Non-aqueous electrolyte and lithium secondary battery comprising same

Abstract

Provided is a non-aqueous electrolyte containing a lithium salt, an organic solvent, a compound represented by Formula 1 as a first additive, and a compound represented by Formula 2 or Formula 3 as a second additive, in Formula 1, R represents any one selected from the group consisting of a C1-5 perfluoroalkyl group, a C2-10 alkenyl group, and a C2-10 alkynyl group; in formula 2, R1 represents a C1-3 alkylene group which may be substituted with fluorine, and R2 to R4 each independently represent any one selected from the group consisting of H, a C1-3 alkyl group, and a nitrile group; in formula 3, R5 represents a C1-8 alkylene group which may be substituted with fluorine, and R6 represents any one selected from the group consisting of H, a C1-10 alkyl group, and a C3-8 cycloalkyl group. (Formula 1) # imgabs0 # (Formula 2) # imgabs1 # (Formula 3) # imgabs2 #

Description

[0001] Cross - reference to related applications

[0002] This application claims priority based on and claims the benefit of Korean Patent Application No. 10 - 2023 - 0046159, filed on April 7, 2023, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to a non - aqueous electrolyte and a lithium secondary battery including the same. Background art

[0004] Recently, the applications of lithium secondary batteries have rapidly expanded from power supply for electric power, electronics, communication, and electronic devices (such as computers) to energy storage and power supply for large - scale devices (such as automobiles and energy storage systems). Therefore, the demand for secondary batteries with high capacity, high power, and high stability is increasing day by day.

[0005] In particular, in lithium secondary batteries for automobiles, the importance of high - capacity, high - power, and long - life characteristics is increasing day by day. To achieve a high capacity of a secondary battery, a positive electrode active material with a high nickel content having a high energy density but low stability can be used, or the secondary battery can be driven at a high voltage. Summary of the invention

[0006] [Technical problem]

[0007] The present invention provides a non - aqueous electrolyte with improved stability at high voltage and high temperature, which can suppress the deterioration of the positive electrode, reduce side reactions between the positive electrode and the electrolyte, and form a stable solid electrolyte interface (SEI) film on the negative electrode.

[0008] In addition, the present invention provides a lithium secondary battery having improved high - voltage cycle characteristics, high - temperature storage characteristics, and thermal stability by including the non - aqueous electrolyte.

[0009] [Technical solution]

[0010] According to one aspect, the present invention provides a non - aqueous electrolyte including a lithium salt, an organic solvent, a compound represented by Formula 1 as a first additive, and a compound represented by Formula 2 or Formula 3 as a second additive.

[0011] (Formula 1)

[0012]

[0013] In Formula 1, R represents any one selected from a perfluoroalkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms.

[0014] (Formula 2)

[0015]

[0016] In Formula 2, R1 represents an alkylene group having 1 to 3 carbon atoms which may be substituted with fluorine, and each of R2 to R4 independently represents any one selected from the group consisting of H, an alkyl group having 1 to 3 carbon atoms, and a nitrile group.

[0017] (Formula 3)

[0018]

[0019] In Formula 3, R5 represents an alkylene group having 1 to 8 carbon atoms which may be substituted with fluorine, and R6 represents any one selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and a cycloalkyl group having 3 to 8 carbon atoms.

[0020] According to another aspect, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and the above non-aqueous electrolyte.

[0021] [Advantageous Effects]

[0022] The compound of Formula 1 provided as the first additive of the present invention is a cyclic sulfate compound, and the film formed by the ring-opening reaction of the cyclic sulfate can contribute to improving high-temperature durability, achieving the effect of improving high-temperature performance. In particular, since the structure of the compound of Formula 1 contains a large amount of O from the COO group, a film with high lithium mobility can be formed. In addition, the compound contains functional groups such as F-based groups, vinyl groups, and propargyl groups in its structure, and these functional groups contribute to improving the stability of the battery by forming an organic / inorganic composite film. Therefore, the first additive of the present invention can inhibit the deterioration of the passivation ability of SEI at high temperatures, prevent the deterioration of the positive electrode, and improve the overall performance (such as charge / discharge characteristics and output) of the lithium secondary battery.

[0023] The compound of formula 2 or formula 3 provided as the second additive of the present invention contains a propargyl group in the molecule, which improves the high-temperature durability. The SEI film generated by the reduction of the negative electrode of the compound of formula 2 or formula 3 contains a propargyl group, and the propargyl group becomes a cross-linking site in the SEI, allowing further reactions. As the additional cross-linking reaction proceeds, a strong SEI film is formed, which effectively inhibits or prevents the performance degradation caused by the negative electrode electrodeposition of the transition metal dissolved from the positive electrode. In addition, the cyclic carbonate functional group and imidazole functional group contained in the additive of formula 2 or formula 3 inhibit the side reactions and positive electrode degradation at the positive electrode surface by forming a stable cathode electrolyte interphase (CEI), thereby improving the performance and reducing the transition metal dissolution that may occur during high-voltage charging. That is, the compound of formula 2 or formula 3 provided as the second additive of the non-aqueous electrolyte of the present invention can form a stable ion-conducting film on the positive and negative electrode surfaces.

