Non-aqueous electrolytes containing additives for non-aqueous electrolytes and lithium secondary batteries containing the same.

Abstract

The present invention provides a non-aqueous electrolyte comprising an additive for the non-aqueous electrolyte, the additive being represented by the following chemical formula 1: [Chemical Formula 1] In chemical formula 1, R1 to R5 are each independently selected from the group consisting of H, alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 10 carbon atoms, and R can be an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms).

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0103602, filed on August 6, 2021, and Korean Patent Application No. 10-2022-0093930, filed on July 28, 2022, the disclosures of which are incorporated herein by reference. Technical Field

[0004] This invention relates to a non-aqueous electrolyte containing additives for a non-aqueous electrolyte, and a lithium secondary battery containing the same. Background Technology

[0005] Recently, as the application of lithium secondary batteries has rapidly expanded not only to power supplies for electronic devices such as electrical appliances, electronic devices, communication devices, and computers, but also to power storage for large devices such as automobiles and energy storage devices, the demand for secondary batteries with high capacity, high output, and high stability is increasing.

[0006] In particular, high capacity, high output, and long lifespan have become important characteristics for lithium-ion secondary batteries used in automotive applications. To improve the capacity of secondary batteries, high-nickel cathode active materials with high energy density but low stability can be used, or the secondary battery can be driven at high voltages.

[0007] However, when the secondary battery is operated under the above conditions, the film or electrode surface structure formed on the positive / negative electrode surfaces deteriorates due to side reactions caused by electrolyte degradation during battery charging and discharging, and transition metal ions may be eluted from the positive electrode surface. As mentioned above, since the eluted transition metal ions reduce the passivation capability of the SEI when electrodeposited on the negative electrode, a problem of negative electrode degradation occurs.

[0008] This degradation of secondary batteries tends to accelerate when the potential of the positive electrode increases or when the battery is exposed to high temperatures.

[0009] Furthermore, when lithium-ion batteries are used continuously for extended periods or left to stand at high temperatures, gas is generated, which causes a phenomenon known as expansion, resulting in an increase in battery thickness. In this case, the amount of gas is known to vary depending on the state of the SEI.

[0010] Therefore, in order to solve this problem, methods have been researched and developed to reduce the swelling phenomenon of secondary batteries and enhance high-temperature stability by suppressing the elution of metal ions from the positive electrode and forming a stable SEI film. Summary of the Invention

[0011] Technical issues

[0012] As a result of various studies to address the aforementioned problems, the present invention aims to provide an additive for non-aqueous electrolytes that can suppress the degradation of the positive electrode, reduce side reactions between the positive electrode and the electrolyte, and form a stable SEI film on the negative electrode.

[0013] Furthermore, the present invention aims to provide a non-aqueous electrolyte whose high-temperature stability is enhanced by including additives for non-aqueous electrolytes.

[0014] Furthermore, the present invention aims to provide a lithium secondary battery that has improved overall performance by including a non-aqueous electrolyte to improve high-temperature cycling characteristics and high-temperature storage characteristics.

[0015] Technical solution

[0016] According to an exemplary embodiment, in order to achieve the aforementioned objective, the present invention provides a non-aqueous electrolyte comprising an additive for use with a non-aqueous electrolyte, said additive being represented by the following chemical formula 1:

[0017] [Chemical Formula 1]

[0018]

[0019] In Formula 1, R1 to R5 can each be independently selected from the group consisting of H, alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 10 carbon atoms, and R can be an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms).

[0020] According to another exemplary embodiment, the present invention provides a lithium secondary battery comprising the above-described non-aqueous electrolyte.

[0021] Beneficial effects

[0022] The compound represented by Chemical Formula 1, provided as an additive for the non-aqueous electrolyte of the present invention, is a coumarin-based compound that can form a stable solid electrolyte interphase (SEI) film on the surface of the negative electrode, while rapidly reducing and decomposing during charging and discharging. Therefore, the degradation of the negative electrode can be prevented by suppressing the decrease in SEI passivation capability at high temperatures. Furthermore, the reactive oxygen species generated at the positive electrode containing the high-nickel positive electrode active material and the coumarin structure contained in the compound represented by Chemical Formula 1 combine with each other to have the effect of suppressing electrolyte decomposition and gas generation.

[0023] Furthermore, the compound represented by Chemical Formula 1, provided as an additive for the non-aqueous electrolyte of the present invention, can form a dense film on the electrode by further including an aliphatic unsaturated hydrocarbon in the coumarin structure. This has the effect of suppressing degradation caused by interfacial reactions at high temperatures.

