Non-aqueous electrolyte and lithium secondary battery comprising the same

Abstract

The present invention relates to a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin-based compound represented by the following [Chemical Formula 1], and a lithium secondary battery comprising said non-aqueous electrolyte. [Chemical Formula 1] 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 any one integer from 1 to 6.

Description

Technology 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 said Korean Patent Application are incorporated herein as part of this specification.

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

[0004] Recently, interest in energy storage technology has been steadily increasing, and as application fields expand to include energy for mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts in the research and development of electrochemical devices are becoming increasingly concrete.

[0005] Among electrochemical devices, there is growing interest in the development of rechargeable secondary batteries, and in particular, lithium secondary batteries developed in the early 1990s are gaining attention for their advantages of high operating voltage and significantly higher energy density.

[0006] A lithium secondary battery is generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode containing a positive active material comprising a transition metal oxide containing lithium and a negative electrode containing a negative active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transmitting lithium ions, and then sealing the case. The non-aqueous electrolyte generally comprises a lithium salt and an organic solvent capable of dissolving the lithium salt.

[0007] Recently, as the demand for high-energy-density secondary batteries, such as those for electric vehicles, has increased, active development is underway for high-voltage secondary batteries that operate at high voltages. However, there is a problem in that when the operating voltage increases, the decomposition of the electrolyte is accelerated due to structural collapse, transition metal leaching, and gas generation at the anode surface, which leads to a rapid degradation of the battery's lifespan characteristics.

[0008] In addition, in order to reduce the manufacturing cost of batteries for electric vehicles, batteries using lithium-rich manganese-rich (Mn-rich) cathode active materials, which are cheaper and have better stability than conventional lithium-nickel-based cathode active materials, are being developed. In the case of batteries using lithium-rich manganese-rich cathode active materials, it is required to perform an initial activation process at a high voltage of 4.6V or higher, but there is a problem in that active oxygen is generated during the activation process, leading to side reactions with the electrolyte and increased resistance.

[0009] Therefore, there is a need to develop non-aqueous electrolytes capable of suppressing gas generation and anode degradation under high voltage conditions. The problem to be solved

[0011] The present invention aims to solve the above-mentioned problems by providing a non-aqueous electrolyte capable of suppressing gas generation or the formation of resistor by-products by removing active oxygen generated under high voltage conditions, by including a coumarin-based compound containing at least one functional group as an additive.

[0012] In addition, the present invention aims to provide a lithium secondary battery that includes a non-aqueous electrolyte as described above and exhibits excellent lifespan characteristics and swelling characteristics even under high voltage conditions. means of solving the problem

[0014] According to one embodiment, the present invention provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin-based compound represented by the following [Chemical Formula 1].

[0015] [Chemical Formula 1]

[0016]

[0017] 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 comprise 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 proparzyl group, -COOR', -0-R”, -COR''', or an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with at least one halogen, wherein R' may be a proparzyl group and R” may be a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms substituted or unsubstituted with at least one halogen.

[0018] More specifically, the above coumarin compound may be a compound represented by the following chemical formula 1-1 or chemical formula 1-2.

[0019] [Chemical Formula 1-1]

[0020]

[0021] [Chemical Formula 1-2]

[0022]

[0023] In the above [Chemical Formula 1-1] and [Chemical Formula 1-2], R may be a substituent comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, specifically, it may include a halogen, a nitrile group, an alkynyl group, a proparzyl 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 proparzyl group, -COOR', -0-R”, -COR''', or an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with at least one halogen, wherein R' may be a proparzyl group and R” may be a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms substituted or unsubstituted with at least one halogen.

[0024] More specifically, the above coumarin compound may be selected from the group consisting of compounds represented by [Chemical Formula 1B], [Chemical Formula 1D] to [Chemical Formula 1G] below.

[0025] [Chemical Formula 1B]

[0026]

[0027] [Chemical Formula 1D]

[0028]

[0029] [Chemical Formula 1E]

[0030]

[0031] [Chemical Formula 1F]

[0032]

[0033] [Chemical Formula 1G]

[0034]

[0036] Meanwhile, the above coumarin compound may be included 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.

[0037] The non-aqueous electrolyte according to the present invention may further comprise a halogenated cyclic carbonate, and the halogenated cyclic carbonate may preferably be fluorinated ethylene carbonate. The halogenated cyclic carbonate may be included in an amount of 0.5 to 10 weight%, preferably 0.5 to 8 weight%, more preferably 1 to 5 weight% based on the total weight of the non-aqueous electrolyte.

