Nonaqueous electrolyte and lithium secondary battery comprising same

Abstract

The present invention provides a non-aqueous electrolyte including a lithium salt, an organic solvent, and an additive, in which the additive includes a compound represented by a specific formula. The nonaqueous electrolyte of the present invention comprises an additive having effects of film protection and electrode HF removal, and thus can improve cycle characteristics and high-temperature storage characteristics of a lithium secondary battery comprising the nonaqueous electrolyte.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2022-0101641 filed on August 12, 2022, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

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

[0004] Recently, as the application fields of lithium secondary batteries are rapidly expanding to power supplies for electronic devices such as electrical devices, electronic devices, communication devices and computers, and power storage power supplies for large devices such as automobiles and power storage devices, the demand for secondary batteries with high capacity, high output and high stability is increasing.

[0005] In particular, high capacity, high output and long life characteristics have become important in lithium secondary batteries for automobiles. In order to increase the high capacity of lithium secondary batteries, high Ni positive electrode active materials with high energy density but low stability can be used, or it can be considered to drive lithium secondary batteries at high voltage.

[0006] However, when the lithium secondary battery is driven under the above conditions, as charging and discharging proceed, the surface structure of the electrode or the film formed on the surface of the positive and negative electrodes deteriorates due to side reactions caused by the deterioration of the electrolyte, so transition metal ions may be dissolved from the surface of the positive electrode. As mentioned above, since the dissolved transition metal ions are electro-deposited on the negative electrode and reduce the passivation ability of the solid electrolyte interface (SEI) of the negative electrode, the limitation of negative electrode degradation occurs. This deterioration phenomenon of the secondary battery tends to be further accelerated when the potential of the positive electrode rises or is exposed to high temperature.

[0007] Furthermore, when lithium secondary batteries are used continuously for a long period of time or left at high temperatures, a so-called swelling phenomenon is known in which 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 SEI.

[0008] Therefore, in order to solve such technical problems, attempts have been made to research and develop methods that can suppress the dissolution of metal ions from the positive electrode, form a stable SEI film on the negative electrode, thereby reducing the expansion phenomenon of the lithium secondary battery and improving the high temperature stability. Summary of the invention

[0009] Technical issues

[0010] One aspect of the present invention provides a nonaqueous electrolyte that can reduce side reactions of an electrolyte by forming a stable film on positive / negative electrodes and has an excellent scavenging effect on Lewis acids such as HF.

[0011] In addition, another aspect of the present invention provides a lithium secondary battery including the above-mentioned nonaqueous electrolyte and having improved high temperature life performance and high temperature storage performance, thereby improving overall performance.

[0012] Technical Solution

[0013] According to one aspect of the present invention, there is provided a non-aqueous electrolyte comprising: a lithium salt; an organic solvent; and an additive, wherein the additive comprises a compound represented by the following formula 1:

[0014] [Formula 1]

[0015]

[0016] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, boron, borate, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate or a combination of two or more thereof, and at least one of R1 to R6 includes an isocyanate group.

[0017] In addition, according to another aspect of the present invention, there is provided a lithium secondary battery comprising: a positive electrode; a negative electrode opposite to the positive electrode; a separator disposed between the negative electrode and the positive electrode; and the above-mentioned nonaqueous electrolyte.

[0018] Beneficial effects

[0019] The non-aqueous electrolyte of the present invention comprises a propane sultone compound substituted with a substituent comprising an isocyanate group as an additive. The additive can form a film with excellent durability in the positive / negative electrode, thereby having the effect of inhibiting the dissolution of transition metals from the positive electrode and the electrolyte side reaction in the electrode. In addition, the additive contains an isocyanate group as a substituent, which can remove Lewis acids such as HF that may be generated during high temperature exposure (HF removal effect), thereby preventing the decomposition of the organic solvent and the decomposition of the electrode film caused by such Lewis acid.

[0020] Therefore, a lithium secondary battery including the above nonaqueous electrolyte may have improved high temperature life performance and high temperature storage performance. DETAILED DESCRIPTION

[0021] It should be understood that the terms or words used in the present specification and claims should not be interpreted as limited to having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical ideas of the present invention based on the principle that the inventor can appropriately define the concepts of the terms to best explain the present invention.

[0022] It should also be understood that the terms “includes,” “comprising,” or “having” in this specification specify the presence of stated features, quantities, steps, elements, or a combination thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or a combination thereof.

