Nonaqueous electrolyte and lithium secondary battery comprising same

Abstract

The present invention relates to a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and additives comprising a first additive and a second additive. The first additive and the second additive each include a compound represented by a specific chemical formula.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of, and priority to, Korean Patent Application No. 10-2023-0046365, filed on April 7, 2023, and Korean Patent Application No. 10-2023-0183781, filed on December 15, 2023, the disclosures of which are hereby incorporated by reference in their entirety. Technical Field

[0003] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the non-aqueous electrolyte. Background Art

[0004] With the progress of personal IT devices and computer networks brought about by the development of the information society, the entire society's dependence on electric energy has increased, and technologies for efficiently storing and utilizing electric energy need to be developed.

[0005] Among the developed technologies related to electric energy, secondary batteries (also known as rechargeable batteries) are one of the most suitable technologies for various applications. Among secondary batteries, the interest in lithium secondary batteries is increasing because lithium secondary batteries have a relatively high energy density and can be miniaturized, and thus can be applied to personal IT devices.

[0006] Generally, a lithium secondary battery is manufactured by injecting or impregnating a non-aqueous electrolyte into an electrode assembly including a positive electrode, a negative electrode, and a porous separator.

[0007] As the positive electrode active material of these lithium secondary batteries, lithium-containing cobalt oxides, LiMnO₂ having a layered crystal structure, LiMn₂O₄ having a spinel crystal structure, lithium-containing nickel oxides (LiNiO₂), and lithium nickel cobalt manganese transition metal oxides are considered.

[0008] Meanwhile, carbon-based active materials such as graphite have been used as the negative electrode active material, but recently silicon-based active materials have also been considered because silicon-based active materials have a higher capacity than carbon-based active materials. Summary of the Invention

[0009] [Technical Problem]

[0010] The present invention provides a non-aqueous electrolyte capable of realizing a lithium secondary battery having improved life performance and storage performance by forming a solid electrolyte interphase (SEI) film with excellent recovery performance and improved durability on the negative electrode.

[0011] [Technical Solution]

[0012] The present invention provides a non-aqueous electrolyte, which comprises a lithium salt, an organic solvent and an additive. The additive includes a first additive and a second additive. Among them, the first additive includes a compound represented by Formula 1 below, and the second additive includes a compound represented by Formula 2 below.

[0013] [Formula 1]

[0014]

[0015] Among them, R1 includes halogen, cyano, propargyl, ester group, ether group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxanyl group, sulfone group, sulfonate group, sulfate group, or a combination of two or more of them. Among them, n is an integer from 0 to 6.

[0016] [Formula 2]

[0017]

[0018] Among them, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3. Among them, m is an integer from 3 to 10.

[0019] [Formula 3]

[0020]

[0021] Among them, L1 is a direct bond, 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 of them. R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a bonding site.

[0022] In addition, the present invention provides a lithium secondary battery, which comprises a negative electrode; a positive electrode opposite to the negative electrode; a separator disposed between the negative electrode and the positive electrode; and the above non-aqueous electrolyte.

[0023] [Beneficial effects]

[0024] The non-aqueous electrolyte of the present invention is characterized in that it includes a first additive containing a coumarin compound of formula 1 and a second additive containing a cyclic siloxane compound of formula 2 as additives. The first additive has strong reducibility at the negative electrode, thus causing a rapid ring-opening reaction during the formation of the initial SEI film, so that a polymer-type SEI film can be formed, and an SEI film with excellent flexibility and recovery performance can be formed. In addition, the second additive can form a siloxane-type SEI film during the reduction process of the negative electrode, which can contribute to the formation of an SEI film with a high shear modulus, excellent thermal stability, and chemical and electrochemical stability. For example, the free radicals formed when the first additive decomposes promote the ring-opening reaction of the second additive, so that an SEI film with excellent flexibility, recovery, and high durability can be formed on the negative electrode through the organic action of the first additive and the second additive. Therefore, a lithium secondary battery containing the non-aqueous electrolyte of the present invention can improve the life performance and storage performance, especially the life performance and storage performance at high temperatures. Detailed Description

[0025] It should be understood that the terms or words used in the specification and claims should not be construed as limited to their conventional meanings and dictionary meanings, but should be interpreted as meanings and concepts corresponding to the technical idea of the present invention based on the principle that allows the inventor to define the terms in order to best explain his invention.

[0026] In the description herein, terms such as "comprising", "providing", and "having" are intended to indicate the presence of the features, numbers, steps, components, or combinations thereof described herein, but should not be construed as excluding the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0027] Meanwhile, unless otherwise specified in the present invention, "*" represents a connecting portion (bonding site) between the ends of the same or different atoms or formulas.

[0028] In addition, in the description of "a to b carbons" in the present invention, "a" and "b" represent the number of carbon atoms contained in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, the term "alkyl having 1 to 5 carbon atoms" means an alkyl having 1 to 5 carbon atoms, such as, for example, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, or (CH3)2CHCH2CH2-.

[0029] In addition, in the description of the present invention, both alkyl and aryl may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted by an element other than a hydrogen atom, for example, substituted by: 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 heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0030] As used herein, considering the inherent manufacturing and material tolerances, "about", "approximately", and "substantially" are used to indicate a numerical range or its degree or approximation, to prevent an infringer from unfairly using the exact numbers or absolute numbers provided to assist in understanding the present invention.

[0031] The advantage of using a silicon-based active material as the negative electrode active material of a lithium secondary battery is its high capacity, but the disadvantage is that the volume expansion / contraction during charge and discharge is relatively large. A relatively large degree of volume expansion / contraction will reduce the conductivity of the negative electrode, resulting in a decline in the life performance of the negative electrode and the lithium secondary battery. In addition, during the initial activation process of the lithium secondary battery, a solid electrolyte interface layer (SEI layer) will form on the surface of the negative electrode. The silicon-based active material has a large volume expansion, which will cause the SEI layer to rupture or continuously form a new negative electrode surface. Therefore, as the SEI film formation reaction continues, the electrolyte side reaction also accelerates, the SEI film thickness becomes thicker, resulting in an increase in resistance.

[0032] The non-aqueous electrolyte of the present invention contains a first additive and a second additive represented by a specific chemical formula in addition to a lithium salt and an organic solvent, thereby providing a lithium secondary battery that overcomes these disadvantages.

[0033] Hereinafter, the present invention will be described in more detail.

