Non-aqueous electrolyte and lithium secondary battery containing the same

Abstract

The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a first additive containing a compound represented by a specific chemical formula and a second additive containing lithium difluorophosphate. The non-aqueous electrolyte according to the present invention can improve the storage characteristics and resistance characteristics at high temperatures of a lithium secondary battery containing the same by forming a stable film on the electrode.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0101642, filed on August 12, 2022, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same.

Background Art

[0003] In recent years, the application fields of lithium secondary batteries have rapidly expanded not only to power supply for electronic devices such as electric, electronic, communication, and computers, but also to power storage and supply for large-area devices such as automobiles and power storage devices. Along with this, the demand for secondary batteries with high capacity, high output, and high stability is increasing.

[0004] In particular, as the interest in solving environmental problems and realizing a sustainable recycling-based society has increased, research on energy storage devices such as lithium-ion batteries and electric double-layer capacitors has been widely conducted. Among them, lithium secondary batteries have attracted attention as a battery system with the highest theoretical energy density among battery technologies.

[0005] The lithium secondary battery generally includes a positive electrode containing a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte serving as a medium for transmitting lithium ions, and a separator. Among these, the electrolyte is known as a constituent component that has a great influence on the stability (stability, safety) of the battery, and much research has been conducted thereon.

[0006] In this regard, generally, as the electrolyte of a lithium secondary battery, a non-aqueous electrolyte containing a lithium salt, an organic solvent, etc. is used, and as the organic solvent, a carbonate-based organic solvent, etc. is used. At this time, as the lithium salt, for example, LiPF6 etc. can be used, but PF6- Since anions are very weak to heat, when the battery is exposed to high temperatures, there is a problem that Lewis acids such as HF and PF5 are generated by thermal decomposition of lithium salts. Lewis acids such as HF and PF5 cause decomposition of the organic solvent itself, destroy the Solid Electrolyte Interface layer (SEI layer) formed on the surface of the negative electrode active material, and cause problems such as increased resistance, reduced lifespan, and storage performance problems of lithium secondary batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One problem of the present invention is to provide a non-aqueous electrolyte that can form a stable film on the electrode to reduce electrolyte side reactions and achieve excellent storage characteristics and resistance characteristics at high temperatures when applied to lithium secondary batteries.

[0008] Another problem of the present invention is to provide a lithium secondary battery containing the aforementioned non-aqueous electrolyte.

Means for Solving the Problems

[0009] The present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a first additive and a second additive, the first additive comprises a compound represented by the following Chemical Formula 1, and the second additive comprises lithium difluorophosphate.

[0010]

Chem.

[0011] In Chemical Formula 1, R1 is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines, or an aryloxy group having 6 to 20 carbon atoms substituted with one or more fluorines, and R2 and R3 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0012] Further, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte.

Effects of the Invention

[0013] The non-aqueous electrolyte of the present invention is characterized by including, as additives, a first additive containing a sulfonamide compound having a specific structural formula and a second additive containing lithium difluorophosphate. The non-aqueous electrolyte according to the present invention can form a stable film on the electrode and reduce electrolyte side reactions, and can achieve excellent storage characteristics and resistance characteristics at high temperatures when applied to a lithium secondary battery.

Modes for Carrying Out the Invention

[0014] Terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept consistent with the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0015] In this specification, terms such as "including", "comprising", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the presence or possibility of addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] On the other hand, before explaining the present invention, unless otherwise specifically mentioned in the present invention, "*" means a connected part (bonding site) between the ends of the same or different atoms or chemical formulas.

[0017] In addition, in this specification, in the description of "carbon atoms from a to b", "a" and "b" mean 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" means an alkyl group containing 1 to 5 carbon atoms, that is, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, (CH3)2CHCH2-, CH3CH2CH2CH2CH2-, (CH3)2CHCH2CH2-, and the like.

[0018] In addition, in this specification, an alkyl group or an aryl group may be either substituted or unsubstituted. The "substitution" means that, unless otherwise defined, at least one or more hydrogens bonded to carbon are substituted with an element other than hydrogen. For example, it means being substituted with 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, a haloaryl group having 6 to 20 carbon atoms, and the like.

[0019] Hereinafter, the present invention will be described in more detail.