[0023] Meanwhile, before describing the present invention, unless otherwise specified in the present invention, the expression "*" represents the same or different atoms or moieties (binding sites) connecting between the terminals of the formula.

[0024] In addition, the expressions "a" and "b" in the description of "a to b carbon atoms" in this specification refer to the number of carbon atoms contained in a particular functional group. That is, the functional group may include "a" to "b" carbon atoms. For example, "an alkyl group having 1 to 5 carbon atoms" refers to an alkyl group containing 1 to 5 carbon atoms, i.e., CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2-, (CH3)2CHCH2-, etc.

[0025] In addition, in the present specification, the alkyl group, the alkenyl group or the alkynyl group may be all substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen, and for example, means 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 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 halogenated aryl group having 6 to 20 carbon atoms, an isocyanate group, a sulfone group, a sulfonate group, an ether group, and the like.

[0026] Hereinafter, the present invention will be described in more detail.

[0027] Non-aqueous electrolytes

[0028] 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.

[0029] The nonaqueous electrolyte of the present invention comprises: a lithium salt; an organic solvent; and an additive, wherein the additive comprises a compound represented by the following formula 1:

[0030] [Formula 1]

[0031]

[0032] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, boron, borate, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate or a combination of two or more thereof, and at least one of R1 to R6 includes an isocyanate group.

[0033] The non-aqueous electrolyte of the present invention comprises a compound represented by the above formula 1 based on the propane sultone structure as an additive. The additive can form a film with excellent durability in the positive / negative electrode, thereby having the effect of inhibiting the dissolution of transition metals from the positive electrode and the electrolyte side reaction in the electrode. In addition, the additive contains an isocyanate group as a substituent, which can remove Lewis acids such as HF that may be generated when exposed to high temperatures (HF removal effect), thereby preventing the decomposition of organic solvents and electrode films caused by such Lewis acids. Therefore, the lithium secondary battery comprising the above-mentioned non-aqueous electrolyte can have improved high temperature cycle characteristics and high temperature storage characteristics.

[0034] (1) Lithium salt

[0035] 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 may include Li + as a cation, and may contain as an anion at least one selected from the group consisting of: F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - 、AlO4 - 、AlCl4 - PF6 - 、SbF6 - 、AsF6 - , B 10 Cl 10 - 、BF2C2O4 - , BC4O8 - PF4C2O4 - PF2C4O8 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2- 、(CF3)5PF - 、(CF3)6P - CF3SO3 - 、C4F9SO3 - CF3CF2SO3 - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - .

[0036] Specifically, the lithium salt may include a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2F)2(LiFSI), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiN(SO2CF2CF3)2(LiBETI). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2F)2(LiFSI), LiN(SO2CF3)2(LiTFSI), LiN(SO2F)2(LiFSI) and LiBETI LiN(SO2CF2CF3)2(LiBETI).

[0037] The lithium salt may be contained in the nonaqueous electrolyte at a concentration of 0.5 M to 5.0 M, specifically 0.8 M to 4.0 M, and more specifically 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion yield (Li + transfer number) and the dissociation level of lithium ions, thereby improving the output characteristics of the battery.

[0038] (2) Organic solvents

[0039] The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as it can minimize decomposition by oxidation reaction or the like during charge and discharge of the secondary battery.

[0040] Specifically, the organic solvent includes 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.

[0041] Specifically, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixture thereof.

[0042] The cyclic carbonate organic solvent is a high-viscosity organic solvent that can effectively dissociate the lithium salt in the electrolyte due to its high dielectric constant. Specifically, it 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 and vinylene carbonate, and more specifically, it may include ethylene carbonate.

[0043] In addition, the straight-chain carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant, and specifically, may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate, and more specifically, may include ethyl methyl carbonate (EMC).

[0044] The organic solvent can be a mixture of a cyclic carbonate organic solvent and a straight-chain carbonate organic solvent. In this case, the cyclic carbonate organic solvent and the straight-chain carbonate organic solvent can be mixed in a volume ratio of 10:90 to 40:60, specifically in a volume ratio of 10:90 to 30:70, more specifically in a volume ratio of 15:85 to 30:70. When the mixing ratio of the cyclic carbonate organic solvent and the straight-chain carbonate organic solvent meets the above range, high dielectric constant and low viscosity characteristics can be satisfied simultaneously, and excellent ionic conductive characteristics can be achieved.

