Lithium secondary battery

Abstract

To provide a lithium secondary battery that can reduce the amount of gas generation at high temperatures while improving charge / discharge characteristics and life characteristics at room temperature and high temperature when stored at high temperatures.SOLUTION: A lithium secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte for the lithium secondary battery including a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound such as triallyl isocyanurate, trimethyl isocyanurate, or trimethallyl isocyanurate, and a second compound such as 2-fluoro-1,3,2-dioxaphosphorane or 2-fluoro-4-methyl-1,3,2-dioxaphosphorane. The positive electrode active material includes a lithium nickel composite oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a lithium secondary battery. [Background technology]

[0002] In recent years, the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles has led to a rapid increase in demand for high-energy-density, high-capacity secondary batteries. To address this, active research and development efforts are being conducted to improve the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode.

[0004] In particular, the characteristics of a lithium secondary battery are determined by the complex reactions between the positive electrode and the electrolyte, and the negative electrode and the electrolyte, and therefore, the use of an appropriate electrolyte is one of the important factors for improving the performance of a lithium secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment is to provide a lithium secondary battery that can reduce the amount of gas generation at high temperatures while improving charge / discharge characteristics and life characteristics at room temperature and high temperature during high-temperature storage. [Means for solving the problem]

[0006] A lithium secondary battery according to one embodiment includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a non-aqueous organic solvent, a lithium salt, and an electrolyte solution for a lithium secondary battery including an additive, wherein the additive includes a first compound represented by Chemical Formula 1 below and a second compound represented by Chemical Formula 2 below, and the positive electrode active material includes a lithium nickel composite oxide represented by Chemical Formula 3 below.

[0007] [ka]

[0008] In chemical formula 1, R 1 ~R 3 are each independently hydrogen, a cyano group, a halogen group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group.

[0009] [ka]

[0010] In chemical formula 2, X 1 is fluorine, chlorine, bromine or iodine, R 4 ~R 9 are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group; n is an integer of 0 or 1.

[0011] [Chemical formula 3] Li w Ni x Mn y M 1 1-x-y O2 In chemical formula 3, 0.5≦w≦1.8, 0.05≦x<1, 0 <y≦0.7であり、 M 1 is Al, Fe, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0012] A lithium secondary battery according to an embodiment can reduce the amount of gas generated at high temperatures while improving charge / discharge characteristics and life characteristics at room temperature and high temperature during high temperature storage. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is given by way of example only, and the present invention is not limited thereto, but is defined only by the scope of the claims that follow.

[0015] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is said to be "on" another part, this includes not only when it is "directly on" the other part, but also when there is another part in between.

[0016] Unless otherwise specified herein, terms used in the singular can also include the plural, and unless otherwise specified, "A or B" can mean "including A, including B, or including A and B."

[0017] As used herein, "combinations thereof" may refer to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0018] Unless otherwise defined herein, particle size may refer to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, measurement can be performed using a measuring device using dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) value can be calculated. Alternatively, measurement can be performed using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac's MT3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0019] Here, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or compound has been replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a C1-C30 amine group, a nitro group, a C1-C40 silyl group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C20 alkoxy group, a C1-C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0020] Specifically, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, halogen, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. For example, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, halogen, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. Alternatively, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, halogen, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. As an example, "substituted" may mean that at least one hydrogen in a substituent or compound has been replaced with deuterium, a cyano group, a halogen, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0021] A lithium secondary battery according to one embodiment includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a non-aqueous organic solvent, a lithium salt, and an electrolyte solution for a lithium secondary battery including an additive, wherein the additive includes a first compound represented by Chemical Formula 1 below and a second compound represented by Chemical Formula 2 below, and the positive electrode active material includes a lithium nickel composite oxide represented by Chemical Formula 3 below.

[0022] [ka] In chemical formula 1, R 1 ~R 3 are each independently hydrogen, cyano, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group.

[0023] [ka] In chemical formula 2, X 1 is fluorine, chlorine, bromine or iodine, R 4 ~R 9 are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group; n is an integer of 0 or 1.

[0024] [Chemical formula 3] Li w Ni x Mn y M 1 1-x-y O2 In chemical formula 3, 0.5≦w≦1.8, 0.05≦x<1, 0 <y≦0.7であり、 M 1 is Al, Fe, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0025] The electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0026] The additive includes a first compound and a second compound.

