Electrolyte solution for lithium secondary battery and lithium secondary battery comprising same

Abstract

An electrolyte solution for a lithium secondary battery according to an embodiment of the present invention may comprise: an additive comprising a compound represented by a specific chemical formula; an organic solvent; and a lithium salt. The present invention may provide a lithium secondary battery including an electrolyte solution for a lithium secondary battery according to an exemplary embodiment, and having improved high temperature characteristics, power characteristics, and lifespan characteristics.

Description

Technical Field

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same. More specifically, the present invention relates to an electrolyte for a lithium secondary battery comprising a solvent and an electrolyte salt and a lithium secondary battery comprising the same. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and are widely used as power sources for portable electronic devices such as mobile phones and laptop computers. Lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in charging speed and light weight, and are therefore being actively developed and applied.

[0003] For example, a lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; and an electrolyte impregnated with the electrode assembly. As the application range of lithium secondary batteries expands, longer life, high capacity, and working stability are required.

[0004] As a positive electrode active material for a lithium secondary battery, a lithium metal oxide can be used. As an example of the lithium metal oxide, a nickel-based lithium metal oxide can be cited. However, due to surface damage of the positive electrode active material caused by repeated charge and discharge and high temperature environment, power and capacity may be reduced, and side reactions between the positive electrode active material and the electrolyte may be caused.

[0005] Therefore, there is a need to develop a lithium secondary battery that provides uniform power and capacity even when charged and discharged repeatedly. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] A technical problem of the present invention is to provide an electrolyte for a lithium secondary battery having improved high temperature characteristics.

[0008] A technical problem of the present invention is to provide a lithium secondary battery having improved high temperature characteristics.

[0009] (II) Technical solution

[0010] The electrolyte for a lithium secondary battery according to the exemplary embodiment may include an additive, an organic solvent, and a lithium salt. The additive may include a compound represented by the following Chemical Formula 1 or a compound represented by the following Chemical Formula 2.

[0011] [Chemical formula 1]

[0012]

[0013] [Chemical formula 2]

[0014]

[0015] In the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each of them may be independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and L may be a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

[0016] In some embodiments, the additive may include a compound represented by the following Chemical Formula 1-1.

[0017] [Chemical formula 1-1]

[0018]

[0019] In the chemical formula 1-1, R 1 To R 4 Each independently may be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0020] In some embodiments, in the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each independently may be an unsubstituted alkyl group having 1 to 3 carbon atoms.

[0021] In some embodiments, in the chemical formula 1 and the chemical formula 2, R 1 To R 7 It may be methyl.

[0022] In some embodiments, the additive may be contained in an amount of 0.1-5 wt % based on the total weight of the electrolyte for lithium secondary batteries.

[0023] In some embodiments, the additive may include the compound represented by the Chemical Formula 1 and the compound represented by the Chemical Formula 2 at the same time.

[0024] In one embodiment, the content ratio of the compound represented by the Chemical Formula 2 to the content ratio of the compound represented by the Chemical Formula 1 may be 0.25 to 4 on a weight basis.

[0025] In some embodiments, the organic solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0026] In some embodiments, the electrolyte for lithium secondary batteries may further include at least one auxiliary additive selected from unsaturated cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, and phosphate-based compounds.

[0027] In some embodiments, the auxiliary additive may be contained in an amount of 0.05-10 wt % based on the total weight of the electrolyte for lithium secondary batteries.

[0028] In some embodiments, the ratio of the content of the auxiliary additive to the content of the additive may be 0.1 to 10 on a weight basis.

[0029] The lithium secondary battery according to the exemplary embodiment may include: a positive electrode; a negative electrode disposed opposite to the positive electrode; and the electrolyte for the lithium secondary battery for impregnating the positive electrode and the negative electrode.

[0030] (III) Beneficial effects

[0031] The electrolyte for a lithium secondary battery according to an exemplary embodiment includes an additive represented by a specific chemical formula, so that a stable solid electrolyte interphase (SEI) can be formed on the surface of an electrode, and a decrease in capacity and an increase in resistance at high temperatures can be suppressed, and high temperature life characteristics of the lithium secondary battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment.

[0033] Figure 2 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment.

