Lithium secondary battery

Abstract

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, the positive electrode active material including a lithium transition metal oxide represented by the following chemical formula A, and the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the additive including a first additive, the first additive including vinyl ethylene carbonate: [Chemical formula A] Li 1+x [Ni a Co b Mn c M 1 d ]O 2+w In the chemical formula A, 0≦x≦0.5, a+b+c+d=1, 0.5≦a≦0.7, 0≦b≦0.15, c=1−abd, 0≦d≦0.1, 0≦b / a≦0.2, 1≦a / c≦3, and 0≦w≦1; 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.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0181142, filed December 21, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

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

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

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

[0005] Meanwhile, in recent years, lithium nickel-cobalt-manganese composite transition metal oxides, which contain 80 mol% or more of nickel relative to the transition metal, have been the focus of research in order to increase the energy density of the positive electrode. However, increasing the nickel content of lithium nickel-cobalt-manganese composite transition metal oxides can lead to a decrease in the thermal stability of the positive electrode.

[0006] To prevent such problems, if the nickel content in the lithium nickel-cobalt-manganese composite transition metal oxide is reduced, the driving voltage must be increased to achieve the required energy density. However, when the battery is driven at such a high voltage, there is a problem that electrolyte side reactions at the positive electrode become severe. Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present invention is to solve the above-mentioned problems and to provide a lithium secondary battery that uses a lithium transition metal oxide with a nickel content reduced to a specific level as a positive electrode active material, and that has improved life performance and storage performance when driven at high voltage. [Means for solving the problem]

[0008] 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, the positive electrode active material including a lithium transition metal oxide represented by the following chemical formula A, and the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, the additive including a first additive, the first additive including vinyl ethylene carbonate:

[0009] [Chemical formula A] Li 1+x [Ni a Co b Mn c M 1 d ]O 2+w

[0010] In the chemical formula A, 0≦x≦0.5, a+b+c+d=1, 0.5≦a≦0.7, 0≦b≦0.15, c=1−abd, 0≦d≦0.1, 0≦b / a≦0.2, 1≦a / c≦3, and 0≦w≦1; M 1is 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. [Effects of the Invention]

[0011] The lithium secondary battery of the present invention is characterized by using a lithium transition metal oxide having a nickel content controlled within a specific range as a positive electrode active material and vinyl ethylene carbonate (VEC) as an additive to a non-aqueous electrolyte. The lithium secondary battery of the present invention can achieve significantly improved life and storage performance when driven at high voltages, especially high-temperature life and high-temperature storage performance. DETAILED DESCRIPTION OF THE INVENTION

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

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

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

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

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

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

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

[0019] The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide represented by the following chemical formula A, and the non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, and the additive includes a first additive, and the first additive includes vinyl ethylene carbonate.

[0020] [Chemical formula A] Li 1+x [Ni a Co b Mn c M 1 d ]O 2+w

[0021] In the chemical formula A, 0≦x≦0.5, a+b+c+d=1, 0.5≦a≦0.7, 0≦b≦0.15, c=1−abd, 0≦d≦0.1, 0≦b / a≦0.2, 1≦a / c≦3, and 0≦w≦1; 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.

[0022] The lithium secondary battery of the present invention is characterized by using a lithium transition metal oxide having a nickel content controlled within a specific range as a positive electrode active material and vinyl ethylene carbonate (VEC) as an additive to a non-aqueous electrolyte. The lithium secondary battery of the present invention can exhibit significantly improved life and storage performance during high-voltage operation, particularly high-temperature life and storage performance.

[0023] 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 facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The lithium secondary battery may be manufactured by placing an electrode assembly including the positive electrode, the negative electrode facing the positive electrode, and the separator interposed between the positive electrode and the negative electrode in a battery case and then injecting the non-aqueous electrolyte.

[0024] (1) Positive electrode The positive electrode includes a positive electrode active material.

[0025] The positive electrode active material includes a lithium transition metal oxide represented by the following chemical formula A:

[0026] [Chemical formula A] Li 1+x [Ni a Co b Mn c M 1 d ]O 2+w

[0027] In the chemical formula A, 0≦x≦0.5, a+b+c+d=1, 0.5≦a≦0.7, 0≦b≦0.15, c=1−abd, 0≦d≦0.1, 0≦b / a≦0.2, 1≦a / c≦3, and 0≦w≦1; 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.