[0045] In addition, in order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate organic solvent selected from cyclic carbonate organic solvents and linear carbonate organic solvents, the organic solvent may also contain at least one ester organic solvent selected from linear ester organic solvents and cyclic ester organic solvents.

[0046] The linear ester-based 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.

[0047] In addition, the cyclic ester organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0048] Meanwhile, if necessary, any organic solvent generally used in non-aqueous electrolytes may be additionally used as the organic solvent without limitation. For example, at least one organic solvent selected from ether organic solvents, glyme organic solvents, and nitrile organic solvents may be further included.

[0049] As the ether solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL) and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL) or a mixture of two or more thereof may be used, but the ether solvent is not limited thereto.

[0050] Glyme solvents are solvents having a higher dielectric constant, lower surface tension and lower reactivity with metals than linear carbonate organic solvents, and may include at least one selected from the group consisting of dimethoxyethane (glyme dimethyl ether, DME), diethoxyethane, diglyme, triglyme and tetraglyme (TEGDME), but are not limited thereto.

[0051] The nitrile organic solvent may include at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanenitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorobenzene acetonitrile and 4-fluorobenzene acetonitrile, but the nitrile organic solvent is not limited thereto.

[0052] (3) Additives

[0053] The nonaqueous electrolyte of the present invention includes a compound represented by the following formula 1:

[0054] [Formula 1]

[0055]

[0056] In the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, boron, borate, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate or a combination of two or more thereof, and at least one of R1 to R6 includes an isocyanate group.

[0057] The compound represented by the above formula 1 can form a film with excellent durability in the positive / negative electrode, thereby having the effect of inhibiting the dissolution of transition metals from the positive electrode and the electrolyte side reaction in the electrode. In addition, the additive includes an isocyanate group as a substituent, which can remove the Lewis acid (such as HF, etc.) of the lithium salt that may be produced when exposed to high temperature (HF removal effect), thereby preventing the decomposition of the organic solvent caused by such Lewis acid and the decomposition of the electrode film. Therefore, the compound represented by the above formula 1 including both the propane sultone structure and the isocyanate group can improve the high temperature life performance and the high temperature storage performance to a significant level.

[0058] In Formula 1, the substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, or substituted or unsubstituted alkoxy group may specifically be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 10 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, and more specifically may be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkenyl group having 1 to 5 carbon atoms, a substituted or unsubstituted alkynyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted alkoxy group having 1 to 5 carbon atoms.

[0059] Specifically, in the compound represented by the above Formula 1, R2 to R6 may each be hydrogen, and R1 may include an isocyanate group, and specifically, may include a compound represented by the following Formula 2.

[0060] [Formula 2]

[0061]

[0062] In the above Formula 2, R1 is defined the same as that of the above Formula 1, and R1 includes an isocyanate group.

[0063] If the compound represented by Formula 1 includes the compound represented by Formula 2 above, it is preferred from the viewpoint of improving the durability of the membrane due to the increase in the molecular weight of the membrane product formed on the positive / negative electrode, and is also preferred from the viewpoint of significantly reducing biological toxicity compared with conventional propane sultone.

[0064] More specifically, the compound represented by the above formula 1 may include a compound represented by the following formula 3:

[0065] [Formula 3]

[0066]

[0067] In the above formula 3, L1 is a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkenylene group, a substituted or unsubstituted alkynylene group, a sulfone group, a sulfonate group, or a combination of two or more thereof. In this case, the alkylene group may be an alkylene group having 1 to 5 carbon atoms, the alkenylene group may be an alkenylene group having 1 to 5 carbon atoms, and the alkynylene group may be an alkynylene group having 1 to 5 carbon atoms.

[0068] The compound represented by the above formula 3 has an isocyanate group substituted on propane sultone via a linker (*-CH2-O-L1-*, where * is a binding site). From the viewpoint of reducing the resistance of the positive / negative electrode by increasing the oxygen content in the film formed on the positive / negative electrode, the linker is preferred.

[0069] More specifically, the compound represented by the above Formula 1 may include at least one selected from the group consisting of a compound represented by the following Formula 4A and a compound represented by the following Formula 4B:

[0070] [Formula 4A]

[0071]

[0072] [Formula 4B]

[0073]

[0074] The compounds represented by the above Formulae 4A and 4B preferably have an isocyanate group substituted on propane sultone via a linking group having a preferred length and functional group, and thus can improve the durability of the film and simultaneously reduce the resistance.