[0027] The first compound is an isocyanurate-based compound that undergoes a radical reaction with other compounds having double bonds in the electrolyte to form a strong and low-resistance cathode electrolyte interphase (CEI) film on the positive electrode, thereby improving the charge / discharge characteristics of the battery when stored at high temperatures, as well as the cycle characteristics at room temperature and high temperatures.

[0028] The first compound may be represented by the following Chemical Formula 1:

[0029] [ka]

[0030] In formula 1, R 1 ~R 3are each independently hydrogen, cyano, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group.

[0031] As an example, R 1 ~R 3 may each independently be a substituted or unsubstituted C1 to C20 alkyl group, or a substituted or unsubstituted C2 to C20 alkenyl group.

[0032] As a more specific example, R 1 ~R 3 may each independently be a substituted or unsubstituted C2 to C20 alkenyl group.

[0033] For example, the compound represented by Chemical Formula 1 may be one or more compounds selected from the compounds listed in Group 1 below.

[0034] [ka]

[0035] By way of example, and without limitation, the first compound may be triallyl isocyanurate, trimethyl isocyanurate, trimethallyl isocyanurate, or combinations thereof.

[0036] The first compound may be contained in an amount of 0.05 to 3% by weight, for example, 0.1 to 2% by weight, or 0.5 to 1% by weight, based on the total weight of the electrolyte solution. When the amount is within this range, a lithium secondary battery with improved high-temperature storage characteristics and life characteristics can be realized.

[0037] The second compound forms a solid electrolyte interface (SEI) film on the negative electrode surface that is highly stable at high temperatures and has excellent ionic conductivity. This suppresses the side reaction of LiPF6 due to the -PO2F functional group, thereby reducing gas generation due to the decomposition reaction of the electrolyte during high-temperature storage.

[0038] Specifically, the second compound can be coordinated with a thermal decomposition product of a lithium salt such as LiPF6 or an anion dissociated from the lithium salt to form a complex. The formation of 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 and the electrolyte. This improves the cycle life characteristics of the lithium secondary battery and prevents gas generation inside the lithium secondary battery, significantly reducing the rate of defects.

[0039] The second compound is represented by the following chemical formula 2.

[0040] [ka]

[0041] In chemical formula 2, X 1 is fluorine, chlorine, bromine or iodine, R 4 ~R 9are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group; n is an integer of 0 or 1.

[0042] Chemical Formula 2 may include a compound represented by the following Chemical Formula 2A or Chemical Formula 2B.

[0043] [ka]

[0044] In Formula 2A and Formula 2B, X 1 is fluorine, chlorine, bromine or iodine, R 4 ~R 9 are each independently hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0045] In Formula 2A, R 6 and R 7 are hydrogen, and R 8 and R 9 At least one of may be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0046] In Formula 2B, R 6 and R 7 are hydrogen, and R 4 , R 5 , R8 and R 9 At least one of may be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0047] For example, R in Formula 2A 6 and R 7 are hydrogen, and R 8 and R 9 At least one of them may be a substituted or unsubstituted C1 to C10 alkyl group.

[0048] As an example, the compound represented by Chemical Formula 2 may be selected from the compounds listed in Group 2 below.

[0049] [ka]

[0050] As an example, the compound represented by Chemical Formula 2 may include 2-fluoro-1,3,2-dioxaphospholane, 2-fluoro-4-methyl-1,3,2-dioxaphospholane, or a combination thereof.

[0051] The second compound may be contained in an amount of 0.05 to 3% by weight, for example, 0.1 to 2% by weight, or 0.5 to 1% by weight, based on the total weight of the electrolyte solution. When the amount is within this range, a lithium secondary battery that generates less gas when stored at high temperatures can be realized.

[0052] Meanwhile, the additive may further include other additives in addition to the above-mentioned compounds.

[0053] Other additives can include vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), 2-fluorobiphenyl (2-FBP), or combinations thereof.

[0054] By further including other additives, the life span can be further improved and gas generated at the positive and negative electrodes during high temperature storage can be effectively controlled.

[0055] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0056] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent, or a combination thereof.

[0057] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0058] The non-aqueous organic solvents can be used alone or in combination of two or more. When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0059] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)borate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0060] positive electrode active material The positive electrode active material may be a compound capable of reversibly inserting and extracting lithium (lithiated insertion compound). Specifically, one or more of composite oxides of lithium and a metal selected from manganese, nickel, and combinations thereof may be used.

