Nonaqueous electrolyte and lithium secondary battery containing 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 August 1, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

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

[0003] In recent years, the application areas of lithium secondary batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, communication, and computer equipment to power storage and supply for large-area devices such as automobiles and power storage devices. Accordingly, there has been an increasing demand for high-capacity, high-power, and highly stable secondary batteries.

[0004] In particular, high capacity, high power output, and long life characteristics are important for lithium secondary batteries for automotive applications. To increase the capacity of lithium secondary batteries, it is possible to use a positive electrode active material with a high nickel content, which has high energy density but low stability, or to operate the lithium secondary battery at a high voltage.

[0005] However, when a lithium secondary battery is operated under the above conditions, as charging and discharging proceeds, side reactions caused by electrolyte degradation can cause deterioration of the coatings formed on the surfaces of the positive and negative electrodes or the structure of the electrode surfaces, leading to the elution of transition metal ions from the surface of the positive electrode. The eluted transition metal ions are then electro-deposited on the negative electrode, reducing the passivation ability of the negative electrode's solid electrolyte interface (SEI) coating, resulting in the degradation of the negative electrode. This degradation of the secondary battery tends to accelerate when the positive electrode potential is increased or the battery is exposed to high temperatures.

[0006] Furthermore, when a lithium secondary battery is used continuously for a long time or left at a high temperature, gas is generated and the thickness of the battery increases, which is called swelling. It is known that the amount of gas generated at this time depends on the state of the SEI.

[0007] Therefore, in order to solve these problems, research and development efforts are being conducted to find 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 lithium secondary batteries, and improve their stability at high temperatures. Summary of the Invention [Problem to be solved by the invention]

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

[0009] Another object of the present invention is to provide a lithium secondary battery that contains the above-mentioned nonaqueous electrolyte, thereby improving high-temperature cycle characteristics and high-temperature storage performance, and thereby improving various performances. [Means for solving the problem]

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

[0011] [ka]

[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: [ka] In the above Chemical Formula 2, R3 is selected from an alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, an alkenyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and an alkynyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, * is a bonding site, [ka] In the above Chemical Formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, an alkenyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and an alkynyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, * is a bonding site, n is an integer of 0 to 5, m is an integer of 1 to 6, and n+m is an integer of 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 non-aqueous electrolyte. [Effects of the Invention]

[0014] The nonaqueous electrolyte of the present invention is characterized by including, as an additive, a compound represented by Chemical Formula 1, which is based on a coumarin structure. The additive is capable of rapidly undergoing reductive decomposition during initial activation to form a stable SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode. In particular, the substituents containing fluorine and an ester or ether group contained in the compound represented by Chemical Formula 1 increase the inorganic content of the SEI coating, thereby improving the durability of the SEI coating at high temperatures. Furthermore, the nonaqueous electrolyte of the present invention has the effect of suppressing electrolyte decomposition and gas generation by binding reactive oxygen compounds generated at the positive electrode with the coumarin structure contained in the compound represented by Chemical Formula 1.

[0015] Therefore, the lithium secondary battery including the non-aqueous electrolyte can have improved high-temperature cycle characteristics and high-temperature storage characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0017] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] On the other hand, before describing the present invention, unless otherwise specified in the present invention, "*" means a linking portion (bonding site) between the ends of the same or different atoms or chemical formulae.

[0019] Furthermore, in the description of "number of carbon atoms a to b" herein, "a" and "b" refer to 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" refers to an alkyl group containing 1 to 5 carbon atoms, i.e., CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, CH3)2CHCH2CH2-, (CH3)2CHCH2CH2-, etc.

[0020] In this specification, the alkyl group, alkenyl group, or alkynyl group may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is replaced with an element other than hydrogen, such as 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.

[0021] The present invention will now 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] [ka]

[0025] In 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.

[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 of 0 to 5, m is an integer of 1 to 6, and n+m is an integer of 1 to 6.

