Electrolyte for lithium secondary battery, and lithium secondary battery comprising the same

Abstract

To provide an electrolyte for a lithium secondary battery which is capable of improving battery performance.SOLUTION: An electrolyte for a lithium secondary battery includes a lithium salt, an organic solvent, and an additive. The additive includes: one or more first compounds selected from the compounds represented by the chemical formulas 1-2 and 1-3 in the figure; and a second compound represented by the chemical formula 2 in the figure. The mixing weight ratio between the first compounds and the second compound is in the range between 1:9 and 9:1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0002] Lithium secondary batteries are used as power sources for portable electronic devices such as video cameras, mobile phones, and laptop computers. Rechargeable lithium secondary batteries have a higher energy density per unit weight and can be charged quickly compared to existing lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries.

[0003] Since lithium secondary batteries operate at high driving voltages, aqueous electrolytes that are highly reactive with lithium cannot be used. Generally, organic electrolytes are used as electrolytes for lithium secondary batteries. These organic electrolytes are prepared by dissolving lithium salts in organic solvents. It is desirable for these organic solvents to be stable at high voltages, have high ionic conductivity and dielectric constant, and have low viscosity.

[0004] However, if an organic electrolyte containing a lithium salt is used as the electrolyte for a lithium secondary battery, side reactions between the negative electrode / positive electrode and the electrolyte may occur, resulting in a decrease in the life characteristics and high-temperature stability of the lithium secondary battery.

[0005] Therefore, there is a need for an electrolyte for a lithium secondary battery that can provide a lithium secondary battery with improved life characteristics and high temperature stability. Summary of the Invention [Problem to be solved by the invention]

[0006] One aspect of the present invention is to provide an electrolyte for a lithium secondary battery that can improve battery performance. Another aspect provides a lithium secondary battery including the above-mentioned electrolyte for lithium secondary batteries. [Means for solving the problem]

[0007] According to one embodiment, there is provided an electrolyte for a lithium secondary battery, comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2, and the mixing weight ratio of the first compound to the second compound is in the range of 1:9 to 9:1:

[0008] [ka]

[0009] In the above Chemical Formula 1, X 1 is a fluoro, chloro, bromo or iodo group, R 1 Or R 6 are each independently hydrogen, cyano, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1, [ka] In the above Chemical Formula 2, A1 and A2 are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms; a carbonyl group; a sulfinyl group; or a divalent group having 2 to 6 carbon atoms to which a plurality of substituted or unsubstituted alkylene units are bonded via ether bonds.

[0010] According to another aspect, there is provided a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the aforementioned electrolyte disposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0011] By using an electrolyte for a lithium secondary battery according to an embodiment, an increase in battery resistance during high-temperature storage can be suppressed, and the life characteristics and high-temperature stability of the lithium secondary battery can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a lithium secondary battery according to an embodiment; [Figure 2] 1 shows the results of measuring the amount of nickel (Ni) eluted from the positive electrode of the lithium secondary batteries according to Example 3 and Comparative Examples 1, 3 and 6 after high-temperature storage. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an electrolyte for a lithium secondary battery and a lithium secondary battery including the same according to an example embodiment will be described in more detail. According to an embodiment, an electrolyte for a lithium secondary battery includes a lithium salt, an organic solvent, and an additive, the additive including a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2, and the mixing weight ratio of the first compound to the second compound is in the range of 1:9 to 9:1:

[0014] [ka] In the above Chemical Formula 1, X 1 is a fluoro, chloro, bromo or iodo group, R 1 Or R 6are each independently hydrogen, cyano, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1, [ka] In the above Chemical Formula 2, A1 and A2 are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, a carbonyl group, a sulfinyl group, or a divalent group having 2 to 6 carbon atoms to which multiple substituted or unsubstituted alkylene units are bonded via ether bonds.

[0015] Lithium secondary batteries with high output and capacity can be fabricated by using a lithium transition metal oxide containing nickel and one or more other transition metals as the positive electrode active material, with the nickel content being, for example, 80 mol % or more relative to the total moles of the transition metals. However, lithium transition metal oxides with a high nickel content have an unstable surface structure, which increases gas generation due to side reactions during the battery charge and discharge process, further exacerbating the leaching of transition metals such as nickel. Therefore, lithium secondary batteries using lithium transition metal oxides with a high nickel content as the positive electrode active material exhibit reduced life characteristics and increased resistance at high temperatures, and therefore require improvement in stability at high temperatures.

[0016] The electrolyte for a lithium secondary battery according to an embodiment may form a low-resistance solid electrolyte interface (SEI) film and / or protective layer by using a combination of the first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 as additives, thereby reducing the internal resistance of the battery. Furthermore, the amount of nickel elution during high-temperature storage is significantly reduced, thereby resolving the above-mentioned problems and enabling the production of a lithium secondary battery with excellent resistance suppression effect at high temperatures, improved life characteristics, and high-temperature stability.

[0017] The reason why the performance of a lithium secondary battery is improved by using a combination of the first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 as an electrolyte additive will be explained in more detail below. However, these explanations are provided to aid in understanding the present invention, and the scope of the present invention is not limited to the scope of the following explanations.

[0018] LiPF6 is commonly used as the lithium salt in electrolytes, but it has problems such as poor thermal stability and susceptibility to hydrolysis by moisture. Thus, LiPF6-containing electrolytes exhibit instability when exposed to moisture and high temperatures. LiPF6 decomposition products are one of the main factors contributing to changes in the composition and stability of the negative electrode interface. Residual moisture and / or surface hydroxyl groups can react with PF6 anions in solution to generate HF and release PF5. The released HF corrodes the positive electrode and, in some cases, the positive electrode, gradually reducing its electrochemical performance.

