Lithium secondary batteries

Abstract

This invention relates to a lithium secondary battery with improved high-temperature cycling performance, specifically to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises lithium iron phosphate oxide as the positive electrode active material, and the positive electrode loading is 32 mg / cm³. 2 Up to 60 mg / cm 2 The electrolyte comprises a lithium salt, a first organic solvent, a second organic solvent, a first additive, and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate organic solvent, the first additive is lithium nitrate (LiNO3), and the second additive is an imidazole compound.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0167270, filed with the Korean Intellectual Property Office on November 27, 2023, and Korean Patent Application No. 10-2024-0165718, filed with the Korean Intellectual Property Office on November 19, 2024, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] This invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery with improved high-temperature cycle performance. Background Technology

[0004] In recent years, lithium-ion batteries have been used in many applications and portable electronic devices such as mobile phones, personal digital assistants (PDAs), and laptops. In particular, due to increasing concerns about environmental issues, researchers have been actively exploring lithium-ion batteries with high energy density and high discharge voltage as a power source for electric vehicles, which could replace cars using fossil fuels (such as gasoline and diesel vehicles). Fossil fuels are one of the main causes of air pollution, and some of these lithium-ion batteries are already in the commercialization stage.

[0005] Meanwhile, in order to use lithium-ion batteries as a power source for electric vehicles, it is necessary to maintain high output stably under high temperature and high voltage. For this reason, carbon materials, lithium metal, sulfur compounds, silicon compounds, tin compounds, etc. are being considered as the main components of negative electrode active materials in lithium-ion batteries, while lithium-containing cobalt oxide (LiCoO2) or lithium nickel-based oxides are mainly used as positive electrode active materials.

[0006] However, for lithium-containing cobalt oxides, energy density and output characteristics have reached practical limits, especially in high-energy-density applications. The structural instability of lithium-containing cobalt oxides can lead to structural deformation under high-temperature charging conditions, releasing oxygen and causing an exothermic reaction with the electrolyte in the battery, potentially leading to secondary battery explosions. For lithium nickel-based oxides, their output drops rapidly in the low SOC range (e.g., below 30%), thus significantly limiting the usable SOC range. Therefore, the application of nickel-based lithium transition metal oxides is restricted in areas where output characteristics are particularly important (e.g., electric vehicles). In particular, lithium nickel-based oxides have low structural stability; therefore, if exposed to high temperatures or high voltages, the transition metal in the positive electrode active material can be leached or undergo side reactions with the electrolyte, resulting in a rapid decline in battery performance.

[0007] Recently, in order to solve the above problems, a method has been studied to replace lithium nickel-based oxides with lithium iron phosphate oxides with olivine structure that have excellent high-temperature stability.

[0008] However, the theoretical capacity of the olivine-structured lithium iron phosphate oxide is lower than that of commonly used lithium nickel-based oxides. Therefore, when designing electrodes under the same conditions, it has the disadvantage of relatively low energy density compared to lithium nickel-based oxides.

[0009] To address the aforementioned issues, in recent years, high-load electrodes have been explored when applying lithium iron phosphate oxide, which increases the amount of electrode active material coated per unit area (load).

[0010] However, high-load electrodes are designed to increase the application of active materials and improve electrode density, resulting in significant electrode compression. This leads to insufficient internal porosity and a decrease in electrolyte impregnation. As mentioned above, decreased electrolyte impregnation reduces charge transfer (the reaction between lithium ions and electrons), which can increase battery resistance.

[0011] Therefore, there is a need to develop a new secondary battery structure that can improve electrolyte impregnation and charge transfer performance when manufacturing secondary batteries with high-load electrodes. Summary of the Invention

[0012] [Technical Issues]

[0013] To address the aforementioned problems, the present invention provides a lithium secondary battery that, when using a high-load positive electrode, incorporates an electrolyte with enhanced impregnation performance due to its specific composition. This allows for the formation of a stable film on the electrode surface, thereby increasing charge transfer. Consequently, it suppresses resistance increases during high-temperature storage and ensures excellent cycle capacity retention.

[0014] [Technical Solution]

[0015] This invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises lithium iron phosphate oxide as the positive electrode active material, and the positive electrode loading is 32 mg / cm³. 2 Up to 60 mg / cm 2 The electrolyte comprises a lithium salt, a first organic solvent, a second organic solvent, a first additive, and a second additive, wherein the first organic solvent is a cyclic lactone compound, the second organic solvent is a carbonate organic solvent, the first additive is lithium nitrate (LiNO3), and the second additive is an imidazole compound.

[0016] [2] In the above [1], the present invention provides a lithium secondary battery, wherein the lithium iron phosphate oxide includes the compound shown in Formula 1.

[0017] [Formula 1]

[0018] Li 1+a Fe x M y (PO 4-b )X' b

[0019] In Equation 1 above, M is any element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, or Y, and X' is one or more elements selected from F, S, or N, where -0.5 ≤ a ≤ 0.5, 0 <x≤1、0≤y≤1、0≤b≤0.3。

[0020] [3] In [1] or [2] above, the present invention provides a lithium secondary battery, wherein the lithium iron phosphate oxide is lithium iron phosphate (LiFePO4) or lithium manganese iron phosphate (LiFeMnPO4).

[0021] [4] In at least one of [1] to [3] above, the present invention provides a lithium secondary battery, wherein the positive electrode further comprises a lithium nickel cobalt manganese oxide represented by the following formula 2: [Equation 2] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2 In Equation 2 above, M 1 M is Mn, Al, or a combination thereof, M 2 It is selected from any one of the groups consisting of Al, Zr, W, Ti, Mg, Ca, or Sr, and 0 ≤ a1 ≤ 0.5 or 0.55. <x1<1.0、0<y1≤0.4、0<z≤0.4、0≤w≤0.1。

[0022] [5] In at least one of [1] to [4] above, the present invention provides a lithium secondary battery, wherein the lithium nickel cobalt manganese oxide is selected from Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.7 Mn 0.2 Co 0.1 O2, Li(Ni) 0.8 Mn 0.1 Co 0.1O2, Li(Ni) 0.8 Co 0.15 Al 0.05 O2, Li(Ni) 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 or Li(Ni) 0.90 Mn 0.05 Co 0.05 Any one of the groups consisting of O2.