[0020] [Non-aqueous electrolyte] The present invention relates to a non-aqueous electrolyte. More specifically, the non-aqueous electrolyte may be a non-aqueous electrolyte for a lithium secondary battery.

[0021] The non-aqueous electrolyte according to the present invention contains a lithium salt, an organic solvent, and an additive, the additive includes a first additive and a second additive, the first additive contains a compound represented by the following Chemical Formula 1, and the second additive is characterized by containing lithium difluorophosphate.

[0022]

Chemical formula

[0023] In Chemical Formula 1, R1 is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines, or an aryloxy group having 6 to 20 carbon atoms substituted with one or more fluorines, and R2 and R3 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0024] The non-aqueous electrolyte of the present invention is characterized by containing, as an additive, a first additive containing a sulfonamide compound having a specific structural formula and a second additive containing lithium difluorophosphate. The non-aqueous electrolyte according to the present invention can form a stable film on the electrode to reduce electrolyte side reactions, and can achieve excellent storage characteristics and resistance characteristics at high temperatures when applied to a lithium secondary battery.

[0025] (1) Lithium salt As the lithium salt used in the present invention, various lithium salts commonly used in non-aqueous electrolytes for lithium secondary batteries can be used without limitation. For example, the lithium salt contains Li as a cation + and, as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , B10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - The present invention may include at least one selected from the group consisting of:

[0026] Specifically, the lithium salt is 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).

[0027] The lithium salt may be contained in the non-aqueous electrolyte at a concentration of 0.5 M to 5.0 M, specifically, a concentration of 0.8 M to 4 M, and more specifically, a concentration of 0.8 M to 2.0 M. When the concentration of the lithium salt satisfies the above range, the lithium ion transference rate (Li + transference number) and the dissociation degree of lithium ions are improved, and the output characteristics of the battery can be improved.

[0028] (2) Organic solvent The organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as decomposition due to oxidation reaction or the like is minimized during the charge and discharge process of the secondary battery.

[0029] Specifically, the organic solvent may contain at least one selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

[0030] Specifically, the organic solvent may contain a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixture thereof.

[0031] The cyclic carbonate-based organic solvent is a high-viscosity organic solvent with a high dielectric constant and is an organic solvent that easily dissociates the lithium salt in the electrolyte. Specifically, it may contain at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. More specifically, it may contain ethylene carbonate.

[0032] In addition, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant. Specifically, it may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. More specifically, it may include ethyl methyl carbonate (EMC).

[0033] The organic solvent may be a mixture of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. At this time, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed at a volume ratio of 10:90 to 40:60, specifically a volume ratio of 10:90 to 30:70, and more specifically a volume ratio of 15:85 to 30:70. When the mixing ratio of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent satisfies the above range, both high dielectric constant and low viscosity characteristics can be satisfied, and excellent ionic conductivity characteristics can be realized.

[0034] In addition, in order to produce an electrolyte having a high ionic conductivity, the organic solvent may further include at least one ester-based organic solvent selected from the group consisting of a linear ester-based organic solvent and a cyclic ester-based organic solvent in at least one carbonate-based organic solvent selected from the group consisting of the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent.

[0035] Specifically, the linear ester-based 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.

[0036] In addition, specifically, the cyclic ester-based organic solvent may contain at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0037] On the other hand, the organic solvent may be added and used as needed without being limited to the organic solvents commonly used in non-aqueous electrolytes. For example, it may further contain at least one or more organic solvents such as ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0038] As the ether-based solvent, 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 can be used, but it is not limited thereto.

[0039] The glyme-based solvent has a higher dielectric constant and a lower surface tension than linear carbonate-based organic solvents and has little reactivity with metals, and may contain at least one or more selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraethylene glycol dimethyl ether (TEGDME), but is not limited thereto.

[0040] The nitrile-based 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.

[0041] (3) Additive The non-aqueous electrolyte according to the present invention contains an additive. The additive includes a first additive and a second additive. The first additive includes a compound represented by Chemical Formula 1. The second additive includes lithium difluorophosphate (LiDFP).