[0019] When the first compound represented by Chemical Formula 1 is used as an electrolyte additive, it forms an SEI film on the negative electrode surface that has high high-temperature stability and excellent ionic conductivity, and it can suppress side reactions of LiPF6 due to the -PO2F functional group. As a result, gas generation due to decomposition reactions of the electrolyte inside the lithium secondary battery during high-temperature storage is suppressed, improving cycle life characteristics. In addition, suppressing gas generation can prevent swelling of the battery.

[0020] In addition, by including the second compound represented by Chemical Formula 2 together with the compound represented by Chemical Formula 1, an SEI film and / or protective layer having low resistance can be formed, thereby reducing the internal resistance of the battery.

[0021] The first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 strongly interact with the transition metal ions of the positive electrode, completely capping and deactivating the reaction centers on the positive electrode surface, thereby preventing dissolution of the transition metal and oxidation of the solvent. That is, a cathode electrolyte interphase (CEI) film with low impedance is formed on the positive electrode surface. The CEI film prevents electrolyte oxidation, prevents the generation of by-products such as gas and HF, and prevents destruction of the electrode structure, improving cycle stability and rate-limiting performance. Furthermore, the formation of the CEI film reduces the resistance at the interface between the electrolyte and the positive electrode and improves lithium ion conductivity, thereby increasing the low-temperature discharge voltage.

[0022] More specifically, the first compound represented by Chemical Formula 1 can be coordinated with a thermal decomposition product of a lithium salt such as LiPF6 or an anion dissociated from the lithium salt to form a complex. The formation of such a complex stabilizes the thermal decomposition product of the lithium salt or the anion dissociated from the lithium salt, thereby suppressing undesired side reactions between the thermal decomposition product of the lithium salt or the anion dissociated from the lithium salt and the electrolyte. This improves the cycle life characteristics of the lithium secondary battery, prevents gas generation inside the lithium secondary battery, and significantly reduces the rate of defects.

[0023] In addition, the second compound represented by Chemical Formula 2 has a higher reduction potential than the first compound represented by Chemical Formula 1, and by participating first in the formation of the SEI film, it is possible to prevent the over-decomposition of the first compound represented by Chemical Formula 1, thereby suppressing side reactions with the electrolyte, thereby forming an SEI film and / or protective layer with low resistance. Chemical Formula 1, whose over-decomposition is suppressed by Chemical Formula 2, can suppress high-temperature thermal decomposition of the lithium salt during high-temperature storage, for example at 60°C, and reduce side reactions of the electrolyte.

[0024] The mixing weight ratio of the compound represented by Chemical Formula 1 to the second compound represented by Chemical Formula 2 may be in the range of 1:9 to 9:1. For example, the mixing weight ratio of the compound represented by Chemical Formula 1 to the second compound represented by Chemical Formula 2 may be in the range of 1:8 to 8:1, more specifically, in the range of 1:7 to 7:1, or in the range of 1:6 to 6:1, for example, in the range of about 1:5 to 5:1. By including them in this mixing weight ratio, an SEI coating having low resistance and excellent thermal stability may be formed, and the decomposition reaction of the electrolyte may be suppressed.

[0025] The content of the first compound represented by Chemical Formula 1 may be in the range of 0.05 to 10 wt %, for example, 0.1 to 10 wt %, 0.2 to 5 wt %, or 0.2 to 3 wt %, based on the total weight of the electrolyte, but is not limited thereto, and may be selectively used in an appropriate amount as long as it does not impair battery characteristics. When the content of the first compound represented by Chemical Formula 1 is in this range, it is possible to obtain effects of improving high-temperature storage and swelling, suppress an increase in interfacial resistance, and prepare a lithium secondary battery with improved high-temperature characteristics and resistance characteristics without deteriorating life characteristics.

[0026] The content of the second compound represented by Formula 2 may be in the range of 0.05 to 10 wt %, for example, 0.1 to 10 wt %, 0.2 to 5 wt %, or 0.2 to 3 wt %, based on the total weight of the electrolyte, but is not limited thereto, and may be selectively used in an appropriate amount as long as it does not impair battery characteristics. When the content of the second compound represented by Formula 2 is in this range, an increase in interfacial resistance can be suppressed, and battery performance such as capacity retention and life characteristics can be improved.

[0027] According to one embodiment, the content of the first compound represented by Chemical Formula 1 is equal to or greater than the content of the second compound represented by Chemical Formula 2. By including the first compound in an amount equal to or greater than the content of the second compound, the DC resistance increase rate during high temperature storage can be further suppressed and the amount of gas generation can be reduced.

[0028] According to one embodiment, the first compound is also represented by the following formula 1-1:

[0029] [ka]

[0030] In the above Chemical Formula 1-1, R 1 Or R 6 , and n are as defined above. The compound represented by Chemical Formula 1-1 has an electron-soluble fluorine substituent directly bonded to the central atom, phosphorus (P(III)), and can improve the stability of the SEI film on top of the positive electrode.

[0031] According to one embodiment, the first compound may also be represented by the following formula 1-1A or 1-1B:

[0032] [ka]

[0033] In the chemical formula 1-1A and 1-1B, R 1 Or R 6 are each independently hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0034] Specifically, the aforementioned R 1 Or R 6 are each independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group, and more specifically, 1 Or R 6 are also hydrogen.

