ₂ ), LiFSI ((LiN(SO ₂ F) ₂ ) and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ).

The above lithium salt may be included in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, specifically at a concentration of 0.8 M to 4 M, and more specifically at a concentration of 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li ⁺ transference number) and the degree of dissociation of lithium ions may be improved, thereby improving the output characteristics of the battery.

(2) Organic solvent

The above organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as decomposition due to oxidation reactions, etc. during the charge/discharge process of the secondary battery can be minimized.

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

Specifically, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixture thereof.

The above cyclic carbonate-based organic solvent is a high-viscosity organic solvent having a high dielectric constant and capable of dissociating a lithium salt in the electrolyte well, and specifically, may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, more specifically, may include at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC), and even more specifically, may include fluoroethylene carbonate (FEC) in terms of contributing to the formation of an inorganic (LiF)-containing SEI film.

In addition, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specifically may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically may include at least one selected from the group consisting of ethylmethyl carbonate (EMC) and diethyl carbonate (DEC), and more specifically may include diethyl carbonate (DEC) in that it can further improve the oxidation stability of the non-aqueous electrolyte.

The above organic solvent may be a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. At this time, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed in a volume ratio of 5:95 to 40:60, specifically, a volume ratio of 7:93 to 25:75. When the mixing ratio of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent satisfies the above range, high dielectric constant and low viscosity characteristics can be simultaneously satisfied, and excellent ion conductivity characteristics can be implemented.

In addition, the organic solvent may further include at least one carbonate organic solvent selected from the group consisting of the cyclic carbonate organic solvent and the linear carbonate organic solvent, and at least one ester organic solvent selected from the group consisting of the linear ester organic solvent and the cyclic ester organic solvent, in order to produce an electrolyte having high ionic conductivity.

The above linear ester organic solvent may specifically include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

In addition, the cyclic ester organic solvent may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

Meanwhile, the organic solvent may be used without limitation by adding an organic solvent commonly used in a non-aqueous electrolyte as needed. For example, at least one organic solvent from among an ether-based organic solvent, a glyme-based solvent, and a nitrile-based organic solvent may be additionally included.

As the above ether solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL) or a mixture of two or more thereof may be used, but is not limited thereto.

The above-mentioned glyme solvent has a high dielectric constant and low surface tension compared to linear carbonate-based organic solvents, and is a solvent with low reactivity with metals, and may include at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, tri-glyme, and tetra-glyme (TEGDME), but is not limited thereto.

The above nitrile solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

(3) Additives

The above non-aqueous electrolyte contains an additive.

The above additive comprises a compound represented by the following chemical formula 1.

[Chemical Formula 1]

In the chemical formula 1, R ₁ and R ₂ independently represent F, Br, Cl, I, a nitrile group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, a substituent represented by the following chemical formula 2, or a combination of two or more thereof, at least one of the R ₁ and R ₂ comprises a substituent represented by the following chemical formula 2, and n is an integer of 3 to 8.

[Chemical formula 2]

In the above chemical formula 2, L ₁ is an alkylene group, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof having 1 to 10 carbon atoms, R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

The compound represented by the above chemical formula 1 is characterized in that R ₁ and/or R ₂ substituted on Si is an alkoxy group having 1 to 10 carbon atoms substituted with at least one F, specifically a cyclic siloxane compound including a substituent represented by the above chemical formula 2.

When the compound represented by the above chemical formula 1 is used as a non-aqueous electrolyte additive, the cyclic siloxane structure is opened upon reduction at the cathode to form a polymer-type siloxane SEI film. This polymer-type siloxane SEI film not only has excellent flexibility and resilience, but also has a high shear modulus and excellent thermal stability, chemical stability, and electrochemical stability.

In addition, the compound represented by the chemical formula 1 includes a substituent represented by the chemical formula 2, and the substituent is reduced at the cathode to form an inorganic SEI film containing an inorganic substance such as LiF. This inorganic SEI film can significantly improve the durability of the SEI film. In particular, since the compound of the chemical formula 1 according to the present invention forms the above-described polymer type/inorganic composite SEI film, the durability, flexibility, and stability of the SEI film can be improved simultaneously.

In addition, the substituent (R ₁ and/or R ₂ ) included in the compound represented by the above chemical formula 1 is characterized by including a fluorine-substituted alkoxy group, specifically a substituent represented by the above chemical formula 2, and the fluorine-substituted alkoxy group is a rather weak electron withdrawn group and functions as a good leaving group. This can induce and promote the formation of an inorganic SEI film such as LiF.

