Non-aqueous electrolyte and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte that can suppress gas generation and the formation of low-level antibody byproducts. It also provides a lithium secondary battery containing the above-mentioned non-aqueous electrolyte. [Solution] The present invention relates to a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin compound represented by the following chemical formula 1, and to a lithium secondary battery comprising the non-aqueous electrolyte. JPEG2026063308000041.jpg51170 (In the above chemical formula 1, R is a substituent containing one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and n is one integer from 1 to 6.)

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0016541, filed on 8 February 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery containing the same, and more particularly to a non-aqueous electrolyte comprising a coumarin compound having at least one substituent, and a lithium secondary battery containing the same. [Background technology]

[0003] In recent years, interest in energy storage technologies has been steadily increasing, and their application areas are expanding to include mobile phones, camcorders, and notebook computers, as well as electric vehicles. Consequently, efforts to research and develop electrochemical devices are becoming more concrete.

[0004] Among electrochemical devices, there is growing interest in the development of rechargeable secondary batteries. In particular, lithium-ion secondary batteries, developed in the early 1990s, are attracting attention due to their advantages such as high operating voltage and remarkably high energy density.

[0005] Lithium secondary batteries are generally manufactured by forming an electrode assembly with a separator interposed between a positive electrode containing a positive electrode active material containing a lithium-containing transition metal oxide and a negative electrode containing a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that acts as a medium for transferring lithium ions, and then sealing it. The non-aqueous electrolyte usually contains a lithium salt and an organic solvent capable of dissolving the lithium salt.

[0006] In recent years, with the increasing demand for secondary batteries with high energy density, such as those used in electric vehicles, the development of high-voltage secondary batteries driven at high voltages has been actively pursued. However, when the driving voltage is high, the decomposition of the electrolyte on the surface of the positive electrode accelerates due to structural collapse, transition metal leaching, and gas generation, which leads to a problem in that the battery's lifespan characteristics rapidly deteriorate.

[0007] Furthermore, in recent years, in order to reduce the manufacturing costs of batteries for electric vehicles, development has been underway on batteries that use perlithitated manganese-rich (Mn-rich) cathode active materials, which are cheaper and more stable than conventional lithium nickel-based cathode active materials. Batteries using perlithitated manganese-rich cathode active materials require an initial activation process at a high voltage of 4.6V or higher, but this activation process generates reactive oxygen species, leading to side reactions with the electrolyte and increased resistance.

[0008] Therefore, there is a need to develop non-aqueous electrolytes that can suppress gas generation and cathode degradation under high voltage conditions. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the above-mentioned problems and to provide a non-aqueous electrolyte that can suppress gas generation and the formation of low antibody byproducts by removing reactive oxygen species generated under high voltage conditions, by including a coumarin compound containing at least one functional group as an additive.

[0010] Furthermore, the present invention aims to provide a lithium secondary battery that exhibits excellent lifespan and swelling characteristics even under high voltage conditions by including the non-aqueous electrolyte described above. [Means for solving the problem]

[0011] According to one embodiment, the present invention provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin compound represented by the following chemical formula 1.

[0012] [ka]

[0013] In the above chemical formula 1, R is a substituent comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and n is an integer from 1 to 6. Specifically, R may include a halogen, a nitrile group, an alkynyl group, a propargyl group, an ester group, an ether group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, or a combination thereof. More specifically, R may be a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen, in which case R' may be a propargyl group, R'' may be a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, and R''' may be a C1-C5 alkyl group substituted with or unsubstituted with at least one halogen.

[0014] More specifically, the coumarin compound may be a compound represented by the following chemical formula 1-1 or chemical formula 1-2.

[0015] [ka]

[0016] [ka]

[0017] In the above chemical formulas 1-1 and 1-2, R may be a substituent containing one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and specifically may include halogens, nitrile groups, alkynyl groups, propargyl groups, ester groups, ether groups, ketone groups, carboxyl groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, boron groups, borate groups, isocyanate groups, isothiocyanate groups, silyl groups, siloxane groups, or combinations thereof. More specifically, R may be a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen, in which case R' may be a propargyl group, R'' may be a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, and R''' may be a C1-C5 alkyl group substituted with or unsubstituted with at least one halogen.

[0018] More specifically, the coumarin compound may be selected from the group consisting of compounds represented by the following chemical formulas 1A to 1G.

[0019] [ka]

[0020] [ka]

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] [ka]

[0026] On the other hand, the coumarin compound may be present in an amount of 0.5% to 3% by weight, preferably 0.5% to 2% by weight, and more preferably 0.5% to 1% by weight, based on the total weight of the non-aqueous electrolyte.

[0027] The non-aqueous electrolyte according to the present invention may further contain a halogenated cyclic carbonate, which is preferably a fluoroethylene carbonate. The halogenated cyclic carbonate may be present in an amount of 0.5 to 10% by weight, preferably 0.5 to 8% by weight, and more preferably 1 to 5% by weight, based on the total weight of the non-aqueous electrolyte.