[0075] The content of the compound represented by the above formula 1 in the non-aqueous electrolyte may be 0.01 wt % to 10 wt %, specifically 0.05 wt % to 5 wt %, more specifically 0.1 wt % to 3 wt %, and further more specifically 0.3 wt % to 2 wt %. If the content of the compound represented by the above formula 1 satisfies the above range, it is preferred from the viewpoints of giving full play to the above-mentioned electrode film-forming effect, preventing the decomposition of the organic solvent, preventing the electrolyte side reaction, HF removal effect, and preventing the resistance of the lithium secondary battery from increasing due to excessive addition, thereby reducing the life performance.

[0076] In addition to the compound of Formula 1, the additive may further include additional additives. The additional additives may be included in the non-aqueous electrolyte to prevent the decomposition of the non-aqueous electrolyte in a high output environment from causing the negative electrode to collapse, or to achieve low temperature high rate discharge characteristics, high temperature stability, prevent overcharge, and suppress the battery expansion at high temperature.

[0077] Specifically, the additional additive can be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiBF4, LiPO2F2, lithium difluorooxalatoborate (LiODFB), lithium bis(oxalate)borate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa) and tris(trimethylsilyl)phosphite (TMSPi), specifically, it can be at least one selected from the group consisting of vinylene carbonate, ethylene sulfate, LiBF4 and LiPO2F2.

[0078] The content of the additional additive in the non-aqueous electrolyte may be 0.1 wt % to 15 wt %.

[0079] Lithium secondary battery

[0080] In addition, the present invention provides a lithium secondary battery including the above-mentioned nonaqueous electrolyte.

[0081] Specifically, the lithium secondary battery may include: a positive electrode; a negative electrode opposite to the positive electrode; a separator disposed between the negative electrode and the positive electrode; and the above-mentioned nonaqueous electrolyte.

[0082] In this case, the lithium secondary battery of the present invention can be prepared according to typical methods known in the art. For example, after forming an electrode assembly by sequentially stacking a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the lithium secondary battery of the present invention can be prepared by inserting the electrode assembly into a battery housing and injecting a nonaqueous electrolyte of the present invention.

[0083] (1) Positive electrode

[0084] The positive electrode may include a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector.

[0085] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, sintered carbon and aluminum-cadmium alloy, preferably aluminum.

[0086] The thickness of the positive electrode current collector is generally 3 μm to 500 μm.

[0087] The positive electrode current collector may have microscopic irregularities formed on the surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various shapes, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven body.

[0088] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one surface or both surfaces of the positive electrode current collector.

[0089] The positive electrode active material layer may contain a positive electrode active material.

[0090] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium. Specifically, it may contain a lithium transition metal composite oxide, which contains lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum, and preferably may contain a lithium transition metal composite oxide containing lithium and a transition metal including nickel, cobalt, and manganese.

[0091] For example, the lithium transition metal composite oxide may include: lithium-manganese oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (such as LiCoO2, etc.), lithium-nickel oxides (such as LiNiO2, etc.), lithium-nickel-manganese oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < z < 2), etc.), lithium-nickel-cobalt oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt oxides (such as 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 oxides (such as Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1 and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2 and p1 + q1 + r2 = 2), etc.) or lithium-nickel-cobalt-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r3 M S2)O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and S2 are each the atomic fraction of an independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < S2 < 1, and p2 + q2 + r3 + S2 = 1), etc.), and may include any one of them or two or more of the compounds thereof. Among these materials, in terms of being able to improve the capacity and stability of the battery, the lithium transition metal composite oxide may be LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 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 when considering the significant improvement effects brought about by controlling the type and content ratio of the elements constituting the lithium transition metal composite oxide, the lithium transition metal composite oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc., and any one of them or a mixture of two or more of them may be used.

[0092] More specifically, the positive electrode active material may be a lithium transition metal composite oxide, and based on the total molar number of transition metals contained in the lithium transition metal composite oxide, the content of nickel may be 60 mol% or more. Specifically, the positive electrode active material is a lithium transition metal composite oxide, and the transition metal includes nickel and at least one selected from manganese, cobalt and aluminum, and based on the total molar number of transition metals, the content of nickel may be 60 mol% or more, specifically 60 mol% to 90 mol%. When using such a lithium transition metal composite oxide with a high nickel content together with the above-mentioned nonaqueous electrolyte, it is preferred in terms of reducing gas byproducts generated by structural collapse.