According to the effects described above, the non-aqueous electrolyte according to the present invention enables improvement of the life performance and storage performance of a lithium secondary battery, particularly improvement of the life performance and storage performance at high temperatures. In particular, the compound represented by the chemical formula 1 can be more preferably applied to an anode using a silicon-based active material. Since Li of lithiated Si formed by activation of an anode including a silicon-based active material and F derived from the compound represented by the chemical formula 1 can have a strong interaction with each other (Glue effect), it can be more advantageous in forming a durable and resilient SEI film on a silicon-based active material which is extremely subject to volume expansion during charge and discharge.

In the chemical formula 1, R ₁ and R ₂ may independently include F, Br, Cl, I, a nitrile group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, a substituent represented by the following chemical formula 2, or a combination of two or more thereof. At this time, at least one of the R ₁ and R ₂ includes a substituent represented by the following chemical formula 2.

[Chemical formula 2]

In the above chemical formula 2, L ₁ is an alkylene group, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof having 1 to 10 carbon atoms, R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

Specifically, in terms of preventing a decrease in reactivity due to steric hindrance, either one of R ₁ and R ₂ may include a substituent represented by the chemical formula 2. For example, in the chemical formula 1, R ₁ It includes a substituent represented by the above chemical formula 2, and the above R ₂ may not include a substituent represented by the above chemical formula 2. Specifically, in the chemical formula 1, the above R ₁ When including a substituent represented by the above chemical formula 2, R ₂ may be an alkyl group having 1 to 5 carbon atoms, more specifically an ethyl group or a methyl group, and even more specifically a methyl group.

In the above chemical formula 2, L ₁ is an alkylene group, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof having 1 to 10 carbon atoms, R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

In the above chemical formula 2, L ₁ can be specifically an alkylene group having 1 to 10 carbon atoms, a sulfone group or a combination thereof, more specifically an alkylene group having 1 to 5 carbon atoms, and even more specifically a methylene group or an ethylene group in terms of easily accepting electrons during cathodic reduction, thereby further improving the reducing property, and even more specifically an ethylene group.

In the above chemical formula 2, R ₃ may be an alkoxy group having 1 to 10 carbon atoms substituted with at least one F, specifically an alkoxy group having 1 to 5 carbon atoms substituted with at least one F, more specifically one selected from the group consisting of -OCF ₃ , -OCF ₂ CF ₃ and -OCF ₂ CF ₂ CF ₃ , and even more specifically -OCF ₃ in terms of preventing a decrease in reactivity due to steric hindrance.

In the above chemical formula 1, n may be an integer of 3 to 8, specifically 3 or 4, and more specifically 3. When n is 3 to 8, R ₁ and/or R ₂ in each repeating unit may be the same or different.

Specifically, the compound represented by the chemical formula 1 may include at least one compound selected from the group consisting of chemical formulas 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, and 1-12, more specifically, may include at least one compound selected from the group consisting of chemical formulas 1-1, 1-3, 1-9, and 1-10, and even more specifically, may include at least one compound selected from the group consisting of chemical formulas 1-1 and 1-3, and even more specifically, may include a compound represented by chemical formula 1-1.

[Chemical Formula 1-1]

[Chemical Formula 1-2]

[Chemical Formula 1-3]

[Chemical Formula 1-4]

[Chemical Formula 1-5]

[Chemical Formula 1-6]

[Chemical Formula 1-7]

[Chemical Formula 1-8]

[Chemical Formula 1-9]

[Chemical Formula 1-10]

[Chemical Formula 1-11]

[Chemical Formula 1-12]

The compound represented by the above chemical formula 1 may be included in an amount of 0.01 wt% to 10 wt%, specifically 0.3 wt% to 7 wt%, more specifically 0.5 wt% to 5 wt%, and even more specifically 1 wt% to 3 wt%, based on the weight of the non-aqueous electrolyte. When the compound represented by the above chemical formula 1 is used in the above-described content range, a flexible and durable SEI film can be formed on the negative electrode, while preventing an increase in resistance when added in excessive amounts.

The above additive may further include an additional additive together with the compound represented by Chemical Formula 1. The above additional additive may be included in the non-aqueous electrolyte to prevent decomposition of the non-aqueous electrolyte in a high-power environment, causing cathode collapse, or to provide low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery expansion at high temperatures.