[0034] Non - aqueous electrolyte

[0035] The present invention provides a non-aqueous electrolyte.

[0036] For example, the non-aqueous electrolyte of the present invention contains a lithium salt, an organic solvent, and an additive. The additive includes a first additive and a second additive. The first additive includes a compound represented by Formula 1 below, and the second additive includes a compound represented by Formula 2 below.

[0037] [Formula 1]

[0038]

[0039] Wherein, R1 includes halogen, cyano, propargyl, ester group, ether group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxanyl group, sulfone group, sulfonate group, sulfate group, or a combination of two or more thereof, wherein, n is an integer from 0 to 6,

[0040] [Formula 2]

[0041]

[0042] Wherein, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3, wherein m is an integer from 3 to 10,

[0043] [Formula 3]

[0044]

[0045] Wherein, L1 is a direct bond, 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, R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

[0046] (1) Lithium salt

[0047] As the lithium salt used herein, various lithium salts commonly used in non-aqueous electrolytes of lithium secondary batteries can be used without limitation. For example, the lithium salt may include Li + as a cation, and include at least one selected from the group consisting of: F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 -, B 10 Cl 10 - , BF₂C₂O₄ - , BC₄O₈ - , PF₄C₂O₄ - , PF₂C₄O₈ - , (CF₃)₂PF₄ - , (CF₃)₃PF₃ - , (CF₃)₄PF₂ - , (CF₃)₅PF - , (CF₃)₆P - , CF₃SO₃ - , C₄F₉SO₃ - , CF₃CF₂SO₃ - , (FSO₂)₂N - , CF₃CF₂(CF₃)₂CO - , (CF₃SO₂)₂CH - , CH₃SO₃ - , CF₃(CF₂)₇SO₃ - , CF₃CO₂ - , CH₃CO₂ - , SCN - and (CF₃CF₂SO₂)₂N - .

[0048] For example, the lithium salt may include at least one selected from the group consisting of: LiCl, LiBr, LiI, LiBF₄, LiClO₄, LiAlO₄, LiAlCl₄, LiPF₆, LiSbF₆, LiAsF₆, LiB 10 Cl 10 , LiBOB (LiB(C₂O₄)₂), LiCF₃SO₃, LiFSI (LiN(SO₂F)₂), LiCH₃SO₃, LiCF₃CO₂, LiCH₃CO₂, and LiBETI (LiN(SO₂CF₂CF₃)₂). For example, the lithium salt may include at least one selected from the group consisting of: LiBF₄, LiClO₄, LiPF₆, LiBOB (LiB(C₂O₄)₂), LiCF₃SO₃, LiTFSI (LiN(SO₂CF₃)₂), LiFSI ((LiN(SO₂F)₂), and LiBETI (LiN(SO₂CF₂CF₃)₂).

[0049] The concentration of the lithium salt in the non-aqueous electrolyte may be about 0.5 M to 5 M, for example about 0.8 M to 4 M, or about 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li +The transference number) and the degree of lithium ion dissociation are improved, thereby improving the output characteristics of the battery.

[0050] (2) Organic solvent

[0051] The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries and is not particularly limited as long as it can minimize the decomposition caused by the oxidation reaction during the charge and discharge process of the secondary battery.

[0052] Examples of the organic solvent may include at least one selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0053] Alternatively, examples of the organic solvent may include cyclic carbonate organic solvents, linear carbonate organic solvents, or a mixture thereof.

[0054] The cyclic carbonate organic solvent is an organic solvent with high viscosity. Due to its relatively high dielectric constant, it can easily dissociate the lithium salt in the electrolyte. Specific examples of the cyclic carbonate organic solvent 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. Alternatively, examples of the cyclic carbonate organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). And according to one embodiment, from the perspective of contributing to the formation of the SEI film containing the inorganic material (LiF), it may include fluoroethylene carbonate (FEC).

[0055] In addition, the linear carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant. Examples of the linear carbonate organic solvent may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. Alternatively, examples of the linear carbonate organic solvent may include at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). And according to one embodiment, from the perspective of further improving the oxidation stability of the non-aqueous electrolyte, it may include diethyl carbonate (DEC).

[0056] The organic solvent can be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. The cyclic carbonate organic solvent and the linear carbonate organic solvent can be mixed in a volume ratio of about 5:95 to 40:60, for example, about 7:93 to 25:75. When the mixing ratio of the cyclic carbonate organic solvent and the linear carbonate organic solvent satisfies the above range, the high dielectric constant and low viscosity characteristics can be satisfied simultaneously, and excellent ionic conductivity can be achieved.

[0057] In addition, in order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate organic solvent selected from the cyclic carbonate organic solvent and the linear carbonate organic solvent, the organic solvent can include at least one ester organic solvent selected from the linear ester organic solvent and the cyclic ester organic solvent.

[0058] Examples of the linear ester organic solvent can 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.

[0059] In addition, examples of the cyclic ester organic solvent can include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0060] Meanwhile, for the organic solvent, organic solvents commonly used in non-aqueous electrolytes can be additionally used as needed without limitation. Examples of the organic solvent can also include at least one organic solvent selected from ether organic solvents, glycol diether organic solvents, and nitrile organic solvents.

[0061] Examples of the ether solvent can include any one or a mixture of two or more selected from 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), but the present invention is not limited thereto.

[0062] The glycol diether solvent is a solvent with a high dielectric constant, low surface tension, and low reactivity with metals compared to the linear carbonate organic solvent. Examples of the glycol diether solvent can include at least one selected from the group consisting of dimethoxyethane (glycol dimethyl ether or DME), diethoxyethane, diglycol dimethyl ether, triglycol dimethyl ether, and tetraethylene glycol dimethyl ether (TEGDME), but the present invention is not limited thereto.

[0063] The nitrile solvent can include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, octanenitrile, heptanenitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, etc., but the present invention is not limited thereto.

[0064] (3) Additive

[0065] The non-aqueous electrolyte contains an additive.

[0066] The additive includes a first additive and a second additive.

[0067] The first additive may include a compound represented by Formula 1 below.

[0068] [Formula 1]

[0069]

[0070] Wherein, R1 includes halogen, cyano, propargyl, ester group, ether group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxanyl group, sulfone group, sulfonate group, sulfate group, or a combination of two or more thereof, and n is an integer from 0 to 6.