[0024] Therefore, since a stable electrode-electrolyte interface with low resistance even at high temperatures is formed when the non-aqueous electrolyte of the present invention, which contains a compound of chemical formula 1, is used, high-temperature cycling characteristics and high-temperature storage characteristics are improved, thus enabling the realization of a lithium secondary battery with improved overall performance. Detailed Implementation

[0025] The terms or words used in the specification and claims should not be construed as limited to their conventional or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the technical spirit of the invention.

[0026] In this invention, the terms “comprising,” “including,” or “having” are intended to indicate the presence of the implemented features, quantities, steps, constituent elements, or any combination thereof, and should be understood to mean that the possibility of having or adding one or more other features or quantities, steps, constituent elements, or any combination thereof is not excluded.

[0027] Furthermore, in the description of "carbon number a to b" in this specification, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. 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)3CH2-, -CH(CH3)CH2-, -CH(CH3)CH2CH2-, etc.

[0028] Furthermore, in this specification, alkyl or alkylene groups may be substituted or unsubstituted, unless otherwise defined. “Substitution” means that at least one hydrogen atom bonded to a carbon atom is replaced by an element other than hydrogen, and specifically refers to substituted alkyl groups having 1 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkoxy groups having 2 to 20 carbon atoms, cycloalkyl groups having 3 to 12 carbon atoms, cycloalkenyl groups having 3 to 12 carbon atoms, heterocycloalkyl groups having 3 to 12 carbon atoms, aryloxy groups having 6 to 12 carbon atoms, halogen atoms, fluoroalkyl groups having 1 to 20 carbon atoms, nitro groups, aryl groups having 6 to 20 carbon atoms, heteroaryl groups having 2 to 20 carbon atoms, haloaryl groups having 6 to 20 carbon atoms, etc.

[0029] The invention will be described in more detail below.

[0030] Non-aqueous electrolytes

[0031] The non-aqueous electrolyte of an exemplary embodiment of the present invention comprises a compound represented by the following chemical formula 1. Secondary batteries containing the non-aqueous electrolyte of the present invention exhibit excellent high-temperature cycling characteristics and excellent high-temperature storage characteristics due to suppression of degradation caused by interfacial reactions at high temperatures.

[0032] [Chemical Formula 1]

[0033]

[0034] In chemical formula 1, R1 to R5 can each be independently selected from the group consisting of H, alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 10 carbon atoms, preferably selected from the group consisting of H, alkyl groups having 1 to 5 carbon atoms and alkoxy groups having 1 to 5 carbon atoms, and most preferably H.

[0035] In Formula 1, R can be an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms, or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms). Preferably, R can be an aliphatic unsaturated hydrocarbon group having 2 to 5 carbon atoms, or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 5 carbon atoms). By further including an aliphatic unsaturated hydrocarbon in the coumarin structure, a dense film can be formed on the electrode, thereby inhibiting degradation caused by interfacial reactions at high temperatures.

[0036] In Formula 1, the aliphatic unsaturated hydrocarbon group may include a triple bond. When R in Formula 1 includes a triple bond, a dense film can be formed on the electrode, thereby suppressing the degradation caused by interfacial reactions at high temperatures.

[0037] Furthermore, in chemical formula 1, R can be an alkenyl or ynyl group having 2 to 5 carbon atoms.

[0038] Specifically, the compound represented by chemical formula 1 of the present invention can be a compound represented by the following chemical formula 1-1.

[0039] [Chemical Formula 1-1]

[0040]

[0041] In chemical formula 1-1, R can be an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms, or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms). Preferably, R can be an aliphatic unsaturated hydrocarbon group having 2 to 5 carbon atoms, or -OR' (R' is an aliphatic unsaturated hydrocarbon group having 2 to 5 carbon atoms). By further including an aliphatic unsaturated hydrocarbon in the coumarin structure, a dense film can be formed on the electrode, thereby inhibiting the degradation caused by interfacial reactions at high temperatures.

[0042] In chemical formula 1-1, the aliphatic unsaturated hydrocarbon group may include a triple bond. When R in chemical formula 1-1 includes a triple bond, a dense film can be formed on the electrode, thereby suppressing the degradation caused by interfacial reactions at high temperatures.

[0043] Furthermore, in chemical formula 1-1, R can be an alkenyl or ynyl group having 2 to 5 carbon atoms.