[0024] Therefore, when using the non-aqueous electrolyte of the present invention containing the first additive and the second additive, the free radicals generated by the cleavage of the ring structure of the first additive promote the film-forming reaction of the second additive. The film formed by the interaction of the first additive and the second additive has high durability at high temperatures and has the effect of inhibiting the dissolution of the positive electrode transition metal. In addition, the film formed by the interaction of the first additive and the second additive has excellent lithium ion transfer characteristics, thus improving the overall performance (such as charge and discharge characteristics and output characteristics) of the lithium secondary battery. The film formed by the interaction of the first additive and the second additive has excellent antioxidant properties, and can inhibit side reactions occurring on the positive and negative electrode films even in the acidic environment of the electrolyte. In addition, the film formed by the interaction of the first additive and the second additive has high resistance to the volume expansion of the negative electrode occurring during charging and discharging. Therefore, the non-aqueous electrolyte of the present invention can form a stable and durable electrode-electrolyte interface even at high temperatures, and can inhibit or prevent unnecessary electrolyte decomposition side reactions, so that the lithium secondary battery can have improved overall performance compared with conventional lithium secondary batteries. Detailed Description

[0025] The terms and words used in this specification and claims should not be construed in accordance with their ordinary or dictionary meanings, but should be defined based on the principle that the inventor can best interpret the present invention, and should be interpreted according to the meanings and concepts that conform to the technical idea of the present invention.

[0026] In this specification, terms such as "comprising / including", "providing" and "having" are intended to specify the presence of the features, numbers, steps, operations, components and parts or combinations thereof described herein, but should not be construed as excluding the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0027] In addition, when "a to b carbon atoms" are mentioned in the specification, "a" and "b" refer to the number of carbon atoms contained in a specific functional group. That is, the functional group may contain "a" to "b" carbon atoms. For example, "an alkylene group having 1 to 5 carbon atoms" refers to an alkylene group containing 1 to 5 carbon atoms, namely, -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2(CH3)CH-, -CH(CH3)CH2-, and -CH(CH3)CH2CH2-.

[0028] In addition, in this specification, the term "alkylene group" refers to a branched or unbranched divalent saturated hydrocarbon group.

[0029] In addition, in this specification, all alkyl groups may be substituted or unsubstituted. Unless otherwise defined, the term "substituted" means that at least one hydrogen bonded to carbon is replaced by an element other than hydrogen, such as an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a heterocycloalkyl group having 3 to 12 carbon atoms, a heterocycloalkenyl group having 3 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, 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, a nitro group, or a nitrile group.

[0030] When a high-nickel cathode active material with a high energy density but low stability is used to increase the capacity of a lithium secondary battery, or when the secondary battery operates at a high voltage, as charging and discharging proceed, due to side reactions caused by electrolyte deterioration, the film formed on the cathode surface or the electrode surface structure deteriorates, such that transition metal ions may dissolve out from the cathode surface. Therefore, the dissolved transition metal ions are electrodeposited on the anode and reduce the passivation ability of the solid electrolyte interface (SEI), resulting in the deterioration of the anode.

[0031] When the potential of the cathode increases or the battery is exposed to high temperature, this deterioration phenomenon of the secondary battery tends to accelerate, and the deterioration phenomenon causes the cycling characteristics of the secondary battery to deteriorate.

[0032] In addition, when a lithium secondary battery is continuously used or placed at a high temperature for a long time, gas is generated, and bulging or swelling occurs, which increases the thickness of the battery. At this time, it is known that the amount of gas generated depends on the state of the SEI.

[0033] The present invention discloses a lithium secondary battery, which contains a non-aqueous electrolyte capable of suppressing the dissolution of metal ions from the positive electrode, forming a stable SEI film on the negative electrode, reducing the swelling of the secondary battery, and improving the high-temperature stability.

[0034] Hereinafter, the present invention will be described in more detail.

[0035] Non-aqueous electrolyte

[0036] According to one aspect of the present invention, the non-aqueous electrolyte contains a lithium salt; an organic solvent; a compound represented by Formula 1 as a first additive, and a compound represented by Formula 2 or Formula 3 as a second additive.

[0037] The non-aqueous electrolyte of the present invention contains a compound represented by Formula 1 as a first additive. The compound of Formula 1 is a cyclic sulfate compound, and the film formed by the ring-opening reaction of the cyclic sulfate can contribute to improving the high-temperature durability and achieving the effect of improving the high-temperature performance. For example, since the structure of the compound of Formula 1 contains a large amount of O from the COO group, a film with high lithium mobility can be formed. In addition, the compound contains functional groups such as F groups, vinyl groups, and propargyl groups in its structure, and these functional groups contribute to improving the stability of the battery by forming an organic / inorganic composite film. Therefore, the first additive of the present invention can inhibit the deterioration of the passivation ability of SEI at high temperatures, prevent the deterioration of the positive electrode, and improve the performance of the lithium secondary battery.

[0038] (Formula 1)

[0039]

[0040] In Formula 1, R can be any one selected from a perfluoroalkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms. For example, R can be a perfluoroalkyl group having 1 to 3 carbon atoms or an alkenyl group having 2 to 5 carbon atoms, and can also be, for example, any one selected from the group consisting of CF3, CF2CF3, and ethynyl. When R is a perfluoroalkyl group, an organic-inorganic composite film can be formed, producing a strong and durable film. The film containing an organic component has excellent lithium transfer properties, but is prone to side reactions in the acidic environment of the electrolyte, while the inorganic film inhibits side reactions in the acidic environment but has poor lithium transfer properties. Therefore, when an organic-inorganic composite film is formed, the overall characteristics of the lithium secondary battery are maximized. When R is an alkenyl group or an alkynyl group, an additional cross-linking reaction can occur to form a stronger film.