[0071] For example, the compound represented by Formula 1 contained in the first additive is a coumarin compound, which has strong reducibility at the negative electrode, thus causing a rapid ring-opening reaction during the formation of the initial SEI film, and thus a PEO-based polymer SEI film can be formed. This polymer SEI film can have excellent flexibility and recovery performance.

[0072] However, when the first additive is used alone, there is a risk that the thermal stability, chemical and electrochemical stability of the SEI film may be reduced, and the durability may also be reduced. For example, when the first additive is used alone, it may be difficult to form a highly durable SEI film on the negative electrode active material (e.g., silicon-based active material) that undergoes volume expansion during charging and discharging. In addition, when the first additive is used alone, the additive may be reduced to form free radicals, which then attack the carbonate solvent, thus causing additional unwanted reduction reactions. In this regard, the non-aqueous electrolyte of the present invention adopts a combination of a first additive and a second additive based on cyclic siloxane. Since the free radical formation of the first additive promotes the ring-opening reaction of the second additive, an SEI film with excellent flexibility, recovery, and durability (e.g., thermal stability) can be formed on the negative electrode.

[0073] For example, the first additive has strong reducibility at the negative electrode, thereby causing a rapid ring-opening reaction during the formation of the initial SEI film, so that a polymer-type SEI film can be formed, and an SEI film with excellent flexibility and recovery performance can be formed. In addition, the second additive can form a silicone-type SEI film during the reduction process of the negative electrode, which can contribute to the formation of an SEI film with a high shear modulus, excellent thermal stability, and chemical and electrochemical stability. For example, the radicals formed when the first additive decomposes promote the ring-opening reaction of the second additive, so that an SEI film with excellent flexibility, recovery, and high durability can be formed on the negative electrode through the organic interaction between the first additive and the second additive. Therefore, the lithium secondary battery containing the non-aqueous electrolyte of the present invention can improve the life performance and storage performance, especially the life performance and storage performance at high temperatures.

[0074] In Formula 1, R1 can be, for example, a halogen (the halogen can be selected from F, Cl, Br, and I, and can be, for example, F), a nitrile group, a propargyl group, an ester group, an ether group, or a combination of two or more thereof. Such substituents can improve the reducibility of the first additive, thereby improving the lithium ion transport performance and enabling the first additive to smoothly form the SEI film.

[0075] In Formula 1, n can be an integer selected from 0 to 6. For example, it can be an integer from 1 to 6, or n can be 1. In Formula 1, when n is 2 or more, each R1 can be the same or different.

[0076] According to one embodiment, the compound represented by Formula 1 may include at least one selected from the group consisting of the compound represented by Formula 1-A and the compound represented by Formula 1-B below.

[0077] [Formula 1-A]

[0078]

[0079] [Formula 1-B]

[0080]

[0081] Wherein R1 is as defined in Formula 1.

[0082] The compounds represented by Formula 1-A and Formula 1-B have structures in which the substituents are located at the 3-position and 7-position of the ring structure (based on the IUPAC nomenclature), and synthesis is advantageous at these positions compared to other substitution positions.

[0083] For example, the compound represented by Formula 1 may include at least one selected from the group consisting of the compounds represented by the following Formulas 1-1 to 1-9. In order for the compound represented by Formula 1 to be reduced more smoothly at the negative electrode and to be more conducive to the formation of the SEI film, the compound represented by Formula 1 may include at least one selected from the compounds represented by, for example, the following Formulas 1-1, 1-2, 1-3, and 1-4. Alternatively, according to one embodiment, the compound represented by Formula 1 may include the compound represented by the following Formula 1-4.

[0084] [Formula 1-1]

[0085]

[0086] [Formula 1-2]

[0087]

[0088] [Formula 1-3]

[0089]

[0090] [Formula 1-4]

[0091]

[0092] [Formula 1-5]

[0093]

[0094] [Formula 1-6]

[0095]

[0096] [Formula 1-7]

[0097]

[0098] [Formula 1-8]

[0099]

[0100] [Formula 1-9]

[0101]

[0102] In the non-aqueous electrolyte, the content of the first additive may be about 0.01% by weight to 10% by weight, for example, about 0.05% by weight to 7% by weight, about 0.1% by weight to 2% by weight, or about 0.3% by weight to 1% by weight. When the dosage of the first additive is within the above range, a soft and highly durable SEI film can be formed on the negative electrode, and an increase in resistance caused by an excessive addition amount of the first additive can be prevented.

[0103] The second additive may contain a compound represented by Formula 2 below.

[0104] [Formula 2]

[0105]

[0106] Wherein, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following Formula 3, where m is an integer from 3 to 10.

[0107] [Formula 3]

[0108]

[0109] Wherein, L1 is a direct bond, 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, R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

[0110] The second additive may form a silicone-type SEI film during the negative electrode reduction process, and may contribute to the formation of an SEI film having a high shear modulus, excellent thermal stability, and chemical and electrochemical stability.

[0111] However, the reduction tendency of the second additive itself is relatively low, so it is difficult to achieve a smooth ring-opening reaction when using the second additive alone. Therefore, when using the second additive alone, it may be difficult to form an SEI film. However, the non-aqueous electrolyte of the present invention is characterized in that the first additive and the second additive are used in combination. When the first additive rapidly decomposes to form free radicals during initial activation, since these free radicals can promote the ring-opening reaction of the second additive, an SEI film with excellent flexibility, recovery, and significantly improved durability can be formed on the negative electrode through the organic action of the first additive and the second additive. For example, when using a silicon-based active material that undergoes significant volume changes during charge and discharge as the negative electrode active material, the effect of combining the first additive and the second additive can be further maximized.

[0112] In Formula 2, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by Formula 3. At this time, at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by Formula 3. In this case, for example, the reduction reaction of the cyclic silicone compound can be further promoted.

[0113] For example, R2 and R3 can be independently selected from alkyl groups having 1 to 5 carbon atoms, alkenyl groups having 2 to 5 carbon atoms, alkynyl groups having 2 to 5 carbon atoms, and substituents represented by the following formula 3-1, and at least one of R2 and R3 can be selected from alkenyl groups having 2 to 5 carbon atoms, alkynyl groups having 2 to 5 carbon atoms, and substituents represented by the following formula 3-1.