[0023] [6] In at least one of [1] to [5] above, the present invention provides a lithium secondary battery, wherein the weight ratio of the lithium iron phosphate oxide to the lithium nickel cobalt manganese oxide is 30:70 to 80:20.

[0024] [7] In at least one of [1] to [6] above, the present invention provides a lithium secondary battery, wherein the positive electrode has a loading of 40 mg / cm³. 2 Up to 60 mg / cm 2 .

[0025] [8] In at least one of [1] to [7] above, the present invention provides a lithium secondary battery, wherein the cyclic lactone compound comprises γ-butyrolactone.

[0026] [9] In at least one of [1] to [6] above, the present invention provides a lithium secondary battery, wherein the carbonate organic solvent is a cyclic carbonate organic solvent.

[0027]

[10] In at least one of [1] to [9] above, the present invention provides a lithium secondary battery, wherein the volume ratio of the first organic solvent to the second organic solvent is 50:50 to 99:1.

[0028]

[11] In at least one of [1] to

[10] above, the present invention provides a lithium secondary battery, wherein the volume ratio of the first organic solvent to the second organic solvent is 80:20 to 99:1.

[0029]

[12] In at least one of [1] to

[11] above, the present invention provides a lithium secondary battery, wherein the content of the first additive is from 0.05% by weight to 3.0% by weight based on the total weight of the electrolyte.

[0030]

[13] In at least one of [1] to [2] above, the present invention provides a lithium secondary battery, wherein the imidazole compound is a compound represented by formula 3 below: [Formula 3] .

[0031] In Formula 3 above, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and R1 to R3 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN.

[0032]

[14] In at least one of [1] to [3] above, the present invention provides a lithium secondary battery, wherein the imidazole compound is a compound represented by the following formula 3A: [Formula 3A] .

[0033]

[15] In at least one of [1] to

[13] above, the present invention provides a lithium secondary battery, wherein the weight ratio of the first additive to the second additive is 1:0.05 to 1:2.

[0034]

[16] In at least one of [1] to

[15] above, the present invention provides a lithium secondary battery, wherein the negative electrode comprises a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material.

[0035] [Beneficial Effects]

[0036] The lithium secondary battery of the present invention improves the impregnation properties of the electrolyte on the high-load positive electrode by employing an organic solvent containing a cyclic lactone compound as the main solvent and an electrolyte containing lithium nitrate (LiNO3) and imidazole compounds as two additives. Simultaneously, it improves the charge transfer performance of the high-load positive electrode surface by forming a low-resistivity film on the surface. Therefore, the lithium secondary battery of the present invention has improved cycle performance and high-temperature storage performance. Detailed Implementation

[0037] It should be understood that the terms or words used in this specification and claims are for describing exemplary embodiments only and should not be construed as having the meanings defined in common dictionaries. Rather, they should be construed as having meanings and concepts consistent with the technical ideas of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best interpret the invention.

[0038] For example, in this specification, it should be understood that the terms “comprising,” “including,” or “having” are intended to specify the presence of the said features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0039] Furthermore, it should be understood in this specification that in the description of "a to b carbon atoms" herein, "a" and "b" each refer to the number of carbon atoms contained in a specific functional group. That is, a functional group may include carbon atoms in the range of "a" to "b". For example, "alkylene with 1 to 5 carbon atoms" refers to an alkylene containing 1 to 5 carbon atoms, namely -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH2)CH-, -CH2CH2CH2CH2CH2-, -CH(CH2)CH2CH2-, etc.

[0040] Additionally, in this specification, the term "alkylene" refers to a branched or unbranched aliphatic hydrocarbon group, or a functional group in which each of the two carbon atoms of an aliphatic hydrocarbon group lacks a hydrogen atom. In one embodiment, the alkylene group may be substituted or unsubstituted. In another embodiment, the alkylene group includes, but is not limited to, methylene, ethylene, propylene, isopropylene, butylene, isobutylene, tert-butylene, pentylene, 3-pentylene, etc., each of which may optionally have substituents.

[0041] In addition, unless otherwise defined, “substitution” in this specification means that at least one hydrogen atom bonded to carbon is replaced by another element (e.g., fluorine).

[0042] Additionally, in this specification, "loading" refers to the amount of active material per unit area obtained by measuring the positive electrode active material layer containing olivine structure lithium iron phosphate oxide formed on the current collector, expressed in "mg / cm²". 2 This indicates that "load capacity" in this specification refers to the sum of the load capacity on both sides of the positive electrode.

[0043] The invention will be described in detail below.

[0044] The lithium secondary battery of the present invention includes at least one of the configurations disclosed below, and may include any combination of technically feasible configurations of the above configurations.

[0045] Lithium secondary batteries

[0046] This invention relates to a lithium secondary battery.

[0047] Specifically, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte.

[0048] The positive electrode may contain lithium iron phosphate oxide as the positive electrode active material.

[0049] The loading capacity of the positive electrode can be from 32 mg / cm² to 60 mg / cm².

[0050] Electrolytes may include lithium salts, a first organic solvent, a second organic solvent, a first additive, and a second additive.

[0051] The first organic solvent may include cyclic lactone compounds; The second organic solvent may include carbonate organic solvents; The first additive may include lithium nitrate (LiNO3).

[0052] The second additive may include imidazole compounds.

[0053] (1) Positive electrode

[0054] The positive electrode of the present invention may contain lithium iron phosphate oxide as the positive electrode active material. Specifically, the lithium iron phosphate oxide may include compounds represented by Formula 1 below.

[0055] [Formula 1]

[0056] Li 1+a Fe x M y (PO 4-b )X' b

[0057] In the above [Equation 1], M is any one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, or Y, and X' is one or more elements selected from F, S, or N, and -0.5 ≤ a ≤ 0.5, 0 <x≤1、0≤y≤1、0≤b≤0.3。

[0058] The lithium iron phosphate oxide represented by Formula 1 above may include lithium iron phosphate (LiFePO4, LFP) or lithium manganese iron phosphate (LiFeMnPO4, LFMP) as representative examples.

[0059] The lithium iron phosphate oxide represented by Equation 1 above can be produced using primary particles of nanoscale size to achieve high lithium-ion input and output, or using secondary particles made by assembling these primary particles into aggregates of primary particles. For example, if primary particles are used as lithium iron phosphate oxide with an olivine structure, the particle size can be from 50 nm to 2000 nm, more specifically from 200 nm to 1100 nm. Furthermore, if these primary particles are assembled into secondary particles as aggregates of primary particles, the average particle size (D) of the secondary particles is... 50 The diameter can range from 0.5 μm to 30 μm.