[0042] In the present invention, the second additive includes lithium difluorophosphate, and the lithium difluorophosphate can react with an organic solvent (for example, ethylene carbonate) to form an SEI film containing an organic component on the negative electrode. However, when only lithium difluorophosphate is used as an additive, there is a problem that inorganic components (for example, LiF, etc.) are insufficient in the SEI film, and the lithium difluorophosphate is decomposed first at the positive electrode, so that the SEI film is not sufficiently formed on the negative electrode. On the other hand, the compound represented by Chemical Formula 1 contained in the first additive is a sulfonamide compound substituted with an alkoxy group or an aryloxy group having one or more fluorines substituted, and the alkoxy group or aryloxy group having one or more fluorines substituted is a relatively weak electron withdrawing group compared to F−, CF3−, etc., so it is easily reduced at the negative electrode and can easily form a film containing inorganic components (for example, LiF). Therefore, the non-aqueous electrolyte of the present invention using the first additive and the second additive in combination can form an SEI film containing both organic and inorganic components on the negative electrode, so it is excellent in preventing electrolyte side reactions and suppressing gas generation, and the storage characteristics and resistance characteristics of the lithium secondary battery at high temperatures can be improved to a high level.

[0043] In addition, the non-aqueous electrolyte of the present invention that uses the first additive and the second additive in combination can form an SEI film in a form in which inorganic components such as LiF are distributed in an organic component-containing SEI film having a flexible property. Therefore, an SEI film with improved flexibility and durability can be formed on the electrode, and various performances such as the high-temperature performance of the lithium secondary battery can be improved to a high level. When only the first additive or only the second additive is included in the non-aqueous electrolyte as an additive, the durability decreases or the flexibility decreases, and the effect of improving the high-temperature performance of the lithium secondary battery aimed at by the present invention cannot be achieved.

[0044] The first additive includes a compound represented by the following Chemical Formula 1.

[0045]

Chemical Formula

[0046] In Chemical Formula 1, R1 is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines, or an aryloxy group having 6 to 20 carbon atoms substituted with one or more fluorines, and R2 and R3 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.

[0047] R1 may be an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines, or an aryloxy group having 6 to 20 carbon atoms substituted with one or more fluorines. Specifically, it is an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines. More specifically, it is an alkoxy group having 1 to 5 carbon atoms substituted with one or more fluorines. More specifically still, it is CF3O-, CF3CF2O-, or CF3CH2O-. Even more specifically, from the viewpoint that an SEI film is likely to be formed on the negative electrode, it may be CF3CH2O-.

[0048] R2 and R3 may each independently be hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms. Specifically, they may be hydrogen or an alkyl group having 1 to 5 carbon atoms. More specifically, from the perspective of achieving a stable reaction during the formation of the SEI film, they may be an alkyl group having 1 to 5 carbon atoms, and even more specifically, a methyl group.

[0049] Specifically, the compound represented by Chemical Formula 1 may contain at least one selected from the group consisting of the compound represented by the following Chemical Formula 2, the compound represented by the following Chemical Formula 3, and the compound represented by the following Chemical Formula 4. Specifically, from the perspective of easily forming an SEI film containing an inorganic component such as LiF on the negative electrode, it may contain the compound represented by the following Chemical Formula 2.

[0050]

Chem.

[0051]

Chem.

[0052]

Chem.

[0053] The first additive may be contained in the non-aqueous electrolyte in an amount of 0.01% by weight to 10% by weight, specifically 0.1% by weight to 2% by weight, more specifically 0.2% by weight to 1% by weight, even more specifically 0.5% by weight to 1% by weight, and even more specifically 0.7% by weight to 1% by weight. When the content of the compound represented by Chemical Formula 1 satisfies the above range, it is preferable in terms of sufficiently imparting durability to the SEI film and preventing an increase in the resistance of the lithium secondary battery due to excessive addition and a consequent decrease in the life performance.

[0054] On the one hand, the second additive contains lithium difluorophosphate. The lithium difluorophosphate can form a SEI film containing organic components on the negative electrode by reacting with an organic solvent (e.g., ethylene carbonate, etc.).

[0055] The second additive may be contained in the non-aqueous electrolyte in an amount of 0.01% to 10% by weight, specifically 0.1% to 2% by weight, more specifically 0.2% to 1% by weight, and still more specifically 0.8% to 1% by weight. When the content of the second additive satisfies the above range, it is advantageous in sufficiently imparting flexibility to the SEI film and improving the resistance characteristics, and is preferable in preventing an increase in the resistance of the lithium secondary battery due to excessive addition and a consequent decrease in the life performance.

