Nonaqueous electrolyte and lithium secondary battery containing same

Abstract

The present invention relates to a non-aqueous electrolyte containing an organic solvent, a lithium salt, and a coumarin-based compound represented by the following chemical formula 1, and a lithium secondary battery containing the non-aqueous electrolyte. JPEG2025502386000042.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 any one integer of 1 to 6.)

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0016541, filed on February 8, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

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

[0003] In recent years, interest in energy storage technology has been growing, and its application fields have expanded to include mobile phones, camcorders, and laptop computers, as well as the energy sources for electric vehicles. Accordingly, efforts to research and develop electrochemical devices have been gaining momentum.

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

[0005] Lithium secondary batteries are generally fabricated by forming an electrode assembly by interposing a separator between a positive electrode including a lithium-containing transition metal oxide and a negative electrode including a lithium-ion-storing negative electrode active material, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte, which serves as a medium for lithium ion transfer, and sealing the battery case. The non-aqueous electrolyte typically includes 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 batteries for electric vehicles, the development of high-voltage secondary batteries that can be driven at high voltages has been actively pursued. However, when the driving voltage increases, the decomposition of the electrolyte on the surface of the positive electrode is accelerated due to structural collapse, transition metal elution, gas generation, etc., which leads to a problem of a rapid decrease in the life characteristics of the battery.

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

[0008] Therefore, there is a need for the development of a non-aqueous electrolyte that can suppress gas generation and positive electrode deterioration under high voltage conditions. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and aims to provide a non-aqueous electrolyte solution that contains a coumarin-based compound having at least one functional group as an additive, thereby suppressing the generation of gas and antibody by-products by removing active oxygen generated under high voltage conditions.

[0010] Another object of the present invention is to provide a lithium secondary battery that contains the above-mentioned nonaqueous electrolyte solution and thus exhibits excellent life characteristics and swelling characteristics even under high voltage conditions. [Means for solving the problem]

[0011] According to one embodiment, the present invention provides a non-aqueous electrolyte including an organic solvent, a lithium salt, and a coumarin-based compound represented by the following Chemical Formula 1:

[0012] [ka]

[0013] In 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 an integer of 1 to 6. Specifically, R may contain 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, an alkynyl group having 2 to 10 carbon atoms, a propargyl group, -COOR', -O-R'', -COR''', or an alkyl group having 1 to 10 carbon atoms which may or may not be substituted 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 alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms which may or may not be substituted with at least one halogen.

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

[0015] [ka]

[0016] [ka]

[0017] In Chemical Formula 1-1 and Chemical Formula 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 contain a halogen, a nitrile group, an alkynyl group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted 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, an alkynyl group having 2 to 10 carbon atoms, a propargyl group, -COOR', -O-R'', -COR''', or an alkyl group having 1 to 10 carbon atoms which may or may not be substituted 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 alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms which may or may not be substituted with at least one halogen.

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

[0019] [ka]

[0020] [ka]

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] [ka]

[0026] Meanwhile, the coumarin compound may be contained 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 solution according to the present invention may further contain a halogenated cyclic carbonate, which may preferably be fluoroethylene carbonate. The halogenated cyclic carbonate may be contained in an amount of 0.5 to 10 wt %, preferably 0.5 to 8 wt %, more preferably 1 to 5 wt %, based on the total weight of the non-aqueous electrolyte.

[0028] According to another embodiment, the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the nonaqueous electrolyte solution 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 [[ID=3...]]

[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.

Effects of the Invention

[0036] The coumarin-based compound of Chemical Formula 1 used as an additive in the non-aqueous electrolyte according to the present invention has a higher reaction energy with active oxygen than organic solvents such as ethylene carbonate, and therefore binds with the active oxygen before the organic solvent when the active oxygen is generated. Therefore, when the non-aqueous electrolyte contains the coumarin-based compound of Chemical Formula 1, the active oxygen generated in the high-voltage battery is scavenged by the coumarin-based compound, thereby suppressing the decomposition of the organic solvent by the active oxygen, thereby minimizing the generation of gases and low-molecular by-products generated by the decomposition of the organic solvent.