[0060] The surface of the lithium iron phosphate oxide represented by Equation 1 above can be coated with an amorphous layer of carbon or metal oxide. In this case, since the amorphous layer of carbon or metal oxide covering the surface is not crystalline, lithium ions can penetrate the amorphous layer of the shell and intercalate and deintercalate within the lithium iron phosphate core. The amorphous layer of carbon or metal oxide coating has excellent electronic conductivity and can transport lithium ions; therefore, it can also act as a current path to the active material, the lithium iron phosphate core, thereby enabling high-rate charge and discharge. Furthermore, coating the surface of the lithium iron phosphate oxide with an amorphous layer of carbon or metal oxide can control unnecessary reactions between the core material and the electrolyte, thereby further improving safety.

[0061] Furthermore, despite the volume changes caused by charging / discharging, the lithium iron phosphate oxide represented by Equation 1 above can also ensure structural and thermal stability because phosphorus and oxygen have strong covalent bonds within the PO4 tetrahedral structure. However, the lithium iron phosphate oxide represented by Equation 1 above has a strongly densely packed oxygen structure, which does not allow for smooth lithium-ion migration and electron flow, and therefore has the disadvantage of relatively low conductivity compared to nickel-based lithium transition metal oxides.

[0062] Therefore, in order to improve conductivity, the positive electrode may further include lithium nickel cobalt manganese oxide represented by Formula 2, which has high conductivity, together with lithium iron phosphate oxide.

[0063] [Equation 2]

[0064] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2

[0065] In Equation 2 above, M 1 M is Mn, Al, or a combination thereof, M 2 It is selected from any one of the groups consisting of Al, Zr, W, Ti, Mg, Ca, or Sr, and 0 ≤ a1 ≤ 0.5 or 0.55. <x1<1.0、0<y1≤0.4、0<z≤0.4、0≤w≤0.1。

[0066] In Equation 2 above, 1+a1 represents the molar ratio of lithium in the lithium nickel cobalt manganese oxide, where 0≤a1≤0.5, preferably 0≤a1≤0.2, and more preferably 0≤a1≤0.1. When the molar ratio of lithium meets the above range, the lithium nickel cobalt manganese oxide can have a stable layered crystal structure. If a1 is greater than 0.5, the initial discharge capacity of the battery may decrease, or the amount of Li byproducts on the surface of the positive electrode active material may increase, thus raising concerns that gas generation may become severe under high-temperature driving conditions.

[0067] x1 represents the molar ratio of nickel among all metals other than lithium in the lithium nickel cobalt manganese oxide, where x1 can satisfy 0.55 < x1 < 1.0, specifically 0.6 ≤ x1 ≤ 0.98, and more specifically 0.6 ≤ x1 ≤ 0.95. If x satisfies the above range, excellent capacity characteristics can be achieved.

[0068] y1 represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel cobalt manganese oxide, and y1 can satisfy 0 < y1 ≤ 0.4, specifically 0 < y1 ≤ 0.3, preferably 0.01 ≤ y1 ≤ 0.3.

[0069] z represents the molar ratio of element M among all metals other than lithium in the lithium nickel cobalt manganese oxide 1 and z can satisfy 0 < z ≤ 0.4, preferably 0 < z ≤ 0.3, and more preferably 0.01 ≤ z ≤ 0.3.

[0070] w represents the molar ratio of element M among all metals other than lithium in the lithium nickel cobalt manganese oxide 2 and w can satisfy 0 < w ≤ 0.1, preferably 0 < z ≤ 0.05.

[0071] The lithium nickel cobalt manganese oxide can be selected from Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 or any one of Li(Ni 0.90 Mn 0.05 Co 0.05 )O2.

[0072] If the lithium nickel cobalt manganese oxide is added to the positive electrode of the present invention, the weight ratio of the lithium iron phosphate oxide to the lithium nickel cobalt manganese oxide can be 30:70 to 80:20, specifically 50:50 to 80:20, or 60:40 to 70:30.

[0073] If the mixing ratio of the olivine-structured lithium iron phosphate oxide and the lithium nickel cobalt manganese oxide satisfies the above range, the high-temperature and high-voltage safety of the battery can be ensured, and the conductivity can be improved at the same time.

[0074] Specifically, if the ratio of olivine-structured lithium iron phosphate oxide to lithium nickel cobalt manganese oxide is less than 80 by weight, excellent capacity characteristics and conductivity can be ensured. If the ratio of olivine-structured lithium iron phosphate oxide to lithium nickel cobalt manganese oxide is greater than 30 by weight, high temperature and high voltage stability can be ensured.

[0075] Meanwhile, in this invention, in order to design an electrode with high capacity, the loading of the positive electrode, comprising lithium iron phosphorus oxide represented by Formula 1 and lithium nickel cobalt manganese oxide represented by Formula 2 as positive electrode active materials, can be 32 mg / cm³. 2 The above (cross-sectional reference load: 16 mg / cm) 2 (Above), specifically 32 mg / cm 2 Up to 60 mg / cm 2 More preferably 40 mg / cm 2 Up to 60 mg / cm 2 If the loading of the positive electrode meets the above range, high energy density and high capacity characteristics can be achieved.

[0076] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector. In this case, the positive electrode mixture layer may contain the aforementioned lithium iron phosphate oxide as the positive electrode active material.

[0077] Positive current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0078] Positive current collectors can form micro-irregular structures on their surface to improve the adhesion of the positive electrode active material. For example, positive current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0079] The positive electrode mixture layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode mixture layer may be disposed on one or both surfaces of the positive electrode current collector.

[0080] Furthermore, to ensure sufficient capacity, the amount of lithium iron phosphate oxide represented by Formula 1 above in the cathode mixture layer can be from 80% to 99% by weight.

[0081] In addition to the aforementioned positive electrode active material, the positive electrode mixture layer may also contain a binder and / or a conductive material.

[0082] The role of the adhesive is to improve the bonding force between the positive electrode active material particles and the adhesion force between the positive electrode active material and the current collector. Examples of adhesives may include fluoropolymer adhesives, including polyvinylidene fluoride (PVDF); rubber adhesives, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyvinyl alcohol adhesives, including polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; or silane adhesives, any one of which may be used alone, or a mixture of two or more of them may be used.

