Non-aqueous electrolyte and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive contains a compound represented by a specific chemical formula. The non-aqueous electrolyte according to the present invention can suppress the deterioration of the positive electrode, reduce the side reaction between the positive electrode and the electrolyte, and form a stable SEI film on the negative electrode, so that the high-temperature cycle characteristics and high-temperature storage characteristics of a lithium secondary battery containing the same can be improved.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0095710, filed on August 1, 2022, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same.

Background Art

[0003] In recent years, the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computer devices, but also to power storage and supply for large-area devices such as automobiles and power storage devices. Along with this, the demand for secondary batteries with high capacity, high output, and high stability has been increasing.

[0004] In particular, in lithium secondary batteries for automotive applications, high capacity, high output, and long-term life characteristics are important. In order to increase the capacity of lithium secondary batteries, it is conceivable to use a positive electrode active material with a high nickel content that has a high energy density but low stability, or to drive the lithium secondary battery at a high voltage.

[0005] However, when driving a lithium secondary battery under the above conditions, as charge and discharge progress, due to side reactions caused by electrolyte deterioration, the film formed on the surface of the positive / negative electrode or the structure of the electrode surface deteriorates, and transition metal ions can be eluted from the surface of the positive electrode. In this way, the eluted transition metal ions are electro-deposited on the negative electrode, reducing the passivation ability of the SEI (Solid electrolyte interface) film of the negative electrode, resulting in a problem that the negative electrode deteriorates. Such a deterioration phenomenon of the secondary battery tends to accelerate when the potential of the positive electrode increases or the battery is exposed to high temperatures.

[0006] In addition, when a lithium secondary battery is continuously used for a long time or left at a high temperature, a so-called swelling phenomenon occurs where gas is generated and the thickness of the battery increases. The amount of gas generated at this time is known to depend on the state of such SEI.

[0007] Therefore, in order to solve such problems, research and development have been conducted on a method that can suppress the elution of metal ions in the positive electrode, form a stable SEI film on the negative electrode, reduce the swelling phenomenon of the lithium secondary battery, and enhance the stability at high temperatures.

Summary of the Invention

Problems to be Solved by the Invention

[0008] One problem of the present invention is to provide a non-aqueous electrolyte that can suppress the deterioration of the positive electrode, reduce the side reaction between the positive electrode and the electrolyte, and form a stable SEI film on the negative electrode.

[0009] Another problem of the present invention is to provide a lithium secondary battery in which the high-temperature cycle characteristics and high-temperature storage performance are improved and various performances are enhanced by including the aforementioned non-aqueous electrolyte.

Means for Solving the Problems

[0010] The present invention provides a non-aqueous electrolyte containing a lithium salt, an organic solvent, and an additive, wherein the additive contains a compound represented by the following Chemical Formula 1.

[0011]

Chem.

[0012] In the above Chemical Formula 1, R1 includes a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy 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 siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof; R2 is a substituent represented by the following Chemical Formula 2 or a substituent represented by the following Chemical Formula 3. [Chemical Formula] In the above Chemical Formula 2, R3 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines; * is a bonding site. [Chemical Formula] In the above Chemical Formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines; * is a bonding site. n is an integer from 0 to 5, m is an integer from 1 to 6, and n + m is an integer from 1 to 6.

[0013] The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte. [Advantages of the Invention]

[0014] The non-aqueous electrolyte of the present invention is characterized by containing, as an additive, a compound represented by the above Chemical Formula 1 based on a coumarin structure. The additive can form a stable SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode while being rapidly reductively decomposed during initial activation. In particular, fluorine contained in the compound represented by the above Chemical Formula 1; and a substituent containing an ester group or an ether group; can increase the inorganic content of the SEI film and improve the durability of the SEI film at high temperatures to a high level. Further, according to the non-aqueous electrolyte according to the present invention, a reactive oxygen compound generated at the positive electrode binds to the coumarin structure contained in the compound represented by the above Chemical Formula 1, and there is an effect of suppressing electrolyte decomposition and gas generation.

[0015] Therefore, a lithium secondary battery containing the above-described non-aqueous electrolyte can have improved high-temperature cycle characteristics and high-temperature storage characteristics.

Mode for Carrying Out the Invention

[0016] Terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in a meaning and concept consistent with the technical idea of the present invention in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0017] In this specification, terms such as "comprising," "including," or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude in advance the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0018] On the other hand, before explaining the present invention, unless otherwise specifically mentioned in the present invention, "*" means a connected part (bonding site) between the ends of the same or different atoms or chemical formulas.