[0028] The lithium transition metal oxide represented by the chemical formula A is distinguished from, for example, a high-nickel lithium transition metal oxide in which the Ni content exceeds 70 mol % relative to the metals excluding lithium. The high-nickel lithium transition metal oxide is undesirable because it contains a large amount of nickel and has reduced thermal stability.

[0029] Meanwhile, the compound represented by Formula A has a lower nickel content than high-nickel lithium transition metal oxides, and therefore needs to be driven at a high voltage (e.g., 4.35 V or higher) to increase the energy density of the positive electrode. However, when driven at such a high voltage, side reactions in the positive electrode electrolyte become more severe, resulting in a significant decrease in lifespan and storage performance.

[0030] In order to achieve both high energy density and excellent life and storage performance, the lithium secondary battery according to the present invention is characterized in that it uses a lithium transition metal oxide represented by the chemical formula A as a positive electrode active material, and vinyl ethylene carbonate (first additive) is used as a non-aqueous electrolyte additive. The vinyl ethylene carbonate (first additive) can form a stable coating on the positive electrode when used at high voltage, and therefore can significantly improve life and storage performance, specifically high-temperature life and high-temperature storage performance, when driven at high voltage.

[0031] The effect of improving battery performance at high voltages obtained by applying the nonaqueous electrolyte can be demonstrated when using a positive electrode active material containing a lithium transition metal oxide having the chemical formula A. For example, a positive electrode active material containing a lithium transition metal oxide having the chemical formula A, which does not satisfy the composition of Li[Ni 0.8 Co 0.1 Mn 0.1 In high-nickel lithium transition metal oxides such as Li[Ni]O2, the proportion of Ni in the transition metal or the molar ratio of Ni / Mn is very high, and during the charge / discharge process, the axis of the lattice changes significantly due to the increase and decrease in the Ni oxidation number. Therefore, the surface side reactions become intense due to the unstable Ni from the energy point of view, and the performance improvement effect of the organic solvents and additives is not easily realized. 0.8 Co 0.1 Mn 0.1 High-nickel lithium transition metal oxides such as Li[Ni]O2 have a high Ni / Mn molar ratio, so when driven at high voltages, a phase change occurs, resulting in the formation of a large amount of rock-salt structures on the surface, which makes it difficult to intercalate and deintercalate lithium ions and form a positive electrode film with the additive.0.6 Co 0.2 Mn 0.2 In lithium transition metal oxides that do not satisfy the chemical formula A, such as

[0023] O2, the proportion of Co in the transition metal is very high, which increases irreversibility within the structure, making it difficult to achieve the performance improvement effect achieved by the formation of a positive electrode coating using an additive. Therefore, in cases where the non-aqueous electrolyte is not a compound represented by the chemical formula A, it is difficult to achieve the desired improvements in life and storage performance, even if the non-aqueous electrolyte according to the present invention is used.

[0032] In the above chemical formula A, x may be 0≦x≦0.5, specifically 0≦x≦0.2.

[0033] In the above chemical formula A, 0.5≦a≦0.7, specifically 0.55≦a≦0.65.

[0034] In Formula A, 0≦b≦0.15. b corresponds to the molar percentage of Co among the metals excluding lithium in the lithium transition metal oxide represented by Formula A. According to the present invention, a low Co content provides cost benefits, while a relatively high Mn content can improve the structural stability of the positive electrode active material. In Formula A, specifically, 0≦b≦0.1, more specifically, 0≦b≦0.05.

[0035] In the formula A, 0≦b / a≦0.2. If b / a exceeds 0.2, the proportion of Co in the transition metal is too high, increasing irreversibility within the structure, making it difficult to achieve the performance improvement effect of forming a positive electrode film by the additive. Specifically, in the formula A, 0.05≦b / a≦0.2 may be satisfied.

[0036] In Formula A, c = 1-abd, and 1≦a / c≦3. c corresponds to the molar percentage of Mn among the metals excluding lithium in the lithium transition metal oxide represented by Formula A. According to the present invention, the molar ratio of Ni to Mn is adjusted to 1≦a / c≦3, thereby improving the structural stability of the positive electrode active material. Specifically, it may be 1.5≦a / c≦2.5.

[0037] In the above chemical formula A, M 1 may be understood as an element to be doped into the lithium transition metal oxide, and may specifically be 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. In this case, d may be 0≦d≦0.1, specifically 0≦d≦0.05.