[0083] In the positive electrode mixture layer, the amount of binder may be from 0.1% to 15% by weight, preferably from 0.1% to 10% by weight.

[0084] Next, conductive materials are used to impart conductivity to the electrodes. Any conductive material can be used without particular restriction, as long as it is electronically conductive and does not cause chemical changes in the battery to be assembled. Specifically, conductive materials can include carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystalline structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powder, aluminum powder, or nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; polyphenylene derivatives, etc.

[0085] In the positive electrode mixture layer, the amount of conductive material added can be from 1% to 30% by weight.

[0086] The positive electrode can be manufactured by coating a positive electrode slurry onto a positive electrode current collector, the positive electrode slurry comprising a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry, followed by drying and rolling the positive electrode slurry. Alternatively, the positive electrode can be manufactured by preparing a membrane by mixing the positive electrode active material and optionally a binder, a conductive material, etc., and then laminating the membrane onto the positive electrode current collector.

[0087] The solvent for forming the positive electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, or isopropanol. Specifically, N-methylpyrrolidone is preferred from the perspective of facilitating the dispersion of the positive electrode active material, binder, and / or conductive material.

[0088] (2) Negative electrode

[0089] Next, the negative electrode will be described.

[0090] The negative electrode may include a negative electrode active material.

[0091] As the negative electrode active material, a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material can be used.

[0092] As the carbon-based active material, various carbon-based active materials used in the art can be used, such as graphite-based materials, such as natural graphite, artificial graphite, Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitch, high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch, soft carbon, hard carbon, etc. The shape of the carbon-based active material is not particularly limited, and materials of various shapes such as irregular shapes, planar shapes, sheet-like shapes, spherical shapes, or fibrous shapes can be used.

[0093] Specifically, either natural graphite or artificial graphite can be used as the carbon-based active material, or natural graphite and artificial graphite can be used together to increase the adhesion to the current collector and inhibit the shedding of the active material.

[0094] In addition, the silicon-based active material may include, for example, one or more selected from the group consisting of: metallic silicon (Si), silicon oxide (SiO x , where 0 < x < 2), silicon carbide (SiC), or a Si-Y alloy (Y is an element selected from the group consisting of: alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, or a combination thereof, and is not Si). The element Y can be selected from the group consisting of: Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

[0095] From the perspective of ensuring the structural stability during charge and discharge processes and reducing side reactions with the electrolyte solution, the average particle size (D 50 ) of the silicon-based active material can be 1 μm to 30 μm, preferably 2 μm to 15 μm.

[0096] In addition, the negative electrode of the present invention may include at least one selected from a carbon-based active material and a silicon-based active material as the negative electrode active material. Specifically, the negative electrode of the present invention may include a carbon-based active material and a silicon-based active material.

[0097] At this point, the weight ratio of silicon-based active material to carbon-based active material can be from 1:99 to 30:70, specifically from 3:97 to 15:85. If the mixing ratio of silicon-based active material to carbon-based active material meets the above range, the volume expansion of silicon-based active material is suppressed while improving capacity performance, thereby ensuring excellent cycle performance.

[0098] The negative electrode may include a negative electrode current collector; and a negative electrode mixture layer disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be contained in the negative electrode mixture layer.

[0099] There are no particular limitations on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Specifically, as the negative electrode current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel that has been surface-treated with one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys, etc., can be used.

[0100] Negative current collectors can typically have a thickness ranging from 3 μm to 500 μm.

[0101] Negative electrode current collectors can form micro-irregular structures on their surface to improve the adhesion of the negative electrode active material. For example, negative electrode current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0102] The negative electrode mixture layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode mixture layer may be disposed on one or both surfaces of the negative electrode current collector.

[0103] From the perspective of minimizing the impact of volume expansion / contraction on the battery and ensuring that the secondary battery exhibits sufficient capacity, the content of negative electrode active material in the negative electrode mixture layer can be from 60% to 99% by weight.

[0104] In addition to the negative electrode active material, the negative electrode mixture layer may also include conductive materials and / or adhesives.

[0105] Conductive materials are components used to further improve the conductivity of the negative electrode active material, and there are no particular restrictions, as long as they are conductive and do not cause chemical changes within the battery. For example, carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black, can be used; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as fluorocarbon powder, aluminum powder, or nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; conductive materials such as polyphenylene derivatives, etc.

[0106] In the negative electrode mixture layer, the amount of conductive material present can be less than 10% by weight, preferably 5% by weight.

[0107] Adhesives are components that assist in bonding conductive materials, active materials, and current collectors. They can typically be fluoropolymer adhesives, such as polyvinylidene fluoride (PVDF); rubber adhesives, including styrene-butadiene rubber (SBR), nitrile rubber, or styrene-isoprene rubber; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyvinyl alcohol adhesives, including polyvinyl alcohol; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; silane adhesives, etc.

[0108] In the negative electrode mixture layer, the amount of binder may be from 0.1% to 15% by weight, preferably from 0.1% to 10% by weight.

[0109] The negative electrode can be manufactured by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and rolling the slurry. The negative electrode slurry includes a negative electrode active material and optionally a binder, a conductive material, and a solvent for forming the negative electrode slurry. Alternatively, a membrane can be prepared by mixing the negative electrode active material with optional binders, conductive materials, etc., and then the membrane can be laminated onto the negative electrode current collector to manufacture the negative electrode.

[0110] The solvent for forming the negative electrode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, or isopropanol, with distilled water being preferred from the perspective of facilitating the dispersion of the negative electrode active material, binder, and / or conductive material.

[0111] (3) Diaphragm

[0112] The separator separates the negative electrode from the positive electrode and provides a transport path for lithium ions. Any separator can be used without particular restrictions, as long as it is a separator commonly used in lithium secondary batteries. Separators with low resistance to ion migration in non-aqueous electrolytes and thus excellent non-aqueous electrolyte moisture retention are particularly preferred.

[0113] Specifically, as the diaphragm, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers, or those having a stacked structure with two or more layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated diaphragms comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0114] (4) Electrolytes

[0115] Next, the electrolyte of the present invention may include lithium salt, a first organic solvent, a second organic solvent, a first additive, and a second additive, and specific examples of each component are described below.