[0114] [Formula 3-1]

[0115]

[0116] Among them, L1 is an alkylene group having 1 to 5 carbon atoms, a sulfone group, or a combination thereof, R4 is an alkoxy group having 1 to 5 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

[0117] For example, R2 and R3 can be independently selected from alkyl groups having 1 to 3 carbon atoms, alkenyl groups having 2 to 3 carbon atoms, alkynyl groups having 2 to 3 carbon atoms, and substituents represented by the following formula 3-2, and at least one of R2 and R3 can be selected from alkenyl groups having 2 to 3 carbon atoms, alkynyl groups having 2 to 3 carbon atoms, and substituents represented by the following formula 3-2. If within the above range, an increase in resistance caused by too high a carbon atom content can be prevented.

[0118] [Formula 3-2]

[0119]

[0120] Among them, L1 is methylene, ethylene, a sulfone group, or a combination of two or more thereof, R4 is one selected from -OCF3, -OCF2CF3, and -OCF2CF2CF3, and * is a binding site.

[0121] Meanwhile, in formula 2, R2 can be an alkyl group having 1 to 10 carbon atoms, for example, an alkyl group having 1 to 5 carbon atoms, and more specifically, an alkyl group having 1 to 3 carbon atoms. In addition, in formula 2, R3 can be selected from alkenyl groups having 2 to 10 carbon atoms, alkynyl groups having 2 to 10 carbon atoms, and substituents represented by formula 3, can be selected from alkenyl groups having 2 to 5 carbon atoms, alkynyl groups having 2 to 5 carbon atoms, and substituents represented by formula 3-1, or can be selected from alkenyl groups having 2 to 3 carbon atoms, alkynyl groups having 2 to 3 carbon atoms, and substituents represented by formula 3-2. When R2 is an alkyl group and R3 is an unsaturated hydrocarbon group or a fluorine-substituted alkoxy group, an increase in resistance caused by the presence of an excessive amount of unsaturated hydrocarbon group can be prevented.

[0122] Examples of the compound represented by Formula 2 may include at least one selected from the group consisting of the compounds represented by Formula 2-1 to Formula 2-16; may include at least one selected from the group consisting of the compounds represented by Formula 2-1, Formula 2-3, Formula 2-4, Formula 2-5, Formula 2-7, Formula 2-13, and Formula 2-14; and may include at least one selected from the group consisting of the compounds represented by Formula 2-1, Formula 2-3, Formula 2-5, and Formula 2-7; or according to one embodiment, may include the compound represented by the following Formula 2-3.

[0123] [Formula 2-1]

[0124]

[0125] [Formula 2-2]

[0126]

[0127] [Formula 2-3]

[0128]

[0129] [Formula 2-4]

[0130]

[0131] [Formula 2-5]

[0132]

[0133] [Formula 2-6]

[0134]

[0135] [Formula 2-7]

[0136]

[0137] [Formula 2-8]

[0138]

[0139] [Formula 2-9]

[0140]

[0141] [Formula 2-10]

[0142]

[0143] [Formula 2-11]

[0144]

[0145] [Formula 2-12]

[0146]

[0147] [Formula 2-13]

[0148]

[0149] [Formula 2-14]

[0150]

[0151] [Formula 2-15]

[0152]

[0153] [Formula 2-16]

[0154]

[0155] The content of the second additive in the non-aqueous electrolyte can be about 0.01 wt% to 10 wt%, such as about 0.05 wt% to 7 wt%, about 0.1 wt% to 2 wt%, or about 0.3 wt% to 1 wt%. When the content of the second additive meets the above range, an SEI film with excellent durability (such as thermal stability) can be effectively formed, and an increase in the resistance of the lithium secondary battery and a corresponding decrease in the life performance due to excessive addition of the additive can be prevented.

[0156] The weight ratio of the first additive to the second additive can be about 1:99 to 99:1, such as 15:85 to 85:15, or 40:60 to 60:40. When the above weight ratio is met, the first additive and the second additive have a good combined effect, so that the improvement effects of the high-temperature life performance, high-temperature storage performance and safety of the lithium secondary battery can be exhibited.

[0157] In addition to the first additive and the second additive, the additive may further contain an additional additive (the third additive). The non-aqueous electrolyte may also contain an additional additive to prevent the non-aqueous electrolyte from decomposing in a high-power environment, resulting in the disintegration of the negative electrode, or to improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection and suppression of battery swelling at high temperatures.

[0158] For example, the additional additive may be at least one selected from vinylene carbonate, ethylene vinyl carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfite, LiBOB (lithium bis(oxalato)borate), TMSPa (3-trimethoxysilylpropyl-N-phenylamine) and TMSPi (tris(trimethylsilyl) phosphite), and for example, it may be vinylene carbonate.

[0159] The non-aqueous electrolyte may contain about 0.1% to 15% by weight of an additional additive.

[0160] Lithium secondary battery

[0161] In addition, the present disclosure provides a lithium secondary battery including the above non-aqueous electrolyte.

[0162] The lithium secondary battery of the present disclosure includes a negative electrode, a positive electrode opposite to the negative electrode, a separator disposed between the negative electrode and the positive electrode, and the above non-aqueous electrolyte.

[0163] The lithium secondary battery can be prepared by accommodating an electrode assembly including a negative electrode, a positive electrode opposite to the negative electrode, and a separator disposed between the negative electrode and the positive electrode in a battery case, and then injecting a non-aqueous electrolyte into the battery case.

[0164] Since the non-aqueous electrolyte has been described above, the negative electrode, the positive electrode, and the separator will be described below.

[0165] (1) Negative electrode

[0166] The negative electrode contains a negative electrode active material.

[0167] Any negative electrode active material used in the art can be used as the negative electrode active material without limitation. For example, the negative electrode active material may include at least one selected from silicon-based active materials and carbon-based active materials, or may include a silicon-based active material.

[0168] Although the silicon-based active material exhibits a higher capacity than the carbon-based active material, the silicon-based active material has a problem of large volume expansion / contraction caused by charge and discharge. However, when the silicon-based active material is used together with the above non-aqueous electrolyte of the present disclosure, an SEI film having flexibility, high resilience, and durability can be formed on the negative electrode, thereby enabling a lithium secondary battery capable of preventing electrolyte side reactions and having improved life and storage performance.

[0169] The silicon-based active material may contain a compound represented by the following formula A.

[0170] [Formula A]

[0171] SiO x (0≤x<2)

[0172] Wherein, SiO2 does not react with lithium ions and cannot store lithium, therefore, x can be within the above range.

[0173] The average particle size (D 50 ) of the silicon-based active material may be about 1 μm to 20 μm.