[0044] Specifically, the compound represented by chemical formula 1 of the present invention can be any one of the compounds represented by chemical formulas 2-1 to 2-8.

[0045] [Chemical Formula 2-1]

[0046]

[0047] [Chemical Formula 2-2]

[0048]

[0049] [Chemical Formula 2-3]

[0050]

[0051] [Chemical Formula 2-4]

[0052]

[0053] [Chemical Formula 2-5]

[0054]

[0055] [Chemical Formula 2-6]

[0056]

[0057] [Chemical Formula 2-7]

[0058]

[0059] [Chemical Formula 2-8]

[0060]

[0061] In this invention, based on 100 parts by weight of the non-aqueous electrolyte, the content of the additive for the non-aqueous electrolyte can be from 0.01 parts by weight to 5 parts by weight, preferably from 0.1 parts by weight to 1 part by weight, and more preferably from 0.1 parts by weight to 0.5 parts by weight. When the content of the compound represented by Chemical Formula 1 is less than the above range, it is insufficient to exhibit an effect of inhibiting degradation, and when the content of the compound represented by Chemical Formula 1 exceeds the above range, the hydrocarbon groups containing unsaturated bonds cause an excessive increase in the resistance of the secondary battery, thus resulting in a problem of deterioration in lifespan characteristics.

[0062] When the content of the compound represented by Formula 1 is less than 0.01 parts by weight, the effect of forming the positive / negative electrode film becomes insignificant with increasing driving time, thus reducing the electrode interface protection effect. Furthermore, when the content of the compound represented by Formula 1 exceeds 5 parts by weight, the viscosity of the electrolyte may increase due to excessive additives, and the rate performance or lifespan characteristics may deteriorate during high-temperature storage. This is because the ion mobility in the battery is adversely affected by the decrease in ionic conductivity caused by increased viscosity. In addition, excessive decomposition of the additives can increase battery resistance and cause side reactions and byproducts.

[0063] The non-aqueous electrolyte of the present invention may also contain lithium salts, organic solvents, and optional other electrolyte additives.

[0064] Lithium salts are used as electrolyte salts in lithium-ion secondary batteries and as a medium for transferring ions. Typically, lithium salts include, for example, Li. + As a cation, and may include F selected from - Cl - ,Br - I - NO3 - 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 - and SCN - At least one of the groups formed.

[0065] Specifically, lithium salts may include a single material selected from the group consisting of, 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(perfluoroethanesulfonyl)imide; LiBETI), and LIN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without limitation.

[0066] Although the lithium salt can be appropriately varied within the range that is generally usable, the concentration of the lithium salt contained can be from 0.5M to 5.0M, preferably from 0.8M to 2.5M, and more preferably from 1.0M to 2.0M, to obtain the best effect of forming an anti-corrosion film on the electrode surface.

[0067] When the concentration of lithium salt is less than 0.5M, conditions of excessive lithium deficiency will occur, which may degrade capacity and cycle characteristics. When the concentration exceeds 5.0M, electrolyte impregnation deteriorates as the viscosity of the non-aqueous electrolyte increases excessively, and performance degradation may occur due to increased battery resistance.

[0068] Non-aqueous organic solvents may include at least one or more organic solvents selected from cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0069] Specifically, organic solvents may include cyclic carbonate organic solvents, linear carbonate organic solvents, or mixtures thereof.

[0070] Cyclic carbonate organic solvents are high-viscosity organic solvents with high dielectric constants, thus enabling them to effectively dissociate lithium salts in electrolytes. Specific examples of such solvents may include at least one or more organic solvents 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, and vinylene carbonate, and ethylene carbonate may include such solvents.

[0071] In addition, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant. Representative examples can be at least one or more organic solvents 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, and specifically, linear carbonate organic solvents can include ethyl methyl carbonate (EMC).

[0072] In addition, in order to prepare an electrolyte with high ionic conductivity, the organic solvent may further include at least one or more ester organic solvents selected from cyclic carbonate organic solvents and linear carbonate organic solvents.

[0073] Specific examples of straight-chain ester organic solvents include at least one or more organic solvents selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

[0074] In addition, examples of cyclic ester organic solvents include γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0075] Furthermore, as an organic solvent, organic solvents commonly used for non-aqueous electrolytes can be added without limitation, if desired. For example, the organic solvent may additionally include at least one or more organic solvents selected from ether organic solvents, glycol dimethyl ether solvents, and nitrile organic solvents.

