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 demand for high-energy-density, high-capacity secondary batteries has been growing rapidly with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles. For this reason, research and development into improving the performance of lithium secondary batteries has been actively carried out.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode, each of which includes an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. When lithium ions are intercalated / deintercalated at the positive electrode and the negative electrode, oxidation and reduction reactions occur, producing electrical energy.

[0004] In particular, the characteristics of a lithium secondary battery are determined by the complex reactions between the positive electrode and the electrolyte, and between 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 an 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 for a lithium secondary battery including an additive, the additive including 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 a hydrogen atom, 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 each independently represents 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 combinations thereof.

[0012] The 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 description of the drawings]

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

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail, but they are given by way of example only and are not intended to limit the present invention, which is defined only by the scope of the claims set forth below.

[0015] Unless otherwise specified in this specification, when a part such as a layer, film, region, plate, etc. 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 in this specification, 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 in this specification, the particle size may be the average particle size. Also, the particle size refers to the average particle size (D50), which means the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution. The average particle size (D50) can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer, or by using a transmission electron microscope or a scanning electron microscope. As another method, the average particle size (D50) can be obtained by measuring using a measuring device using dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, the average particle size (D50) can be measured 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., MT3000 by Microtrac) and irradiated with ultrasound of approximately 28 kHz at an output of 60 W, after which the average particle size (D50) based on the 50% standard of the particle size distribution in the measuring device can be calculated.

[0019] Here, unless otherwise defined, "substituted" means that at least one hydrogen in a substituent or compound is 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" may mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C10 fluoroalkyl group, or cyano group. For example, "substituted" may mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1-C20 alkyl group, C6-C30 aryl group, C1-C10 fluoroalkyl group, or cyano group. Alternatively, "substituted" may mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1-C5 alkyl group, C6-C18 aryl group, C1-C5 fluoroalkyl group, or cyano group. As an example, "substituted" may mean that at least one hydrogen in a substituent or compound is 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 an 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 for a lithium secondary battery including an additive, the additive including a first compound represented by Chemical Formula 1 below and a second compound which is a 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 a hydrogen atom, a cyano group, a halogen atom, 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 each independently represents 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 combinations 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, which undergoes a radical reaction with other compounds having double bonds in the electrolyte to form a CEI (Cathod Electrolyte Interphase) film on the positive electrode that is strong and has low resistance, thereby improving the charge / discharge characteristics of the battery when stored at high temperatures, and the cycle characteristics at room temperature and high temperature.

[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 a hydrogen atom, a cyano group, a halogen atom, 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 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% by weight to 3% by weight, for example, 0.1% by weight to 2% by weight, or 0.5% by weight to 1% by weight, based on the total weight of the electrolyte. When the amount is within this range, a lithium secondary battery having improved high-temperature storage characteristics and life characteristics can be realized.

[0037] The second compound forms a solid electrolyte interface (SEI) membrane on the negative electrode surface that has high high-temperature stability and excellent ionic conductivity, and 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 to 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 these complexes 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, thereby improving the cycle life characteristics of the lithium secondary battery and preventing gas generation inside the lithium secondary battery, thereby 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 9each independently represents 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 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.

[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 them 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% by weight to 3% by weight, for example, 0.1% by weight to 2% by weight, or 0.5% by weight to 1% by weight, based on the total weight of the electrolyte. When the amount is within this range, a lithium secondary battery that generates less gas during storage 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 (LiBF4), lithium difluorophosphate (LiPO2F2), 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 the 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 the carbonate solvent 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 the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of the ketone solvent include cyclohexanone. Examples of the alcohol solvent include ethyl alcohol and isopropyl alcohol. Examples of the aprotic solvent include nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and 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 kinds. When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can 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 in the battery to enable basic lithium secondary battery operation and to facilitate 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 from 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 combinations 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; and 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 the chemical formula 3 is M of the chemical formula 3. 1 As the dopant, one or more of B, Ce, Cr, F, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, and Zr can be further included. These additional elements can partially deform the lattice structure of each positive electrode active material as a dopant and improve the reversible insertion and desorption of lithium.