[0034] Figure 3 is a graph showing the H-NMR results of the compound represented by Chemical Formula 1-2.

[0035] Figure 4 is a graph showing the H-NMR results of the compound represented by Chemical Formula 2-1.

[0036] Figure 5 Graph showing the capacity retention rates of Example 1, Example 3, and Comparative Example 1. DETAILED DESCRIPTION

[0037] According to an embodiment of the present invention, there are provided an electrolyte for a lithium secondary battery and a lithium secondary battery including the electrolyte for a lithium secondary battery.

[0038] The lithium secondary battery according to the embodiment of the present invention can be widely used in electric vehicles, battery charging stations, other green technology fields such as solar power generation and wind power generation using batteries. In addition, the lithium secondary battery according to the embodiment of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0039] When the compound represented by a chemical formula used in the present invention has isomers, the compound represented by the chemical formula refers to a representative chemical formula including the isomers.

[0040] The term "~ radical compound" used in the present invention may refer to a compound having a "~ radical compound" and a derivative of the compound.

[0041] <Electrolyte for lithium secondary batteries>

[0042] The electrolyte for a lithium secondary battery according to the exemplary embodiment may include a lithium salt, an organic solvent, and an additive.

[0043] Hereinafter, the electrolyte solution for lithium secondary batteries will be described in more detail.

[0044] additive

[0045] The additive may include a compound represented by the following Chemical Formula 1 or a compound represented by the following Chemical Formula 2.

[0046] [Chemical formula 1]

[0047]

[0048] [Chemical formula 2]

[0049]

[0050] In the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each independently may be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0051] For example, the alkyl group may refer to an alkane (C n H 2n+2 ) is in the form of a hydrogen atom being detached. The part from which the hydrogen atom is detached can become a bonding site with an adjacent atom.

[0052] The term "substituted" used in the present specification may mean that at least one of the hydrogen atoms of the alkyl group or the alkylene group is substituted with a substituent and a substituent is further bonded to a carbon atom of the alkyl group or the alkylene group.

[0053] For example, the substituent may be a halogen atom, an amino group, a nitro group, a cyano group, a sulfinyl group, a sulfonyl group, a carbonyl group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or a cycloalkyl group or a heterocycloalkyl group having 3 to 7 carbon atoms.

[0054] In the Chemical Formula 1, L may be a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

[0055] For example, the alkylene group may refer to an alkane (C n H 2n+2 ) is separated from two hydrogen atoms. The part from which the hydrogen atom is separated can become a bonding site with an adjacent atom.

[0056] The additive includes a compound having a tertiary amine structure, and since the ester group is bonded with the nitrogen atom as the center, it can more easily form a chelate with lithium ions. Therefore, the lithium ion conductivity of the electrolyte can be increased, and the power characteristics and fast charging characteristics of the lithium secondary battery can be improved.

[0057] For example, the amine compound can form a thin film with low resistance on the surface of an electrode or an active material. Therefore, the increase in the initial resistance of the secondary battery can be suppressed, and the fast charging performance and life characteristics can also be significantly improved.

[0058] Therefore, by causing the electrolyte to include the compound represented by the Chemical Formula 1 or the Chemical Formula 2 as an additive, decomposition of the electrolyte can be prevented, and generation of gas and increase in battery thickness can be significantly reduced.

[0059] In addition, due to the alkyl group (R 1 To R 7 ) is bonded to the end of the carboxylate bonded to nitrogen, so the high temperature performance of the lithium secondary battery can be improved. For example, the amine compound can form a solid electrolyte interface (SEI) with thermal stability on the surface of the electrode or active material. Therefore, even under repeated charge and discharge, overvoltage and high temperature environment, the decomposition of the SEI film can be suppressed, and the irreversible loss of the electrolyte can be prevented, so that the high capacity and high ionic conductivity of the lithium secondary battery can be maintained.

[0060] In some embodiments, in the Chemical Formula 1, L may be an unsubstituted alkylene group having a carbon number of 1 to 3. For example, L may be a methylene group, an ethylene group, or a propylene group.

[0061] Preferably, in Chemical Formula 1, L may be an ethylene group. For example, the additive may include a compound represented by the following Chemical Formula 1-1.