[0076] As an ether-based solvent, any one or a mixture of two or more of 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) can be used, but ether solvents are not limited thereto.

[0077] Glycol dimethyl ether solvents are solvents with high dielectric constant and low surface tension and lower reactivity to metals compared with straight-chain carbonate organic solvents, and may include at least one or more selected from the group consisting of dimethoxyethane (glycol dimethyl ether, DME), diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether (TEGDME).

[0078] Nitrile solvents may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanoic acid, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but are not limited thereto.

[0079] Furthermore, if necessary, the non-aqueous electrolyte of the present invention may further include known electrolyte additives to prevent electrode collapse caused by the decomposition of the non-aqueous electrolyte in a high-voltage environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and battery expansion suppression effect at high temperatures.

[0080] Representative examples of these other electrolyte additives may include at least one or more additives for forming SEI films, selected from the group consisting of cyclic carbonates, halogen-substituted carbonates, sulfonyl lactones, sulfates / salts, phosphates / salts, borates / salts, nitriles, benzenes, amines, silanes, and lithium salts.

[0081] Examples of cyclic carbonate compounds include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0082] Examples of halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0083] Examples of sulfonyl compounds include at least one or more compounds selected from the group consisting of 1,3-propanesulfonyl lactone (PS), 1,4-butanesulfonyl lactone, ethylenesulfonyl lactone, 1,3-propenesulfonyl lactone (PRS), 1,4-butenesulfonyl lactone and 1-methyl-1,3-propenesulfonyl lactone.

[0084] Examples of sulfate ester / salt compounds include ethylene sulfate (Esa), trimethylol sulfate (TMS), or methyltrimethylol sulfate (MTMS).

[0085] Examples of phosphate ester / salt compounds include one or more compounds selected from lithium difluoro(bis(oxalato)phosphate), lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, or tris(trifluoroethyl) phosphite.

[0086] Examples of borate esters / salts include tetraphenylborate, lithium oxaloyl difluoroborate (LiODFB), and lithium bis(oxaloyl)borate (LiB(C2O4)2, LiBOB).

[0087] Examples of nitrile compounds include at least one or more compounds selected from the group consisting of succinic anionyl, adiponitrile, acetonitrile, propionitrile, butyronitrile, valerate, octanoic anionyl, heptanoic anionyl, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0088] Examples of benzene compounds include fluorobenzene, examples of amine compounds include triethanolamine and ethylenediamine, and examples of silane compounds include tetravinylsilane.

[0089] Lithium salts are compounds that are different from lithium salts contained in non-aqueous electrolytes. Examples include lithium difluorophosphate (LiDFP) and LiPO2F2.

[0090] When combined with other electrolyte additives such as vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP), a more robust SEI film can be formed on the negative electrode surface during the initial activation process of the secondary battery, and the high-temperature stability of the secondary battery can be improved by suppressing the generation of gases that can be produced by the decomposition of the electrolyte at high temperatures.

[0091] Meanwhile, other electrolyte additives can be used in mixtures of two or more, and their content can be from 0.01 to 20% by weight, specifically from 0.01 to 10% by weight, and preferably from 0.05 to 5% by weight, based on the total weight of the non-aqueous electrolyte. When the content of other electrolyte additives is less than 0.01% by weight, the effect of improving the high-temperature storage characteristics and high-temperature life characteristics of the battery is not significant, while when the content of other electrolyte additives exceeds 20% by weight, side reactions in the electrolyte may occur excessively during battery charging and discharging. In particular, when excessive amounts of other electrolyte additives are added, the additives do not decompose sufficiently at high temperatures, and therefore may exist in the electrolyte as unreacted or precipitated substances at room temperature. Therefore, side reactions that degrade the life or resistance characteristics of the secondary battery may occur.

[0092] Lithium secondary batteries

[0093] The present invention also provides a lithium secondary battery comprising the above-mentioned non-aqueous electrolyte.

[0094] Specifically, a lithium secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator inserted between the positive and negative electrodes, and the aforementioned non-aqueous electrolyte.

[0095] In this case, the lithium secondary battery of the present invention can be manufactured by conventional methods known in the art. For example, after sequentially stacking a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes to form an electrode assembly, the lithium secondary battery can be manufactured by inserting the electrode assembly into a battery case and injecting the non-aqueous electrolyte of the present invention into the result.

