Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a perlithiated manganese-rich oxide containing 50 mol % or more of Mn among all metals excluding lithium and having a molar ratio of lithium to transition metals exceeding 1, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the additive includes a first additive and a second additive, and the first additive and the second additive each include a compound represented by a specific chemical formula.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0171809, filed December 9, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery. [Background technology]

[0003] In recent years, the application areas of lithium secondary batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, communication, and computer equipment to power storage and supply for large-area devices such as automobiles and power storage devices. Accordingly, there has been an increasing demand for high-capacity, high-power, and highly stable secondary batteries.

[0004] The lithium secondary battery typically comprises a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte serving as a medium for transferring lithium ions, and a separator. The negative electrode active material may be a carbon-based active material or a silicon-based active material. The positive electrode active material may be a lithium transition metal oxide such as lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), or lithium nickel-cobalt-manganese composite oxide.

[0005] Recently, perlithiated manganese-rich oxide has been attracting attention as a next-generation positive electrode active material. Perlithiated manganese-rich oxide has the advantage of high capacity due to its increased content of manganese (Mn), which is relatively inexpensive and abundant in reserves. However, its use has been limited due to issues such as reactive oxygen generated by phase transformation of the positive electrode active material during activation and charge / discharge processes, which causes rapid decomposition of the electrolyte and significantly increases gas generation, and transition metals eluted from the positive electrode active material are electrodeposited on the negative electrode, destroying the SEI coating on the negative electrode. These issues become even more serious during high-temperature and high-voltage operation. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to solve the above-mentioned problems and to provide a lithium secondary battery that contains a perlithiated manganese-rich oxide as a positive electrode active material, which reduces gas generation during initial activation and charge / discharge and suppresses elution of transition metals from the positive electrode active material, thereby achieving excellent high-temperature cycle characteristics and high-temperature storage characteristics. [Means for solving the problem]

[0007] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises a perlithiated manganese-rich oxide containing 50 mol % or more of Mn among all metals excluding lithium and having a molar ratio of lithium to transition metals exceeding 1, and the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, the first additive comprises a compound represented by the following Chemical Formula 1, and the second additive comprises a compound represented by the following Chemical Formula 2:

[0008] [Chemical formula 1] [ka]

[0009] [Chemical formula 2] [ka]

[0010] In the above Chemical Formula 1, each R1 independently represents a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof; n represents an integer of 0 to 6; in the above Chemical Formula 2, A represents a substituted or unsubstituted heteroaryl group having 3 to 5 carbon atoms, and R2 represents an alkylene group having 1 to 3 carbon atoms. [Effects of the Invention]

[0011] The lithium secondary battery of the present invention is characterized by using a perlithiated manganese-rich oxide as a positive electrode active material and a first additive and a second additive having specific chemical formula structures as additives to a non-aqueous electrolyte. The first additive is a coumarin-based compound that scavenges reactive oxygen during initial activation, preventing consumption of the organic solvent in the non-aqueous electrolyte and preventing gas generation due to decomposition of the organic solvent. The second additive is a compound containing a heteroaromatic ring that can remove HF generated by decomposition of the lithium salt, thereby preventing manganese from being eluted from the positive electrode active material by HF and preventing desorption of reactive oxygen, thereby significantly reducing gas generation. As a result, when the first additive and the second additive are used in combination, the initial activation and gas generation during charge and discharge of a lithium secondary battery containing the perlithiated manganese-rich oxide are reduced, and the elution of transition metals from the positive electrode active material is suppressed, thereby significantly improving the high-temperature cycle performance and high-temperature storage performance of the lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0013] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] On the other hand, before describing the present invention, unless otherwise specified in the present invention, "*" means a linking portion (bonding site) between the ends of the same or different atoms or chemical formulae.

[0015] Furthermore, in the description of "number of carbon atoms a to b" herein, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "an alkyl group having 1 to 5 carbon atoms" refers to an alkyl group containing 1 to 5 carbon atoms, i.e., CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, CH3)2CHCH2CH2-, (CH3)2CHCH2CH2-, etc.

[0016] In addition, in this specification, any alkyl group, alkenyl group, alkynyl group, alkoxy group, aryl group, or heteroaryl group may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen atom bonded to a carbon atom is substituted with an element other than hydrogen, and includes, for example, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a cycloalkynyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkynyl group having 2 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, a fluoroalkyl group having 1 to 20 carbon atoms, a nitro group, an aryl group having 6 to 20 carbon atoms, a heteroaryl group having 2 to 20 carbon atoms, or a haloaryl group having 6 to 20 carbon atoms.

[0017] The present invention will now be described in more detail.

[0018] Lithium secondary battery The present invention relates to a lithium secondary battery.