[0035] The first compound represented by Chemical Formula 1 is, for example, one or more compounds selected from the compounds represented by Chemical Formulas 1-2 to 1-9 below.

[0036] [ka] [ka]

[0037] According to one embodiment, the first compound is also the compound represented by Formula 1-2. According to one embodiment, the second compound is also represented by the following formula 2-1:

[0038] [ka]

[0039] In the above Chemical Formula 1-1, R 1 Or R 4are each independently hydrogen, cyano, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1, m is an integer from 1 to 5; The second compound represented by Chemical Formula 2 is, for example, one or more compounds selected from the compounds represented by Chemical Formulas 2-2 to 2-19 below.

[0040] [ka] [ka] [ka]

[0041] According to one embodiment, the second compound is also a compound represented by Formula 2-2. According to an embodiment, the lithium salt may be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (2≦x≦20, 2≦y≦20), LiCl, LiI, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), LiPO2F2, and compounds represented by the following formulas 3 to 6, but are not limited thereto. Any material that can be used as a lithium salt in the art may be used.

[0042] [ka]

[0043] In the electrolyte, the concentration of the lithium salt is 0.01 to 5.0 M, for example, 0.05 to 5.0 M, for example, 0.1 to 5.0 M, for example, 0.1 to 2. When the concentration of the lithium salt is within the above range, further improved lithium secondary battery characteristics can be obtained.

[0044] The organic solvent may be at least one selected from the group consisting of carbonate-based solvents, ester-based solvents, ether-based solvents, and ketone-based solvents.

[0045] Carbonate solvents include ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and butylene carbonate (BC). Ester solvents include methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, and acetic acid. Examples of suitable solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, γ-butyrolactone, decanolide, γ-valerolactone, mevalonolactone, and caprolactone. Examples of suitable ether solvents include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. Examples of suitable ketone solvents include cyclohexanone. Examples of suitable nitrile solvents include acetonitrile (AN), succinonitrile (SN), and adiponitrile. Examples of suitable solvents include, but are not limited to, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and tetrahydrofuran. Any solvent known in the art that can be used as an organic solvent can be used. For example, the organic solvent may be a mixed solvent of 50 to 95 vol% of a chain carbonate and 5 to 50 vol% of a cyclic carbonate, or a mixed solvent of 70 to 95 vol% of a chain carbonate and 5 to 30 vol% of a cyclic carbonate. For example, the organic solvent may be a mixed solvent of three or more organic solvents.

[0046] According to one embodiment, the organic solvent may include at least one selected from the group consisting of ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), butylene carbonate, ethyl propionate, propyl propionate, ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone, and tetrahydropurane, but is not limited thereto. Any organic solvent known in the art may be used.

[0047] The electrolyte may be in a liquid or gel state, or may be prepared by adding a lithium salt and the above-mentioned additives to an organic solvent. A lithium secondary battery according to another embodiment includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the above-described electrolyte disposed between the positive electrode and the negative electrode.

[0048] By including the electrolyte additive for lithium secondary batteries, the lithium secondary battery is prevented from increasing in initial resistance, and gas generation due to side reactions is suppressed, thereby improving the life characteristics.

[0049] The positive electrode active material includes a lithium transition metal oxide containing nickel and other transition metals, wherein the nickel content is 60 mol% or more, for example, 75 mol% or more, for example, 80 mol% or more, for example, 85 mol% or more, for example, 90 mol% or more, based on the total moles of the transition metals.

[0050] For example, the lithium transition metal oxide is also a compound represented by the following chemical formula 7: [Chemical Formula 7] Li a Ni x Co y M z O 2-b A b In the above Chemical Formula 7, 1.0 ≦ a ≦ 1.2, 0 ≦ b ≦ 0.2, 0.6 ≦ x < 1, 0 < y ≦ 0.3, 0 < z ≦ 0.3, and x + y + z = 1, M is one or more selected from the group consisting of manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), and boron (B), A is F, S, Cl, Br, or a combination thereof.

[0051] For example, 0.7 ≦ x < 1, 0 < y ≦ 0.3, 0 < z ≦ 0.3; 0.8 ≦ x < 1, 0 < y ≦ 0.3, 0 < z ≦ 0.3; 0.8 ≦ x < 1, 0 < y ≦ 0.2, 0 < z ≦ 0.2; 0.83 ≦ x < 0.97, 0 < y ≦ 0.15, 0 < z ≦ 0.15; or 0.85 ≦ x < 0.95, 0 < y ≦ 0.1, 0 < z ≦ 0.1; also holds.

[0052] For example, the lithium transition metal oxide is at least one of the compounds represented by the following Chemical Formulas 4 and 5: [Chemical Formula 4] LiNi x Co y Mn z O2 In the above Chemical Formula 4, 0.6 ≦ x ≦ 0.95, 0 < y ≦ 0.2, 0 < z ≦ 0.1. For example, 0.7 ≦ x ≦ 0.95, 0 < y ≦ 0.3, 0 < z ≦ 0.3. [Chemical Formula 5] LiNi x Co y Al z O2 In the above Chemical Formula 5, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, 0 < z ≤ 0.1. For example, 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0 < z ≤ 0.3. For example, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0 < z ≤ 0.3. For example, 0.82 ≤ x ≤ 0.95, 0 < y ≤ 0.15, 0 < z ≤ 0.15. For example, 0.85 ≤ x ≤ 0.95, 0 < y ≤ 0.1, 0 < z ≤ 0.1.