[0039] According to another embodiment, the present invention provides a lithium secondary battery comprising: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and a non-aqueous electrolyte according to the present invention as described above.

[0040] Preferably, the positive electrode active material may include a lithium manganese-based oxide represented by the following [Chemical Formula 2].

[0041] [Chemical Formula 2]

[0042] Li 1+a [Ni b Co c Mn d M 1 e ]O 2+a

[0043] In the above 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 It is at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0044] More specifically, the positive active material may include a lithium manganese-based oxide represented by the following chemical formula 2-1.

[0045] [Chemical Formula 2-1]

[0046] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w ]O2

[0047] In the above [Chemical Formula 2-1], 0.3≤X≤0.5, 0.5≤y<1, 0≤z≤0.3, 0≤w≤0.2, and M 1 It is at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0048] Meanwhile, the above-mentioned negative electrode active material may include a silicon-based negative electrode active material. The above-mentioned silicon-based negative electrode active material is, for example, Si, SiOm (where 0 <m≤2), Si-C 복합체, Si-M a Alloy (M a The negative electrode active material may be selected from the group consisting of one or more materials selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni, and combinations thereof. If necessary, the negative electrode active material may further include a carbon-based negative electrode active material. Effects of the invention

[0050] The coumarin compound of Formula 1, used as an additive to the non-aqueous electrolyte according to the present invention, has a reaction energy with active oxygen that is higher than that of organic solvents such as ethylene carbonate, so it combines with active oxygen before the organic solvent when active oxygen is generated. Therefore, when the coumarin compound of Formula 1 is included in the non-aqueous electrolyte, active oxygen generated in the high-voltage battery is scavenged by the coumarin compound, thereby suppressing the decomposition of the organic solvent by the active oxygen, and consequently, the generation of gas or resistor byproducts caused by the decomposition of the organic solvent can be minimized.

[0051] In addition, the coumarin compound of Chemical 1 includes a substituent comprising one or more elements selected from the group consisting of C, O, N, S, P, Si, and F, and by forming an SEI film on the surface of the anode and / or cathode, direct contact between the electrode and the electrolyte is suppressed, thereby enabling the reduction of gas generation and swelling at high temperatures and the improvement of lifespan.

[0052] When the non-aqueous electrolyte according to the present invention is applied to a lithium secondary battery using a lithium-rich manganese oxide as a positive electrode active material, 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. Specific details for implementing the invention

[0054] The present invention will be described in detail below.

[0055] Unless otherwise defined, the term “substituted” means that at least one hydrogen bonded to a carbon is substituted with an element other than hydrogen, for example, that at least one hydrogen bonded to a carbon is substituted 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 nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, a haloaryl group having 6 to 20 carbon atoms, etc. It means.

[0057] Non-aqueous electrolytes

[0058] The non-aqueous electrolyte according to the present invention comprises (1) an organic solvent, (2) a lithium salt, and (3) a coumarin-based compound represented by the following [Chemical Formula 1].

[0060] (1) Organic solvent

[0061] In the present invention, the organic solvent may include a cyclic carbonate-based solvent, a linear carbonate-based solvent, a linear ester-based solvent, or a mixture thereof.

[0062] The above-mentioned cyclic carbonate-based solvent is a high-viscosity organic solvent that has a high dielectric constant and can effectively dissociate 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 above-mentioned cyclic carbonate solvent may be ethylene carbonate, propylene carbonate, and mixtures thereof.

[0063] The above linear carbonate-based 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, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate.

[0064] The above linear ester-based 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.

[0065] Preferably, the organic solvent may be a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent. In this case, the cyclic carbonate-based solvent and the linear carbonate-based solvent may be mixed in a volume ratio of 10 to 40:60 to 90, preferably 10 to 30:70 to 90, and more preferably 15 to 30:70 to 85. When the content of the cyclic carbonate-based solvent and the linear carbonate-based solvent satisfies the above range, high dielectric constant and low viscosity characteristics are simultaneously satisfied, and excellent ionic conductivity characteristics can be achieved.

[0067] (2) Lithium salt

[0068] As the lithium salt used in the present invention, various lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, the lithium salt is Li as a cation. + It includes, and as 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 a group consisting of

[0069] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10Examples include 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 include a single substance or a mixture of two or more 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).

[0070] The above lithium salt may be included 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 yield (Li+ transference number) and the degree of dissociation of lithium ions are improved, and the output characteristics of the battery can be improved.

[0072] (3) Coumarin compounds

[0073] The non-aqueous electrolyte according to the present invention comprises a coumarin-based compound represented by the following [Chemical Formula 1].

