Electrolyte for lithium secondary battery and lithium secondary battery containing same

Abstract

Provided is an electrolyte for a lithium secondary battery, comprising a lithium salt; an organic solvent; and a compound represented by the following Chemical Formula 1, and a lithium secondary battery comprising the same. JPEG2024506152000036.jpg33170In Chemical Formula 1, L, X, X1, X2, and X3 are as defined in the detailed description.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing 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] Because lithium secondary batteries operate at high operating voltages, aqueous electrolytes, which are highly reactive with lithium, cannot be used. Organic electrolytes are typically used as electrolytes for lithium secondary batteries. Organic electrolytes are prepared by dissolving lithium salts in organic solvents. Organic solvents are preferred because they are stable at high voltages, have high ionic conductivity and dielectric constant, and low viscosity. However, if an organic electrolyte containing lithium salt is used as an electrolyte for a lithium secondary battery, side reactions between the anode / cathode and the electrolyte may result in a decrease in the lifespan and high-temperature stability of the lithium secondary battery.

[0004] 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]

[0005] One aspect of the present invention is to provide an electrolyte for a lithium secondary battery that can improve battery performance.

[0006] Another aspect of the present invention is to provide a lithium secondary battery containing the above-mentioned electrolyte for a lithium secondary battery and having improved performance. [Means for solving the problem]

[0007] According to one aspect, there is provided an electrolyte for a lithium secondary battery, comprising: a lithium salt; an organic solvent; and a compound represented by the following Chemical Formula 1:

[0008] [ka]

[0009] In Chemical Formula 1, L is —C(R1)(R2)—, —N(R1)—, O, S, or —C(═O)—; X and X1 are each independently O, S, or -S(=O)-; X2 is -{C(R3)(R4)} n or -C=N-R1, X3 is -{C(R3)(R4)}m- or -C=N-R1; R1 to R4 are independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C4 20 Alkyl groups, substituted or unsubstituted C1 to C 20 Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20 Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 It is a heteroarylene group, or at least one of R1 and R4 and at least one of R3 and R4 are linked to form a ring, and n and m are each independently an integer of 1 to 4.

[0010] In 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 above-described 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 is suppressed, thereby improving the life characteristics of the lithium secondary battery. [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 is a graph showing changes in DC resistance during high-temperature storage in lithium secondary batteries of Example 3 and Comparative Example 2-3. 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.

[0014] According to an embodiment, an electrolyte for a lithium secondary battery includes a lithium salt; an organic solvent; and a compound represented by the following Chemical Formula 1:

[0015] [ka]

[0016] In Chemical Formula 1, L is —C(R1)(R2)—, —N(R1)—, O, S, or —C(═O)—; X and X1 are each independently O, S, or -S(=O)-; X2 is -{C(R3)(R4)} n or -C=N-R1, X3 is -{C(R3)(R4)}m- or -C=N-R1, and R1 to R4 are independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C4 20 Alkyl groups, substituted or unsubstituted C1 to C 20 Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 a heteroarylene group, or at least one of R and R and at least one of R and R are linked to form a ring; n and m are each independently an integer of 1 to 4.

[0017] When a positive electrode active material using a lithium transition metal oxide with a nickel content of 80 mol% or more is used, it is possible to fabricate a lithium secondary battery with high output and capacity. However, a positive electrode active material with a high nickel content has an unstable surface structure, which increases gas generation due to side reactions during the battery charge and discharge process. Lithium secondary batteries using such a positive electrode active material may have reduced life characteristics. In addition, resistance increases at high temperatures, so high-temperature stability needs to be improved.

[0018] According to an embodiment, an electrolyte for a lithium secondary battery can form a low-resistance SEI (solid electrolyte interface) film and / or protective layer using the compound represented by Chemical Formula 1 as an additive. As a result, by using such an electrolyte, a lithium secondary battery with reduced internal resistance can be manufactured. In addition, a lithium secondary battery with excellent resistance suppression effect at high temperatures and improved lifespan and high-temperature stability can be manufactured.