[0053] For example, the lithium transition metal oxide is LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.2 O2 or LiNi 0.88 Co 0.1 Al 0.02 O2 as well.

[0054] According to another embodiment, the positive electrode active material includes at least one active material selected from the group consisting of Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4).

[0055] The negative electrode active material also includes one or more selected from silicon-based compounds, carbon-based materials, composites of silicon-based compounds and carbon-based compounds, and silicon oxides (SiO x (0 < x < 2)).

[0056] The silicon-based compound may be silicon particles, silicon alloy particles, etc. The size of the silicon-based compound is less than 200 nm, for example, 10 to 150 nm. The term "size" may refer to the average particle size when the silicon-based compound is spherical, or to the average major axis length when the silicon particles are non-spherical.

[0057] When the size of the silicon-based compound is within this range, the lifespan characteristics are excellent, and when an electrolyte according to an embodiment is used, the lifespan of a lithium secondary battery is further improved.

[0058] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc.

[0059] The composite of a silicon-based compound and a carbon-based compound may be a composite having a structure in which silicon nanoparticles are disposed on the carbon-based compound, a composite in which silicon particles are contained on the surface of the carbon-based compound and inside the carbon-based compound, or a composite in which silicon particles are coated on the carbon-based compound and contained inside the carbon-based compound. In the composite of a silicon-based compound and a carbon-based compound, the carbon-based compound may be graphite, graphene, graphene oxide, or a combination thereof.

[0060] The composite of a silicon-based compound and a carbon-based compound is an active material obtained by dispersing silicon nanoparticles with an average particle size of about 200 nm or less on carbon-based compound particles and then performing carbon coating, and is also an active material in which silicon (Si) particles are present in and on the upper part of graphite. The average secondary particle size of the composite of the silicon-based compound and the carbon-based compound is also 5 μm to 20 μm. The average particle size of the silicon nanoparticles is also 5 nm or more, for example, 10 nm or more, for example, 20 nm or more, for example, 50 nm or more, for example, 70 nm or more. The average particle size of the silicon nanoparticles is also 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, 10 nm or less. For example, the average particle size of the silicon nanoparticles is also 100 nm to 150 nm.

[0061] The average secondary particle size of the composite of the silicon-based compound and the carbon-based compound is also 5 μm to 18 μm, for example, 7 μm to 15 μm, for example, 10 μm to 13 μm.

[0062] As other examples of the composite of the silicon-based compound and the carbon-based compound, the porous silicon composite cluster of Korean Patent Publication No. 10-2018-0031585 and the porous silicon composite cluster structure disclosed in Korean Patent Publication No. 10-2018-0056395 can be used. Korean Patent Publication Nos. 10-2018-0031586 and 10-2018-0056395 are incorporated herein by reference.

[0063] The silicon-carbon-based compound composite according to one embodiment is a porous silicon composite cluster including a porous core including porous silicon composite secondary particles and a shell including a second graphene disposed on the upper part of the core, wherein the porous silicon composite secondary particles include aggregates of two or more silicon composite primary particles, and the silicon composite primary particles include silicon, silicon oxide (SiO x )(O<x<2), and a first graphene disposed on the silicon oxide, and is also a porous silicon composite cluster.

[0064] According to another embodiment, a silicon-carbon compound composite includes a porous silicon composite secondary particle and a second carbon flake on at least one surface of the porous silicon composite secondary particle, and includes a porous silicon composite cluster; and a carbon-based coating film containing amorphous carbon disposed on top of the porous silicon composite cluster. The porous silicon composite secondary particle includes an aggregate of two or more silicon composite primary particles. The silicon composite primary particle includes silicon, silicon oxide (SiO x )(where 0 < x < 2), and a first carbon flake on at least one surface of the silicon oxide. The silicon oxide is also a porous silicon composite cluster structure existing in the state of a film, a matrix, or a combination thereof.

[0065] The first carbon flake and the second carbon flake may each exist in the state of a film, a particle, a matrix, or a combination thereof. And the first carbon flake and the second carbon flake are each also graphene, graphite, carbon fiber, graphene oxide, etc.

[0066] The composite of the aforementioned silicon-based compound and carbon-based compound is also a composite having a structure in which silicon nanoparticles are disposed on top of the carbon-based compound, a composite in which silicon particles are included in the surface and the interior of the carbon-based compound, and a composite in which silicon particles are coated on the carbon-based compound and included in the interior of the carbon-based compound. In the composite of the silicon-based compound and the carbon-based compound, the carbon-based compound is also graphite, graphene, graphene oxide, or a combination thereof.

[0067] The form of the lithium secondary battery is not particularly limited and includes a lithium ion battery, a lithium ion polymer battery, a lithium sulfur battery, etc. The lithium secondary battery is also manufactured by the following method.

[0068] First, the positive electrode is prepared. For example, a positive electrode active material composition is prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and the film may be peeled off from the support and laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the forms listed above, and may have forms other than those listed above.

[0069] The positive electrode active material is a lithium-containing metal oxide, and any commonly used material in the art may be used without limitation. For example, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. Specific examples thereof include Li a A 1-b B 1 b D 1 2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b B 1 b O 2-c D 1 c (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); LiE 2-b B 1 b O 4-c D 1 c (wherein 0≦b≦0.5, 0≦c≦0.05); Li a Ni 1-b-c Co b B 1 c D 1 α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li a Ni 1-b-c Co b B 1 c O2-α F 1 α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 2 (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Mn b B 1 c D α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 2 (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG bO2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) A compound represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2);LiFePO4 can be used.