[0019] In addition, in this specification, in the description of "carbon number a to b", "a" and "b" mean the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, an "alkyl group having 1 to 5 carbon atoms" means an alkyl group containing 1 to 5 carbon atoms, that is, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, etc.

[0020] In addition, in this specification, an alkyl group, an alkenyl group, or an alkynyl group may or may not be substituted. The above-mentioned "substitution" means that at least one or more hydrogens bonded to carbon are substituted with elements other than hydrogen, unless otherwise defined. For example, it means being substituted with 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, a haloaryl group having 6 to 20 carbon atoms, etc.

[0021] Hereinafter, the present invention will be described in more detail.

[0022] Non-aqueous electrolyte The present invention relates to a non-aqueous electrolyte. More specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

[0023] The non-aqueous electrolyte according to the present invention includes a lithium salt, an organic solvent, and an additive, and the additive includes a compound represented by the following Chemical Formula 1.

[0024] [Chemical formula]

[0025] In the above Chemical formula 1, R1 includes halogen, nitrile group, propargyl group, ester group, ether group, ketone group, carboxy 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, siloxane group, sulfone group, sulfonate group, sulfate group, or a combination of two or more of these.

[0026] In the above Chemical formula 1, R2 is a substituent represented by the following Chemical formula 2 or a substituent represented by the following Chemical formula 3, n is an integer from 0 to 5, m is an integer from 1 to 6, and n + m is an integer from 1 to 6.

[0027] [Chemical formula]

[0028] In the above Chemical formula 2, R3 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and * is a bonding site.

[0029] [Chemical formula]

[0030] In the above Chemical formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and * is a bonding site.

[0031] The non-aqueous electrolyte of the present invention is characterized by containing, as an additive, a compound represented by the above Chemical Formula 1 based on a coumarin structure. The additive can form a stable SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode while being rapidly reductively decomposed during initial activation. In particular, fluorine contained in the compound represented by the above Chemical Formula 1; and a substituent containing an ester group or an ether group; can increase the inorganic content of the SEI film and improve the durability of the SEI film at high temperatures to a high level. Further, according to the non-aqueous electrolyte according to the present invention, a reactive oxygen compound generated at the positive electrode binds to the coumarin structure contained in the compound represented by the above Chemical Formula 1, and there is an effect of suppressing the decomposition of the electrolyte and gas generation. Therefore, a lithium secondary battery containing the non-aqueous electrolyte according to the present invention can have improved high-temperature cycle characteristics and high-temperature storage characteristics.

[0032] (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, as an anion, 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 - It may contain at least any one selected from the group consisting of

[0033] Specifically, the lithium salt is 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 may contain at least one selected from the group consisting of LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may contain 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). Specifically, the lithium salt may contain LiPF6; or LiPF6 and LiFSI;

[0034] The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, specifically, 0.8 M to 4 M, more specifically, 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transport rate (Li +The transference number) and the degree of dissociation of lithium ions are improved, and the output characteristics of the battery can be improved.

[0035] (2) Organic solvent The 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 reaction or the like during the charge and discharge process of the secondary battery is minimized.

[0036] Specifically, the organic solvent may contain at least one selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

[0037] Specifically, the organic solvent may contain a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixture thereof.

[0038] The cyclic carbonate-based organic solvent is a high-viscosity organic solvent, has a high dielectric constant, and is an organic solvent that easily dissociates lithium salts in the electrolyte. Specifically, it may contain at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, and vinylene carbonate. More specifically, it may contain at least one selected from the group consisting of ethylene carbonate and fluoroethylene carbonate, and more specifically, it may contain fluoroethylene carbonate.

[0039] In addition, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant. Specifically, it may contain 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. More specifically, it may contain diethyl carbonate (DEC).

[0040] The 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 at a volume ratio of 1:99 to 40:60, specifically a volume ratio of 5:95 to 30:70, and more specifically a volume ratio of 5:95 to 20:80. When the mixing ratio of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent satisfies the above range, both high dielectric constant and low viscosity characteristics can be satisfied, and excellent ion conductivity characteristics can be realized.

[0041] In addition, in order to produce an electrolyte having a high ion conductivity, the organic solvent may further contain at least one ester-based organic solvent selected from the group consisting of a linear ester-based organic solvent and a cyclic ester-based organic solvent in at least one carbonate-based organic solvent selected from the group consisting of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent.