[0038] In Chemical Formula A, a / (b×c) may be 18 to 50, specifically 18 to 40, and more specifically 20 to 35. When the ratio is within the above range, the contents of nickel, cobalt, and manganese in Chemical Formula A are well-balanced, which can improve both the performance improvement effect due to the formation of a positive electrode coating by the additive and the structural stability of the positive electrode active material.

[0039] The positive electrode active material may be in the form of particles. Specifically, the positive electrode active material may be in the form of a single particle consisting of one single nodule, or a quasi-single particle which is a composite of 30 or less nodules. Specifically, the positive electrode active material may be a quasi-single particle which is a composite of 2 to 20, more specifically 2 to 10, nodules, or a form containing these. In this case, particle cracking during electrode manufacturing of the positive electrode active material is prevented, and internal cracking due to volume expansion / contraction of the nodules during charge / discharge is prevented, thereby improving high-temperature life characteristics and high-temperature storage characteristics.

[0040] The average particle size (D 50 ) may be 1 μm to 10 μm, specifically 2 μm to 8 μm, more specifically 3 μm to 7 μm, even more specifically 3 μm to 5 μm, and even more specifically 3.5 μm to 4.5 μm. When the thickness satisfies the above range, the processability during electrode production is excellent, the electrolyte impregnation is high, the electrochemical properties can be improved, and the resistance can be reduced, resulting in improved output characteristics.

[0041] The specific surface area of ​​the positive electrode active material is 0.1 m 2 / g~3.0m2 / g, specifically 0.3m 2 / g~2.5m 2 / g, more specifically 0.4m 2 / g~1.8m 2 / g, more specifically 0.5m 2 / g~1.0m 2 / g, more specifically 0.7m 2 / g~0.9m 2 When the above range is satisfied, the rolling characteristics of the electrode may be improved, particle cracking may be reduced, and side reactions with the electrolyte may be suppressed.

[0042] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode active material may be contained in the positive electrode active material layer.

[0043] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and preferably aluminum.

[0044] The positive electrode current collector usually has a thickness of 3 μm to 500 μm.

[0045] 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.

[0046] The positive electrode active material layer may be disposed on at least one surface of the positive electrode current collector, specifically, on one or both surfaces of the positive electrode current collector.

[0047] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 92% by weight to 98.5% by weight, in consideration of sufficient capacity of the positive electrode active material.

[0048] The other positive electrode active materials have been described above and will not be described again.

[0049] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material.

[0050] The binder is a component that assists in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0051] The binder may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0052] The conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the positive electrode conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, 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, and preferably includes carbon nanotubes in order to improve conductivity.

[0053] In order to ensure sufficient electrical conductivity, the conductive material may be contained in the positive electrode active material layer in an amount of 1 to 20% by weight, preferably 1.2 to 10% by weight.

[0054] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 40 μm to 200 μm.

[0055] 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.

[0056] The solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the solid content of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0057] (2) Negative electrode The negative electrode faces the positive electrode.

[0058] The negative electrode includes a negative electrode active material.

[0059] 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 (quasi)metal-based active material, and lithium metal, and specifically may include at least one selected from a carbon-based active material and a (quasi)metal-based active material.

[0060] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of artificial graphite and natural graphite.

[0061] The average particle size (D 50 ) may be 10 μm to 30 μm, preferably 15 μm to 25 μm, in order to ensure structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0062] Specifically, the (quasi-)metallic active material may include at least one (quasi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of at least one (quasi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (quasi-)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0063] More specifically, the (quasi)metallic active material may include a silicon-based active material.

[0064] The silicon-based active material is SiO x (0≦x<2). SiO2 does not react with lithium ions and therefore cannot store lithium. Therefore, x is preferably within the above range, and more preferably, the silicon-based active material may be SiO.

[0065] The average particle size (D 50 ) may be 1 μm to 30 μm, preferably 2 μm to 15 μm, from the viewpoint of improving structural stability during charge and discharge and reducing side reactions with the electrolyte.

[0066] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material may be contained in the negative electrode active material layer.

[0067] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0068] The negative electrode current collector usually has a thickness of 3 μm to 500 μm.

[0069] 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.

[0070] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector, specifically, on one or both surfaces of the negative electrode current collector.

[0071] The negative electrode active material may be contained in the negative electrode active material layer in an amount of 60% by weight to 99% by weight, preferably 75% by weight to 95% by weight.

[0072] The other positive electrode active materials are as described above and will not be described here.

[0073] The negative electrode active material layer may further include a binder and / or a conductive material in addition to the negative electrode active material.

[0074] 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.

[0075] The binder may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0076] 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.