[0041] For example, the compound of Formula 1 can be any one selected from the group consisting of Formulas 1-1 to 1-3:

[0042] (Formula 1-1)

[0043]

[0044] (Formula 1-2)

[0045]

[0046] (Formula 1-3)

[0047]

[0048] The non-aqueous electrolyte of the present invention contains a compound represented by Formula 2 or Formula 3 as a second additive. The compound of Formula 2 or Formula 3 containing a propargyl group is easily reduced on the surface of the negative electrode and can easily form a film on the surface of the negative electrode. The stability of this film is higher than that of the SEI film formed by the reductive decomposition of a conventional electrolyte, has a lower electronic conductivity to inhibit further electrolyte decomposition reactions, and has the advantage of not being easily damaged due to the volume change of the negative electrode. That is, by using the compound of Formula 2 or Formula 3 as an additive to the electrolyte, the stability of the interface between the negative electrode and the electrolyte can be ensured.

[0049] The compound of Formula 2 contains an oxygen atom and a propargyl group with a triple bond that is known to have metal ion adsorption properties. Thus, the propargyl group separated due to the bond breakage of the nitrogen (N) atom and carbon (C) atom of the imidazole group adsorbs metal impurities (such as Fe, Co, Mn, and Ni) dissolved from the positive electrode during the high-voltage charging process of the lithium secondary battery and effectively inhibits the negative electrode deterioration phenomenon caused by the electrodeposition of metal impurities on the surface of the negative electrode. In addition, because the lone pair electrons of the nitrogen (N) atom of the imidazole group react with an alkyl carbonate, the compound represented by Formula 2 is reduced on the surface of the negative electrode, and the alkyl carbonate is a decomposition product of ethylene carbonate (EC) used as an organic solvent. Therefore, a stable ion-conductive film can be formed on the surface of the negative electrode. Therefore, not only can further electrolyte decomposition reactions during charging and discharging be inhibited, but also it can contribute to the absorption and release of lithium ions from the negative electrode during overcharging or high-temperature storage, thereby improving the cycle life characteristics and high-temperature storage performance of the secondary battery.

[0050] (Formula 2)

[0051]

[0052] In Formula 2, R1 may be an alkylene group having 1 to 3 carbon atoms which may be substituted with fluorine, and each of R2 to R4 independently represents any one selected from the group consisting of H, an alkyl group having 1 to 3 carbon atoms, and a nitrile group.

[0053] For example, the compound of Formula 2 of the present invention may be a compound of Formula 2-1:

[0054] (Formula 2-1)

[0055]

[0056] The compound of Formula 3 contains an ester functional group and an unsaturated hydrocarbon group in its molecular structure. It decomposes before other components of the electrolyte during the initial charging process of the secondary battery and forms a film mainly composed of compounds based on carbon-oxygen single bonds (C-O) or carbon-oxygen double bonds (C=O) on the negative electrode surface. In addition, the compound of Formula 3 containing a propargyl group is easily reduced on the negative electrode surface and can easily form a film on the negative electrode surface. The stability of this film is higher than that of the SEI film formed by the reductive decomposition of conventional electrolytes, has a lower electronic conductivity to inhibit further electrolyte decomposition reactions, and has the advantage of not being easily damaged by the volume change of the negative electrode.

[0057] (Formula 3)

[0058]

[0059] In Formula 3, R5 can be an alkylene group having 1 to 8 carbon atoms, preferably 1 to 5 carbon atoms, which may be substituted with fluorine.

[0060] In Formula 3, R6 represents any one selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and a cycloalkyl group having 3 to 8 carbon atoms.

[0061] The compound of Formula 3 can be the compound of Formula 3-1:

[0062] (Formula 3-1)

[0063]

[0064] In Formula 3-1, n can be a natural number from 1 to 8, such as a natural number from 1 to 5, or a natural number from 1 to 3.

[0065] In Formula 3-1, R6 is H, an alkyl group having 1 to 10 carbon atoms, preferably H or methyl.

[0066] For example, the compound of Formula 3 of the present invention can be the compound of Formula 3-2:

[0067] (Formula 3-2)

[0068]

[0069] When using the non-aqueous electrolyte of the present invention containing a first (Formula 1) and a second (Formula 2 or Formula 3) additive, the radicals generated by the cleavage of the ring structure of the first additive promote the film-forming reaction of the second additive. The film formed through the interaction of the first additive and the second additive has an oxadiazoline, imidazole, cyclic carbonate structure or a structure derived therefrom between the aliphatic alkyl-based films, resulting in a film form with excellent lithium ion transport properties. This improves the overall performance (such as charge / discharge characteristics and output characteristics) of the lithium secondary battery. The film formed through the interaction of the first additive and the second additive has excellent antioxidant properties, and can inhibit or prevent side reactions occurring on the films of the positive and negative electrodes even in the acidic environment of the electrolyte. In addition, the film formed through the interaction of the first additive and the second additive has high resistance to the volume change of the negative electrode occurring during charging and discharging. Therefore, the non-aqueous electrolyte of the present invention can form a stable and durable electrode-electrolyte interface even at high temperatures, and can inhibit or prevent unnecessary electrolyte decomposition side reactions, thereby enabling the lithium secondary battery to have improved overall performance.