[0062] [Chemical formula 1-1]

[0063]

[0064] By appropriately adjusting the number of carbon atoms between nitrogen atoms, the electrochemical stability, heat resistance, and flame retardancy of the electrolyte or a thin film formed from the electrolyte can be improved, and the lithium ion conductivity and power characteristics can be further enhanced.

[0065] In one embodiment, in the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each independently may be an unsubstituted alkyl group having 1 to 10 carbon atoms. Since the unsubstituted hydrocarbon group is located at the end of the amine compound, the high temperature stability can be further improved. In addition, by adjusting the carbon number of the alkyl group to an appropriate range, the electrolyte and the film formed by the electrolyte can have low resistance and high ion conductivity.

[0066] In some embodiments, in the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each of them may be independently an unsubstituted alkyl group having 1 to 3 carbon atoms, for example, a methyl group.

[0067] For example, the additive may include a compound represented by the following Chemical Formula 1-2 or the following Chemical Formula 2-1.

[0068] [Chemical formula 1-2]

[0069]

[0070] [Chemical formula 2-1]

[0071]

[0072] For example, since the alkyl group with a small number of carbon atoms is located at the end of the additive, steric hindrance and reduction of ion conductivity can be prevented. Therefore, the flame retardancy and heat resistance of the electrolyte can be further improved by the additive, and the electrolyte can have high lithium ion conductivity.

[0073] Therefore, the room temperature characteristics, rapid charging characteristics and initial resistance characteristics can be improved while improving the high temperature storage characteristics. In addition, the decomposition of the electrolyte caused by the reaction between the electrolyte and the electrode is suppressed, so that the generation of gas can be reduced.

[0074] In one embodiment, the content of the additive can be 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, or 1 wt % or more of the total weight of the electrolyte. Within the above range, a stable film can be uniformly formed on the electrode.

[0075] In one embodiment, the content of the additive can be 10% by weight or less, 9% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4.5% by weight or less, 4% by weight or less, 3.5% by weight or less, 3% by weight or less, or 2% by weight or less in the total weight of the electrolyte. Within the above range, the lithium ion conductivity in the electrolyte and the activity of the electrode active material can be improved.

[0076] For example, the content of the additive can be 0.1-5 wt % or 0.2-2 wt % in the total weight of the electrolyte. Within the above range, the migration of lithium ions and the activity of the positive electrode active material will not be excessively hindered, the capacity retention rate can be improved under high temperature environment, and the electrode thickness and resistance can be kept low.

[0077] In some embodiments, the additive may include both the compound represented by the Chemical Formula 1 and the compound represented by the Chemical Formula 2. By further increasing the affinity for lithium ions, the ion conductivity may be increased, and the electrochemical stability and thermal stability of the film may be further improved.

[0078] In one embodiment, the content of the compound represented by the chemical formula 2 may be 0.25 to 4, 0.3 to 4, 0.5 to 2, or 0.5 to 1.5, based on weight. Within the above range, the power characteristics of the lithium secondary battery can be further improved, while heat resistance and flame retardancy can be improved.

[0079] Auxiliary additives

[0080] The electrolyte for a lithium secondary battery according to the exemplary embodiment may further include an auxiliary additive.

[0081] By adding the auxiliary additive, the durability and stability of the electrode can be further enhanced. The auxiliary additive can be contained in an appropriate content within a range that does not hinder the migration of lithium ions in the electrolyte.

[0082] In one embodiment, the auxiliary additive may include, for example, unsaturated cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, and phosphate-based compounds.

[0083] In one embodiment, considering the effect with the compound represented by the Chemical Formula 1 or the Chemical Formula 2, for example, in the total weight of the lithium secondary battery electrolyte, the content of the auxiliary additive may be 10 wt % or less, 9 wt % or less, 8 wt % or less, 7 wt % or less, 6 wt % or less, 5 wt % or less, 4 wt % or less, 3 wt % or less, 2 wt % or less, or 1 wt % or less.

[0084] In one embodiment, in the total weight of the lithium secondary battery electrolyte, the content of the auxiliary additive may be 0.01 wt % or more, 0.02 wt % or more, 0.03 wt % or more, 0.05 wt % or more, 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, or 0.5 wt % or more. Within the above range, a more stable film can be formed on the surface of the electrode.