[0028] According to other embodiments, the present invention provides a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the non-aqueous electrolyte according to the present invention described above.

[0029] Preferably, the positive electrode active material may include a lithium manganese-based oxide represented by the following chemical formula 2.

[0030] [Chemical formula 2] Li 1+a [Ni b Coc Mn d M 1 e O 2+a

[0031] In Chemical Formula 2, 0.05 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.1, 0.5 ≦ d ≦ 1.0, 0 ≦ e ≦ 0.2, and M 1 is at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0032] More specifically, the positive electrode active material may contain a lithium manganese-based oxide represented by the following Chemical Formula 2-1.

[0033] [Chemical Formula 2-1] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w O2

[0034] In Chemical Formula 2-1, 0.3 ≦ X ≦ 0.5, 0.5 ≦ y < 1, 0 ≦ z ≦ 0.3, 0 ≦ w ≦ 0.2, and M 1 is at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0035] On the other hand, the negative electrode active material may contain a silicon-based negative electrode active material. The silicon-based negative electrode active material is, for example, Si, SiO m (where 0 < m ≦ 2), Si-C composite, Si-M a alloy (M a is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), and may be selected from the group consisting of combinations thereof. If necessary, the negative electrode active material may further contain a carbon-based negative electrode active material.

Advantages of the Invention

[0036] The coumarin compound of chemical formula 1 used as an additive in the non-aqueous electrolyte according to the present invention has a reaction energy with reactive oxygen species that is higher than that of organic solvents such as ethylene carbonate. Therefore, when reactive oxygen species are generated, the coumarin compound binds to them before the organic solvent. Consequently, when the non-aqueous electrolyte contains the coumarin compound of chemical formula 1, the reactive oxygen species generated in the high-voltage battery are scavenged by the coumarin compound, suppressing the decomposition of the organic solvent by the reactive oxygen species. This minimizes the generation of gases and low-antibody byproducts generated by the decomposition of the organic solvent.

[0037] Furthermore, the coumarin compound of chemical formula 1 contains substituents comprising one or more elements selected from the group consisting of C, O, N, S, P, Si, and F. By forming an SEI film on the surface of the positive and / or negative electrode, direct contact between the electrode and the electrolyte is suppressed, resulting in reduced gas generation and swelling at high temperatures, as well as improved lifespan.

[0038] When the non-aqueous electrolyte according to the present invention is applied to a lithium secondary battery using a positive electrode active material containing perlithitated manganese oxide, which requires a high-voltage activation process of 4.6V or higher, particularly excellent effects can be obtained in terms of gas reduction and resistance reduction. [Modes for carrying out the invention]

[0039] The present invention will be described in detail below.

[0040] Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is replaced by an element other than hydrogen, for example, by a halogen, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C1-C20 alkoxy group, a C3-C12 cycloalkyl group, a C3-C12 cycloalkenyl group, a C3-C12 heterocycloalkyl group, a C3-C12 heterocycloalkenyl group, a C6-C12 aryloxy group, a C1-C20 fluoroalkyl group, a nitrile group, a C6-C20 aryl group, a C2-C20 heteroaryl group, a C6-C20 haloaryl group, etc.

[0041] [Non-aqueous electrolytes] The non-aqueous electrolyte according to the present invention comprises (1) an organic solvent, (2) a lithium salt, and (3) a coumarin compound represented by the following chemical formula 1.

[0042] (1) Organic solvents In the present invention, the organic solvent may include a cyclic carbonate solvent, a linear carbonate solvent, a linear ester solvent, or a mixture thereof.

[0043] The cyclic carbonate solvent is a highly viscous organic solvent with a high dielectric constant that readily dissociates lithium salts in the electrolyte. For example, it may be at least one 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. Specifically, the cyclic carbonate solvent may be ethylene carbonate, propylene carbonate, or mixtures thereof.

[0044] The linear carbonate solvent is an organic solvent having low viscosity and low dielectric constant, and may be at least one selected from the group consisting of, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0045] The linear ester solvent may be at least one selected from the group consisting of, for example, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0046] Preferably, the organic solvent may be a mixture of a cyclic carbonate solvent and a linear carbonate solvent. In this case, the cyclic carbonate solvent and the linear carbonate solvent may be mixed in a volume ratio of 10-40:60-90, preferably 10-30:70-90, and more preferably 15-30:70-85. When the content of the cyclic carbonate solvent and the linear carbonate solvent meets the above range, both high dielectric constant and low viscosity characteristics can be satisfied, and excellent ionic conductivity characteristics can be achieved.

[0047] (2) Lithium salt The lithium salt used in this invention is not limited to any lithium salt commonly used in electrolytes for lithium secondary batteries. For example, the lithium salt may contain Li as a cation. + It includes, as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - AlO4 - AlCl4 - PF6 - SbF6 -AsF6 - B 10 Cl 10 - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - , C4F9SO3 - CF3CF2SO3 - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CH3SO3 - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - It may include at least one selected from the group consisting of the following.