[0093] In addition, the positive electrode active material may include a lithium composite transition metal oxide represented by the following Formula 5:

[0094] [Formula 5]

[0095] Li 1+x (Ni a Co b Mn c M d )O2

[0096] In the above formula 5, M is at least one selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, 1+x, a, b, c and d are each independent atomic fractions of the element, wherein 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。

[0097] 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.

[0098] In addition, a, b, c and d may be 0.80≤a≤0.95, 0.025≤b≤0.15, 0.025≤c≤0.15 and 0≤d≤0.05, respectively.

[0099] In addition, 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.

[0100] The content of the positive electrode active material in the positive electrode active material layer may be 80 wt % to 99 wt %, preferably 92 wt % to 98.5 wt %, in consideration of exhibiting sufficient capacity of the positive electrode active material.

[0101] The positive electrode active material layer may further include a conductive agent and / or a binder in addition to the above-mentioned positive electrode active material.

[0102] The binder is a component that helps the bonding between the active material and the conductive agent and the bonding with the current collector, and may specifically include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber or fluororubber, and may preferably include polyvinylidene fluoride.

[0103] In terms of ensuring sufficient bonding strength between components such as the positive electrode active material, the content of the binder in the positive electrode active material layer may be 1 wt % to 20 wt %, preferably 1.2 wt % to 10 wt %.

[0104] The conductive agent is not particularly limited as long as it can be used to help and improve the conductivity of the secondary battery and has conductivity without causing chemical changes. Specifically, the positive electrode conductive agent may include at least one selected from the group consisting of: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbons; metal powders, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives, and in terms of improving conductivity, the conductive material may preferably include carbon black.

[0105] In terms of ensuring sufficient electron conductivity, the content of the conductive agent in the positive electrode active material layer may be 1 wt % to 20 wt %, preferably 1.2 wt % to 10 wt %.

[0106] The thickness of the positive electrode active material may be 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0107] The positive electrode may be prepared by coating a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive agent, and a solvent for forming the positive electrode slurry onto a positive electrode collector, and then drying and roll-pressing the coated positive electrode collector.

[0108] The positive electrode slurry forming solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The positive electrode slurry may have a solid content of 40 wt % to 90 wt %, specifically 50 wt % to 80 wt %.

[0109] (2) Negative electrode

[0110] The negative pole is opposite to the positive pole.

[0111] 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.

[0112] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause adverse chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or aluminum-cadmium alloy surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the negative electrode current collector.

[0113] The thickness of the negative electrode current collector may generally be 3 μm to 500 μm.

[0114] The negative electrode current collector may have microscopic irregularities formed on the surface to improve the adhesion of the negative electrode active material. Specifically, the negative electrode current collector may be used in various shapes, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a nonwoven fabric body.

[0115] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector.

[0116] The negative electrode active material layer may include a negative electrode active material.

[0117] The negative electrode active material is a compound that can reversibly embed and deintercalate lithium ions, and may include at least one selected from the group consisting of carbon-based active materials, metal (metalloid)-based active materials and lithium metal. Specifically, it may include at least one selected from the group consisting of carbon-based active materials and metal (metalloid)-based active materials.

[0118] 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 fiber carbon, preferably at least one selected from the group consisting of artificial graphite and natural graphite.

[0119] From the perspective of ensuring structural stability during charge and discharge while reducing side reactions with the electrolyte solution, the average particle size (D 50 ) can be 10 μm to 30 μm, preferably 15 μm to 25 μm.

[0120] Specifically, the metal (metalloid) active material may include at least one metal (metalloid) selected from 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 metal (metalloid) selected from 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 metal (metalloid) selected from 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.

[0121] More specifically, the metal (metalloid)-based active material may include a silicon-based active material.

[0122] The silicon-based active material may include SiO x (0≤x<2). Since SiO2 does not react with lithium ions and therefore cannot store lithium, x is preferably within the above range, and more preferably the silicon-based oxide may be SiO.

