Lithium secondary battery and method for manufacturing the same

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 comprises a positive electrode active material, the positive electrode active material comprising 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, the non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, the organic solvents comprising a first organic solvent and a second organic solvent, the first organic solvent comprising ethylene carbonate and the second organic solvent comprising diethyl carbonate, and the additive comprising a cyclic sulfur oxide represented by a specific chemical formula.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0040007 filed on March 27, 2023, and Korean Patent Application No. 10-2023-0183782 filed on December 15, 2023, and all contents disclosed in the documents of said Korean patent applications 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] On the other hand, in order to construct a high-capacity secondary battery, improvements have been made to the properties of each of the positive electrode, negative electrode, electrolyte, and separator. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a lithium secondary battery that includes a perlithiated manganese-rich oxide as a positive electrode active material, which reduces the amount of gas such as CO2 generated at the positive electrode interface during high-voltage or high-temperature operation, reduces gas generation during initial activation and charge / discharge, and suppresses elution of transition metals from the positive electrode active material, thereby improving the lifespan at high temperatures, reducing resistance, improving durability, and preventing gas generation. [Means for solving the problem]

[0007] The present invention provides a lithium secondary battery including 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 positive electrode active material, and the positive electrode active material includes a perlithiated manganese-rich oxide containing about 50 mol % or more of Mn among all metals excluding lithium and having a molar ratio of lithium to transition metals of more than about 1; the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, wherein the organic solvent includes a first organic solvent and a second organic solvent, the first organic solvent includes ethylene carbonate, and the second organic solvent includes diethyl carbonate and ethyl methyl carbonate; and the additive includes a compound represented by the following Chemical Formula 1:

[0008] [Chemical formula 1] [ka]

[0009] In the above Chemical Formula 1, n is 1 or 2; L1 and L2 each independently represent a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms; R1 and R2 each independently represent a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by the following Chemical Formula 2, [Chemical formula 2] [ka] In the above Chemical Formula 2, m is 1 or 2, and X1 and X2 each independently represent -O- or -C(R 31 )(R 32 )-, wherein at least one of X1 and X2 is -O-, and R 31 ~R 36 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4, or -R5-OC(=O)-R6, and R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, R5 is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, and L1, L The substituents of R2, R4, R5, and R6 are each independently one or more selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2, and -SO3, and * indicates the position of bonding to L1 or L2. When both L1 and L2 are direct bonds, R1 and R2 are not simultaneously CS-7 below; when both L1 and L2 are methylene groups and n is 2, R1 and R2 are not simultaneously CS-2 below. [ka] [Effects of the Invention]

[0010] The lithium secondary battery of the present invention uses a perlithiated manganese-rich oxide as a positive electrode active material, and the nonaqueous electrolyte contains a lithium salt, an organic solvent, and an additive, the organic solvent including ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, and the additive includes a cyclic sulfur oxide represented by a specific chemical formula. According to the present invention, the combination of the above organic solvents significantly reduces the amount of gas generation at the interface of the positive electrode containing the perlithiated manganese-rich oxide, improving the life performance of the negative electrode. As a result, a lithium secondary battery with excellent capacity retention and reduced gas generation can be realized. For example, the cyclic sulfur oxide contained as the additive has a low consumption rate within the secondary battery, thereby continuously improving long-term durability during operation of the secondary battery. Therefore, the lithium secondary battery of the present invention can achieve improved life, reduced resistance, improved durability, and gas generation prevention, particularly at high temperatures and high voltages. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0012] 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.

[0013] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50) can be measured, for example, by the laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0014] As used in this specification, the terms "about," "approximately," and "substantially" are used to mean a numerical value, a range of degree, or a value close to that range, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly taking advantage of the disclosure content in which exact or absolute numerical values ​​provided for understanding the present invention are mentioned.

[0015] Manganese-rich perlithiated oxides have been attracting attention as a next-generation cathode active material for constructing high-capacity batteries. Manganese-rich perlithiated oxides contain a high content of manganese (Mn), which is relatively inexpensive and abundant in reserves. Lithium secondary batteries incorporating these materials have the advantage of high capacity. However, when using these materials, there is a problem with the generation of gases such as CO2 due to electrolyte side reactions at the cathode interface during high-voltage (e.g., 4.35 V or higher) or high-temperature operation. Furthermore, the use of manganese-rich perlithiated oxides is limited due to the following issues: reactive oxygen generated by the phase transformation of the cathode active material during activation and charge / discharge processes accelerates electrolyte decomposition, resulting in a significant increase in CO2 and other gases; and transition metals eluted from the cathode active material are electrodeposited on the anode, destroying the anode's solid electrolyte interphase (SEI) coating.

[0016] The present invention provides a lithium secondary battery that uses a perlithiated manganese-rich oxide as a positive electrode active material, while overcoming the aforementioned problems of gas generation and destruction of the SEI film on the negative electrode.