[0048] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10The lithium salt may be at least one selected from the group consisting of LiBOB(LiB(C2O4)2), LiCF3SO3, LiTFSI(LiN(SO2CF3)2), LiFSI(LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI(LiN(SO2CF2CF3)2). Specifically, the lithium salt may consist of a single substance 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), or a mixture of two or more substances.

[0049] The lithium salt may be present in the electrolyte at a concentration of 0.8 M to 4 M, preferably 0.8 M to 2 M, and more preferably 0.8 M to 1.6 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transference number (Li+ transference number) and the degree of lithium ion dissociation are improved, and the output characteristics of the battery can be improved.

[0050] (3) Coumarin compounds The non-aqueous electrolyte according to the present invention contains a coumarin compound represented by the following chemical formula 1.

[0051] [ka]

[0052] In the above chemical formula 1, R is a substituent comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and n is an integer from 1 to 6. Specifically, R may include halogens, nitrile groups, alkynyl groups, propargyl groups, ester groups, ether groups, ketone groups, carboxyl groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, boron groups, borate groups, isocyanate groups, isothiocyanate groups, silyl groups, siloxane groups, or combinations thereof. More specifically, R may be a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR'''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen, in which case R' may be a propargyl group, R'' may be a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, and R'''' may be a C1-C5 alkyl group substituted with or unsubstituted with at least one halogen.

[0053] The coumarin compound represented by chemical formula 1 has a higher reaction energy with reactive oxygen species than organic solvents such as ethylene carbonate. Therefore, when reactive oxygen species are generated, it binds to them before the organic solvent. Consequently, when the coumarin compound of chemical formula 1 is included in a non-aqueous electrolyte, the reactive oxygen species generated in the initial activation stage of a high-voltage battery are scavenged by the coumarin compound, suppressing the decomposition of the organic solvent by the reactive oxygen species. This minimizes the generation of gases and low-antibody byproducts generated by the decomposition of the organic solvent.

[0054] Furthermore, the coumarin compound of chemical formula 1 contains substituents comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F. By forming an SEI film on the surface of the positive and / or negative electrode, direct contact between the electrode and the electrolyte is suppressed, resulting in reduced gas generation and swelling at high temperatures, as well as improved lifespan.

[0055] More specifically, the coumarin compound may be a compound represented by the following chemical formula 1-1 or chemical formula 1-2.

[0056] [ka]

[0057] [ka]

[0058] In the above chemical formulas 1-1 and 1-2, R may be a substituent containing one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and specifically may include halogens, nitrile groups, alkynyl groups, propargyl groups, ester groups, ether groups, ketone groups, carboxyl groups, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkoxy groups, boron groups, borate groups, isocyanate groups, isothiocyanate groups, silyl groups, siloxane groups, or combinations thereof. More specifically, R may be a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR'''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen, in which case R' may be a propargyl group, R'' may be a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, and R'''' may be a C1-C5 alkyl group substituted with or unsubstituted with at least one halogen.

[0059] More specifically, the coumarin compound may be selected from the group consisting of compounds represented by the following chemical formulas 1A to 1G.

[0060] [ka]

[0061] [ka]

[0062] [ka]

[0063] [ka]

[0064] [ka]

[0065] [ka]

[0066] [ka]

[0067] On the other hand, the coumarin compound may be present in an amount of 0.5% to 3% by weight, preferably 0.5% to 2% by weight, and more preferably 0.5% to 1% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the coumarin compound meets the above range, a strong SEI film can be formed on the positive and negative electrodes, which can help improve battery performance by effectively removing oxygen radical compounds generated at the positive electrode. If the content of the coumarin compound is excessively high, resistance may increase, potentially adversely affecting battery performance.

[0068] (4) Other ingredients On the other hand, the non-aqueous electrolyte according to the present invention may further contain additives in addition to the above-mentioned components, although this is not necessarily required, in order to further improve the physical properties of the secondary battery.

[0069] Examples of such additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0070] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate (VEC).

[0071] The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0072] The sultone compound may be, for example, 1,3-propanesultone or 1,3-propenesultone.

[0073] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0074] The phosphate compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate.

[0075] The borate compound may be, for example, tetraphenylborate or lithium oxalyl difluoroborate (LiODFB).

[0076] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0077] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2), and LiBF4).

[0078] On the other hand, the additives may be used individually or in a mixture of two or more types.

[0079] The total amount of the additive may be 0.1 to 20% by weight, preferably 0.1 to 15% by weight, based on the total weight of the electrolyte. When the additive is included within the above range, a stable film is formed on the electrode, suppressing ignition during overcharging, and preventing side reactions from occurring during the initial activation process of the secondary battery, as well as preventing the additive from remaining or precipitating.

