Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, in which the positive electrode contains a positive electrode active material, the positive electrode active material contains a lithium transition metal oxide represented by the following Chemical Formula A, the non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive, the additive contains a first additive, and the first additive contains ethylene vinyl carbonate. [Chemical Formula A] Li1 + x [NiaCobMncM1d] O2 + w in which 0 < = x < = 0.5, a + b + c + d = 1, 0.5 < = a < = 0.7, 0 < = b < = 0.15, c = 1-a-b-d, 0 < = d < = 0.1, 0 < = b / a < = 0.2, 1 < = a / c < = 3, 0 < = w < = 1, and M1 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.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefit of Korean Patent Application No. 10-2022-0181142, filed on December 21, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a lithium secondary battery. Background Art

[0004] Recently, as the applications of lithium secondary batteries have expanded not only to power sources for electric power, electronics, telecommunications, and electronic devices such as computers, but also to power storage and power supply for large devices such as automobiles and power storage devices, the demand for secondary batteries with high capacity, high power, and high stability has been increasing.

[0005] A lithium secondary battery generally consists of 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 lithium ion migration, and a separator. As the negative electrode active material, carbon-based active materials and silicon-based active materials can be used. In addition, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel cobalt manganese composite transition metal oxides can be used as the positive electrode active material.

[0006] Recently, in order to increase the energy density of the positive electrode, lithium nickel cobalt manganese composite transition metal oxides having a nickel content of 80 mol% or more relative to the transition metal have been studied. However, when the nickel content of the lithium nickel cobalt manganese composite transition metal oxide increases, the thermal stability of the positive electrode decreases.

[0007] In order to reduce the nickel content of the nickel cobalt manganese composite transition metal oxide to prevent the above problems, it is necessary to increase the driving voltage to achieve the required energy density, but when operating at such a high voltage, there is a problem that the electrolyte side reaction at the positive electrode becomes more intense. Summary of the Invention

[0008] [Technical Problem]

[0009] The present invention aims to solve the above problems and aims to provide a lithium secondary battery that improves life performance and storage performance when operating at a high voltage, and the lithium secondary battery uses a lithium transition metal oxide with a reduced nickel content to a certain level as the positive electrode active material.

[0010] [Technical Solution]

[0011] The present invention provides a lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed 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 comprises a lithium transition metal oxide represented by the following Chemical Formula A, the non-aqueous electrolyte comprises a lithium salt, an organic solvent, and an additive, the additive comprises a first additive, and the first additive comprises vinylene ethylene carbonate.

[0012] [Chemical Formula A]

[0013] Li 1+x [Ni a Co b Mn c M 1 d O 2+w

[0014] In Chemical Formula A, 0 ≤ x ≤ 0.5, a + b + c + d = 1, 0.5 ≤ a ≤ 0.7, 0 ≤ b ≤ 0.15, c = 1 - a - b - d, 0 ≤ d ≤ 0.1, 0 ≤ b / a ≤ 0.2, 1 ≤ a / c ≤ 3, 0 ≤ w ≤ 1, and 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.

[0015] [Advantageous Effects]

[0016] The lithium secondary battery of the present invention uses a lithium transition metal oxide with a nickel content adjusted to a certain range as the positive electrode active material, and uses vinylene ethylene carbonate (VEC) as an additive to the non-aqueous electrolyte. When operating at high voltages, especially at high temperatures, the lithium secondary battery of the present invention can significantly improve the life performance and storage performance. Detailed Embodiments

[0017] The terms and words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted based on the principle that the inventor can appropriately define the terms to best describe his invention, as meanings and concepts consistent with the technical concept of the present invention.

[0018] In this specification, the terms "comprising", "providing", or "having" are intended to indicate the presence of the implemented features, quantities, steps, elements, or combinations thereof, and it should be understood that the presence or addition of other features, quantities, steps, elements, or combinations thereof is not precluded in advance.

[0019] Before describing the present invention, unless otherwise specified in the present invention, "*" refers to a connecting portion (bonding site) between the same or different atoms or at the end portion of a chemical formula.

[0020] In the description of "C a to C b " herein, "a" and "b" are the number of carbon atoms contained in a specific functional group. In other words, the functional group may contain "a" to "b" carbon atoms. For example, "C1 to C5 alkyl" is an alkyl group containing 1 to 5 carbon atoms, such as CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, etc.

[0021] In the present specification, all alkyl or aryl groups may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen. For example, substituted with C1 to C 20 alkyl, C2 to C 20 alkenyl, C2 to C 20 alkynyl, C1 to C 20 alkoxy, C3 to C 12 cycloalkyl, C3 to C 12 cycloalkenyl, C3 to C 12 cycloalkynyl, C3 to C 12 heterocycloalkyl, C3 to C 12 heterocycloalkenyl, C2 to C 12 heterocycloalkynyl, C6 to C 12 aryloxy, halogen atom, C1 to C 20 fluoroalkyl, nitro, C6 to C 20 aryl, C2 to C 20 heteroaryl and C6 to C 20 haloaryl.

[0022] Hereinafter, the present invention will be described in more detail.

[0023] Lithium secondary battery

[0024] The present invention relates to a lithium secondary battery.

[0025] The lithium secondary battery of the present invention includes: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Among them, the positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium transition metal oxide represented by the following chemical formula A, the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the additive includes a first additive, and the first additive includes vinylene ethylene carbonate.

[0026] [Chemical Formula A]

[0027] Li 1+x [Ni a Co b Mn c M 1 d O 2+w

[0028] In Chemical Formula A, 0 ≤ x ≤ 0.5, a + b + c + d = 1, 0.5 ≤ a ≤ 0.7, 0 ≤ b ≤ 0.15, c = 1 - a - b - d, 0 ≤ d ≤ 0.1, 0 ≤ b / a ≤ 0.2, 1 ≤ a / c ≤ 3, 0 ≤ w ≤ 1, and 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.

[0029] The lithium secondary battery of the present invention uses a lithium transition metal oxide with a nickel content adjusted to a certain range as a positive electrode active material and uses vinylene carbonate (VEC) as a non-aqueous electrolyte additive. When operating at a high voltage, especially at a high temperature, the lithium secondary battery of the present invention can significantly improve the life performance and storage performance.