[0077] The conductive material may be contained in the negative electrode active material layer in an amount of 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0078] The thickness of the negative electrode active material layer may be 10 μm to 200 μm, and preferably 20 μm to 150 μm.

[0079] 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.

[0080] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methyl-2-pyrrolidone (NMP), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive material. The solid content of the negative electrode slurry may be 30% by weight to 80% by weight, specifically 40% by weight to 70% by weight.

[0081] (3) Separator The separator may be interposed between the positive electrode and the negative electrode.

[0082] The separator may be a conventional porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, either alone or in a laminate, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of a high-melting point glass fiber or polyethylene terephthalate fiber, but is not limited to these. Furthermore, to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0083] (4) Nonaqueous electrolyte The non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive.

[0084] 1) Lithium salt As the lithium salt used in the present invention, various lithium salts that are commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without any limitation. For example, the lithium salt may contain Li as a cation. + and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - The composition may include at least one selected from the group consisting of:

[0085] Specifically, the lithium salts include LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 , LiBOB (LiB(C2O4)2), LiCF3SO3, LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0086] The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.5 M to 5 M, specifically, at a concentration of 0.8 M to 4 M, more specifically, at a concentration of 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transport number (Li + The transference number and dissociation degree of lithium ions are improved, which can improve the output characteristics of the battery.

[0087] 2) Organic solvents The organic solvent is not particularly limited as long as it is a non-aqueous solvent commonly used in lithium secondary batteries and minimizes decomposition due to oxidation reactions during charging and discharging of the secondary battery.

[0088] 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.

[0089] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture thereof.

[0090] The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and easily dissociates the lithium salt in the electrolyte. Specifically, the cyclic carbonate organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. More specifically, the cyclic carbonate organic solvent may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). Even more specifically, the cyclic carbonate organic solvent may include ethylene carbonate (EC).

[0091] The linear carbonate organic solvent is an organic solvent having low viscosity and low dielectric constant, and may specifically include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, more specifically at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and even more specifically ethyl methyl carbonate (EMC).

[0092] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. In this case, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed at a volume ratio of 5:95 to 40:60, specifically, a volume ratio of 10:90 to 25:75. When the mixing ratio of the cyclic carbonate organic solvent and the linear carbonate organic solvent satisfies the above range, both high dielectric constant and low viscosity characteristics are satisfied, and excellent ionic conductivity characteristics can be realized.

[0093] In order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents in addition to the at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents.

[0094] Specifically, the linear ester organic solvent may include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0095] 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.

[0096] Meanwhile, the organic solvent may further include, as needed, any organic solvent commonly used in non-aqueous electrolytes, for example, at least one of an ether-based organic solvent, a glyme-based organic solvent, and a nitrile-based organic solvent.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 4) Additives The non-aqueous electrolyte contains an additive.

[0101] The additives include a first additive, and the first additive includes vinyl ethylene carbonate (VEC).

[0102] The vinyl ethylene carbonate can form a coating on the positive electrode when the lithium secondary battery is operated at a high voltage (e.g., 4.35 V or higher). Therefore, when combined with the positive electrode active material according to the present invention, which requires high voltage operation to increase energy density, it can significantly prevent electrolyte side reactions and improve life and storage performance 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 is operated at a low operating voltage (e.g., 4.2 V), and the vinyl ethylene carbonate forms a coating on the negative electrode rather than the positive electrode, which fails to achieve the object of the present invention of preventing electrolyte side reactions on the positive electrode.

[0103] The first additive may be included in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 1 wt %, and even more specifically 0.3 wt % to 0.7 wt %. When the first additive is used in the above content range, the aforementioned effects of life performance and storage performance can be achieved and an increase in resistance when an excessive amount is added can be prevented.

[0104] The additive may further include a second additive together with the first additive.

[0105] Specifically, the second additive may include at least one selected from the group consisting of a lithium salt additive, a nitrogen-containing heterocyclic compound additive, a cyclic sulfur compound additive, and a propargyl group-containing cyclic carbonate additive. The second additive may be used together with the first additive to form a stronger and more stable positive electrode coating.

[0106] Specifically, the lithium salt additive may include at least one selected from the group consisting of LiBF, LiBOB (lithium bis(oxalato)borate, LiB(C2O4)2), LiODFB (lithium difluoro(oxalato)borate, LiF2OB), LiDFP (lithium difluorophosphate, LiPO2F2), and LiDFOP (lithium difluoro(bisoxalato)phosphate), and more specifically may include LiDFP.