[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 present invention provides a lithium secondary battery including 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 positive electrode active material, and the positive electrode active material includes a perlithiated manganese-rich oxide containing about 50 mol % or more of Mn among all metals excluding lithium, and having a molar ratio of lithium to transition metals of more than about 1, the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the organic solvents including a first organic solvent and a second organic solvent, the first organic solvent including ethylene carbonate, and the second organic solvent including diethyl carbonate and ethyl methyl carbonate, and the additive includes a compound represented by the following Chemical Formula 1:

[0020] [Chemical formula 1] [ka]

[0021] In the above Chemical Formula 1, n is 1 or 2; L1 and L2 each independently represent a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms; R1 and R2 each independently represent a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by the following Chemical Formula 2, [Chemical formula 2] [ka] In the above Chemical Formula 2, m is 1 or 2, and X1 and X2 each independently represent -O- or -C(R 31 )(R 32)-, wherein at least one of X1 and X2 is -O-, and R 31 ~R 36 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4, or -R5-OC(=O)-R6, and R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, R5 is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, and L1, L The substituents of R2, R4, R5, and R6 are each independently one or more selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2, and -SO3, and * indicates the position of bonding to L1 or L2. When both L1 and L2 are direct bonds, R1 and R2 are not simultaneously CS-7 below; when both L1 and L2 are methylene groups and n is 2, R1 and R2 are not simultaneously CS-2 below. [ka]

[0022] The lithium secondary battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. For example, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by placing an electrode assembly including the positive electrode, the negative electrode facing the positive electrode, and a separator interposed between the positive electrode and the negative electrode in a battery case and then injecting the non-aqueous electrolyte.

[0023] (1) Positive electrode The positive electrode includes a positive electrode active material.

[0024] According to one embodiment, the cathode active material includes a perlithiated manganese-rich oxide, which may contain at least about 50 mol% Mn based on all metals excluding lithium, and may have a lithium to transition metal molar ratio greater than about 1.

[0025] While perlithiated manganese-rich oxide has been attracting attention as a next-generation high-capacity cathode active material, its application is limited due to its inherent structural degradation. For example, when perlithiated manganese-rich oxide is used as a cathode active material, electrolyte side reactions occur at the cathode interface, resulting in significant increases in the generation of gases such as carbon dioxide (CO2). Furthermore, during the initial activation of a lithium secondary battery containing perlithiated manganese-rich oxide, reactive oxygen released from the perlithiated manganese-rich oxide decomposes and consumes the organic solvent (e.g., ethylene carbonate) contained in the nonaqueous electrolyte, thereby generating gas byproducts, 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, manganese (Mn) is leached out due to charge balance achieved by the release of reactive oxygen. In this case, the eluted manganese is electrodeposited on the negative electrode, causing problems such as destruction of the SEI (Solid Electrolyte Interphase) coating. Furthermore, reactive oxygen released during the charge / discharge process continues to decompose and consume the organic solvent in the non-aqueous electrolyte, resulting in increased generation of gas by-products. The consumption of the non-aqueous electrolyte, the structural collapse of the perlithiated manganese-rich oxide, and the increase in gas by-products significantly reduce the lifespan, resistance characteristics, and safety of lithium secondary batteries. Furthermore, these problems become even more severe under high temperature and high voltage conditions.

[0026] To solve these problems, the lithium secondary battery of the present invention is characterized in that the organic solvent of the non-aqueous electrolyte contains ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, and the additive contains the compound represented by Chemical Formula 1, as described below. According to the present invention, the combination of components of the non-aqueous electrolyte described above significantly reduces the amount of gas generation at the interface of the positive electrode containing the perlithiated manganese-rich oxide, improving the life performance of the negative electrode. As a result, a lithium secondary battery with superior capacity retention and reduced gas generation performance compared to conventional lithium secondary batteries can be realized. The lithium secondary battery of the present invention can exhibit excellent life performance and reduced gas generation performance, particularly at high temperatures and high voltages.

[0027] The perlithiated manganese-rich oxide may include a compound represented by the following formula X:

[0028] [Chemical formula X] Li 1+s [Ni t Co u Mn V M 1 w ]O 2+z

[0029] In the above chemical formula X, M 1 is one or more elements selected from 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 the conditions 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. For example, in the chemical formula X, the conditions may be 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. Alternatively, 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 may be satisfied.

[0030] In one embodiment, the perlithiated manganese-rich oxide may include a compound represented by the following formula Y:

[0031] [Chemical formula Y] XLi2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M 1 w ]O2

[0032] In the above chemical formula Y, M 1 is one or more elements selected from 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. In addition, in the chemical formula Y, 0.1≦X≦0.5, 0.5≦y<1, 0≦z≦0.3, 0≦w≦0.2 may be satisfied, for example, 0.2≦X≦0.5, 0.5≦y<1, 0≦z≦0.1, 0≦w≦0.2, or 0.3≦X≦0.5, 0.6≦y<1, 0≦z≦0.1, 0≦w≦0.2.

[0033] 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, wherein the positive electrode active material is contained in the positive electrode active material layer.

[0034] 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. For example, 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, or in one embodiment, may include aluminum.

[0035] The positive electrode current collector usually has a thickness of about 3 μm to 500 μm.

[0036] The positive electrode current collector may have a surface with fine irregularities to enhance 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.

[0037] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector, for example, on one surface or both surfaces of the positive electrode current collector.

[0038] The positive electrode active material may be contained in the positive electrode active material layer in an amount of about 80% by weight to 99% by weight, for example, about 92% by weight to 98.5% by weight, in consideration of sufficient capacity of the positive electrode active material.

[0039] Other details about the positive electrode active material have been described above and will be omitted here.

[0040] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material.

[0041] The binder is a component that assists in binding the active material and conductive material, etc., and in binding to the current collector, and may include, for example, 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 terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, or in one embodiment, may include polyvinylidene fluoride.

[0042] The binder may be contained in the positive electrode active material layer in an amount of about 1 wt % to 20 wt %, for example, about 1.2 wt % to 10 wt %, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0043] 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 has conductivity. For example, 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, ketjen black, 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. In one embodiment, the positive electrode conductive material may include carbon nanotubes to improve conductivity.

[0044] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of about 1% by weight to 20% by weight, for example, about 1.2% by weight to 10% by weight.