[0074] [Chemical Formula 1]

[0075]

[0076] 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 comprise a halogen, a nitrile group, an alkynyl group, a proparzyl 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 an alkynyl group having 2 to 10 carbon atoms, a proparzyl group, -COOR', -0-R", or -COR''', wherein R' may be a proparzyl group and R" may be a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms substituted with at least one halogen.

[0077] The coumarin compound represented by [Chemical Formula 1] above has a reaction energy with active oxygen that is higher than that of organic solvents such as ethylene carbonate, so it combines with active oxygen before the organic solvent when active oxygen is generated. Therefore, when the coumarin compound of Chemical Formula 1 is included in the non-aqueous electrolyte, active oxygen generated during the initial activation stage of the high-voltage battery is scavenged by the coumarin compound, thereby suppressing the decomposition of the organic solvent by active oxygen, and consequently, the generation of gas or resistor byproducts caused by the decomposition of the organic solvent can be minimized.

[0078] In addition, the coumarin compound of Chemical Formula 1 includes a substituent comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, and by forming an SEI film on the surface of the anode and / or cathode, direct contact between the electrode and the electrolyte is suppressed, thereby enabling the reduction of gas generation and swelling at high temperatures and the improvement of lifespan.

[0080] More specifically, the above coumarin compound may be a compound represented by the following chemical formula 1-1 or chemical formula 1-2.

[0081] [Chemical Formula 1-1]

[0082]

[0083] [Chemical Formula 1-2]

[0084]

[0085] In the above [Chemical Formula 1-1] and [Chemical Formula 1-2], R may be a substituent comprising one or more elements selected from the group consisting of C, O, N, B, S, P, Si, and F, specifically, it may include a halogen, a nitrile group, an alkynyl group, a proparzyl 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 an alkynyl group having 2 to 10 carbon atoms, a proparzyl group, -COOR', -0-R", or -COR''', wherein R' may be a proparzyl group and R" may be a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, and R''' may be an alkyl group having 1 to 5 carbon atoms substituted with at least one halogen.

[0086] More specifically, the above coumarin compound may be selected from the group consisting of compounds represented by [Chemical Formula 1B], [Chemical Formula 1D] to [Chemical Formula 1G] below.

[0087] [Chemical Formula 1B]

[0088]

[0090] [Chemical Formula 1D]

[0091]

[0092] [Chemical Formula 1E]

[0093]

[0094] [Chemical Formula 1F]

[0095]

[0096] [Chemical Formula 1G]

[0097]

[0099] Meanwhile, the above coumarin-based compound may be included 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-based compound satisfies the above range, a robust SEI film can be formed on the anode and cathode, and oxygen radical compounds generated at the anode can be effectively removed, thereby helping to improve battery performance. If the content of the coumarin-based compound becomes too high, the resistance increases, which may have an adverse effect on battery performance.

[0101] (4) Other ingredients

[0102] Meanwhile, the non-aqueous electrolyte according to the present invention may additionally include additives in addition to the above components, although this is not essential, to further improve the physical properties of the secondary battery.

[0103] Examples of such additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0104] The above-mentioned cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate (VEC).

[0105] The above halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC), etc.

[0106] The above sulfone-based compound may be, for example, 1,3-propanesulfone, 1,3-propensulfone, etc.

[0107] The above sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0108] The above phosphate-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0109] The above borate-based compounds may be, for example, tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), etc.

[0110] The above benzene-based compound may be, for example, fluorobenzene, etc., the above amine-based compound may be triethanolamine or ethylenediamine, etc., and the above silane-based compound may be tetravinylsilane, etc.

[0111] The above lithium salt-based compound is a compound different from the lithium salt included in the above non-aqueous electrolyte, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate toborate (LiB(C2O4)2)) and LiBF4.

[0112] Meanwhile, the above additives may be used alone or in combination of two or more types.

[0113] The total amount of the above additive may be 0.1 to 20 weight%, preferably 0.1 to 15 weight%, based on the total weight of the electrolyte. When the additive is included within the above range, a stable film can be formed on the electrode and ignition can be suppressed during overcharging, while preventing side reactions from occurring or the additive from remaining or precipitating during the initial activation process of the secondary battery.