Specifically, the additional additive may include at least one selected from the group consisting of lithium difluorophosphate (LiDFP), vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, lithium bis-(oxalato)borate (LiBOB), 3-trimethoxysilanyl-propyl-N-aniline (TMSPa), and tris(trimethylsilyl) phosphate (TMSPi), and specifically, lithium difluorophosphate (LiDFP).

The above additional additive may be included in the non-aqueous electrolyte in an amount of 0.1 wt% to 15 wt%, more specifically 0.3 wt% to 3 wt%.

When the non-aqueous electrolyte further includes the additional additive, the weight ratio of the compound represented by the chemical formula 1 and the additional additive may be 45:55 to 99:1, specifically 50:50 to 95:5, and more specifically 70:30 to 85:15, and when within the above range, the life performance and high-temperature storage performance may be improved to a more desirable level.

Lithium secondary battery

In addition, the present invention provides a lithium secondary battery including the above-described non-aqueous electrolyte.

Specifically, a lithium secondary battery according to the present invention includes a negative electrode; a positive electrode opposite to the negative electrode; a separator interposed between the negative electrode and the positive electrode; and the non-aqueous electrolyte described above.

The above lithium secondary battery can be manufactured by housing an electrode assembly including the negative electrode; a positive electrode opposing the negative electrode; and a separator interposed between the negative electrode and the positive electrode in a battery case, and then injecting the above-described non-aqueous electrolyte.

Since the description of the non-aqueous electrolyte has been provided above, the cathode, anode, and separator will be described below.

(1) Cathode

The above negative electrode includes a negative electrode active material.

The above negative active material may be any material used as a negative active material in the relevant field without limitation. The above negative active material may specifically include at least one selected from a silicon-based active material and a carbon-based active material, and more specifically may include a silicon-based active material.

The above silicon-based active material exhibits higher capacity than the carbon-based active material, but has a problem in that the degree of volume expansion/contraction due to charge/discharge is large. However, when the above silicon-based active material and the above-mentioned non-aqueous electrolyte are used together, a flexible, resilient, and durable SEI film can be formed on the negative electrode, thereby preventing electrolyte side reactions and enabling the implementation of a lithium secondary battery having high life performance and storage performance.

The above silicon-based active material may include a compound represented by the following chemical formula A.

[Chemical Formula A]

SiO _x (0 ≤ x < 2)

In the above chemical formula A, since SiO ₂ does not react with lithium ions and thus cannot store lithium, it is preferable that x is within the above range. More specifically, the silicon-based active material may be Si.

The average particle diameter (D ₅₀ ) of the above silicon-based active material may be 1 μm to 20 μm.

The above carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include graphite. The graphite may include at least one selected from the group consisting of artificial graphite and natural graphite.

The average particle diameter (D ₅₀ ) of the above carbon-based active material may be 10 ㎛ to 30 ㎛, preferably 15 ㎛ to 25 ㎛, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

The above negative electrode may include a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be included in the negative electrode active material layer.

The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc.

The above negative electrode collector may typically have a thickness of 3 to 500 μm.

The above negative electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the above negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector.

The above negative active material may be included in the negative active material layer at 60 wt% to 99 wt% in order to sufficiently express the capacity in the secondary battery while minimizing the effect of volume expansion/contraction on the battery.

The above negative active material layer may further include a conductive material and/or a binder together with the silicon-based active material.

The above binder can be used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector described later, or to improve the bonding strength between silicon-based active materials.

Specifically, the binder comprises at least one selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluoro rubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM), in that it can further improve electrode adhesion and provide sufficient resistance to volume expansion/contraction of the silicon-based active material. Can be.

The above binder may be included in the negative electrode active material layer at 1 wt% to 30 wt%, and when present in the above range, the negative electrode active material may be better bound, thereby minimizing the problem of volume expansion of the active material, while at the same time facilitating dispersion of the binder during the preparation of a slurry for forming the negative electrode active material layer, thereby improving the coatability and phase stability of the slurry.

The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing a chemical change. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

The above-mentioned conductive agent may be included in the negative electrode active material layer at 1 wt% to 20 wt%, and when within the above range, it is preferable in that it can form an excellent conductive network while alleviating the increase in resistance due to the binder.

The thickness of the above negative active material layer may be 5 ㎛ to 500 ㎛, preferably 5 ㎛ to 100 ㎛.