[0045] The thickness of the positive electrode active material layer may be about 30 μm to 400 μm, for example, about 40 μm to 110 μm.

[0046] The positive electrode may be fabricated 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.

[0047] 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 about 40% by weight to 90% by weight, for example, about 50% by weight to 80% by weight.

[0048] (2) Negative electrode The negative electrode faces the positive electrode.

[0049] The negative electrode includes a negative electrode active material.

[0050] 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, for example, at least one selected from a carbon-based active material and a (semi)metal-based active material.

[0051] 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 may include, for example, at least one selected from the group consisting of artificial graphite and natural graphite.

[0052] The average particle size (D 50 ) may be about 10 μm to 30 μm, for example, about 15 μm to 25 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0053] For example, the (semi)metal-based active material may include at least one selected from the group consisting of a (semi)metal, an alloy of a (semi)metal and lithium, an oxide of a (semi)metal, lithium titanium oxide (LTO), and lithium vanadium oxide.

[0054] The (semi)metal may include at least one 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.

[0055] The alloy of (semi)metal and lithium may comprise 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.

[0056] The (semi)metal oxide may contain at least one 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.

[0057] In one embodiment, the (semi)metal-based active material may include a silicon-based active material.

[0058] The silicon-based active material is SiO x (0≦x<2). Since SiO2 does not react with lithium ions and therefore cannot store lithium, x is selected within the above range, excluding 2, and in one embodiment, the silicon-based active material may be SiO.

[0059] The average particle size (D 50 ) may be about 1 μm to 30 μm, for example, about 2 μm to 15 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0060] 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 is contained in the negative electrode active material layer.

[0061] 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. For example, 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.

[0062] The negative electrode current collector usually has a thickness of about 3 μm to 500 μm.

[0063] 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.

[0064] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector, for example, on one or both surfaces of the negative electrode current collector.

[0065] The negative electrode active material may be contained in the negative electrode active material layer in an amount of about 60% to 99% by weight, for example, about 75% to 95% by weight.

[0066] Other details about the negative electrode active material have been described above and will be omitted here.

[0067] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0068] 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.

[0069] The binder may be included in the negative electrode active material layer in an amount of about 0.5% by weight to 10% by weight, for example, about 1% by weight to 5% by weight.

[0070] 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, ketjen black, 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 conductive materials such as polyphenylene derivatives may be used.

[0071] The conductive material may be contained in the negative electrode active material layer in an amount of about 0.5% by weight to 10% by weight, for example, about 1% by weight to 5% by weight.

[0072] The thickness of the negative electrode active material layer may be about 10 μm to 200 μm, for example, about 20 μm to 150 μm.

[0073] 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.

[0074] 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, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material. In one embodiment, the solvent may include distilled water. The solid content of the negative electrode slurry may be about 30% by weight to 80% by weight, for example, about 40% by weight to 70% by weight.

[0075] (3) Separator The separator may be interposed between the positive electrode and the negative electrode.

[0076] The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homocopolymer, a propylene homocopolymer, 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.

[0077] (4) Nonaqueous electrolyte The non-aqueous electrolyte contains a lithium salt and an organic solvent.

[0078] 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 as an anion, 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 present invention may include at least one selected from the group consisting of:

[0079] For example, the lithium salt may be LiCl, LiBr, LiI, LiBF, LiClO, LiAlO, LiAlCl, LiPF, LiSbF, LiAsF, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). For example, 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).

[0080] The lithium salt may be contained in the non-aqueous electrolyte at a concentration of about 0.5 M to 5 M, for example, about 0.8 M to 4 M, or about 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.

[0081] 2) Organic solvents The organic solvent includes a first organic solvent and a second organic solvent.

[0082] The first organic solvent includes ethylene carbonate.

[0083] The ethylene carbonate is a highly viscous organic solvent having a high dielectric constant, and can function as an organic solvent that easily dissociates the lithium salt in the electrolyte.

[0084] The first organic solvent may further include, in addition to the ethylene carbonate, at least one selected from the group consisting of fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, but is not limited thereto.

[0085] The second organic solvent includes diethyl carbonate and ethyl methyl carbonate.

[0086] The lithium secondary battery of the present invention includes diethyl carbonate as the second organic solvent, which improves the oxidation stability of the non-aqueous electrolyte and reduces gas generation, thereby significantly improving the lifespan of lithium secondary batteries containing perlithiated manganese-rich oxide. On the other hand, using only diethyl carbonate as the linear carbonate can cause problems such as reduced ionic conductivity, decreased electrolyte impregnation due to increased viscosity, and increased initial resistance. However, these drawbacks can be offset by the addition of ethyl methyl carbonate, which has a relatively low viscosity and excellent ionic conductivity. The use of ethyl methyl carbonate provides superior benefits compared to the use of other linear carbonates other than ethyl methyl carbonate, such as dimethyl carbonate.

[0087] Furthermore, in the present invention, by using the first organic solvent (containing ethylene carbonate) and the second organic solvent (containing diethyl carbonate and ethyl methyl carbonate), it is possible to achieve excellent capacity retention, reduce gas generation, and prevent volume expansion of the cell. Meanwhile, in this embodiment, a combination of diethyl carbonate and ethyl methyl carbonate is used as the second organic solvent, but this is not limited thereto. Any solvent or combination of solvents can be used as the second organic solvent as long as it can reduce the amount of carbon dioxide (CO2) generated when a perlithiated manganese-rich oxide is used as a positive electrode component and has low reactivity with reactive oxygen that can be released from the perlithiated manganese-rich oxide.