[0115] Among the above additives, it is particularly desirable to additionally include a halogen-substituted carbonate compound, for example, fluoroethylene carbonate (FEC). When the above halogen-substituted carbonate compound is used as an additive, the oxidative stability of the electrolyte is increased, thereby improving high voltage, and an SEI film is formed on the anode surface, stabilizing the anode interface and improving long-life characteristics. However, if fluoroethylene carbonate is used alone, excessive oxidative decomposition reactions occur at the anode interface, causing LiF components to be deposited on the anode surface, which increases resistance. Additionally, side effects may occur, such as increased CO2 gas generation and HF formation side reactions, which accelerate the electrolyte decomposition reaction. However, when the halogen-substituted carbonate compound and a coumarin compound are used together, the anode oxidation reaction of the halogen-substituted carbonate compound is suppressed due to the anode film formation mechanism of the coumarin compound, thereby minimizing the occurrence of such side effects.

[0117] At this time, the halogen-substituted carbonate-based compound may be included 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-based compound satisfies the above range, the effect of improving high voltage performance by increasing the oxidation stability of the electrolyte and improving lifespan characteristics by forming an SEI film can be obtained.

[0119] lithium secondary battery

[0120] Next, a lithium secondary battery according to the present invention will be described.

[0121] A lithium secondary battery according to the present invention comprises a positive electrode including a positive active material, a negative electrode including a negative active material, and a non-aqueous electrolyte. More specifically, it may comprise a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In this case, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention described above, that is, a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin-based compound represented by [Chemical Formula 1]. Since the non-aqueous electrolyte has been described above, a description thereof is omitted, and other components are described below.

[0123] anode

[0124] The above-mentioned anode may include an anode active material layer comprising an anode active material, and, if necessary, the anode active material layer may further include a conductive material and / or a binder.

[0125] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and is one of various cathode active materials used in the industry, for example, lithium-manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2(0 <Y<1), LiMn 2-z Ni z O4 (O < Z < 2), lithium-nickel-cobalt oxide (e.g., LiNi 1-Y1 Co Y1 O2(0 <Y1<1), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(0 <Y2<1), LiMn 2-z1 Co z1 O4 (O < Z1 < 2), lithium-nickel-manganese-cobalt oxide (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 Mn r2 )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 each atomic fractions of independent elements, 0<p3<1, 0<q3<1, 0<r3<1, 0<s3<1, p2+q2+r3+s2=1) etc. may be used.

[0127] Preferably, the positive electrode active material may include a lithium manganese-rich oxide containing 50 mol% or more of Mn among the total metals excluding lithium, and having a molar ratio of lithium to transition metals exceeding 1.

[0128] When lithium manganese-based oxides containing an excess of lithium are used as cathode active materials, the irreversible capacity of Si is compensated by the excess lithium contained in the cathode active material during the initial activation process. Consequently, balance with the silicon-based anode can be achieved without separate compensation materials, such as sacrificial cathode materials, or prior lithium compensation processes like pre-lithiation. Specifically, in the case of over-lithium manganese-rich oxides, the cathode active material has a structure in which layered (LMO2) and rock salt phases (Li2MnO3) are mixed; the irreversible capacity of Si is compensated by the lithium generated as the rock salt phase lithium manganese oxide decomposes during the initial activation process. However, this requires the initial activation process to be performed at a high voltage of 4.6V or higher, and reactive oxygen species are generated during the decomposition of the rock salt phase lithium manganese oxide. These reactive oxygen species attack and decompose organic solvents such as ethylene carbonate, generating gases and resistor byproducts that degrade battery properties. However, since the present invention includes a coumarin-based compound that is more reactive with active oxygen than the organic solvent in the non-aqueous electrolyte, the active oxygen generated during the initial activation process combines with the coumarin-based compound before the organic solvent, thereby minimizing side effects caused by the decomposition of the organic solvent.

[0130] Specifically, the lithium manganese-based oxide may be represented by the following chemical formula 2.

[0131] [Chemical Formula 2]

[0132] Li 1+a [Ni b Co c Mn d M 1 e ]O 2+a

[0133] In the above chemical formula 1, 0.05≤a≤1, 0≤b≤0.5, 0≤c≤0.3, 0.5≤d<1.0, and 0≤e≤0.2 may be used. 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 -1.0≤f≤1.0 may be used. More preferably, 0.10≤a≤0.50, 0.1≤b≤0.5, 0≤c≤0.1, 0.6≤d<1.0, and 0≤e≤0.1 may be used.

[0134] Also, M 1 It may be at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0136] More specifically, the lithium manganese-based oxide may be represented by the following chemical formula 2-1.