[0056] The weight ratio of the first additive to the second additive may be 10:90 to 90:10, specifically 20:80 to 80:20, more specifically 32:68 to 70:30, still more specifically 35:65 to 60:40, and even more specifically 53:47 to 60:40. When the weight ratio is as described above, the flexibility and durability of the SEI film can both be improved to preferable levels, which is preferable.

[0057] The additive may further contain an additional additive together with the first additive and the second additive. The additional additive may be contained in the non-aqueous electrolyte to prevent the non-aqueous electrolyte from decomposing in a high-power environment and causing the collapse of the negative electrode, or for purposes such as low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and suppression of battery swelling at high temperatures.

[0058] Specifically, the additional additive may be at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiODFB (Lithium difluorooxalatoborate), LiBOB (Lithium bis-(oxalato)borate), TMSPa (3-trimethoxysilanyl-propyl-N-aniline), and TMSPi (Tris(trimethylsilyl)Phosphite). Specifically, it may be vinylene carbonate.

[0059] The additional additive may be contained in the non-aqueous electrolyte in an amount of 0.1% by weight to 15% by weight.

[0060] [Lithium secondary battery] The present invention also provides a lithium secondary battery including the aforementioned non-aqueous electrolyte.

[0061] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the aforementioned non-aqueous electrolyte.

[0062] At this time, the lithium secondary battery of the present invention can be manufactured by a conventional method known in the art. For example, after forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially laminated between the positive electrode and the negative electrode, the electrode assembly is inserted into the interior of a battery case, and the non-aqueous electrolyte according to the present invention is injected to manufacture it.

[0063] (1) Positive electrode 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.

[0064] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change 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, fired carbon, and an aluminum-cadmium alloy, preferably aluminum.

[0065] The thickness of the positive electrode current collector generally has a thickness of 3 μm to 500 μm.

[0066] The positive electrode current collector may strengthen the bonding force of the positive electrode active material by forming fine irregularities on the surface. For example, the positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0067] The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer may be disposed on one or both surfaces of the positive electrode current collector.

[0068] The positive electrode active material layer may contain a positive electrode active material.

[0069] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium transition metal composite oxide containing at least one transition metal selected from nickel, cobalt, manganese, and aluminum and lithium, preferably a lithium transition metal composite oxide containing a transition metal containing nickel, cobalt, and manganese and lithium.

[0070] For example, as the lithium transition metal composite oxide, lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.). Any one or two or more of these compounds may be included. Among them, from the viewpoint of enhancing the capacity characteristics and stability of the battery, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), etc. may be used. Considering the remarkable improvement effect by controlling the type and content ratio of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide is Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc. may be used, and any one or a mixture of two or more of these can be used.

[0071] More specifically, the positive electrode active material is a lithium transition metal composite oxide, which may contain 60 mol% or more of nickel based on the total number of moles of transition metals contained in the lithium transition metal composite oxide. Specifically, the positive electrode active material is a lithium transition metal composite oxide, the transition metal includes nickel; and at least one selected from manganese, cobalt, and aluminum, and the nickel is 60 mol% or more, specifically 60 mol% to 90 mol% based on the total number of moles of the transition metals. When using a lithium transition metal composite oxide with such a high content of nickel together with the aforementioned non-aqueous electrolyte, it is preferable in that it can reduce by-products in the gas generated by structural collapse.

[0072] Further, the positive electrode active material may contain a lithium composite transition metal oxide represented by the following Chemical Formula 5.

[0073] [Chemical Formula 5] Li 1+x (Ni a Co b Mn c M d )O2

[0074] In Chemical Formula 5, M 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, and 1+x, a, b, c, and d are atomic fractions of independent elements, respectively, where 0≦x≦0.2, 0.50≦a<1, 0<b≦0.25, 0<c≦0.25, 0≦d≦0.1, and a+b+c+d=1.

[0075] Preferably, a, b, c, and d may be 0.70≦a≦0.95, 0.025≦b≦0.20, 0.025≦c≦0.20, and 0≦d≦0.05, respectively.