[0088] As described above, the effects of the present invention, such as the characteristic of reducing the amount of gas generated in a lithium secondary battery, are effects that are manifested specifically when a perlithiated manganese-rich oxide is used as a positive electrode active material. However, for limited purposes, the organic solvent of the present invention may also be used in combination with other positive electrode active materials, such as high-nickel lithium-nickel-manganese-cobalt transition metal oxides (e.g., NCM-based active materials containing 80 mol % or more of Ni among the transition metals), in which the generation of reactive oxygen and excessive elution of Mn are not significant problems.

[0089] On the other hand, the second organic solvent may further contain other additional organic solvents in addition to the diethyl carbonate, as long as the above-mentioned effects are not impaired.

[0090] For example, the second organic solvent may further include at least one selected from the group consisting of dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0091] The volume ratio of the first organic solvent to the second organic solvent may be about 10:90 to 50:50, for example, about 15:85 to 40:60, or about 15:85 to 35:65. When the volume ratio is within the above range, the non-aqueous electrolyte can achieve high ion transfer properties and an appropriate level of viscosity, while reducing gas generation in the perlithiated manganese-rich oxide and further improving the life performance of the positive and negative electrodes.

[0092] The organic solvent may contain about 10% to 50% by volume of the ethylene carbonate, about 5% to 80% by volume of the diethyl carbonate, and about 5% to 80% by volume of the ethyl methyl carbonate; for example, about 15% to 40% by volume of the ethylene carbonate, about 8% to 75% by volume of the diethyl carbonate, and about 8% to 75% by volume of the ethyl methyl carbonate; for example, about 15% to 35% by volume of the ethylene carbonate, about 8% to 50% by volume of the diethyl carbonate, and about 30% to 75% by volume of the ethyl methyl carbonate. When the concentrations are within the above ranges, the nonaqueous electrolyte achieves high ion transfer properties and an appropriate level of viscosity, while reducing gas generation in the perlithiated manganese-rich oxide and further improving the lifespan of the positive and negative electrodes.

[0093] Meanwhile, the organic solvent may be any organic solvent commonly used in non-aqueous electrolytes, without limitation, if necessary, and may include at least one additional organic solvent selected from the group consisting of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 3) Additives The non-aqueous electrolyte contains an additive.

[0098] The additive includes a compound represented by the following Chemical Formula 1:

[0099] [Chemical formula 1] [ka]

[0100] In the above Chemical Formula 1, n is 1 or 2; L1 and L2 each independently represent a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms; R1 and R2 each independently represent a substituent represented by the following Chemical Formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; and at least one of R1 and R2 is a substituent represented by the following Chemical Formula 2, [Chemical formula 2] [ka] In the above Chemical Formula 2, m is 1 or 2, and X1 and X2 each independently represent -O- or -C(R 31 )(R 32 )-, wherein at least one of X1 and X2 is -O-, and R 31 ~R 36 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, -C(=O)-R4, or -R5-OC(=O)-R6, and R4 and R6 are each independently a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, R5 is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, and L1, L The substituents of R2, R4, R5, and R6 are each independently one or more selected from the group consisting of deuterium, -F, -Cl, -Br, -I, -CN, -NO2, and -SO3, and * indicates the position of bonding to L1 or L2. When both L1 and L2 are direct bonds, R1 and R2 are not simultaneously CS-7 below; when both L1 and L2 are methylene groups and n is 2, R1 and R2 are not simultaneously CS-2 below. [ka]

[0101] The compound represented by Chemical Formula 1 is characterized by containing a sulfur oxide structure in the center and having a cyclic sulfur oxide structure at at least one of the two ends. The adoption of such a chemical structure can induce stable anion formation when used as a nonaqueous electrolyte additive, and furthermore, can enable the formation of a stable SEI layer. For example, the compound represented by Chemical Formula 1 has a lower consumption rate in a secondary battery than other cyclic sulfur oxides (e.g., 1,3-propane sultone), and therefore remains during operation of the secondary battery, thereby having the effect of continuously improving the high-temperature durability of the secondary battery.

[0102] For these reasons, when a perlithiated manganese-rich oxide, which generates a lot of gas and releases reactive oxygen or manganese at high temperatures and high voltages, is used as a positive electrode active material, the compound represented by Chemical Formula 1 can continuously form a stable and strong coating on the positive electrode, thereby helping to improve the high-temperature durability, gas reduction, and life performance of a secondary battery using the perlithiated manganese-rich oxide. For example, the effects of improving the life performance, durability, and gas reduction at high temperatures of the secondary battery according to the present invention can be achieved by using the above-mentioned organic solvent and additive in combination with the nonaqueous electrolyte.

[0103] Furthermore, the effects of the present invention are achieved by the perlithiated manganese-rich oxide, and other positive electrode active materials, such as high-nickel lithium-nickel-manganese-cobalt transition metal oxides (e.g., NCM-based active materials containing Ni at approximately 80 mol % or more among the transition metals), do not suffer from problems such as reactive oxygen generation or excessive Mn elution, and therefore the intended effects are not achieved even when the above-mentioned organic solvents are used in combination. On the contrary, when a nonaqueous electrolyte containing the above-mentioned organic solvent and additives is applied to a positive electrode active material other than the perlithiated manganese-rich oxide, these nonaqueous electrolyte components may act as resistance, resulting in a decrease in battery life.

[0104] In the above chemical formula 1, R1 and R2 are each independently selected from a substituent represented by the following chemical formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group, and at least one of R1 and R2 is a substituent represented by the following chemical formula 2. For example, in the above chemical formula 1, R1 and R2 may both be a substituent represented by the above chemical formula 2.