The above negative electrode can be manufactured by coating a negative electrode slurry including a negative electrode active material and optionally a binder, a conductive material, and a solvent for forming a negative electrode slurry on the negative electrode current collector, and then drying and rolling.

The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder and/or conductive agent.

(2) Bipolar

The above positive electrode contains a positive electrode active material.

The above positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium-transition metal composite oxide including lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum, preferably a lithium-transition metal composite oxide including lithium and a transition metal selected from nickel, cobalt, and manganese.

For example, the lithium transition metal composite oxides include lithium-manganese oxides (e.g., LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt oxides (e.g., LiCoO ₂ , etc.), lithium-nickel oxides (e.g., LiNiO ₂ , etc.), lithium-nickel-manganese oxides (e.g., LiNi _1-Y Mn _Y O ₂ (wherein, 0<Y<1), LiMn _2-z Ni _z O ₄ (wherein, 0<Z<2)), lithium-nickel-cobalt oxides (e.g., LiNi _1-Y1 Co _Y1 O ₂ (wherein, 0<Y1<1)), lithium-manganese-cobalt oxides (e.g., LiCo _1-Y2 Mn _Y2 O ₂ (wherein, 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (wherein, (0＜Z1＜2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni _p Co _q Mn _r1 )O ₂ (wherein, 0＜p＜1, 0＜q＜1, 0＜r1＜1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (wherein, 0＜p1＜2, 0＜q1＜2, 0＜r2＜2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, 0＜p2＜1, 0＜q2＜1, 0＜r3＜1, 0＜s2＜1, p2+q2+r3+s2=1), etc.), and one or more compounds among these may be included. Among these, the lithium transition metal composite oxide may be LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel-manganese-cobalt oxide (for example, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , or lithium nickel cobalt aluminum oxide (for example, Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc.), and considering the prominence of the improvement effect according to the control of the type and content ratio of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide may be The oxide may be _Li ( _{Ni0.6Mn0.2Co0.2 ) O2 , Li(Ni0.5Mn0.3Co0.2)O2, Li(Ni0.7Mn0.15Co0.15)O2 or Li(Ni0.8Mn0.1Co0.1 ) O2 , and any one of these or} a mixture _of two or more thereof may be _used .

More specifically, the cathode active material may be a lithium-transition metal composite oxide, and may contain nickel in an amount of 60 mol% or more based on the total mole number of transition metals included in the lithium-transition metal composite oxide. Specifically, the cathode active material may be a lithium-transition metal composite oxide, wherein the transition metal includes nickel; and at least one selected from manganese, cobalt, and aluminum, and may contain nickel in an amount of 60 mol% or more, specifically 60 to 90 mol%, based on the total mole number of transition metals. When such a lithium-transition metal composite oxide using a high nickel content is used together with the above-described non-aqueous electrolyte, it is preferable in that by-products in a gas phase generated by structural collapse can be reduced.

In addition, the positive electrode active material may include a lithium composite transition metal oxide represented by the following chemical formula B.

[Chemical Formula B]

Li _1+x (Ni _a Co _b Mn _c M _d )O ₂

In the chemical formula B, M is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+x, a, b, c, and d are atomic fractions of independent elements, respectively, 0≤x≤0.2, 0.50≤a<1, 0<b≤0.25, 0<c≤0.25, 0≤d≤0.1, a+b+c+d=1.

Preferably, a, b, c and d may be 0.70≤a≤0.95, 0.025≤b≤0.20, 0.025≤c≤0.20, 0≤d≤0.05, respectively.

Additionally, a, b, c, and d may be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15, and 0≤d≤0.05, respectively.

Additionally, a, b, c, and d may be 0.85≤a≤0.90, 0.05≤b≤0.10, 0.05≤c≤0.10, and 0≤d≤0.03, respectively.

The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material layer may include the above-described positive electrode active material.

The thickness of the above positive electrode collector can typically be 3 to 500 μm.

The above-mentioned positive electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the above-mentioned positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one surface or both surfaces of the positive electrode current collector.

The above cathode active material may be included in the cathode active material layer at 80 to 99 wt%, taking into account sufficient capacity of the cathode active material.

The above-described positive electrode active material layer may further include a binder and/or a conductive material together with the above-described positive electrode active material.