[0030] The lithium secondary battery includes: a positive electrode; a negative electrode; a separator; and a non-aqueous electrolyte. Specifically, the lithium secondary battery includes: a positive electrode; a negative electrode opposite to the positive electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by accommodating an electrode assembly including a positive electrode, a negative electrode opposite to the positive electrode, and a separator disposed between the positive electrode and the negative electrode in a battery case and then injecting a non-aqueous electrolyte.

[0031] (1) Positive Electrode

[0032] The positive electrode includes a positive electrode active material.

[0033] The positive electrode active material includes a lithium transition metal oxide represented by the following Chemical Formula A.

[0034] [Chemical Formula A]

[0035] Li 1+x [Ni a Co b Mn c M 1 d O 2+w

[0036] In chemical formula A, 0 ≤ x ≤ 0.5, a + b + c + d = 1, 0.5 ≤ a ≤ 0.7, 0 ≤ b ≤ 0.15, c = 1 - a - b - d, 0 ≤ d ≤ 0.1, 0 ≤ b / a ≤ 0.2, 1 ≤ a / c ≤ 3, 0 ≤ w ≤ 1, and 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.

[0037] The lithium transition metal oxide represented by chemical formula A is different from, for example, a high-nickel lithium transition metal oxide in which the Ni content relative to a metal other than lithium exceeds 70 mol%. High-nickel lithium transition metal oxides are not preferred because they contain a large amount of nickel, which reduces thermal stability.

[0038] Since the nickel content of the compound represented by chemical formula A is less than that of the high-nickel lithium transition metal oxide, it is necessary to operate at a high voltage (e.g., 4.35 V or higher) to increase the energy density of the positive electrode. However, since the electrolyte side reaction at the positive electrode becomes more intense, there is a problem that the life performance and storage performance are significantly reduced.

[0039] The lithium secondary battery of the present invention uses the lithium transition metal oxide represented by chemical formula A as a positive electrode active material in order to simultaneously achieve a high energy density and excellent life performance and storage performance, and uses vinylene carbonate (first additive) as a non-aqueous electrolyte additive. When operating at a high voltage, vinylene carbonate (first additive) can form a stable film on the positive electrode, thereby being able to significantly improve the life performance and storage performance, particularly the life performance and storage performance at high temperatures, when operating at a high voltage.

[0040] When using a positive electrode active material containing a lithium transition metal oxide having chemical formula A, by applying this non-aqueous electrolyte, the effect of improving battery performance at a high voltage can be achieved. For example, in the case of a high-nickel lithium transition metal oxide (e.g., Li[Ni 0.8 Co 0.1 Mn 0.1 O2) that does not satisfy the composition of chemical formula A, the proportion of Ni or the molar ratio of Ni / Mn in the transition metal is very high. During charge and discharge, due to the increase and decrease of the Ni oxidation number, the axial change in the lattice is large, and the surface side reaction becomes more intense due to Ni, which is energetically unstable. Therefore, it is difficult to achieve the effect of performance improvement through organic solvents and additives. In addition, high-nickel lithium transition metal oxides (e.g., Li[Ni 0.8 Co 0.1 Mn 0.1O2) has a high Ni / Mn molar ratio. When operating at high voltages, due to phase transitions, a large amount of rock salt structure exists on the surface, making it difficult to intercalate and deintercalate lithium ions and form a positive electrode film through additives. In the case of lithium transition metal oxides that do not satisfy the chemical formula A (for example, Li[Ni 0.6 Co 0.2 Mn 0.2 O2), the proportion of Co in the transition metals is very high, which increases the irreversibility within the structure. Therefore, it is difficult to form a positive electrode film through additives to achieve the effect of performance improvement. Therefore, in the case of using a compound not represented by the chemical formula A, even when using the non-aqueous electrolyte of the present invention, it is difficult to improve the life performance and storage performance to the required level.

[0041] In the chemical formula A, x can satisfy 0 ≤ x ≤ 0.5, and specifically, 0 ≤ x ≤ 0.2.

[0042] In the chemical formula A, a can satisfy 0.5 ≤ a ≤ 0.7, and specifically, 0.55 ≤ a ≤ 0.65.

[0043] In the chemical formula A, b satisfies 0 ≤ b ≤ 0.15. b is the molar percentage of Co in the metals other than lithium in the lithium transition metal oxide represented by the chemical formula A. According to the present invention, cost effectiveness can be achieved by reducing the Co content, and the structural stability of the positive electrode active material can be improved by relatively increasing the proportion of Mn. In the chemical formula A, b can specifically satisfy 0 ≤ b ≤ 0.1, and more specifically, 0 ≤ b ≤ 0.05.

[0044] In the chemical formula A, a and b satisfy 0 ≤ b / a ≤ 0.2. When b / a exceeds 0.2, the proportion of Co in the transition metals is very high, and the irreversibility within the structure increases, resulting in difficulty in forming a positive electrode film through additives to achieve the effect of performance improvement. Specifically, in the chemical formula A, a and b can satisfy 0.05 ≤ b / a ≤ 0.2.

[0045] In the chemical formula A, a, b, c, and d satisfy c = 1 - a - b - d and 1 ≤ a / c ≤ 3. c is the molar percentage of Mn in the metals other than lithium in the lithium transition metal oxide represented by the chemical formula A. According to the present invention, the structural stability of the positive electrode active material can be improved by adjusting the molar ratio of Ni to Mn to 1 ≤ a / c ≤ 3. Specifically, 1.5 ≤ a / c ≤ 2.5 can be satisfied.

[0046] In the chemical formula A, M 1It can be understood as a doping element of the lithium transition metal oxide, and can specifically be selected from one or more 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. d can satisfy 0 ≤ d ≤ 0.1, and specifically, 0 ≤ d ≤ 0.05.

[0047] In chemical formula A, a / (b×c) can be 18 to 50, specifically 18 to 40, and more specifically 20 to 35. Within this range, the contents of nickel, cobalt, and manganese in chemical formula A are coordinately adjusted, so that the performance improvement effect of forming the positive electrode film by the additive and the structural stability of the positive electrode active material can be improved simultaneously.