[0027] [ka]

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

[0029] [ka]

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

[0031] The nonaqueous electrolyte of the present invention is characterized by including a compound represented by Chemical Formula 1, which has a coumarin structure, as an additive. The additive can be rapidly reductively decomposed during initial activation to form a stable SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode. In particular, the substituents containing fluorine and an ester or ether group contained in the compound represented by Chemical Formula 1 increase the inorganic content of the SEI coating, thereby improving the durability of the SEI coating at high temperatures. Furthermore, the nonaqueous electrolyte of the present invention effectively inhibits electrolyte decomposition and gas generation by binding reactive oxygen compounds generated at the positive electrode with the coumarin structure contained in the compound represented by Chemical Formula 1. Therefore, lithium secondary batteries containing the nonaqueous electrolyte of the present invention can exhibit 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 that are commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without any limitation. For example, the lithium salt may contain Li as a cation. + and the anion is 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 - The composition may include at least one selected from the group consisting of:

[0033] Specifically, the lithium salts include 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). Specifically, 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). Specifically, the lithium salt may include 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, at a concentration of 0.8 M to 4 M, more specifically, at a concentration of 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transport number (Li +The transference number and dissociation degree of lithium ions are improved, which can improve the output characteristics of the battery.

[0035] (2) Organic Solvent The organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries and minimizes decomposition due to oxidation reactions during charging and discharging of the secondary battery.

[0036] Specifically, 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.

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

[0038] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and easily dissociates a lithium salt in the electrolyte. Specifically, the cyclic carbonate organic solvent may include 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, and more specifically, may include at least one organic solvent selected from the group consisting of ethylene carbonate and fluoroethylene carbonate, more specifically, fluoroethylene carbonate.

[0039] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and may specifically 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, and more specifically may include diethyl carbonate (DEC).

[0040] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. In this case, the cyclic carbonate organic solvent and the linear carbonate 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 organic solvent and the linear carbonate organic solvent satisfies the above range, both high dielectric constant and low viscosity characteristics are satisfied, and excellent ionic conductivity characteristics can be achieved.

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

[0042] Specifically, the linear ester organic solvent may 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.

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

[0044] Meanwhile, the organic solvent may further include, as needed, any organic solvent commonly used in non-aqueous electrolytes, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0045] The ether solvent may be 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, but is not limited thereto.

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

[0047] The nitrile 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) Additives The non-aqueous electrolyte according to the present invention contains a compound represented by the following chemical formula 1.

[0049] [ka]

[0050] In 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.

[0051] 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, where n is an integer of 0 to 5, m is an integer of 1 to 6, and n+m is an integer of 1 to 6. In this case, when n and m are each 2 or more, two or more R1s may be the same or different, and two or more R2s may be the same or different.

[0052] [ka]

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

[0054] [ka]

[0055] In Chemical Formula 3, R4 is selected from an alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, an alkenyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and an alkynyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and * represents 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 higher reaction energy with active oxygen than organic solvents such as ethylene carbonate, so when active oxygen is generated, it binds with the active oxygen before the organic solvent does. Therefore, when the compound represented by Chemical Formula 1 is contained in a non-aqueous electrolyte, the reactive oxygen compounds generated at the positive electrode bind with the coumarin structure contained in the compound represented by Chemical Formula 1, thereby suppressing electrolyte decomposition and gas generation.

[0057] Furthermore, the compound represented by Chemical Formula 1 can be rapidly reductively decomposed during initial activation to form a stable SEI (Solid Electrolyte Interphase) coating on the surface of the negative electrode. 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 initial activation of the lithium secondary battery, allowing the formation of a polyethylene oxide-based polymer-type SEI layer. Such a polymer-type SEI layer has the advantages of excellent flexibility and recovery. Furthermore, the substituents containing fluorine and an ester group (Chemical Formula 2) and / or 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 coating and significantly improve the durability of the SEI coating at high temperatures. In particular, the ester group or ether group connecting the fluorine-containing substituent and the coumarin structure contains oxygen, which is preferable because it helps improve lithium ion conductivity during SEI coating formation and accelerates the SEI coating formation reaction by reducing the electron density of the substituent.

[0058] Therefore, a non-aqueous electrolyte containing the compound of Chemical Formula 1, which contains 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, thereby significantly improving the high-temperature cycle characteristics and high-temperature storage characteristics of a lithium secondary battery containing the same.

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

[0060] [ka]

[0061] [ka]

[0062] In the chemical formula 1-A and the chemical formula 1-B, R1, R2, and n are defined as above (as defined in the chemical formula 1).