[0085] The content of the auxiliary additive in the total weight of the electrolyte is preferably about 0.05-10 wt %, more preferably 0.1-5 wt %. Within the above range, the durability of the electrode protection film can be enhanced without hindering the effect of the main additive, and the high temperature storage characteristics and life characteristics can be further improved.

[0086] In one embodiment, in the electrolyte, the ratio of the weight of the auxiliary additive to the weight of the additive may be 0.1 to 10, more than 1 and less than 10, or 5 to less than 10. By adjusting the content of the auxiliary additive relative to the main additive to an appropriate range, the cycle characteristics and high temperature storage characteristics of the lithium secondary battery can be improved simultaneously due to the interaction between the additives.

[0087] The unsaturated cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0088] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC).

[0089] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0090] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0091] The phosphate-based compound may include lithium bis(oxalate)phosphate as an oxalatophosphate-based compound.

[0092] In some embodiments, as the auxiliary additive, a fluorine-substituted carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, and an oxalatophosphate-based compound may be used together.

[0093] Organic solvents and lithium salts

[0094] The organic solvent may include, for example, an organic compound that has sufficient solubility for the lithium salt, the additive, and / or the auxiliary additive and is not reactive in the battery.

[0095] For example, the organic solvent may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0096] In one embodiment, the organic solvent may include a carbonate-based solvent.

[0097] In some embodiments, the carbonate-based solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0098] For example, the linear carbonate-based solvent may include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and dipropyl carbonate.

[0099] For example, the cyclic carbonate-based solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

[0100] In some embodiments, in the organic solvent, the content of the linear carbonate-based solvent may be greater than the content of the cyclic carbonate-based solvent on a volume basis.

[0101] For example, the mixing volume ratio of the linear carbonate-based solvent and the cyclic carbonate-based solvent may be 1:1 to 9:1, and preferably may be 1.5:1 to 4:1.

[0102] For example, the ester-based solvent may include at least one of methyl acetate (MA), ethylacetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP) and ethylpropionate (EP).

[0103] For example, the ether-based solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0104] For example, the ketone-based solvent may include cyclohexanone.

[0105] For example, the alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0106] For example, the aprotic solvent may include at least one of a nitrile-based solvent, an amide-based solvent (eg, dimethylformamide), a dioxolane-based solvent (eg, 1,3-dioxolane), and a sulfolane-based solvent.

[0107] The electrolyte may include a lithium salt, and the lithium salt may be composed of Li + X - express.

[0108] For example, the anion (X - ) can be F - , Cl - Br - ,I - 、NO3- 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - At least one of .

[0109] In some embodiments, the lithium salt may include at least one of LiBF4 and LiPF6.

[0110] In one embodiment, the concentration of the lithium salt relative to the organic solvent may be 0.01-5 M, preferably 0.01-2 M. Within the above concentration range, lithium ions and electrons can migrate smoothly in the electrolyte, and the fast charging characteristics and power characteristics of the lithium secondary battery can be further improved.

[0111] <Lithium Secondary Battery>

[0112] A lithium secondary battery according to an exemplary embodiment may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the above-mentioned electrolyte for a lithium secondary battery.

[0113] Figure 1 and Figure 2 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line I-I'.

[0114] Reference Figure 1 and Figure 2The lithium secondary battery may include a positive electrode 100 and a negative electrode 130 disposed opposite to the positive electrode 100 .

[0115] For example, the positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 on the positive electrode current collector 105 .

[0116] For example, the positive electrode active material layer 110 may include a positive electrode active material, and may include a positive electrode binder and a conductive material as needed.

[0117] For example, the positive electrode 100 may be manufactured by mixing and stirring a positive active material, a positive binder, a conductive material, a dispersion medium, etc. to prepare a positive electrode slurry, and then coating the positive electrode slurry on the positive electrode collector 105 and performing drying and rolling.

[0118] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, for example, may include aluminum or an aluminum alloy.

[0119] For example, the positive active material may include lithium metal oxide particles that can reversibly intercalate and deintercalate lithium ions.

[0120] In one embodiment, the positive active material may include lithium metal oxide particles containing nickel.