[0096] (1) Positive electrode

[0097] The positive electrode can be manufactured by coating the positive current collector with a slurry containing a positive electrode active material, binder, conductive material, solvent, etc.

[0098] There are no particular restrictions on the positive current collector, as long as the current collector is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, and silver can be used.

[0099] The positive electrode active material is a compound capable of reversibly inserting and deintercalating lithium. Specifically, the positive electrode active material may include lithium metal oxides, which include lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, examples of lithium metal oxides include 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.), and lithium nickel manganese-based oxides (e.g., LiNi... 1-Y Mn YO₂ (wherein 0<Y<1), LiMn 2-z Ni z O₄ (wherein 0<Z<2), etc.), lithium nickel cobalt-based oxides (for example LiNi 1-Y1 Co Y1 O₂ (wherein 0<Y1<1), etc.), lithium manganese cobalt-based oxides (for example LiCo 1-Y2 Mn Y2 O₂ (wherein 0<Y2<1), LiMn 2-z1 Co z1 O₄ (wherein 0<Z1<2), etc.), lithium nickel manganese cobalt-based oxides (for example Li(Ni p Co q Mn r1 )O₂ (wherein 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O₄ (wherein 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium nickel cobalt transition metal (M) oxides (for example, Li(Ni p2 Co q2 Mn r3 M S2 )O₂ (wherein M is selected from Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2 are each independently the atomic fraction of the element, and 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, and p2+q2+r3+s2=1), etc.), etc., and any one or two or more of the compounds may be included.

[0100] Wherein, in consideration of improving the capacity characteristics and stability of the battery, the lithium metal oxide may be LiCoO₂, LiMnO₂, LiNiO₂, lithium nickel manganese cobalt oxides (for example Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O₂, 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, Li(Ni 0.8 Mn 0.1 Co 0.1 )O₂, etc.), lithium nickel cobalt aluminum oxides (for example Li(Ni 0.8 Co 0.15 Al0.05 Furthermore, considering the significant improvement effect caused by controlling the type and content ratio of the constituent elements forming lithium composite metal oxides, lithium composite metal oxides can be 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, Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, etc., in which any one or more mixtures can be used.

[0101] Among these, a positive electrode active material with a nickel content of 80 atm% or higher in the total transition metal content can be used, as this can maximize the capacity characteristics of the battery. For example, the positive electrode active material may include a lithium transition metal oxide represented by the following [Chemical Formula 3].

[0102] [Chemical Formula 3]

[0103] Li x Ni a Co b M 1 c M 2 d O2

[0104] In chemical formula 3, M 1 It is selected from one or more of Mn or Al, and preferably Mn or a combination of Mn and Al.

[0105] M 2 It can be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S.

[0106] x represents the atomic fraction of lithium in the lithium transition metal oxide, and can be 0.90≤x≤1.1, preferably 0.95≤x≤1.08, and more preferably 1.0≤x≤1.08.

[0107] 'a' represents the atomic fraction of nickel in the lithium transition metal oxide (excluding lithium), and can be 0.80 ≤ a < 1.0, preferably 0.80 ≤ a ≤ 0.95, and more preferably 0.80 ≤ a ≤ 0.90. When the nickel content meets the above range, high capacity characteristics can be achieved.

[0108] b represents the atomic fraction of cobalt among metal elements other than lithium in the lithium transition metal oxide, and may satisfy 0<b<0.2, 0<b≤0.15 or 0.01≤b≤0.10.

[0109] c represents M among metal elements other than lithium in the lithium transition metal oxide 1 and the atomic fraction thereof, and may satisfy 0<c<0.2, 0<c≤0.15 or 0.01≤c≤0.10.

[0110] d represents M among metal elements other than lithium in the lithium transition metal oxide 2 and the atomic fraction thereof, and may satisfy 0≤d≤0.1 or 0≤d≤0.05.

[0111] Based on the total weight of solids in the positive electrode mixture slurry, the content of the positive electrode active material may be 60 to 99 wt%, preferably 70 to 99 wt%, and more preferably 80 to 98 wt%.

[0112] The binder is a component that facilitates adhesion between the active material and the conductive material, as well as adhesion to the current collector.

[0113] Examples of such a binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene, sulfonated ethylene-propylene-diene, styrene-butadiene rubber, fluororubber, various copolymers thereof, and the like.

[0114] Typically, based on the total weight of solids in the positive electrode mixture slurry, the content of the binder may be 1 to 20 wt%, preferably 1 to 15 wt%, and more preferably 1 to 10 wt%.