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

[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, and more specifically, may include a compound represented by the following Chemical Formula 1-a:

[0065] [ka]

[0066] [ka]

[0067] In the chemical formula 1-a and the chemical formula 1-b, R2 is defined as above (as defined in the chemical formula 1).

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

[0069] More specifically, R3 is selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group, and even more specifically, R3 may be a nonafluorobutyl group, which is preferable in that it has a molecular weight that does not inhibit the mobility of lithium ions and the like, and also contains an appropriate level of inorganic matter, allowing the formation of a polymer coating with improved durability.

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

[0071] More specifically, R4 is selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group, and even more specifically, R3 may be a nonafluorobutyl group, which is preferable in that it has a molecular weight that does not inhibit the mobility of lithium ions and the like, and also contains an appropriate level of inorganic matter, allowing the formation of a polymer coating with improved durability.

[0072] In the above Chemical Formula 1, R2 may be a substituent represented by the above Chemical Formula 2 or a substituent represented by the above Chemical Formula 3, specifically, a substituent represented by the above Chemical Formula 2.

[0073] Furthermore, the compound represented by Chemical Formula 1 may specifically include at least one selected from the group consisting of compounds represented by 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] [ka]

[0075] [ka]

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

[0087] The additive may further include an additional additive in addition to the compound of Formula 1. The additional additive may be included in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from being decomposed and causing the collapse of the negative electrode in a high-power environment, or to improve low-temperature high-rate discharge characteristics, high-temperature stability, prevent overcharge, and suppress battery expansion 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 included in the non-aqueous electrolyte in an amount of 0.1 wt % to 15 wt %.

[0090] Lithium secondary battery The present invention also provides a lithium secondary battery containing the above-mentioned 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 non-aqueous electrolyte.

[0092] The lithium secondary battery of the present invention can be manufactured by a conventional method known in the art, for example, by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially stacked between the positive electrode and the negative electrode, inserting the electrode assembly into a battery case, and injecting the nonaqueous electrolyte according to the present invention into the battery case.

[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 surface of the positive electrode current collector.

[0094] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes 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, sintered carbon, and an aluminum-cadmium alloy, and preferably aluminum.

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

[0096] The positive electrode current collector may have a surface with fine irregularities to strengthen the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[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 of 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<000​​​​​​​​​​​​​​​)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<e000060>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 point that the capacity characteristics and stability of the battery can be enhanced, 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, and 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)O2, etc., and any one or a mixture of two or more of these can be used.

[0101] More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing 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 may be a lithium transition metal composite oxide, the transition metals of which include nickel and at least one selected from manganese, cobalt, and aluminum, and the nickel content may be 60 mol % or more, specifically 60 mol % to 90 mol % or more, based on the total number of moles of the transition metals. When such a lithium transition metal composite oxide containing a high content of nickel is used together with the nonaqueous electrolyte solution, it is preferable because it can reduce by-products in the gas generated by structural collapse.

[0102] The positive electrode active material may include 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 the above 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 each independent element, and 0≦x≦0.2, 0.50≦a<1, 0 <b≦0.25、0<c≦0.25、0≦d≦0.1、a+b+c+d=1である。

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

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

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

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

[0109] The positive electrode active material layer may further contain a binder and / or a conductive material in addition to the positive electrode active material.

[0110] The binder is a component that assists in binding the active material and conductive material and the current collector, and specifically includes polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, and ethylene-propylene-diene. Tar The rubber composition may contain at least one selected from the group consisting of polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0111] The binder may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight, in order to ensure sufficient binding strength 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 chemical changes 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, and 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, the positive electrode conductive material may include carbon black in order to improve conductivity.

[0113] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

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

[0115] The positive electrode may be fabricated 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), and the solid content of the positive electrode slurry may be 40 wt % to 90 wt %, specifically 50 wt % to 80 wt %.

[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 surface of the negative electrode current collector.

[0119] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

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

[0121] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength 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, mesh, porous material, foam, or nonwoven fabric.

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

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

[0124] The negative electrode active material is a material capable of reversibly intercalating / deintercalating lithium ions, and may include at least one selected from the group consisting of a carbon-based active material, a (quasi)metal-based active material, and lithium metal, and specifically may include at least one selected from a carbon-based active material and a (quasi)metal-based active material.