[0037] In addition, the coumarin compound of Chemical Formula 1 contains a substituent containing one or more elements selected from the group consisting of C, O, N, S, P, Si, and F, and forms an SEI film on the surface of the positive electrode and / or negative electrode, thereby suppressing direct contact between the electrode and the electrolyte, reducing gas generation and swelling at high temperatures, and improving the battery life.

[0038] When the nonaqueous electrolyte solution according to the present invention is applied to a lithium secondary battery that uses a positive electrode active material containing a perlithiated manganese oxide and that requires a high-voltage activation step of 4.6 V or more, it is possible to obtain particularly excellent effects in terms of gas reduction and resistance reduction. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be specifically described below.

[0040] Unless otherwise defined, the term "substituted" means that at least one or more hydrogen atoms bonded to a carbon atom are replaced with an element other than hydrogen. For example, at least one or more hydrogen atoms bonded to a carbon atom are replaced with a halogen, 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, an aryloxy group having 6 to 12 carbon atoms, a fluoroalkyl group having 1 to 20 carbon atoms, a nitrile group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, or the like.

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

[0042] (1) Organic Solvent 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 that has a high dielectric constant and thus easily dissociates the lithium salt in the electrolyte, and may be, for example, 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 a mixture thereof.

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

[0045] The linear ester solvent may be, for example, at least one selected from the group consisting of 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 at a volume ratio of 10-40:60-90, preferably 10-30:70-90, and more preferably 15-30:70-85. When the contents of the cyclic carbonate solvent and the linear carbonate solvent satisfy the above ranges, both high dielectric constant and low viscosity characteristics are satisfied, and excellent ionic conductivity characteristics can be achieved.

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

[0048] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10, 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 include 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 contained 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 transportence number (Li+ transference number) and the degree of dissociation of lithium ions 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-based compound represented by the following chemical formula 1.

[0051] [ka]

[0052] 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 an integer of 1 to 6. Specifically, R may contain a halogen, a nitrile group, an alkynyl group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted 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, an alkynyl group having 2 to 10 carbon atoms, a propargyl group, -COOR', -O-R'', -COR''', or an alkyl group having 1 to 10 carbon atoms which may or may not be substituted 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 alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms which may or may not be substituted with at least one halogen.

[0053] The coumarin-based compound represented by Chemical Formula 1 has a higher reaction energy with active oxygen than organic solvents such as ethylene carbonate, and therefore binds with the active oxygen before the organic solvent does. Therefore, when the coumarin-based compound represented by Chemical Formula 1 is contained in a non-aqueous electrolyte, the active oxygen generated during the initial activation stage of a high-voltage battery is scavenged by the coumarin-based compound, thereby suppressing the decomposition of the organic solvent by the active oxygen, thereby minimizing the generation of gases and low-molecular by-products generated by the decomposition of the organic solvent.

[0054] In addition, the coumarin compound of Chemical Formula 1 contains a substituent containing one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and forms an SEI film on the surface of the positive electrode and / or negative electrode, thereby suppressing direct contact between the electrode and the electrolyte, reducing gas generation and swelling at high temperatures, and improving the battery life.

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

[0056] [ka]

[0057] [ka]

[0058] In Chemical Formula 1-1 and Chemical Formula 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 contain a halogen, a nitrile group, an alkynyl group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted 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, an alkynyl group having 2 to 10 carbon atoms, a propargyl group, -COOR', -O-R'', -COR''', or an alkyl group having 1 to 10 carbon atoms which may or may not be substituted 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 alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms which may or may not be substituted with at least one halogen.

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

[0060] [ka]

[0061] [ka]

[0062] [ka]

[0063] [ka]

[0064] [ka]

[0065] [ka]

[0066] [ka]

[0067] Meanwhile, the coumarin-based compound may be included in an amount of 0.5 wt % to 3 wt %, preferably 0.5 wt % to 2 wt %, and more preferably 0.5 to 1 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the coumarin-based compound satisfies the above range, a strong SEI coating can be formed on the positive electrode and negative electrode, and oxygen radical compounds generated at the positive electrode can be effectively removed, thereby helping to improve battery performance. If the content of the coumarin-based compound is too high, resistance may increase, adversely affecting battery performance.