[0064] The lithium nickel composite oxide represented by Chemical Formula 3 has a problem that, under high voltage driving conditions, the decomposition of the electrolyte is promoted due to the increase in Ni activity, and a large amount of Ni is dissolved and then reduced on the negative electrode surface, accelerating the deterioration of the life. However, when used together with an electrolyte containing the above-mentioned first compound and second compound, the decomposition of the electrolyte can be suppressed, the amount of gas generation can be reduced, and the charge / discharge characteristics and life characteristics of the battery can be improved.

[0065] In addition, the lithium nickel composite oxide represented by Chemical Formula 3 can achieve relatively stable performance at a driving voltage of 4.2 V or less, but when the driving voltage is 4.3 V or more, especially 4.35 V or more, side reactions with the electrolyte become intense, causing transition metal ions to be eluted, resulting in a rapid decrease in battery performance, and the decrease in battery performance can become more serious at high temperatures. However, when the lithium nickel composite oxide represented by Chemical Formula 3 is used together with an electrolyte containing the above-mentioned first and second compounds, 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-based 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; L 1 is Mn, Al or a combination thereof.

[0069] As an 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 and 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 The positive electrode for a lithium secondary battery may 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 may further include a binder and / or a conductive material.

[0071] As an example, the positive electrode can 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 adhere the positive electrode active material particles well to each other and to adhere the positive electrode active material well to the current collector. Representative examples of the binder 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 electrical conductivity to the electrodes, and any material that is electronically conductive and does not undergo chemical changes in the battery that is constructed can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes, metal-based materials in the form of metal powder or metal fibers 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 and dedoped with 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 used, which can include, 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, an Si-based negative electrode active material or an 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), an 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, an 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 and amorphous carbon are coated 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. The amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles can be dispersed and present in the 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 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 The 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 adhere the negative electrode active material particles to each other and to the current collector well. 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 capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K, or Li may be used.

[0089] The dry binder may be 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 electrical conductivity to the electrodes, and any material that is electronically conductive and does not undergo chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotubes, 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. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers of these can be used, and 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 can be used.

[0093] The separator can include a porous substrate and a coating layer comprising an organic, an inorganic, 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, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, 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 inorganics can include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, 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 laminated.

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

[0099] 1 to 4 are schematic diagrams showing a lithium secondary battery according to an embodiment, in which FIG. 1 shows a circular battery, FIG. 2 shows a rectangular 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 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. 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 above-mentioned high-voltage operating environment, when the lithium nickel composite oxide represented by Chemical Formula 3 is used together with the electrolyte solution containing the above-mentioned first compound and second compound, stable battery performance can be achieved under high-voltage / high-temperature conditions.

[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 electric devices, but the present invention is not limited thereto.

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

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

[0108] An electrolyte 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 basic electrolyte. At this time, the first compound was contained at 0.5 wt% and the second compound was contained at 0.5 wt% relative to the total electrolyte.

[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 an aluminum foil (Al) current collector with a thickness of 14 μm, dried at 110°C, and then rolled to prepare a positive electrode.

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

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

[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 during preparation of 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 produced 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 direct current 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 inside the batteries, and the batteries were stored in this state at high temperature (60° C.) for 30 days, after which the direct current resistance (DCIR) was measured.

[0119] The DCIR increase rate (%) was calculated according to 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)}X100

[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 room temperature life characteristics 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 produced in the examples and comparative examples 1 to 5 were charged at an upper limit charging 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 ratio of the discharge capacity 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 the 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 generated on the 7th day) / (gas generated on the 1st day)}X100

[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 is therefore superior in room temperature life characteristics.

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

[0133] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and can be embodied in various modified forms within the scope of the claims, the detailed description of the invention, and the attached drawings, which of course 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, and The present invention relates to an electrolyte for a lithium secondary battery, the electrolyte comprising a non-aqueous organic solvent, a lithium salt, and an additive, The additive includes a first compound represented by the following formula 1 and a second compound represented by the following 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 a hydrogen atom, a cyano group, a halogen atom, a substituted or unsubstituted C1-C20 alkyl 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 C2-C20 heterocycloalkyl group, a substituted or unsubstituted C3-C20 cycloalkenyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-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-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; [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 is each independently 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 Formula 1 is at least one selected from the group consisting of the compounds listed in Group 1 below: 【Chemistry 3】

4. The compound represented by Chemical Formula 2 includes a compound represented by Chemical Formula 2A or 2B below: 【Chemistry 4】 In the above Chemical Formula 2A and the above Chemical 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 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. The lithium secondary battery according to claim 4.

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

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 the 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.

Images