[0080] Among the additives mentioned above, it is particularly preferable to further include halogen-substituted carbonate compounds, such as fluoroethylene carbonate (FEC). When the halogen-substituted carbonate compound is used as an additive, the oxidation stability of the electrolyte is increased, improving the high-voltage performance. A SEI film is formed on the surface of the positive electrode, stabilizing the interface of the positive electrode and improving the long-life characteristics. However, when fluoroethylene carbonate is used alone, excessive oxidative decomposition reactions may occur at the interface of the positive electrode, leading to the accumulation of LiF components on the surface of the positive electrode, increasing resistance, increasing CO2 gas generation and HF production as side reactions, and accelerating the decomposition reaction of the electrolyte. However, when both halogen-substituted carbonate compounds and coumarin compounds are used, the positive electrode film formation mechanism of the coumarin compound suppresses the positive electrode oxidation reaction of the halogen-substituted carbonate compound, minimizing the occurrence of the above-mentioned side effects.

[0081] In this case, the halogen-substituted carbonate compound may be present in an amount of 0.5% to 10% by weight, preferably 0.5% to 8% by weight, and more preferably 1% to 5% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the halogen-substituted carbonate compound satisfies the above range, improvements in high-voltage performance due to increased oxidation stability of the electrolyte and improvements in lifespan characteristics due to the formation of an SEI film can be obtained.

[0082] [Lithium-ion secondary battery] Next, the lithium secondary battery according to the present invention will be described.

[0083] The lithium secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte. More specifically, it may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. At this time, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention described above, that is, a non-aqueous electrolyte containing an organic solvent, a lithium salt, and a coumarin compound represented by Chemical Formula 1. Since the non-aqueous electrolyte has been described above, the description thereof will be omitted, and other components will be described below.

[0084] 〔Positive Electrode〕 The positive electrode includes a positive electrode active material layer containing a positive electrode active material. If necessary, the positive electrode active material layer may further contain a conductive material and / or a binder.

[0085] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and various positive electrode active materials used in the art, such as 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(0<Y<1), LiMn 2-Z Ni Z O4(0<Z<2), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2(0<Y1<1), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2(0<Y2<1), LiMn 2-Z1 Co Z1 O4(0<Z1<2), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2(0<p1<1, 0<q1<1, 0<r1<1, p1+q1+r1=1) or Li(Ni p2 Co q2 Mnr2 )O4 (0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p3 Co q3 Mn r3 M s3 )O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are atomic fractions of independent elements, where 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, and p3 + q3 + r3 + s3 = 1) can be used, etc.

[0086] Preferably, the positive electrode active material may contain a hyper-lithiated manganese-rich oxide that contains 50 mol% or more of Mn in all metals excluding lithium and has a molar ratio of lithium to transition metal exceeding 1.

[0087] When lithium manganese oxide containing excess lithium is used as the positive electrode active material, the irreversible capacity of Si is compensated for by the excess lithium contained in the positive electrode active material during the initial activation process. Therefore, a balance can be achieved with the silicon negative electrode without the need for other compensating materials such as sacrificial cathode materials or processes that pre-compensate for lithium, such as pre-lithification. Specifically, perlithitated manganese-rich oxide has a structure in which layered (LMO2) and rock salt phase (Li2MnO3) are mixed in the positive electrode active material. During the initial activation process, the irreversible capacity of Si is compensated for by the lithium generated as the lithium manganese oxide in the rock salt phase decomposes. However, this requires the initial activation process to be carried out at a high voltage of 4.6V or higher, and reactive oxygen species are generated during the decomposition of the lithium manganese oxide in the rock salt phase. Reactive oxygen species attack and decompose organic solvents such as ethylene carbonate, generating gases and low antibody byproducts that degrade the physical properties of the battery. However, in this invention, since the non-aqueous electrolyte contains a coumarin compound that is more reactive with reactive oxygen species than organic solvents, the reactive oxygen species generated in the initial activation step bind to the coumarin compound before the organic solvent, thereby minimizing side effects caused by the decomposition of the organic solvent.

[0088] Specifically, the lithium manganese oxide may be represented by the following chemical formula 2.

[0089] [Chemical formula 2] Li 1+a [Ni b Co c Mn d M 1 e ]O 2+a

[0090] In Chemical Formula 1, 0.05 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.3, 0.5 ≦ d < 1.0, 0 ≦ e ≦ 0.2 may be satisfied, preferably, 0.05 ≦ a ≦ 1.0, 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.1, 0.5 ≦ d < 1.0, 0 ≦ e ≦ 0.2 may be satisfied, more preferably, 0.10 ≦ a ≦ 0.50, 0.1 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.1, 0.6 ≦ d < 1.0, 0 ≦ e ≦ 0.1 may be satisfied.

[0091] Also, M 1 may be at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0092] More specifically, the lithium manganese oxide may be represented by the following Chemical Formula 2-1.