[0019] The reason for improving the performance of lithium secondary batteries using the compound represented by Formula 1 as an electrolyte additive will be explained in more detail below. However, this explanation is provided for the purpose of aiding in understanding the present invention and is not intended to limit the scope of the present invention. LiPF6 is commonly used as the lithium salt contained in the electrolyte, but it has problems such as poor thermal stability and is easily hydrolyzed by moisture. Thus, LiPF6-containing electrolytes exhibit instability when exposed to moisture and high temperatures. The decomposition products of LiPF6 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.

[0020] When the compound represented by Formula 1 is used as an electrolyte additive, it forms a solid electrolyte interface (SEI) film on the negative electrode surface that has high high-temperature stability and excellent ionic conductivity, and it can suppress the side reaction of LiPF6 due to the -PO2F functional group. As a result, gas generation due to the decomposition reaction 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.

[0021] In addition, since the electrolyte contains the compound represented by Chemical Formula 1, a low-resistance SEI film and / or protective layer is formed, thereby providing a lithium secondary battery with reduced internal resistance.

[0022] The first compound represented by Chemical Formula 1 strongly interacts 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, it forms a cathode electrolyte interphase (CEI) film with low impedance characteristics on the positive electrode surface. The CEI film prevents electrolyte oxidation, inhibits 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, improving lithium ion conductivity and thereby increasing low-temperature discharge voltage.

[0023] To explain the above-mentioned effects in more detail, the first compound represented by Chemical Formula 1 is 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 this 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 and prevents gas generation inside the lithium secondary battery, thereby significantly reducing the rate of defects.

[0024] The content of the compound represented by Chemical Formula 1 is in the range of 0.05 to 20 wt % based on the total weight of the electrolyte. The content of the compound represented by Chemical Formula 1 is, for example, 0.1 to 10 wt %, 0.5 to 5 wt %, 1 to 3 wt %, or 1.5 to 2.5 wt %. When the content of the first compound represented by Chemical Formula 1 is in this range, high-temperature storage characteristics are improved, and an increase in interfacial resistance is suppressed, so that a lithium secondary battery with improved high-temperature characteristics and resistance characteristics can be manufactured without deteriorating life characteristics.

[0025] The compound represented by Chemical Formula 1 is a compound represented by Chemical Formula 2 below.

[0026] [ka]

[0027] In Chemical Formula 2, L is —C(R1)(R2)—, —N(R1)—, O, S, or —C(═O)—; X and X1 are each independently O, S, or -S(=O)-; X2 is -{C(R3)(R4)} n - and R1 to R4 are independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C4 20 Alkyl groups, substituted or unsubstituted C1 to C 20 Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20 Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 a heteroarylene group, or at least one of R and R and at least one of R and R are linked to form a ring; n is an integer from 1 to 4.

[0028] The compound represented by Chemical Formula 1 is, for example, a compound represented by Chemical Formula 3 below.

[0029] [ka]

[0030] In Chemical Formula 3, L is —C(R1)(R2)—, —N(R1)—, O, S, or —C(═O)—; X and X1 are each independently O, S, or -S(=O)-; X2 is -{C(R3)(R4)} n - and R1 to R4 are each independently a substituted or unsubstituted C1 to C 20 Alkyl groups, substituted or unsubstituted C1 to C 20Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20 Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 It is a heteroaryl group.

[0031] The compound represented by Chemical Formula 1 is a compound represented by Chemical Formula 4 below.

[0032] [ka]

[0033] In Chemical Formula 4, L is —C(R1)(R2)—, —N(R1)—, O, S, or —C(═O)—; X and X1 are each independently O, S, or -S(=O)-; X2 is -C(R3)-; R1 and R4 are independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C4 20 Alkyl groups, substituted or unsubstituted C1 to C 20 Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20 Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 is a heteroaryl group, R2 and R3 are substituted or unsubstituted C1 to C 20 Alkylene groups, substituted or unsubstituted C2 to C 20 Alkenylene groups, substituted or unsubstituted C2 to C 20 Alkynylene groups, substituted or unsubstituted C3 to C 20 Cycloalkylene groups, substituted or unsubstituted C6 to C 20an arylene group, or a substituted or unsubstituted C to C 20 is a heteroarylene group, n is an integer from 1 to 4.

[0034] The compound represented by Chemical Formula 1 is selected from the compounds represented by Chemical Formulas 5 to 8 below.