The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

The above binder may be included in the positive electrode active material layer at 1 to 20 wt%, preferably 1.2 to 10 wt%, in order to sufficiently secure binding force between components such as the positive electrode active material.

The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing a chemical change. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably, the positive electrode conductive material may include carbon nanotubes in terms of improving conductivity.

The above-mentioned conductive material may be included in the positive electrode active material layer at 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in order to sufficiently secure electrical conductivity.

The thickness of the above positive electrode active material layer may be 5 µm to 500 µm, preferably 20 µm to 200 µm.

The above positive electrode can be manufactured by coating a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming a positive electrode slurry on the positive electrode current collector, and then drying and rolling.

(3) Membrane

The above separator may be interposed between the anode and the cathode.

As the above-mentioned separator, a conventional porous polymer film used as a conventional separator, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, can be used alone or in a laminated manner, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can be used, but is not limited thereto. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be in the shape of a cylinder, a square, a pouch, or a coin using a can.

Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are merely examples to help understand the present invention and do not limit the scope of the present invention. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present description, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

Examples and Comparative Examples

Example 1

(Manufacture of non-aqueous electrolyte)

A mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90 was used as an organic solvent.

A non-aqueous electrolyte was prepared by adding LiPF ₆ as a lithium salt, a compound represented by the chemical formula 1-1 as an additive, and lithium difluorophosphate (LiDFP) to the organic solvent.

The above LiPF ₆ was included in the non-aqueous electrolyte at a molar concentration of 1.5 M.

The compound represented by the following chemical formula 1-1 was included in the non-aqueous electrolyte at 2 wt%, and lithium difluorophosphate was included in the non-aqueous electrolyte at 0.5 wt%.

(Lithium secondary battery manufacturing)

A positive electrode mixture slurry (solid content 75.5 wt%) was prepared by adding positive electrode active material (Li[Ni _0.85 Co _{0.05 Mn 0.07 Al 0.03} ]O ₂ ): conductive material (carbon nanotube): binder (polyvinylidene fluoride) in a weight ratio of 97.74:0.70:1.56 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was applied to one surface of a positive electrode current collector (Al thin film) having a thickness of 12 ㎛, and drying and roll pressing were performed to prepare a positive electrode.

A negative electrode mixture slurry (solid content 26 wt%) was prepared by adding negative active material (silicon-based active material, Si): conductive agent (carbon black): binder (styrene-stadiene rubber) to distilled water as a solvent in a weight ratio of 70.0:20.3:9.7. The negative electrode mixture slurry was applied to one surface of a 15 ㎛ thick negative electrode current collector (Cu thin film), and drying and roll pressing were performed to prepare a negative electrode.

A polyethylene porous film separator was interposed between the positive and negative electrodes manufactured above in a dry room, and then the non-aqueous electrolyte manufactured above was injected to manufacture a secondary battery.

Example 2

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by the chemical formula 1-1 was added to the non-aqueous electrolyte in an amount of 0.5 wt% instead of 2 wt%.

Example 3

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by the chemical formula 1-1 was added to the non-aqueous electrolyte in an amount of 5 wt% instead of 2 wt%.

Example 4

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the chemical formula 1-9 was added to the non-aqueous electrolyte in an amount of 2 wt% instead of the compound represented by the chemical formula 1-1.

Comparative Example 1

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the compound represented by the chemical formula 1-1 was not added.

Comparative Example 2

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the chemical formula X was added to the non-aqueous electrolyte in an amount of 2 wt% instead of the compound represented by the chemical formula 1-1.

[chemical formula X]

Comparative Example 3

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the chemical formula Y was added to the non-aqueous electrolyte in an amount of 2 wt% instead of the compound represented by the chemical formula 1-1.

[chemical formula Y]

Comparative Example 4

A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a compound represented by the chemical formula Z was added to the non-aqueous electrolyte in an amount of 2 wt% instead of the compound represented by the chemical formula 1-1.

[chemical formula Z]

Experimental example

Experimental Example 1: Evaluation of High Temperature Cycle Performance

The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 4 above were charged to 4.2 V, 0.05 C using an electrochemical charger/discharger under CC/CV, 1 C conditions at 45°C, and then discharged to 3.0 V under CC, 0.5 C conditions, which constituted one cycle, and 200 charge/discharge cycles were performed.

The capacity retention rate is calculated using the formula below, and the results are shown in Table 1 below.