[0123] In terms of ensuring structural stability during charge and discharge while reducing side reactions with the electrolyte solution, the average particle size (D 50 ) can be 1 μm to 30 μm, preferably 2 μm to 15 μm.

[0124] The content of the negative electrode active material in the negative electrode active material layer may be 60 wt % to 99 wt %, more preferably 75 wt % to 95 wt %.

[0125] The negative electrode active material layer may further include a binder and / or a conductive agent in addition to the negative electrode active material.

[0126] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector and to improve the performance of the battery, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or materials whose hydrogen is substituted by Li, Na or Ca, and may also include various copolymers thereof.

[0127] The content of the binder in the negative electrode active material layer may be 0.5 wt % to 30 wt %, preferably 1 wt % to 5 wt %.

[0128] The conductive agent is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, the following conductive materials can be used: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbon powder; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives.

[0129] The content of the conductive agent in the negative electrode active material layer may be 0.5 wt % to 10 wt %, preferably 1 wt % to 5 wt %.

[0130] The thickness of the negative electrode active material layer may be 10 μm to 100 μm, preferably 50 μm to 80 μm.

[0131] The negative electrode may be prepared by coating at least one surface of a negative electrode collector with a negative electrode slurry including a negative electrode active material, a binder, a conductive agent, and a solvent for forming a negative electrode slurry, and then drying and roll-pressing the coated negative electrode collector.

[0132] The negative electrode slurry forming solvent may include, for example, at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol and isopropanol, and preferably includes distilled water in terms of promoting the dispersion of the negative electrode active material, the binder and / or the conductive agent. The solid content in the negative electrode slurry may be 30 wt % to 80 wt %, and in particular, 40 wt % to 70 wt %.

[0133] (3) Diaphragm

[0134] In addition, as a separator, a common porous polymer film commonly used as a separator can be used alone or in a laminated form, for example, a porous polymer film prepared from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. In addition, a typical porous non-woven fabric can be used, such as a non-woven fabric formed of a high melting point glass fiber or a polyethylene terephthalate fiber, but the present disclosure is not limited thereto. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be selectively used.

[0135] The shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape may be used.

[0136] Hereinafter, the present disclosure will be described in more detail according to the embodiments. However, the following embodiments are merely presented to illustrate the present invention, and the scope of the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes are possible within the scope and technical spirit of the present invention. Such modifications and changes fall within the scope of the claims included herein.

[0137] Examples and Comparative Examples

[0138] Example 1

[0139] (Preparation of non-aqueous electrolyte)

[0140] As the organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 was used.

[0141] The non-aqueous electrolyte is prepared by adding LiPF6 as a lithium salt; a compound represented by the following formula 4A; and vinylene carbonate (VC), ethylene sulfate (ESa), LiPO2F2, and LiBF4 as additional additives to an organic solvent.

[0142] LiPF6 is contained in the non-aqueous electrolyte at a concentration of 1.2M.

[0143] The compound represented by the following Formula 4A was contained in the nonaqueous electrolyte in an amount of 0.5 wt %.

[0144] In addition, the nonaqueous electrolyte includes 0.5 wt % of vinylene carbonate (VC), 0.5 wt % of ethylene sulfate (ESa), 1.0 wt % of LiPO 2 F 2 , and 0.2 wt % of LiBF 4 .

[0145] [Formula 4A]

[0146]

[0147] (Preparation of lithium secondary battery)

[0148] The positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2): Conductive agent (carbon nanotube): Binder (polyvinylidene fluoride) was added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 98.0:0.7:1.3 to prepare a positive electrode material mixture slurry (solid content: 76.5 wt%). The positive electrode material mixture slurry was coated on one surface of a positive electrode current collector (Al film) with a thickness of 12 μm, and then rolled after drying to prepare a positive electrode.

[0149] The negative electrode active material (artificial graphite): conductive agent (carbon black): binder (styrene-butadiene rubber) was added to distilled water at a weight ratio of 96.5:1.5:2.0 to prepare a negative electrode material mixture slurry (solid content: 26 weight %). The negative electrode material mixture slurry was coated on one surface of a negative electrode current collector (Cu film) with a thickness of 8 μm, and then rolled after drying to prepare a negative electrode.

[0150] In a dry room, a polyethylene porous film separator was disposed between the positive electrode and the negative electrode prepared above, and then the prepared nonaqueous electrolyte was injected therein, thereby preparing a secondary battery.