[0042] Specifically, the linear ester-based organic solvent may contain at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0043] In addition, specifically, the cyclic ester-based organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0044] On the other hand, the organic solvent may be added and used without being limited to the organic solvents commonly used in non-aqueous electrolytes as needed. For example, it may further include at least one or more of ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0045] As the ether-based 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 of these can be used, but it is not limited thereto.

[0046] The glyme-based solvent has a higher dielectric constant and a lower surface tension than linear carbonate-based organic solvents and has less reactivity with metals. It may include at least one or more selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME), but is not limited thereto.

[0047] The nitrile-based solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0048] (3) Additive The non-aqueous electrolyte according to the present invention contains a compound represented by the following Chemical Formula 1.

[0049]

Chemical formula

[0050] In the Chemical Formula 1, R1 includes halogen, nitrile group, propargyl group, ester group, ether group, ketone group, carboxy 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, siloxane group, sulfone group, sulfonate group, sulfate group, or a combination of two or more thereof.

[0051] In the Chemical Formula 1, R2 is a substituent represented by the following Chemical Formula 2 or a substituent represented by the following Chemical Formula 3, n is an integer from 0 to 5, m is an integer from 1 to 6, and n + m is an integer from 1 to 6. At this time, when n and m are each 2 or more, two or more R1s may be the same as or different from each other, and two or more R2s may be the same as or different from each other.

[0052]

Chemical formula

[0053] In the Chemical Formula 2, R3 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and * is a bonding site.

[0054]

Chemical formula

[0055] In Chemical Formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and * is a bonding site.

[0056] The compound represented by Chemical Formula 1 is a coumarin-based compound containing a substituent containing fluorine and an ester group (Chemical Formula 2) and / or a substituent containing fluorine and an ether group (Chemical Formula 3). The coumarin structure contained in Chemical Formula 1 has a reaction energy with active oxygen higher than that of an organic solvent such as ethylene carbonate, and thus will bind to active oxygen prior to the organic solvent when active oxygen is generated. Therefore, when the compound of Chemical Formula 1 is contained in a non-aqueous electrolyte, the reactive oxygen compound generated at the positive electrode binds to the coumarin structure contained in the compound represented by Chemical Formula 1, having the effect of suppressing the decomposition of the electrolyte and the generation of gas.

[0057] Also, the compound represented by Chemical Formula 1 can form a stable SEI (Solid Electrolyte Interphase) film on the surface of the negative electrode while being rapidly reductively decomposed during initial activation. The coumarin structure contained in the compound represented by Chemical Formula 1 has strong reducibility at the negative electrode, and the ring structure is opened during the initial activation of the lithium secondary battery, enabling the formation of a polyethylene oxide-based polymer-type SEI layer. Such a polymer-type SEI layer has the advantages of excellent flexibility and recoverability. In addition, the substituent containing fluorine and an ester group (Chemical Formula 2) and / or a substituent containing fluorine and an ether group (Chemical Formula 3) contained in the compound represented by Chemical Formula 1 can increase the inorganic content of the SEI film and improve the durability of the SEI film at high temperatures to a high level. In particular, the ester group or ether group connecting the fluorine-containing substituent and the coumarin structure contains oxygen, which helps improve the lithium ion conductivity during the formation of the SEI film, and is preferable in that it promotes the SEI film formation reaction due to the decrease in the electron density of the substituent.

[0058] Therefore, a non-aqueous electrolyte containing a compound of Chemical Formula 1 containing both a coumarin structure and a fluorine- and ester group-containing substituent as an additive can rapidly form an organic / inorganic composite SEI film on the negative electrode, so that the high-temperature cycle characteristics and high-temperature storage characteristics of a lithium secondary battery containing the same can be improved at a remarkable level.

[0059] Specifically, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-A and a compound represented by the following Chemical Formula 1-B. More specifically, it may include a compound represented by the following Chemical Formula 1-A.

[0060]

Chemical formula

[0061]

Chemical formula

[0062] In Chemical Formula 1-A and Chemical Formula 1-B, the definitions of R1, R2, and n are as described above (as defined in Chemical Formula 1).

[0063] When R2 is substituted with coumarin as in Chemical Formula 1-A and Chemical Formula 1-B, it is preferable in terms of promoting the SEI film formation reaction of the coumarin structure itself. When R2 is substituted with coumarin as in Chemical Formula 1-A, the steric hindrance at the carbon in the 4th position (according to the IUPAC standard) of the ring structure of Chemical Formula 1 where an electrochemical reaction can occur is reduced, and the SEI film formation reaction can be further promoted.