[0093] [Chemical Formula 2-1] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w O2

[0094] In Chemical Formula 2-1, 0.1 ≦ X ≦ 0.5, 0.5 ≦ y < 1, 0 ≦ z ≦ 0.3, 0 ≦ w ≦ 0.2 may be satisfied, preferably, 0.2 ≦ X ≦ 0.5, 0.5 ≦ y < 1, 0 ≦ z ≦ 0.1, 0 ≦ w ≦ 0.2, more preferably, 0.3 ≦ X ≦ 0.5, 0.6 ≦ y < 1, 0 ≦ z ≦ 0.1, 0 ≦ w ≦ 0.2 may be satisfied.

[0095] Also, M 1 may be at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0096] The lithium manganese oxide can be produced by mixing a transition metal precursor and a lithium raw material, followed by calcination. In this process, the transition metal precursor and the lithium raw material can be mixed in amounts such that the molar ratio of the total transition metal (Ni+Co+Mn) to Li is 1:1.05 to 1:2. The calcination temperature may be 600°C to 1000°C, and the calcination time may be 5 to 30 hours. The calcination atmosphere may be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20% ​​to 100% by volume of oxygen.

[0097] Examples of the lithium raw material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). One of these can be used alone, or a mixture of two or more.

[0098] On the other hand, the transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. Using a precursor in the form of a carbonate is more preferable because it allows for the production of a positive electrode active material with a relatively high specific surface area.

[0099] The transition metal precursor can be produced by a coprecipitation process. For example, the transition metal precursor can be produced by dissolving each transition metal-containing raw material in a solvent to produce a metal solution, then mixing the metal solution, an ammonium cation complex-forming agent, and a basic compound, and then proceeding with a coprecipitation reaction. Furthermore, if necessary, an oxidizing agent or oxygen gas may be added during the coprecipitation reaction.

[0100] In this case, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or the like of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt acetate, cobalt halide, or the like.

[0101] The ammonium cation complex-forming agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3.

[0102] The basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may change depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a precursor in the form of a hydroxide is obtained, and when Na2CO3 is used as the basic compound, a precursor in the form of a carbonate is obtained. Also, when both a basic compound and an oxidizing agent are used, a precursor in the form of an oxide is obtained.

[0103] On the other hand, the positive electrode active material according to the present invention may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, and the average particle size D50 of the secondary particles may be 2 μm to 10 μm, preferably 2 μm to 8 μm, and more preferably 4 μm to 8 μm.

[0104] Furthermore, the positive electrode active material has a BET specific surface area of ​​1 m². 2 / g or more, 3m 2 / g~8m 2 / g, or 4m 2 / g~6m 2 / g is also acceptable.

[0105] Furthermore, the positive electrode active material according to the present invention preferably has an initial irreversible capacity of approximately 5% to 70%, 5% to 50%, or 10% to 30%. When the initial irreversible capacity of the positive electrode active material satisfies the above range, the irreversible capacity of the silicon-based negative electrode active material can be compensated without the need for another compensating material such as a sacrificial positive electrode material or a process to compensate for lithium in advance, such as pre-lithification.

[0106] On the other hand, examples of the conductive material include spherical or flaky graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone, or a mixture of two or more. The conductive material may be included in an amount of 0.1% to 20% by weight, 1% to 20% by weight, or 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0107] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these can be used alone, or a mixture of two or more can be used. The binder may be present in amounts of 1% to 20% by weight, 2% to 20% by weight, or 2% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0108] The positive electrode of the present invention described above can be manufactured by a method for manufacturing positive electrodes known in the art. For example, the positive electrode can be manufactured by a method in which a positive electrode slurry, prepared by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent, is applied to a positive electrode current collector, and then dried and rolled; or by a method in which the positive electrode slurry is cast onto another support, the support is peeled off, and the resulting film is laminated onto the positive electrode current collector.

[0109] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 μm to 500 μm, and the adhesion to the positive electrode active material layer may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0110] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone, or a mixture of two or more. The amount of solvent used is not particularly limited, and should be adjusted to the extent that the cathode composite material has an appropriate viscosity, taking into consideration the coating thickness of the cathode composite material, the manufacturing yield, and the workability of the workability.

[0111] [Negative electrode] The negative electrode according to the present invention comprises a negative electrode active material layer containing a negative electrode active material, the negative electrode active material layer may further contain a conductive material and / or a binder as needed.

[0112] As the negative electrode active material, various negative electrode active materials used in the art, for example, silicon-based negative electrode active materials, carbon-based negative electrode active materials, metal alloys, etc. may be used.

[0113] Preferably, the negative electrode active material contains a silicon-based negative electrode active material.

[0114] The silicon-based negative electrode active material is, for example, Si, SiO m (where 0 < m < 2), Si-C composite, Si-M a alloy (M a is selected from the group consisting of one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), and may be selected from the group consisting of combinations thereof.

[0115] Also, the silicon-based negative electrode active material may be doped with M b metal, and at this time, the M b metal may be an alkali metal element of Group 1 and / or an alkaline earth metal element of Group 2, and may be, for example, Li, Mg, etc. Specifically, the silicon negative electrode active material is M b metal-doped Si, SiO m (where 0 < m < 2), Si-C composite, etc. may also be used. Although the capacity of the metal-doped silicon-based negative electrode active material decreases due to the doping element, it has high efficiency, so a high energy density can be realized.