[0068] (4) Other ingredients Meanwhile, the non-aqueous electrolyte according to the present invention may further contain, in addition to the above components, an additive, although this is not essential, 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 vinyl ethylene 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-propane sultone, 1,3-propene sultone, or the like.

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

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

[0075] The borate-based compound may be, for example, tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or the like.

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

[0078] On the other hand, the additives may be used alone or in combination of two or more.

[0079] The total amount of the additives may be 0.1 to 20 wt %, preferably 0.1 to 15 wt %, based on the total weight of the electrolyte solution. When the additives are contained within the above range, a stable coating is formed on the electrode, which can suppress ignition during overcharge, and can prevent side reactions from occurring during the initial activation step of the secondary battery, and can prevent the additives from remaining or being precipitated.

[0080] Among the additives, it is particularly preferred to further include a halogen-substituted carbonate-based compound, such as fluoroethylene carbonate (FEC). The use of the halogen-substituted carbonate-based compound as an additive can increase the oxidation stability of the electrolyte, resulting in improved high voltage performance. Furthermore, the formation of an SEI film on the surface of the positive electrode stabilizes the positive electrode interface, resulting in improved long-life characteristics. However, when fluoroethylene carbonate is used alone, excessive oxidative decomposition reactions occur at the positive electrode interface, leading to the deposition of LiF components on the positive electrode surface, increasing resistance, and increasing CO2 gas generation and HF generation side reactions, which can accelerate the electrolyte decomposition reaction. However, when a halogen-substituted carbonate-based compound and a coumarin-based compound are used together, the positive electrode film formation mechanism of the coumarin-based compound suppresses the positive electrode oxidation reaction of the halogen-substituted carbonate-based compound, minimizing the occurrence of these side effects.

[0081] In this case, the halogen-substituted carbonate compound may be contained in an amount of 0.5 wt % to 10 wt %, preferably 0.5 wt % to 8 wt %, and more preferably 1 wt % to 5 wt %, based on the total weight of the non-aqueous electrolyte. When the content of the halogen-substituted carbonate compound satisfies the above range, the oxidation stability of the electrolyte is increased, thereby improving high-voltage performance, and the life characteristics are improved by forming an SEI film.

[0082] [Lithium 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 above-described present invention, 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 is 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 a 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 the atomic fractions of independent elements, where 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, and p3 + q3 + r3 + s3 = 1) etc. can be used.

[0086] Preferably, the positive electrode active material may contain a hyperlithiated manganese-rich oxide in which Mn is contained at 50 mol% or more in all metals excluding lithium, and the molar ratio of lithium to transition metal exceeds 1.

[0087] When lithium-manganese oxide containing excess lithium is used as a cathode active material, the excess lithium in the cathode active material compensates for the irreversible capacity of silicon during the initial activation process, thereby achieving a balance with a silicon-based anode without the need for a separate compensation material, such as a sacrificial cathode material, or a pre-lithiation process to compensate for the lithium. Specifically, perlithiated manganese-rich oxide has a mixed structure of layered (LMO2) and rock salt (Li2MnO3) phases in the cathode active material. During the initial activation process, the lithium generated during the decomposition of the rock salt phase lithium manganese oxide compensates for the irreversible capacity of silicon. However, this requires the initial activation process to be performed at a high voltage of 4.6 V or higher, and the decomposition of the rock salt phase lithium manganese oxide generates reactive oxygen. Reactive oxygen attacks and decomposes organic solvents, such as ethylene carbonate, producing gases and antibody byproducts that degrade the battery's physical properties. However, in the present invention, since the non-aqueous electrolyte contains a coumarin-based compound that is more reactive with active oxygen than the organic solvent, the active oxygen generated in the initial activation process binds to the coumarin-based compound before the organic solvent does, thereby minimizing side effects caused by the decomposition of the organic solvent.

[0088] Specifically, the lithium manganese-based 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, the following relationships may be satisfied: 0.05≦a≦1, 0≦b≦0.5, 0≦c≦0.3, 0.5≦d<1.0, 0≦e≦0.2, preferably 0.05≦a≦1.0, 0.1≦b≦0.5, 0≦c≦0.1, 0.5≦d<1.0, 0≦e≦0.2, and 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.