[0048] The positive electrode active material can be in the form of particles. Specifically, the positive electrode active material is in the form of a single particle composed of a single nodule, or in the form of a quasi-single particle that is a composite of 30 or fewer nodules. Specifically, the positive electrode active material can be a quasi-single particle that is a composite of 2 to 20, and more specifically 2 to 10 nodules, or a combination thereof. In this case, when manufacturing the electrode of the positive electrode active material, particle breakage is prevented, and internal cracking caused by the volume expansion / contraction of the nodules during charge and discharge is prevented, and the effect of improving the life characteristics and storage characteristics at high temperatures can be improved.

[0049] The average particle size (D 50 ) of the positive electrode active material can be 1 μm to 10 μm, specifically 2 μm to 8 μm, more specifically 3 μm to 7 μm, more specifically 3 μm to 5 μm, and even more specifically 3.5 μm to 4.5 μm. Within the above range, excellent processability in electrode manufacturing can be achieved. Due to high electrolyte impregnation, the electrochemical performance can be improved, the resistance can be reduced, and the output characteristics can be improved.

[0050] The specific surface area of the positive electrode active material can be 0.1 m 2 / g to 3.0 m 2 / g, specifically 0.3 m 2 / g to 2.5 m 2 / g, more specifically 0.4 m 2 / g to 1.8 m 2 / g, even more specifically 0.5 m 2 / g to 1.0 m 2 / g, and even more specifically 0.7 m 2 / g to 0.9 m 2 / g. Within the above range, the roll pressing characteristics of the electrode can be improved, and due to reduced particle breakage, side reactions with the electrolyte can be suppressed.

[0051] The positive electrode may include: a positive electrode current collector; and a positive electrode active material layer provided on at least one side of the positive electrode current collector. The positive electrode active material may be included in the positive electrode active material layer.

[0052] The positive electrode current collector is not particularly limited as long as it has high electrical conductivity and does not cause chemical changes in the battery. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum cadmium alloy, and preferably aluminum.

[0053] The thickness of the positive electrode current collector is generally 3 μm to 500 μm.

[0054] The positive electrode current collector may form fine irregularities on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven material.

[0055] The positive electrode active material layer may be provided on at least one side of the positive electrode current collector, and specifically, on one or both sides of the positive electrode current collector.

[0056] Considering that the positive electrode active material exhibits sufficient capacity, the content of the positive electrode active material in the positive electrode active material layer may be 80% by weight to 99% by weight, preferably 92% by weight to 98.5% by weight.

[0057] Since other positive electrode active materials have been described above, their descriptions will be omitted.

[0058] In addition to the positive electrode active material, the positive electrode active material layer may further include a binder and / or a conductive material.

[0059] The binder is a component that helps the combination of the active material and the conductive material and the combination with the current collector, and may specifically include 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.

[0060] The content of the binder in the positive electrode active material layer may be 1% by weight to 20% by weight, and preferably 1.2% by weight to 10% by weight, to ensure sufficient adhesion between the components including the positive electrode active material.

[0061] The conductive material can be used to assist and improve the conductivity of the secondary battery, and there is no particular limitation as long as it has conductivity without causing chemical changes. Specifically, the positive electrode conductive material can include at least one selected from the group consisting of: graphite, including natural graphite or artificial graphite; carbon black, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, including carbon fibers and metal fibers; conductive tubes, including carbon nanotubes; fluorocarbons; metal powders, including aluminum powder and nickel powder; conductive whiskers, including zinc oxide and potassium titanate; conductive metal oxides, including titanium oxide; and polyphenylene derivatives, preferably carbon nanotubes to improve conductivity.

[0062] The content of the conductive material in the positive electrode active material layer can be 1% by weight to 20% by weight, and preferably 1.2% by weight to 10% by weight to ensure sufficient conductivity.

[0063] The thickness of the positive electrode active material layer can be 30 μm to 400 μm, and preferably 40 μm to 200 μm.

[0064] The positive electrode can be manufactured by the following method: coating a positive electrode current collector with a positive electrode paste containing a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode paste, and then drying and rolling.

[0065] The solvent for forming the positive electrode paste can include organic solvents such as N-methyl-2-pyrrolidone (NMP). The solid content of the positive electrode paste can be 40% by weight to 90% by weight, and specifically 50% by weight to 80% by weight.

[0066] (2) Negative electrode

[0067] The negative electrode can face the positive electrode.

[0068] The negative electrode contains a negative electrode active material.

[0069] The negative electrode active material is a material capable of reversibly inserting / extracting lithium ions, and can include at least one selected from the group consisting of carbonaceous active materials, metal / metalloid active materials, and lithium metal, and can specifically include at least one selected from the group consisting of carbonaceous active materials and metal / metalloid active materials.

[0070] The carbonaceous active materials can 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 at least one selected from the group consisting of artificial graphite and natural graphite.

[0071] The average particle size (D 50) can be from 10 μm to 30 μm, and preferably from 15 μm to 25 μm, to ensure the structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0072] Specifically, the metal / metalloid active material can include: at least one metal / metalloid 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 and at least one metal / metalloid 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 metal / metalloid 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, etc.

[0073] More specifically, the metal / metalloid active material can include a silicon-based active material.

[0074] The silicon-based active material can include a compound represented by SiO x (0 ≤ x < 2). In the case of SiO2, considering that SiO2 does not react with lithium ions and cannot store lithium, x is preferably within the above range. More preferably, the silicon-based active material can be SiO.

[0075] The average particle size (D 50 ) of the silicon-based active material can be from 1 μm to 30 μm, and preferably from 2 μm to 15 μm, to ensure the structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0076] The negative electrode can include: a negative electrode current collector; and a negative electrode active material layer provided on at least one side of the negative electrode current collector. The negative electrode active material can be included in the negative electrode active material layer.

[0077] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, the negative electrode current collector can be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel treated with carbon, nickel, titanium, silver, etc., aluminum cadmium alloy, etc.

[0078] The thickness of the negative electrode current collector can generally be from 3 μm to 500 μm.

[0079] The negative electrode current collector can form fine irregularities on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, and non-woven materials.

[0080] The negative electrode active material layer can be provided on at least one side of the negative electrode current collector, and specifically, on one or both sides of the negative electrode current collector.