[0121] As an example of the positive electrode active material, it may include one or more compounds selected from lithium cobalt-based oxides, lithium manganese-based oxides, lithium nickel-based oxides, or lithium composite oxides, etc. For example, the positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); lithium iron phosphate oxide, etc.

[0122] In one embodiment, the lithium metal oxide particles may be represented by the following Chemical Formula 3.

[0123] [Chemical formula 3]

[0124] Li a Ni b M 1-b O2

[0125] In Chemical Formula 3, 0.95≤a≤1.08, b may be b≥0.5, and M may be at least one element selected from the group consisting of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0126] In one embodiment, the positive active material may include nickel (Ni), and may further include at least one of cobalt (Co) or manganese (Mn). For example, a nickel-cobalt-manganese (NCM)-based lithium oxide may be used.

[0127] For example, nickel (Ni) can be provided as a metal related to the capacity of a lithium secondary battery. As the nickel content increases, the capacity and power of the lithium secondary battery can be improved, but when the nickel content increases excessively, the lifespan may be reduced and may be disadvantageous in terms of mechanical stability and electrical stability.

[0128] In one embodiment, conductivity or resistance of a lithium secondary battery may be improved by cobalt (Co), and mechanical stability and electrical stability of a lithium secondary battery may be improved by manganese (Mn).

[0129] The chemical structure represented by Chemical Formula 3 represents the bonding relationship contained in the lattice structure or crystal structure of the positive active material, and does not exclude other additional elements. For example, M can be provided as the main active element of the positive active material. Chemical Formula 3 is provided to represent the bonding relationship of the main active element, and should be understood as a formula including the introduction and substitution of additional elements.

[0130] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the crystal structure may be further included. The auxiliary element may be mixed into the crystal structure together and form a bond, and it should be understood that this situation is also included in the chemical structure represented by Chemical Formula 3.

[0131] For example, the positive electrode binder may include an organic binder such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, polymethyl methacrylate, etc.; a water-based binder such as styrene-butadiene rubber (SBR), etc. In addition, for example, the positive electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0132] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; tin, tin oxide, titanium oxide; metal-based conductive materials such as perovskite materials such as LaSrCoO3 and LaSrMnO3.

[0133] For example, the negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125 .

[0134] For example, the negative electrode active material layer 120 may include a negative electrode active material and may include a negative electrode binder and a conductive material as needed.

[0135] For example, the negative electrode 130 may be manufactured by the following method: mixing and stirring a negative electrode active material, a negative electrode binder, a conductive material, a solvent, etc. to prepare a negative electrode slurry, and then coating the negative electrode slurry on the negative electrode current collector 125 and drying and rolling it.

[0136] For example, the negative electrode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably, may include copper or a copper alloy.

[0137] For example, the negative electrode active material may be a material that allows lithium ions to be inserted and extracted. For example, the negative electrode active material may include a lithium alloy, a carbon-based material, a silicon-based material, etc.

[0138] For example, the lithium alloy may include metal elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0139] For example, the carbon-based material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0140] For example, the amorphous carbon may be hard carbon, coke, mesocarbon microbead (MCMB) calcined at a temperature below 1500 °C, mesophase pitch-based carbon fiber (MPCF), etc. The crystalline carbon may be, for example, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0141] For example, the silicon-based material may include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si metal (Metal), etc. In this case, a lithium secondary battery with a high capacity can be achieved.

[0142] When the silicon-based material reacts with lithium, the volume change may be relatively large. Therefore, when the negative electrode active material includes a silicon-based material, due to repeated charge and discharge, the thickness of the battery may increase, and short circuit and fire may occur. The lithium secondary battery according to an exemplary embodiment can alleviate the battery thickness increase rate by including the above electrolyte.

[0143] The negative electrode binder and the conductive material may be substantially the same or similar to the positive electrode binder and the conductive material. For example, the negative electrode binder may be a water-based binder such as styrene-butadiene rubber (SBR). In addition, for example, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0144] For example, the separator 140 may be interposed between the positive electrode 100 and the negative electrode 130 .

[0145] In some embodiments, the area of ​​the negative electrode 130 may be greater than that of the positive electrode 100. In this case, lithium ions generated from the positive electrode 100 may smoothly migrate to the negative electrode 130 without being precipitated in the middle.