[0116] (4-1) Lithium salts

[0117] First, any lithium salt commonly used in electrolytes for lithium secondary batteries can be used as a lithium salt without limitation; for example, lithium salts may include Li. + As a cation, and may include any one selected from the group consisting of: F - Cl - ,Br - I - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - (CF3CF2SO2)2N - (CF3SO2)2N - (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - or SCN - .

[0118] Specifically, the lithium salt may include a single material or a mixture of two or more materials selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI) or LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), specifically, may include any one selected from the group consisting of: LiBF4, LiPF6, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2 (lithium bis(pentafluoroethanesulfonyl)imide, LiBETI) or LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI). In addition to the examples above, any lithium salt commonly used in electrolytes for lithium secondary batteries can be used without limitation.

[0119] Although appropriate variations can be made within the typical range of lithium salt usage, the concentration of lithium salt in the electrolyte solution can be from 0.8 M to 3.0 M, specifically from 1.0 M to 2.0 M, and preferably from 1.0 M to 1.8 M, in order to achieve the best effect of forming an anti-corrosion film on the electrode surface.

[0120] If the concentration of lithium salt is within the above range, the viscosity of the electrolyte can be controlled to achieve optimal impregnation and improve the migration performance of lithium ions, thereby improving the capacity and cycle performance of lithium secondary batteries.

[0121] (4-2) First organic solvent

[0122] Next, the first organic solvent will be described.

[0123] The first organic solvent may include cyclic lactone compounds; Cyclic lactones are compounds with high dielectric constant and high ionic conductivity, which can improve the charge transfer degradation caused by driving high-load electrodes.

[0124] Cyclic lactones can include γ-butyrolactone.

[0125] Based on the total weight of the electrolyte, the amount of the first organic solvent may be from 39% to 80% by weight, specifically from 48% to 80% by weight, more preferably from 52% to 70% by weight.

[0126] If the content of the first organic solvent of the present invention meets the above range, the migration performance of lithium ions can be improved, thereby achieving the effect of reducing battery resistance.

[0127] (4-3) Second organic solvent

[0128] Next, the second organic solvent will be described.

[0129] The second organic solvent may include carbonate organic solvents to minimize decomposition caused by oxidation reactions during the charging / discharging of the secondary battery, and to work with the additives to achieve the desired performance.

[0130] Specifically, carbonate organic solvents preferably include any one selected from the group consisting of cyclic carbonate organic solvents having high ionic conductivity and high dielectric constant, and linear carbonate organic solvents having low viscosity and low dielectric constant, and may specifically include cyclic carbonate organic solvents.

[0131] The cyclic carbonate organic solvent can be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, vinylene carbonate, or fluoroethylene carbonate (FEC), or two or more of these organic solvents, wherein ethylene carbonate can maintain a stable SEI film passivation capability.

[0132] In addition, the linear carbonate organic solvent can be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate or ethyl propyl carbonate, or two or more of the above organic solvents, wherein the linear carbonate organic solvent can be dimethyl carbonate (DMC) with small molecular size or low viscosity characteristics.

[0133] When a cyclic carbonate organic solvent is used in combination with a linear carbonate organic solvent as a second organic solvent, in order to ensure low viscosity characteristics, the cyclic carbonate organic solvent and the linear carbonate organic solvent can be mixed in a volume ratio of about 1:99 to 50:50, or in a volume ratio of 20:80 to 40:60.

[0134] Meanwhile, in this invention, the volume ratio of the first organic solvent to the second organic solvent can be from 50:50 to 99:1, specifically from 70:30 to 99:1, and more specifically from 70:30 to 90:10.

[0135] If the mixing ratio of the first organic solvent to the second organic solvent meets the above-mentioned range, high ion migration performance can be achieved, and battery performance with low resistance characteristics can be ensured. That is, if the volume ratio of the first organic solvent is 50 or higher, the ion migration performance can be ensured, while if the volume ratio is 99 or lower, battery life performance can be improved by forming a stable film.

[0136] (4-4) First Additive

[0137] Next, the first additive will be described.

[0138] The first additive may include lithium nitrate (LiNO3).

[0139] In the activation step, lithium nitrate (LiNO3) included in the first additive can form an inorganic film containing lithium-nitrogen bonds and lithium-oxygen bonds on the negative electrode surface. Since this inorganic film increases the surface energy and acts as an ion carrier capable of uniformly transporting lithium ions, it can improve the electrode impregnation performance of the electrolyte and induce more efficient charge transfer reactions.

[0140] In addition, the lithium nitrate (LiNO3) contained in the first additive can form coordination bonds with transition metals dissolved from the positive electrode under high temperature conditions, or with Lewis acids produced by lithium salt decomposition products, thereby preventing transition metal ions from electrodepositing on the negative electrode surface, preventing reversible lithium loss, and thus reducing the degradation of cycle performance.

[0141] Meanwhile, the first additive may have a specific content in the electrolyte. Specifically, based on the total weight of the electrolyte, the amount of the first organic solvent may be from 0.05% by weight to 3.0% by weight, more specifically from 0.05% by weight to 2.0% by weight, more specifically from 0.1% by weight to 2.0% by weight, and preferably from 0.1% by weight to 1.5% by weight.

[0142] If the content of the first additive of the present invention meets the above-mentioned range, an inorganic film containing lithium-nitrogen bonds and lithium-oxygen bonds will be uniformly formed on the surface of the negative electrode, thus acting as an effective ion carrier rather than a resistor. That is, if the content of the first additive is 0.05% by weight or more, battery performance degradation can be prevented by suppressing the increase in battery resistance, while if the content of the first additive is 3.0% by weight or less, unnecessary activation gases can be prevented by suppressing side reactions, thereby preventing degradation of high-temperature cycling performance and high-temperature storage performance.

[0143] Furthermore, preferably, the content of the first additive and the loading of the positive electrode in the electrolyte satisfy the following relationship 1.

[0144] [Relation 1]

[0145] 0.0001 ≤ ≤0.050

[0146] In Equation 1 above, A represents the total amount of electrolyte injected into the lithium secondary battery (g), B represents the lithium nitrate (LiNO3) content (wt%) in the injected electrolyte, and C represents the positive electrode loading (g / cm³). 2 D is the total surface area of ​​the positive electrode current collector (cm²). 2 ).

[0147] If the content of the first additive in the electrolyte of the present invention satisfies the above-mentioned relationship, the impregnation of the electrolyte to the negative electrode can be improved, and an effective inorganic film that can improve ion migration performance can be formed, thereby ensuring excellent battery performance.