[0061] The composite oxide may be a lithium transition metal composite oxide, and an example thereof includes a cobalt-free nickel-manganese oxide, which is a lithium nickel composite oxide represented by the following chemical formula 3. [Chemical formula 3] Li w Ni x Mn y M 1 1-x-y O2 In chemical formula 3, 0.5≦w≦1.8, 0.05≦x<1, 0 <y≦0.7であり、 M 1is Al, Fe, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0062] The lithium nickel composite oxide represented by Chemical Formula 3 is a so-called cobalt-free (Co-free) positive electrode active material, and in Chemical Formula 3, 0.5≦w≦1.8, 0.6≦w≦1.8, 0.7≦w≦1.8, 0.8≦w≦1.8, 0.9≦w≦1.8, 0.9≦w≦1.7, 0.9≦w≦1.6, 0.9≦w≦1.5, 0.9≦w≦1.4, 0.9≦w≦1.3, 0.9≦w≦1.2, or 0.9≦w≦1.1; 0.05≦x<1, 0.3≦x<1, 0.4≦x<1, 0.5≦x<1, 0.6≦x<1, 0.7≦x<1, 0.8≦x<1, or 0.9≦x<1; <y≦0.7、0<y≦0.6、0<y≦0.5、0<y≦0.4、0<y≦0.3、0<y0.2または0<y≦0.1でもよい。

[0063] The lithium nickel composite oxide represented by chemical formula 3 is 1 The positive electrode active material may further include one or more of B, Ce, Cr, F, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, and Zr as dopants. These additional elements act as dopants to partially modify the lattice structure of each positive electrode active material and improve the reversible insertion and desorption of lithium.

[0064] The lithium nickel composite oxide represented by Chemical Formula 3 has the problem that under high-voltage driving conditions, increased Ni activity accelerates electrolyte decomposition, causing a large amount of Ni to be dissolved and then reduced on the negative electrode surface, accelerating deterioration of battery life. However, when used with an electrolyte containing the first and second compounds described above, decomposition of the electrolyte can be suppressed, reducing the amount of gas generated and improving the charge / discharge characteristics and life characteristics of the battery.

[0065] Furthermore, the lithium nickel composite oxide represented by Chemical Formula 3 can achieve relatively stable performance at driving voltages of 4.2 V or less, but when the driving voltage is 4.3 V or more, particularly 4.35 V or more, side reactions with the electrolyte become intense, causing transition metal ions to leach out and resulting in a rapid decline in battery performance, and the decline in battery performance can become even more severe at high temperatures. However, when the lithium nickel composite oxide represented by Chemical Formula 3 is used with an electrolyte containing the first and second compounds described above, stable battery performance can be achieved under high voltage / high temperature conditions.

[0066] The positive electrode active material may further include, in addition to the cobalt-free nickel-manganese oxide, a lithium nickel-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, or a combination thereof.

[0067] For example, the positive electrode active material may further include a compound represented by any one of the following chemical formulas: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Lia Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8)

[0068] In the above chemical formula, A is Ni, Mn, or a combination thereof; X is Al, Ni, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al or a combination thereof.

[0069] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more but 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0070] positive electrode A positive electrode for a lithium secondary battery can include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material and can further include a binder and / or a conductive material.

[0071] As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0072] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive material may be 0.5% by weight to 5% by weight each relative to 100% by weight of the positive electrode active material layer.

[0073] The binder serves to effectively adhere the positive electrode active material particles to each other and to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0074] The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical change in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0075] The current collector may be made of aluminum (Al), but is not limited thereto.

[0076] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0077] As a substance capable of reversibly inserting / desorbing lithium ions, a carbon-based negative electrode active material can be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0078] As an alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0079] As a substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0080] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0081] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer disposed on the core.

[0082] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0083] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0084] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0085] The binder serves to effectively adhere the negative electrode active material particles to each other and to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0086] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymers, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0087] The water-based binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0088] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity can be further included. The cellulose-based compound can be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal can be sodium, potassium, or lithium.