[0070] In the above formula, A is Ni, Co, Mn, or a combination thereof; B 1 is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof, and D 1 is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F 1 is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0071] For example, LiCoO2, LiMn x O 2x (x=1, 2), LiNi 1-x Mn x O 2x (0 <x<1)、LiNi 1-x-y Co x Mn y O2 (0≦x≦0.5, 0≦y≦0.5), LiFePO4, etc.

[0072] It goes without saying that the compound may have a coating layer on its surface, or the compound may be mixed with a compound having a coating layer. The coating layer may include a coating element compound such as an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The coating layer compound may be amorphous or crystalline. The coating element contained in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer formation process may use any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material and is well understood by those skilled in the art, so a detailed description will be omitted.

[0073] The conductive material may be, but is not limited to, carbon black, graphite particles, etc., and any material that can be used as a conductive material in the art may be used.

[0074] The binder may be vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and mixtures thereof, or styrene-butadiene rubber-based polymers, but is not limited thereto, and any material known in the art that can be used as a binder may be used.

[0075] The solvent may be N-methylpyrrolidone, acetone, water, or the like, but is not limited thereto, and any solvent that can be used in the art may be used.

[0076] The contents of the positive electrode active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries. Depending on the application and configuration of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0077] Next, the negative electrode is prepared. For example, a negative electrode active material composition may be prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition may be directly coated on a metal current collector and dried to produce a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and the film may be peeled off from the support and laminated on a metal current collector to produce a negative electrode plate.

[0078] The negative electrode active material may be any material known in the art that can be used as a negative electrode active material for lithium batteries, including at least one selected from the group consisting of lithium metal, metals that can be alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbonaceous materials.

[0079] For example, the metal capable of being alloyed with lithium may be Si, Sn, Al, Ge, Pb, Bi, an SbSi-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Si), or an Sn-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, or a combination thereof, and is not Sn). The element Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0080] For example, the transition metal oxide can be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc. For example, the non-transition metal oxide is SnO2, SiO x (0 <x<2)などでもある。 The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc.

[0081] In the negative electrode active material composition, the same conductive material and binder as those in the positive electrode active material composition can be used. The contents of the negative electrode active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries. Depending on the application and configuration of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0082] Next, a separator to be inserted between the positive electrode and the negative electrode is prepared. The separator may be any material commonly used in lithium batteries. Materials that have low resistance to ion migration of the electrolyte and excellent electrolyte wetting ability may be used. For example, the separator may be selected from glass fiber, polyester, Teflon (registered trademark), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven or woven fabric. For example, a rollable separator such as polyethylene or polypropylene may be used for a lithium ion battery, while an organic separator with excellent electrolyte wetting ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured by the following method.

[0083] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition can be directly coated on the electrode and dried to form a separator. Alternatively, the separator composition can be cast on a support, dried, and then peeled off from the support, and the resulting separator film can be laminated on the electrode to form a separator.

[0084] The polymer resin used to manufacture the separator is not particularly limited, and any material used as a binder for electrode plates can be used, such as vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof. The separator may include, but is not limited to, polyethylene separator (PES), polypropylene separator (PPS), ceramic coated separator (CCS), polymer coated separator (PCS), multi-layer coated separator (MCS), multi-functional separator (MFS), and combinations thereof.

[0085] Next, the above-mentioned electrolyte solution is prepared. As can be seen from FIG. 1, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2, and the separator 4 are wound or folded and housed in a battery case 5. An organic electrolyte is then injected into the battery case 5, which is then sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may be cylindrical, prismatic, thin-film, or the like. For example, the lithium battery may be a large-sized thin-film battery. The lithium battery may also be a lithium-ion battery.

[0086] A cylindrical battery may include a cylindrical electrode assembly formed by winding a separator between a positive electrode and a negative electrode, inserted into a cylindrical can, and then filled with an electrolyte. The cylindrical can may be made of steel, a steel alloy, nickel-plated steel, a nickel-plated steel alloy, aluminum, an aluminum alloy, or an equivalent, but the material is not limited thereto. Furthermore, the cylindrical can may have a beading portion recessed inward at its bottom and a crimping portion bent inward at its top, centered around the cap assembly, to prevent the cap assembly from coming off.

[0087] A plurality of battery structures each having a separator disposed between the positive electrode and the negative electrode are stacked to form a battery pack, which can be used in any device requiring high capacity and high output, such as a laptop computer, a smartphone, or an electric vehicle.

[0088] The lithium secondary battery according to an embodiment has a significantly lower DCIR (direct current internal resistance) increase rate than a lithium secondary battery using a conventional nickel-rich lithium-nickel composite oxide as a positive electrode active material, and can exhibit excellent battery characteristics.

[0089] The operating voltage of a lithium secondary battery using the above-mentioned positive electrode, negative electrode, and electrolyte is, for example, 2.5-2.8V at the lower limit and 4.1V or higher, for example, 4.1-4.45V at the upper limit.

[0090] In addition, the lithium secondary battery can be used in, but is not limited to, power tools powered by a battery-type motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0091] As used herein, the term "alkyl group" refers to a branched or unbranched aliphatic hydrocarbon group. In one embodiment, the alkyl group can be substituted or unsubstituted. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and the like, each of which can be optionally substituted in other embodiments. In other embodiments, the alkyl group can contain 1 to 6 carbon atoms. For example, alkyl groups containing 1 to 6 carbon atoms include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, pentyl, 3-pentyl, hexyl, and the like.