[0070] In the non-aqueous electrolyte of the present invention, based on 100 parts by weight of the non-aqueous electrolyte, the content of the first additive can be about 0.01 part by weight to 10 parts by weight, for example, about 0.05 part by weight to 5.0 parts by weight, or about 0.10 part by weight to 3.0 parts by weight. When the content of the first additive satisfies the above range, the film-forming effect on the negative electrode is sufficient, which has the effect of excellent high-temperature life characteristics and high-temperature storage characteristics.

[0071] In the non-aqueous electrolyte of the present invention, based on 100 parts by weight of the non-aqueous electrolyte, the content of the second additive can be about 0.01 part by weight to 5 parts by weight, for example, about 0.05 part by weight to 3.0 parts by weight, or about 0.10 part by weight to 2.5 parts by weight. When the content of the second additive satisfies the above range, the film-forming effect on the negative electrode is sufficient, which has the effect of excellent high-temperature life characteristics and high-temperature storage characteristics.

[0072] In the non-aqueous electrolyte of the present invention, the weight ratio of the content of the first additive to the second additive can be 1:0.001 to 1:500, preferably 1:0.01 to 1:300, more preferably 1:0.02 to 1:250. When the above range is satisfied, the elasticity of the SEI film can be within an appropriate range, enabling the SEI film to remain firm during charging and discharging or at high temperatures.

[0073] The non-aqueous electrolyte of the present invention may contain a lithium salt. The lithium salt serves as an electrolyte salt for ion transfer in the lithium secondary battery. Generally, for example, the lithium salt contains Li + as a cation, and contains at least one anion selected from the group consisting of F- , 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 - .

[0074] Specific examples of the lithium salt include a single substance or a mixture of two or more selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, LiAlCl4, LiAlO2, LiPF6, LiSO3CF3, LiCO2CH3, LiCO2CF3, LiAsF6, LiSbF6, LiSO3CH3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethylsulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition, any lithium salt commonly used in the electrolyte of a lithium secondary battery can be used without limitation.

[0075] The lithium salt can be appropriately changed within the generally available range. However, in order to obtain the best effect of forming a corrosion-resistant film on the electrode surface, the concentration of the lithium salt contained in the electrolyte can be 0.1 M to 4.0 M, preferably 1.0 M to 3.0 M, and more preferably 1.2 M to 2.5 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during the high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, so that the impregnation property of the electrolyte can be improved.

[0076] The non-aqueous electrolyte of the present invention may contain an organic solvent. The organic solvent may include at least one organic solvent selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0077] In some embodiments, the additive is effective when a cyclic carbonate solvent is used. When a conventional electrolyte additive is used together with a cyclic carbonate solvent, due to the volume change of the negative electrode occurring during cycling, the SEI film formed by the decomposition of the cyclic carbonate solvent is difficult to maintain, resulting in continuous decomposition of the solvent. As a result, there are problems of a decrease in the ionic conductivity of the electrolyte and deterioration of the cycle characteristics. However, when the additive combination of the present invention is used together with a cyclic carbonate solvent, a strong SEI film can be formed, thereby maintaining high cycle characteristics.

[0078] The cyclic carbonate organic solvent is, for example, a high-viscosity organic solvent having a high dielectric constant and capable of easily dissociating the lithium salt in the electrolyte. Specific examples thereof include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate, and among them, fluoroethylene carbonate (FEC) may be included.

[0079] In addition, linear carbonate organic solvents are organic solvents having, for example, low viscosity and low dielectric constant, and representative examples thereof 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, and among them, diethyl carbonate (DEC) may be included.

[0080] In addition, in order to prepare an electrolyte having high ionic conductivity, the organic solvent may include at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents, and further includes at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0081] Specific examples of the linear ester organic solvents 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.

[0082] In addition, examples of the cyclic ester organic solvents include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0083] Meanwhile, the organic solvent may also include, as needed, but not limited to, organic solvents commonly used in non-aqueous electrolytes. For example, the organic solvent may also include at least one selected from the group consisting of ether organic solvents, glycol diether solvents, and nitrile organic solvents.

[0084] The ether solvent used herein may be any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof, but not limited thereto.

[0085] Compared with linear carbonate organic solvents, glycol diether (glyme) solvents have a higher dielectric constant and a lower surface tension, and have low reactivity with metals, and may include at least one 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), but not limited thereto.

[0086] The nitrile solvent may be selected from at least one of the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, hexanenitrile, heptanenitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but not limited thereto.

[0087] In addition, the non-aqueous electrolyte of the present invention may further contain any other known electrolyte additives in the non-aqueous electrolyte as needed to prevent the non-aqueous electrolyte from decomposing in a high-power environment and causing the negative electrode to disintegrate, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, battery swelling suppression effect at high temperatures, etc.