[0076] Also, a, b, c, and d may be 0.80≦a≦0.95, 0.025≦b≦0.15, 0.025≦c≦0.15, and 0≦d≦0.05, respectively.

[0077] Also, a, b, c, and d may be 0.85≦a≦0.90, 0.05≦b≦0.10, 0.05≦c≦0.10, and 0≦d≦0.03, respectively.

[0078] Considering sufficient capacity performance of the positive electrode active material, etc., the positive electrode active material may be contained in the positive electrode active material layer at 80 wt% to 99 wt%, preferably 92 wt% to 98.5 wt%.

[0079] The positive electrode active material layer may further contain a binder and / or a conductive material together with the aforementioned positive electrode active material.

[0080] The binder is a component that aids in binding the active material and conductive material, etc., and also in binding to the current collector. Specifically, it 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, preferably polyvinylidene fluoride.

[0081] From the viewpoint of sufficiently ensuring the binding force between components such as the positive electrode active material, the binder may be contained in the positive electrode active material layer at 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%.

[0082] 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 a chemical change and has conductivity. Specifically, the positive electrode conductive material may contain 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, 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 may contain carbon black from the viewpoint of improving conductivity.

[0083] From the viewpoint of sufficiently ensuring electrical conductivity, the conductive material may be contained in the positive electrode active material layer at 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%.

[0084] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 40 μm to 110 μm.

[0085] The positive electrode can be manufactured by coating a positive electrode active material and a positive electrode slurry selectively containing a binder, a conductive material, and a solvent for forming the positive electrode slurry on the positive electrode current collector, and then drying and rolling.

[0086] The solvent for forming the positive electrode slurry may contain an organic solvent such as NMP (N-methyl-2-pyrrolidone). The content of the solid component of the positive electrode slurry may be 40% by weight to 90% by weight, specifically 50% by weight to 80% by weight.

[0087] (2) Negative electrode The negative electrode faces the positive electrode.

[0088] 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.

[0089] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. Specifically, examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, and aluminum-cadmium alloys.

[0090] The negative electrode current collector usually has a thickness of 3 μm to 500 μm.

[0091] The negative electrode current collector may strengthen the binding force of the negative electrode active material by forming fine irregularities on the surface. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0092] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0093] The negative electrode active material layer may contain a negative electrode active material.

[0094] The negative electrode active material is a material capable of reversibly intercalating / deintercalating lithium ions, and may contain at least one selected from the group consisting of carbon-based active materials, (semi)metal-based active materials, and lithium metal. Specifically, it may contain at least one selected from carbon-based active materials and (semi)metal-based active materials. Alternatively, the negative electrode active material may contain a carbon-based active material and a (semi)metal-based active material.

[0095] The carbon-based active material may contain at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may contain graphite.

[0096] The average particle size (D 50 ) may be 10 μm to 30 μm, preferably 15 μm to 25 μm, from the viewpoint of achieving structural stability during charge and discharge and reducing side reactions with the electrolyte.

[0097] Specifically, the (semi)metal-based active material may include at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn and lithium; an oxide of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like.

[0098] More specifically, the (semi)metal-based active material may include a silicon-based active material.

[0099] The silicon-based active material may include a compound represented by SiO x (0 ≦ x < 2). Since SiO2 does not react with lithium ions, it cannot store lithium. Therefore, x is preferably within the above range, and more preferably, the silicon-based active material may be SiO.

[0100] The average particle diameter (D 50 ) of the silicon-based active material may be 1 μm to 30 μm, preferably 2 μm to 15 μm, in order to achieve structural stability during charge and discharge and reduce side reactions with the electrolyte.

[0101] The negative electrode active material may be contained in the negative electrode active material layer at 60% to 99% by weight, preferably 75% to 98% by weight.

[0102] The negative electrode active material layer may further contain a binder and / or a conductive material together with the negative electrode active material.

[0103] The binder is used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector and thus improve the performance of the battery. For example, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and at least any one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., or various copolymers thereof may be included.

[0104] The binder may be contained in the negative electrode active material layer at 0.5% by weight to 10% by weight.

[0105] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. 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, 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; conductive materials such as polyphenylene derivatives and the like may be used.

[0106] The conductive material may be contained in the negative electrode active material layer at 0.5% by weight to 10% by weight, preferably 1% by weight to 5% by weight.

