Nonaqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same

Abstract

Provided is a nonaqueous electrolyte solution for a lithium secondary battery, which includes: a lithium salt; a nonaqueous solvent; a compound represented by Chemical Formula 1; and a compound represented by Chemical Formula 2; wherein the volume ratio of the compound represented by Chemical Formula 1 and the compound represented by Chemical Formula 2 contained is 1:0.1 to 1:1.5. In addition, a lithium secondary battery having improved high-temperature storage safety is provided by containing the nonaqueous electrolyte solution for a lithium secondary battery.

Description

TECHNICAL FIELD

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2020-0127441, filed on September 29, 2020, the disclosure of which is incorporated herein by reference. TECHNICAL FIELD

[0004] The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery comprising an additive capable of improving flame retardancy, and a lithium secondary battery improving high-temperature storage safety by comprising the non-aqueous electrolyte solution. BACKGROUND

[0005] With the recent development of personal IT devices and computer networks along with the development of the information society and the consequent increase in the dependence of the entire society on electric power, there is a need to develop technology for effectively storing and utilizing electric power.

[0006] In particular, with the emergence of interest in solving environmental problems and realizing a sustainable recycling society, there has been extensive research on power storage devices such as electric double layer capacitors and lithium secondary batteries represented by lithium ion batteries.

[0007] Among them, since lithium secondary batteries can be miniaturized to be suitable for personal IT devices, have high energy density and operating voltage, and have recently emerged as clean energy with low carbon dioxide emissions, lithium secondary batteries have been actively researched as power sources for energy storage, electric vehicles, and notebook computers and mobile phones.

[0008] Lithium secondary batteries use a material including a transition metal oxide containing lithium as a main component as a positive electrode, use a lithium alloy or a carbonaceous material represented by graphite as a negative electrode, have a separator disposed between the positive electrode and the negative electrode, and use a non-aqueous electrolyte solution as a medium for lithium (Li) ion movement. As the non-aqueous electrolyte solution, one in which an electrolyte such as lithium hexafluorophosphate (LiPF6) is dissolved in an organic solvent (e.g., ethylene carbonate, dimethyl carbonate) having a high dielectric constant is widely used.

[0009] Most of the organic solvents used in the non-aqueous electrolyte solution are volatile flammable substances, among which they become a cause of safety deterioration of the battery under high-temperature storage since they can cause fire and explosion when an emergency occurs in the battery.

[0010] Therefore, there is a need for a non-aqueous electrolyte solution composition that has no risk of fire and can improve overall battery performance, such as high-rate charge and discharge characteristics, and safety when used in large-capacity batteries such as power storage power sources or electric vehicle power sources. SUMMARY

[0011] Technical Problem

[0012] One aspect of the present application provides a nonaqueous electrolyte solution for a lithium secondary battery having improved safety.

[0013] Another aspect of the present application provides a lithium secondary battery in which high-temperature storage safety is improved by including the nonaqueous electrolyte solution for a lithium secondary battery.

[0014] Technical Solution

[0015] According to one aspect of the present application, a nonaqueous electrolyte solution for a lithium secondary battery is provided, which includes:

[0016] a lithium salt;

[0017] a nonaqueous solvent;

[0018] a compound represented by Formula 1, and

[0019] a compound represented by Formula 2,

[0020] wherein the volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included is 1:0.1 to 1:1.5:

[0021] [Formula 1]

[0022]

[0023] In Formula 1,

[0024] R1 to R3 are each independently an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine element.

[0025] [Formula 2]

[0026]

[0027] In Formula 2,

[0028] R4 and R5 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms,

[0029] R6 to R8 are each independently hydrogen, fluorine, or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, and

[0030] R9 is an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine.

[0031] According to another aspect of the present application, a lithium secondary battery including the nonaqueous electrolyte solution for a lithium secondary battery is provided.