[0019] The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a perlithiated manganese-rich oxide containing 50 mol % or more of Mn among all metals excluding lithium and having a molar ratio of lithium to transition metals exceeding 1, and the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, wherein the additive includes a first additive and a second additive, the first additive includes a compound represented by the following Chemical Formula 1, and the second additive includes a compound represented by the following Chemical Formula 2:

[0020] [Chemical formula 1] [ka]

[0021] [Chemical formula 2] [ka]

[0022] In the above Chemical Formula 1, each R1 independently represents a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof; n represents an integer of 0 to 6; in the above Chemical Formula 2, A represents a substituted or unsubstituted heteroaryl group having 3 to 5 carbon atoms, and R2 represents an alkylene group having 1 to 3 carbon atoms.

[0023] The lithium secondary battery of the present invention is characterized by using a perlithiated manganese-rich oxide as a positive electrode active material and a first additive and a second additive having specific chemical formula structures as additives to a non-aqueous electrolyte. The first additive is a coumarin-based compound that scavenges reactive oxygen during initial activation, preventing consumption of the organic solvent in the non-aqueous electrolyte and preventing gas generation due to decomposition of the organic solvent. The second additive is a compound containing a heteroaromatic ring that can remove HF generated by decomposition of the lithium salt, thereby preventing manganese from being eluted from the positive electrode active material by HF and preventing desorption of reactive oxygen, thereby significantly reducing gas generation. As a result, when the first additive and the second additive are used in combination, the initial activation and gas generation during charge and discharge of a lithium secondary battery containing the perlithiated manganese-rich oxide are reduced, and the elution of transition metals from the positive electrode active material is suppressed, thereby significantly improving the high-temperature cycle performance and high-temperature storage performance of the lithium secondary battery.

[0024] The lithium secondary battery includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. Specifically, the lithium secondary battery includes a negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by placing an electrode assembly including the negative electrode, a positive electrode facing the negative electrode, and a separator interposed between the negative electrode and the positive electrode in a battery case and then injecting the non-aqueous electrolyte.

[0025] (1) Positive electrode The positive electrode includes a positive electrode active material.

[0026] The positive electrode active material includes a perlithiated manganese-rich oxide, which may contain 50 mol % or more of Mn among all metals excluding lithium, and may have a molar ratio of lithium to transition metals greater than 1.

[0027] While perlithiated manganese-rich oxide has been attracting attention as a next-generation high-capacity positive electrode active material, its application has been limited due to structural degradation inherent to the material. Specifically, reactive oxygen released from perlithiated manganese-rich oxide during initial activation decomposes and consumes the organic solvent (e.g., ethylene carbonate) contained in the non-aqueous electrolyte, generating gas by-products, resulting in reduced lifespan, increased resistance, and reduced safety. Furthermore, during the charge and discharge process of a lithium secondary battery containing perlithiated manganese-rich oxide, HF, a decomposition product of the lithium salt, dissolves manganese from the perlithiated manganese-rich oxide. This leads to the release of oxygen, specifically reactive oxygen, from the perlithiated manganese-rich oxide to achieve charge balance. The dissolved manganese is electrodeposited on the negative electrode, causing damage to the SEI film. Furthermore, the released reactive oxygen during the charge and discharge process continuously decomposes and consumes the organic solvent in the non-aqueous electrolyte, increasing the generation of gas by-products. The consumption of non-aqueous electrolyte, structural collapse of the perlithiated manganese-rich oxide, and increase in gas by-products significantly reduce the life performance, resistance characteristics, and safety of lithium secondary batteries, and these problems become even more severe under high temperature and high voltage conditions.

[0028] To solve these problems, the lithium secondary battery of the present invention is characterized by using a first additive and a second additive, which will be described later, in combination as additives for the nonaqueous electrolyte. When both the first additive and the second additive are used, the generation of reactive oxygen during the initial activation process and during the operation of the lithium secondary battery is significantly suppressed, structural collapse of the perlithiated manganese-rich oxide is prevented, and consumption of organic solvents is significantly reduced, thereby realizing a lithium secondary battery with excellent high-temperature cycle characteristics, high-temperature storage characteristics, and safety. These effects are difficult to achieve with other lithium transition metal oxides, in which elimination of reactive oxygen is not a significant problem.

[0029] The perlithiated manganese-rich oxide may include a compound represented by the following formula X:

[0030] [Chemical formula X] Li 1+s [Ni t Co u Mn V M 1 w ]O 2+z

[0031] In the above chemical formula X, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and satisfies 0.05≦s≦1, 0≦t≦0.5, 0≦u≦0.3, 0.5≦v<1.0, 0≦w≦0.2, and 0≦z≦1. Preferably, in the chemical formula X, the following may be satisfied: 0.05≦s≦1.0, 0.1≦t≦0.5, 0≦u≦0.1, 0.5≦v<1.0, 0≦w≦0.2, and 0≦z≦1. More preferably, in the chemical formula X, 0.10≦s≦0.50, 0.1≦t≦0.5, 0≦u≦0.1, 0.6≦v<1.0, 0≦w≦0.1, and 0≦z≦0.50.

[0032] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material may be contained in the positive electrode active material layer.

[0033] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and preferably aluminum.