[0174] The carbon-based active material may include at least one selected from graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and may include graphite according to one embodiment. The graphite may include at least one selected from artificial graphite and natural graphite.

[0175] From the viewpoint of ensuring the structural stability during charge and discharge and reducing side reactions with the electrolyte, the average particle size (D 50 ) of the carbon-based active material may be about 10 μm to 30 μm, for example, about 15 μm to 25 μm.

[0176] The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material may be contained in the negative electrode active material layer.

[0177] The negative electrode current collector is not particularly limited and may be any negative electrode current collector having a high conductivity and not causing chemical changes in the battery. For example, the negative electrode current collector may be copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum cadmium alloy.

[0178] The thickness of the negative electrode current collector may generally be about 3 μm to 500 μm.

[0179] The negative electrode current collector may form minute irregularities on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0180] The negative electrode active material layer is provided on at least one surface of the negative electrode current collector. For example, the negative electrode active material layer may be provided on one surface or both surfaces of the negative electrode current collector.

[0181] In order to fully exhibit the capacity in the secondary battery and minimize the influence of volume expansion / contraction on the battery, the content of the negative electrode active material in the negative electrode active material layer may be about 60 wt% to 99 wt%.

[0182] In addition to the silicon-based active material, the negative electrode active material layer may further contain a conductive material and / or a binder.

[0183] The binder can be used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector described below or the binding force between the silicon-based active materials.

[0184] For example, from the viewpoint of further improving the electrode adhesion and providing sufficient resistance to the volume expansion / contraction of silicon-based active materials, the binder may include at least one selected from styrene-butadiene rubber (SBR), nitrile rubber (NBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM).

[0185] The content of the binder in the negative electrode active material layer may be about 1 wt% to 30 wt%. When the binder is within this range, the negative electrode active material can be better adhered to minimize the volume expansion problem of the active material, while promoting the dispersion of the binder when preparing the slurry for forming the negative electrode active material layer, and improving the coating property and phase stability of the slurry.

[0186] The conductive material can be used to assist and improve the conductivity in the secondary battery, and can be any material having conductivity without causing chemical changes without particular limitation. Specifically, examples of the conductive material may include at least one selected from the following: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum or nickel powders; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0187] The content of the conductive material in the negative electrode active material layer may be about 1 wt% to 20 wt%. When the conductive material is within this range, an excellent conductive network can be formed while reducing the resistance increase caused by the binder.

[0188] The thickness of the negative electrode active material layer may be about 5 μm to 500 μm, for example, about 5 μm to 100 μm.

[0189] The negative electrode can be prepared by coating a negative electrode current collector with a negative electrode slurry containing a negative electrode active material and optionally a binder, a conductive material, and a solvent for forming the negative electrode slurry, and then drying and rolling.

[0190] From the viewpoint of promoting the dispersion of the negative electrode active material, the binder, and / or the conductive material, the solvent for forming the negative electrode slurry may include, for example, at least one selected from distilled water, ethanol, methanol, and isopropyl alcohol. According to one embodiment, the solvent may include distilled water.

[0191] (2) Positive electrode

[0192] The positive electrode contains a positive electrode active material.

[0193] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and may include, for example, a lithium transition metal composite oxide containing lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum, or may include a lithium transition metal composite oxide containing lithium and a transition metal containing nickel, cobalt, and manganese.

[0194] Examples of the lithium transition metal composite oxide may include: lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4), lithium cobalt-based oxides (e.g., LiCoO2), lithium nickel-based oxides (e.g., LiNiO2), lithium nickel manganese-based oxides (e.g., LiNi 1- Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2)), lithium nickel cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1)), lithium manganese cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2)), lithium nickel manganese cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1 and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2 and p1 + q1 + r2 = 2) and lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M s2 )O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1 and p2 + q2 + r3 + s2 = 1)), and may include any one or two or more thereof. Among these materials, from the viewpoint of being able to improve the capacity characteristics and stability of the battery, the lithium transition metal composite oxide may be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co0.2 ) O2, Li(Ni 0.5 Mn 0.3 Co 0.2 ) O2, Li(Ni 0.7 Mn 0.15 Co 0.15 ) O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 ) O2), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 ) O2). Considering the significant improvement effect produced by controlling the types and content ratios of the components constituting the lithium transition metal composite oxide, the lithium transition metal composite oxide can be Li(Ni 0.6 Mn 0.2 Co 0.2 ) O2, Li(Ni 0.5 Mn 0.3 Co 0.2 ) O2, Li(Ni 0.7 Mn 0.15 Co 0.15 ) O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 ) O2, and any one of them or a mixture of two or more thereof can be used.

[0195] According to one embodiment, the positive electrode active material is a lithium transition metal composite oxide, and based on the total number of moles of the transition metals contained in the lithium transition metal composite oxide, it can contain more than about 60 mol% of nickel. For example, the positive electrode active material is a lithium transition metal composite oxide, the transition metals can include nickel and at least one selected from manganese, cobalt, and aluminum, and based on the total number of moles of the transition metals, the content of nickel can be more than about 60 mol%, for example, about 60 mol% to 90 mol%. When a lithium transition metal composite oxide with a high nickel content is used together with the above non-aqueous electrolyte, the gas-phase by-products generated due to structural collapse can be reduced.

[0196] In addition, the positive electrode active material can include a lithium composite transition metal oxide represented by the following formula B:

[0197] [Formula B]

[0198] Li 1+x (Ni a Co b Mn c M d ) O2

[0199] Among them, 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. 1 + x, a, b, c, and d are atomic fractions of independent elements, where 0 ≤ x ≤ 0.2, 0.50 ≤ a < 1, 0 < b ≤ 0.25, 0 < c ≤ 0.25, 0 ≤ d ≤ 0.1, and a + b + c + d = 1.

[0200] According to one embodiment, a, b, c, and d can be 0.70 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.20, 0.025 ≤ c ≤ 0.20, and 0 ≤ d ≤ 0.05, respectively.

[0201] In addition, a, b, c, and d can be 0.80 ≤ a ≤ 0.95, 0.025 ≤ b ≤ 0.15, 0.025 ≤ c ≤ 0.15, and 0 ≤ d ≤ 0.05, respectively.

[0202] Furthermore, a, b, c, and d can be 0.85 ≤ a ≤ 0.90, 0.05 ≤ b ≤ 0.10, 0.05 ≤ c ≤ 0.10, and 0 ≤ d ≤ 0.03, respectively.