[0032] Advantageous Effects

[0033] The non-aqueous electrolyte solution of the present application can improve the flash point of the electrolyte solution by including two types of compounds as additives, which contain a terminal group substituted with at least one fluorine element. As a result, it is possible to prevent or inhibit the non-aqueous electrolyte solution from igniting at high temperatures. Accordingly, when the non-aqueous electrolyte solution is included, it is possible to realize a lithium secondary battery having improved safety and battery characteristics during high-temperature storage. DETAILED DESCRIPTION

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

[0035] It should be understood that the words or terms used in the specification and claims are not to be interpreted as having a meaning defined in commonly used dictionaries, and it should be further understood that the words or terms are to be interpreted as having a meaning that is consistent with the principles of the application in their context to best interpret the inventors' intent. Accordingly, the specification and claims should be regarded as giving examples rather than limiting the scope of the application.

[0036] The organic solvents used as the main component of the non-aqueous electrolyte solution in the preparation of lithium ion secondary batteries are volatile flammable substances, and since they can cause fire and explosion when an emergency occurs in the battery, they can reduce the safety of the battery during high-temperature storage.

[0037] Accordingly, the present application aims to provide a non-aqueous electrolyte solution for a secondary battery, which includes two additives capable of imparting flame retardancy to prevent or inhibit ignition of the electrolyte solution during high-temperature storage. In addition, the present application aims to provide a lithium secondary battery, which improves safety and battery characteristics during high-temperature storage by including the non-aqueous electrolyte solution.

[0038] Nonaqueous electrolyte solution for lithium secondary battery

[0039] First, the non-aqueous electrolyte solution for a lithium secondary battery of the present application will be described.

[0040] The non-aqueous electrolyte solution for a lithium secondary battery of the present application includes:

[0041] a lithium salt;

[0042] a non-aqueous solvent;

[0043] a compound represented by Formula 1, and

[0044] a compound represented by Formula 2,

[0045] wherein the volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included is 1:0.1 to 1:1.5:

[0046] [Formula 1]

[0047]

[0048] In Formula 1,

[0049] R1 to R3 are each independently an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine element.

[0050] [Formula 2]

[0051]

[0052] In Formula 2,

[0053] R4 and R5 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms,

[0054] R6 to R8 are each independently hydrogen, fluorine, or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, and

[0055] R9 is an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine.

[0056] (1) Lithium salt

[0057] Any lithium salt commonly used in electrolyte solutions for lithium secondary batteries can be used as the lithium salt without limitation, for example, the lithium salt can include LiPF6, LiBF4, LiClO4, LiAsF6, LiSbF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiN(CF3CF2SO2)2, LiN(CF3SO2)2, LiN(FSO2)2, LiBF2C2O4, LiBC4O8, LiPF4C2O4, or the like, as a cation, and can include F-, Cl-, Br-, I-, NO3-, N(CN)2-, BF4-, ClO4-, BCl4-, AlCl4-, AlO4-, PF6-, CF3SO3-, CH3CO2-, CF3CO2-, AsF6-, SbF6-, CH3SO3-, (CF3CF2SO2)2N-, (CF3SO2)2N-, (FSO2)2N-, BF2C2O4-, BC4O8-, PF4C2O4-, or the like, as an anion. + as a cation, and can include F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO4 - , 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 selected from the group consisting of PF6-, BF4-, ClO4-, AsF6-, SbF6-, CH3SO3-, CF3SO3-, CF3CO2-, Cu, and SCN- as an anion.

[0058] Specifically, the lithium salt can include a single material selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, lithium bis(fluorosulfonyl)imide (LiFSI: LiN(SO2F)2), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI: LiN(SO2CF2CF3)2), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI: LiN(SO2CF3)2), or a mixture of two or more thereof. In addition to this, any lithium salt commonly used in the electrolytic solution of a lithium secondary battery can be used without limitation.

[0059] The lithium salt can be appropriately changed within a normal use range, but can be contained in the electrolytic solution at a concentration of 0.8 M to 3.0 M, for example, 1.0 M to 3.0 M to obtain the best effect of forming a film for preventing corrosion of the electrode surface.

[0060] In the case where the concentration of the lithium salt satisfies the above range, the viscosity of the non-aqueous electrolytic solution can be controlled, whereby the best impregnation can be achieved, and an effect of improving the capacity characteristics and cycle characteristics of the lithium secondary battery can be obtained by increasing the mobility of lithium ions.