[0091] Also, M 1 may be at least one or more metal ions 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-based 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, the relationships may be 0.1≦X≦0.5, 0.5≦y<1, 0≦z≦0.3, and 0≦w≦0.2, preferably 0.2≦X≦0.5, 0.5≦y<1, 0≦z≦0.1, and 0≦w≦0.2, and more preferably 0.3≦X≦0.5, 0.6≦y<1, 0≦z≦0.1, and 0≦w≦0.2.

[0095] Also, M 1 may be at least one or more metal ions 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-based oxide can be prepared by mixing a transition metal precursor and a lithium source material, followed by firing. The transition metal precursor and the lithium source material can be mixed in amounts such that the molar ratio of total transition metals (Ni+Co+Mn) to Li is 1:1.05 to 1:2. The firing temperature can be 600°C to 1000°C, the firing time can be 5 hours to 30 hours, and the firing atmosphere can be air or oxygen, for example, an atmosphere containing 20% ​​to 100% oxygen by volume.

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

[0098] The transition metal precursor may be in the form of a hydroxide, oxide, or carbonate, and is preferably in the form of a carbonate, since it can produce a positive electrode active material with a relatively high specific surface area.

[0099] The transition metal precursor may be prepared by a co-precipitation process. For example, the transition metal precursor may be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, followed by a co-precipitation reaction. If necessary, an oxidizing agent or oxygen gas may be added during the co-precipitation reaction.

[0100] In this case, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. 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, etc.

[0101] The ammonium cation complexing 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 vary 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. Furthermore, when a basic compound and an oxidizing agent are used together, 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 agglomeration 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] The positive electrode active material has a BET specific surface area of ​​1 m 2 / g or more, 3m 2 / g~8m 2 / g, or 4m 2 / g~6m 2 / g.

[0105] Furthermore, the positive electrode active material according to the present invention preferably has an initial irreversible capacity of about 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 for without the need for a separate compensation material such as a sacrificial positive electrode material or a step of pre-compensating for lithium such as prelithiation.

[0106] Examples of the conductive material include spherical or flaky graphite; carbonaceous 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.1 wt % to 20 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt %, 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One of these can be used alone, or two or more can be used in combination. The binder may be contained in an amount of 1 to 20 wt%, 2 to 20 wt%, or 2 to 10 wt%, based on the total weight of the positive electrode active material layer.

[0108] The positive electrode of the present invention as described above may be manufactured by a method known in the art. For example, the positive electrode may be manufactured by dissolving or dispersing a positive electrode active material, a binder, and / or a conductive material in a solvent to prepare a positive electrode slurry, which is then coated on a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode slurry on a separate support, peeling off the support, and laminating the resulting film on a 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 whose surface has been surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion to the positive electrode active material layer. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0110] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is not particularly limited, as long as it is sufficient to adjust the viscosity of the cathode composite to an appropriate level, taking into consideration the coating thickness of the cathode composite, production yield, workability, etc.

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

[0112] As the negative electrode active material, various negative electrode active materials used in the art, such as 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 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 in this case, 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. The metal-doped silicon-based negative electrode active material has a reduced active material capacity due to the doping element, but 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 carbon coating amount may be 20% by weight or less, preferably 0.1% 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). <​​50 is 3 μm to 8 μm, preferably 4 μm to 7 μm, and D min ~D max The thickness is 0.5 μm to 30 μm, preferably 0.5 μm to 20 μm, and more preferably 1 μm to 15 μm.

[0118] In addition, the negative electrode may further include a carbon-based negative electrode active material as a negative electrode active material, if necessary. The carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but is not limited thereto.

[0119] Meanwhile, the silicon-based negative electrode active material may be included in an amount of 1 wt % to 100 wt %, 1 wt % to 50 wt %, 1 wt % to 30 wt %, 1 wt % to 15 wt %, 10 wt % to 70 wt %, or 10 wt % to 50 wt % based on the total weight of the negative electrode active material.