[0146] For example, the separator 140 may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. In addition, for example, the separator 140 may include a non-woven fabric formed of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0147] For example, a battery cell may be formed by including a positive electrode 100 , a negative electrode 130 , and a separator 140 .

[0148] For example, the electrode assembly 150 may be formed by stacking a plurality of battery cells. For example, the electrode assembly 150 may be formed by winding, lamination, folding, etc. of the separator 140 .

[0149] The lithium secondary battery according to the exemplary embodiment may include a positive electrode lead 107 connected to the positive electrode 100 and protruding outside the case 160 , and a negative electrode lead 127 connected to the negative electrode 130 and protruding outside the case 160 .

[0150] For example, the positive electrode lead 107 may be electrically connected to the positive electrode collector 105. The negative electrode lead 127 may be electrically connected to the negative electrode collector 125.

[0151] For example, the positive electrode current collector 105 may include a protrusion (positive electrode tab, not shown) on one side. The positive electrode active material layer 110 may not be formed on the positive electrode tab. The positive electrode tab may be integrally formed with the positive electrode current collector 105 or connected by welding or the like. The positive electrode current collector 105 and the positive electrode lead 107 may be electrically connected through the positive electrode tab.

[0152] For example, the negative electrode current collector 125 may include a protrusion (negative electrode tab, not shown) on one side. The negative electrode active material layer 120 may not be formed on the negative electrode tab. The negative electrode tab may be integrally formed with the negative electrode current collector 125 or connected by welding or the like. The negative electrode current collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab.

[0153] According to an exemplary embodiment, the electrode assembly 150 and the electrolyte described above may be housed together in a case 160 to define a lithium secondary battery. The lithium secondary battery may be manufactured in a cylindrical, prismatic, pouch, or coin shape, for example, using a can.

[0154] Preferred embodiments are presented below to help understand the present invention, but these embodiments are only used to illustrate the present invention and are not used to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and such changes and modifications obviously also fall within the scope of the claims.

[0155] Examples and Comparative Examples

[0156] (1) Synthesis Example 1: Tetramethyl 2,2',2'',2'''-[ethane-1,2-diylbis(azanetriyl)]tetraacetate (Additive A, Chemical Formula 1-2)

[0157] Ethylenediaminetetraacetic acid (2.9 g, 10 mmol) and methanol (100 mL) were added to a round-bottom flask in sequence and then cooled to 0°C. Thionyl chloride (5.8 mL, 80 mmol) was slowly added dropwise to the mixture while maintaining 0°C, and then stirred at room temperature for 16 hours. After the reaction was completed, the mixture was decompressed to remove the remaining thionyl chloride and methanol. The remaining mixture after decompression was redissolved in ether (50 mL) solvent, and a saturated sodium bicarbonate solution (50 mL) was slowly added dropwise, and stirred for 1 hour to neutralize the mixture. After the reaction was completed, the organic layer was separated and the moisture was removed by treatment with calcium carbonate. Thereafter, the solvent of the organic layer was removed under reduced pressure and dried to obtain 1.46 g of a colorless liquid sample. The obtained compound 1 The H-NMR results are as follows.

[0158] 1 H-NMR(CDCl3, 500MHz): 3.69(s, 12H), 3.61(s, 8H), 2.89(s, 4H)

[0159] Figure 3 is a graph showing the H-NMR results of the compound represented by Chemical Formula 1-2.

[0160] (2) Synthesis Example 2: Trimethyl 2,2',2''-nitrilotriacetate (Additive B, Chemical Formula 2-1)

[0161] Nitrilotriacetic acid (1.9 g, 10 mmol) and methanol (100 mL) were added to a round-bottom flask in sequence and then cooled to 0°C. Thionyl chloride (4.4 mL, 60 mmol) was slowly added dropwise to the mixture while maintaining 0°C, and then stirred at room temperature for 16 hours. After the reaction was completed, the mixture was decompressed to remove the remaining thionyl chloride and methanol. The remaining mixture after decompression was redissolved in ether (50 mL) solvent, and a saturated sodium bicarbonate solution (50 mL) was slowly added dropwise, and stirred for 1 hour to neutralize the mixture. After the reaction was completed, the organic layer was separated and the moisture was removed by treatment with calcium carbonate. Thereafter, the solvent of the organic layer was removed under reduced pressure and dried to obtain 1.65 g of a transparent yellow liquid sample. The obtained compound 1 The H-NMR results are as follows.