[0081] The content of the negative electrode active material in the negative electrode active material layer can be 60% by weight to 99% by weight, and preferably 75% by weight to 95% by weight.

[0082] Since other negative electrode active materials have been described above, their descriptions will be omitted.

[0083] In addition to the negative electrode active material, the negative electrode active material layer can also contain a binder and / or a conductive material.

[0084] The binder is used to improve the battery performance by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and can include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, 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 materials in which hydrogen is replaced by Li, Na, or Ca, and can also include various copolymers thereof.

[0085] The content of the binder in the negative electrode active material layer can be 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0086] There is no particular limitation on the conductive material as long as it has conductivity and does not cause chemical changes in the battery. For example, conductive materials such as graphite, including natural graphite or artificial graphite; carbon black, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, including carbon fibers and metal fibers; conductive tubes, including carbon nanotubes; fluorocarbons; metal powders, including aluminum powder and nickel powder; conductive whiskers, including zinc oxide and potassium titanate; conductive metal oxides, including titanium oxide; and polyphenylene derivatives can be used.

[0087] The content of the conductive material in the negative electrode active material layer can be 0.5% by weight to 10% by weight, and preferably 1% by weight to 5% by weight.

[0088] The thickness of the negative electrode active material layer may be from 10 μm to 200 μm, and preferably from 20 μm to 150 μm.

[0089] The negative electrode can be manufactured by the following method: coating at least one side of the negative electrode current collector with a negative electrode paste containing a negative electrode active material, a binder, a conductive material, and / or a solvent for forming the negative electrode paste, and then drying and rolling.

[0090] The solvent for forming the negative electrode paste 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 easily disperse the negative electrode active material, the binder, and / or the conductive material, and preferably distilled water. The solid content of the negative electrode paste may be from 30% by weight to 80% by weight, and specifically from 40% by weight to 70% by weight.

[0091] (3) Separator

[0092] The separator can be disposed between the positive electrode and the negative electrode.

[0093] The separator can be a conventional porous polymer film commonly used as a separator, and for example, a porous polymer film prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers can be used alone or by laminating it, or a commonly used porous nonwoven material, such as a nonwoven material made of high melting point glass fibers and polyethylene terephthalate fibers, can be used, but not limited thereto. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer can be used, and a single-layer or multi-layer structure can be optionally used.

[0094] (4) Non-aqueous electrolyte

[0095] The non-aqueous electrolyte contains a lithium salt, an organic solvent, and an additive.

[0096] 1) Lithium salt

[0097] As the lithium salt used in the present invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt may contain Li + as a cation and contain a selected from the group consisting of 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 - at least one selected from the group consisting of as an anion.

[0098] Specifically, the lithium salt may include at least one selected from the group consisting of 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).

[0099] The concentration of the lithium salt contained in the non-aqueous electrolyte can be from 0.5 M to 5 M, specifically from 0.8 M to 4 M, and more specifically from 0.8 M to 2.0 M. When the lithium salt concentration satisfies the above range, the Li + transference number and the dissociation degree of lithium ions are improved, and thus the output characteristics of the battery can be improved.

[0100] 2) Organic solvents

[0101] The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries and is not particularly limited as long as it can minimize the decomposition caused by the oxidation reaction during the charge and discharge process of the secondary battery.

[0102] 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.

[0103] Specifically, the organic solvent may include cyclic carbonate organic solvents, linear carbonate organic solvents, or a mixture thereof.

[0104] The cyclic carbonate organic solvent is a high-viscosity organic solvent and can easily dissociate the lithium salt in the electrolyte due to its high dielectric constant. The cyclic carbonate organic solvent may specifically 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, it includes at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). Even more specifically, it includes ethylene carbonate (EC).

[0105] The linear carbonate organic solvent is a low-viscosity and low-dielectric-constant organic solvent 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, it includes at least one selected from the group consisting of EMC and DEC. Even more specifically, it includes EMC.

[0106] The organic solvent may be a mixture of cyclic carbonate organic solvents and linear carbonate organic solvents. The cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed at a volume ratio of 5:95 to 40:60, and specifically 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, not only can the high dielectric constant and low viscosity characteristics be achieved, but also excellent ionic conductivity can be achieved.

[0107] In order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents, 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.

[0108] The linear ester organic solvent may specifically include at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0109] 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.

[0110] When necessary, the organic solvent can be used by adding organic solvents commonly used in non-aqueous electrolytes without limitation. For example, it may further contain at least one of ether organic solvents, alcohol ether solvents, and nitrile organic solvents.

[0111] The ether solvent may be at least 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 thereof, but is not limited thereto.

[0112] Compared with linear carbonate organic solvents, alcohol ether solvents have a high dielectric constant and low surface tension, and their reactivity with metals is low. Alcohol ether solvents may include at least one selected from the group consisting of dimethoxyethane (ethylene glycol dimethyl ether, DME), diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether (TEGDME), but is not limited thereto.

[0113] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, hexanenitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0114] 3) Additive

[0115] The non-aqueous electrolyte contains an additive.

[0116] The additive contains a first additive. The first additive contains vinylene carbonate (VEC).

[0117] When a lithium secondary battery operates at a high voltage (e.g., above 4.35 V), vinylene ethylene carbonate can form a film on the positive electrode. Therefore, when combined with the positive electrode active material of the present invention that requires high-voltage operation to improve the energy density, electrolyte side reactions can be significantly prevented, and the life performance and storage performance can be improved to a high level. On the other hand, when a high-nickel lithium transition metal oxide is used as the positive electrode active material, the lithium secondary battery operates at a low driving voltage (e.g., 4.2 V), and vinylene ethylene carbonate forms a film on the negative electrode rather than the positive electrode, so the object of preventing electrolyte side reactions of the positive electrode of the present invention cannot be achieved.

[0118] The content of the first additive in the non-aqueous electrolyte can be 0.01 wt% to 10 wt%, specifically 0.05 wt% to 7 wt%, more specifically 0.1 wt% to 1 wt%, and still more specifically 0.3 wt% to 0.7 wt%. When the first additive is used within the above range, the effects of improving the life performance and storage performance as described above can be achieved, and at the same time, the problem of increased resistance caused by excessive addition can be prevented.