[0035] [ka]

[0036] In Chemical Formula 5, R1 to R4 are hydrogen, C1-C 20 Alkyl groups, or C6-C 20 is an aryl group, n and m are each independently an integer from 1 to 4;

[0037] [ka]

[0038] In Chemical Formula 6, R1 to R4 are hydrogen, C1-C 20 Alkyl groups, or C6-C 20 is an aryl group, n and m are each independently an integer from 1 to 4;

[0039] [ka]

[0040] In Chemical Formula 7, R1 to R4 are hydrogen, C1-C 20 Alkyl groups, or C6-C 20 is an aryl group, R is hydrogen, C1-C 20 Alkyl groups, or C6-C 20 In the aryl group, n and m are each independently an integer from 1 to 4;

[0041] [ka]

[0042] In Chemical Formula 8, R1 to R4 are hydrogen, C1-C 20 Alkyl groups, or C6-C 20 is an aryl group, n and m are each independently an integer of 1 to 4.

[0043] In Chemical Formulae 5 to 8, n is 1 to 3, 1 to 2, or 1; and m is 1 to 3, 1 to 2, or 2.

[0044] The compound represented by Chemical Formula 2 is, for example, a compound selected from the compounds represented by Chemical Formulas 9 to 19 below.

[0045] [ka]

[0046] In Chemical Formula 18, Me represents a methyl group.

[0047] [ka]

[0048] In Chemical Formula 19, Ph represents a phenyl group.

[0049] 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(oxalato)borate (LiBOB), LiPO2F2, and one or more compounds represented by the following formulas 21 to 24, but are not limited thereto, and any compound used as a lithium salt in the art may be used.

[0050] [ka]

[0051] The concentration of the lithium salt in the electrolyte 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 2.0 M. When the concentration of the lithium salt is within the above range, further improved lithium secondary battery characteristics can be obtained.

[0052] The organic solvent is one or more selected from the group consisting of carbonate-based solvents, ester-based solvents, ether-based solvents, and ketone-based solvents.

[0053] Examples of carbonate solvents that can be used 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), and butylene carbonate (BC).

[0054] Examples of ester solvents include methyl propionate, ethyl propionate, ethyl butyrate, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, γ-butyrolactone, decanolide, γ-valerolactone, mevalonolactone, and caprolactone. Examples of ether solvents include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents include cyclohexanone. Examples of nitrile solvents include acetonitrile (AN), succinonitrile (SN), and adiponitrile. Examples of other solvents that may be used include, but are not limited to, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and tetrahydrofuran. Any solvent that is known in the art as an organic solvent may be used. For example, the organic solvent may contain 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 also be a mixed solvent of three or more organic solvents.

[0055] According to one embodiment, the organic solvent may be at least one selected from the group consisting of ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), butylene carbonate, ethyl propionate, ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone, and tetrahydrofuran, but is not limited thereto, and any organic solvent commonly used in the art may be used.

[0056] According to an embodiment, the electrolyte for a lithium secondary battery may further include a disultone-based compound. The disultone-based compound has a higher reduction potential than the compound represented by Chemical Formula 1 and participates first in the formation of the SEI film, thereby preventing over-decomposition of the compound represented by Chemical Formula 1, thereby suppressing side reactions with the electrolyte, thereby forming a low-resistance SEI film and / or protective layer. The compound represented by Chemical Formula 1, whose over-decomposition is suppressed by the disultone-based compound, can suppress high-temperature thermal decomposition of the lithium salt during high-temperature storage, for example, and reduce side reactions of the electrolyte.

[0057] The content of the disultone compound is, for example, 0.05 to 20 wt %, 0.1 to 10 wt %, 0.5 to 5 wt %, 1 to 3 wt %, or 1.5 to 2.5 wt % based on the total weight of the electrolyte. When the content of the disultone compound is within this range, an increase in interfacial resistance is suppressed, thereby further improving capacity and lifespan, and an SEI coating with low resistance and excellent thermal stability is formed, thereby suppressing decomposition of the electrolyte.

[0058] The disultone compound is, for example, a compound represented by the following chemical formula 20.

[0059] [ka]

[0060] In Chemical Formula 20, 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.

[0061] The disultone compound is, for example, a compound represented by the following chemical formula 20-1.