[0061] (2) Non-aqueous solvent

[0062] The non-aqueous solvent of the present application can include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

[0063] The cyclic carbonate-based organic solvent is an organic solvent that can be used as a high-viscosity organic solvent and can well dissociate a lithium salt in an electrolyte solution due to a high dielectric constant, and specific examples of the cyclic carbonate-based organic solvent can be at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butanediol carbonate, 2,3-butanediol carbonate, 1,2-pentanediol carbonate, 2,3-pentanediol carbonate, and vinylene carbonate, and the cyclic carbonate-based organic solvent can include ethylene carbonate.

[0064] Further, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, and typical examples of the linear carbonate-based organic solvent can be at least one organic solvent 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 the linear carbonate-based organic solvent can specifically include ethyl methyl carbonate (EMC).

[0065] In order to secure a high ionic conductivity of the non-aqueous electrolyte solution of the present application, the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent can be used by being mixed at a volume ratio of 10:90 to 50:50, for example, 15:85 to 30:70.

[0066] Further, the non-aqueous solvent can further include at least one organic solvent selected from a linear ester-based organic solvent and a cyclic ester-based organic solvent, which has a lower melting point and a higher high-temperature stability than the cyclic ester-based organic solvent and / or the linear carbonate-based organic solvent, thereby preparing an electrolyte solution having a high ionic conductivity.

[0067] Specific examples of the linear ester-based organic solvent can be at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0068] Further, the cyclic ester-based organic solvent can include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-hexalactone, σ-valerolactone, and ε-hexalactone.

[0069] If necessary, the non-aqueous solvent can be used without limitation by adding an organic solvent that is generally used in an electrolyte solution for a lithium secondary battery. For example, the non-aqueous solvent can further include at least one organic solvent selected from an ether-based organic solvent, an amide-based organic solvent, and a nitrile-based organic solvent.

[0070] (3) a compound represented by formula 1: first additive

[0071] In this invention, in order to prevent the non-aqueous electrolyte solution from catching fire and exploding during high-temperature storage and to prevent the safety of the battery from deteriorating, a compound represented by Formula 1 may be included as a first additive capable of imparting flame retardancy to the non-aqueous electrolyte solution.

[0072] [Formula 1]

[0073]

[0074] In Equation 1,

[0075] R1 to R3 are each independently an alkyl group having 1 to 6 carbon atoms that has at least one fluorine element substituted.

[0076] Because the compound represented by Formula 1 includes a terminal group in its molecular structure in which at least one fluorine element is substituted, it has a high flash point. Therefore, it can improve the flame retardancy of the electrolyte solution and form a robust solid electrolyte interface (SEI) including the fluorine component on the electrode surface. In addition, because the compound represented by Formula 1 contains an ether group in its molecular structure, it helps to improve lithium solubility. Therefore, it can reduce the viscosity of the electrolyte solution and improve ionic conductivity through interaction with lithium ions.

[0077] Therefore, since the non-aqueous electrolyte solution of the present invention contains a compound represented by Formula 1 as a first additive, its viscosity and volatility are reduced and its flash point temperature is increased, thus suppressing ignition during high-temperature storage. Therefore, a lithium secondary battery with improved safety and battery characteristics during high-temperature storage can be obtained.

[0078] Specifically, in Formula 1, R1 to R3 can each be an alkyl group having 1 to 4 carbon atoms that has substituted at least one fluorine element, and R1 to R3 can each be an alkyl group having 1 to 3 carbon atoms that has substituted at least one fluorine element.

[0079] More specifically, the compound represented by Formula 1 can be a compound represented by the following [Formula 1-1].

[0080] [Equation 1-1]

[0081]

[0082] (2-Trifluoromethyl-3-methoxyperfluoropentane (TMMP))

[0083] (4) The compound represented by formula 2: the second additive

[0084] The non-aqueous electrolyte solution for lithium secondary batteries of the present invention may simultaneously contain a compound represented by Formula 2 as a second additive to further improve the flame retardant effect.