[0203] The positive electrode can include a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer can include the above positive electrode active material.

[0204] The positive electrode current collector generally can have a thickness of about 3 μm to 500 μm.

[0205] The positive electrode current collector can form minute unevenness on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0206] The positive electrode active material layer is provided on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be provided on one surface or both surfaces of the positive electrode current collector.

[0207] Considering the sufficient capacity of the positive electrode active material being exhibited, the content of the positive electrode active material in the positive electrode active material layer can be about 80 wt% to 99 wt%.

[0208] In addition to the above positive electrode active material, the positive electrode active material layer can further contain a binder and / or a conductive material.

[0209] The binder is a component that helps bind the active material to the conductive material and to the current collector, and can include, for example, at least one selected from polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber. For example, the binder can include polyvinylidene fluoride.

[0210] From the perspective of ensuring sufficient binding force between components such as the positive electrode active material, the content of the binder in the positive electrode active material layer can be about 1 wt% to 20 wt%, for example, 1.2 wt% to 10 wt%.

[0211] The conductive material can be used to assist and improve the conductivity in the secondary battery and is not particularly limited, and can be any material with conductivity that does not cause chemical changes. Examples of the positive electrode conductive material can include at least one selected from the following: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, such as carbon fibers, metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide, potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives. According to one embodiment, in order to improve the conductivity, the positive electrode conductive material can include carbon nanotubes.

[0212] In terms of ensuring sufficient conductivity, the content of the conductive material in the positive electrode active material layer can be about 1 wt% to 20 wt%, for example, about 1.2 wt% to 10 wt%.

[0213] The thickness of the positive electrode active material layer can be about 5 μm to 500 μm, for example, about 20 μm to 200 μm.

[0214] The positive electrode can be prepared as follows: coating the positive electrode current collector with a positive electrode paste containing the positive electrode active material and optionally a binder, a conductive material, and a solvent for the positive electrode paste, and then drying and rolling.

[0215] (3) Separator

[0216] The separator is disposed between the positive electrode and the negative electrode.

[0217] The separator can be any porous polymer membrane commonly used as a separator, for example, a porous polymer membrane prepared from polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer), which can be used alone or in a stacked manner. Alternatively, the separator can be any common porous non-woven fabric, such as a non-woven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, but is not limited thereto. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can also be used, and a separator having a single-layer or multi-layer structure can be selectively used.

[0218] The external shape of the lithium secondary battery of the present disclosure is not particularly limited, and a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can can be used.

[0219] Hereinafter, the present disclosure will be described in more detail according to specific exemplary embodiments. However, the following embodiments are provided only for illustrating the present disclosure, and the scope of the present disclosure is not limited thereto. It will be obvious to those skilled in the art that various modifications and changes can be made within the scope and technical spirit of the present disclosure, and such modifications and changes fall within the scope of the claims included herein.

[0220] Examples and Comparative Examples

[0221] Example 1

[0222] (Preparation of non-aqueous electrolyte)

[0223] A mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) with a volume ratio of 10:90 was used as the organic solvent.

[0224] LiPF6 as a lithium salt, a compound represented by Formula 1-4 as a first additive, and a compound represented by Formula 2-3 as a second additive were added to the organic solvent to prepare a non-aqueous electrolyte.

[0225] The molar concentration of LiPF6 contained in the non-aqueous electrolyte was 1.5 M.

[0226] The content of the compound represented by Formula 1-4 in the non-aqueous electrolyte was 0.5 wt%, and the content of the compound represented by Formula 2-3 in the non-aqueous electrolyte was 0.5 wt%.

[0227] (Manufacture of lithium secondary battery)

[0228] The positive electrode active material (Li[Ni 0.85 Co 0.05 Mn 0.07 Al 0.03Oxygen (O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 97.74:0.70:1.56 to prepare a positive electrode mixture slurry (solid content: 75.5 wt%). The positive electrode mixture slurry was coated on one surface of a positive electrode current collector (Al film) with a thickness of 12 μm, dried, and roll-pressed to prepare a positive electrode.

[0229] A negative electrode active material (silicon-based active material, Si), a conductive material (carbon black), and a binder (styrene-butadiene rubber) were added to distilled water as a solvent in a weight ratio of 70.0:20.3:9.7 to prepare a negative electrode mixture slurry (solid content: 26 wt%). The negative electrode mixture slurry was coated on one surface of a negative electrode current collector (Cu film) with a thickness of 15 μm, dried, and roll-pressed to prepare a negative electrode.

[0230] In a drying chamber, a polyethylene porous separator was placed between the prepared positive electrode and negative electrode, and then the prepared non-aqueous electrolyte was injected to prepare a secondary battery.

[0231] Example 2

[0232] A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 1-1 was added to the non-aqueous electrolyte instead of the compound represented by Formula 1-4 as the first additive. That is, in Example 2, a different compound represented by Formula 1-1 from that in Example 1 was used as the first additive, and the same compound represented by Formula 2-3 as in Example 1 was used as the second additive to manufacture a non-aqueous electrolyte and a lithium secondary battery.

[0233] Example 3

[0234] A non-aqueous electrolyte and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 2-1 was added to the non-aqueous electrolyte instead of the compound represented by Formula 2-3 as the second additive. That is, in Example 3, the same compound represented by Formula 1-4 as in Example 1 was used as the first additive, and a different compound represented by Formula 2-1 from that in Example 1 was used as the second additive to manufacture a non-aqueous electrolyte and a lithium secondary battery.