[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 includes at least one selected from the group consisting of artificial graphite and natural graphite.

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

[0127] Specifically, the (quasi-)metallic active material may include at least one (quasi-)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 (quasi-)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 oxide of at least one (quasi-)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 (quasi)metallic active material may include a silicon-based active material.

[0129] The silicon-based active material is SiO x (0≦x<2). SiO2 does not react with lithium ions and therefore cannot store lithium. Therefore, it is preferable that x is within the above range.

[0130] The average particle size (D 50 ) may be 1 μm to 30 μm, preferably 2 μm to 15 μm, from the viewpoint of improving structural stability during charge and discharge and reducing side reactions with the electrolyte.

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

[0132] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0133] The binder is used to improve the adhesive strength between the negative electrode active material layer and the negative electrode current collector, thereby improving battery performance. For example, the binder may include at least one selected from the group consisting of 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 substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0134] The binder may be contained in the negative electrode active material layer in an amount of 0.5 wt % to 30 wt %.

[0135] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and 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 conductive materials such as polyphenylene derivatives may be used.

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

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

[0138] The negative electrode may be prepared 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 include at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol, and isopropyl alcohol, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry may be 20% by weight to 80% by weight.

[0140] (3) Separator The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of a high-melting point glass fiber or polyethylene terephthalate fiber, but is not limited to these. Furthermore, to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

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

[0142] The present invention will be described in more detail below 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 will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0143] Examples and Comparative Examples Example 1 (Production 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] A non-aqueous electrolyte was prepared by adding lithium salts, LiPF6 and LiFSI; a compound represented by the following chemical formula 1-a-1; and additional additives, such as vinylene carbonate (VC), propane sultone (PS), ethylene sulfate (ESa), lithium difluorophosphate (LiDFP), and LiBF4, to the organic solvent.

[0145] The LiPF6 and 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 wt %.

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

[0148] [ka]

[0149] (Lithium secondary battery manufacturing) Cathode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 A cathode mixture slurry (solid content 76.5 wt%) was prepared by adding O2, a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) in a weight ratio of 98.0:0.7:1.3 to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0150] Anode active material (Si), conductive material (carbon black), binder (styrene-butadiene rubber)-carboxymethyl cellulose (CMC) were mixed in a weight ratio of 70.0:20.3:9.7 with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare anode mixture slurry (solid content 26 wt%). The anode mixture slurry was applied to one side of a 15 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

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

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

[0153] [ka]

[0154] Example 3 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 1-a-1 was added to the non-aqueous electrolyte in an amount of 0.1 wt % instead of 0.5 wt % to prepare the non-aqueous electrolyte.

[0155] Example 4 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 1-a-1 was added to the non-aqueous electrolyte in an amount of 4 wt % instead of 0.5 wt % to prepare the non-aqueous electrolyte.

[0156] Example 5 A nonaqueous electrolyte and a lithium secondary battery were manufactured 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 nonaqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by Chemical Formula 1-a-1.

[0157] [ka]

[0158] Example 6 A nonaqueous electrolyte and a lithium secondary battery were manufactured 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 nonaqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by Chemical Formula 1-a-1.

[0159] [ka]

[0160] Example 7 A nonaqueous electrolyte and a lithium secondary battery were manufactured 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 nonaqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by Chemical Formula 1-a-1.

[0161] [ka]

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

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

[0164] [ka]

[0165] Experimental Example Experimental Example 1: Evaluation of high-temperature cycle capacity retention The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 and 2 manufactured above were charged to 4.2 V at 45° C. under CC / CV conditions at 0.33 C using an electrochemical charger / discharger, and then discharged to 2.5 V under CC conditions at 0.33 C, with one cycle being defined as 300 charge / discharge cycles, and the capacity retention rate was measured.

[0166] The capacity retention rate was calculated using 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) x 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 and 2 manufactured above were subjected to 300 charge / discharge cycles, with one cycle being charging to 4.2 V at 45°C under CC / CV conditions at 0.33 C, and then discharging to 2.5 V under CC conditions at 0.33 C.