[0085] [Formula 2]

[0086]

[0087] In Formula 2,

[0088] R4 and R5 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms,

[0089] R6 to R8 are each independently hydrogen, fluorine, or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, and

[0090] R9 is an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine.

[0091] Since the compound represented by Formula 2 includes a terminal group substituted with at least one fluorine element in the molecular structure, it has a high flash point, and thus, it can further improve the flame retardancy of the electrolyte solution, and at the same time, a robust SEI including a fluorine component can be formed on the electrode surface.

[0092] Therefore, since the non-aqueous electrolyte solution of the present application includes the compound represented by Formula 2, the flash point temperature can be increased to suppress ignition during high-temperature storage, and thus, a lithium secondary battery having improved safety and battery characteristics during a high-temperature storage period can be implemented.

[0093] Specifically, in Formula 2, R4 and R5 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, R6 is fluorine or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, R7 and R8 are each independently hydrogen or fluorine, and R9 is an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine.

[0094] Preferably, the compound represented by Formula 2 can include at least one of the compounds represented by the following [Formula 2-1] and [Formula 2-2].

[0095] [Formula 2-1]

[0096]

[0097] (2-trifluoro-2-fluoro-3-difluoropropoxy-3-difluoro-4-fluoro-5-trifluoropentane; TPTP)

[0098] [Formula 2-2]

[0099]

[0100] (1H, 1H, 5H-octafluoropentyl-1, 1, 2, 2-tetrafluoroethyl ether (OTE))

[0101] Further, the volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included in the non-aqueous electrolyte solution of the present application can be 1:0.1 to 1:1.5.

[0102] If the compound represented by Formula 2 is included in the above range, since it is possible to prevent ignition by improving the flame retardant properties of the battery and it is possible to minimize performance deterioration, high-temperature storage safety can be further improved. That is, if the volume ratio of the second additive included is less than 0.1, the flame retardant improvement effect can not be significant. Further, if the volume ratio of the second additive included is greater than 1.5, the battery performance can be deteriorated while the dissociation degree of the lithium salt is lower than that of the general electrolyte solution.

[0103] Specifically, the volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included can be 1:0.2 to 1:1.

[0104] The volume ratio of the non-aqueous organic solvent and the additive (i.e., the compound represented by Formula 1 and the compound represented by Formula 2) included in the non-aqueous electrolyte solution of the present application can be 10:90 to 80:20, for example, 30:70 to 70:30.

[0105] If the additive including the compound represented by Formula 1 and the compound represented by Formula 2 of the present application is included in the above range, it is possible to further improve the high-temperature storage properties and the battery properties by improving the flame retardancy of the electrolyte solution.

[0106] If the total amount of the additive including the compound represented by Formula 1 and the compound represented by Formula 2 is greater than 90 in volume ratio, the flame retardant effect is significantly improved, but the side reaction can increase to the extent that the battery performance, such as the rate performance and the cycle characteristics, is reduced. Further, if the total amount of the additive including the compound represented by Formula 1 and the compound represented by Formula 2 is less than 20 in volume ratio, since it is difficult to continuously maintain the flame retardant effect, the effect of improving the flame retardancy and the battery properties can be reduced over time.

[0107] (5) Third Additive

[0108] The non-aqueous electrolyte solution for a lithium secondary battery of the present application can further include a third additive, which is called a flame retardant, to improve the flame retardancy.

[0109] The third additive can include at least one compound selected from the group consisting of butanedinitrile (SN), trimethyl phosphate (TMP), and di-(2,2,2-trifluoroethyl) carbonate (DFDEC).

[0110] In this case, the volume ratio of the compound represented by Formula 1 and the third additive included can be 1:0.1 to 1:5, for example, 1:0.2 to 1:1.5.

[0111] If the third additive is included in the above range, the flame retardancy of the electrolyte solution can be further improved. If the amount of the third additive is less than 0.1 in volume ratio, the flame retardant effect can not be significant, and if the amount of the third additive is greater than 5 in volume ratio, the resistance can increase as the film thickness increases due to side reactions caused by the excess additive, and thus the battery performance can be deteriorated.