[0092] One or more hydrogen atoms in the alkyl group may be a halogen atom, a C1-C 20 Alkyl groups (e.g., CF3, CHF2, CH2F, CCl3, etc.), C1-C 20 Alkoxy groups, C2-C 20 Alkoxyalkyl groups, hydroxy groups, nitro groups, cyano groups, amino groups, amidino groups, hydrazines, hydrazones, carboxyl groups and their salts, sulfonyl groups, sulfamoyl groups, sulfonic acid groups and their salts, phosphoric acid groups and their salts, C1-C20 Alkyl groups, C2-C 20 Alkenyl groups, C2-C 20 Alkynyl groups, C1-C 20 Heteroalkyl groups, C6-C 20 Aryl groups, C7-C 20 Aryl alkyl groups, C6-C 20 Heteroaryl groups of C7-C 20 Heteroarylalkyl groups, C6-C 20 Heteroaryloxy group, or C6-C 20 It may be substituted with a heteroaryloxyalkyl group.

[0093] As used herein, the term "alkenyl group" refers to a hydrocarbon group having 2 to 20 carbon atoms and containing one or more carbon-carbon double bonds, including, but not limited to, ethenyl, 1-propenyl, 2-propenyl, 2-methyl-1-propenyl, 1-butenyl, 2-butenyl, cyclopropenyl, cyclopentenyl, cyclohexenyl, and cyclopentenyl groups. In other embodiments, the alkenyl group is substituted or unsubstituted. In other embodiments, the alkenyl group has 2 to 40 carbon atoms.

[0094] As used herein, the term "alkynyl group" refers to a hydrocarbon group containing 2 to 20 carbon atoms and one or more carbon-carbon triple bonds, including, but not limited to, ethynyl, 1-propynyl, 1-butynyl, 2-butynyl, and the like. In other embodiments, the alkynyl group is substituted or unsubstituted. In other embodiments, the alkynyl group has 2 to 40 carbon atoms.

[0095] As used herein, a substituent is derived from an unsubstituted parent group, where one or more hydrogen atoms have been replaced with another atom or group. Unless otherwise indicated, if a group is considered "substituted," it means that the group is C1-C 20 Alkyl groups, C2-C 20 Alkenyl groups, C2-C 20 Alkynyl groups, C1-C20 It means that the functional group is substituted with one or more substituents independently selected from the group consisting of alkoxy, halogen, cyano, hydroxy, and nitro. If a functional group is described as being "optionally substituted," the functional group can be substituted with the aforementioned substituents.

[0096] The term "halogen" includes fluorine, bromine, chlorine, iodine, and the like. The term "alkoxy group" refers to "alkyl-O-", and the alkyl group is as defined above. Examples of the alkoxy group include a methoxy group, an ethoxy group, a 2-propoxy group, a butoxy group, a t-butoxy group, a pentyloxy group, and a hexyloxy group. One or more hydrogen atoms in the alkoxy group may be substituted with the same substituents as those in the alkyl group.

[0097] The term "heteroaryl group" refers to a monocyclic or bicyclic organic group containing one or more heteroatoms selected from N, O, P, or S, with the remaining ring atoms being carbon. The heteroaryl group may contain, for example, 1 to 5 heteroatoms and may contain 5 to 10 ring members. The S or N may be oxidized to various oxidation states.

[0098] Examples of heteroaryl groups include thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, isothiazol-3-yl, isothiazol-4-yl, isothiazol-5-yl, oxazol-2-yl, and oxazol-4-yl. The compound may have a tetrazolyl group, a pyrid-2-yl group, a pyrid-3-yl group, a 2-pyrazin-2-yl group, a pyrazin-4-yl group, a pyrazin-5-yl group, a 2-pyrimidin-2-yl group, a 4-pyrimidin-2-yl group, or a 5-pyrimidin-2-yl group.

[0099] The term "heteroaryl group" includes cases where a heteroaromatic ring is optionally fused to one or more aryl groups, cycloaliphatic groups, or heterocyclic groups. The term "carbocyclic group" refers to a saturated or partially unsaturated non-aromatic monocyclic, bicyclic, or tricyclic hydrocarbon group.

[0100] Examples of the monocyclic hydrocarbon group include a cyclopentyl group, a cyclopentenyl group, a cyclohexyl group, and a cyclohexenyl group. Examples of the bicyclic hydrocarbon group include a bornyl group, a decahydronaphthyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.1.1]heptyl group, a bicyclo[2.2.1]heptenyl group, or a bicyclo[2.2.2]octyl group.

[0101] An example of the tricyclic hydrocarbon group is an adamantly group. One or more hydrogen atoms in the carbocyclic ring may be substituted with the same substituents as in the alkyl group described above.

[0102] The present invention will be described in more detail through the following examples and comparative examples. However, the examples are merely for illustrating the present invention and do not limit the scope of the present invention. [Example]

[0103] (Lithium secondary battery manufacturing) Example 1 1.5M LiPF6 and vinylene carbonate were added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 2:4:4, and then 1.0 wt% of the compound represented by Chemical Formula 1-2 and 0.2 wt% of the compound represented by Chemical Formula 2-2 were added based on the total weight of the electrolyte to prepare an electrolyte for a lithium secondary battery.