[0116] Also, the silicon-based negative electrode active material may further include a carbon coating layer on the surface of the particles. At this time, the amount of carbon coating may be 20% by weight or less, preferably 0.1% by weight to 20% by weight, based on the total weight of the silicon-based negative electrode active material. The carbon coating layer can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc.

[0117] Also, the particle size D of the silicon-based negative electrode active material50 The size is 3 μm to 8 μm, preferably 4 μm to 7 μm, and D min ~D max The particle size is 0.5 μm to 30 μm, preferably 0.5 μm to 20 μm, and more preferably 1 μm to 15 μm.

[0118] Furthermore, the negative electrode may, if necessary, further contain a carbon-based negative electrode active material. The carbon-based negative electrode active material may be, but is not limited to, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc.

[0119] On the other hand, the silicon-based anode active material may be included in amounts of 1% to 100% by weight, 1% to 50% by weight, 1% to 30% by weight, 1% to 15% by weight, 10% to 70% by weight, or 10% to 50% by weight, based on the total weight of the anode active material.

[0120] The carbon-based anode active material may be included in amounts of 0% to 99% by weight, 50% to 99% by weight, 70% to 99% by weight, 85% to 99% by weight, 30% to 90% by weight, or 50% to 90% by weight, based on the total weight of the anode active material.

[0121] According to one embodiment, the anode active material may be a mixture of a silicon-based anode active material and a carbon-based anode active material. In this case, the mixing ratio of the silicon-based anode active material and the carbon-based anode active material may be 1:99 to 50:50 by weight, preferably 3:97 to 30:70. When the mixing ratio of the silicon-based anode active material and the carbon-based anode active material satisfies the above range, the capacity characteristics are improved, the volume expansion of the silicon-based anode active material is suppressed, and excellent cycle performance can be ensured.

[0122] The negative electrode active material may be present in an amount of 80% to 99% by weight, based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material meets the above range, excellent capacitance characteristics and electrochemical properties can be obtained.

[0123] Examples of the conductive material include spherical or flaky graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone, or a mixture of two or more. The conductive material may be included in an amount of 0.1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight, based on the total weight of the negative electrode active material layer.

[0124] Preferably, single-walled carbon nanotubes can be used as the conductive material. When single-walled carbon nanotubes are used as the conductive material, conductive paths are uniformly formed on the surface of the negative electrode active material, thereby improving the cycle characteristics.

[0125] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one can be used alone or a mixture of two or more. The binder may be present in amounts of 1% to 20% by weight, 2% to 20% by weight, or 2% to 10% by weight, based on the total weight of the negative electrode active material layer.

[0126] The negative electrode may have a single negative electrode active material layer or a multilayer structure composed of two or more layers. In the case of a multilayer structure composed of two or more negative electrode active material layers, each layer may have different types and / or contents of negative electrode active material, binder, and / or conductive material. For example, in the negative electrode according to the present invention, the lower layer may be formed with a higher content of carbon-based negative electrode active material than the upper layer, and the upper layer may be formed with a higher content of silicon-based negative electrode active material. In this case, compared to the case where the negative electrode active material layer is formed as a single layer, an effect of improved rapid charging performance can be obtained.

[0127] The negative electrode active material layer may have a porosity of 20% to 70% or 20% to 50%.

[0128] The negative electrode can be manufactured by a negative electrode manufacturing method known in the art. For example, the negative electrode can be manufactured by coating a negative electrode slurry, prepared by dissolving or dispersing a negative electrode active material, a binder, and a conductive material selectively in a solvent, onto a negative electrode current collector, rolling and drying it, or by casting the negative electrode slurry onto another support, peeling off the support, and laminating the resulting film onto the negative electrode current collector.

[0129] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0130] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone, or a mixture of two or more. The amount of solvent used is not particularly limited, and should be adjusted so that the negative electrode slurry has an appropriate viscosity, taking into consideration the coating thickness of the negative electrode mixture, the production yield, and the workability.

[0131] [Separator] In the lithium secondary battery of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions. It can be used without particular limitations as long as it is a separator that is normally used in lithium secondary batteries, and is particularly preferred if it has low resistance to the movement of ions in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.

[0132] The lithium secondary battery according to the present invention, as described above, can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0133] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0134] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

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

[0136] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0137] The present invention will be specifically described below with reference to concrete examples.

[0138] Comparative Example 1 A nonaqueous electrolyte was prepared by dissolving LiPF6 in a nonaqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate in a volume ratio of 20:60:20 to a concentration of 1.2 M. Then, 0.5 wt% vinylene carbonate (VC), 0.5 wt% propane sultone (PS), 1 wt% ethylene sulfate (ESa), 40.5 wt% LiBF, 1 wt% lithium difluorophosphate (LiDFP), and 3 wt% fluorinated ethylene carbonate (FEC) were added to the mixture.