[0115] The conductive material is a component for further improving the conductivity of the positive electrode active material.

[0116] Such a conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and the following may be used: for example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black or thermal carbon black; graphite powders such as natural graphite, artificial graphite or graphite; conductive fibers such as carbon fibers, carbon nanotubes or metal fibers; carbon fluoride powder; conductive powders such as aluminum powder 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, etc.

[0117] Typically, based on the total weight of solids in the positive electrode mixture slurry, the content of the conductive material may be 1 to 20 wt%, preferably 1 to 15 wt%, and more preferably 1 to 10 wt%.

[0118] The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and its amount may be such that a preferred viscosity can be obtained when the positive electrode active material and optionally binders and conductive materials are included. For example, the solvent content may be such that the concentration of the solids containing the positive electrode active material and optionally binders and conductive materials is 50 to 95% by weight, preferably 70 to 90% by weight, more preferably 70 to 90% by weight.

[0119] (2) Negative electrode

[0120] The negative electrode can be manufactured, for example, by coating the negative electrode current collector with a negative electrode mixture slurry containing negative electrode active material, binder, conductive material, solvent, etc., or a graphite electrode made of carbon (C) or the metal itself can be used as the negative electrode.

[0121] For example, when a negative electrode is manufactured by coating a negative electrode current collector with a negative electrode mixture slurry, the negative electrode current collector typically has a thickness of 3 to 500 μm. There are no particular limitations on the negative electrode current collector, as long as it has high conductivity without causing chemical changes in the battery. Materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, similar to the positive electrode current collector, the adhesion of the negative electrode active material can be increased by forming fine irregularities on the surface of the negative electrode current collector, and the current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0122] In addition, the negative electrode active material may include at least one or more selected from the group consisting of lithium metal, carbon material capable of reversibly inserting / de-inserting lithium ions, metal or alloy of these metals with lithium, metal composite oxide, material capable of doping and de-doping lithium, and transition metal oxide.

[0123] As a carbon material capable of reversibly inserting / deintercalating lithium ions, any carbon-based anode active material commonly used in lithium-ion secondary batteries can be used without particular limitation, and as representative examples, crystalline carbon, amorphous carbon, or combinations thereof can be used. Examples of crystalline carbon include graphite, such as amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, and examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbides, calcined coke, etc.

[0124] As a metal or an alloy of these metals with lithium, a 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 and Sn or an alloy of these metals with lithium may be used.

[0125] As the metal composite oxide, one selected from the group consisting of PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, Bi₂O₅, Li x Fe₂O₃ (0≤x≤1), Li x WO₂ (0≤x≤1) and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2 and Group 3 of the periodic table, and halogens; 0<x≤1; 1≤y≤3; and 1≤z≤8).

[0126] Examples of materials capable of doping and dedoping lithium include Si, SiO x (0<x≤2), Si-Y alloys (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 and combinations thereof, and is not Si), Sn, SnO₂, Sn-Y (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 and combinations thereof, and is not Sn), etc. At least one of the foregoing and SiO₂ may also be used in mixture. Element Y may 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, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof.

[0127] Examples of transition metal oxides include lithium-containing titanium composite oxides (LTO), vanadium oxides, lithium vanadium oxides, etc.

[0128] Based on the total weight of solids in the negative electrode mixture slurry, the content of the negative electrode active material may be 60 to 99% by weight, preferably 70 to 99% by weight, and more preferably 80 to 98% by weight.

[0129] Adhesives are components that facilitate adhesion between active materials, conductive materials, and current collectors. Examples of such adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and their various copolymers.

[0130] Typically, based on the total weight of solids in the negative electrode mixture slurry, the binder content can be 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight.

[0131] Conductive materials are components that 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 in the battery. Examples include: carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powders such as natural graphite, artificial graphite, or graphite; conductive fibers such as carbon fibers, carbon nanotubes, or metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0132] Based on the total weight of solids in the negative electrode mixture slurry, the content of conductive material can be 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight.

[0133] The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and its amount is such that a preferred viscosity can be obtained when the negative electrode active material and optional binders, conductive materials, etc., are included. For example, the solvent content may be such that the concentration of the solids containing the negative electrode active material and optional binders and conductive materials is 50% to 95% by weight, preferably 70% to 90% by weight.