[0062] [ka]

[0063] In Chemical Formula 20-1, R1 to R4 are each independently hydrogen, a cyano group, or a substituted or unsubstituted C1 to C4 20 Alkyl groups, substituted or unsubstituted C1 to C 20 Alkoxy groups, substituted or unsubstituted C2 to C 20 Alkenyl groups, substituted or unsubstituted C2 to C 20 Alkynyl groups, substituted or unsubstituted C3 to C 20 Cycloalkyl groups, substituted or unsubstituted C6 to C 20 Aryl group or substituted or unsubstituted C2 to C 20 is a heteroaryl group, n is an integer of 0 or 1, m is an integer from 1 to 5;

[0064] The compound represented by Chemical Formula 20 is, for example, one or more selected from the compounds represented by the following Chemical Formulas 20-2 to 20-19.

[0065] [ka] [ka]

[0066] The disultone compound is, for example, a compound represented by the above chemical formula 20-2.

[0067] The electrolyte may be in a liquid or gel state, and may be prepared by adding a lithium salt and the above-mentioned additives to an organic solvent.

[0068] 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.

[0069] By including the electrolyte additive for a lithium secondary battery described above, the lithium secondary battery suppresses an increase in initial resistance, suppresses gas generation due to side reactions, and improves life characteristics.

[0070] The positive electrode active material includes a lithium transition metal oxide containing nickel and other transition metals. In the lithium transition metal oxide containing nickel and other transition metals, the content of nickel 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 with respect to the total number of moles of transition metals.

[0071] For example, the lithium transition metal oxide is also a compound represented by the following Chemical Formula 7-1: [Chemical Formula 7-1] Li a Ni x Co y M z O 2-b A b In Chemical Formula 7-1, 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.

[0072] In Chemical Formula 7-1, 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.

[0073] For example, the lithium transition metal oxide is at least one of the compounds represented by the following chemical formulas 4-1 and 5-1: [Chemical formula 4-1] LiNi x Co y Mn z O2 In chemical formula 4-1, 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 5-1] LiNi x Co y [[ID=Id=18]]Al z O2 In chemical formula 5-1, 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.

[0074] 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 O as well.

[0075] 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). The negative electrode active material may include 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 , where 0 < x < 2). The silicon-based compound may also be silicon particles, silicon alloy particles, etc.

[0076] The size of the silicon-based compound is less than 200 nm, for example, 10 to 150 nm. The term "size" may indicate the average particle size when the silicon-based compound is spherical, and may indicate the average major axis length when the silicon particles are non-spherical.

[0077] When the size of the silicon-based compound is within the above range, the life characteristics are excellent, and when using an electrolyte according to an embodiment, the life of the lithium secondary battery is further improved.

[0078] The carbon-based material may also be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may also be graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon may also be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0079] 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 and inside of the carbon-based compound, or a composite in which silicon particles are coated on the carbon-based compound and then contained inside of 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.

[0080] The composite of a silicon-based compound and a carbon-based compound can be an active material obtained by dispersing silicon nanoparticles with an average particle size of approximately 200 nm or less on carbon-based compound particles and then carbon-coating them, or an active material in which silicon (Si) particles are present on and inside graphite. The composite of a silicon-based compound and a carbon-based compound can have an average secondary particle size of 5 μm to 20 μm. The average particle size of the silicon nanoparticles can be 5 nm or more, for example, 10 nm or more, for example, 20 nm or more, for example, 50 nm or more, or for example, 70 nm or more. The average particle size of the silicon nanoparticles can be 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 10 nm or less. For example, the average particle size of the silicon nanoparticles can be 100 nm to 150 nm.

[0081] The average secondary particle size of the composite of the silicon-based compound and the carbon-based compound is 5 μm to 18 μm, for example, 7 μm to 15 μm, or for example, 10 μm to 13 μm.

[0082] Other examples of the composite of the silicon-based compound and the carbon-based compound include the porous silicon composite cluster disclosed in Korean Patent Publication No. 10-2018-0031585 and the porous silicon composite cluster structure disclosed in Korean Patent Publication No. 10-2018-0056395. Korean Patent Publication Nos. 10-2018-0031586 and 10-2018-0056395 are incorporated herein by reference.