[0107] The nitrogen-containing heterocyclic compound additive may specifically include at least one compound selected from the group consisting of compounds represented by the following chemical formulas 1-1, 1-2, and 1-3, and more specifically, may include a compound represented by the following chemical formula 1-1.

[0108] [ka]

[0109] [ka]

[0110] [ka]

[0111] In Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, R1 is an alkylene group having 1 to 3 carbon atoms; R2, R3, and R4 are each independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, and —CN; h is an integer of 0 to 3; i is an integer of 0 to 3; and j is an integer of 0 to 4.

[0112] Specifically, in Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, R1 may be an alkylene group having 1 to 3 carbon atoms, more specifically, a methylene group (—CH2—). Furthermore, in Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, R2, R3, and R4 may each be hydrogen, and h, i, and j may each be 0.

[0113] More specifically, the nitrogen-containing heterocyclic compound additive may include a compound represented by the following formula 1-1-A:

[0114] [ka]

[0115] Specifically, the cyclic sulfur compound additive may include at least one compound selected from the group consisting of compounds represented by the following chemical formulas 2-1 to 2-17, and specifically, may include a compound represented by the following chemical formula 2-1.

[0116]

change

[0117]

change

[0118]

change

[0119]

change

[0120]

change

[0121]

change

[0122]

change

[0123]

change

[0124]

change

[0125]

change

[0126]

change

[0127] [ka]

[0128] [ka]

[0129] [ka]

[0130] [ka]

[0131] [ka]

[0132] [ka]

[0133] Specifically, the propargyl group-containing cyclic carbonate additive may include a compound represented by the following Chemical Formula 3:

[0134] [ka]

[0135] In the above chemical formula 3, R5 is an alkylene group having 1 to 5 carbon atoms, and R6 is an alkyl group having 1 to 5 carbon atoms.

[0136] More specifically, the propargyl group-containing cyclic carbonate additive may include a compound represented by the following formula 3-1:

[0137] [ka]

[0138] The second additive may be included in the non-aqueous electrolyte in an amount of 0.01 wt % to 10 wt %, specifically 0.05 wt % to 7 wt %, more specifically 0.1 wt % to 5 wt %, and even more specifically 0.3 wt % to 2 wt %. When the content of the second additive satisfies the above range, a stable and strong positive electrode film can be formed, and the life performance and storage performance of the lithium secondary battery during high-voltage operation can be improved to a more excellent level.

[0139] The weight ratio of the first additive to the second additive may be 5:95 to 95:5, specifically 10:90 to 92:8, and more specifically 30:70 to 70:30. When the weight ratio is as described above, the effects of using the first additive and the second additive in combination are achieved in a balanced manner, and as a result, the effects of improving the high-temperature life performance and high-temperature storage performance of the lithium secondary battery can be more preferably exhibited.

[0140] The additive may further include an additional additive in addition to the first additive, or the first and second additives. The additional additive may be included in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing and causing the negative electrode to collapse in a high-power environment, or to improve low-temperature high-rate discharge characteristics, high-temperature stability, prevent overcharge, and suppress battery expansion at high temperatures.

[0141] Specifically, the additional additive may be at least one selected from the group consisting of fluoroethylene carbonate, succinonitrile, adiponitrile, TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (Tris(trimethylsilyl)Phosphite).

[0142] The additional additive may be included in the non-aqueous electrolyte in an amount of 0.1 wt % to 15 wt %.

[0143] The driving voltage of the lithium secondary battery of the present invention may be 4.3 V or higher, specifically 4.35 V or higher, and more specifically 4.4 V or higher. The lithium secondary battery of the present invention can achieve excellent energy density and improved life and storage performance at a high driving voltage by combining the above-mentioned positive electrode and non-aqueous electrolyte.

[0144] 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.

[0145] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0146] Examples and Comparative Examples Example 1 (Production of non-aqueous electrolyte) The organic solvent used was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 20:80.

[0147] A non-aqueous electrolyte was prepared by adding LiPF6 as a lithium salt and vinyl ethylene carbonate (VEC) as a first additive to the organic solvent.

[0148] The LiPF6 was contained in the non-aqueous electrolyte at a molar concentration of 1.2M.

[0149] The vinyl ethylene carbonate (VEC) was contained in the non-aqueous electrolyte at 0.5 wt %.