[0107] The thickness of the negative electrode active material layer may be 10 μm to 100 μm, preferably 50 μm to 80 μm.

[0108] The negative electrode can be manufactured by coating 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 on at least one surface of a negative electrode current collector, followed by drying and rolling.

[0109] The solvent for forming the negative electrode slurry may be, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably containing distilled water, from the viewpoint of facilitating the dispersion of the negative electrode active material, the binder, and / or the 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.

[0110] (3) Separator As the separator, a normal porous polymer film that has been conventionally used as a separator, for example, a porous polymer film made of a polyolefin polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer may be used alone, or these may be laminated and used, or a normal porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fibers, polyethylene terephthalate fibers, etc. may be used, but it is not limited thereto. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single layer or a multi-layer structure.

[0111] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can.

[0112] Hereinafter, the present invention will be described more specifically 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 is obvious to those skilled in the art that various changes and modifications can be made within the scope of the description and the technical idea, and it goes without saying that such modifications and changes belong to the scope of the appended claims.

[0113] [Examples and Comparative Examples] Example 1 (Manufacture of non-aqueous electrolyte) As the organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 was used.

[0114] To the organic solvent, LiPF6 as a lithium salt, a compound represented by the following Chemical Formula 2 as a first additive, lithium difluorophosphate as a second additive, and vinylene carbonate (VC) as an additional additive were added to produce a non-aqueous electrolyte.

[0115] The LiPF6 was contained in the non-aqueous electrolyte at a concentration of 1.2 M.

[0116] The compound represented by Chemical Formula 2 was contained in the non-aqueous electrolyte at 0.5% by weight, and the lithium difluorophosphate was contained in the non-aqueous electrolyte at 0.8% by weight. Further, the vinylene carbonate was contained in the non-aqueous electrolyte at 0.5% by weight.

[0117] [Chemical Formula]

[0118] (Manufacture of Lithium Secondary Battery) The positive electrode active material (LiNi 0.90 Co 0.06 Mn 0.03 Al 0.01 O2), the conductive material (carbon black), and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP), which is a solvent, at a weight ratio of 97.6:0.8:1.6 to produce a positive electrode mixture slurry (solid content: 60% by weight). The positive electrode mixture slurry was applied to one surface of a positive electrode current collector (Al thin film) with a thickness of 13.5 μm, and drying and roll press were performed to produce a positive electrode.

[0119] The negative electrode active material (a mixture of graphite and SiO mixed at a weight ratio of 90:10), the conductive material (carbon black), and the binder (styrene-butadiene rubber / carboxymethyl cellulose) were added to distilled water, which is a solvent, at a weight ratio of 97.6:1.6:0.8 to produce a negative electrode mixture slurry (solid content: 60% by weight). The negative electrode mixture slurry was applied to one surface of a negative electrode current collector (Cu thin film) with a thickness of 6 μm, and drying and roll press were performed to produce a negative electrode.

[0120] In a dry room, after interposing a polyethylene porous film separator between the positive electrode and the negative electrode manufactured above, the non-aqueous electrolyte manufactured above was injected to manufacture a lithium secondary battery.

[0121] Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 2 was included in the non-aqueous electrolyte at 0.1% by weight instead of 0.5% by weight as the first additive.

[0122] Example 3 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the compound represented by Chemical Formula 2 was included in the non-aqueous electrolyte at 1% by weight instead of 0.5% by weight as the first additive.

[0123] Example 4 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that lithium difluorophosphate was included in the non-aqueous electrolyte at 0.5% by weight instead of 0.8% by weight as the second additive.

[0124] Example 5 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that lithium difluorophosphate was included in the non-aqueous electrolyte at 1% by weight instead of 0.8% by weight as the second additive.

[0125] 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.

[0126] Comparative Example 2 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that neither the first additive nor the second additive was added.

[0127] Comparative Example 3 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the second additive was not added, and 0.5% by weight of the compound represented by the following Chemical Formula 6 was added to the non-aqueous electrolyte instead of the compound represented by Chemical Formula 2 as the first additive.

[0128]

Chem.

[0129] Comparative Example 4 A non-aqueous electrolyte and a lithium secondary battery were produced in the same manner as in Example 1, except that the second additive was not added.