[0148] (4-5) Second additive

[0149] Next, the second additive will be explained.

[0150] In this invention, imidazole compounds may be included as a second additive.

[0151] Imidazole compounds may include compounds shown in Formula 3 below.

[0152] [Formula 3]

[0153] In Formula 3 above, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and R1 to R3 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN.

[0154] Specifically, in the compound shown in Formula 3 above, the non-covalent electron pairs of the nitrogen element contained in the structure can act as Lewis bases to remove Lewis acids such as HF and PF5, which are lithium salt decomposition products. Simultaneously, it can suppress the formation of Lewis acids by stabilizing the lithium salt anions. Therefore, the degradation of the film on the positive or negative electrode surface caused by Lewis acids can be suppressed, and further electrolyte decomposition caused by this can be prevented. As a result, the self-discharge of the secondary battery can be reduced, thereby improving high-temperature performance characteristics.

[0155] Furthermore, the compound represented by Formula 3 contains a propargyl functional group that is easily reduced on the surface of the negative electrode. Therefore, a SEI film with high passivation capability can be formed on the surface of the negative electrode to prevent additional reduction and decomposition reactions of the electrolyte solution due to the instability of the SEI film, and to improve the high-temperature durability of the negative electrode itself, thereby suppressing the self-discharge reaction of the negative electrode. In particular, the propargyl group contained in the compound represented by Formula 1 can be adsorbed onto the surface of metal impurities contained in the positive electrode to suppress the dissolution of impurities, thereby suppressing the deposition of metal ions on the surface of the negative electrode and thus preventing internal short circuits.

[0156] In Formula 3 above, R can be a substituted or unsubstituted alkylene group having 1 to 3 carbon atoms, specifically, it can be an unsubstituted alkylene group having 1 or 2 carbon atoms.

[0157] Additionally, in Formula 3 above, R1 can be hydrogen, an alkyl group having one carbon atom, or -CN, or it can be hydrogen, an alkyl group having one carbon atom, or -CN. Specifically, it can be hydrogen or -CN.

[0158] Additionally, in Formula 3 above, R2 can be hydrogen, an alkyl group having one carbon atom, or -CN, or it can be hydrogen, an alkyl group having one carbon atom, or -CN. Specifically, it can be hydrogen or -CN.

[0159] Additionally, in Formula 3 above, R3 can be hydrogen, an alkyl group having one carbon atom, or -CN, or it can be hydrogen, an alkyl group having one carbon atom, or -CN. Specifically, it can be hydrogen or -CN.

[0160] Preferably, the compound represented by Formula 3 above can be a compound represented by Formula 3A below.

[0161] [Formula 3A]

[0162] Meanwhile, in the electrolyte of the present invention, the weight ratio of the first additive to the second additive can be 1:0.05 to 1:2, 1:0.1 to 1:2, or more preferably 1:0.1 to 1:1.

[0163] If the composition ratio of the first additive to the second additive meets the above-mentioned range, a stable film can be formed on the surfaces of the positive and negative electrodes, thereby improving cycle performance and OCV during high-voltage driving and enhancing high-temperature storage performance. In other words, if the second additive is included in a weight ratio of less than 2, a uniform film can be formed on the negative electrode surface, preventing the film from acting as a resistor and delaying the decomposition reaction of the electrolyte itself. However, if the content of the second additive is slightly higher, the increased amount of second additive that is reduced and decomposed on the negative electrode surface leads to an increased film thickness, allowing the film to function as a resistor. Furthermore, the undecomposed second additive remaining after activation may degrade electrolyte performance.

[0164] (4-6) Other additives

[0165] Meanwhile, to prevent the electrolyte from decomposing under high-output conditions and causing negative electrode collapse, or to further improve low-temperature high-rate discharge performance, high-temperature stability, overcharge protection, and the effect of suppressing battery high-temperature expansion, the lithium secondary battery of the present invention may contain other additives in the electrolyte as needed. If other additives are included, these other additives may be referred to as third additives.

[0166] Representative examples of the other additives mentioned above include any additive selected from the group consisting of cyclic carbonates, sulfonyl lactones, phosphates / esters, borates / esters, nitriles, benzenes, amines, silanes, or lithium salts.

[0167] Cyclic carbonate compounds can be vinylene carbonate (VC).

[0168] Sulfolide compounds can be any one of the following groups: 1,3-propane sulfolide (PS), 1,4-butane sulfolide, ethylene sulfolide, 1,3-propene sulfolide (PRS), 1,4-butene sulfolide or 1-methyl-1,3-propene sulfolide.

[0169] The phosphate / ester compound may be one or more compounds selected from the group consisting of: lithium difluoro(bis(oxalate) phosphate), lithium difluorophosphate, tri(trimethylsilyl) phosphate, tri(2,2,2-trifluoroethyl) phosphate or tri(trifluoroethyl) phosphate.

[0170] The borates / esters can be tetraphenylborate or lithium oxaloyl difluoroborate.

[0171] Nitrile compounds can be any one of the following groups: butadionitrile, adiponitrile, acetonitrile, propionitrile, butadionitrile, valerate, octanoic acid, heptanonitrile, cyclovalerate, cyclohexanoic acid, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, or 4-fluorophenylacetonitrile.

[0172] Benzene compounds can be fluorobenzene, amine compounds can be triethanolamine, ethylenediamine, etc., and silane compounds can be tetravinylsilane.

[0173] Lithium salts are compounds that are different from the lithium salts contained in electrolytes, and can be one or more compounds selected from the group consisting of: LiPO2F2, LiODFB, lithium bis(oxalatoborate) (LiBOB, (LiB(C2O4)2)), LiBF4, or LiDFOP.

[0174] The other additives mentioned above can be used as a mixture of two or more of them. Based on the total weight of the electrolyte, their content can be less than 10% by weight, specifically from 0.01% by weight to 8.0% by weight, preferably from 0.05% by weight to 5.0% by weight. If the content of the other additives meets the above range, side reactions caused by unreacted additives can be suppressed, further improving the effects of improving the battery's low-temperature output, high-temperature storage characteristics, and high-temperature lifespan characteristics.

[0175] The lithium secondary battery of the present invention, as described above, can be effectively used in portable devices (e.g., mobile phones, laptops, and digital cameras), electric vehicles (e.g., hybrid electric vehicles (HEVs)), and other fields.