Capacity retention rate (%) = {(discharge capacity after 200 cycles/discharge capacity after 1 cycle)} × 100

Experimental Example 2: Evaluation of High Temperature Storage Performance

The lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 4 above were charged to 4.2 V, 0.05 C under CC/CV, 0.33 C conditions at 25°C and discharged to 2.5 V at 0.33 C to perform initial charge/discharge, and then charged to 4.2 V, 0.05 C under CC/CV, 0.33 C conditions at 25°C and stored at 60°C for 8 weeks.

After 8 weeks of storage, the lithium secondary battery was charged to 4.2 V, 0.05 C at 25°C under 0.33 C conditions and discharged to 3.0 V at 0.33 C to measure the capacity during discharge.

The capacity retention rate was evaluated according to the following formula, and the results are shown in Table 1 below.

Capacity retention rate (%) = (discharge capacity after 8 weeks of storage/initial discharge capacity) × 100

Referring to Table 1 above, it can be confirmed that the lithium secondary batteries of Examples 1 to 4 using the non-aqueous electrolyte according to the present invention exhibit significantly superior capacity retention rates during high-temperature cycle charge/discharge and high-temperature storage compared to Comparative Examples 1 to 4 that do not use the non-aqueous electrolyte.

Claims (12)

1. Containing lithium salt, organic solvent and additives,

   The above additive is a non-aqueous electrolyte comprising a compound represented by the following chemical formula 1:

   [Chemical Formula 1]

   

   In the chemical formula 1, R ₁ and R ₂ independently comprise F, Br, Cl, I, a nitrile group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, a substituent represented by the following chemical formula 2, or a combination of two or more thereof,

   At least one of the above R ₁ and R ₂ comprises a substituent represented by the following chemical formula 2,

   n is an integer from 3 to 8,

   [Chemical formula 2]

   

   In the above chemical formula 2, L ₁ is an alkylene group having 1 to 10 carbon atoms, an ester group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof,

   R ₃ is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine,

   * is the binding site.
2. In claim 1,

   A non-aqueous electrolyte in the above chemical formula 1, wherein n is 3 or 4.
3. In claim 1,

   A non-aqueous electrolyte wherein the above R ₃ comprises one selected from the group consisting of -OCF ₃ , -OCF ₂ CF _{3 ,} and -OCF ₂ CF ₂ CF ₃ .
4. In claim 1,

   The above R ₁ A non-aqueous electrolyte comprising a substituent represented by the above chemical formula 2, wherein R ₂ does not comprise a substituent represented by the above chemical formula 2.
5. In claim 4,

   A non-aqueous electrolyte wherein R ₂ is an alkyl group having 1 to 5 carbon atoms.
6. In claim 1,

   The compound represented by the above chemical formula 1 is a non-aqueous electrolyte including at least one compound selected from the group consisting of the following chemical formulas 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11 and 1-12:

   [Chemical Formula 1-1]

   

   [Chemical Formula 1-2]

   

   [Chemical Formula 1-3]

   

   [Chemical Formula 1-4]

   

   [Chemical Formula 1-5]

   

   [Chemical Formula 1-6]

   

   [Chemical Formula 1-7]

   

   [Chemical Formula 1-8]

   

   [Chemical Formula 1-9]

   

   [Chemical Formula 1-10]

   

   [Chemical Formula 1-11]

   

   [Chemical Formula 1-12]

   

   .
7. In claim 1,

   A non-aqueous electrolyte in which the compound represented by the chemical formula 1 is contained in an amount of 0.01 wt% to 10 wt% based on the weight of the non-aqueous electrolyte.
8. In claim 1,

   A non-aqueous electrolyte comprising at least one lithium salt selected from the group consisting of LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiBOB (LiB(C ₂ O ₄ ) ₂ ), LiCF ₃ SO ₃ , LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ ).
9. In claim 1,

   A non-aqueous electrolyte wherein the lithium salt is contained in the non-aqueous electrolyte at a molar concentration of 0.5 M to 5.0 M.
10. In claim 1,

    A non-aqueous electrolyte wherein the organic solvent comprises at least one selected from the group consisting of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.
11. cathode;

    An anode opposite to the cathode;

    A separator interposed between the cathode and the anode; and

    A lithium secondary battery comprising a non-aqueous electrolyte according to claim 1.
12. In claim 11,

    The above negative electrode contains a negative electrode active material,

    A lithium secondary battery wherein the negative active material includes a silicon-based active material.