[0112] (6) Other additive

[0113] The non-aqueous electrolyte solution for a lithium secondary battery according to the present application can further include an other additive, which can form a strong film on the electrode surface or can improve the moisture retention ability by increasing the dispersibility of the electrolyte solution, thereby further improving effects such as cycle characteristics and rate capability.

[0114] The other additive can include at least one compound selected from the group consisting of FEC, a non-ionic surfactant, cetrimonium chloride (CTAC), a cationic cetyltrimethylammonium bromide (CTAB), and an anionic sodium dodecylbenzenesulfonate (SDBS).

[0115] The non-ionic surfactant can include a compound represented by the following Formula 3.

[0116] [Formula 3]

[0117]

[0118] In Formula 3,

[0119] R is hydrogen, acetyl, methyl, or benzoyl, and at least one of the two Rs is not hydrogen; m and n are each independently an integer of 2 to 20.

[0120] The content of the other additive can be less than 4 wt%, for example, 0.1 wt% to 3 wt%, based on the total weight of the non-aqueous electrolyte solution.

[0121] If the amount of the other additive is less than 0.1 wt%, the effects of improving the low-temperature capacity of the battery and improving the high-temperature storage characteristics and high-temperature life characteristics are not significant, and, if the content of the other additive is greater than 4 wt%, side reactions in the electrolyte solution can excessively occur during the charge and discharge process of the battery. In particular, if an excessive amount of the additive for forming SEI is added, the additive for forming SEI can not be sufficiently decomposed at high temperatures, and thus they can exist in the form of unreactants or precipitates in the electrolyte solution at room temperature. Therefore, side reactions that can deteriorate the battery life or the resistance characteristics can occur.

[0122] Lithium secondary battery

[0123] Next, the present application provides a lithium secondary battery including the above-described non-aqueous electrolyte solution for a lithium secondary battery.

[0124] The lithium secondary battery of the present application can include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte solution of the present application.

[0125] Since the above-described non-aqueous electrolyte solution of the present application has been described, a description thereof will be omitted, and the following describes other components.

[0126] (1) Positive electrode

[0127] The positive electrode can be prepared by coating a positive electrode current collector with a positive electrode slurry including a positive electrode active material, a binder, a conductive agent, and a solvent, and then drying and roll-pressing the coated positive electrode current collector.

[0128] The positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing an adverse chemical change to the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used.

[0129] Further, the positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, wherein the positive electrode active material can include a lithium transition metal oxide including lithium and at least one metal selected from cobalt, manganese, nickel, or aluminum, and can specifically include at least one of a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.) having high capacity characteristics and battery safety and a lithium nickel manganese cobalt-based oxide represented by Formula 4 below. Specifically, the positive electrode active material can include the lithium nickel manganese cobalt-based oxide.

[0130] [Formula 4]

[0131] Li(Ni x Co y Mn z )O2

[0132] (In Formula 4, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1)

[0133] As a representative example, the positive electrode active material can include Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co0.15 )O2and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2.

[0134] In particular, the positive electrode active material of the present application preferably contains Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, wherein the content of nickel among the transition metals is 60 atomic % or more. That is, since the amount of nickel among the transition metals is increased, higher capacity can be achieved, and thus it is more advantageous to use a transition metal having a nickel content of 60 atomic % or more in order to achieve high capacity. In the case of using a transition metal oxide having a high nickel (Hi-Ni) content having a Ni content of more than 0.55 as a positive electrode active material, the output characteristics of a lithium secondary battery can be improved by securing a high energy density.

[0135] For a high Ni (Hi-Ni) oxide having a Ni content of more than 0.55, since the sizes of Li +1 ions and Ni +2 ions are similar, a cation mixing phenomenon occurs in which the positions of Li +1 ions and Ni +2 ions in the layered structure of the positive electrode active material are exchanged with each other during charge and discharge. That is, the nickel transition metal having a d orbital must have an octahedral structure as the oxidation number of Ni contained in the positive electrode active material changes when it is coordinately bonded in an environment such as high temperature, but the crystal structure of the positive electrode active material can be deformed and collapsed, and a distorted octahedron is formed due to a reversal of the energy level order or a non-uniform reaction of the oxidation number change due to an external energy supply. In addition, another side reaction in which the transition metal, particularly nickel metal, is eluted from the positive electrode active material occurs due to a side reaction of the positive electrode active material with the electrolyte solution upon high-temperature storage, and thus the overall performance of the secondary battery is deteriorated due to the structural collapse of the positive electrode active material and the depletion of the electrolyte solution.