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

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

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

[0172] Experimental Example 3: Evaluation of volume increase rate after high-temperature cycle charge / discharge The lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 and 2 manufactured above were subjected to 300 cycles of charge and discharge in the same manner as in Experimental Example 1. At this time, the volumes of the lithium secondary batteries before charge and discharge (initial volumes) and after 300 cycles were measured, and the volume increase rates were calculated using 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 seen that the lithium secondary batteries of Examples 1 to 7, which use a nonaqueous electrolyte containing the compound represented by Chemical Formula 1, have superior high-temperature cycle life performance compared to the lithium secondary batteries of Comparative Examples 1 and 2, and also have a lower rate of resistance increase due to cycling and a smaller volume increase due to cycling.

[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 and 2 prepared above were initially charged at room temperature under constant current / constant voltage (CC / CV) conditions of 0.33 C / 4.25 V to 4.25 V / 55 mA, and then discharged at 0.33 C to 2.5 V, thereby conducting an initial charge-discharge. Subsequently, they were charged at room temperature under constant current / constant voltage (CC / CV) conditions of 0.33 C / 4.25 V to 4.25 V / 55 mA, and then 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 0.33 C / 4.25 V to 4.25 V / 55 mA, and then discharged at 0.33 C to 2.5 V, and the discharge capacities were measured.

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

[0178] Capacity retention rate (%) = (discharge capacity after 12 weeks of storage / initial discharge capacity) x 100

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

[0180] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) x 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 and 2 prepared above were initially charged and discharged in the same manner as in Experimental Example 4. Each battery was set to an SOC of 50 based on the discharge capacity, and the volume was measured and defined as the initial volume. The volume measured after 12 weeks of high-temperature storage at 60°C with an SOC of 100% was defined as the final volume, and the volume increase rate of the battery was calculated using the following formula. The results are shown in Table 2 below.

[0182] Volume increase rate (%) = (final volume - initial volume) / initial volume) x 100

[0183] [Table 2]

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

Claims

1. A lithium salt, an organic solvent; an additive, The additive comprises a non-aqueous electrolyte containing a compound represented by the following Chemical Formula 1: 【Chemistry 1】 (In the above chemical formula 1, R １ does not exist, R ２ is a substituent represented by the following chemical formula 2 or a substituent represented by the following chemical formula 3, 【Chemistry 2】 In the above chemical formula 2, R ３ is selected from an alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, an alkenyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and an alkynyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, * is a bonding site, 【Transformation 3】 In the above chemical formula 3, R ４ is selected from an alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, an alkenyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, and an alkynyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms, * is a bonding site, n is 0, m is an integer from 1 to 6, and n+m is an integer from 1 to 6.

2. The compound represented by Chemical Formula 1 includes at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-A and compounds represented by the following Chemical Formula 1-B: 【Chemistry 4】 (In the above Chemical Formula 1-A and the above Chemical Formula 1-B, R １ , R ２ , n is defined as in Chemical Formula 1.

3. The compound represented by Chemical Formula 1 includes at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-a and compounds represented by the following Chemical Formula 1-b: 【Transformation 5】 (In the chemical formula 1-a and the chemical formula 1-b, R ２ is defined as in Chemical Formula 1 above.)

4. R ３ and R ４ and are each selected from the group consisting of a pentafluoroethyl group, a nonafluorobutyl group, and a heptadecafluoroheptyl group.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, wherein the compound represented by Chemical Formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01 wt% to 5 wt%.

6. The lithium salts include LiCl, LiBr, LiI, and 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 2. The non-aqueous electrolyte according to claim 1, comprising at least one selected from the group consisting of:

7. 2. 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. 2. The nonaqueous electrolyte according to claim 1, wherein the organic solvent includes at least one selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent.

9. The additives include vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO ２ F ２ 2. The non-aqueous electrolyte of claim 1, further comprising at least one additional additive selected from the group consisting of LiODFB (lithium difluorooxalatoborate), LiBOB (lithium bis(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (tris(trimethylsilyl)phosphite).

10. A positive electrode and a negative electrode facing the positive electrode; a separator interposed between the positive electrode and the negative electrode; A lithium secondary battery comprising the non-aqueous electrolyte according to claim 1.

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