[0120] The carbon-based negative electrode active material may be included in an amount of 0 wt % to 99 wt %, 50 wt % to 99 wt %, 70 wt % to 99 wt %, 85 wt % to 99 wt %, 30 wt % to 90 wt %, or 50 wt % to 90 wt % based on the total weight of the negative electrode active material.

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

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

[0123] Examples of the conductive material include spherical or flaky graphite; carbonaceous 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.1 wt % to 30 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt %, 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 cycle characteristics.

[0125] Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One of these can be used alone, or two or more can be used in combination. The binder may be included in an amount of 1 to 20 wt%, 2 to 20 wt%, or 2 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0126] The negative electrode may have a single-layer negative electrode active material layer or a multi-layer structure composed of two or more layers. When the negative electrode active material layer has a multi-layer structure composed of two or more layers, each layer may have a different type and / or content 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 so that the content of carbon-based negative electrode active material is higher than that of the upper layer, and the upper layer may be formed so that the content of silicon-based negative electrode active material is higher. In this case, the effect of improving fast charging performance compared to a case where the negative electrode active material layer is formed as a single layer 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 may be manufactured by a method known in the art, for example, by coating a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector, followed by rolling and drying, or by casting the negative electrode slurry onto a separate 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 surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys may be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0130] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is not particularly limited as long as it is sufficient to adjust the viscosity of the negative electrode slurry to an appropriate level, taking into consideration the coating thickness of the negative electrode composite, production yield, workability, etc.

[0131] [Separator] In the lithium secondary battery of the present invention, the separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material can also be used, and it can be selectively used in a single-layer or multi-layer structure.

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

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

[0134] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as 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, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[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 as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

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

[0138] Comparative Example 1 LiPF6 was dissolved to a concentration of 1.2 M in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate in a volume ratio of 20:60:20, and then 0.5 wt% vinylene carbonate (VC), 0.5 wt% propane sultone (PS), 1 wt% ethylene sulfate (ESa), 0.5 wt% LiBF4, 1 wt% lithium difluorophosphate (LiDFP), and 3 wt% fluorinated ethylene carbonate (FEC) were added to prepare a non-aqueous electrolyte.

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

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

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

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

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

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

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

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

[0149] <Manufacturing lithium secondary batteries> (Cathode manufacturing) Lithium manganese oxide Li was used as the positive electrode active material particle. 1.3 (Ni 0.35 Mn 0.65 )O 2.33Carbon black as a conductive material and polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1:3 to prepare a cathode active material slurry (solid content 48 wt%). The cathode active material slurry was applied to a cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0150] (Manufacturing of negative electrodes) Negative electrode active material (artificial graphite: SiO m Anode active material slurry (solid content: 70 wt%) 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 as a solvent. The anode active material slurry was applied to anode current collector (Cu thin film), dried, and roll-pressed to prepare an anode.

[0151] (Secondary battery manufacturing) The positive and negative electrodes prepared by the above-mentioned methods were sequentially stacked together with a polyethylene porous film to prepare an electrode assembly by a conventional method, and then the assembly was placed in a pouch-shaped secondary battery case. The non-aqueous electrolyte prepared in Examples 1 to 8 and Comparative Examples 1 and 2 was injected into the case to prepare a lithium secondary battery.

[0152] Experimental Example 1 Each lithium secondary battery fabricated as described above was subjected to a pre-aging step of storing it at room temperature for 2 days to ensure sufficient wetting of the electrolyte. 2 After charging to SOC 3% at 0.2C under the same temperature and pressure conditions, the battery was charged to SOC 17% at 0.3C, and then charged to SOC 17% at 5kgf / cm 2 The battery was charged at 0.3 C under a pressure of 1000 kJ / cm2 to an SOC of 30%. Then, high-temperature aging was carried out at 60°C for 15 hours, during which a film stabilization and gas release process were carried out.

[0153] Next, 45℃, 5kgf / cm2 The positive electrode was activated by charging the battery at 0.3 C to 4.6 V under a pressure of 1000 kJ / cm2, and then discharged at 0.5 C to 2 V to complete the activation process.