[0136] Therefore, for the lithium secondary battery of the present application, since a positive electrode containing a high nickel (Hi-Ni) transition metal oxide as a positive electrode active material and a non-aqueous electrolyte solution containing an additive having a specific configuration are used, a strong ion conductive film is formed on the surface of the positive electrode, and thus the movement of Li +1 ions and Ni +2The cation mixing phenomenon of ions, effective inhibition of side reactions between the cathode and the electrolyte solution, and metal dissolution phenomenon are thus effectively suppressed, and thus the structural instability of the high-capacity electrode can be alleviated. Thus, since an adequate amount of nickel transition metal for securing the capacity of the lithium secondary battery can be ensured, the energy density can be increased to prevent a decrease in output characteristics.

[0137] The content of the cathode active material can be 80 to 99% by weight, for example, 90 to 99% by weight, based on the total weight of the solid components in the cathode slurry. In this case, when the amount of the cathode active material is 80% by weight or less, the capacity can be decreased due to a decrease in energy density.

[0138] The binder is a component that contributes to adhesion between the active material and the conductive agent and adhesion to the current collector, and the amount of the binder added is generally 1 to 30% by weight, based on the total weight of the solid components in the cathode slurry. Examples of the binder can be fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene or polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0139] Further, the conductive agent is a material that provides electrical conductivity without causing adverse chemical changes in the battery, and the amount thereof added can be 1 to 20% by weight, based on the total weight of the solid components in the cathode slurry.

[0140] As typical examples of the conductive agent, the following conductive materials can be used, for example: carbon powder such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black; graphite powder such as natural graphite, artificial graphite, or graphite having a well-developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0141] Further, the solvent can include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and the amount thereof used can be such that a desired viscosity is obtained when the cathode active material and, optionally, the binder and the conductive agent are contained. For example, the content of the solvent can be such that the concentration of the solid components in the slurry containing the cathode active material and, optionally, the binder and the conductive agent is 10 to 60% by weight, for example, 20 to 50% by weight.

[0142] (2) Negative electrode

[0143] The negative electrode can be prepared by coating a negative electrode current collector with a negative electrode slurry including a negative electrode active material, a binder, a conductive agent, and a solvent, and then drying and roll-pressing the coated negative electrode current collector.

[0144] The negative electrode current collector generally has a thickness of 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 an adverse chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy, etc. can be used. In addition, similarly to the positive electrode current collector, the negative electrode current collector can have fine surface roughness to improve the binding strength with the negative electrode active material, and the negative electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a mesh, a porous body, a foam body, and a nonwoven fabric body, etc.

[0145] In addition, the negative electrode active material can include at least one selected from the group consisting of a lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of lithium and the metal, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0146] As the carbon material capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material generally used in lithium ion secondary batteries can be used without particular limitation, and as typical examples, crystalline carbon and / or amorphous carbon can be used. Examples of the crystalline carbon can be graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide, and baked coke, etc.

[0147] As the metal or the alloy of lithium and the metal, a metal selected from the group consisting of copper (Cu), nickel (Ni), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium (Ba), radium (Ra), germanium (Ge), aluminum (Al), and tin (Sn), or an alloy of lithium and the metal can be used.

[0148] As the metal composite oxide, a metal composite oxide 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: manganese (Mn), iron (Fe), Pb, or Ge; Me': Al, boron (B), phosphorus (P), Si, Group I, II, and III elements in the Periodic Table of Elements, or halogen; 0 < x < 1; 1 < y < 3; 1 < z < 8).