[0137] [Chemical Formula 2-1]

[0138] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w ]O2

[0139] In the above [Chemical Formula 2-1], 0.1≤X≤0.5, 0.5≤y<1, 0≤z≤0.3, and 0≤w≤0.2 may be used, preferably 0.2≤X≤0.5, 0.5≤y<1, 0≤z≤0.1, and 0≤w≤0.2, more preferably 0.3≤X≤0.5, 0.6≤y<1, 0≤z≤0.1, and 0≤w≤0.2.

[0140] Also, M 1 It may be at least one selected from the group consisting of metal ions Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0142] The above lithium manganese-based oxide can be manufactured by mixing a transition metal precursor and a lithium raw material and then calcining. At this time, the transition metal precursor and the lithium raw material may be mixed in an amount such that the molar ratio of the total transition metal (Ni+Co+Mn) : Li is 1 : 1.05 to 1 : 2, the calcination temperature may be 600°C to 1000°C, the calcination time may be 5 hours to 30 hours, and the calcination atmosphere may be an atmospheric atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100 volume% of oxygen.

[0143] Examples of the above lithium raw materials include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O), etc.), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3), etc.), chlorides (e.g., lithium chloride (LiCl), etc.), and one of these alone or a mixture of two or more of these may be used.

[0144] Meanwhile, the above 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 in that it allows for the production of an anode active material with a relatively high specific surface area.

[0145] The above transition metal precursor can be manufactured through a co-precipitation process. For example, the transition metal precursor can be manufactured by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, then mixing the metal solution, an ammonium cation complex forming agent, and a basic compound, and subsequently proceeding with a co-precipitation reaction. Additionally, if necessary, an oxidizing agent or oxygen gas may be further introduced during the co-precipitation reaction.

[0146] At this time, the transition metal-containing raw material may be an 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, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt acetate, cobalt halide, etc.

[0147] The above 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.

[0148] The above 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, if NaOH is used as the basic compound, a precursor in the form of a hydroxide can be obtained, and if Na2CO3 is used as the basic compound, a precursor in the form of a carbonate can be obtained. In addition, if the basic compound and an oxidizing agent are used together, a precursor in the form of an oxide can be obtained.

[0150] Meanwhile, the positive active material according to the present invention may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle size D50 of the secondary particles may be 2㎛ to 10㎛, preferably 2㎛ to 8㎛, more preferably 4㎛ to 8㎛.

[0151] In addition, the above-mentioned positive active material has a BET specific surface area of ​​1 m² 2 / g or more, 3 ~ 8m 2 / g or 4 ~ 6m 2 It can be / g.

[0152] In addition, 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 without a separate compensation material such as a sacrificial positive electrode material or a prior lithium compensation process such as pre-lithiation.

[0154] Meanwhile, the conductive material may include, for example, spherical or flake-like 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 nanotube, multi-walled carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 to 20 weight%, 1 to 20 weight%, or 1 to 10 weight% based on the total weight of the positive active material layer.

[0155] In addition, the binder may include, for example, 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, and one of these alone or a mixture of two or more may be used. The binder may be included in an amount of 1 to 20% by weight, 2 to 20% by weight, or 2 to 10% by weight based on the total weight of the anode active material layer.

[0157] The anode of the present invention as described above may be manufactured according to an anode manufacturing method known in the art. For example, the anode may be manufactured by a method of applying an anode slurry, prepared by dissolving or dispersing an anode active material, a binder, and / or a conductive material in a solvent, onto an anode current collector, followed by drying and rolling, or by a method of casting the anode slurry onto a separate support, peeling off the support, and then laminating the resulting film onto an anode current collector.

[0159] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase adhesion to the positive active material layer. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0160] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is not particularly limited, provided that it is sufficient to allow the anode composite to have an appropriate viscosity by considering the coating thickness, manufacturing yield, and workability of the anode composite.

[0162] cathode

[0163] The cathode according to the present invention comprises a cathode active material layer comprising a cathode active material, and the cathode active material layer may further comprise a conductive material and / or a binder as needed.

[0164] Various cathode active materials used in the industry, such as silicon-based cathode active materials, carbon-based cathode active materials, and metal alloys, may be used as the above-mentioned cathode active material.

[0165] Preferably, the negative electrode active material comprises a silicon-based negative electrode active material.

[0166] The above silicon-based negative electrode active material is, for example, Si, SiO m (here, 0 <m<2), Si-C 복합체, Si-M a Alloy (M a It may be selected from the group consisting of one or more types selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni) and combinations thereof.