[0088] These other electrolyte additives may include at least one SEI film-forming additive selected from the group consisting of: cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate / salt compounds, phosphate / salt compounds, borate / salt compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0089] The cyclic carbonate compound may be vinylene carbonate (VC) or ethylene vinyl carbonate.

[0090] The halogenated carbonate compound may be fluoroethylene carbonate (FEC).

[0091] The sultone compound may be at least one selected from the group consisting of: 1,3-propane sultone (PS), 1,4-butane sultone, ethylene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0092] The sulfate / salt compound may be ethylene sulfite (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0093] The phosphate / salt compound may be at least one selected from the group consisting of: lithium difluoro (bisoxalato) phosphate, lithium difluorophosphate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,2-trifluoroethyl) phosphite.

[0094] The borate / salt compound may be tetraphenylborate, lithium difluoro (oxalato) borate (LiODFB), and lithium bisoxalato borate (LiB(C2O4)2, LiBOB).

[0095] The nitrile compound may be at least one selected from the group consisting of: succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, hexanenitrile, heptanenitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0096] The benzene compound may be fluorobenzene, the amine compound may be triethanolamine or ethylenediamine, and the silane compound may be tetravinylsilane.

[0097] The lithium salt compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may be lithium difluorophosphate (LiDFP), LiPO2F2 or LiBF4.

[0098] Among these other electrolyte additives, when a combination of vinylene carbonate (VC), 1,3-propane sultone (PS), ethylene sulfite (Esa) and lithium difluorophosphate (LiDFP) is additionally included, a stronger SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery, and gas generation caused by the decomposition of the electrolyte at high temperatures can be suppressed, thereby improving the high-temperature stability of the secondary battery.

[0099] Meanwhile, the other electrolyte additives can be used in combinations of two or more, and based on the total weight of the non-aqueous electrolyte, the content of the other electrolyte additives can be 0.050 to 20% by weight, specifically 0.10 to 15% by weight, preferably 0.30 to 10% by weight. When the content of the other electrolyte additives satisfies the above range, the effects of improving ionic conductivity and cycle characteristics are more excellent.

[0100] Lithium secondary battery

[0101] The present invention also provides a lithium secondary battery comprising the above non-aqueous electrolyte.

[0102] For example, the lithium secondary battery includes: a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator disposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte as described above.

[0103] At this time, the lithium secondary battery of the present invention can be manufactured according to conventional methods known in the art. For example, the lithium secondary battery of the present invention can be manufactured by the following method: stacking the positive electrode, the negative electrode and the separator between the positive electrode and the negative electrode in sequence to form an electrode assembly, then placing the electrode assembly into a battery case, and injecting the non-aqueous electrolyte of the present invention therein.

[0104] (1) Positive electrode

[0105] The positive electrode can be prepared by coating a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector.

[0106] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver.

[0107] The positive electrode active material is, for example, a compound capable of reversibly inserting and extracting lithium, and may include a lithium metal oxide containing lithium and one or more metal elements (such as cobalt, manganese, nickel, or aluminum). Examples of the lithium metal oxide include lithium manganese oxides (such as LiMnO2 and LiMn2O4), lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium nickel manganese oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1) and LiMn 2-Z Ni Z O4 (where 0 < Z < 2)), lithium nickel cobalt oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1)), lithium manganese cobalt oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1) and LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2)), lithium nickel manganese cobalt oxides (such as Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) and Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2)) and lithium nickel cobalt transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1)), and these oxides can be used alone or in a mixture of two or more of them.

[0108] Among them, from the perspective of improving the capacity characteristics and stability of the battery, the lithium metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (such as 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 Mn0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, and these materials can be used alone or in a mixture of two or more of them.

[0109] Based on the total weight of the solids other than the solvent in the positive electrode mixture slurry, the content of the positive electrode active material can be 60% by weight to 99% by weight, preferably 70% by weight to 99% by weight, more preferably 80% by weight to 98% by weight.

[0110] The binder is a component that aids in the binding of the active material to the conductive material and to the current collector.

[0111] Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorinated rubber, and various copolymers thereof.

[0112] Generally, based on the total weight of the solids other than the solvent in the positive electrode mixture slurry, the content of the binder can be about 1% by weight to 20% by weight. For example, it can be 1% by weight to 15% by weight or 1% by weight to 10% by weight.

[0113] The conductive material is a component used to further improve the conductivity of the positive electrode active material, and based on the total weight of the solids in the positive electrode mixture slurry, its addition amount can be about 1% by weight to 20% by weight. There is no particular limitation on the conductive material as long as it has conductivity without causing chemical changes in the battery, and examples thereof include carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; graphite powders such as natural graphite, artificial graphite, and graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; fluorocarbon powders; 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.

[0114] Generally, based on the total weight of the solids other than the solvent in the positive electrode mixture slurry, the content of the conductive material can be 1% by weight to 20% by weight, preferably 1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight.

[0115] The solvent may include organic solvents such as NMP (N-methyl-2-pyrrolidone), and the amount thereof may be such that the desired viscosity is achieved when the positive electrode active material and optionally a binder and a conductive material are included. For example, the content of the solvent may be such that the solid concentration including the positive electrode active material and optionally a binder and a conductive material may be 50 to 95% by weight, preferably 70 to 95% by weight, more preferably 70 to 90% by weight.