[0139] Comparative Example 2 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of an unsubstituted coumarin compound represented by chemical formula A was added.

[0140] [ka]

[0141] Example 1 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1A was added.

[0142] Example 2 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 1% by weight of the compound represented by chemical formula 1A was added.

[0143] Example 3 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1B was added.

[0144] Example 4 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1C was added.

[0145] Example 5 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1D was added.

[0146] Example 6 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1E was added.

[0147] Example 7 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1F was added.

[0148] Example 8 A non-aqueous electrolyte was prepared in the same manner as in Comparative Example 1, except that 0.5% by weight of the compound represented by chemical formula 1G was added.

[0149] <Manufacturing of lithium-ion secondary batteries> (Manufacturing of positive electrodes) Lithium manganese oxide as positive electrode active material particles 1.3 (Ni 0.35 Mn 0.65 )O 2.33A positive electrode active material slurry (48% solids by weight) was prepared by adding carbon black as a conductive material and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 96:1:3 to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode active material slurry was applied to a positive electrode current collector (a thin aluminum film) and dried, and the positive electrode was manufactured by roll pressing.

[0150] (Manufacturing of negative electrodes) Negative electrode active material (artificial graphite: SiO2) m A negative electrode active material slurry (solid content: 70% by weight) was prepared by adding PVDF as a binder and carbon black as a conductive material in a weight ratio of 95:2:3 to NMP, a solvent. The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) and dried, and the negative electrode was manufactured by roll pressing.

[0151] (Manufacturing of secondary batteries) After manufacturing an electrode assembly by a conventional method in which the positive electrode and negative electrode manufactured by the method described above are sequentially laminated together with a polyethylene porous film, the assembly is placed in a pouch-type secondary battery case, and a lithium secondary battery is manufactured by injecting the non-aqueous electrolyte manufactured in Examples 1 to 8 and Comparative Examples 1 to 2.

[0152] Experimental Example 1 Each lithium secondary battery manufactured as described above underwent a pre-aging step, being stored at room temperature for two days to ensure the electrolyte was sufficiently wetted. Next, the temperature was set to 45°C and the pressure was increased to 0.5 kgf / cm². 2 Under the following pressure conditions, the battery was charged to a state of charge (SOC) of 3% at 0.2C, then charged to a state of charge (SOC) of 17% at 0.3C under the same temperature and pressure conditions, and then charged to 5 kgf / cm². 2 Under this pressure, the battery was charged to 30% SOC at 0.3C. Subsequently, high-temperature aging was carried out at 60°C for 15 hours, during which coating stabilization and gas discharge processes were performed.

[0153] Next, 45℃, 5kgf / cm²2 Under this pressure, the positive electrode was activated by charging to 4.6V at 0.3C, and then the activation process was completed by discharging to 2V at 0.5C.

[0154] On the other hand, the cell volume of the lithium secondary battery before and after the activation process was measured at room temperature using a buoyancy method, and the cell volume increase rate during the activation process was calculated using the following formula (1).

[0155] Equation (1): Cell volume change rate (%) = {(Volume after positive electrode activation process - Initial cell volume) / Initial cell volume} × 100

[0156] The measurement results are shown in Table 1 below.

[0157] [Table 1]

[0158] In the activation step, charging is performed up to a high voltage of 4.6V, which generates reactive oxygen compounds at the positive electrode. These reactive oxygen compounds react with the electrolyte to produce gases such as CO and CO2. The more reactive oxygen compounds there are, the greater the amount of gas generated, which increases the cell volume. Therefore, a small increase in cell volume means that the amount of reactive oxygen compounds is small. From Table 1, it can be seen that the lithium secondary batteries of Examples 1 to 8, which used a coumarin compound having one or more substituents as an additive, showed less increase in cell volume after the activation step compared to Comparative Examples 1 to 2. This indicates that the coumarin compound having one or more substituents effectively removed reactive oxygen.

[0159] On the other hand, Comparative Example 2, which used an unsubstituted coumarin compound as an additive, showed a lower cell volume increase rate compared to Comparative Example 1, but a higher rate than Examples 1-8. In other words, it can be seen that using a coumarin compound substituted with one or more functional groups provides an even better gas generation suppression effect compared to using an unsubstituted coumarin compound. This is judged to be because the functional groups substituted with coumarin form a strong SEI film on the electrode surface, which suppresses side reactions at the electrode interface and further suppresses the generation of activated gas.

[0160] Experimental Example 2 Each lithium secondary battery manufactured as described above was activated using the same method as in Experimental Example 1, and then fully charged to 100% SOC at 4.35V under CC / CV and 0.33C conditions at 25°C. Afterward, the fully charged lithium secondary batteries were stored at 60°C for 8 weeks, and then the cell volume increase rate and capacity retention rate were measured.