[0064] More specifically, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-a and a compound represented by the following Chemical Formula 1-b. More specifically, it may include a compound represented by the following Chemical Formula 1-a.

[0065] [Chem.]

[0066] [Chem.]

[0067] In the aforementioned Chemical Formula 1-a and Chemical Formula 1-b, the definition of R2 is as described above (as defined in Chemical Formula 1).

[0068] In the aforementioned Chemical Formula 2, R3 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines. Specifically, it may be an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines. More specifically, it may be an alkyl group having 1 to 8 carbon atoms substituted with one or more fluorines. Even more specifically, it may be an alkyl group having 2 to 7 carbon atoms substituted with one or more fluorines. Even more specifically, it may be an alkyl group having 3 to 5 carbon atoms substituted with one or more fluorines.

[0069] More specifically, R3 is selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group. Even more specifically, R3 may be a nonafluorobutyl group. In this case, it is preferable in that it has a molecular weight that does not inhibit the mobility of lithium ions or the like, contains an appropriate level of inorganic substances, and can form a polymer film with improved durability.

[0070] In Chemical Formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines. Specifically, it may be an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines. More specifically, it may be an alkyl group having 1 to 8 carbon atoms substituted with one or more fluorines. Even more specifically, it may be an alkyl group having 2 to 7 carbon atoms substituted with one or more fluorines. Even more specifically, it may be an alkyl group having 3 to 5 carbon atoms substituted with one or more fluorines.

[0071] More specifically, R4 is selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group. Even more specifically, R3 may be a nonafluorobutyl group. In this case, it is preferable in that it has a molecular weight that does not inhibit the mobility of lithium ions or the like, contains an appropriate level of inorganic substances, and can form a polymer film with improved durability.

[0072] In Chemical Formula 1, R2 may be a substituent represented by Chemical Formula 2 or a substituent represented by Chemical Formula 3. Specifically, it may be a substituent represented by Chemical Formula 2.

[0073] Also, the compound represented by Chemical Formula 1 may specifically contain at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-a-1, Chemical Formula 1-a-2, Chemical Formula 1-a-3, Chemical Formula 1-b-1, Chemical Formula 1-b-2, Chemical Formula 1-b-3, Chemical Formula 1-c-1, Chemical Formula 1-c-2, Chemical Formula 1-c-3, Chemical Formula 1-d-1, Chemical Formula 1-d-2, and Chemical Formula 1-d-3.

[0074]

Chemical Structure

[0075]

Chemical Structure

[0076] [Chemistry]

[0077] [Chemistry]

[0078] [Chemistry]

[0079] [Chemistry]

[0080] [Chemistry]

[0081] [Chemistry]

[0082] [Chemistry]

[0083] [Chemistry]

[0084] [Chemistry]

[0085] [Chemistry]

[0086] The compound represented by the above Chemical Formula 1 may be contained in the non-aqueous electrolyte at 0.01% to 5% by weight, specifically 0.05% to 4.5% by weight, more specifically 0.1% to 4% by weight, and even more specifically 0.3% to 2.5% by weight. When the content of the compound represented by the above Chemical Formula 1 satisfies the above range, it can sufficiently exhibit the above-mentioned electrode interface protection effect, organic solvent decomposition and side reaction prevention effect, and is preferable in terms of preventing the increase in the resistance of the lithium secondary battery due to excessive addition and the resulting decrease in life performance.

[0087] The additive may further contain an additional additive together with the compound of Chemical Formula 1. The additional additive may be contained in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing and causing the collapse of the negative electrode in a high-power environment, or for reasons such as low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0088] Specifically, the additional additive may be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO2F2, LiODFB (lithium difluorooxalatoborate), LiBOB (lithium bis-(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (tris(trimethylsilyl)phosphite).

[0089] The additional additive may be contained in the non-aqueous electrolyte at 0.1% by weight to 15% by weight.

[0090] Lithium secondary battery Further, the present invention provides a lithium secondary battery including the aforementioned non-aqueous electrolyte.

[0091] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte.

[0092] At this time, the lithium secondary battery of the present invention can be manufactured by a conventional method known in the art. For example, after forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially laminated between the positive electrode and the negative electrode, the electrode assembly is inserted into the inside of a battery case, and the non-aqueous electrolyte according to the present invention is injected to manufacture it.