[0167] In addition, the silicon-based negative electrode active material is M b It may be doped with metal, and in this case, the above M b The metal may be a Group 1 alkali metal element and / or a Group 2 alkaline earth metal element, for example, Li, Mg, etc. Specifically, the silicon negative electrode active material is M b Metal-doped Si, SiO m (here, 0 <m<2), Si-C 복합체 등일 수 있다. 금속 도핑된 실리콘계 음극 활물질의 경우, 도핑 원소로 인해 활물질 용량은 저하되나 높은 효율을 갖기 때문에, 높은 에너지 밀도를 구현할 수 있다.

[0168] In addition, the silicon-based negative electrode active material may further include a carbon coating layer on the particle surface. At this time, the amount of the carbon coating 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 may be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0170] In addition, the particle size of the silicon-based negative electrode active material is D 50 3~8 µm, preferably 4~7 µm, and D min ~ D max The thickness is 0.5 to 30 μm, preferably 0.5 to 20 μm, more preferably 1 to 15 μm.

[0172] Additionally, the above-mentioned cathode may further include a carbon-based cathode active material as a cathode active material, if necessary. The carbon-based cathode 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.

[0174] Meanwhile, the silicon-based negative electrode active material may be included in an amount of 1 to 100 wt%, 1 to 50 wt%, 1 to 30 wt%, 1 to 15 wt%, 10 to 70 wt%, or 10 to 50 wt% based on the total weight of the negative electrode active material.

[0175] The carbon-based negative electrode active material may be included in an amount of 0 to 99 wt%, 50 to 99 wt%, 70 to 99 wt%, 85 to 99 wt%, 30 to 90 wt%, or 50 to 90 wt% based on the total weight of the negative electrode active material.

[0177] 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, wherein 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 by weight, preferably 3:97 to 30:70. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, excellent cycle performance can be secured by suppressing the volume expansion of the silicon-based negative electrode active material while improving capacity characteristics.

[0179] The above-mentioned negative electrode active material may be included 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 satisfies the above range, excellent capacity characteristics and electrochemical characteristics can be obtained.

[0181] Examples of the conductive material include spherical or flake-like 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 nanotube, multi-walled carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 to 30 weight%, 1 to 20 weight%, or 1 to 10 weight% based on the total weight of the negative electrode active material layer.

[0182] 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 evenly formed on the surface of the cathode active material, thereby achieving the effect of improved cycle characteristics.

[0184] Examples of the above binders 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, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 1 to 20 weight%, 2 to 20 weight%, or 2 to 10 weight% based on the total weight of the negative electrode active material layer.

[0186] The above-mentioned cathode may have a multilayer structure in which the cathode active material layer is composed of a single layer or two or more layers. When the cathode active material layer is a multilayer structure composed of two or more layers, the types and / or contents of the cathode active material, binder, and / or conductive material in each layer may differ from one another. For example, the cathode according to the present invention may have a higher content of carbon-based cathode active material in the lower layer compared to the upper layer, and a higher content of silicon-based cathode active material in the upper layer, and in this case, the effect of improving rapid charging performance can be obtained compared to the case where the cathode active material layer is formed as a single layer.

[0187] The above negative electrode active material layer may have a porosity of 20% to 70% or 20% to 50%.

[0189] The above-mentioned cathode may be manufactured according to cathode manufacturing methods known in the art. For example, the above-mentioned cathode may be manufactured by applying a cathode slurry prepared by dissolving or dispersing a cathode active material, optionally a binder and a conductive material in a solvent, onto a cathode current collector, and then rolling and drying, or by casting the cathode slurry onto a separate support and then peeling off the support to obtain a film, which is then laminated onto a cathode current collector.

[0190] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0191] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is not particularly limited, provided that it is sufficient to adjust the cathode slurry to have an appropriate viscosity, taking into account the coating thickness of the cathode composite material, manufacturing yield, workability, etc.

[0193] Separator

[0194] In the lithium secondary battery of the present invention, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0196] The lithium secondary battery according to the present invention as described above can be usefully applied in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0197] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0198] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0199] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0200] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0202] The present invention will be specifically explained below through specific embodiments.

[0204] Comparative Example 1

[0205] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.2 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC): ethylmethyl carbonate (EMC): diethyl carbonate in a volume ratio of 20:60:20, and then adding 0.5 wt% vinylene carbonate (VC), 0.5 wt% propanesulfone (PS), 1 wt% ethylene sulfate (ESa), 0.5 wt% LiBF4, 1 wt% lithium difluorophosphate (LiDFP), and 3 wt% fluorinated ethylene carbonate (FEC).

[0207] Comparative Example 2

[0208] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of an unsubstituted coumarin compound represented by chemical formula A was additionally added.