[0151] Example 2

[0152] A nonaqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that 0.1 wt % of the compound represented by the above Formula 4A was added to the nonaqueous electrolyte in Example 1.

[0153] Example 3

[0154] A nonaqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that 3.0 wt % of the compound represented by the above Formula 4A was added to the nonaqueous electrolyte in Example 1.

[0155] Example 4

[0156] A nonaqueous electrolyte and a secondary battery were prepared in the same manner as in Example 1, except that 0.5 wt % of a compound represented by the following Formula 4B was added to the nonaqueous electrolyte of Example 1 instead of the compound represented by the above Formula 4A.

[0157] [Formula 4B]

[0158]

[0159] Example 5

[0160] A nonaqueous electrolyte and a secondary battery were prepared in the same manner as in Example 4, except that 0.1 wt % of the compound represented by the above Formula 4B was added to the nonaqueous electrolyte in Example 4.

[0161] Example 6

[0162] A nonaqueous electrolyte and a secondary battery were prepared in the same manner as in Example 4, except that 3.0 wt % of the compound represented by the above Formula 4B was added to the nonaqueous electrolyte in Example 4.

[0163] Comparative Example 1

[0164] A nonaqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by the above Formula 4A was not added.

[0165] Comparative Example 2

[0166] A nonaqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that a compound represented by the following Formula 6 was added instead of the compound represented by the above Formula 4.

[0167] [Formula 6]

[0168]

[0169] Experimental example

[0170] Experimental Example 1: Evaluation of high temperature cycle capacity retention

[0171] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 2 prepared as above were each charged to 4.2 V and 1 / 40 C under the conditions of CC / CV at 45° C. and 0.33 C using an electrochemical charger and discharger, and then discharged to 3.0 V under the conditions of CC and 0.33 C, which was set as one cycle, and 300 charge and discharge cycles were performed to measure the capacity retention rate.

[0172] The capacity retention rate was calculated by the following equation, and the results are shown in Table 1 below.

[0173] Capacity retention rate (%) = (discharge capacity after 300 cycles / discharge capacity after 1 cycle) × 100

[0174] Experimental Example 2: Evaluation of the resistance increase rate during high temperature cycles

[0175] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 2 prepared as above were each charged to 4.2 V and 1 / 40 C at CC / CV at 45° C. and 0.33 C, and then discharged to 2.5 V at CC and 0.33 C, which was set as one cycle, and 300 charge and discharge cycles were performed.

[0176] After one charge and discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charger and discharger, the state of charge (SOC) was adjusted to 50%, and then a 2.5C pulse was applied for 10 seconds to calculate the initial resistance by the difference between the voltage before and after the pulse application.

[0177] After 300 charge and discharge cycles, the resistance after 300 cycles was calculated in the same manner as above, and the resistance increase rate was calculated by using the following equation. The results are shown in Table 1.

[0178] Resistance increase rate (%) = {(resistance after 300 cycles - initial resistance) / (initial resistance)} × 100

[0179] Experimental Example 3: Evaluation of volume increase rate after high-temperature cyclic charge and discharge

[0180] In the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 2 prepared as described above, 300 charge and discharge cycles were performed in the same manner as in Experimental Example 1. In this case, 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, and the volume increase rate was calculated by the following equation, and the results are shown in Table 3 below.

[0181] Volume increase rate (%) = {(volume of lithium secondary battery after 300 cycles - initial volume) / (initial volume)} × 100

[0182] Table 1

[0183]

[0184] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 6 using the non-aqueous electrolyte containing the compound represented by Formula 1 have excellent high-temperature cycle life performance, low resistance increase rate with cycling, and low volume increase with cycling, compared with the lithium secondary batteries of Comparative Examples 1 to 2.

[0185] Experimental Example 4: Evaluation of capacity retention after high temperature storage

[0186] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 2 prepared as described above were charged to 4.2 V and 1 / 40 C under CC / CV and 0.33 C at 25° C., discharged to 2.5 V under 0.33 C, initially charged and discharged, then charged to 4.2 V and 1 / 40 C under CC / CV and 0.33 C, and then stored at 60° C. for 12 weeks. After storage, the secondary batteries were charged to 4.2 V and 1 / 40 C under CC / CV and 0.33 C at 25° C., and discharged to 2.5 V under CC and 0.33 C to determine the capacity at discharge.