[0034] The positive electrode current collector usually has a thickness of 3 to 500 μm.

[0035] The positive electrode current collector may have a surface with fine irregularities to strengthen the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0036] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector, specifically, on one or both surfaces of the positive electrode current collector.

[0037] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 92% by weight to 98.5% by weight, in consideration of sufficient capacity of the positive electrode active material.

[0038] The positive electrode active material layer may further contain a binder and / or a conductive material in addition to the positive electrode active material.

[0039] The binder is a component that assists in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0040] The binder may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0041] The conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK (registered trademark), channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Preferably, the positive electrode conductive material may include carbon nanotubes in order to improve conductivity.

[0042] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

[0043] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, and preferably 40 μm to 110 μm.

[0044] The positive electrode may be prepared by coating a positive electrode slurry containing a positive electrode active material, and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry, on the positive electrode current collector, followed by drying and rolling.

[0045] The solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the solid content of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0046] (2) Negative electrode The negative electrode faces the positive electrode.

[0047] The negative electrode includes a negative electrode active material.

[0048] The negative electrode active material is a material capable of reversibly intercalating / deintercalating lithium ions, and may include at least one selected from the group consisting of a carbon-based active material, a (semi)metal-based active material, and lithium metal, and specifically may include at least one selected from a carbon-based active material and a (semi)metal-based active material.

[0049] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of artificial graphite and natural graphite.

[0050] The average particle size (D 50 ) may be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0051] Specifically, the (semi)metal-based active material may include at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0052] More specifically, the (semi)metallic active material may include a silicon-based active material.

[0053] The silicon-based active material is SiO x (0≦x<2). SiO2 does not react with lithium ions and therefore cannot store lithium. Therefore, x is preferably within the above range, and more preferably, the silicon-based active material may be SiO.

[0054] The average particle size (D 50 ) may be 1 μm to 30 μm, preferably 2 μm to 15 μm, from the viewpoint of improving structural stability during charge and discharge and reducing side reactions with the electrolyte.

[0055] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material may be contained in the negative electrode active material layer.

[0056] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0057] The negative electrode current collector usually has a thickness of 3 to 500 μm.

[0058] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0059] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector, specifically, on one or both surfaces of the negative electrode current collector.

[0060] The negative electrode active material may be contained in the negative electrode active material layer in an amount of 60% by weight to 99% by weight, preferably 75% by weight to 95% by weight.

[0061] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0062] The binder is used to improve the adhesive strength between the negative electrode active material layer and the negative electrode current collector, thereby improving battery performance. For example, the binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0063] The binder may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0064] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK (registered trademark), channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0065] The conductive material may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0066] The thickness of the negative electrode active material layer may be 10 μm to 200 μm, and preferably 20 μm to 150 μm.

[0067] The negative electrode may be prepared by coating at least one surface of a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and / or a solvent for forming the negative electrode slurry, followed by drying and rolling.

[0068] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry may be 30% by weight to 80% by weight, specifically 40% by weight to 70% by weight.

[0069] (3) Separator The separator may be interposed between the positive electrode and the negative electrode.

[0070] The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of a high-melting point glass fiber or polyethylene terephthalate fiber, but is not limited to these. Furthermore, to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0071] (4) Nonaqueous electrolyte The non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive.

[0072] 1) Lithium salt As the lithium salt used in the present invention, various lithium salts that are commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without any limitation. For example, the lithium salt may contain Li as a cation. + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - The composition may include at least one selected from the group consisting of:

[0073] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0074] The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, specifically, at a concentration of 0.8 M to 4 M, more specifically, at a concentration of 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transport number (Li +The transference number and dissociation degree of lithium ions are improved, which can improve the output characteristics of the battery.

[0075] 2) Organic solvents The organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries and minimizes decomposition due to oxidation reactions during charging and discharging of the secondary battery.

[0076] Specifically, the organic solvent may include at least one selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0077] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture thereof.

[0078] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and easily dissociates the lithium salt in the electrolyte. Specifically, the cyclic carbonate organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. More specifically, the cyclic carbonate organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). Even more specifically, the cyclic carbonate organic solvent may include ethylene carbonate (EC).

[0079] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and may specifically include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, more specifically, may include at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and even more specifically, may include ethyl methyl carbonate (EMC).

[0080] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. In this case, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed at a volume ratio of 5:95 to 40:60, specifically, a volume ratio of 10:90 to 25:75. When the mixing ratio of the cyclic carbonate organic solvent and the linear carbonate organic solvent satisfies the above range, both high dielectric constant and low viscosity characteristics are satisfied, and excellent ionic conductivity characteristics can be realized.

[0081] In order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents in addition to the at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents.

[0082] Specifically, the linear ester organic solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0083] The cyclic ester organic solvent may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0084] Meanwhile, the organic solvent may further include, as needed, any organic solvent commonly used in non-aqueous electrolytes, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0085] The ether solvent may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more of these, but is not limited thereto.