[0093] (1) Positive electrode The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0094] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, preferably aluminum.

[0095] The thickness of the positive electrode current collector usually has a thickness of 3 μm to 500 μm.

[0096] The positive electrode current collector may strengthen the binding force of the positive electrode active material by forming fine irregularities on the surface. For example, the positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0097] The positive electrode active material layer is disposed on at least one side of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one side or both sides of the positive electrode current collector.

[0098] The positive electrode active material layer may contain a positive electrode active material.

[0099] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium transition metal composite oxide containing at least one transition metal among nickel, cobalt, manganese, and aluminum and lithium, preferably a lithium transition metal composite oxide containing a transition metal containing nickel, cobalt, and manganese and lithium.

[0100] For example, as the lithium transition metal composite oxide, there are lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), 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), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), 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), etc.), 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, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2)O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and the like may be mentioned, and any one or two or more of these compounds may be included. Among them, from the viewpoint of being able to enhance the capacity characteristics and stability of the battery, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., 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, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and the like may be, considering the significance of the improvement effect by controlling the types and content ratios of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide is 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) It may be O2 or the like, and a mixture of any one or two or more of these can be used.

[0101] More specifically, the positive electrode active material may be a lithium transition metal composite oxide, and may contain 60 mol% or more of nickel based on the total number of moles of transition metals contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material is a lithium transition metal composite oxide, and the transition metal contains nickel; and at least one selected from manganese, cobalt, and aluminum, and the nickel contains 60 mol% or more, specifically 60 mol% to 90 mol% or more based on the total number of moles of the transition metals. When using a lithium transition metal composite oxide with such a high content of nickel together with the aforementioned non-aqueous electrolyte, it is preferable in that by-products in the gas generated by structural collapse can be reduced.

[0102] Further, the positive electrode active material may contain a lithium composite transition metal oxide represented by the following Chemical Formula 5.

[0103] [Chemical Formula 5] Li 1+x (Ni a Co b Mn c M d )O2

[0104] In Chemical Formula 5, M is one or more 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, 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.

[0105] Preferably, a, b, c, and d may be 0.70 ≦ a ≦ 0.95, 0.025 ≦ b ≦ 0.20, 0.025 ≦ c ≦ 0.20, and 0 ≦ d ≦ 0.05, respectively.

[0106] Further, a, b, c, and d may be respectively 0.80 ≦ a ≦ 0.95, 0.025 ≦ b ≦ 0.15, 0.025 ≦ c ≦ 0.15, and 0 ≦ d ≦ 0.05.

[0107] Further, a, b, c, and d may be respectively 0.85 ≦ a ≦ 0.90, 0.05 ≦ b ≦ 0.10, 0.05 ≦ c ≦ 0.10, and 0 ≦ d ≦ 0.03.

[0108] The positive electrode active material may be contained in the positive electrode active material layer at 80% to 99% by weight, preferably 92% to 98.5% by weight, in consideration of sufficient capacity exhibition of the positive electrode active material and the like.

[0109] The positive electrode active material layer may further contain a binder and / or a conductive material together with the aforementioned positive electrode active material.

[0110] The binder is a component that assists in binding the active material and the conductive material, etc., and binding to the current collector. Specifically, it may contain 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 fluorine rubber, preferably polyvinylidene fluoride.

[0111] The binder may be contained in the positive electrode active material layer at 1% to 20% by weight, preferably 1.2% to 10% by weight, from the viewpoint of sufficiently ensuring the binding force between components such as the positive electrode active material.

[0112] The conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause a chemical change and has conductivity. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, from the viewpoint of improving conductivity, it may contain carbon black.

[0113] From the viewpoint of sufficiently ensuring electrical conductivity, the conductive material may be contained in the positive electrode active material layer at 1% by weight to 20% by weight, preferably 1.2% by weight to 10% by weight.

[0114] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0115] The positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, followed by drying and rolling.

[0116] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0117] (2) Negative electrode The negative electrode faces the positive electrode.

[0118] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0119] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. Specifically, examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, and aluminum-cadmium alloys, etc. may be used.

[0120] The negative electrode current collector usually has a thickness of 3 μm to 500 μm.

[0121] The negative electrode current collector may strengthen the binding force of the negative electrode active material by forming fine irregularities on its surface. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven bodies.

[0122] The negative electrode active material layer is disposed on at least one side of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one side or both sides of the negative electrode current collector.

[0123] The negative electrode active material layer may contain a negative electrode active material.