[0161] In this case, the capacity retention rate was calculated by substituting the discharge capacity of the lithium secondary battery measured before high-temperature storage and the discharge capacity of the lithium secondary battery measured after high-temperature storage into the following formula (2).

[0162] Equation (2): Capacity retention rate (%) = (Discharge capacity after high-temperature storage / Discharge capacity before high-temperature storage) × 100

[0163] The rate of change in cell volume was calculated by substituting the initial volume before high-temperature storage and the volume after high-temperature storage into the following formula (3).

[0164] Equation (3): Cell volume change rate (%) = {(Volume after high-temperature storage - Initial volume) / Initial volume} × 100

[0165] The measurement results are shown in Table 2 below.

[0166] [Table 2]

[0167] From Table 2 above, it can be seen that the lithium secondary batteries of Examples 1 to 8, which used coumarin compounds containing one or more substituents as additives, have a higher capacity retention rate and a smaller cell volume increase rate after high-temperature storage compared to the lithium secondary batteries of Comparative Examples 1 and 2. This is judged to be because a strong SEI film is formed on the electrode surface by the functional group substituted with coumarin, thereby suppressing side reactions at the electrode interface.

Claims

1. A non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin compound represented by the following chemical formula 1. 【Chemistry 1】 (In the above chemical formula 1, R is a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR'''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen. R' is a propargyl group, R'' is a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, R''' is an alkyl group substituted with at least one halogen or unsubstituted with C1-C5, and n is any integer from 1 to 6.

2. The non-aqueous electrolyte according to claim 1, wherein the coumarin compound is a compound represented by the following chemical formula 1-1 or chemical formula 1-2. 【Chemistry 2】 【Transformation 3】 (In the above chemical formulas 1-1 and 1-2, R is a nitrile group, a C2-C10 alkynyl group, a propargyl group, -COOR', -O-R'', -COR'''', or a C1-C10 alkyl group substituted with or unsubstituted with at least one halogen, R' is a propargyl group, R'' is a propargyl group or a silyl group substituted with at least one C1-C5 alkyl group, and R''' is an alkyl group substituted with at least one halogen or unsubstituted with C1-C5.

3. The non-aqueous electrolyte according to claim 1, wherein the coumarin compound is selected from the group consisting of compounds represented by the following chemical formulas 1A to 1G. 【Chemistry 4】 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】

4. The non-aqueous electrolyte according to claim 1, wherein the coumarin compound is contained in an amount of 0.5% to 3% by weight, based on the total weight of the non-aqueous electrolyte.

5. The non-aqueous electrolyte according to claim 1, further comprising a halogen-substituted cyclic carbonate.

6. The non-aqueous electrolyte according to claim 5, wherein the halogen-substituted cyclic carbonate is fluoroethylene carbonate.

7. The nonaqueous electrolyte according to claim 6, wherein the halogen-substituted cyclic carbonate is contained in an amount of 0.5% to 10% by weight, based on the total weight of the nonaqueous electrolyte.

8. A positive electrode containing a positive electrode active material, A negative electrode containing a negative electrode active material, A lithium secondary battery comprising a non-aqueous electrolyte according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, wherein the positive electrode active material contains a perlithitated manganese-rich oxide in which 50 mol% or more of Mn is present in the total metals excluding lithium, and the molar ratio of lithium to the transition metal is greater than 1.

10. The lithium secondary battery according to claim 9, wherein the perlithitated manganese-rich oxide is represented by the following chemical formula 2. [Chemical formula 2] Li １＋ａ [Ni ｂ Co ｃ Mn ｄ M １ ｅ ]O ２＋ａ (In the above chemical formula 2, 0.05 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.3, 0.5 ≤ d < 1.0, 0 ≤ e ≤ 0.2, M １ (This is at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.)

11. The lithium secondary battery according to claim 9, wherein the perlithitated manganese-rich oxide is represented by the following chemical formula 2-1. [Chemical formula 2-1] XLi ２ MnO ３ ・(1-^)L[Ni １－ｙ－ｚ－ｗ Mn ｙ Co ｚ M １ ｗ ]O ２ (In the above chemical formula 2-1, 0.1 ≤ X ≤ 0.5, 0.5 ≤ y < 1, 0 ≤ z ≤ 0.3, 0 ≤ w ≤ 0.2, M １ (This is at least one metal ion selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.)

12. The lithium secondary battery according to claim 8, wherein the negative electrode active material includes a silicon-based negative electrode active material.

13. The silicon-based negative electrode active material is Si, SiO ｍ (Here, 0 < m ≤ 2), Si-C composite, Si-M ａ Alloy (M ａ The lithium secondary battery according to claim 12, wherein is selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni, and combinations thereof.

14. The lithium secondary battery according to claim 12, wherein the negative electrode active material further comprises a carbon-based negative electrode active material.

15. The lithium secondary battery according to claim 8, wherein the coumarin compound is selected from the group consisting of compounds represented by the following chemical formulas 1A to 1G. 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】 【Chemistry 15】 【Chemistry 16】 【Chemistry 17】

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