[0105] The alkyl group having 1 to 10 carbon atoms may be selected from alkyl groups having 1 to 3 carbon atoms, that is, a methyl group, an ethyl group, and a propyl group, for example.

[0106] The alkyl group having 1 to 10 carbon atoms and substituted with one or more fluorine atoms may specifically be an alkyl group having 1 to 3 carbon atoms and substituted with one or more fluorine atoms, and may be, for example, an alkyl group selected from *-CF3, *-CH2CF3, *-CF2CF3, *-CH2CH2CF3, *-CH2CF2CF3, and *-CF2CF2CF3. In the present invention, the symbol "*" represents a bonding site.

[0107] The substituent represented by Chemical Formula 2 may be selected from the group consisting of the following CS-1 to CS-15. [ka] [ka]

[0108] The above-listed substituent structures CS-1 to CS-15 are preferred examples of the substituent represented by Chemical Formula 2 or R1 and R2 of Chemical Formula 1, and when the substituents CS-1 to CS-15 are applied to R1 and R2 of Chemical Formula 1, the overall compound has excellent structural stability and can smoothly function as an additive for a non-aqueous electrolyte. For example, it is preferred that R1 and R2 are each independently any one selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10, and CS-11 from the viewpoints of structural stability and ease of synthesis.

[0109] On the other hand, in the compound represented by Chemical Formula 1 of the present invention, when both L1 and L2 are direct bonds and R1 and R2 are CS-7, or when both L1 and L2 are methylene groups, n is 2, and R1 and R2 are both CS-2, the compound itself has low structural stability and is easily decomposed, which may make synthesis of the compound difficult. For example, compounds that satisfy the above conditions have the disadvantage that the ring-shaped R1 and R2 structures are easily decomposed during the synthesis process, and even if the compound is finally synthesized, it is easily decomposed during storage and has a significantly low synthesis yield. Therefore, the present invention excludes compounds when both L1 and L2 are direct bonds and R1 and R2 are CS-7, and compounds when n is 2 and R1 and R2 are both CS-2.

[0110] In the compound represented by Chemical Formula 1, L1 and L2 may each independently represent a direct bond, a methylene group, or an ethylene group, for example, a methylene group. When L1 and L2 are methylene groups, the compound can be easily synthesized and decomposition of the compound after synthesis can be suppressed.

[0111] It is particularly preferable that the compound represented by Chemical Formula 1 contains at least one compound selected from the group consisting of the following compounds A to U, for example, at least one compound selected from the group consisting of the following compounds A, F, and J. [ka] [ka] [ka] [ka] [ka] [ka] [ka]

[0112] When the compound represented by Chemical Formula 1 has the structure described above, it has the advantage that a low resistance and stable SEI layer can be formed even at a lower content compared to conventionally used additives.

[0113] The compound represented by Chemical Formula 1 may be included in the non-aqueous electrolyte at about 0.01 wt % to 10 wt %, for example, about 0.1 wt % to 5 wt %, about 0.2 wt % to 3 wt %, about 0.5 wt % to 2 wt %, or about 0.7 wt % to 1.5 wt %. This range is preferable because it can prevent an increase in resistance due to the use of excessive additives while still achieving the effect of improving the high-temperature durability of the secondary battery.

[0114] Meanwhile, in addition to the compound represented by Chemical Formula 1, any additive may be selected and used as long as it can continuously function to form a stable and strong coating on the positive electrode when a perlithiated manganese-rich oxide, which generates a lot of gas at high temperatures and high voltages and releases reactive oxygen or manganese significantly, is used as the positive electrode active material, and can help improve the high-temperature durability, gas reduction, and life performance of a secondary battery using the perlithiated manganese-rich oxide.

[0115] The non-aqueous electrolyte may further include an additive in addition to the compound represented by Formula 1. The additive may be included in the non-aqueous electrolyte to strengthen the SEI coating of the positive and negative electrodes to prevent gas generation due to electrolyte side reactions, to prevent the non-aqueous electrolyte from being decomposed 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 overcharge, and suppress battery expansion at high temperatures.

[0116] For example, the additional additive may include at least one selected from the group consisting of sulfate-based compounds, phosphate-based compounds, borate-based compounds, nitrile-based compounds, benzene-based compounds, and lithium salt-based compounds.

[0117] The sulfate-based compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be contained in an amount of about 5 wt % or less based on the total weight of the electrolyte.

[0118] The phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite, and may be contained in an amount of about 5 wt % or less based on the total weight of the electrolyte.

[0119] The borate-based compounds include tetraphenylborate and lithium oxalyldifluoroborate, and may be contained in an amount of about 5 wt % or less based on the total weight of the electrolyte.

[0120] The nitrile compound is a nitrile compound other than decanenitrile (DN) and 1,4-dicyano-2-butene (DCB), and typical examples thereof include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and 1,3,6-hexanetricarbonitrile.

[0121] The nitrile compound may be present in an amount of about 5 wt % to 8 wt %, for example, about 6 wt % to 8 wt %, based on the total weight of the non-aqueous electrolyte. If the amount of the nitrile compound in the electrolyte exceeds 8 wt %, the resistance may increase due to an increase in the coating formed on the surface of the electrode, which may result in a deterioration of battery performance.

[0122] The benzene-based compound may be fluorobenzene, the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane.

[0123] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C2O4)2)), and LiBF4, and may be contained in an amount of about 5 wt% or less based on the total weight of the electrolyte.