[0176] The shape of the lithium secondary battery of the present invention is not particularly limited, and it can be cylindrical, square, bag-shaped, coin-shaped, etc.

[0177] The lithium secondary battery of the present invention can be used in single cells as power sources for small devices, and is also preferably used as a cell in medium and large battery modules comprising multiple single cells.

[0178] The present invention will be described in detail below through embodiments. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to provide a more complete description of the invention to those skilled in the art.

[0179] Example

[0180] Example 1.

[0181] (Preparation of electrolytes)

[0182] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 0.05 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive was 1:2). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0183] (The manufacture of the positive electrode)

[0184] A positive electrode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1:3 to prepare a positive electrode active material slurry (67% by weight solids). The positive electrode active material slurry was coated onto a 15 μm thick positive electrode current collector (Al film), and then dried and rolled to form a positive electrode (double-sided loading: 48 mg / cm²). 2 Cross-sectional reference load: 24 mg / cm 2 ).

[0185] (Manufacturing of the negative electrode)

[0186] A negative electrode active material (artificial graphite), CMC-SBR as a binder, and carbon black as a conductive material were added to distilled water as a solvent in a weight ratio of 96:3.5:0.5 to prepare a negative electrode active material slurry (solid content 53% by weight). The negative electrode active material slurry was coated onto a negative electrode current collector (Cu film) with a thickness of 8 μm, and then dried and rolled to form a negative electrode.

[0187] (Manufacturing of secondary batteries)

[0188] The positive and negative electrodes prepared according to the above method are stacked sequentially with a polyethylene porous membrane to prepare an electrode assembly according to conventional methods. The electrode assembly is then housed in a pouch-type secondary battery case, and the lithium secondary battery prepared above is injected into the case with electrolyte to manufacture a lithium secondary battery.

[0189] Example 2.

[0190] (Preparation of electrolytes)

[0191] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 0.1 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive was 1:1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0192] (Manufacturing of secondary batteries)

[0193] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0194] Example 3.

[0195] (Preparation of electrolytes)

[0196] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.5 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.15 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0197] (Manufacturing of secondary batteries)

[0198] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0199] Example 4.

[0200] (Preparation of electrolytes)

[0201] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 3.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.15 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.05). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0202] (Manufacturing of secondary batteries)

[0203] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0204] Example 5.

[0205] (Preparation of electrolytes)

[0206] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0207] (Manufacturing of secondary batteries)

[0208] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0209] Example 6.

[0210] (Preparation of electrolytes)

[0211] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.2 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.2). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0212] (Manufacturing of secondary batteries)

[0213] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0214] Example 7.

[0215] (Preparation of electrolytes)

[0216] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 99:1. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte of the present invention for lithium secondary batteries.

[0217] (Manufacturing of secondary batteries)

[0218] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0219] Example 8.

[0220] (Preparation of electrolytes)

[0221] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 50:50. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0222] (Manufacturing of secondary batteries)

[0223] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0224] Example 9.

[0225] (Preparation of electrolytes)

[0226] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 4.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.4 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0227] (Manufacturing of secondary batteries)

[0228] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0229] Example 10.

[0230] (Preparation of electrolytes)

[0231] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 3.0 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive was 1:3). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0232] (Manufacturing of secondary batteries)

[0233] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0234] Example 11.

[0235] (Preparation of electrolytes)

[0236] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 40:60. Then, 0.1 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive was 1:1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare the electrolyte for lithium secondary batteries of the present invention.

[0237] (Manufacturing of secondary batteries)

[0238] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0239] Example 12.

[0240] (The manufacture of the positive electrode)

[0241] A positive electrode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1:3 to prepare a positive electrode active material slurry (67% by weight solids). The positive electrode active material slurry was coated onto a 15 μm thick positive electrode current collector (Al film), and then dried and rolled to form a positive electrode (double-sided loading: 32 mg / cm²). 2 Cross-sectional reference load: 16 mg / cm 2 ).

[0242] (Manufacturing of secondary batteries)

[0243] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0244] Example 13.

[0245] (The manufacture of the positive electrode)

[0246] A positive electrode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1:3 to prepare a positive electrode active material slurry (67% by weight solids). The positive electrode active material slurry was coated onto a 15 μm thick positive electrode current collector (Al film), and then dried and rolled to form a positive electrode (double-sided loading: 60 mg / cm²). 2 Cross-sectional reference load: 30 mg / cm 2 ).

[0247] (Manufacturing of secondary batteries)

[0248] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0249] Comparative Example 1.

[0250] (Preparation of electrolytes)

[0251] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.0 wt% lithium nitrate (LiNO3) was added as a first additive, without any second additive. Subsequently, 3.0 wt% vinylene carbonate (VC) and 1.0 wt% ethylene sulfate (Esa) were added as other additives to prepare an electrolyte.

[0252] (Manufacturing of secondary batteries)

[0253] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared above was injected.

[0254] Compare Example 2.

[0255] (Preparation of electrolytes)

[0256] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, without the first additive, 1.0 wt% of an imidazole compound of formula 3A was added as a second additive, followed by 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) as other additives to prepare an electrolyte.

[0257] (Manufacturing of secondary batteries)

[0258] A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that the electrolyte prepared above was injected.

[0259] Comparative Example 3.

[0260] (Preparation of electrolytes)

[0261] LiPF6 was dissolved to 1.0 M in an organic solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 20:80. Then, 1.0 wt% of lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive = 1:0.1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare an electrolyte.

[0262] (Manufacturing of secondary batteries)

[0263] A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that the electrolyte prepared above was injected.

[0264] Comparative Example 4.

[0265] (Preparation of electrolytes)

[0266] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 1.0 wt% of LiBF4 was added as a first additive and 1.0 wt% of an imidazole compound of formula 3A was added as a second additive (the weight ratio of the first additive to the second additive was 1:1). Subsequently, 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of ethylene sulfate (Esa) were added as other additives to prepare an electrolyte.

[0267] (Manufacturing of secondary batteries)

[0268] A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that the electrolyte prepared above was injected.

[0269] Comparative Example 5.