[0086] The glyme-based solvent has a higher dielectric constant and lower surface tension than linear carbonate-based organic solvents and is less reactive with metals, and may include at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME), but is not limited thereto.

[0087] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0088] 4) Additives The non-aqueous electrolyte contains additives, which include a first additive and a second additive.

[0089] The first additive includes a compound represented by the following Chemical Formula 1:

[0090] [Chemical formula 1] [ka]

[0091] In Chemical Formula 1, each R1 independently represents a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof; and n is an integer of 0 to 6.

[0092] The compound represented by Chemical Formula 1 contained in the first additive is a coumarin-based compound that can capture reactive oxygen released from the perlithiated manganese-rich oxide during initial activation. Therefore, the use of the first additive can prevent the decomposition of organic solvents and the increased generation of gas by-products that may occur when reactive oxygen is generated during the initial activation process.

[0093] However, apart from being able to remove reactive oxygen during the initial activation process, the first additive is ineffective at removing reactive oxygen generated during charge / discharge or storage of a lithium secondary battery. Reactive oxygen generated during charge / discharge or storage of such a lithium secondary battery generates HO as a by-product of its reaction with the electrolyte, and HO decomposes the lithium salt to generate HF. This HF dissolves manganese from the perlithiated manganese-rich oxide and releases oxygen, potentially accelerating the deterioration of life and storage performance. To solve this problem, the present invention uses a second additive in addition to the first additive to remove HF generated during charge / discharge, storage, and other conditions, thereby preventing the generation of reactive oxygen during charge / discharge, storage, and other conditions of the lithium secondary battery. Therefore, the present invention uses both the first additive and the second additive to suppress the generation of reactive oxygen, which is particularly problematic in perlithiated manganese-rich oxides, thereby improving the life, storage, and safety of the lithium secondary battery, particularly during high-temperature, high-voltage operation.

[0094] In Chemical Formula 1, R1 may specifically be a halogen (the halogen may be selected from F, Cl, Br, and I, and specifically may be F), a nitrile group, a propargyl group, an ester group, an ether group, or a combination of two or more thereof. Such a substituent improves the reducing ability of the first additive, and can also realize the effects of smoothly forming an SEI film and improving lithium ion transport performance, along with the reactive oxygen capturing ability of the first additive.

[0095] In the above Chemical Formula 1, n is an integer selected from 0 to 6, specifically, may be an integer selected from 1 to 6, more specifically, n may be 1. In the above Chemical Formula 1, when n is 2 or more, each R may be the same or different.

[0096] Specifically, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by Chemical Formula 1-A and compounds represented by Chemical Formula 1-B below.

[0097] [Chemical formula 1-A] [ka]

[0098] [Chemical formula 1-B] [ka]

[0099] In Chemical Formula 1-A and Chemical Formula 1-B, R1 is as defined in Chemical Formula 1.

[0100] The compounds represented by Chemical Formula 1-A and Chemical Formula 1-B each have a structure in which substituents are present at positions 3 and 7 (IUPAC nomenclature standard) of the ring structure, and in this case, synthesis at these positions is preferred because it is more advantageous than other substitution positions.

[0101] Specifically, the compound represented by Chemical Formula 1 may include at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 to 1-9. The compound represented by Chemical Formula 1 may specifically include at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 to 1-4, more specifically at least one selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 and 1-2, and even more specifically, may include the compound represented by the following Chemical Formula 1-1, in view of being more smoothly reduced to the negative electrode and being more advantageous in forming an SEI coating.

[0102] [Chemical formula 1-1] [ka]

[0103] [Chemical Formula 1-2]

change

[0104] [Chemical Formulas 1-3]

change

[0105] [Chemical Formulas 1-4]

change

[0106] [Chemical Formulas 1-5]

change

[0107] [Chemical Formulas 1-6]

change

[0108] [Chemical Formulas 1-7]

change

[0109] [Chemical Formulas 1-8]

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[0110] [Chemical Formulas 1-9]

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[0111] The first additive may be included in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 1 wt %, and even more specifically 0.3 wt % to 0.7 wt %. When the first additive is used in the above content range, it can sufficiently capture reactive oxygen generated during initial activation and prevent concerns about increased resistance when an excessive amount is added.

[0112] The second additive may include a compound represented by the following Chemical Formula 2:

[0113] [Chemical formula 2] [ka]

[0114] In the above chemical formula 2, A is a substituted or unsubstituted heteroaryl group having 3 to 5 carbon atoms, and R2 is an alkylene group having 1 to 3 carbon atoms.

[0115] Generally, reactive oxygen is generated in perlithiated manganese-rich oxide during charging, discharging, storage, etc. of lithium secondary batteries. This reactive oxygen reacts with the organic solvent in the non-aqueous electrolyte to generate by-products such as CO, CO2, and HO. Among these, HO decomposes the lithium salt to generate HF. This HF dissolves manganese from the perlithiated manganese-rich oxide and releases oxygen, which can accelerate the deterioration of life and storage performance.