[0149] The material that can be doped and de-doped with lithium can include Si, SiO x (0 < x < 2), Si-Y alloys (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, and is 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, and is not Sn), mixtures of SiO2and at least one of the foregoing can also be used. The element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), (Rf), vanadium (V), niobium (Nb), (Db), chromium (Cr), molybdenum (Mo), (Sg), technetium (Tc), rhenium (Re), (Bh), Fe, Pb, ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), Cu, silver (Ag), gold (Au), Zn, cadmium (Cd), B, Al, gallium (Ga), Sn, In, Ge, P, arsenic (As), Sb, bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0150] The transition metal oxide can include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0151] The content of the negative active material can be 80 to 99% by weight, based on the total weight of the solid components in the negative electrode slurry.

[0152] The binder is a component that contributes to adhesion between the conductive agent, the active material, and the current collector, and the amount of the binder added is generally 1 to 30% by weight, based on the total weight of the solid components in the negative electrode slurry. Examples of the binder can be fluororesin-based binders including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders including styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose-based binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol-based binders including polyvinyl alcohol; polyolefin-based binders including polyethylene or polypropylene; polyimide-based binders; polyester-based binders; and silane-based binders.

[0153] The conductive agent is a component for further improving the electrical conductivity of the negative active material, and the amount of the conductive agent added can be 1 to 20% by weight, based on the total weight of the solid components in the negative electrode slurry. Any conductive agent can be used without particular limitation, as long as it has electrical conductivity and does not cause an adverse chemical change in the battery. For example, the following conductive materials can be used, such as: carbon powder, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal crack carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite having a well-developed crystal structure; conductive fibers, such as carbon fibers and metal fibers; conductive powders, such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0154] The binder and the conductive agent can be the same as or different from those of the positive electrode.

[0155] The solvent can include water or an organic solvent, such as NMP and alcohol, and the amount thereof can be such that the desired viscosity is obtained when the negative active material, and optionally the binder and the conductive agent, are included. For example, the content of the solvent can be such that the concentration of the solid components in the negative electrode slurry including the negative active material, and optionally the binder and the conductive agent, is 50 to 75% by weight, such as 50 to 65% by weight.

[0156] (3) Separator

[0157] Typical porous polymer films commonly used, such as porous polymer films prepared from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, can be used alone or laminated together as the separator included in the lithium secondary battery of the present application, and in addition, typical porous nonwoven fabrics, such as nonwoven fabrics formed from high-melting point glass fibers or polyethylene terephthalate fibers, can be used, but the present application is not limited thereto.

[0158] The shape of the lithium secondary battery of the present application is not particularly limited, but a cylindrical type, a prismatic type, a pouch type, or a coin type using a can can be used.

[0159] Hereinafter, the present application will be described in greater detail according to examples. The present application may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0160] Examples

[0161] I. Preparation of non-aqueous electrolyte solution for lithium secondary battery

[0162] Example 1.

[0163] The non-aqueous electrolyte solution was prepared by adding an additive to a non-aqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90 at a volume ratio of 50:50, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-2 were mixed at a volume ratio of 1:0.25, and used as the additive.

[0164] Example 2.

[0165] The non-aqueous electrolyte solution was prepared by adding an additive to a non-aqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90 at a volume ratio of 50:50, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-1 were mixed at a volume ratio of 1:0.25, and used as the additive.

[0166] Example 3.

[0167] The non-aqueous electrolyte solution was prepared by adding an additive to a non-aqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 10:90 at a volume ratio of 40:60, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1, the compound represented by Formula 2-2, and butanedinitrile (SN) were mixed at a volume ratio of 1:0.25:0.25, and used as the additive.

[0168] Example 4.

[0169] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-2 were mixed in a volume ratio of 1:0.52 and used as the additive.

[0170] Example 5.

[0171] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-1 were mixed in a volume ratio of 1:0.52 and used as the additive.

[0172] Example 6.

[0173] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-2 were mixed in a volume ratio of 1:1 and used as the additive.

[0174] Example 7.

[0175] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-1 were mixed in a volume ratio of 1:1 and used as the additive.

[0176] Example 8.