[0150] (Lithium secondary battery manufacturing) Cathode active material (Li[Ni 0.60 Co 0.05Mn 0.35 ]O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to a solvent, N-methyl-2-pyrrolidone (NMP), in a weight ratio of 97.74:0.70:1.56 to prepare a positive electrode slurry (solid content 75.5 wt%). The positive electrode slurry was applied to one side of a 15 μm-thick positive electrode current collector (Al thin film), dried, and roll-pressed to form a positive electrode active material layer (thickness: 136.6 μm), which served as the positive electrode. The positive electrode active material was in the form of single particles or pseudo-single particles.

[0151] A negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) were mixed in a weight ratio of 96.15:1.55:2.30 with distilled water as a solvent to prepare a negative electrode slurry (solid content (wt%)). The negative electrode slurry was applied to one side of a 15 μm-thick negative electrode current collector (Cu thin film), dried, and roll-pressed to form a negative electrode active material layer (thickness: 179.8 μm), which served as the negative electrode.

[0152] 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.

[0153] Example 2 A lithium secondary battery was produced in the same manner as in Example 1, except that 0.5 wt % of LiDFP based on the weight of the non-aqueous electrolyte was further added to the non-aqueous electrolyte as a second additive.

[0154] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 2-1 was further added to the non-aqueous electrolyte as a second additive in an amount of 0.5 wt % based on the weight of the non-aqueous electrolyte.

[0155] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-1-A was further added as a second additive to the non-aqueous electrolyte in an amount of 0.5 wt % based on the weight of the non-aqueous electrolyte.

[0156] Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 3-1 was further added to the non-aqueous electrolyte as a second additive in an amount of 0.5 wt % based on the weight of the non-aqueous electrolyte.

[0157] Example 6 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by 1-1-A and the compound represented by Chemical Formula 3-1 were further added to the non-aqueous electrolyte in amounts of 0.5 wt % and 0.5 wt %, respectively, based on the weight of the non-aqueous electrolyte, as second additives.

[0158] Comparative Example 1 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the first additive was not added.

[0159] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that vinylene carbonate (VC) was added to the non-aqueous electrolyte at a content of 0.5 wt % instead of vinylethylene carbonate as the first additive.

[0160] [Table 1]

[0161] Experimental example Experimental example 1: Evaluation of high-temperature cycle performance The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 manufactured as described above were charged to 4.4 V, 0.05 C under CC / CV conditions at 45°C and 0.33 C, and then discharged to 2.5 V under CC conditions at 0.33 C using an electrochemical charger / discharger, and 300 charge / discharge cycles were carried out.

[0162] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 2 below.

[0163] Capacity retention rate (%) = {(discharge capacity after 300 cycles / discharge capacity after 1 cycle)} × 100

[0164] (2) Resistance increase rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device, and after adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0165] After 300 cycles of charge and discharge, the resistance after 300 cycles was calculated in the same manner as above, and the resistance increase rate was calculated using the following formula. The results are shown in Table 2 below.

[0166] Resistance increase rate (%) = (resistance after 300 cycles - initial resistance) / initial resistance x 100

[0167] [Table 2]

[0168] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 6, which are lithium secondary batteries combining a positive electrode containing a lithium transition metal oxide represented by Chemical Formula A and a non-aqueous electrolyte containing the first additive (VEC) as an additive, have a higher capacity retention rate and a lower resistance increase rate during high-temperature cycle charge / discharge compared to Comparative Examples 1 and 2.

[0169] Experimental example 2: Evaluation of high-temperature storage performance The lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 prepared above were initially charged at 25° C. under CC / CV conditions at 0.33 C to 4.4 V at 0.05 C, and then discharged at CC at 0.33 C to 2.5 V. Subsequently, they were charged at 25° C. under CC / CV conditions at 0.33 C to 4.4 V at 0.05 C, and then stored at 60° C. for 12 weeks.

[0170] (1) Capacity maintenance rate After 12 weeks of storage, the lithium secondary battery was charged at 25° C. under CC / CV, 0.33 C conditions to 4.4 V, 0.05 C, and then discharged at CC, 0.33 C to 2.5 V, and the discharge capacity was measured.

[0171] The capacity retention rate was evaluated using the following formula, and the results are shown in Table 3 below.

[0172] Capacity retention rate (%) = (discharge capacity after 12 weeks of storage / initial discharge capacity) x 100

[0173] (2) Resistance increase rate After the initial charge and discharge, the capacity was confirmed at room temperature, and then the battery was charged to 50% SOC based on the discharge capacity and discharged at a current of 2.5 C for 10 seconds. The resistance was measured from the difference in voltage drop at this time and recorded as the initial resistance. After storing at 60°C for 12 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 3 below.