[0116] To solve this problem, the present invention uses the second additive as a non-aqueous electrolyte additive. The second additive is a Lewis base compound capable of capturing HF, a Lewis acid, and includes the compound represented by Chemical Formula 2, thereby blocking the generation of reactive oxygen by HF. Therefore, the use of the second additive can significantly contribute to improving the high-temperature life performance, high-temperature storage performance, and safety of lithium secondary batteries containing perlithiated manganese-rich oxides.

[0117] However, because it is difficult for the second additive to directly remove reactive oxygen, the reactive oxygen generated during initial activation cannot be controlled by the use of the second additive alone. If the reactive oxygen generated during initial activation is not removed, the structural collapse of the perlithiated manganese-rich oxide accelerates. Consequently, when the second additive alone is used as a nonaqueous electrolyte additive, it is difficult to improve the life and storage performance. However, the present invention uses the first additive, which is effective in removing reactive oxygen generated during initial activation, together with the second additive, thereby improving the high-temperature life, high-temperature storage performance, and safety of lithium secondary batteries.

[0118] In the above Chemical Formula 2, A may be a substituted or unsubstituted heteroaryl group having 3 to 5 carbon atoms, specifically a substituted or unsubstituted nitrogen-containing heteroaryl group having 3 to 5 carbon atoms, more specifically a substituent selected from imidazole, pyrazole, pyrrole, pyridine, and pyrimidine.

[0119] In the above chemical formula 2, R2 may be an alkylene group having 1 to 3 carbon atoms, more specifically, a methylene group (-CH2-).

[0120] Specifically, the compound represented by Chemical Formula 2 may include at least one selected from the group consisting of a compound represented by Chemical Formula 2-A below, a compound represented by Chemical Formula 2-B below, and a compound represented by Chemical Formula 2-C below, and more specifically, may include a compound represented by Chemical Formula 2-A below.

[0121] [Chemical formula 2-A] [ka]

[0122] [Chemical formula 2-B] [ka]

[0123] [Chemical formula 2-C] [ka]

[0124] In Chemical Formula 2-A, Chemical Formula 2-B, and Chemical Formula 2-C, R2 is as defined in Chemical Formula 2, R3, R4, and R5 are each independently selected from an alkyl group having 1 to 3 carbon atoms and —CN, h is an integer of 0 to 3, i is an integer of 0 to 3, and j is an integer of 0 to 4.

[0125] Specifically, in Chemical Formula 2-A, Chemical Formula 2-B, and Chemical Formula 2-C, h, i, and j may each be 0.

[0126] More specifically, the compound represented by Chemical Formula 2 may include a compound represented by the following Chemical Formula 2-1.

[0127] [Chemical formula 2-1] [ka]

[0128] The second additive may be included in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 5 wt %, and even more specifically 0.3 wt % to 2 wt %. When the content of the second additive satisfies the above range, it is preferable in that the HF capturing effect is fully realized and an increase in the resistance of the lithium secondary battery due to the addition of an excessive amount and a resulting decrease in life performance are prevented.

[0129] The weight ratio of the first additive to the second additive may be 5:95 to 95:5, specifically 10:90 to 92:8, more specifically 30:70 to 70:30, and even more specifically 40:60 to 60:40. When the weight ratio is as described above, the effects of using the first additive and the second additive in combination are harmonized, and as a result, the effects of improving the high-temperature life performance, high-temperature storage performance, and safety of the lithium secondary battery can be preferably exhibited.

[0130] The additive may further include an additional additive in addition to the first and second additives. The additional additive may be included in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing and causing the negative electrode to collapse in a high-power environment, or to improve low-temperature high-rate discharge characteristics, high-temperature stability, prevent overcharging, and suppress battery expansion at high temperatures.

[0131] Specifically, the additional additive may be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiBOB (lithium bis-(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (tris(trimethylsilyl)phosphite), and may specifically be vinylene carbonate.

[0132] The additional additive may be included in the non-aqueous electrolyte in an amount of 0.1 wt % to 15 wt %.

[0133] The non-aqueous electrolyte can be prepared by the following method. First, the organic solvent is prepared. Next, the lithium salt is dissolved in the organic solvent, for example, at a concentration of 0.5M to 5M, specifically 0.8M to 4M, and more specifically 0.8M to 2.0M. Next, the first additive and the second additive are added to the organic solvent containing the dissolved lithium salt. In this case, the first additive may be contained in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 5 wt %, and even more specifically 0.3 wt % to 2 wt %, based on the weight of the non-aqueous electrolyte, and the second additive may be contained in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 5 wt %, and even more specifically 0.3 wt % to 2 wt %, based on the weight of the non-aqueous electrolyte. The non-aqueous electrolyte may further contain the additional additives described above.

[0134] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0135] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0136] Examples and Comparative Examples Example 1 (Production of non-aqueous electrolyte) The organic solvent used was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70.