[0162] 1 H-NMR(CDCl3, 500MHz): 3.70(s, 9H), 3.67(s, 6H)

[0163] Figure 4 is a graph showing the H-NMR results of the compound represented by Chemical Formula 2-1.

[0164] (3) Preparation of electrolyte

[0165] Prepare 1 M LiPF6 solution (EC / EMC mixed solvent with a volume ratio of 25:75).

[0166] Based on the total weight of the electrolyte, additives and auxiliary additives were added to the LiPF6 solution at the contents (weight %) listed in Table 1 below and mixed to prepare the electrolytes of the Examples and Comparative Examples. In the case of Examples 5 to 10, Additive A and Additive B were mixed together.

[0167] (4) Manufacturing of lithium secondary batteries

[0168] Will Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, carbon black and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) in a weight ratio of 98:1:1 to prepare a positive electrode slurry.

[0169] The positive electrode slurry was uniformly coated on an aluminum foil having a thickness of 12 μm, dried, and rolled, thereby manufacturing a positive electrode.

[0170] A negative electrode slurry was prepared by dispersing a negative electrode active material prepared by mixing artificial graphite and natural graphite at a weight ratio of 7:3, a conductive material, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a weight ratio of 96:3:1:1 in water. The negative electrode slurry was uniformly coated on a copper foil having a thickness of 8 μm, dried and rolled to manufacture a negative electrode.

[0171] The manufactured positive electrodes and negative electrodes were alternately and repeatedly stacked with a separator (thickness of 13 μm, polyethylene film) interposed between the positive electrodes and the negative electrodes, thereby manufacturing an electrode assembly.

[0172] The electrode assembly was housed in a soft bag, the electrolyte prepared in (3) was injected and sealed, and immersed for 12 hours, thereby manufacturing a lithium secondary battery.

[0173] [Table 1]

[0174]

[0175] The components described in Table 1 are as follows.

[0176] Additive A: a compound represented by the chemical formula 1-2

[0177] Additive B: a compound represented by the chemical formula 2-1

[0178] Additive C: a compound represented by the following chemical formula 4

[0179] <Chemical Formula 4>

[0180]

[0181] Additive D: a compound represented by the following chemical formula 5

[0182] <Chemical Formula 5>

[0183]

[0184] FEC: Fluorinated Ethylene Carbonate

[0185] PS: 1,3-propane sultone

[0186] PRS: Prop-1-ene-1,3-sultone

[0187] <Experimental example>

[0188] (1) Evaluation of solubility

[0189] After the electrolytes according to the examples and comparative examples were left at room temperature for 3 hours, visual observation was made to see whether precipitation or layer separation occurred. If no precipitation or layer separation occurred, it was indicated by "0", and if precipitation or layer separation occurred, it was indicated by "X".

[0190] (2) Measurement of initial resistance (DCIR)

[0191] At room temperature (25°C), the lithium secondary batteries of the examples and comparative examples were charged at 0.5C CC / CV (4.2V0.05C cut-off (CUT-OFF)) to a state of charge (SOC) of 60%, and then discharged at 0.5C CC (2.7V cut-off). After that, they were charged to SOC 60%, and when SOC was 60%, the C-rate was changed to 0.2C, 0.5C, 1C, 1.5C, 2C, and 2.5C, and the discharge and supplementary charging were performed for 10 seconds respectively, thereby measuring the initial resistance.

[0192] (3) Evaluation of high temperature life at 45°C

[0193] (3-1) Capacity retention at 45℃

[0194] At 45°C, the lithium secondary batteries of the embodiments and comparative examples were charged to SOC 96% at a rate of 1.0C and discharged to SOC 2% at 1.0C, which was repeated 900 times. At this time, the first initial discharge capacity was measured, and the capacity retention rate during high temperature life was measured by dividing the 900th discharge capacity by the first discharge capacity.