[0083] A silicon-carbon compound composite according to an embodiment includes a porous core including porous silicon composite secondary particles and a shell including a second graphene disposed on top of the core, and the porous silicon composite secondary particles include aggregates of two or more silicon composite primary particles. The silicon composite primary particles include silicon; silicon oxide (SiO x )(where 0 < x < 2) disposed on the silicon and a first graphene disposed on the silicon oxide, and is also a porous silicon composite cluster.

[0084] A silicon-carbon compound composite according to another embodiment includes a porous silicon composite cluster including porous silicon composite secondary particles and a second carbon flake on at least one surface of the porous silicon composite secondary particles; and a carbon-based coating film including amorphous carbon disposed on top of the porous silicon composite cluster. The porous silicon composite secondary particles include aggregates of two or more silicon composite primary particles. The silicon composite primary particles include silicon; silicon oxide (SiO x )(where 0 < x < 2) disposed on at least one surface of the silicon and a first carbon flake on at least one surface of the silicon oxide, and is also a porous silicon composite cluster structure in which the silicon oxide exists in a state of a film, a matrix, or a combination thereof.

[0085] The first carbon flake and the second carbon flake also exist in a state of a film, a particle, a matrix, or a combination thereof, respectively. And the first carbon flake and the second carbon flake are also graphene, graphite, carbon fiber, graphene oxide, etc., respectively.

[0086] The composite of the silicon-based compound and the 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 and inside of the carbon-based compound, or a composite in which silicon particles are coated on the carbon-based compound and then contained inside of the carbon-based compound. In the composite of the silicon-based compound and the carbon-based compound, the carbon-based compound may be graphite, graphene, graphene oxide, or a combination thereof.

[0087] The lithium secondary battery is not particularly limited in type, and may include a lithium ion battery, a lithium ion polymer battery, a lithium sulfur battery, and the like.

[0088] The lithium secondary battery can also be manufactured by the following method.

[0089] First, the positive electrode is provided.

[0090] For example, a positive electrode active material composition may be prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent. The positive electrode active material composition may be directly coated on a metal current collector to prepare 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 prepare a positive electrode plate. The positive electrode is not limited to the above-listed forms and may have other forms.

[0091] The positive electrode active material is a lithium-containing metal oxide, and any of those commonly used in the art can be used without limitation. For example, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used. Specific examples 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 O2-c D 1 c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B 1 b O 4-c D 1 c (wherein 0≦b≦0.5 and 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, and 0<α≦2); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 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, and 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, and 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, and 0<α<2); Li a Ni 1-b-c Mn b B 1c O 2-α F 1 2 (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 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, and 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, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (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) Compounds represented by one of the following chemical formulas can be used: Fe2(PO4)3(0≦f≦2); LiFePO4:

[0092] 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 1is 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. 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.

[0093] Of course, 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, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The coating layer compound may be amorphous or crystalline. The coating element included 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 be performed using any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the properties of the positive electrode active material. This is well understood by those skilled in the art, so a detailed description will be omitted.

[0094] The conductive material may be, but is not limited to, carbon black, graphite fine particles, or the like, and any material used as a conductive material in the art may be used.

[0095] 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 that can be used as a binder in the art may be used.

[0096] The solvent may be N-methylpyrrolidone, acetone, water, or the like, but is not limited thereto, and any solvent commonly used in the art may be used.

[0097] The amounts of the positive electrode active material, conductive material, binder, and solvent are the same as those typically 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.

[0098] The negative electrode is then applied.

[0099] 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.

[0100] The negative electrode active material may be any material known in the art as a negative electrode active material for lithium batteries, and may include, for example, at least one selected from the group consisting of lithium metal, metals capable of being alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0101] For example, the metal capable of alloying with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-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 a 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.

[0102] For example, the transition metal oxide can be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0103] For example, the non-transition metal oxide is SnO2, SiO x (0 <x<2)などでもある。

[0104] 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.

[0105] 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.

[0106] The contents of the negative electrode active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries, and one or more of the conductive material, binder, and solvent may be omitted depending on the application and configuration of the lithium battery.

[0107] Next, a separator is provided that is inserted between the positive electrode and the negative electrode.

[0108] 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, 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.

[0109] 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 and dried, and then the separator film can be peeled off from the support and laminated on the electrode to form a separator.

[0110] 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.

[0111] The electrolyte solution described above is then applied.