[0137] To the organic solvent, LiPF6 as a lithium salt, the compound represented by the above chemical formula 1-1 as a first additive, and the compound represented by the above chemical formula 2-1 as a second additive were added to prepare a non-aqueous electrolyte.

[0138] The LiPF6 was contained in the non-aqueous electrolyte at a molar concentration of 1.2M.

[0139] The compound represented by Chemical Formula 1-1 was contained in the non-aqueous electrolyte at 0.5 wt %, and the compound represented by Chemical Formula 2-1 was contained in the non-aqueous electrolyte at 0.5 wt %.

[0140] (Lithium secondary battery manufacturing) Cathode active material (Li 1.35 [Ni 0.360 Co 0.005 Mn 0.635 ]O2, perlithiated manganese-rich oxide), conductive material (carbon nanotubes), and binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96.0:1.5:2.5 to prepare a cathode mixture slurry (solid content 65 wt%). The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0141] Anode active material (artificial graphite and natural graphite mixed in a weight ratio of 50.3:49.7), conductive material (carbon black), and binder (styrene-butadiene rubber) were added to distilled water as a solvent in a weight ratio of 96.7:1.0:2.3 to prepare anode mixture slurry (solid content 50 wt%). The anode mixture slurry was applied to one side of an 8 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

[0142] A polyethylene porous film separator was interposed between the positive electrode and negative electrode prepared above in a dry room, and the non-aqueous electrolyte prepared above was then injected to prepare a secondary battery.

[0143] Example 2 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-2 was added to the non-aqueous electrolyte at a content of 0.5 wt % instead of the compound represented by Chemical Formula 1-1 as the first additive.

[0144] Example 3 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that, as the first additive, the compound represented by Chemical Formula 1-3 was added to the non-aqueous electrolyte in an amount of 0.5 wt % instead of the compound represented by Chemical Formula 1-1.

[0145] Example 4 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-4 was added to the non-aqueous electrolyte at a content of 0.5 wt % instead of the compound represented by Chemical Formula 1-1 as the first additive.

[0146] Example 5 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was added to the non-aqueous electrolyte in an amount of 0.05 wt % as the first additive.

[0147] Example 6 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 1-1 was added to the non-aqueous electrolyte in an amount of 7 wt % as the first additive.

[0148] Example 7 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 2-1 was added to the non-aqueous electrolyte in an amount of 0.05 wt % as the second additive.

[0149] Example 8 A non-aqueous electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that the compound represented by Formula 2-1 was added to the non-aqueous electrolyte in an amount of 7 wt % as the second additive.

[0150] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the first additive and the second additive were not added.

[0151] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the second additive was not added.

[0152] Comparative Example 3 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 2, except that the second additive was not added.

[0153] Comparative Example 4 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the first additive was not added.

[0154] [Table 1]

[0155] Experimental example Experimental example 1: Evaluation of high-temperature cycle performance The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 manufactured as described above were charged to 4.35 V, 1 / 40 C under CC / CV, 0.33 C conditions at 45°C using an electrochemical charger / discharger, and then discharged to 2.0 V under CC, 0.33 C conditions, with one cycle being defined as 200 charge / discharge cycles.

[0156] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 2 below.

[0157] Capacity retention rate (%) = {(discharge capacity after 200 cycles) / (discharge capacity after 1 cycle)} × 100

[0158] (2) Resistance increase rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device, and after adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0159] After 200 cycles of charge and discharge, the resistance after 200 cycles was calculated in the same manner as above, and the resistance increase rate was calculated using the following formula. The results are shown in Table 2 below.

[0160] Resistance increase rate (%) = (resistance after 200 cycles - initial resistance) / initial resistance x 100

[0161] (3) Amount of gas generated After 200 charge / discharge cycles, the amount of gas generated in the lithium secondary battery was measured using GC-FID / TCD, and the results are shown in Table 2 below.

[0162] (4) Transition metal elution amount After 200 charge / discharge cycles, the concentration of all metals dissolved into the non-aqueous electrolyte was measured. The amounts of metals measured using ICP analysis are shown in Table 2 below.

[0163] [Table 2]

[0164] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 8, which are lithium secondary batteries combining a positive electrode containing a perlithiated manganese-rich oxide with a nonaqueous electrolyte containing both the first additive and the second additive as additives, have a higher capacity retention rate during high-temperature cycle charge / discharge, a lower resistance increase rate, and a smaller amount of gas generation, and are prevented from eluting transition metals, compared to Comparative Examples 1 to 4.

[0165] Experimental example 2: Evaluation of high-temperature storage performance The lithium secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 prepared above were initially charged to 4.35 V, 1 / 40 C under CC / CV, 0.33 C conditions at 25°C, and then discharged to 2.0 V at 0.33 C. Thereafter, they were charged to 4.35 V, 1 / 40 C under CC / CV, 0.33 C conditions at 25°C, and then stored at 60°C for 8 weeks.