[0134] When the metal itself is used as the negative electrode, the negative electrode can be manufactured by physically bonding, rolling, or depositing the metal onto the metal film itself or onto the negative electrode current collector. As deposition methods, electrodeposition methods for metals or chemical vapor deposition methods can be used.

[0135] For example, the metal that is bonded / rolled / deposited on the metal film itself or the negative electrode current collector may include one or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu) and indium (In).

[0136] (3) Diaphragm

[0137] Furthermore, as a separator, conventional porous polymer membranes used as separators in the prior art can be used alone, such as porous polymer membranes made of polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or their laminated materials can be used, or conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., but the separator is not limited to these. In addition, coated separators containing 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.

[0138] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, prismatic, bag-shaped or coin-shaped.

[0139] The invention will be described in more detail below through specific embodiments. However, the following embodiments are merely examples to facilitate understanding of the invention and do not limit its scope. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the invention, and such changes and modifications also fall within the scope of the appended claims.

[0140] Example

[0141] Example 1

[0142] (Preparation of non-aqueous electrolytes)

[0143] A non-aqueous electrolyte was prepared by dissolving LiPF6, vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP) in an organic solvent (volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7), such that the amounts of LiPF6, vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP) were 1.0 M, 0.5 wt%, 0.5 wt%, 1.0 wt%, and 0.8 wt%, respectively, and by adding 0.1 g of 7-ethynylcoumarin (a compound of chemical formula 2-1) to 99.9 g of the non-aqueous solvent.

[0144] (Manufacturing of lithium secondary batteries)

[0145] By mixing the positive electrode active material (LiNi) at a weight ratio of 98.0:0.7:1.3 0.85 Co 0.05 Mn 0.07 Al 0.03A cathode mixture slurry (75.5% wt% solids) was prepared by adding O2, a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) to N-methyl-2-pyrrolidone (NMP) as a solvent. The cathode was manufactured by applying the cathode mixture slurry to one surface of a 12 μm thick cathode current collector and drying and rolling the result.

[0146] A negative electrode mixture slurry (50% wt% solids) was prepared by adding a negative electrode active material (artificial graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber) to distilled water as a solvent in a weight ratio of 96.5:1.5:2.0. The negative electrode was then manufactured by applying the negative electrode mixture slurry to the surface of an 8 μm thick negative electrode current collector (Cu film), followed by drying and rolling.

[0147] After inserting a polyethylene porous membrane separator between the prepared positive and negative electrodes in a drying chamber, a secondary battery is manufactured by injecting the prepared non-aqueous electrolyte.

[0148] Example 2

[0149] The secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 0.3 g of 7-ethynylcoumarin (a compound of chemical formula 2-1) to 99.7 g of the non-aqueous solvent prepared in Example 1.

[0150] Example 3

[0151] The secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 0.5 g of 7-ethynylcoumarin (a compound of chemical formula 2-1) to 99.5 g of the non-aqueous solvent prepared in Example 1.

[0152] Example 4

[0153] The secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte was prepared by adding 1.0 g of 7-ethynylcoumarin (a compound of chemical formula 2-1) to 99.0 g of the non-aqueous solvent prepared in Example 1.

[0154] Example 5

[0155] The secondary battery was manufactured in the same manner as in Example 2, except that the non-aqueous electrolyte was prepared by replacing 0.3 g of 7-(propynyloxy)coumarin (the compound of chemical formula 2-6) with 0.3 g of 7-ethynylcoumarin (the compound of chemical formula 2-1) in 99.7 g of the non-aqueous solvent prepared in Example 2.

[0156] Comparative Example 1

[0157] The secondary battery was manufactured in the same manner as in Example 1, except that 100g of the non-aqueous solvent prepared in Example 1 was used to prepare the non-aqueous electrolyte.

[0158] Experimental Example 1: Evaluation of High-Temperature Cycling Characteristics

[0159] Cycle characteristics were evaluated for each secondary battery manufactured in Examples 1 to 5 and Comparative Example 1.

[0160] Specifically, by charging each battery manufactured in Examples 1 to 5 and Comparative Example 1 to 4.2V at a constant current of 0.33C at 45°C and discharging it to 3.0V at a constant current of 0.33C, respectively, as one cycle, the capacity retention rate compared to the initial capacity was measured after 100 cycles. The results are shown in Table 1 below.