[0209] <Chemical Formula A>

[0210]

[0212] Example 1

[0213] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of a compound represented by Chemical Formula 1B was additionally added.

[0215] Example 2

[0216] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of a compound represented by chemical formula 1D was additionally added.

[0218] Example 3

[0219] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of a compound represented by chemical formula 1E was additionally added.

[0221] Example 4

[0222] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of a compound represented by the chemical formula 1F was additionally added.

[0224] Example 5

[0225] A non-aqueous electrolyte was prepared in the same manner as Comparative Example 1, except that 0.5% by weight of a compound represented by the chemical formula 1G was additionally added.

[0227] Lithium secondary battery manufacturing

[0228] (Anode manufacturing)

[0229] Lithium manganese-based oxide Li as positive electrode active material particles 1.3 (Ni 0.35 Mn 0.65 )O 2.33 A positive electrode active material slurry (solid content 48 wt%) was prepared by adding carbon black as a conductive material and polyvinylidene fluoride (PVDF) as a binder to N-methyl-2-pyrrolidone (NMP), a solvent, in a weight ratio of 96:1:3. The positive electrode active material slurry was coated onto a positive electrode current collector (Al thin film), dried, and then rolled to produce a positive electrode.

[0231] (Cathode manufacturing)

[0232] Cathode active material (artificial graphite: SiO₂) m = 94.5:5.5 weight ratio), PVDF as a binder, and carbon black as a conductive material were added to NMP, a solvent, in a weight ratio of 95:2:3 to prepare a cathode active material slurry (solid content: 70 wt%). The cathode active material slurry was applied to a cathode current collector (Cu thin film), dried, and rolled to produce a cathode.

[0234] (Secondary battery manufacturing)

[0235] An electrode assembly was manufactured by sequentially laminating the positive and negative electrodes prepared by the above-described method together with a polyethylene porous film using a conventional method, and then the assembly was placed in a pouch-type secondary battery case, and a lithium secondary battery was manufactured by injecting the non-aqueous electrolyte prepared according to Examples 1 to 5 and Comparative Examples 1 to 2.

[0237] Experimental Example 1

[0238] Each lithium secondary battery manufactured as described above was subjected to a pre-aging step of being stored at room temperature for 2 days to allow the electrolyte to be sufficiently wetted. Then, at 45℃ and 0.5kgf / cm² 2 After charging to SOC 3% at 0.2C under [pressure], charge to SOC 17% at 0.3C under the same temperature and pressure conditions, and then, 5kgf / cm² 2 It was charged to SOC 30% at 0.3C under pressure. Then, film stabilization and gas evacuation processes were performed while conducting high-temperature aging at 60℃ for 15 hours.

[0239] Next, 45℃, 5kgf / cm² 2 The positive activation process was carried out by charging to 4.6V at 0.3C under pressure, and then the activation process was completed by discharging to 2V at 0.5C.

[0240] Meanwhile, the volume of the lithium secondary battery cell before and after the above activation process was measured at room temperature using the buoyancy method, and the cell volume increase rate in the activation process was calculated according to the following equation (1).

[0241] Equation (1): Cell volume change rate (%) = {(Volume after anode activation process - Initial cell volume) / Initial cell volume} × 100

[0242] The measurement results are shown in [Table 1] below.

[0243] Cell volume increase rate (%) before and after the activation process Comparative Example 1 158% Comparative Example 2 134.3% Example 1 118.5% Example 2 113.8% Example 3 115.3% Example 4 118.5% Example 5 83.7%

[0244] In the above activation process, since charging is performed up to a high voltage of 4.6V, reactive oxygen compounds are generated at the anode, and these reactive oxygen compounds 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, and consequently, the cell volume increases. Therefore, a small increase in cell volume means that the amount of reactive oxygen compounds is small.

[0245] Through Table 1 above, it can be confirmed that the lithium secondary batteries of Examples 1 to 5, which used a coumarin compound having one or more substituents as an additive, showed less increase in cell volume after the activation process compared to Comparative Examples 1 and 2, which indicates that the coumarin compound having one or more substituents effectively removed reactive oxygen.

[0246] Meanwhile, in the case of Comparative Example 2, which used an unsubstituted coumarin compound as an additive, the cell volume increase rate was lower than that of Comparative Example 1, but higher than that of Examples 1 to 5. In other words, it can be seen that when a coumarin compound substituted with one or more functional groups is used, the gas generation suppression effect is superior compared to when an unsubstituted coumarin compound is used. This is believed to be because a robust SEI film is formed on the electrode surface due to the functional groups substituted on the coumarin, and as a result, side reactions at the electrode interface are suppressed, thereby further suppressing the generation of activated gas.