[0166] (1) Capacity maintenance rate After 8 weeks of storage, the lithium secondary battery was charged at 25° C. under CC / CV, 0.33 C conditions to 4.35 V, 1 / 40 C, and then discharged at 0.33 C to 2.0 V, and the discharge capacity was measured.

[0167] The capacity retention rate was evaluated using the following formula, and the results are shown in Table 3 below.

[0168] Capacity retention rate (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) x 100

[0169] (2) Resistance increase rate After the initial charge / discharge, the capacity was confirmed at room temperature, and then the battery was charged to 50% SOC based on the discharge capacity and discharged at a current of 2.5 C for 10 seconds. The resistance was measured from the difference in voltage drop at this time and recorded as the initial resistance. After storing at 60°C for 8 weeks, the resistance was measured using the same method and recorded as the final resistance. The resistance increase rate was calculated using the following formula. The results are shown in Table 3 below.

[0170] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) x 100

[0171] (3) Amount of gas generated After 8 weeks of storage, the amount of gas generated in the lithium secondary battery was measured using GC-FID / TCD, and the results are shown in Table 3 below.

[0172] (4) Transition metal elution amount After 8 weeks of storage, the concentration of all metals dissolved in the non-aqueous electrolyte was measured. The amounts of metals measured using ICP analysis are shown in Table 3 below.

[0173] [Table 3]

[0174] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 8, which are lithium secondary batteries combining a positive electrode containing a perlithiated manganese-rich oxide with a nonaqueous electrolyte containing both the first additive and the second additive as additives, have a higher capacity retention rate during high-temperature storage, a lower resistance increase rate, and a smaller amount of gas generation, and are prevented from eluting transition metals, compared to Comparative Examples 1 to 4.

[0175] Reference example Reference example 1 (1) Production of non-aqueous electrolyte A non-aqueous electrolyte was produced in the same manner as in Example 1.

[0176] (2) Manufacture of lithium secondary batteries Cathode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 A cathode mixture slurry (solid content 76.5 wt%) was prepared by adding 02), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 98.0:0.7:1.3. The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film), dried, and roll-pressed to prepare a cathode.

[0177] Anode active material (artificial graphite), conductive material (carbon black), and binder (styrene-butadiene rubber) were mixed in a weight ratio of 96.5:1.5:2.0 with distilled water as a solvent to prepare anode mixture slurry (solid content 50 wt%). The anode mixture slurry was applied to one side of an 8 μm-thick anode current collector (Cu thin film), dried, and roll-pressed to prepare anode.

[0178] A polyethylene porous film separator was interposed between the positive electrode and negative electrode prepared above in a dry room, and the non-aqueous electrolyte prepared above was then injected to prepare a secondary battery.

[0179] Reference example 2 A lithium secondary battery was produced in the same manner as in Reference Example 1, except that the nonaqueous electrolyte produced in Comparative Example 1 was used instead of the nonaqueous electrolyte produced in Example 1.

[0180] Reference Experiment Example The lithium secondary batteries of Reference Examples 1 and 2 prepared above were initially charged at 25°C under CC / CV, 0.33C conditions to 4.2V, 1 / 40C, and discharged at 0.33C to 2.5V, and then charged again under CC / CV, 0.33C conditions to 4.2V, 1 / 40C, and then stored at 60°C for 8 weeks.

[0181] (1) Capacity maintenance rate After 8 weeks of storage, the lithium secondary battery was charged at 25° C. under CC / CV, 0.33 C conditions to 4.2 V, 1 / 40 C, and then discharged at 0.33 C to 2.5 V, and the discharge capacity was measured.

[0182] The capacity retention rate was evaluated using the following formula, and the results are shown in Table 4 below.

[0183] Capacity retention rate (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) x 100

[0184] (2) Resistance increase rate After the initial charge / discharge, the capacity was confirmed at room temperature, and then the battery was charged to 50% SOC based on the discharge capacity and discharged at a current of 2.5 C for 10 seconds. The resistance was measured from the difference in voltage drop at this time and recorded as the initial resistance. After storing at 60°C for 8 weeks, the resistance was measured in the same manner and recorded as the final resistance. The resistance increase rate was calculated using the following formula. The results are shown in Table 4 below.

[0185] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) x 100

[0186] (3) Amount of gas generated After 8 weeks of storage, the amount of gas generated in the lithium secondary battery was measured using GC-FID / TCD, and the results are shown in Table 4 below.

[0187] (4) Transition metal elution amount After 8 weeks of storage, the concentration of all metals eluted into the non-aqueous electrolyte was measured. The amounts of metals measured using ICP analysis are shown in Table 4 below.

[0188] [Table 4]

[0189] Referring to Table 4, it can be seen that the secondary battery of Reference Example 1 has a lower capacity retention rate during high-temperature storage, an increased resistance, and an increased amount of eluted transition metals compared to Reference Example 2. This confirms that when a perlithiated manganese-rich oxide is not used as the positive electrode active material, it is difficult to improve high-temperature storage performance even when the first additive and the second additive are used.