[0119] In addition to the first additive, the additive can further include a second additive.

[0120] Specifically, the second additive can include at least one selected from the group consisting of lithium salt additives, nitrogen-containing heterocyclic compound additives, cyclic sulfur compound additives, and cyclic carbonates containing propargyl. The second additive can be used together with the first additive to form a stronger and more stable positive electrode film.

[0121] The lithium salt additives can specifically include at least one selected from the group consisting of LiBF4, lithium bis(oxalate)borate (LiB(C2O4)2, LiBOB), lithium difluoro(oxalate)borate (LiF2OB, LiODFB), lithium difluorophosphate (LiPO2F2, LiDFP), and lithium difluoro(bisoxalate)phosphate (LiDFOP), and more specifically include LiDFP.

[0122] The nitrogen-containing heterocyclic compound additives can specifically include at least one compound selected from the group consisting of the compounds represented by the following Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, and more specifically, include the compound represented by the following Chemical Formula 1-1.

[0123] [Chemical Formula 1-1]

[0124]

[0125] [Chemical Formula 1-2]

[0126]

[0127] [Chemical Formula 1-3]

[0128]

[0129] In Chemical Formulas 1-1, 1-2, and 1-3, R1 is a C1-C3 alkylene group, R2, R3, and R4 are independently selected from hydrogen, C1-C3 alkyl groups, 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.

[0130] Specifically, in Chemical Formulas 1-1, 1-2, and 1-3, R1 is a C1-C3 alkylene group, and more specifically, it is a methylene group (-CH2-). In Chemical Formulas 1-1, 1-2, and 1-3, R2, R3, and R4 can be hydrogen, and h, i, and j can be 0.

[0131] More specifically, the nitrogen-containing heterocyclic compound class additives can include the compound represented by the following Chemical Formula 1-1-A.

[0132] [Chemical Formula 1-1-A]

[0133]

[0134] The cyclic sulfur compound class additives can include at least one compound selected from the group consisting of the compounds represented by Chemical Formulas 2-1 to 2-17. Specifically, it includes the compound represented by the following Chemical Formula 2-1.

[0135] [Chemical Formula 2-1]

[0136]

[0137] [Chemical Formula 2-2]

[0138]

[0139] [Chemical Formula 2-3]

[0140]

[0141] [Chemical Formula 2-4]

[0142]

[0143] [Chemical Formula 2-5]

[0144]

[0145] [Chemical Formula 2-6]

[0146]

[0147] [Chemical Formula 2-7]

[0148]

[0149] [Chemical formula 2-8]

[0150]

[0151] [Chemical formula 2-9]

[0152]

[0153] [Chemical formula 2-10]

[0154]

[0155] [Chemical formula 2-11]

[0156]

[0157] [Chemical formula 2-12]

[0158]

[0159] [Chemical formula 2-13]

[0160]

[0161] [Chemical formula 2-14]

[0162]

[0163] [Chemical formula 2-15]

[0164]

[0165] [Chemical formula 2-16]

[0166]

[0167] [Chemical formula 2-17]

[0168]

[0169] The cyclic carbonate additives containing propargyl can specifically include the compounds shown in the following Chemical formula 3:

[0170] [Chemical formula 3]

[0171]

[0172] In Chemical formula 3, R5 is a C1-C5 alkylene group, and R6 is a C1-C5 alkyl group.

[0173] More specifically, the propargyl group-containing cyclic carbonate additive may include a compound represented by the following Chemical Formula 3-1.

[0174] [Chemical Formula 3-1]

[0175]

[0176] The content of the second additive in the non-aqueous electrolyte may be from 0.01 wt% to 10 wt%, specifically from 0.05 wt% to 7 wt%, more specifically from 0.1 wt% to 5 wt%, and still more specifically from 0.3 wt% to 2 wt%. When the second additive satisfies the above range, a stable and firm positive electrode film can be formed, and when operating at a high voltage, the life performance and storage performance of the lithium secondary battery can be improved to an excellent level.

[0177] The weight ratio of the first additive to the second additive may be from 5:95 to 95:5, specifically from 10:90 to 92:8, and more specifically from 30:70 to 70:30. Within the above weight ratio range, the effects of using the first additive and the second additive in combination can be achieved, so the life performance and storage performance of the lithium secondary battery at high temperatures can be preferably exhibited.

[0178] In addition to the first additive or in combination with the first and second additives, the additive may further include an additional additive. The additional additive may be included in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing under high-power conditions and causing the negative electrode to disintegrate, improve the low-temperature high-rate discharge characteristics and high-temperature stability, prevent overcharging, or reduce battery swelling at high temperatures.

[0179] Specifically, the additional additive may be at least one selected from the group consisting of fluoroethylene carbonate, succinonitrile, adiponitrile, 3-trimethoxysilyl-propyl-N-phenylamine (TMSPa), and tris(trimethylsilyl) phosphite (TMSPi).

[0180] The content of the additional additive in the non-aqueous electrolyte may be from 0.1 wt% to 15 wt%.

[0181] The driving voltage of the lithium secondary battery of the present invention may be 4.3 V or more, specifically 4.35 V or more, and more specifically 4.4 V or more. Due to the combination of the above positive electrode and non-aqueous electrolyte, the lithium secondary battery of the present invention can achieve excellent energy density and improved life performance and storage performance at a high driving voltage.

[0182] The shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, prismatic, pouch-shaped, or coin-shaped using a can.

[0183] Hereinafter, embodiments of the present invention will be described in detail. However, the following embodiments are intended to illustrate 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 and technical concept of this specification, and these changes and modifications are included within the scope of the appended claims.

[0184] Examples and Comparative Examples

[0185] Example 1

[0186] (Preparation of Non-aqueous Electrolyte)

[0187] As the organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 20:80 was used.

[0188] The non-aqueous electrolyte was prepared by adding LiPF6 as a lithium salt and vinylene carbonate (VEC) as a first additive to the organic solvent.

[0189] The molar concentration of LiPF6 contained in the non-aqueous electrolyte was 1.2 M.

[0190] The content of vinylene carbonate (VEC) in the non-aqueous electrolyte was 0.5 wt%.