[0154] Meanwhile, the cell volumes of the lithium secondary batteries before and after the activation step were measured at room temperature by a buoyancy method, and the cell volume increase rate during the activation step was calculated using the following formula (1).

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

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

[0157] [Table 1]

[0158] During the activation process, charging is performed up to a high voltage of 4.6 V, generating reactive oxygen compounds at the positive electrode, which react with the electrolyte to generate gases such as CO and CO2. The more reactive oxygen compounds there are, the greater the amount of gas generated, resulting in an increase in cell volume. Therefore, a small increase in cell volume indicates a small amount of reactive oxygen compounds. Table 1 shows that the lithium secondary batteries of Examples 1 to 8, which used a coumarin-based compound having one or more substituents as an additive, showed a smaller increase in cell volume after the activation process than those of Comparative Examples 1 and 2, indicating that the coumarin-based compound having one or more substituents effectively removed reactive oxygen.

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

[0160] Experimental Example 2 Each of the lithium secondary batteries prepared as described above was activated in the same manner as in Experimental Example 1, and then fully charged to 100% SOC at 4.35 V under CC / CV conditions at 0.33 C at 25°C. The fully charged lithium secondary batteries were then stored at 60°C for 8 weeks, after which 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 cell volume change rate 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] It can be seen from Table 2 that the lithium secondary batteries of Examples 1 to 8, which used a coumarin-based compound containing one or more substituents as an additive, had 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 believed to be because a strong SEI film was formed on the surface of the electrode due to the functional groups substituted on the coumarin, thereby suppressing side reactions at the electrode interface.

Claims

1. A positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; A lithium secondary battery comprising: The non-aqueous electrolyte includes an organic solvent, a lithium salt, and a coumarin-based compound represented by the following Chemical Formula 1: 【Chemistry 1】 In the above Chemical Formula 1, R is an alkynyl group having 2 to 10 carbon atoms, a propargyl group, —COOR′, —O—R″, or —COR′″; R' is a propargyl group, R'' is a propargyl group or a silyl group substituted with at least one alkyl group having 1 to 5 carbon atoms, R''' is an alkyl group having 1 to 5 carbon atoms which is substituted with at least one or more halogen atoms or is not substituted, and n is an integer of 1 to 6, the positive electrode active material contains a perlithiated manganese-rich oxide containing 50 mol % or more of Mn among all metals excluding lithium, and having a molar ratio of lithium to transition metals of greater than 1; The perlithiated 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, 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.)

2. 2. The lithium secondary battery according to claim 1, wherein the coumarin-based compound is a compound represented by the following Chemical Formula 1-1 or 1-2: 【Chemistry 2】 【Transformation 3】 (In the above Chemical Formula 1-1 and Chemical Formula 1-2, R represents an alkynyl group having 2 to 10 carbon atoms, a propargyl group, —COOR′, —O—R″, or —COR′″; R' is a propargyl group, R'' is a propargyl group or a silyl group substituted with at least one alkyl group having 1 to 5 carbon atoms, and R''' is an alkyl group having 1 to 5 carbon atoms which is substituted with at least one or more halogens or is unsubstituted.

3. 2. The lithium secondary battery of claim 1, wherein the coumarin-based compound is selected from the group consisting of compounds represented by the following Formula 1B, 1D, 1E, 1F, 1G, and 1G: 【Chemistry 4】 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】

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

5. A lithium secondary battery as described in claim 1, wherein the non-aqueous electrolyte further contains a halogen-substituted carbonate-based compound.

6. 6. The lithium secondary battery according to claim 5, wherein the halogen-substituted carbonate compound is fluoroethylene carbonate.

7. 7. The lithium secondary battery according to claim 6, wherein the halogen-substituted carbonate compound is contained in an amount of 0.5% by weight to 10% by weight based on the total weight of the non-aqueous electrolyte.

8. 2. The lithium secondary battery of claim 1, wherein the perlithiated 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, 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.

9. The lithium secondary battery according to claim 1 , wherein the negative electrode active material comprises a silicon-based negative electrode active material.

10. The silicon-based negative electrode active material is 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 combinations thereof.

11. The lithium secondary battery according to claim 9 , wherein the negative electrode active material further comprises a carbon-based negative electrode active material.

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