[0124] For example, the additional additives include coumarine, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiDFP (lithium difluorophosphate), LiBF4 (lithium tetrafluoroborate), LiODFB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), The compound may contain at least one selected from the group consisting of N-(3-trimethoxysilanyl-propyl-N-aniline), N-(3-trimethoxysilanyl-propyl-N-aniline), N-(3-trimethoxysilanyl-propyl-N-aniline), N-(3-trimethoxysilanyl-propyl-N-aniline), and N-(3-trimethylsilyl-propyl-N-aniline), and a compound represented by the following chemical formula 3:

[0125] [Chemical formula 3] [ka]

[0126] The additive may include, for example, at least one selected from the group consisting of vinylene carbonate, propane sultone, ethylene sulfate, LiDFP, LiBF4, and the compound represented by Chemical Formula 1.

[0127] The additive may be contained in the non-aqueous electrolyte in an amount of about 0.1% by weight to 15% by weight.

[0128] The additional additive may be included in the non-aqueous electrolyte in an amount of about 0.1 wt % to 15 wt %.

[0129] 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.

[0130] The present invention will be described in more detail below with reference to 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 modifications and variations are possible within the scope and technical concept of the present description, and it goes without saying that such modifications and variations are within the scope of the appended claims.

[0131] Examples and Comparative Examples Example 1 (Production of non-aqueous electrolyte) The organic solvent used was a mixture of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:10:70.

[0132] A non-aqueous electrolyte was prepared by adding LiPF as a lithium salt, the compound A as an additive, and propane sultone (PS), ethylene sulfate (ESa), LiDFP, LiBF as additional additives, and the compound represented by the formula 3 to the organic solvent.

[0133] The LiPF6 was contained in the non-aqueous electrolyte at a molar concentration of 1.2M.

[0134] The compound A was contained in the non-aqueous electrolyte at a content of 1 wt %.

[0135] The non-aqueous electrolyte contained 0.5 wt % vinylene carbonate, 0.8 wt % propane sultone, 1.0 wt % ethylene sulfate, 1.0 wt % LiDFP, 0.5 wt % LiBF4, and 0.1 wt % of the compound represented by Chemical Formula 1.

[0136] (Lithium secondary battery manufacturing) Cathode active material (Li 1.3 [Ni 0.35 Mn 0.65 ]O 2.33 A cathode mixture slurry (solid content 48 wt%) was prepared by adding a conductive material (carbon nanotubes) and a binder (PVdF) in a weight ratio of 97.4:0.6:2.0 to a solvent, N-methyl-2-pyrrolidone (NMP). 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.

[0137] Anode active material (a mixture of artificial graphite, natural graphite, and SiO), conductive material (carbon black), and binder (PVdF) were mixed in a weight ratio of 95.7:1.0:3.3 with distilled water as a solvent to prepare anode mixture slurry (solid content 70 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.

[0138] 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.

[0139] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the compound A was added to the non-aqueous electrolyte in an amount of 0.5 wt % instead of 1 wt %. That is, in Example 2, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were used as organic solvents, and the amount of the compound A used as an additive was different from that in Example 1 to fabricate a lithium secondary battery.

[0140] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the compound A was added to the non-aqueous electrolyte in an amount of 2.0 wt % instead of 1 wt %. That is, in Example 3, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were used as organic solvents, and the amount of the compound A used as an additive was different from that in Examples 1 and 2 to fabricate a lithium secondary battery.

[0141] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that Compound S was used instead of Compound A. That is, in Example 4, a lithium secondary battery was manufactured using ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents and Compound S as an additive instead of Compound A in Example 1.

[0142] Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1, except that the compound A was not added to the non-aqueous electrolyte. That is, in Example 1, the compound A was used as an additive in addition to ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents, whereas in Comparative Example 1, a lithium secondary battery was produced without using any additives in addition to these three types of organic solvents.

[0143] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1,3-propane sultone (PS) was used in the non-aqueous electrolyte instead of Compound A. That is, in Comparative Example 2, a lithium secondary battery was manufactured using ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as organic solvents, and 1,3-propane sultone (PS) instead of Compound A as an additive.

[0144] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 20:80 was used as the organic solvent for the non-aqueous electrolyte. That is, in Comparative Example 3, a lithium secondary battery was manufactured using only two organic solvents, ethylene carbonate and ethyl methyl carbonate, and Compound A as the additive.

[0145] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 20:80 was used as the organic solvent for the non-aqueous electrolyte. That is, in Comparative Example 4, a lithium secondary battery was manufactured using only two organic solvents, ethylene carbonate and diethyl carbonate, and Compound A as the additive.

[0146] Comparative Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:10:70 was used as the organic solvent for the nonaqueous electrolyte. That is, in Comparative Example 5, a lithium secondary battery was manufactured using dimethyl carbonate instead of diethyl carbonate among the three organic solvents used in Example 1.

[0147] Experimental example Experimental example 1: Evaluation of high-temperature cycle charge / discharge performance The lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 5 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 200 charge / discharge cycles being considered as one cycle.

[0148] Experimental Example 1-A: Evaluation of capacity retention rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0149] Capacity retention rate (%) = {(discharge capacity after 200 cycles / discharge capacity after 1 cycle)} × 100

[0150] Experimental Example 1-B: Evaluation of Resistance Increase Rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charger / discharger, and the SOC (State of Charge) was adjusted to 50%. A 2.5C pulse was then applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0151] 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 1 below.

[0152] Resistance increase rate (%) = (resistance after 200 cycles - initial resistance) / initial resistance x 100

[0153] [Table 1]

[0154] Referring to Table 1, it can be seen that the lithium secondary batteries of Examples 1 to 4, which are lithium secondary batteries in which the nonaqueous electrolyte according to the present invention is combined with a positive electrode containing a perlithiated manganese-rich oxide, have a higher capacity retention rate and a reduced rate of increase in resistance during high-temperature cycle charge and discharge, compared to Comparative Examples 1 to 5, which do not.