[0174] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) x 100

[0175] [Table 3]

[0176] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 6, which are lithium secondary batteries combining a positive electrode containing a lithium transition metal oxide represented by Chemical Formula A and a non-aqueous electrolyte containing the first additive (VEC) as an additive, have a higher capacity retention rate and a lower resistance increase rate during high-temperature storage compared to Comparative Examples 1 and 2.

[0177] Reference example A Reference Example 1A (1) Production of non-aqueous electrolyte A non-aqueous electrolyte was produced in the same manner as in Example 1.

[0178] (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), dried, and roll-pressed to prepare a cathode. The cathode active material was in the form of secondary particles formed by the aggregation of numerous primary particles.

[0179] 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.

[0180] 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.

[0181] Reference example 2A A lithium secondary battery was manufactured in the same manner as in Reference Example 1A, except that the nonaqueous electrolyte prepared in Comparative Example 1 was used instead of the nonaqueous electrolyte prepared in Example 1.

[0182] Reference example 3A A lithium secondary battery was manufactured in the same manner as in Reference Example 1A, except that the nonaqueous electrolyte prepared in Comparative Example 2 was used instead of the nonaqueous electrolyte prepared in Example 1.

[0183] Reference Experiment A The lithium secondary batteries of Reference Examples 1A to 3A manufactured above were charged to 4.2 V, 1 / 40 C under CC / CV, 0.33 C conditions at 45°C using an electrochemical charger / discharger, and then discharged to 2.5 V under CC, 0.33 C conditions, with one cycle being defined as 300 charge / discharge cycles.

[0184] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 4 below.

[0185] Capacity retention rate (%) = {(discharge capacity after 300 cycles / discharge capacity after 1 cycle)} × 100

[0186] (2) Resistance increase rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device, and after adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0187] After 300 cycles of charge and discharge, the resistance after 300 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 4 below.

[0188] Resistance increase rate (%) = (resistance after 300 cycles - initial resistance) / initial resistance x 100

[0189] [Table 4]

[0190] Referring to Table 4, it can be seen that the lithium secondary battery of Reference Example 1A, although using vinyl ethylene carbonate as a non-aqueous electrolyte additive, shows no improvement in performance compared to Reference Examples 2A and 3A. That is, the positive electrode active material used was a high nickel lithium transition metal oxide (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.03 Reference Examples 1A to 3A, which used O2), were operated at a relatively low voltage (4.2 V), and because vinyl ethylene carbonate was mainly decomposed at the negative electrode to form a coating, it was found that it was difficult to prevent electrolyte side reactions at the positive electrode even when vinyl ethylene carbonate was used as a non-aqueous electrolyte additive. In particular, a comparison of the performance of Reference Examples 1A with Reference Examples 2A and 3A shows that in the lithium secondary battery of Reference Example 1A, the vinyl ethylene carbonate used as a non-aqueous electrolyte additive acts as a resistor.

[0191] Reference example B Reference example 1B (1) Production of non-aqueous electrolyte A non-aqueous electrolyte was produced in the same manner as in Example 1.

[0192] (2) Manufacture of lithium secondary batteries Cathode active material (LiNi 0.6 Co 0.2 Mn 0.2 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), dried, and roll-pressed to prepare a cathode. The cathode active material was in the form of secondary particles formed by the aggregation of numerous primary particles.

[0193] 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.

[0194] 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.

[0195] Reference example 2B A lithium secondary battery was manufactured in the same manner as in Reference Example 1B, except that the nonaqueous electrolyte prepared in Comparative Example 1 was used instead of the nonaqueous electrolyte prepared in Example 1.

[0196] Reference example 3B A lithium secondary battery was manufactured in the same manner as in Reference Example 1B, except that the nonaqueous electrolyte prepared in Comparative Example 2 was used instead of the nonaqueous electrolyte prepared in Example 1.

[0197] Reference Experiment B The lithium secondary batteries of Reference Examples 1B to 3B manufactured above were charged to 4.2 V, 1 / 40 C under CC / CV, 0.33 C conditions at 45°C using an electrochemical charger / discharger, and then discharged to 2.5 V under CC, 0.33 C conditions, with 300 charge / discharge cycles being considered as one cycle.

[0198] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 5 below.