[0089] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0090] The conductive material is used to impart conductivity to the electrode and can be any electron-conductive material that does not undergo chemical change in the battery that is constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in powder or fiber form, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0091] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0092] Separator Depending on the type of lithium secondary battery, a separator may be provided between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials, such as a mixed multilayer film, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0093] The separator can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0094] The porous substrate may be a polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer membrane formed from a copolymer or mixture of two or more of these.

[0095] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0096] The inorganic material can include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, YO3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0097] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be stacked.

[0098] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, and other types depending on their shape.

[0099] 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment, and FIG. 1 shows a circular battery, FIG. 2 shows a square battery, and FIGS. 3 and 4 show a pouch battery.

[0100] 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown).

[0101] The lithium secondary battery 100 may include a sealing member 60 that seals the case 50 as shown in FIG.

[0102] As shown in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12 , a negative electrode lead tab 21 , and a negative electrode terminal 22 .

[0103] As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0104] For example, the operating voltage of the lithium secondary battery may be 4.3 V or more, or 4.35 V or more. Even in the high-voltage operating environment described above, stable battery performance can be achieved under high-voltage / high-temperature conditions when the lithium nickel composite oxide represented by Chemical Formula 3 is used together with an electrolyte solution containing the first compound and the second compound described above.

[0105] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0106] Examples of the present invention and comparative examples are described below, but the following examples are merely examples of the present invention and the present invention is not limited to the following examples. [Example]

[0107] Example 1 A basic electrolyte solution was prepared by dissolving 1.15 M LiPF6 lithium salt in a non-aqueous organic solvent consisting of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) mixed in a volume ratio of 20:40:40.

[0108] An electrolyte solution was prepared by adding triallyl isocyanurate as the first compound and 2-fluoro-4-methyl-1,3,2-dioxaphospholane as the second compound to the base electrolyte solution. At this time, the first compound was contained at 0.5 wt% and the second compound was contained at 0.5 wt% of the total electrolyte solution.

[0109] NMX (LiNi 0.75 Mn 0.23 Al 0.02O2), polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 97:2:1 and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated onto a 14 μm thick aluminum foil (Al) current collector, dried at 110°C, and then rolled to prepare a positive electrode.

[0110] The negative electrode active material slurry was prepared by mixing artificial graphite as the negative electrode active material, styrene-butadiene rubber as the binder, and carboxymethyl cellulose as the thickener in a weight ratio of 97:1:2 and dispersing the mixture in distilled water. The negative electrode active material slurry was coated onto a 10 μm-thick copper foil (Cu) current collector, dried at 100°C, and rolled to prepare the negative electrode.

[0111] An electrode assembly was prepared by placing a 25 μm thick polyethylene-polypropylene multilayer separator between the prepared positive electrode and negative electrode, and the assembly was inserted into a circular battery case. The prepared electrolyte was then injected into the case to prepare a 4.45 V lithium secondary battery of Example 1.

[0112] Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1, except that the first compound and the second compound were not added when preparing the electrolyte solution.

[0113] Comparative Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the second compound was not added when preparing the electrolyte solution.

[0114] Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 1, except that the first compound was not added when preparing the electrolyte solution.

[0115] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 1, except that triallyl cyanurate represented by the following chemical formula a was added instead of triallyl isocyanurate, which is the first compound, when preparing the electrolyte solution.

[0116] [ka]

[0117] Comparative Example 5 NCA (LiNi 0.5 Co 0.2 Al 0.3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode was formed using ZnO.

[0118] Evaluation example Evaluation example 1: Evaluation of high-temperature storage characteristics The initial DC resistance (DCIR) was measured using the ΔV / ΔI (change in voltage / change in current) value for the lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 5. The batteries were then fully charged (SOC 100%) to create a maximum energy state within the battery, and the batteries were stored in this state at high temperature (60°C) for 30 days, after which the DC resistance (DCIR) was measured.

[0119] The DCIR increase rate (%) was calculated using the following formula 1. The results are shown in Table 1 below.

[0120] [Formula 1] DCIR increase rate (%) = {(DCIR after 30 days - initial DCIR) / (initial DCIR)} x 100

[0121] [Table 1]

[0122] Referring to Table 1, it can be seen that Example 1 has a lower DCIR increase rate at high temperatures than Comparative Examples 1 to 5, and is therefore superior in high-temperature storage characteristics.

[0123] Evaluation example 2: Evaluation of life characteristics at room temperature The lithium secondary batteries produced in Example 1 and Comparative Examples 1 to 5 were charged and discharged once at 0.2 C, and the charge and discharge capacities were measured.