[0124] The negative electrode active material is a material that can reversibly intercalate / deintercalate lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, (semi)metal-based active materials, and lithium metal. Specifically, it may include at least one selected from carbon-based active materials and (semi)metal-based active materials.

[0125] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0126] The average particle size (D 50 ) of the carbonaceous active material may be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to achieve structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0127] Specifically, the (semi)metallic active material may include at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn and lithium; an oxide of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0128] More specifically, the (semi)metallic active material may include a silicon-based active material.

[0129] The silicon-based active material may include a compound represented by SiO x (0 ≦ x < 2). Since SiO2 does not react with lithium ions, it cannot store lithium. Therefore, x is preferably within the above range.

[0130] The average particle size (D 50 ) of the silicon-based active material may be 1 μm to 30 μm, preferably 2 μm to 15 μm, in order to achieve structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0131] The negative electrode active material may be contained in the negative electrode active material layer at 60% by weight to 99% by weight.

[0132] The negative electrode active material layer may further contain a binder and / or a conductive material together with the negative electrode active material.

[0133] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector and thus improve the performance of the battery. For example, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., or various copolymers thereof may be included.

[0134] The binder may be contained in the negative electrode active material layer at 0.5% by weight to 30% by weight.

[0135] The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0136] The conductive material may be contained in the negative electrode active material layer at 0.5% by weight to 30% by weight.

[0137] The thickness of the negative electrode active material layer may be 10 μm to 200 μm.

[0138] The negative electrode can be manufactured by coating at least one surface of a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and / or a solvent for forming the negative electrode slurry, followed by drying and rolling.

[0139] The solvent for forming the negative electrode slurry may contain at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, for example, from the viewpoint of facilitating the dispersion of the negative electrode active material, the binder, and / or the conductive material. The solid content of the negative electrode slurry may be 20% by weight to 80% by weight.

[0140] (3) Separator In addition, as the separator, a normal porous polymer film conventionally used as a separator, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer may be used alone or in a laminated form, or a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used, but it is not limited thereto. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multilayer structure.

[0141] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can.

[0142] Hereinafter, the present invention will be described more specifically with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the technical idea, and it goes without saying that such variations and modifications belong to the scope of the appended claims.

[0143] Examples and Comparative Examples Example 1 (Manufacture of Non-aqueous Electrolyte) As the organic solvent, a mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 10:90 was used.

[0144] To the organic solvent, LiPF6 and LiFSI as lithium salts; the compound represented by the following Chemical Formula 1-a-1; and as additional additives, vinylene carbonate (VC), propane sultone (PS), ethylene sulfate (ESa), lithium difluorophosphate (LiDFP), and LiBF4 were added to produce a non-aqueous electrolyte.

[0145] The LiPF6 and the LiFSI were contained in the non-aqueous electrolyte at concentrations of 0.5 M and 1.0 M, respectively.

[0146] The compound represented by the following Chemical Formula 1-a-1 was contained in the non-aqueous electrolyte at 0.5% by weight.

[0147] The vinylene carbonate (VC), propane sultone (PS), ethylene sulfate (ESa), lithium difluorophosphate (LiDFP), and LiBF4 were contained in the non-aqueous electrolyte at 0.5% by weight, respectively.

[0148]

Chemical Formula

[0149] (Manufacture of Lithium Secondary Battery) Positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2), a conductive material (carbon nanotube), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP), which is a solvent, at a weight ratio of 98.0:0.7:1.3 to produce a positive electrode mixture slurry (solid content: 76.5% by weight). The positive electrode mixture slurry was applied to one surface of a positive electrode current collector (Al thin film) with a thickness of 12 μm, and drying and roll press were performed to produce a positive electrode.

[0150] A negative electrode active material (Si), a conductive material (carbon black), and a binder (styrene-butadiene rubber)-carboxymethyl cellulose (CMC) were added to N-methyl-2-pyrrolidone (NMP), which is a solvent, at a weight ratio of 70.0:20.3:9.7 to produce a negative electrode mixture slurry (solid content: 26% by weight). The negative electrode mixture slurry was applied to one surface of a negative electrode current collector (Cu thin film) with a thickness of 15 μm, and drying and roll press were performed to produce a negative electrode.

[0151] In a dry room, a polyethylene porous film separator was interposed between the positive electrode and the negative electrode produced above, and then the non-aqueous electrolyte produced above was injected to produce a secondary battery.