[0191] (Manufacture of Lithium Secondary Battery)

[0192] The positive electrode active material (Li[Ni 0.60 Co 0.05 Mn 0.35 O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 97.74:0.70:1.56 to prepare a positive electrode paste (solid content: 75.5 wt%). The positive electrode paste was applied to one side of a positive electrode current collector (Al film) with a thickness of 15 μm, dried, and roll-pressed to form a positive electrode active material layer (thickness: 136.6 μm), which was used as the positive electrode. The positive electrode active material was in the form of single particles or quasi-single particles.

[0193] The negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) were added to distilled water as a solvent at a weight ratio of 96.15:1.55:2.30 to prepare a negative electrode paste (solid content: () wt%). The negative electrode paste was coated on one side of a negative electrode current collector (Cu film) with a thickness of 15 μm, dried, and roll-pressed to form a negative electrode active material layer (thickness: 179.8 μm), which was used as the negative electrode.

[0194] In a drying chamber, a polyethylene porous membrane separator is disposed between the obtained positive electrode and negative electrode, and then the obtained non-aqueous electrolyte is injected to fabricate a secondary battery.

[0195] Example 2

[0196] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5% by weight of LiDFP as a second additive was further added to the non-aqueous electrolyte based on the weight of the non-aqueous electrolyte.

[0197] Example 3

[0198] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5% by weight of the compound represented by Chemical Formula 2-1 as a second additive was further added to the non-aqueous electrolyte based on the weight of the non-aqueous electrolyte.

[0199] Example 4

[0200] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5% by weight of the compound represented by Chemical Formula 1-1-A as a second additive was further added to the non-aqueous electrolyte based on the weight of the non-aqueous electrolyte.

[0201] Example 5

[0202] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5% by weight of the compound represented by Chemical Formula 3-1 as a second additive was further added to the non-aqueous electrolyte based on the weight of the non-aqueous electrolyte.

[0203] Example 6

[0204] A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5% by weight of the compound represented by Chemical Formula 1-1-A and 0.5% by weight of the compound represented by Chemical Formula 3-1 as second additives were further added to the non-aqueous electrolyte based on the weight of the non-aqueous electrolyte.

[0205] Comparative Example 1

[0206] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that the first additive was not added.

[0207] Comparative Example 2

[0208] A non-aqueous electrolyte and a lithium secondary battery were fabricated in the same manner as in Example 1, except that 0.5% by weight of vinylene carbonate (VC) as the first additive was added to the non-aqueous electrolyte instead of vinyl ethyl carbonate.

[0209] [Table 1]

[0210]

[0211] Experimental Examples

[0212] Experimental Example 1: Evaluation of High-Temperature Cycling Performance

[0213] Using an electrochemical charge-discharge device, the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 manufactured above were charged to 4.4 V at 0.33 C and 45 °C under CC / CV conditions and 0.05 C, and then discharged to 2.5 V at 0.33 C under CC conditions, which was regarded as one cycle, and 300 charge-discharge cycles were performed.

[0214] (1) Capacity Retention Rate

[0215] The capacity retention rate was calculated using the following equation, and the results are shown in Table 2 below.

[0216] Capacity retention rate (%) = {(discharge capacity after 300 cycles / discharge capacity after 1 cycle)} × 100

[0217] (2) Resistance Increase Rate

[0218] After one charge-discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge-discharge device, the SOC was adjusted to 50%, and then a pulse of 2.5 C was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0219] After 300 charge-discharge cycles, the resistance after 300 cycles was calculated in the same manner as above, and the resistance increase rate was calculated using the following equation, and the results are shown in Table 2 below.

[0220] Resistance increase rate (%) = (resistance after 300 cycles - initial resistance) / initial resistance × 100

[0221] [Table 2]

[0222] Capacity retention rate (%) Resistance increase rate (%) Example 1 82 22 Example 2 93 10 Example 3 90 12 Example 4 93 13 Example 5 91 12 Example 6 92 11 Comparative Example 1 77 28 Comparative Example 2 70 27

[0223] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 6 combine a positive electrode containing a lithium transition metal oxide represented by Chemical Formula A with a non-aqueous electrolyte containing a first additive (VEC) as an additive, and compared with Comparative Example 1 and Comparative Example 2, the lithium secondary batteries of Examples 1 to 6 have a high capacity retention rate and a low resistance increase rate during high-temperature charge-discharge cycling.

[0224] Experimental Example 2: Evaluation of High-Temperature Storage Performance

[0225] The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 manufactured above were charged to 4.4 V at 0.33 C and 25 °C under CC / CV conditions and 0.05 C, and discharged to 2.5 V at 0.33 C under CC conditions for initial charge and discharge. Then, the batteries were charged to 4.4 V at 0.33 C and 25 °C under CC / CV conditions and 0.05 C, and stored at 60 °C for 12 weeks.

[0226] (1) Capacity retention

[0227] After storing for 12 weeks, the lithium secondary battery was charged to 4.4 V at 0.33 C and 25 °C under CC / CV conditions and 0.05 C, and discharged to 2.5 V at 0.33 C under CC conditions to measure the capacity during discharge.

[0228] The capacity retention was evaluated according to the following equation, and the results are shown in Table 3.

[0229] Capacity retention (%) = (Discharge capacity after 12 weeks of storage / Initial discharge capacity) × 100

[0230] (2) Resistance increase rate

[0231] After initial charge and discharge, the capacity at room temperature was checked. Based on the discharge capacity, the battery was charged to 50% SOC and discharged at 2.5 C for 10 seconds. At this time, the resistance was measured using the voltage drop difference and used as the initial resistance. After storing at 60 °C for 12 weeks, the resistance was measured in the same manner and designated as the final resistance. The resistance increase rate was calculated using the following equation, and the results are shown in Table 3 below.

[0232] Resistance increase rate (%) = (Final resistance - Initial resistance) / (Initial resistance) × 100

[0233] [Table 3]

[0234] Capacity retention rate (%) Resistance increase rate (%) Example 1 83 26 Example 2 90 13 Example 3 93 12 Example 4 91 12 Example 5 92 10 Example 6 92 11 Comparative Example 1 76 33 Comparative Example 2 75 38

[0235] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 6 combine a positive electrode containing a lithium transition metal oxide represented by Chemical Formula A with a non-aqueous electrolyte containing a first additive (VEC) as an additive. Compared with Comparative Example 1 and Comparative Example 2, the lithium secondary batteries of Examples 1 to 6 have a high capacity retention and a low resistance increase rate when stored at high temperatures.