Claims

1. a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte; the positive electrode comprises a perlithiated manganese-rich oxide containing 50 mol % or more of Mn among all metals excluding lithium, and having a lithium to transition metal molar ratio of greater than 1; the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the additives include a first additive and a second additive; The first additive includes a compound represented by the following Chemical Formula 1: The second additive comprises a compound represented by the following Chemical Formula 2: [Chemical formula 1] 【Chemistry 1】 [Chemical formula 2] 【Chemistry 2】 (In the above chemical formula 1, R １ each independently comprises a halogen, a nitrile group, a propargyl group, an ester group, an ether group, a ketone group, a carboxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a boron group, a borate group, an isocyanate group, an isothiocyanate group, a silyl group, a siloxane group, a sulfone group, a sulfonate group, a sulfate group, or a combination of two or more thereof, and n is an integer of 0 to 6; In the above Chemical Formula 2, A is a substituted or unsubstituted heteroaryl group having 3 to 5 carbon atoms, and R ２ is an alkylene group having 1 to 3 carbon atoms.

2. 2. The lithium secondary battery of claim 1, wherein the first additive comprises at least one selected from the group consisting of a compound represented by the following Chemical Formula 1-A and a compound represented by the following Chemical Formula 1-B: [Chemical formula 1-A] 【Transformation 3】 [Chemical formula 1-B] 【Chemistry 4】 (In the above Chemical Formula 1-A and Chemical Formula 1-B, R １ is as defined in Chemical Formula 1 above.

3. The lithium secondary battery according to claim 1 or 2, wherein the first additive comprises at least one selected from the group consisting of compounds represented by the following Chemical Formula 1-1 to the following Chemical Formula 1-9: [Chemical formula 1-1] 【Transformation 5】 [Chemical formula 1-2] 【Transformation 6】 [Chemical formula 1-3] 【Transformation 7】 [Chemical formula 1-4] 【Transformation 8】 [Chemical formula 1-5] 【Chemistry 9】 [Chemical formula 1-6] 【Chemistry 10】 [Chemical formula 1-7] 【Chemistry 11】 [Chemical formula 1-8] 【Chemistry 12】 [Chemical formula 1-9] 【Chemistry 13】

4. 3. The lithium secondary battery of claim 1, wherein the first additive is contained in an amount of 0.01 wt % to 10 wt % based on the weight of the non-aqueous electrolyte.

5. 3. The lithium secondary battery according to claim 1, wherein the second additive comprises at least one selected from the group consisting of a compound represented by the following chemical formula 2-A, a compound represented by the following chemical formula 2-B, and a compound represented by the following chemical formula 2-C: [Chemical formula 2-A] 【Chemistry 14】 [Chemical formula 2-B] 【Chemistry 15】 [Chemical formula 2-C] 【Chemistry 16】 (In the above Chemical Formula 2-A, Chemical Formula 2-B, and Chemical Formula 2-C, R ２ is as defined in Chemical Formula 2 above, R ３ , R ４ , and R ５ are each independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, and —CN; h is an integer from 0 to 3, i is an integer from 0 to 3, and j is an integer from 0 to 4.

6. 3. The lithium secondary battery according to claim 1, wherein the second additive comprises a compound represented by the following chemical formula 2-1: [Chemical formula 2-1] 【Chemistry 17】

7. 3. The lithium secondary battery of claim 1, wherein the second additive is contained in an amount of 0.01 wt % to 10 wt % based on the weight of the non-aqueous electrolyte.

8. 3. The lithium secondary battery according to claim 1, wherein the weight ratio of the first additive to the second additive is 10:90 to 90:

10.

9. The lithium salts include LiCl, LiBr, LiI, and LiBF. ４ , LiClO ４ , LiAlO ４ , LiAlCl ４ , LiPF ６ , LiSbF ６ , LiAsF ６ , LiB １０ Cl １０ , LiBOB(LiB(C ２ O ４ ) ２ ), LiCF ３ SO ３ , LiFSI (LiN(SO ２ F) ２ ), LiCH ３ SO ３ , LiCF ３ CO ２ , LiCH ３ CO ２ , and LiBETI(LiN(SO ２ CF ２ CF ３ ) ２ 3. The lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of:

10. 3. The lithium secondary battery according to claim 1, wherein the lithium salt is contained in the non-aqueous electrolyte at a molar concentration of 0.5 M to 5.0 M.

11. 3. The lithium secondary battery according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent.

12. 3. The lithium secondary battery according to claim 1, wherein the perlithiated manganese-rich oxide is a compound represented by the following chemical formula X: [Chemical formula X] Li １＋ｓ [Ni ｔ Co ｕ Mn Ｖ M １ ｗ ]O ２＋ｚ (In the above chemical formula X, M １ is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 0.05≦s≦1, 0≦t≦0.5, 0≦u≦0.3, 0.5≦v<1.0, 0≦w≦0.2, 0≦z≦1.)

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