[0235] Example 4

[0236] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.1 wt% instead of 0.5 wt% of the first additive was added to the non-aqueous electrolyte. That is, in Example 4, the compound represented by Formula 1-4, which is the same as that used in Example 1, was used as the first additive, and the compound represented by Formula 2-3, which is the same as that used in Example 1, was used as the second additive. However, the amount of the first additive, 0.1 wt%, was different from that in Example 1 to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0237] Example 5

[0238] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 2 wt% instead of 0.5 wt% of the first additive was added to the non-aqueous electrolyte. That is, in Example 5, the compound represented by Formula 1-4, which is the same as that used in Example 1, was used as the first additive, and the compound represented by Formula 2-3, which is the same as that used in Example 1, was used as the second additive. However, the amount of the first additive, 2 wt%, was different from that in Example 1 to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0239] Example 6

[0240] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.1 wt% instead of 0.5 wt% of the second additive was added to the non-aqueous electrolyte. That is, in Example 6, the compound represented by Formula 1-4, which is the same as that used in Example 1, was used as the first additive, and the compound represented by Formula 2-3, which is the same as that used in Example 1, was used as the second additive. However, the amount of the second additive, 0.1 wt%, was different from that in Example 1 to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0241] Example 7

[0242] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 2 wt% instead of 0.5 wt% of the second additive was added to the non-aqueous electrolyte. That is, in Example 7, the compound represented by Formula 1-4, which is the same as that used in Example 1, was used as the first additive, and the compound represented by Formula 2-3, which is the same as that used in Example 1, was used as the second additive. However, the amount of the second additive, 2 wt%, was different from that in Example 1 to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0243] Example 8

[0244] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 1-2 was added to the non-aqueous electrolyte as the first additive instead of the compound represented by Formula 1-4. That is, in Example 8, a compound represented by Formula 1-2 different from that in Example 1 was used as the first additive, and a compound represented by Formula 2-3 identical to that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0245] Example 9

[0246] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 1-3 was added to the non-aqueous electrolyte as the first additive instead of the compound represented by Formula 1-4. That is, in Example 9, a compound represented by Formula 1-3 different from that in Example 1 was used as the first additive, and a compound represented by Formula 2-3 identical to that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0247] Example 10

[0248] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 1-8 was added to the non-aqueous electrolyte as the first additive instead of the compound represented by Formula 1-4. That is, in Example 10, a compound represented by Formula 1-8 different from that in Example 1 was used as the first additive, and a compound represented by Formula 2-3 identical to that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0249] Example 11

[0250] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 2-4 was added to the non-aqueous electrolyte as the second additive instead of the compound represented by Formula 2-3. For example, in Example 11, a compound represented by Formula 2-3 identical to that in Example 1 was used as the first additive, and a compound represented by Formula 2-4 different from that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0251] Example 12

[0252] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 2-5 was added to the non-aqueous electrolyte instead of the compound represented by Formula 2-3 as the second additive. For example, in Example 12, the same compound represented by Formula 2-3 as in Example 1 was used as the first additive, and a different compound represented by Formula 2-5 from that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0253] Example 13

[0254] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5 wt% of the compound represented by Formula 2-13 was added to the non-aqueous electrolyte instead of the compound represented by Formula 2-3 as the second additive. For example, in Example 13, the same compound represented by Formula 2-3 as in Example 1 was used as the first additive, and a different compound represented by Formula 2-13 from that in Example 1 was used as the second additive to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0255] Comparative Example 1

[0256] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that no first additive and second additive were added. That is, in Comparative Example 1, the additives added in Example 1 were not used to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0257] Comparative Example 2

[0258] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that no second additive was added. For example, in Comparative Example 2, the compound represented by Formula 2-3 was used as the first additive in the same manner as in Example 1 to fabricate the non-aqueous electrolyte and the lithium secondary battery, without using the second additive.

[0259] Comparative Example 3

[0260] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that no first additive was added to the electrolyte. That is, in Comparative Example 3, the first additive of Example 1 was not used, and the second additive was used to fabricate the non-aqueous electrolyte and the lithium secondary battery.

[0261] Experimental Examples

[0262] Experimental Example 1: High-temperature cycle performance evaluation

[0263] Using an electrochemical charge-discharge device, the lithium secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 3 manufactured above were charged to 4.2 V at a constant current / constant voltage (CC / CV) condition of 0.33C and 0.05C at 45°C, and then discharged to 3.0 V at a constant current (CC) condition of 0.33C. This was regarded as one cycle, and the lithium secondary batteries were charged and discharged for 200 cycles.

[0264] The capacity retention rate was calculated using the following equation, and the results are shown in Table 1 below.

[0265] Capacity retention rate (%) = {(discharge capacity after 200 cycles / discharge capacity after 1 cycle)} × 100

[0266] Experimental Example 2: Evaluation of high-temperature storage performance

[0267] The lithium secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 3 manufactured above were initially charged and discharged as follows: charged to 4.2 V at CC / CV and 0.33C conditions at 25°C and 0.05C, and then discharged to 3.0 V at a constant current (CC) and 0.33C conditions. Then, the lithium secondary batteries were charged to 4.2 V at CC / CV and 0.33C conditions at 25°C and 0.05C, and then stored at 60°C for 8 weeks.

[0268] After storing for 8 weeks, the lithium secondary batteries were charged to 4.2 V at 25°C and 0.33C conditions and 0.05C, and then discharged to 3.0 V at 0.33C conditions to measure the capacity during discharge.

[0269] The capacity retention rate was calculated according to the following formula, and the results are shown in Table 1 below.

[0270] Capacity retention rate (%) = (discharge capacity after storing for 8 weeks / initial discharge capacity) × 100

[0271] [Table 1]

[0272]

[0273] As can be confirmed with reference to Table 1, for each of the lithium secondary batteries of Examples 1 to 13 manufactured using the non-aqueous electrolyte of the present invention, the capacity retention rate is above 80% after 200 cycles and after 8 weeks of storage. In contrast, for Comparative Examples 1 to 3 that did not adopt the present invention, the capacity retention rate is below 80% under the same conditions. Therefore, it can be confirmed that, compared with Comparative Examples 1 to 3, the lithium secondary batteries of Examples 1 to 13 of the present invention exhibit a very excellent level of capacity retention rate during high-temperature cycle charge and discharge and high-temperature storage. In other words, it can be confirmed that the life performance and storage performance of the lithium secondary battery including the non-aqueous electrolyte of the present invention containing the above first additive and second additive are improved, particularly the life performance and storage performance at high temperatures.

[0274] Although the present invention has been described above with reference to the embodiments, those skilled in the art or those with ordinary knowledge in the relevant technical field should understand that the various embodiments described herein are for illustrative purposes only. Without departing from the scope and spirit of the present invention, various modifications and changes can be made. Therefore, the various embodiments disclosed herein are not restrictive, and its true scope and spirit are set forth by the appended claims.