[0236] Reference Example A

[0237] Reference Example 1A

[0238] (1) Preparation of non-aqueous electrolyte

[0239] Prepare the non-aqueous electrolyte in the same manner as in Example 1.

[0240] (2) Manufacture of lithium secondary battery

[0241] Add the positive electrode active material (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2), the conductive material (carbon nanotubes), and the binder (polyvinylidene fluoride) to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 98.0:0.7:1.3 to prepare a positive electrode mixture slurry (solid content: 76.5 wt%). Apply the positive electrode mixture slurry to one side of a positive electrode current collector (Al film) with a thickness of 12 μm, dry and roll-press it to prepare the positive electrode. The positive electrode active material is in the form of secondary particles aggregated from a plurality of primary particles.

[0242] Add the negative electrode active material (artificial graphite), the conductive material (carbon black), and the binder (styrene-butadiene rubber) to distilled water as a solvent in a weight ratio of 96.5:1.5:2.0 to prepare a negative electrode mixture slurry (solid content: 50 wt%). Apply the negative electrode mixture slurry to one side of a negative electrode current collector (Cu film) with a thickness of 8 μm, dry and roll-press it to prepare the negative electrode.

[0243] Place a polyethylene porous membrane separator between the prepared positive electrode and negative electrode in a drying chamber, and then inject the prepared non-aqueous electrolyte to manufacture the secondary battery.

[0244] Reference Example 2A

[0245] Manufacture a lithium secondary battery in the same manner as in Reference Example 1A, except that the non-aqueous electrolyte prepared in Comparative Example 1 is used instead of the non-aqueous electrolyte prepared in Example 1.

[0246] Reference Example 3A

[0247] Manufacture a lithium secondary battery in the same manner as in Reference Example 1A, except that the non-aqueous electrolyte prepared in Comparative Example 2 is used instead of the non-aqueous electrolyte prepared in Example 1.

[0248] Reference Experimental Example A

[0249] Use an electrochemical charge-discharge device to charge the lithium secondary batteries of Reference Examples 1A to 3A manufactured above under CC / CV conditions at 0.33C and 45 °C to 4.2V and discharge them at 1 / 40C under CC conditions at 0.33C to 2.5V. Consider this as one cycle, and perform 300 charge-discharge cycles.

[0250] (1) Capacity Retention Rate

[0251] The capacity retention rate is calculated according to the following equation, and the results are shown in Table 4.

[0252] Capacity Retention Rate (%) = {(Discharge Capacity after 300 Cycles / Discharge Capacity after 1 Cycle)} × 100

[0253] (2) Resistance Increase Rate

[0254] After one charge-discharge cycle, the discharge capacity after one cycle is measured using an electrochemical charge-discharge device. The SOC is adjusted to 50%, and then a 2.5C pulse is applied for 10 seconds. The initial resistance is calculated from the difference in voltage before and after the pulse application.

[0255] After 300 charge-discharge cycles, the resistance after 300 cycles is calculated in the same manner as above. The resistance increase rate is calculated using the following equation, and the results are shown in Table 4 below.

[0256] Resistance Increase Rate (%) = (Resistance after 300 Cycles - Initial Resistance) / Initial Resistance × 100

[0257] [Table 4]

[0258] Capacity retention rate (%) Resistance increase rate (%) Reference Example 1A 83 26 Reference Example 2A 82 25 Reference Example 3A 85 23

[0259] Referring to Table 4, it can be seen that compared with Reference Example 2A and Reference Example 3A, although vinylene carbonate is used as a non-aqueous electrolyte additive, there is no improvement in the performance of the lithium secondary battery of Reference Example 1A. In other words, considering that Reference Examples 1A to 3A using high-nickel lithium transition metal oxide (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 O2) as the positive electrode active material operate at a relatively low voltage (4.2V), vinylene carbonate mainly decomposes at the negative electrode and forms a film. It can be seen that even when vinylene carbonate is used as a non-aqueous electrolyte additive, it is difficult to prevent electrolyte side reactions at the positive electrode. In particular, in the case of the lithium secondary battery of Reference Example 1A, by comparing the performance with that of Reference Example 2A and Reference Example 3A, it can be seen that vinylene carbonate used as a non-aqueous electrolyte additive actually acts as a resistance.

[0260] Reference Example B

[0261] Reference Example 1B

[0262] (1) Preparation of Non-aqueous Electrolyte

[0263] The non-aqueous electrolyte is prepared in the same manner as in Example 1.

[0264] (2) Fabrication of Lithium Secondary Battery

[0265] The positive electrode active material (LiNi 0.6 Co 0.2 Mn 0.2 O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 98.0:0.7:1.3 to prepare a positive electrode mixture slurry (solid content: 76.5 wt%). The positive electrode mixture slurry was applied to one side of a positive electrode current collector (Al film) with a thickness of 12 μm, dried, and roll-pressed to prepare a positive electrode. The positive electrode active material is in the form of secondary particles aggregated from a plurality of primary particles.

[0266] The negative electrode active material (artificial graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) were added to distilled water as a solvent in a weight ratio of 96.5:1.5:2.0 to prepare a negative electrode mixture slurry (solid content: 50 wt%). The negative electrode mixture slurry was applied to one side of a negative electrode current collector (Cu film) with a thickness of 8 μm, dried, and roll-pressed to prepare a negative electrode.

[0267] In a drying chamber, a polyethylene porous membrane separator was placed between the prepared positive electrode and negative electrode, and then the prepared non-aqueous electrolyte was injected to fabricate a secondary battery.

[0268] Reference Example 2B

[0269] A lithium secondary battery was fabricated in the same manner as in Reference Example 1B, except that the non-aqueous electrolyte prepared in Comparative Example 1 was used instead of the non-aqueous electrolyte prepared in Example 1.

[0270] Reference Example 3B

[0271] A lithium secondary battery was fabricated in the same manner as in Reference Example 1B, except that the non-aqueous electrolyte prepared in Comparative Example 2 was used instead of the non-aqueous electrolyte prepared in Example 1.