[0187] The capacity retention rate was evaluated according to the following equation and the results are shown in Table 2.

[0188] Capacity retention rate (%) = (discharge capacity after 12 weeks of storage / initial discharge capacity) × 100

[0189] Experimental Example 5: Evaluation of the resistance increase rate after high-temperature storage

[0190] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 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. The lithium secondary batteries were charged at an SOC of 50% based on the discharge capacity, and discharged at a current of 2.5C for 10 seconds. The resistance was measured using the voltage drop difference at this time, and defined as the initial resistance. The resistance was measured in the same manner after storage at 60°C for 12 weeks, and defined as the final resistance. The resistance increase rate was calculated by the following equation. The results are shown in Table 2 below.

[0191] Resistance increase rate (%) = {(final resistance - initial resistance) / (initial resistance)} × 100

[0192] Experimental Example 6: Evaluation of volume increase rate after high temperature storage

[0193] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 2 prepared above were initially charged and discharged in the same manner as in Experimental Example 4, and the volume of each battery was measured by setting it to SOC 50 based on the discharge capacity and defined as the initial volume, and the volume measured after storage at SOC 100% and 60°C for 12 weeks was defined as the final volume, and the volume increase rate of the battery was calculated by using the following equation. The results are shown in Table 2 below.

[0194] Volume increase rate (%) = {(final volume - initial volume) / (initial volume)} × 100

[0195] Table 2

[0196]

[0197] Referring to Table 2, it can be confirmed that the lithium secondary batteries of Examples 1 to 6 using the nonaqueous electrolyte containing the compound represented by Formula 1 have excellent high temperature storage life performance, low resistance increase rate and low volume increase compared to the lithium secondary batteries of Comparative Examples 1 to 2.

Claims

1. A non-aqueous electrolyte comprising: Lithium salts; organic solvents; and additive, in, The additive includes a compound represented by the following formula 1: [Formula 1] Wherein, in the above formula 1, R1 to R6 each independently include hydrogen, halogen, nitrile, propargyl, ester, ether, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, boron, borate, isocyanate, isothiocyanate, silyl, siloxane, sulfone, sulfonate, sulfate or a combination of two or more thereof, and At least one of R1 to R6 contains an isocyanate group.

2. The nonaqueous electrolyte according to claim 1, wherein The compound represented by the above formula 1 includes the compound represented by the following formula 2: [Formula 2] Wherein, in the above formula 2, the definition of R1 is the same as that in the above formula 1, and R1 contains an isocyanate group.

3. The nonaqueous electrolyte according to claim 1, wherein The compound represented by the above formula 1 includes the compound represented by the following formula 3: [Formula 3] Wherein, in the above formula 3, L1 is a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkenylene group, a substituted or unsubstituted alkynylene group, a sulfone group, a sulfonate group or a combination of two or more thereof.

4. The nonaqueous electrolyte according to claim 1, wherein The compound represented by the above formula 1 includes at least one selected from the group consisting of a compound represented by the following formula 4A and a compound represented by the following formula 4B: [Formula 4A] [Formula 4B] 5. The nonaqueous electrolyte according to claim 1, wherein The content of the compound represented by the above Formula 1 in the non-aqueous electrolyte is 0.01 wt % to 10 wt %.

6. The nonaqueous electrolyte according to claim 1, wherein The lithium salt comprises a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiB(C2O4)2(LiBOB), LiCF3SO3, LiN(SO2F)2(LiFSI), LiCH3SO3, LiCF3CO2, LiCH3CO2 and LiN(SO2CF2CF3)2(LiBETI).

7. The nonaqueous electrolyte according to claim 1, wherein The lithium salt is contained in the nonaqueous electrolyte at a molar concentration of 0.5M to 5.0M.

8. The nonaqueous electrolyte according to claim 1, wherein The organic solvent includes 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 nonaqueous electrolyte according to claim 1, wherein The additive further comprises at least one additional additive selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propylene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiPO2F2, lithium difluorooxalatoborate (LiODFB), lithium bis(oxalato)borate (LiBOB), 3-trimethoxysilyl-propyl-N-aniline (TMSPa) and tris(trimethylsilyl)phosphite (TMSPi).

10. A lithium secondary battery comprising: positive electrode; a negative electrode opposite to the positive electrode; A separator disposed between the positive electrode and the negative electrode; and The nonaqueous electrolyte according to claim 1.

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