[0116] (2) Negative electrode

[0117] The negative electrode can be prepared, for example, by coating a negative electrode mixture slurry containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, or by using a graphite electrode composed of carbon (C) or a metal itself as the negative electrode.

[0118] For example, when the negative electrode is prepared by coating a negative electrode mixture slurry on a negative electrode current collector, the thickness of the negative electrode current collector is generally about 3 μm to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, and aluminum-cadmium alloy. In addition, like the positive electrode current collector, the negative electrode current collector may have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous material, foam, and nonwoven material.

[0119] In addition, the negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly inserting / extracting lithium ions, a metal or an alloy of a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0120] As the carbon material capable of reversibly inserting / extracting lithium ions, any carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, and combinations thereof. Examples of crystalline carbon include graphite, such as natural graphite or artificial graphite in amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, and calcined coke.

[0121] The metal or the alloy of a metal and lithium may be 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 and lithium.

[0122] The metal composite oxide may be 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, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8).

[0123] Materials capable of doping and undoping lithium include, for example, Si, SiO x (0 < x ≤ 2) and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earths and combinations thereof, but not Si), Sn, SnO2 and Sn-Y (where 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, but not Sn), and at least one of these materials may be mixed with SiO2. The 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.

[0124] Transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide and lithium vanadium oxide.

[0125] When Si or SiO x (0 < x ≤ 2) is used as the negative electrode active material, the additive of the present invention is effective. For example, in the case of using a silicon-based negative electrode active material, if a strong SEI layer is not formed on the negative electrode surface during the initial activation process, the deterioration of the life characteristics will be accelerated due to the extreme volume expansion and contraction during cycling. However, the additive of the present invention can form an elastic and strong SEI layer on the negative electrode surface, thereby improving the life and storage characteristics of the secondary battery using the silicon-based negative electrode active material.

[0126] Based on the total weight of the solids other than the solvent in the negative electrode mixture slurry, the content of the negative electrode active material can be 60% to 99% by weight, preferably 70% to 99% by weight, more preferably 80% to 98% by weight.

[0127] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof. For example, from the perspective of high viscosity, styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC) can be used.

[0128] Generally, based on the total weight of the solids other than the solvent in the negative electrode mixture slurry, the content of the binder can be 1% to 20% by weight, preferably 1% to 15% by weight, or more preferably 1% to 10% by weight.

[0129] The conductive material is a component for further improving the conductivity of the negative electrode active material, and based on the total weight of the solids in the negative electrode mixture slurry, its addition amount can be about 1% to 20% by weight. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; graphite powders such as natural graphite, artificial graphite, and graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; fluorocarbon powders; 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.

[0130] Based on the total weight of the solids other than the solvent in the negative electrode mixture slurry, the content of the conductive material can be 1% to 20% by weight, preferably 1% to 15% by weight, more preferably 1% to 10% by weight.

[0131] The solvent can include organic solvents such as NMP (N-methyl-2-pyrrolidone), and its amount can be such that the desired viscosity is achieved when the negative electrode active material and optionally the binder and the conductive material are included. For example, the content of the solvent can be such that the solid concentration including the negative electrode active material and optionally the binder and the conductive material can be about 50% to 95% by weight, for example, about 70 to 90% by weight.

[0132] When a metal itself is used as the negative electrode, the negative electrode can be manufactured by physically bonding, roll-pressing, or depositing the metal on the metal film itself or the negative electrode current collector. The metal deposition method can be by electroplating or chemical vapor deposition.

[0133] For example, the metal to be combined / rolled / deposited on the metal thin film itself or the negative electrode current collector is selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two of them.

[0134] (3) Separator

[0135] In addition, the separator that can be used herein can be any porous polymer film commonly used as a separator, such as a porous polymer film made of polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), which can be used alone or laminated therewith. Alternatively, the separator that can be used herein can be any porous non-woven fabric, such as a non-woven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, but is not limited thereto. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can optionally be used in a single-layer or multi-layer structure.

[0136] For example, the separator included in the electrode assembly of the present invention can be a safety-enhanced separator (SRS) formed with a coating containing a ceramic component or a polymer material to ensure heat resistance or mechanical strength.

[0137] For example, the separator included in the electrode assembly of the present invention includes a porous separator substrate and a porous coating layer completely coated on one or both sides of the separator substrate, and the coating layer contains a mixture of inorganic particles selected from the group consisting of metal oxides, metalloid oxides, metal fluorides, metal hydroxides, and combinations thereof, and a binder polymer that connects and fixes the inorganic particles to each other.

[0138] The coating layer can contain more than one inorganic particle selected from the group consisting of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, and MgF. Herein, the inorganic particles can improve the thermal stability of the separator. In other words, the inorganic particles can prevent the separator from shrinking at high temperatures. In addition, the binder polymer can improve the mechanical stability of the separator by fixing the inorganic particles.

[0139] The shape of the lithium secondary battery of the present invention is not particularly limited, but can be cylindrical, square, pouch-shaped, or coin-shaped using a can.

[0140] Hereinafter, the present invention will be described in more detail with specific examples. However, the following embodiments are intended to clarify the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of this specification and the technical concept, and these changes and modifications fall within the scope of the appended claims.