Claims

1. A non-aqueous electrolyte, comprising: a lithium salt; an organic solvent; and an additive, the additive comprising a first additive and a second additive, Among them, the first additive comprising a compound represented by the following formula 1, [Formula 1] wherein, R1 includes a halogen, a cyano group, a propargyl group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxanyl group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof, wherein, n is an integer from 0 to 6, wherein, the second additive comprises a compound represented by the following formula 2, [Formula 2] wherein, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms and a substituent represented by the following formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms and a substituent represented by the following formula 3, wherein m is an integer from 3 to 10, [Formula 3] wherein, L1 is a direct bond, 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, R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

2. The non-aqueous electrolyte according to claim 1, wherein, The compound represented by formula 1 comprises at least one compound selected from the group consisting of a compound represented by formula 1-A and a compound represented by formula 1-B, [Formula 1-A] [Formula 1-B] wherein R1 is as defined in formula 1.

3. The non-aqueous electrolyte according to claim 1, wherein The compound represented by formula 1 comprises at least one compound selected from the group consisting of the compounds represented by the following formula 1-1 to formula 1-9: [Formula 1-1] [Formula 1-2] [Formula 1-3] [Formula 1-4] [Formula 1-5] [Formula 1-6] [Formula 1-7] [Formula 1-8] [Formula 1-9] 4. The non-aqueous electrolyte according to claim 1, wherein Based on the weight of the non-aqueous electrolyte, the content of the first additive is 0.01 wt% to 10 wt%.

5. The non-aqueous electrolyte according to claim 1, wherein, In formula 2, R2 is an alkyl group having 1 to 10 carbon atoms, and R3 is selected from an alkenyl group having 2 to 10 carbon atoms and an alkynyl group having 2 to 10 carbon atoms.

6. The non-aqueous electrolyte according to claim 1, wherein The compound represented by formula 2 comprises at least one compound selected from the group consisting of the compounds represented by the following formula 2-1 to formula 2-16: [Formula 2-1] [Formula 2-2] [Formula 2-3] [Formula 2-4] [Formula 2-5] [Formula 2-6] [Formula 2-7] [Formula 2-8] [Formula 2-9] [Formula 2-10] [Formula 2-11] [Formula 2-12] [Formula 2-13] [Formula 2-14] [Formula 2-15] [Formula 2-16] 7. The non-aqueous electrolyte according to claim 1, wherein Based on the weight of the non-aqueous electrolyte, the content of the second additive is 0.01 wt% to 10 wt%.

8. The non-aqueous electrolyte according to claim 1, wherein The weight ratio of the first additive to the second additive is 1:99 to 99:

1.

9. The non-aqueous electrolyte according to claim 1, wherein The lithium salt includes at least one selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2).

10. The non-aqueous electrolyte according to claim 1, wherein, The molar concentration of the lithium salt contained in the non-aqueous electrolyte is 0.5 M to 5.0 M.

11. The non-aqueous electrolyte according to claim 1, wherein The organic solvent includes at least one selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

12. The non-aqueous electrolyte according to claim 1, wherein The organic solvent includes cyclic carbonate organic solvents and linear carbonate organic solvents, wherein, the cyclic carbonate organic solvent includes fluoroethylene carbonate, and wherein, the linear carbonate organic solvent includes diethyl carbonate.

13. A lithium secondary battery, comprising: a negative electrode, a positive electrode opposite to the negative electrode, a separator disposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte, comprising: a lithium salt; an organic solvent; and an additive, the additive comprising a first additive and a second additive, Among them, the first additive includes a compound represented by the following formula 1, [Formula 1] wherein, R1 includes halogen, cyano, propargyl, ester group, ether group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxanyl group, sulfone group, sulfonate group, sulfate group, or a combination of two or more thereof, wherein, n is an integer from 0 to 6, wherein, the second additive includes a compound represented by the following formula 2, [Formula 2] wherein, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following formula 3, wherein m is an integer from 3 to 10, [Formula 3] wherein, L1 is a direct bond, 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, R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

14. The lithium secondary battery according to claim 13, wherein, The negative electrode contains a negative electrode active material containing a silicon-based active material.

15. A method for preparing a non-aqueous electrolyte, the preparation method comprising: adding a lithium salt and an additive to an organic solvent, the additive including a first additive and a second additive, wherein, the first additive includes a compound represented by the following formula 1, [Formula 1] wherein, R1 includes halogen, cyano, propargyl, ester group, ether group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, boron group, borate group, isocyanate group, isothiocyanate group, silyl group, siloxanyl group, sulfone group, sulfonate group, sulfate group, or a combination of two or more thereof, wherein, n is an integer from 0 to 6, wherein, the second additive includes a compound represented by the following formula 2, [Formula 2] Among them, R2 and R3 are independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following formula 3, and at least one of R2 and R3 is selected from an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and a substituent represented by the following formula 3, where m is an integer from 3 to 10. [Formula 3] Among them, L1 is a direct bond, 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, R4 is an alkoxy group having 1 to 10 carbon atoms substituted with at least one fluorine atom, and * is a binding site.

16. The preparation method according to claim 15, wherein, The compound represented by formula 1 includes at least one selected from the group consisting of the compounds represented by the following formula 1-A and the compounds represented by the following formula 1-B: [Formula 1-A] [Formula 1-B] Wherein R1 is as defined in formula 1.

17. The preparation method according to claim 15, wherein, The compound represented by formula 1 includes at least one compound selected from the group consisting of the compounds represented by the following formula 1-1 to formula 1-9: [Formula 1-1] [Formula 1-2] [Formula 1-3] [Formula 1-4] [Formula 1-5] [Formula 1-6] [Formula 1-7] [Formula 1-8] [Formula 1-9] 18. The preparation method according to claim 15, wherein, Based on the weight of the non-aqueous electrolyte, the content of the first additive is 0.01% by weight to 10% by weight.

19. The preparation method according to claim 15, wherein, In formula 2, R2 is selected from an alkyl group having 1 to 10 carbon atoms, and R3 is selected from an alkenyl group having 2 to 10 carbon atoms and an alkynyl group having 2 to 10 carbon atoms.

20. The preparation method according to claim 15, wherein, The compound represented by formula 2 includes at least one compound selected from the group consisting of the compounds represented by the following formula 2-1 to formula 2-16: [Formula 2-1] [Formula 2-2] [Formula 2-3] [Formula 2-4] [Formula 2-5] [Formula 2-6] [Formula 2-7] [Formula 2-8] [Formula 2-9] [Formula 2-10] [Formula 2-11] [Formula 2-12] [Formula 2-13] [Formula 2-14] [Formula 2-15] [Formula 2-16]

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