[0270] (Preparation of electrolytes)

[0271] LiPF6 was dissolved to 1.0 M in an organic solvent in which γ-butyrolactone and ethylene carbonate were mixed in a volume ratio of 70:30. Then, 0.1 wt% lithium nitrate (LiNO3) was added as a first additive and 0.1 wt% lithium bis(trifluoromethanesulfonyl)imine (LiN(SO2CF3)2, LiTFSI) was added as a second additive (the weight ratio of the first additive to the second additive was 1:1). Subsequently, 3.0 wt% vinylene carbonate (VC) and 1.0 wt% ethylene sulfate (Esa) were added as other additives to prepare an electrolyte.

[0272] (Manufacturing of secondary batteries)

[0273] A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that the electrolyte prepared above was injected.

[0274] Comparative Example 6.

[0275] (The manufacture of the positive electrode)

[0276] A positive electrode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) were added to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 96:1:3 to prepare a positive electrode active material slurry (67% by weight solids). The positive electrode active material slurry was coated onto a 15 μm thick positive electrode current collector (Al film), and then dried and rolled to form a positive electrode (double-sided loading: 62 mg / cm²). 2 Cross-sectional reference load: 31 mg / cm 2 ).

[0277] (Manufacturing of secondary batteries)

[0278] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0279] [Experimental Example]

[0280] Experimental Example 1. High Temperature (45℃) Cyclic Performance Evaluation

[0281] The lithium secondary batteries prepared in the examples and comparative examples were charged to SOC 64% at a rate of 0.1C at a high temperature (55°C), and then aged (48 hours) and degassed to activate the batteries.

[0282] After the activation process is completed, each lithium secondary battery is charged to 3.8 V at a rate of 0.1C under constant current / constant voltage conditions at room temperature (25°C), and then discharged to 2.5 V at a rate of 0.33C under constant current conditions to confirm the initial capacity.

[0283] Each lithium-ion battery was then charged to 3.8 V at a constant current / constant voltage rate of 0.33 C under high temperature (45°C), and then discharged to 2.5 V under constant current at a constant current rate of 0.33 C. This process constituted one cycle, and 100 cycles were performed. The discharge capacity was then measured. A PNA-0506 charger / discharger (manufacturer: PNE solution) was used to drive the lithium-ion batteries.

[0284] The high-temperature cycling capacity retention rate was calculated using the 100th discharge ratio relative to the obtained initial capacity, and the results are shown in Table 1 below.

[0285] [Table 1]

[0286] Referring to Table 1 above, it can be confirmed that, compared with the lithium secondary batteries of Comparative Examples 1 to 6, the capacity retention rate (%) of the lithium secondary batteries manufactured in Examples 1 to 13 of the present invention after high voltage and high temperature cycling is improved.

[0287] Although the invention has been described with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes in form and detail may be made without departing from the spirit and scope of the invention as set forth in the following claims. Therefore, the scope of the invention is not limited to what is set forth in the detailed description of the specification, but is defined by the appended claims.

Claims

1. A lithium secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein, the positive electrode contains lithium iron phosphorus oxide as a positive electrode active material, and the loading amount of the positive electrode is 32 mg / cm² to 60 mg / cm²; and the electrolyte includes a lithium salt, a first organic solvent, a second organic solvent, a first additive, and a second additive, wherein, the first organic solvent is a cyclic ester compound; the second organic solvent is a carbonate-based organic solvent; the first additive is lithium nitrate (LiNO3); the second additive is an imidazole compound.

2. The lithium secondary battery as described in claim 1, wherein, The lithium iron phosphorus oxide contains a compound represented by Formula 1 below: [Formula 1] Li 1+a Fe x M y (PO 4-b )X b wherein, in Formula 1 above, M is any one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X is one or more elements selected from the group consisting of F, S, and N, and -0.5 ≤ a ≤ 0.5, 0 < x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ b ≤ 0.

3.

3. The lithium secondary battery as described in claim 2, wherein, The lithium iron phosphorus oxide is lithium iron phosphate (LiFePO4) or lithium iron manganese phosphate (LiFeMnPO4).

4. The lithium secondary battery as described in claim 1, wherein, The positive electrode further contains a lithium nickel cobalt manganese oxide represented by Formula 2: [Formula 2] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2 In Equation 2 above, M 1 M is Mn, Al, or a combination thereof, M 2 It is selected from any one of the groups consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0 ≤ a1 ≤ 0.5 or 0.

55. <x1<1.0、0<y1≤0.4、0<z≤0.4、0≤w≤0.1。 5. The lithium secondary battery as described in claim 4, wherein, The lithium nickel cobalt manganese oxide is selected from Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.7 Mn 0.2 Co 0.1 O2, Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, Li(Ni) 0.8 Co 0.15 Al 0.05 O2, Li(Ni) 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2 and Li(Ni 0.90 Mn 0.05 Co 0.05 Any one of the groups consisting of O2.

6. The lithium secondary battery as described in claim 4, wherein, The weight ratio of the lithium iron phosphorus oxide to the lithium nickel cobalt manganese oxide is 70:30 to 80:

20.

7. The lithium secondary battery as described in claim 1, wherein, The loading of the positive electrode is 40 mg / cm³. 2 Up to 60 mg / cm 2 .

8. The lithium secondary battery as described in claim 1, wherein, The cyclic ester compound is γ-butyrolactone.

9. The lithium secondary battery as described in claim 1, wherein, The carbonate-based organic solvent is a cyclic carbonate-based organic solvent.

10. The lithium secondary battery as described in claim 1, wherein, The volume ratio of the first organic solvent to the second organic solvent is 50:50 to 99:

1.

11. The lithium secondary battery as described in claim 1, wherein, The volume ratio of the first organic solvent to the second organic solvent is 70:30 to 99:

1.

12. The lithium secondary battery as described in claim 1, wherein, Based on the total weight of the electrolyte, the content of the first additive is 0.05 wt% to 3.0 wt%.

13. The lithium secondary battery as described in claim 1, wherein, The imidazole compound is a compound represented by Formula 3 below: [Formula 3] wherein, in Formula 3 above, R is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and R1 to R3 are each independently hydrogen, an alkyl group having 1 to 3 carbon atoms, or -CN.

14. The lithium secondary battery as described in claim 13, wherein, The imidazole compound is a compound represented by Formula 3A: [Formula 3A] 。 15. The lithium secondary battery as described in claim 1, wherein, The weight ratio of the first additive to the second additive is 1:0.05 to 1:

2.

16. The lithium secondary battery as claimed in claim 1, wherein, The negative electrode contains a carbon-based active material, a silicon-based active material, or a mixture of a carbon-based active material and a silicon-based active material.

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