[0130] 〔Experimental Example〕 Experimental Example 1: Evaluation of Capacity Retention Rate after High-Temperature Storage After performing an activation (formation) process on the lithium secondary batteries produced in the above Examples and Comparative Examples, at 25°C, constant current / constant voltage (CC / CV) charging up to 4.2V at a 0.33C rate (0.05C Cut off) was performed, and constant current (CC) discharge was carried out up to 2.80V at a 0.33C rate to measure the initial discharge capacity.

[0131] Thereafter, the lithium secondary batteries were fully charged to SOC100% under the above charging conditions and stored at a high temperature (60°C) for 8 weeks. Thereafter, after transferring to a normal temperature (25°C) charger, discharge was performed under the above discharge conditions to measure the discharge capacity. The capacity retention rate was calculated by the following formula, and the results are shown in Table 1 below.

[0132] Capacity retention rate (%) = (Discharge capacity after high-temperature storage / Initial discharge capacity) × 100

[0133] Experimental Example 2: Evaluation of Resistance Increase Rate after High-Temperature Storage After performing an activation (formation) process on the lithium secondary batteries produced in the above Examples and Comparative Examples, at 25°C, constant current / constant voltage (CC / CV) charging up to 4.2V at a 0.33C rate (0.05C Cut off) was performed, and constant current (CC) discharge was carried out up to 2.80V at a 0.33C rate to measure the initial resistance.

[0134] Thereafter, the lithium secondary battery was fully charged to SOC 100% under the above charging conditions and stored at a high temperature (60 °C) for 8 weeks. Thereafter, after being transferred to a charger at room temperature (25 °C), the resistance was measured. The resistance increase rate was calculated by the following formula, and the results are shown in Table 1 below.

[0135] Resistance increase rate (%) = {(resistance after high-temperature storage - initial resistance) / (initial resistance)} × 100

[0136]

Table 1

[0137] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Examples 1 to 5 using the non-aqueous electrolyte containing the first additive and the second additive according to the present invention are excellent in high-temperature storage life performance and have a low resistance increase rate compared to the lithium secondary batteries of Comparative Examples 1 to 4.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a first additive and a second additive, the first additive includes a compound represented by the following Chemical Formula 1, and the second additive includes lithium difluorophosphate. 【Chemical 1】 (In the above chemical formula 1, R １ is an alkoxy group having 1 to 10 carbon atoms with one or more fluorine atoms substituted thereon, or an aryloxy group having 6 to 20 carbon atoms with one or more fluorine atoms substituted thereon, and R ２ and R ３ are, independently of each other, hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms.)

2. The non-aqueous electrolyte according to Claim 1, wherein the compound represented by Chemical Formula 1 includes at least one selected from the group consisting of a compound represented by the following Chemical Formula 2, a compound represented by the following Chemical Formula 3, and a compound represented by the following Chemical Formula 4. 【Chemical Formula 2】 [Chemical Formula 3] 【Chemical Formula 4】

3. The non-aqueous electrolyte according to Claim 1, wherein the first additive is contained in the non-aqueous electrolyte at 0.1% by weight to 10% by weight.

4. The non-aqueous electrolyte according to Claim 1, wherein the second additive is contained in the non-aqueous electrolyte at 0.1% by weight to 10% by weight.

5. The non-aqueous electrolyte according to Claim 1, wherein the weight ratio of the first additive to the second additive is 10:90 to 90:

10.

6. The lithium salt is LiCl, LiBr, LiI, 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 The non-aqueous electrolyte according to claim 1, comprising at least one selected from the group consisting of

7. The non-aqueous electrolyte 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.

8. The non-aqueous electrolyte according to Claim 1, wherein the organic solvent includes at least one selected from the group consisting of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.

9. The non-aqueous electrolyte according to Claim 1, wherein the additive further includes at least one additional additive selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, propane sultone, propene sultone, succinonitrile, adiponitrile, ethylene sulfate, LiBOB (Lithium bis-(oxalato)borate), LiODFB (Lithium difluorooxalatoborate), TMSPA (3-trimethoxysilyl-propyl-N-aniline), and TMSPi (Tris(trimethylsilyl)Phosphite).

10. A lithium secondary battery comprising a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte according to any one of Claims 1 to 9.

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