[0199] Capacity retention rate (%) = {(discharge capacity after 300 cycles / discharge capacity after 1 cycle)} × 100

[0200] (2) Resistance increase rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device, and after adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0201] After 300 cycles of charge and discharge, the resistance after 300 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 5 below.

[0202] Resistance increase rate (%) = (resistance after 300 cycles - initial resistance) / initial resistance x 100

[0203] [Table 5]

[0204] Referring to Table 5, it can be seen that the lithium secondary battery of Reference Example 1B, although using vinyl ethylene carbonate as a non-aqueous electrolyte additive, exhibits a lower effect than Reference Examples 2B and 3B. That is, the positive electrode active material used was a high nickel lithium transition metal oxide (LiNi 0.6 Co 0.2 Mn 0.2 Reference Examples 1B to 3B, which used O2), were driven at a relatively low voltage (4.2 V), and because vinyl ethylene carbonate decomposed mainly at the negative electrode to form a coating, it was found that it was difficult to prevent electrolyte side reactions at the positive electrode even when vinyl ethylene carbonate was used as a non-aqueous electrolyte additive. In particular, the lithium secondary battery of Reference Example 1B had a lower capacity retention rate and increased resistance compared to Reference Example 2B, which did not use vinyl ethylene carbonate, and Reference Example 3B, which used vinylene carbonate instead of vinyl ethylene carbonate.

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 includes 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 additives include a first additive; The lithium secondary battery, wherein the first additive comprises vinyl ethylene carbonate. [Chemical formula A] Li １＋ｘ [Ni ａ Co ｂ Mn ｃ M １ ｄ ]O ２＋ｗ (In the 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, and 0≦w≦1; 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. 2. The lithium secondary battery according to claim 1, wherein the first additive is contained in the non-aqueous electrolyte in an amount of 0.1% by weight to 10% by weight.

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

4. The lithium salt additive is LiBF ４ , LiBOB (lithium bis(oxalato)borate): LiB(C ２ O ４ ) ２ ), LiODFB (lithium difluoro(oxalato)borate: LiF ２ OB), LiDFP (lithium difluorophosphate: LiPO ２ F ２ 4. The lithium secondary battery according to claim 3, comprising at least one selected from the group consisting of lithium difluorobis(oxalate)phosphate (LiDFOP) and lithium difluorobis(oxalate)phosphate (LiDFOP).

5. The nitrogen-containing heterocyclic compound additive comprises at least one compound selected from the group consisting of compounds represented by the following Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3. The lithium secondary battery according to claim 3. 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 (In the above Chemical Formula 1-1, Chemical Formula 1-2, and Chemical Formula 1-3, R １ is an alkylene group having 1 to 3 carbon atoms, and R ２ , R ３ , and R ４ are each independently selected from hydrogen, an alkyl group having 1 to 3 carbon atoms, and —CN, h is an integer of 0 to 3, i is an integer of 0 to 3, and j is an integer of 0 to 4.

6. 4. The lithium secondary battery according to claim 3, wherein the nitrogen-containing heterocyclic compound additive comprises a compound represented by the following chemical formula 1-1-A: 【Chemistry 4】

7. 4. The lithium secondary battery according to claim 3, wherein the cyclic sulfur compound additive comprises at least one compound selected from the group consisting of compounds represented by the following chemical formulas 2-1 to 2-17: 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】 【Chemistry 15】 【Chemistry 16】 【Chemistry 17】 [Chemistry 18] 【Chemistry 19】 【Chemistry 20】 【Chemistry 21】

8. The lithium secondary battery according to claim 3 , wherein the propargyl group-containing cyclic carbonate additive comprises a compound represented by the following Chemical Formula 3: 【Chemistry 22】 (In the above chemical formula 3, R ５ is an alkylene group having 1 to 5 carbon atoms, and R ６ is an alkyl group having 1 to 5 carbon atoms.

9. 4. The lithium secondary battery according to claim 3, wherein the propargyl group-containing cyclic carbonate additive comprises a compound represented by the following Chemical Formula 3-1: 【Chemistry 23】

10. 4. The lithium secondary battery according to claim 3, wherein the second additive is contained in the non-aqueous electrolyte in an amount of 0.1% by weight to 3% by weight.

11. 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:

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

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

14. The lithium secondary battery according to claim 1 or 2, wherein the positive electrode active material is in the form of a single particle consisting of one single nodule or a pseudo-single particle which is a composite of 30 or less nodules.

15. 3. The lithium secondary battery according to claim 1, wherein in said chemical formula A, a / (b×c) is 18 to 50.

Images