[0104] [ka]

[0105] As the positive electrode active material, LiNi 0.8 Co 0.1 Al 0.1A mixture of 97 wt% O2, 0.5 wt% artificial graphite powder (as a conductive material), 0.8 wt% carbon black (Ketjen black), 0.2 wt% modified acrylonitrile rubber, and 1.5 wt% polyvinylidene fluoride (PVdF) was added to N-methyl-2-pyrrolidone and stirred for 30 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was then coated onto a 20 μm thick aluminum current collector using a doctor blade to a thickness of approximately 60 μm, dried in a hot air oven at 100°C for 0.5 hours, and then further dried in a vacuum at 120°C for 4 hours. The cathode was then rolled to prepare a cathode.

[0106] Anode active material slurry was prepared by mixing artificial graphite as anode active material and polyvinylidene fluoride as a binder in a weight ratio of 98:2 and dispersing the mixture in N-methylpyrrolidone. The slurry was applied to a 10 μm-thick copper current collector using a doctor blade to a thickness of approximately 60 μm, dried in a hot air oven at 100°C for 0.5 hours, further dried in a vacuum at 120°C for 4 hours, and roll-pressed to prepare anodes. A cylindrical lithium secondary battery was fabricated using the above-prepared positive and negative electrodes, a 14 μm thick polyethylene separator, and the above-prepared electrolyte.

[0107] Example 2 A lithium secondary battery was manufactured by the same process as in Example 1, except that the contents of the compound represented by Chemical Formula 1-2 and the compound represented by Chemical Formula 2-2 were 1.0 wt % and 0.5 wt %, respectively.

[0108] Example 3 A lithium secondary battery was manufactured by the same process as in Example 1, except that the contents of the compound represented by Chemical Formula 1-2 and the compound represented by Chemical Formula 2-2 were 1.0 wt % and 1.0 wt %, respectively.

[0109] Example 4 A lithium secondary battery was manufactured by the same process as in Example 1, except that the contents of the compound represented by Chemical Formula 1-2 and the compound represented by Chemical Formula 2-2 were 0.5 wt % and 1.0 wt %, respectively.

[0110] Example 5 A lithium secondary battery was manufactured by the same process as in Example 1, except that the contents of the compound represented by Chemical Formula 1-2 and the compound represented by Chemical Formula 2-2 were 0.2 wt % and 1.0 wt %, respectively.

[0111] Comparative Example 1 A lithium secondary battery was manufactured by the same process as in Example 1, except that an electrolyte containing neither the compound represented by Chemical Formula 1-2 nor the compound represented by Chemical Formula 2-2 was used.

[0112] Comparative Examples 2 to 4 Lithium secondary batteries were manufactured in the same manner as in Example 1, except that the content of the compound represented by Chemical Formula 1-2 was changed to 0.2 wt %, 1.0 wt %, and 1.5 wt %, respectively, and the compound represented by Chemical Formula 2-2 was not added.

[0113] Comparative Examples 5 to 7 Lithium secondary batteries were manufactured in the same manner as in Example 1, except that the content of the compound represented by Chemical Formula 2-2 was changed to 0.2 wt %, 1.0 wt %, and 1.5 wt %, respectively, and the compound represented by Chemical Formula 1-2 was not added.

[0114] Evaluation example 1: Evaluation of initial DC resistance (DC-IR) at room temperature (25°C) and DC resistance increase rate after high-temperature storage The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were tested at 25°C under conditions of 1C / 10 seconds discharge (SOC 100), and the initial DC resistance (DCIR) was measured using the ΔV / ΔI (voltage change / current change) value for the lithium secondary batteries before they were stored at high temperature (60°C) in an oven at 60°C. The results are shown in Table 1 below. After measuring the initial DC resistance (DCIR), the batteries were stored at high temperature (60°C) for 60 days, after which the resistance was measured and the DC resistance change rate (%) was calculated using Equation 1 below.

[0115] [Number 1] DC resistance change rate = DCIR(60d.) / DCIR(0d.) x 100% In Equation 1, DCIR(60 d.) represents the DCIR after 60 days, and DCIR(0 d.) represents the DCIR immediately before storage. The measurement results of the initial DC resistance, the DC resistance after high-temperature storage, and the rate of change in resistance are shown in Table 1 below.

[0116] [Table 1]

[0117] As shown in Table 1, when stored at high temperature for a long period of time, the lithium secondary battery of Example 1 exhibited a lower DC resistance and a lower DC resistance increase rate when stored at high temperature compared to Comparative Example 1, which did not contain the compound of Chemical Formula 1-2 or the compound of Chemical Formula 2-2, and Comparative Examples 2 to 7, which contained only one of the compounds of Chemical Formula 1-2 or the compound of Chemical Formula 2-2.

[0118] Evaluation example 2: Evaluation of gas generation during high-temperature storage The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 9 were charged at 0.1 C under constant current conditions at 25°C until the voltage reached 4.2 V (vs. Li), and then charged to a 0.05 C cut-off while maintaining 4.2 V in constant voltage mode. The lithium secondary batteries were then disassembled, and the positive electrode plate was placed in a pouch together with the electrolyte, which was then stored in an oven at 60°C. The mass change due to the volume change of the pouch was calculated using Archimedes' method, and the results are shown in Table 1.

[0119] The electrolyte is a solution in which 1.5M LiPF6 is dissolved in a mixed solvent (volume ratio of 2:4:4) of EC (ethylene carbonate), DEC (diethyl carbonate) and EMC (ethyl methyl carbonate).

[0120] The Archimedes method involves measuring the weight of the pouch in a water tank filled with water at specific intervals (for example, every four days), converting the change in weight into volume, and measuring the amount of gas generated. Referring to Table 1, it can be seen that the lithium secondary battery of Example 1 had a suppressed rate of resistance change and a reduced amount of gas generation compared to the lithium secondary batteries of Comparative Examples 1 to 7.