[0112] As shown in 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, and the battery case is sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may be cylindrical, prismatic, or thin-film. For example, the lithium battery may be a large-sized thin-film battery. The lithium battery may also be a lithium-ion battery.

[0113] A separator may be disposed between the positive and negative electrodes to form a battery structure, and the battery structures may be stacked in a bi-cell structure, impregnated with an organic electrolyte solution, and the resulting structure may be placed in a pouch and sealed to form a lithium ion polymer battery.

[0114] In addition, a plurality of the battery structures may be stacked to form a battery pack, which may be used in various devices requiring high capacity and high output, such as laptop computers, smartphones, and electric vehicles.

[0115] The lithium secondary battery according to an embodiment has a significantly reduced DCIR increase rate compared to a lithium secondary battery using a general nickel-rich lithium-nickel composite oxide as a positive electrode active material, and can exhibit excellent battery characteristics.

[0116] The operating voltage of a lithium secondary battery using the positive electrode, negative electrode, and electrolyte is, for example, 2.5-2.8V at the lower limit and 4.1V or more at the upper limit, e.g., 4.1-4.45V.

[0117] In addition, the lithium secondary battery can be used in, but is not limited to, power tools operated by battery motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric bicycles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0118] 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 having 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. One or more hydrogen atoms of the alkyl 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 group, hydroxy group, nitro group, cyano group, amino group, amidino group, hydrazine, hydrazone, carboxyl group or its salt, sulfonyl group, sulfamoyl group, sulfonic acid group or its salt, phosphoric acid group or its salt, or C1-C 20 Alkyl groups, C2-C 20 Alkenyl groups, C2-C20 Alkynyl groups, C1-C 20 Heteroalkyl groups of C6-C 20 Aryl groups, C7-C 20 Aryl alkyl groups, C6-C 20 Heteroaryl groups of C7-C 20 Heteroarylalkyl groups of C6-C 20 or a heteroaryloxy group of C6-C 20 and the heteroaryloxyalkyl group may be substituted with a heteroaryloxyalkyl group of the formula:

[0119] 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. In other embodiments, the alkenyl group is substituted or unsubstituted. In other embodiments, the alkenyl group has 2 to 40 carbon atoms. 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, etc. In other embodiments, the alkynyl group is substituted or unsubstituted. In other embodiments, the alkynyl group has 2 to 40 carbon atoms.

[0120] As used herein, a substituent is derived from an unsubstituted parent group, in which one or more hydrogen atoms have been replaced with another atom or functional group. Unless otherwise indicated, when a functional group is described as "substituted," it means that the functional group is C1-C 20 Alkyl, C2-C 20 Alkenyl group, C2-C 20 Alkynyl groups, C1-C 20It 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. When a functional group is described as being "optionally substituted," the functional group can be substituted with the substituents described above.

[0121] The term "halogen" includes fluorine, bromine, chlorine, iodine, and the like.

[0122] "Alkoxy" refers to "alkyl-O-", where alkyl 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 may be substituted with the same substituents as those in the alkyl group described above. "Heteroaryl" 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, 1-5 heteroatoms and 5-10 ring members. The S or N may be oxidized to various oxidation states.

[0123] Examples of heteroaryl 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 substituents may be oxazol-5-yl, isoxazol-3-yl, isoxazol-4-yl, isoxazol-5-yl, 1,2,4-triazol-3-yl, 1,2,4-triazol-5-yl, 1,2,3-triazol-4-yl, 1,2,3-triazol-5-yl, tetrazolyl, pyrid-2-yl, pyrid-3-yl, 2-pyrazin-2-yl, pyrazin-4-yl, pyrazin-5-yl, 2-pyrimidin-2-yl, 4-pyrimidin-2-yl, or 5-pyrimidin-2-yl.

[0124] The term "heteroaryl" includes cases where a heteroaromatic ring is optionally fused to one or more aryl, cycloaliphatic, or heterocycle rings.

[0125] The term "carbocycle" means a saturated or partially unsaturated non-aromatic monocyclic, bicyclic, or tricyclic hydrocarbon group.

[0126] Examples of the monocyclic hydrocarbon include cyclopentyl, cyclopentenyl, cyclohexyl, and cyclohexenyl.