[0155] Experimental example 2: Evaluation of high-temperature storage performance The lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 5 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 under CC, 0.33 C conditions. 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.

[0156] Experimental Example 2-A: Evaluation of capacity retention rate After 8 weeks of storage, the lithium secondary battery was 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 under CC, 0.33 C conditions, and the capacity at the time of discharge was measured.

[0157] The capacity retention rate was evaluated using the following formula, and the results are shown in Table 2 below.

[0158] Capacity retention rate (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) x 100

[0159] Experimental Example 2-B: Evaluation of 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 the battery 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 2 below.

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

[0161] [Table 2]

[0162] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 4, which are lithium secondary batteries in which the nonaqueous electrolyte according to the present invention is combined with a positive electrode containing a perlithiated manganese-rich oxide, have a higher capacity retention rate and a reduced rate of increase in resistance during high-temperature cycle charge and discharge, compared to Comparative Examples 1 to 5, which do not.

[0163] 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.

[0164] (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 a conductive material (carbon nanotubes) and a binder (polyvinylidene fluoride) in a weight ratio of 98.0:0.7:1.3 to a solvent, N-methyl-2-pyrrolidone (NMP). The cathode mixture slurry was applied to one side of a 12 μm-thick cathode current collector (Al thin film), followed by drying and roll pressing to prepare a cathode. That is, in Reference Example 1, a cathode was prepared using a different type of cathode active material from that used in Example 1, for example, a high-nickel lithium-nickel-cobalt-manganese oxide.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] Reference Experiment Example 1: Evaluation of high-temperature cycle charge / discharge performance The lithium secondary batteries of Reference Examples 1 and 2 manufactured above were charged to 4.2 V, 1 / 40 C under CC / CV, 0.33 C conditions at 45°C, and then discharged to 2.5 V at 0.33 C using an electrochemical charger / discharger, and 200 charge / discharge cycles were performed, with one cycle consisting of charging and discharging.

[0169] Reference Experiment Example 1-A: Evaluation of Capacity Retention Rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 3 below.

[0170] Capacity retention rate (%) = {(discharge capacity after 200 cycles / discharge capacity after 1 cycle)} × 100

[0171] Reference Experiment Example 1-B: Evaluation of 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.

[0172] 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 3 below.

[0173] Resistance increase rate (%) = (resistance after 200 cycles - initial resistance) / initial resistance x 100

[0174] [Table 3]

[0175] Referring to Table 3, it can be seen that in Reference Example 1, which used a high-nickel lithium-nickel-cobalt-manganese oxide instead of a perlithiated manganese-rich oxide, the effect of improving cycle charge-discharge performance at high temperatures was limited, even when the same nonaqueous electrolyte as in Example 1 was used. In fact, in Reference Example 1, the use of Compound A as a nonaqueous electrolyte additive caused problems such as a decreased capacity retention rate and increased resistance compared to Reference Example 2, which did not use Compound A. This demonstrates that the nonaqueous electrolyte according to the present invention exhibits effects specific to the use of a perlithiated manganese-rich oxide as the positive electrode active material.

[0176] Reference Experiment Example 2: Evaluation of high-temperature storage performance The lithium secondary batteries of Reference Examples 1 and 2 prepared above were initially charged and discharged using an electrochemical charger / discharger at 25°C under CC / CV conditions at 0.33C up to 4.2V, 1 / 40C, and then discharged at 0.33C down to 2.5V. Subsequently, they were charged at 25°C under CC / CV conditions at 0.33C up to 4.2V, 1 / 40C, and then stored at 60°C for 8 weeks.

[0177] Reference Experiment Example 2-A: Evaluation of Capacity Retention Rate After 8 weeks of storage, the lithium secondary battery was charged to 4.2 V, 1 / 40 C under CC / CV, 0.33 C conditions at 25° C., and then discharged to 2.5 V at 0.33 C, and the capacity at discharge was measured.

[0178] The capacity retention rate was evaluated using the following formula, and the results are shown in Table 4 below.

[0179] Capacity retention rate (%) = (discharge capacity after 8 weeks of storage / initial discharge capacity) x 100

[0180] Reference Experiment Example 2-B: Evaluation of 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 the battery 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.

[0181] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) x 100

[0182] [Table 4]

[0183] Referring to Table 4, it can be seen that in Reference Example 1, which uses a high-nickel lithium-nickel-cobalt-manganese oxide instead of a perlithiated manganese-rich oxide, the effect of improving high-temperature storage performance is limited even when the same nonaqueous electrolyte as in Example 1 is used. In fact, Reference Example 1, which uses Compound A as a nonaqueous electrolyte additive, suffers from the problem of increased resistance compared to Reference Example 2, which does not use Compound A. This demonstrates that the nonaqueous electrolyte according to the present invention exhibits effects specific to the use of a perlithiated manganese-rich oxide as the positive electrode active material.

[0184] Although the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art or those having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as defined in the appended claims. Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification, but is determined solely by the claims.