[0124] In addition, the lithium secondary batteries manufactured in Example and Comparative Examples 1 to 5 were charged at an upper limit charge voltage of 4.4 V, and then discharged at a constant current of 0.2 C to 2.5 V to measure the initial discharge capacity.

[0125] Again, 200 cycles of 0.33 C charge (CC / CV, 4.4 V, 0.025 C cut-off) / 1.0 C discharge (CC, 2.5 V cut-off) were performed at 25°C, and the discharge capacity was measured.

[0126] The discharge capacity ratio to the initial discharge capacity is shown in Table 2 below as the capacity recovery rate (%, recovery).

[0127] Evaluation example 3: Evaluation of gas generation amount after high temperature storage The lithium secondary batteries manufactured in Examples and Comparative Examples 1 to 5 were left at 60°C for 7 days, and the amount of gas generated (ml) on the first and seventh days was measured using a refinery gas analyzer (RGA). The results are shown in Table 2 below.

[0128] The gas increase rate (%) calculated by the following formula 2 is shown in Table 2 below.

[0129] [Formula 2] Gas increase rate (%) = {(gas generation amount on day 7) / (gas generation amount on day 1)} x 100

[0130] [Table 2]

[0131] Referring to Table 2, it can be seen that Example 1 has a larger capacity recovery rate at room temperature than Comparative Examples 1 to 5, and therefore has excellent room temperature life characteristics.

[0132] Furthermore, referring to Table 2, it can be seen that in Example 1, the rate of increase in gas after high-temperature storage is significantly smaller than in Comparative Examples 1 to 5.

[0133] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0134] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; The present invention relates to an electrolyte solution for a lithium secondary battery, the electrolyte solution including a non-aqueous organic solvent, a lithium salt, and an additive, The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2: The positive electrode active material includes a lithium nickel composite oxide represented by the following chemical formula 3: 【Chemistry 1】 In the above Chemical Formula 1, R １ ~R ３ are each independently hydrogen, cyano, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; 【Chemistry 2】 In the above Chemical Formula 2, X １ is fluorine, chlorine, bromine or iodine, R ４ ~R ９ are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; n is an integer of 0 or 1; [Chemical formula 3] Li ｗ Ni ｘ Mn ｙ M １ １－ｘ－ｙ O ２ In the above Chemical Formula 3, 0.5≦w≦1.8, 0.05≦x<1, 0<y≦0.7, M １ is Al, Fe, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

2. In Formula 1, R １ ~R ３ and each independently represent a substituted or unsubstituted C1 to C20 alkyl group or a substituted or unsubstituted C2 to C20 alkenyl group.

3. 2. The lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 1 is at least one selected from the group consisting of the compounds listed in Group 1 below: 【Transformation 3】

4. The compound represented by Chemical Formula 2 includes a compound represented by Chemical Formula 2A or 2B: 【Chemistry 4】 In the formula 2A and the formula 2B, X １ is fluorine, chlorine, bromine or iodine, R ６ ~R ９ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

5. R of Formula 2A ６ and R ７ are both hydrogen, R ８ and R ９ at least one of which is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

6. The lithium secondary battery of claim 1 , wherein the second compound represented by Chemical Formula 2 is at least one selected from the group consisting of compounds listed in Group 2 below: 【Transformation 5】

7. The lithium secondary battery according to claim 1, wherein the first compound is contained in an amount of 0.05% by weight to 3% by weight based on the total weight of the electrolyte solution.

8. 2. The lithium secondary battery according to claim 1, wherein the second compound is contained in an amount of 0.05% by weight to 3% by weight based on the total weight of the electrolyte solution.

9. 2. The lithium secondary battery according to claim 1, wherein the additive further comprises vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate, adiponitrile, succinonitrile, 1,3,6-hexanetricyanide, propene sultone, propane sultone, lithium tetrafluoroborate, lithium difluorophosphate, 2-fluorobiphenyl, or a combination thereof.

10. 2. The lithium secondary battery according to claim 1, wherein in Chemical Formula 3, 0.9≦w≦1.1, 0.6≦x<1, and 0<y≦0.

4.

11. 2. The lithium secondary battery according to claim 1, wherein the driving voltage of the lithium secondary battery is 4.3 V or more.

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