[0195] (3-2) Resistance increase rate at 45℃

[0196] At 45°C, the lithium secondary batteries of the embodiments and comparative examples were charged to SOC 60% every 100 cycles from the first cycle, and then the rate was changed to 0.2C, 0.5C, 1C, 1.5C, 2C, and 2.5C when the SOC was 60%, and the discharge and supplementary charging were performed for 10 seconds respectively to measure the internal resistance. The resistance increase rate during high temperature life was measured by dividing the 900th resistance by the resistance value of the first cycle.

[0197] The evaluation results are shown in Table 2 below.

[0198] [Table 2]

[0199]

[0200] Referring to Table 2, in the case of the embodiment containing additive A or additive B, the initial resistance at room temperature and the resistance increase rate at high temperature are low, or the high temperature capacity retention rate is improved. In the case of the embodiment containing both additive A and additive B, the initial resistance and the high temperature resistance increase rate or the high temperature capacity and the high temperature capacity retention rate are improved at the same time.

[0201] In the case of Comparative Example 1 including only the auxiliary additive, the high temperature capacity and the high temperature life performance (45° C.) were reduced.

[0202] Figure 5 is a graph showing the high temperature capacity retention rate according to the cycle. Figure 5 In the lithium secondary battery of Comparative Example 1, compared with the lithium secondary batteries of Examples 1 and 3, the capacity decreases sharply as the number of cycles increases.

[0203] The electrolytes of Comparative Examples 2 and 3 respectively contain an amino compound having a carboxyl group at the end (additive C) and an amino compound containing a lithium salt (additive D) as additives. The solubility of additives C and additive D in the electrolyte is very low, so the composition after mixing is not uniform, and the performance of the lithium secondary battery cannot be evaluated.

Claims

1. An electrolyte for a lithium secondary battery, comprising: An additive, the additive comprising a compound represented by the following Chemical Formula 1 or a compound represented by the following Chemical Formula 2; organic solvents; and Lithium salts, [Chemical formula 1] [Chemical formula 2] In the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each is independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and L is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms.

2. The electrolyte for lithium secondary battery according to claim 1, wherein The additive includes a compound represented by the following Chemical Formula 1-1, [Chemical formula 1-1] In the chemical formula 1-1, R 1 To R 4 Each is independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

3. The electrolyte for lithium secondary battery according to claim 1, wherein In the chemical formula 1 and the chemical formula 2, R 1 To R 7 Each is independently an unsubstituted alkyl group having 1 to 3 carbon atoms.

4. The electrolyte for lithium secondary battery according to claim 1, wherein In the chemical formula 1 and the chemical formula 2, R 1 To R 7 It is methyl.

5. The electrolyte for lithium secondary battery according to claim 1, wherein The additive includes a compound represented by the following Chemical Formula 1-2 or a compound represented by the following Chemical Formula 2-1, [Chemical formula 1-2] [Chemical formula 2-1] 6. The electrolyte for lithium secondary battery according to claim 1, wherein The content of the additive is 0.1-5% by weight in the total weight of the electrolyte for lithium secondary batteries.

7. The electrolyte for lithium secondary battery according to claim 1, wherein The additive includes the compound represented by the Chemical Formula 1 and the compound represented by the Chemical Formula 2 at the same time.

8. The electrolyte for lithium secondary battery according to claim 7, wherein The content ratio of the compound represented by the Chemical Formula 2 to the content ratio of the compound represented by the Chemical Formula 1 is 0.25 to 4 on a weight basis.

9. The electrolyte for lithium secondary battery according to claim 1, wherein The organic solvent includes a linear carbonate-based solvent and a cyclic carbonate-based solvent.

10. The electrolyte for lithium secondary battery according to claim 1, wherein The electrolyte for lithium secondary batteries further comprises at least one auxiliary additive selected from unsaturated cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds and phosphate-based compounds.

11. The electrolyte for lithium secondary battery according to claim 10, wherein The content of the auxiliary additive is 0.05-10 wt % in the total weight of the electrolyte for lithium secondary battery.

12. The electrolyte for lithium secondary battery according to claim 10, wherein The ratio of the content of the auxiliary additive to the content of the additive is 0.1 to 10 on a weight basis.

13. A lithium secondary battery comprising: positive electrode; A negative electrode, the negative electrode being arranged opposite to the positive electrode; as well as The electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte for a lithium secondary battery is used to impregnate the positive electrode and the negative electrode.

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