[0127] Examples of the bicyclic hydrocarbon include bornyl, decahydronaphthyl, bicyclo[2.1.1]hexyl, bicyclo[2.1.1]heptyl, bicyclo[2.2.1]heptenyl, or bicyclo[2.2.2]octyl.

[0128] An example of the tricyclic hydrocarbon is adamantly.

[0129] One or more hydrogen atoms in the carbon ring can be substituted with the same substituents as in the alkyl group described above.

[0130] The present invention will be described in more detail with reference to the following examples and comparative examples, but the examples are provided for illustrative purposes only and are not intended to limit the scope of the present invention.

[0131] (Lithium secondary battery manufacturing) Example 1 An electrolyte for a lithium secondary battery was prepared by adding 1.5M LiPF6 and vinylene carbonate to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:10:70, and then adding 0.1 wt% of the compound represented by Chemical Formula 9 based on the total weight of the electrolyte. The compound represented by Chemical Formula 9 was synthesized by the method disclosed in Energy & Fuels 1991, 5, 786-791.

[0132] [ka]

[0133] 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, 0.2 wt% modified acrylonitrile rubber, and 1.5 wt% polyvinylidene fluoride 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 to a thickness of approximately 60 μm on a 20 μm thick aluminum current collector using a doctor blade, dried in a hot air oven at 100°C for 0.5 hours, and then dried again in a vacuum at 120°C for 4 hours. The cathode was then rolled to prepare a cathode.

[0134] 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 to a thickness of approximately 60 μm using a doctor blade, dried in a hot air oven at 100°C for 0.5 hours, and then dried again in a vacuum at 120°C for 4 hours. The resulting mixture was then rolled to prepare anodes.

[0135] A lithium secondary battery was fabricated using the prepared positive and negative electrodes, a 14 μm thick polyethylene separator, and the electrolyte.

[0136] Examples 2-5 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 was changed to 0.5 wt%, 1.0 wt%, 2.0 wt%, and 10 wt%, respectively.

[0137] Comparative Example 1 A lithium secondary battery was manufactured by the same process as in Example 1, except that an electrolyte containing no compound represented by Formula 9 was used.

[0138] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that an electrolyte containing only 1.0 wt % of the compound represented by Chemical Formula 9-1 was used. The compound represented by Chemical Formula 9-1 was synthesized by the method disclosed in the paper (Heteroatom Chemistry 2010, 21, 515-520).

[0139] [ka]

[0140] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that an electrolyte containing only 1.0 wt % of the compound represented by Chemical Formula 9-1 was used. The compound represented by Chemical Formula 9-2 was synthesized by the method disclosed in Korean Patent Publication No. 10-2015-075052.

[0141] [ka]

[0142] Evaluation example 1: Evaluation of high temperature (60°C) initial DC resistance (DC-IR) and DC resistance increase rate after high temperature storage The lithium secondary batteries prepared in Examples 1-4 and Comparative Example 1 were left at 25°C and 0.2C 4.2V charging conditions in an oven at 60°C for 30 days, and then the DC-IR was measured to evaluate the rate of increase in resistance before and after leaving them. The evaluation results are shown in Table 1 below. The initial DC resistance (DCIR) before leaving them was measured, and then they were stored at high temperature (60°C) for 30 days, after which the resistance was measured and the rate of change in DC resistance (%) was calculated using Equation 1 below.

[0143] <Expression 1> DC resistance change rate = [DCIR(60d.)] / DCIR(0d.) x 100% In formula 1, DCIR(60 d.) represents the DCIR after 60 days, and DCIR(0 d.) represents the DCIR immediately before storage.

[0144] 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. Table 1 below shows the change in DC resistance depending on the storage days.

[0145] [Table 1]

[0146] As shown in Table 1, the lithium secondary batteries of Examples 1 to 4 exhibited lower DC resistance and a reduced rate of increase in DC resistance when stored at high temperatures for a long period of time, compared to the lithium secondary battery of Comparative Example 1, which did not contain the compound of Chemical Formula 1. Furthermore, the initial DC resistance (DC-IR) at high temperature (60°C) and the rate of increase in DC resistance after high-temperature storage were evaluated for the lithium secondary batteries of Example 3 and Comparative Examples 2 and 3. The evaluation results are shown in Table 2 and FIG. 2.