[0141] Example

[0142] Example 1

[0143] (Preparation of Non-aqueous Electrolyte)

[0144] LiPF6 was dissolved in an organic solvent (volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 20:70:10) to a concentration of 1.2 M to prepare a non-aqueous solvent, and 0.01 g of the compound of Formula 1-1 and 0.01 g of the compound of Formula 2-1 were added to 99.98 g of the non-aqueous solvent to prepare a non-aqueous electrolyte.

[0145] (Formula 1-1)

[0146]

[0147] (Formula 2-1)

[0148]

[0149] (Preparation of Lithium Secondary Battery)

[0150] The positive electrode active material (LiNi 0.6 Co 0.1 Mn 0.3 O2), a conductive material (carbon nanotubes), and a binder (polyvinylidene fluoride) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of about 97.74:0.7:1.56 to prepare a positive electrode slurry (75.5 wt% solids). The positive electrode slurry was coated on one side of a positive electrode current collector (Al film) with a thickness of 15 μm, dried, and roll-pressed to prepare a positive electrode.

[0151] The negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (styrene-butadiene rubber (SBR)-carboxymethyl cellulose (CMC)) were added to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of about 70:20.3:9.7 to prepare a negative electrode slurry (26 wt% solids). The negative electrode slurry was applied to one side of a negative electrode current collector (Cu film) with a thickness of 15 μm, dried, and roll-pressed to prepare a negative electrode.

[0152] In a drying chamber, a polyolefin porous separator coated with inorganic particles (Al2O3) is disposed between the prepared positive electrode and negative electrode, and then the prepared non-aqueous electrolyte is injected to prepare a secondary battery.

[0153] Example 2

[0154] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-1 and 0.01 g of the compound of Formula 3-2 were added to 99.98 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0155] (Formula 3-2)

[0156]

[0157] Example 3

[0158] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-1 and 5 g of the compound of Formula 2-1 were added to 94.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0159] Example 4

[0160] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-1 and 5 g of the compound of Formula 3-2 were added to 94.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0161] Example 5

[0162] A secondary battery was prepared in the same manner as in Example 1, except that 5 g of the compound of Formula 1-1 and 1 g of the compound of Formula 2-1 were added to 94 g of the non-aqueous solvent prepared in Example 1 above to prepare a non-aqueous electrolyte.

[0163] Example 6

[0164] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-1 and 0.01 g of the compound of Formula 2-1 were added to 89.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0165] Example 7

[0166] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-1 and 5 g of the compound of Formula 2-1 were added to 85 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0167] Example 8

[0168] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-1 and 0.01 g of the compound of Formula 3-2 were added to 89.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0169] Example 9

[0170] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-1 and 5 g of the compound of Formula 3-2 were added to 85 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0171] Example 10

[0172] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-2 and 0.01 g of the compound of Formula 2-1 were added to 99.98 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0173] (Formula 1-2)

[0174]

[0175] Example 11

[0176] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-2 and 0.01 g of the compound of Formula 2-1 were added to 89.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0177] Example 12

[0178] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-2 and 5 g of the compound of Formula 2-1 were added to 94.99 g of the non-aqueous solvent prepared in Example 1 above to prepare a non-aqueous electrolyte.

[0179] Example 13

[0180] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-2 and 5 g of the compound of Formula 2-1 were added to 85 g of the non-aqueous solvent prepared in Example 1 above to prepare a non-aqueous electrolyte.

[0181] Example 14

[0182] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-3 and 0.01 g of the compound of Formula 2-1 were added to 99.98 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0183] (Formula 1-3)

[0184]

[0185] Example 15

[0186] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-3 and 0.01 g of the compound of Formula 2-1 were added to 89.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0187] Example 16

[0188] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-3 and 5 g of the compound of Formula 2-1 were added to 94.99 g of the non-aqueous solvent prepared in Example 1 above to prepare a non-aqueous electrolyte.

[0189] Example 17

[0190] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-3 and 5 g of the compound of Formula 2-1 were added to 85 g of the non-aqueous solvent prepared in Example 1 above to prepare a non-aqueous electrolyte.

[0191] Comparative Example 1

[0192] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 1-1 was added to 99.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0193] Comparative Example 2

[0194] A secondary battery was prepared in the same manner as in Example 1, except that 10 g of the compound of Formula 1-1 was added to 90 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0195] Comparative Example 3

[0196] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 2-1 was added to 99.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0197] Comparative Example 4

[0198] A secondary battery was prepared in the same manner as in Example 1, except that 5 g of the compound of Formula 2-1 was added to 95 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0199] Comparative Example 5

[0200] A secondary battery was prepared in the same manner as in Example 1, except that 0.01 g of the compound of Formula 3-2 was added to 99.99 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0201] Comparative Example 6

[0202] A secondary battery was prepared in the same manner as in Example 1, except that 5 g of the compound of Formula 3-2 was added to 95 g of the non-aqueous solvent prepared in Example 1 to prepare a non-aqueous electrolyte.

[0203] Experimental Example 1 - Evaluation of high-temperature cycle characteristics

[0204] The cycle characteristics of each of the secondary batteries prepared in Examples 1 to 17 and Comparative Examples 1 to 6 were evaluated.