[0248] Experimental Example 2

[0249] Each lithium secondary battery prepared as described above was activated in the same manner as in Experimental Example 1, and then fully charged to 100% SOC at 4.35V under CC / CV and 0.33C conditions at 25℃. Then, the fully charged lithium secondary batteries were stored at 60℃ for 8 weeks, and then the cell volume increase rate and capacity retention rate were measured.

[0250] At this time, 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 equation (2).

[0252] Equation (2): Capacity retention rate (%) = (Discharge capacity after high-temperature storage / Discharge capacity before high-temperature storage) × 100

[0253] 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 equation (3).

[0254] Equation (3): Cell volume change rate (%) = {(Volume after high-temperature storage - Initial volume) / Initial volume} × 100

[0255] The measurement results are shown in [Table 2] below.

[0256] Volume increase rate (%) Capacity retention rate (%) Comparative Example 1 14.0 78.8 Comparative Example 2 12.2 79.2 Example 1 8.5 80.8 Example 2 9.7 82.4 Example 3 10.9 83.3 Example 4 7.8 82.7 Example 5 6.6 84.2

[0257] Through [Table 2] above, it can be confirmed that the lithium secondary batteries of Examples 1 to 5, which used coumarin-based compounds containing one or more substituents as additives, showed a higher capacity retention rate after high-temperature storage and a smaller cell volume increase rate compared to the lithium secondary batteries of Comparative Examples 1 and 2. This is believed to be because a robust SEI film is formed on the electrode surface due to the functional groups substituted on the coumarin, thereby suppressing side reactions at the electrode interface.

Claims

Claim 1 A non-aqueous electrolyte comprising an organic solvent, a lithium salt, and a coumarin compound represented by the following [Chemical Formula 1]. [Chemical Formula 1] In the above [Chemical Formula 1], R is an alkynyl group having 2 to 10 carbon atoms, a proparzyl group, -COOR', -0-R”, or -COR''', R' is a proparzyl group, R” is a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, R''' is an alkyl group having 1 to 5 carbon atoms substituted with at least one halogen, and n is any integer from 1 to 6. Claim 2 In claim 1, the coumarin compound is a non-aqueous electrolyte that is a compound represented by the following chemical formula 1-1 or chemical formula 1-2. [Chemical Formula 1-1] [Chemical Formula 1-2] In the above [Chemical Formula 1-1] and [Chemical Formula 1-2], R is an alkynyl group having 2 to 10 carbon atoms, a proparzyl group, -COOR', -0-R”, or -COR''', R' is a proparzyl group, R” is a silyl group substituted with a proparzyl group or at least one alkyl group having 1 to 5 carbon atoms, and R''' is an alkyl group having 1 to 5 carbon atoms substituted with at least one halogen. Claim 3 The non-aqueous electrolyte according to claim 1, wherein the coumarin compound is selected from the group consisting of compounds represented by [Chemical Formula 1B], [Chemical Formula 1D] to [Chemical Formula 1G] below. [Chemical Formula 1B] [Chemical Formula 1D] [Chemical Formula 1E] [Chemical Formula 1F] [Chemical Formula 1G] Claim 4 The non-aqueous electrolyte according to claim 1, wherein the coumarin compound is included in an amount of 0.5% to 3% by weight based on the total weight of the non-aqueous electrolyte. Claim 5 A non-aqueous electrolyte according to claim 1, further comprising a halogen-substituted cyclic carbonate. Claim 6 In claim 5, the halogen-substituted cyclic carbonate is a non-aqueous electrolyte that is fluorinated ethylene carbonate. Claim 7 In claim 6, the non-aqueous electrolyte is one in which the halogen-substituted cyclic carbonate is included in an amount of 0.5 to 10 weight percent based on the total weight of the non-aqueous electrolyte. Claim 8 A lithium secondary battery comprising: a positive electrode comprising a positive active material; a negative electrode comprising a negative active material; and a non-aqueous electrolyte according to any one of claims 1 to 7. Claim 9 A lithium secondary battery according to claim 8, wherein the negative electrode active material comprises a silicon-based negative electrode active material. Claim 10 In claim 9, the silicon-based negative electrode active material is Si, SiOm(wherein 0 <m≤2), Si-C 복합체, Si-M a Alloy (M a A lithium secondary battery selected from the group consisting of one or more types selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni) and combinations thereof. Claim 11 A 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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