[0152] Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by the following Chemical Formula 1-b-1 was used instead of the compound represented by Chemical Formula 1-a-1.

[0153]

Chemical Formula

[0154] Example 3 An electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a compound represented by the chemical formula 1-a-1 was added to the non-aqueous electrolyte in a content of 0.1% by weight instead of 0.5% by weight to produce the non-aqueous electrolyte.

[0155] Example 4 An electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a compound represented by the chemical formula 1-a-1 was added to the non-aqueous electrolyte in a content of 4% by weight instead of 0.5% by weight to produce the non-aqueous electrolyte.

[0156] Example 5 An electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a compound represented by the following chemical formula 1-a-2 was added to the non-aqueous electrolyte in a content of 0.5% by weight instead of the compound represented by the chemical formula 1-a-1 to produce the non-aqueous electrolyte.

[0157]

Chemical formula

[0158] Example 6 An electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a compound represented by the following chemical formula 1-a-3 was added to the non-aqueous electrolyte in a content of 0.5% by weight instead of the compound represented by the chemical formula 1-a-1 to produce the non-aqueous electrolyte.

[0159]

Chemical formula

[0160] Example 7 An electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that a compound represented by the following chemical formula 1-c-1 was added to the non-aqueous electrolyte in a content of 0.5% by weight instead of the compound represented by the chemical formula 1-a-1 to produce the non-aqueous electrolyte.

[0161] [Chemical formula]

[0162] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-a-1 was not added.

[0163] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by the following Chemical Formula 4 was added instead of the compound represented by Chemical Formula 1-a-1.

[0164] [Chemical formula]

[0165] Experimental Example Experimental Example 1: Evaluation of High-Temperature Cycle Capacity Retention Rate The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above were charged to 4.2 V under the conditions of CC / CV and 0.33C at 45°C using an electrochemical charger / discharger, and then discharged to 2.5 V under the conditions of CC and 0.33C. One cycle was defined as one charge-discharge process, and 300 cycles of charge-discharge were performed to measure the capacity retention rate.

[0166] The capacity retention rate was calculated by the following formula, and the results are shown in Table 1 below.

[0167] Capacity retention rate (%) = (Discharge capacity after 300 cycles / Discharge capacity after 1 cycle) × 100

[0168] Experimental Example 2: Evaluation of High-Temperature Cycle Resistance Increase Rate The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above were charged to 4.2 V under the conditions of CC / CV and 0.33C at 45°C, and then discharged to 2.5 V under the conditions of CC and 0.33C. One cycle was defined as one charge-discharge process, and 300 cycles of charge-discharge were performed.

[0169] After one cycle of charge and discharge, the discharge capacity after one cycle was measured using an electrochemical charger. After adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference between the voltage before the pulse application and the voltage after the application.

[0170] After 300 cycles of charge and discharge, the resistance after 300 cycles was calculated by the same method as above, the resistance increase rate was calculated using the following formula, and the results are shown in Table 1 below.

[0171] Resistance increase rate (%) = (Resistance after 300 cycles - Initial resistance) / Initial resistance × 100

[0172] Experimental Example 3: Evaluation of volume increase rate after high-temperature cycle charge and discharge For the lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above, charge and discharge were performed for 300 cycles by the same method as in Experimental Example 1. At this time, the volume of the lithium secondary battery before charge and discharge (initial volume) and the volume of the lithium secondary battery after 300 cycles were measured, the volume increase rate was calculated by the following formula, and the results are shown in Table 3 below.

[0173] Volume increase rate (%) = (Volume of lithium secondary battery after 300 cycles - Initial volume) / Initial volume) × 100

[0174]

Table 1

[0175] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 7 using the non-aqueous electrolyte containing the compound represented by Chemical Formula 1 are superior in high-temperature cycle life performance, have a lower resistance increase rate due to cycling, and less volume increase due to cycling compared to the lithium secondary batteries of Comparative Examples 1 to 2.

[0176] Experimental Example 4: Evaluation of capacity retention rate after high-temperature storage The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above were charged at room temperature under constant current / constant voltage (CC / CV) conditions of 0.33C / 4.25V up to 4.25V / 55mA, and discharged at 0.33C down to 2.5V to perform initial charge and discharge. Thereafter, after charging up to 4.25V / 55mA at room temperature under constant current / constant voltage (CC / CV) of 0.33C / 4.25V, they were stored at 60°C for 12 weeks. After storage, the secondary batteries were charged at room temperature under constant current / constant voltage (CC / CV) conditions of 0.33C / 4.25V up to 4.25V / 55mA, and discharged at 0.33C down to 2.5V to measure the capacity during discharge.