[0205] For example, each of the batteries prepared in Examples 1 to 17 and Comparative Examples 1 to 6 was charged at a rate of 0.33C (cut-off at 0.05C) to 4.2V under constant current / constant voltage conditions at 45°C, and discharged at a constant current of 0.33C to 3.0V, which was regarded as one cycle. Then, 200 charge and discharge cycles were performed, and the capacity retention rate relative to the initial capacity after the first cycle was measured after 200 cycles. In addition, the resistance increase rate relative to the initial resistance after the first cycle was measured after 200 cycles. The results are shown in Table 1 below.

[0206] [Table 1]

[0207] Capacity retention rate (%) Resistance increase rate (%) Example 1 92 10 Example 2 93 9 Example 3 92 9 Example 4 93 9 Example 5 94 7 Example 6 93 10 Example 7 91 8 Example 8 93 8 Example 9 92 8 Example 10 93 10 Example 11 92 9 Example 12 91 8 Example 13 92 8 Example 14 93 9 Example 15 93 10 Example 16 92 8 Example 17 91 8 Comparative Example 1 64 56 Comparative Example 2 66 55 Comparative Example 3 66 56 Comparative Example 4 63 54 Comparative Example 5 65 55 Comparative Example 6 63 55

[0208] Experimental Example 2 - Evaluation of high-temperature storage characteristics

[0209] The high-temperature storage characteristics of each of the secondary batteries prepared in Examples 1 to 17 and Comparative Examples 1 to 6 were evaluated.

[0210] For example, each of the secondary batteries of Examples 1 to 17 and Comparative Examples 1 to 6 was fully charged to 4.2V, and then stored at 60°C for 8 weeks.

[0211] Before storage, the capacity of the fully charged secondary battery was measured and set as the initial capacity of the secondary battery.

[0212] After 8 weeks, the capacity of the stored secondary battery was measured, and the decreased capacity during the 8-week storage period was calculated. The capacity retention rate after 8 weeks was obtained by calculating the percentage of the decreased capacity relative to the initial capacity of the secondary battery. In addition, the percentage of the increased resistance to the initial resistance of the secondary battery was calculated to obtain the resistance increase rate after 8 weeks. The results are shown in Table 2 below.

[0213] [Table 2]

[0214] Capacity retention rate (%) Resistance increase rate (%) Example 1 96 8 Example 2 97 9 Example 3 95 7 Example 4 95 8 Example 5 97 6 Example 6 96 7 Example 7 95 8 Example 8 96 6 Example 9 94 7 Example 10 95 9 Example 11 95 8 Example 12 94 7 Example 13 94 8 Example 14 95 9 Example 15 96 8 Example 16 94 7 Example 17 95 7 Comparative Example 1 70 53 Comparative Example 2 69 54 Comparative Example 3 71 52 Comparative Example 4 68 51 Comparative Example 5 70 52 Comparative Example 6 69 52

Claims

1. A non-aqueous electrolyte, comprising: a lithium salt; an organic solvent; a compound represented by Formula 1 as a first additive; and a compound represented by Formula 2 or Formula 3 as a second additive: (Formula 1) Among them, R represents any one selected from a perfluoroalkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms; (Formula 2) wherein, R1 represents an alkylene group having 1 to 3 carbon atoms which is unsubstituted or substituted with fluorine, and R2 to R4 each independently represent any one selected from the group consisting of H, an alkyl group having 1 to 3 carbon atoms, and a nitrile group; and (Formula 3) wherein, R5 represents an alkylene group having 1 to 8 carbon atoms which is unsubstituted or substituted with fluorine, and R6 represents any one selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and a cycloalkyl group having 3 to 8 carbon atoms.

2. The non-aqueous electrolyte according to claim 1, wherein The compound represented by Formula 1 is any one selected from the group consisting of Formula 1-1 to Formula 1-3: (Formula 1-1) (Formula 1-2) (Formula 1-3) 3. The non-aqueous electrolyte according to claim 1, wherein, The compound represented by Formula 2 is the compound represented by Formula 2-1: (Formula 2-1) 4. The non-aqueous electrolyte according to claim 1, wherein The compound represented by Formula 3 is the compound represented by Formula 3-1: (Formula 3-1) wherein, n is a natural number from 1 to 8, R6 is H or a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

5. The non-aqueous electrolyte according to claim 1, wherein The compound represented by Formula 3 is the compound represented by Formula 3-2: (Formula 3-2) 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 first additive is from 0.01 part by weight to 10 parts by weight.

7. The non-aqueous electrolyte according to claim 1, wherein Based on 100 parts by weight of the non-aqueous electrolyte, the content of the second additive is from 0.01 part by weight to 5 parts by weight.

8. The non-aqueous electrolyte according to claim 1, wherein, The weight ratio of the first additive to the second additive is from 1:0.001 to 1:

500.

9. The non-aqueous electrolyte according to claim 1, wherein, The lithium salt is selected from at least one of the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiSO3CF3, LiCO2CH3, LiCO2CF3, LiAsF6, LiSbF6, LiSO3CH3, LiN(SO2F)2, LiN(SO2CF2CF3)2, and LiN(SO2CF3)2.

10. The non-aqueous electrolyte according to claim 1, wherein, The concentration of the lithium salt is from 0.1 M to 4.0 M.

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

12. A lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator; and the non-aqueous electrolyte according to claim 1.

13. An electronic device, comprising the lithium secondary battery according to claim 12.

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