[0147] [Table 2]

[0148] As shown in Table 2 and FIG. 2, the lithium secondary battery of Example 3 had lower initial DC resistance and DC resistance during high-temperature storage, and also had a lower DC resistance increase rate, compared to the lithium secondary batteries of Comparative Examples 2 and 3.

[0149] Evaluation example 2: Evaluation of gas generation rate during high-temperature storage The lithium secondary batteries prepared in Examples 1-5 and Comparative Example 1 were charged at 0.2 C under constant current conditions at 25°C until the voltage reached 4.4 V, and then charged to a 0.05 C cut-off in constant voltage mode while maintaining 4.4 V. They were then stored in an oven at 85°C for 8 hours. The mass change due to the volume change of the pouch was calculated using Archimedes' method, and the results are shown in Table 3 below.

[0150] Meanwhile, the electrolyte is a solution in which 1.5M LiPF6 is dissolved in a mixed solvent (volume ratio 2:4:4) of EC (ethylene carbonate), DEC (diethyl carbonate) and EMC (ethyl methyl carbonate).

[0151] The Archimedes method is a method in which the weight of the pouch is measured in a water tank filled with water at specific intervals (for example, every four days), and the amount of gas generated is measured by converting the change in weight into volume.

[0152] [Table 3]

[0153] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 5 generated less gas than the lithium secondary battery of Comparative Example 1.

[0154] Evaluation example 3: High temperature (60°C) lifespan characteristic evaluation The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 9 were charged at a constant current of 0.5 C at 60°C until the voltage reached 4.2 V (vs. Li), and then continuously charged in a constant voltage mode with a current cutoff of 0.05 C while maintaining 4.2 V. Then, the batteries were 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.

[0155] In all the charge / discharge cycles, a 10-minute rest period was allowed after each charge / discharge cycle.

[0156] The life characteristics at high temperatures and the capacity retention rates at 150 and 300 cycles were evaluated, and the results are shown in Table 3. The capacity retention rate at 300 cycles is defined by the following formula 2.

[0157] <Expression 2> Capacity retention rate = [discharge capacity at 300 cycles / discharge capacity at first cycle] x 100

[0158] The results of the capacity retention evaluation are shown in Table 4 below.

[0159] [Table 4]

[0160] As a result of the evaluation of the charge and discharge characteristics, as shown in Table 4, it can be seen that the lithium secondary batteries of Examples 1 to 5 have improved life characteristics at high temperatures compared to the lithium secondary battery of Comparative Example 1.

[0161] As can be seen from the results of Evaluation Examples 1 to 3 described above, the lithium secondary battery employing the electrolyte of the present invention has a reduced initial resistance and an improved gas reduction effect.

[0162] Although one embodiment has been described above with reference to the drawings and examples, this is merely an example, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the scope of protection of the present invention should be determined by the following claims.

Claims

1. a lithium salt; an organic solvent; and a compound of the following formula 9: 【Chemical 1】 a compound represented by the formula: the organic solvent consists of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC); and The solvent is composed of 80 to 95% by volume of a chain carbonate (ethyl methyl carbonate and dimethyl carbonate) and 5 to 20% by volume of a cyclic carbonate (ethylene carbonate), with the total volume of the organic solvent being 100% by volume. Electrolyte for lithium secondary batteries.

2. The electrolyte for a lithium secondary battery according to claim 1 , further comprising vinylene carbonate.

3. 3. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the compound represented by Formula 9 is in the range of 0.05 to 20 wt % based on the total weight of the electrolyte.

4. 4. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the compound represented by Chemical Formula 9 is in the range of 0.1 to 10 wt % based on the total weight of the electrolyte.

5. 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(oxalato)borate (LiBOB), LiPO ２ F ２ and one or more compounds selected from the group consisting of compounds represented by the following chemical formulas 21 to 24: 【Chemistry 2】

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

7. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the electrolyte according to any one of claims 1 to 6, disposed between the positive electrode and the negative electrode.

8. 8. The lithium secondary battery of claim 7, wherein the positive electrode comprises a compound represented by the following Chemical Formula 7-1: [Chemical formula 7-1] Li ａ Ni ｘ Co ｙ M ｚ O ２－ｂ A ｂ In Chemical Formula 7-1, 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.

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