[0161] [Table 1]

[0162] Example 1 94.2 Example 2 93.8 Example 3 93.1 Example 4 89.7 Example 5 95.3 Comparative Example 1 87.8

[0163] As shown in Table 1, it can be confirmed that Examples 1 to 5 using the non-aqueous electrolyte additive of the present invention have excellent lifetime characteristics due to high capacity retention compared to Comparative Example 1 without the additive.

[0164] Experimental Example 2: Evaluation of High-Temperature Storage Characteristics

[0165] The high-temperature storage characteristics of each secondary battery manufactured in Examples 1 to 5 and Comparative Example 1 were evaluated.

[0166] Specifically, each of the secondary batteries in Examples 1 to 5 and Comparative Example 1 was fully charged to 4.2V and then stored at 60°C for 8 weeks.

[0167] Before storing the secondary battery, the thickness of the battery body portion of the fully charged secondary battery is measured using a flat plate measuring device, and this thickness is set as the initial thickness of the secondary battery.

[0168] After 8 weeks, the thickness of the battery body portion of the stored secondary battery was measured again using a flat plate measuring device to calculate the increase in thickness during the 8-week storage period. The thickness increase rate after 8 weeks was obtained by calculating the thickness increase as a percentage of the initial thickness of the secondary battery. The results are shown in Table 2 below.

[0169] [Table 2]

[0170] Example 1 25.0 Example 2 22.1 Example 3 19.6 Example 4 17.3 Example 5 25.2 Comparative Example 1 32.7

[0171] As shown in Table 2, it can be confirmed that the secondary batteries of Examples 1 to 5 have a smaller thickness increase rate compared with the secondary battery of Comparative Example 1, and therefore generate less gas after 4 weeks at high temperature.

Claims

1. A non-aqueous electrolyte comprising an additive represented by chemical formula 1: [Chemical Formula 1] In chemical formula 1, R1 to R5 are each independently selected from the group consisting of H, alkyl groups having 1 to 10 carbon atoms, and alkoxy groups having 1 to 10 carbon atoms, and R is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms or -OR', where R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms.

2. The non-aqueous electrolyte according to claim 1, wherein, R contains a triple bond.

3. The non-aqueous electrolyte according to claim 1, wherein, R is an alkenyl group having 2 to 5 carbon atoms or an alkynyl group having 2 to 5 carbon atoms.

4. The non-aqueous electrolyte according to claim 1, wherein, The additive represented by chemical formula 1 is one or more selected from the group consisting of compounds represented by chemical formula 1-1: [Chemical Formula 1-1] In chemical formula 1-1, R is an aliphatic unsaturated hydrocarbon group or -OR' having 2 to 10 carbon atoms, where R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms.

5. The non-aqueous electrolyte according to claim 1, wherein, The additive represented by chemical formula 1 is one or more selected from the group consisting of compounds represented by chemical formulas 2-1 to 2-8: [Chemical Formula 2-1] [Chemical Formula 2-2] [Chemical Formula 2-3] [Chemical Formula 2-4] [Chemical Formula 2-5] [Chemical Formula 2-6] [Chemical Formula 2-7] [Chemical Formula 2-8] 6. The non-aqueous electrolyte according to claim 1, wherein, Based on 100 parts by weight of the non-aqueous electrolyte, the content of the additive is from 0.01 parts by weight to 5 parts by weight.

7. The non-aqueous electrolyte according to claim 1, further comprising a lithium salt and an organic solvent.

8. The non-aqueous electrolyte according to claim 7, wherein, The lithium salt is selected from LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB. 10 Cl 10 One or more of the following groups: LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2, LiN(SO2CF2CF3)2 and LIN(SO2CF3)2.

9. The non-aqueous electrolyte according to claim 7, wherein, The concentration of the lithium salt contained is from 0.5M to 5.0M.

10. The non-aqueous electrolyte according to claim 7, wherein, The organic solvent comprises one or more organic solvents selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

11. A lithium secondary battery, comprising: A positive electrode containing positive electrode active material; A negative electrode containing a negative electrode active material; A diaphragm inserted between the positive and negative electrodes; as well as The non-aqueous electrolyte according to claim 1.

12. The lithium secondary battery according to claim 11, wherein, The positive electrode active material comprises a lithium transition metal oxide represented by chemical formula 3: [Chemical Formula 3] Li x Ni a Co b M 1 c M 2 d O2 In chemical formula 3, M 1 It is selected from one or more of Mn or Al. M 2 It is selected from one or more of the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≤x≤1.1, 0.80≤a<1.0, 0 <b<0.2,0<c<0.2,0≤d≤0.1。

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