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 includes a positive electrode active material, the positive electrode active material 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 of greater than 1; the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the organic solvent comprises a first organic solvent and a second organic solvent; the first organic solvent comprises ethylene carbonate; the second organic solvent comprises diethyl carbonate and ethyl methyl carbonate; The additive comprises a compound represented by the following Chemical Formula 1: [Chemical formula 1] 【Chemistry 1】 (In the above Chemical Formula 1, n is 1 or 2; L １ and L ２ are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, R １ and R ２ are each independently selected from a substituent represented by the following chemical formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; R １ and R ２ At least one of the groups is a substituent represented by the following chemical formula 2: [Chemical formula 2] 【Chemistry 2】 In the above Chemical Formula 2, m is 1 or 2; X １ and X ２ are each independently —O— or —C(R ３１ ) (R ３２ )-, wherein said X １ and X ２ at least one of is —O—; R ３１ ~R ３６ are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, or —C(═O)—R ４ , or -R ５ -OC(=O)-R ６ and The R ４ and R ６ each independently represents a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, The R ５ is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, Said L １ , L ２ , R ４ , R ５ , and R ６ The substituents are each independently deuterium, —F, —Cl, —Br, —I, —CN, or —NO ２ , and -SO ３ and one or more selected from the group consisting of: * indicates L １ or L ２ At the position where it binds to L １ and L ２ When both of R １ and R ２ At the same time, it is not the CS-7 below, L １ and L ２ are methylene groups and n is 2, １ and R ２ At the same time, it is not CS-2 below.) 【Transformation 3】

2. 2. 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 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.)

3. 2. The lithium secondary battery according to claim 1, wherein a volume ratio of the first organic solvent to the second organic solvent is 10:90 to 50:

50.

4. 2. The lithium secondary battery according to claim 1, wherein the substituent represented by Chemical Formula 2 is selected from the group consisting of CS-1 to CS-15 below. 【Chemistry 4】 【Transformation 5】

5. The R １ and R ２ are each independently any one selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10, and CS-11.

6. Said L １ and L ２ The lithium secondary battery according to claim 1 , wherein is a methylene group.

7. 2. The lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 1 includes at least one compound selected from the group consisting of the following compounds A to U: 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】

8. 2. The lithium secondary battery of claim 1, wherein the compound represented by Chemical Formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %.

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 2. The lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of:

10. 2. 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. The additives include coumarin, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiDFP (lithium difluorophosphate), and LiBF ４ 2. The lithium secondary battery of claim 1, further comprising at least one selected from the group consisting of lithium tetrafluoroborate (Li), lithium difluoro(oxalato)borate (LiODFB), lithium bis(oxalato)borate (LiBOB), lithium bis(oxalato)borate (Li), lithium bis(oxalato)borate (TMSPa), lithium bis(oxalato)borate (TMSPa), lithium bis(trimethylsilanyl)phosphite (TMSPi), and a compound represented by the following formula 3: [Chemical formula 3] 【Chemistry 13】

12. housing an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode in a battery case; and injecting a non-aqueous electrolyte into the battery case containing the electrode assembly. the positive electrode includes a positive electrode active material, the positive electrode active material 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 of greater than 1; the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive; the organic solvent comprises a first organic solvent and a second organic solvent; the first organic solvent comprises ethylene carbonate; the second organic solvent comprises diethyl carbonate and ethyl methyl carbonate; The additive comprises a compound represented by the following Chemical Formula 1: [Chemical formula 1] 【Chemistry 14】 (In the above Chemical Formula 1, n is 1 or 2; L １ and L ２ are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, R １ and R ２ are each independently selected from a substituent represented by the following chemical formula 2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorine atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphate group, and a nitrile group; R １ and R ２ At least one of the groups is a substituent represented by the following chemical formula 2: [Chemical formula 2] 【Chemistry 15】 In the above Chemical Formula 2, m is 1 or 2; X １ and X ２ are each independently —O— or —C(R ３１ ) (R ３２ )-, wherein said X １ and X ２ at least one of is —O—; R ３１ ~R ３６ are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, or —C(═O)—R ４ , or -R ５ -OC(=O)-R ６ and The R ４ and R ６ each independently represents a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, The R ５ is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, Said L １ , L ２ , R ４ , R ５ , and R ６ The substituents are each independently deuterium, —F, —Cl, —Br, —I, —CN, or —NO ２ , and -SO ３ and one or more selected from the group consisting of: * indicates L １ or L ２ At the position where it binds to L １ and L ２ When both of R １ and R ２ At the same time, it is not the CS-7 below, L １ and L ２ are methylene groups and n is 2, １ and R ２ At the same time, it is not CS-2 below.) 【Chemistry 16】

13. The method for producing a lithium secondary battery according to claim 12, 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 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.)

14. 13. The method for producing a lithium secondary battery according to claim 12, wherein a volume ratio of the first organic solvent to the second organic solvent is 10:90 to 50:

50.

15. The method for manufacturing a lithium secondary battery according to claim 12, wherein the substituent represented by Chemical Formula 2 is selected from the group consisting of the following CS-1 to CS-15: 【Chemistry 17】 [Chemistry 18]

16. The R １ and R ２ are each independently any one selected from the group consisting of CS-1, CS-2, CS-5, CS-8, CS-10, and CS-11.

17. Said L １ and L ２ The method for producing a lithium secondary battery according to claim 12 , wherein is a methylene group.

18. The method for manufacturing a lithium secondary battery according to claim 12, wherein the compound represented by Chemical Formula 1 includes at least one compound selected from the group consisting of the following compounds A to U: 【Chemistry 19】 【Chemistry 20】 【Chemistry 21】 【Chemistry 22】 【Chemistry 23】 【Chemistry 24】 【Chemistry 25】

19. 13. The method for manufacturing a lithium secondary battery according to claim 12, wherein the compound represented by Chemical Formula 1 is contained in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %.

20. 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 13. The method for producing a lithium secondary battery according to claim 12, wherein the lithium secondary battery comprises at least one selected from the group consisting of:

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