[0177] The capacity retention rate was evaluated according to the following formula, and the results are shown in Table 2 below.

[0178] Capacity retention rate (%) = (Discharge capacity after 12-week storage / Initial discharge capacity) × 100

[0179] Experimental Example 5: Evaluation of resistance increase rate after high-temperature storage The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above were initially charged and discharged by the same method as in Experimental Example 4, and after confirming the capacity at room temperature, they were charged at SOC50 based on the discharge capacity and discharged at a current of 3C for 10 seconds. The resistance was measured from the voltage drop difference at this time as the initial resistance. Also, after storage at 60°C for 12 weeks, the resistance was measured by the same method as the final resistance, and the resistance increase rate was calculated according to the following formula. The results are shown in Table 2 below.

[0180] Resistance increase rate (%) = (Final resistance - Initial resistance) / (Initial resistance) × 100

[0181] Experimental Example 6: Evaluation of volume increase rate after high-temperature storage The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 2 manufactured above were initially charged and discharged by the same method as in Experimental Example 4, and each battery was set to SOC50 based on the discharge capacity to measure the volume, which was defined as the initial volume. The volume measured after high-temperature storage at 60°C for 12 weeks at SOC100% was defined as the final volume, and the volume increase rate of the battery was calculated according to the following formula. The results are shown in Table 2 below.

[0182] Volume increase rate (%) = ((Final volume - Initial volume) / Initial volume) × 100

[0183]

Table 2

[0184] Referring to Table 2, it can be confirmed that the lithium secondary batteries of Examples 1 to 7 using the non-aqueous electrolyte containing the compound represented by Chemical Formula 1 are excellent in high-temperature storage life performance, have a low resistance increase rate, and little volume increase, compared with the lithium secondary batteries of Comparative Examples 1 to 2.

Claims

1. A lithium salt, an organic solvent, and an additive, and the non-aqueous electrolyte contains: The additive contains a compound represented by the following Chemical Formula 1: 【Chemical 1】 (In the above chemical formula 1, R １ represents a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy 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 siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof, R ２ is a substituent represented by the following chemical formula 2 or a substituent represented by the following chemical formula 3, 【Chemical 2】 In the above chemical formula 2, R ３ is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, * is a bonding site, [Chemical Formula 3] In the above chemical formula 3, R ４ is selected from an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, an alkenyl group having 1 to 10 carbon atoms substituted with one or more fluorines, and an alkynyl group having 1 to 10 carbon atoms substituted with one or more fluorines, * is a bonding site, n is an integer from 0 to 5, m is an integer from 1 to 6, and n + m is an integer from 1 to 6.)

2. The non-aqueous electrolyte according to Claim 1, wherein the compound represented by Chemical Formula 1 contains at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-A and a compound represented by the following Chemical Formula 1-B: 【Chemical Formula 4】 (In the above Chemical Formula 1-A and Chemical Formula 1-B, the definitions of R １ , R ２ , and n are as defined in the above Chemical Formula 1.)

3. The non-aqueous electrolyte according to Claim 1, wherein the compound represented by Chemical Formula 1 contains at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-a and a compound represented by the following Chemical Formula 1-b: 【Chemical Formula 5】 (In the above Chemical Formula 1-a and Chemical Formula 1-b, the definition of R ２ is as defined in the above Chemical Formula 1.)

4. R ３ and R ４ is each selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group, the non-aqueous electrolyte according to claim 1.

5. The non-aqueous electrolyte according to Claim 1, wherein the compound represented by Chemical Formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01% by weight to 5% by weight.

6. The lithium salt is 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 ), and the non-aqueous electrolyte according to claim 1, comprising at least one selected from the group consisting of.

7. The non-aqueous electrolyte according to Claim 1, wherein the lithium salt is contained in the non-aqueous electrolyte at a molar concentration of 0.5 M to 5.0 M.

8. The non-aqueous electrolyte according to Claim 1, wherein the organic solvent contains 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.

9. The additive is at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO ２ F ２ , LiODFB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalato)borate), TMSSa (3-trimethoxysilyl-propyl-N-aniline), and TMSSi (tris(trimethylsilyl)phosphite), and further includes at least one additional additive selected from the group consisting of, the non-aqueous electrolyte according to claim 1.

10. a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte according to Claim 1, a lithium secondary battery.

Images