[0121] Evaluation example 3: Evaluation of life characteristics at room temperature (25°C) The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 7 were charged at a constant current of 0.5 C at 25°C until the voltage reached 4.2 V (vs. Li), and then cut off at a current of 0.05 C while maintaining 4.2 V in constant voltage mode. They were then discharged at a constant current of 1.0 C until the voltage reached 2.8 V (vs. Li). This charge-discharge cycle was repeated 300 times.

[0122] In all of the above-mentioned charge / discharge cycles, a 10-minute rest period was allowed after each charge / discharge cycle. The life characteristics at room temperature were evaluated based on the capacity retention rate at the 300th cycle, and the results are shown in Table 2 below. The capacity retention rate at the 300th cycle is defined by the following equation 2. [Number 2] Capacity retention rate = [discharge capacity at 300th cycle / discharge capacity at first cycle] x 100

[0123] [Table 2]

[0124] As can be seen from Table 2, the results of the charge / discharge characteristic evaluation show that the lithium secondary batteries of Examples 1 to 5 have improved life characteristics at room temperature compared to the lithium secondary batteries of Comparative Examples 1 to 7.

[0125] Evaluation example 4: Evaluation of Ni elution For the lithium secondary batteries produced in Example 3 and Comparative Examples 1, 3 and 6, the amount of Ni elution was measured by the following method. The lithium secondary battery was 100% charged to 4.2 V at 0.2 C and then stored at high temperature (60°C) for 60 days. The battery was then disassembled and the positive electrode plate was separated. The Ni content was measured by ICP-MS analysis, and the results are shown in Figure 2.

[0126] 2, it can be seen that the lithium secondary battery prepared in Example 3 had a very small amount of Ni eluted from the electrode plate. However, it was confirmed that the lithium secondary batteries prepared in Comparative Examples 1, 3, and 6 had a significantly larger amount of nickel (Ni) eluted compared to the lithium secondary battery of Example 1. Therefore, it can be seen that the lithium secondary batteries according to the examples can significantly reduce the amount of gas generated during high-temperature storage and can also reduce the amount of Ni ions eluted due to reaction with the electrolyte.

[0127] Although one embodiment has been described above with reference to the drawings and examples, it is understood that the same is merely illustrative and that various modifications and equivalent embodiments are possible from the above description, and the scope of protection of the present invention is defined by the following claims.

Claims

1. a lithium salt, an organic solvent, and an additive; The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2: An electrolyte for a lithium secondary battery, wherein the mixing weight ratio of the first compound and the second compound is in the range of 1:9 to 9:1: 【Chemical 1】 In the above Chemical Formula 1, X １ is a fluoro, chloro, bromo or iodo group, R １ Or R ６ are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1, 【Chemistry 2】 In the above Chemical Formula 2, A １ and A ２ are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms; a carbonyl group; a sulfinyl group; or a divalent group having 2 to 6 carbon atoms in which a plurality of substituted or unsubstituted alkylene units are bonded via ether bonds.

2. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein a mixing weight ratio of the first compound represented by Chemical Formula 1 to the second compound represented by Chemical Formula 2 ranges from 1:5 to 5:

1.

3. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the first compound is in the range of 0.05 to 10 wt % based on the total weight of the electrolyte.

4. 2. The electrolyte for a lithium secondary battery of claim 1, wherein the content of the second compound is in the range of 0.05 to 10 wt % based on the total weight of the electrolyte.

5. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is represented by the following chemical formula 1-1: 【Chemistry 3】 In the above Chemical Formula 1-1, R １ Or R ６ are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1.

6. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is represented by the following Chemical Formula 1-1A or 1-1B: 【Chemistry 4】 In the formulas 1-1A and 1-1B, R １ Or R ６ are each independently hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

7. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-2 to 1-9: 【Chemistry 5A】 【Chemistry 5B】 。

8. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound is represented by the following chemical formula 2-1: 【Chemistry 6】 In the above Chemical Formula 1-1, R １ Or R ４ are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1, m is an integer from 1 to 5;

9. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound is at least one selected from the group consisting of compounds represented by the following Chemical Formulas 2-2 to 2-19: 【Chemistry 7A】 【Chemistry 7B】 【Chemistry 7C】 。

10. The lithium salt is LiPF ６ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiClO ４ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , LiAlO ２ , LiAlCl ４ , LiN(C ｘ F ２ｘ＋１ SO ２ ) (C ｙ F ２ｙ＋１ SO ２ ) (2≦x≦20, 2≦y≦20), LiCl, LiI, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), LiPO ２ F ２ 2. The electrolyte for a lithium secondary battery according to claim 1, comprising at least one compound selected from the group consisting of compounds represented by the following chemical formulas 3 to 6: 【Chemistry 8】 。

11. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.01 to 5.0M.

12. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; The electrolyte according to claim 1 , disposed between the positive electrode and the negative electrode; A lithium secondary battery comprising:

13. The lithium secondary battery according to claim 12, wherein the positive electrode comprises a compound represented by the following chemical formula 7: [Chemical formula 7] Li ａ Ni ｘ Co ｙ M ｚ O ２－ｂ A ｂ In the above Chemical Formula 7, 1.0≦a≦1.2, 0≦b≦0.2, 0.6≦x<1, 0<y≦0.3, 0<z≦0.3, x+y+z=1, M is one or more selected from the group consisting of manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), and boron (B); A is F, S, Cl, Br, or a combination thereof.

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