[0272] Reference Experimental Example B

[0273] Using an electrochemical charge-discharge device, the lithium secondary batteries of Reference Examples 1B to 3B fabricated above were charged to 4.2 V at 0.33C and 45 °C under CC / CV conditions and 1 / 40C, and discharged to 2.5 V at 0.33C under CC conditions. This was regarded as one cycle, and 300 charge-discharge cycles were performed.

[0274] (1) Capacity Retention Rate

[0275] The capacity retention rate is calculated according to the following equation, and the results are shown in Table 5.

[0276] Capacity retention rate (%) = {(Discharge capacity after 300 cycles / Discharge capacity after 1 cycle)} × 100

[0277] (2) Resistance increase rate

[0278] After one charge-discharge cycle, the discharge capacity after one cycle is measured using an electrochemical charge-discharge device. The SOC is adjusted to 50%, and then a pulse of 2.5C is applied for 10 seconds. The initial resistance is calculated from the difference in voltage before and after the pulse application.

[0279] After 300 charge-discharge cycles, the resistance after 300 cycles is calculated in the same manner as above. The resistance increase rate is calculated using the following equation, and the results are shown in Table 5 below.

[0280] Resistance increase rate (%) = (Resistance after 300 cycles - Initial resistance) / Initial resistance × 100

[0281] [Table 5]

[0282] Capacity retention rate (%) Resistance increase rate (%) Reference Example 1B 84 35 Reference Example 2B 84 34 Reference Example 3B 85 30

[0283] Referring to Table 5, it can be seen that compared with Reference Examples 2B and 3B, although vinylene carbonate is used as a non-aqueous electrolyte additive, the lithium secondary battery of Reference Example 1B has a lower effect. In other words, considering that Reference Examples 1B to 3B using high-nickel lithium transition metal oxide (LiNi 0.6 Co 0.2 Mn 0.2 O2) as the positive electrode active material operate at a relatively low voltage (4.2V), and vinylene carbonate mainly decomposes at the negative electrode to form a film. It can be seen that even when vinylene carbonate is used as a non-aqueous electrolyte additive, it is difficult to prevent electrolyte side reactions at the positive electrode. In particular, compared with Reference Example 2B that does not use vinylene carbonate and Reference Example 3B that uses vinylene carbonate instead of vinylene carbonate, the lithium secondary battery of Reference Example 1B has a low capacity retention rate and an increased resistance.

Claims

1. A lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium transition metal oxide represented by the following Chemical Formula A, the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the additive includes a first additive, and the first additive includes vinylene ethylene carbonate: [Chemical Formula A] Li 1+x [Ni a Co b Mn c M 1 d O 2+w In Chemical Formula A, 0 ≤ x ≤ 0.5, a + b + c + d = 1, 0.5 ≤ a ≤ 0.7, 0 ≤ b ≤ 0.15, c = 1 - a - b - d, 0 ≤ d ≤ 0.1, 0 ≤ b / a ≤ 0.2, 1 ≤ a / c ≤ 3, 0 ≤ w ≤ 1, and 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.

2. The lithium secondary battery according to claim 1, wherein, the content of the first additive in the non-aqueous electrolyte is 0.1 wt% to 10 wt%.

3. The lithium secondary battery according to claim 1, wherein, The additive further includes a second additive, and the second additive includes at least one selected from the group consisting of lithium salt additives, nitrogen-containing heterocyclic compound additives, cyclic sulfur compound additives, and cyclic carbonates containing propargyl.

4. The lithium secondary battery according to claim 3, wherein, The lithium salt additives include at least one selected from the group consisting of LiBF4, LiBOB, LiODFB, LiDFP, and LiDFOP.

5. The lithium secondary battery according to claim 3, wherein, The nitrogen-containing heterocyclic compound additives include at least one compound selected from the group consisting of the compounds represented by Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3: [Chemical Formula 1-1] [Chemical Formula 1-2] [Chemical Formula 1-3] In Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, R1 is a C1 to C3 alkylene group, R2, R3, and R4 are independently selected from hydrogen, a C1 to C3 alkyl group, 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. The lithium secondary battery according to claim 3, wherein, The nitrogen-containing heterocyclic compound additives include a compound represented by the following Formula 1-1-A: [Chemical Formula 1-1-A] 7. The lithium secondary battery according to claim 3, wherein, The cyclic sulfur compound additives include at least one compound selected from the group consisting of the compounds represented by Chemical Formula 2-1 to Chemical Formula 2-17: [Chemical Formula 2-1] [Chemical Formula 2-2] [Chemical Formula 2-3] [Chemical Formula 2-4] [Chemical Formula 2-5] [Chemical Formula 2-6] [Chemical Formula 2-7] [Chemical Formula 2-8] [Chemical Formula 2-9] [Chemical Formula 2-10] [Chemical Formula 2-11] [Chemical Formula 2-12] [Chemical Formula 2-13] [Chemical Formula 2-14] [Chemical Formula 2-15] [Chemical Formula 2-16] [Chemical Formula 2-17] 8. The lithium secondary battery according to claim 3, wherein, The cyclic carbonate containing propargyl additives include a compound represented by Chemical Formula 3: [Chemical Formula 3] In Chemical Formula 3, R5 is a C1 to C5 alkylene group, and R6 is a C1 to C5 alkyl group.

9. The lithium secondary battery according to claim 3, wherein, The cyclic carbonate containing propargyl additives include a compound represented by Chemical Formula 3-1: [Chemical Formula 3-1] 10. The lithium secondary battery according to claim 3, wherein, The content of the second additive in the non-aqueous electrolyte is 0.1 wt% to 3 wt%.

11. The lithium secondary battery according to claim 1, wherein, The lithium salt includes at least one selected from the group consisting of 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).

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

13. The lithium secondary battery according to claim 1, wherein, The organic solvent includes 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.

14. The lithium secondary battery according to claim 1, wherein, The positive electrode active material is in the form of a single particle composed of a single nucleus, or in the form of a quasi-single particle as a composite of 30 or fewer nuclei.

15. The lithium secondary battery according to claim 1, wherein, In Chemical Formula A, a / (b×c) is from 18 to 50.

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