[0177] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6so that the concentration of LiPF6was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-2 were mixed in a volume ratio of 1:1.5 and used as the additive.

[0178] Comparative Example 1.

[0179] The nonaqueous electrolyte solution was prepared by dissolving LiPF6 in a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 5:95, so that the concentration of LiPF6 was 1.2 M.

[0180] Comparative Example 2.

[0181] The nonaqueous electrolyte solution was prepared by mixing ethylene carbonate (EC) and succinonitrile (SN) at a volume ratio of 5:95, and dissolving LiPF6 so that the concentration of LiPF6 was 1.2 M.

[0182] Comparative Example 3.

[0183] The nonaqueous electrolyte solution was prepared by adding an additive (fluoroethylene carbonate (FEC)) to a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DEC) were mixed at a volume ratio of 30:60 at a volume ratio of 90:10, and dissolving LiPF6 so that the concentration of LiPF6 was 1.2 M.

[0184] Comparative Example 4.

[0185] The nonaqueous electrolyte solution was prepared by adding an additive to a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DEC) were mixed at a volume ratio of 10:90 at a volume ratio of 50:50, and dissolving LiPF6 so that the concentration of LiPF6 was 1.2 M. In this case, a compound represented by Formula 1-1 was used alone as the additive.

[0186] Comparative Example 5.

[0187] The nonaqueous electrolyte solution was prepared by adding an additive to a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DEC) were mixed at a volume ratio of 10:90 at a volume ratio of 50:50, and dissolving LiPF6 so that the concentration of LiPF6 was 1.2 M. In this case, a compound represented by Formula 1-1 and a compound represented by Formula 2-2 were mixed at a volume ratio of 1:0.09, and used as the additive.

[0188] Comparative Example 6.

[0189] The nonaqueous electrolyte solution was prepared by adding an additive in a volume ratio of 50:50 to a nonaqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and dissolving LiPF6 so that the concentration of LiPF6 was 1.2 M. In this case, the compound represented by Formula 1-1 and the compound represented by Formula 2-2 were mixed in a volume ratio of 1:1.7 and used as the additive.

[0190] Table 1

[0191]

[0192] In Table 1, the abbreviations of each compound have the following meanings.

[0193] SN: Succinonitrile

[0194] FEC: Fluoroethylene carbonate

[0195] II. Preparation of lithium secondary battery

[0196] Example 9.

[0197] A positive electrode active material (Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), a conductive agent (carbon black), and a binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.5:1:1.5 to prepare a positive electrode slurry (solid content: 50 wt%). A 12-μm-thick aluminum (Al) film, which served as a positive electrode current collector, was coated with the positive electrode slurry, dried, and then roll-pressed to prepare a positive electrode.

[0198] A negative electrode active material (graphite), a binder (SBR-CMC), and a conductive agent (carbon black) were added to water as a solvent in a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry (solid content: 60 wt%). A 6-μm-thick copper (Cu) film, which served as a negative electrode current collector, was coated with the negative electrode slurry, dried, and then roll-pressed to prepare a negative electrode.

[0199] An electrode assembly was prepared by sequentially stacking the positive electrode, a polyolefin-based porous separator coated with inorganic particles (Al2O3), and the negative electrode.

[0200] The electrode assembly was accommodated in a pouch-type battery case, and the nonaqueous electrolyte solution for lithium secondary batteries of Example 1 was injected thereinto to prepare a lithium secondary battery.

[0201] Example 10.

[0202] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 2 instead of the nonaqueous electrolytic solution of Example 1.

[0203] Example 11.

[0204] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 3 instead of the nonaqueous electrolytic solution of Example 1.

[0205] Example 12.

[0206] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 4 instead of the nonaqueous electrolytic solution of Example 1.

[0207] Example 13.

[0208] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 5 instead of the nonaqueous electrolytic solution of Example 1.

[0209] Example 14.

[0210] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 6 instead of the nonaqueous electrolytic solution of Example 1.

[0211] Example 15.

[0212] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 7 instead of the nonaqueous electrolytic solution of Example 1.

[0213] Example 16.

[0214] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Example 8 instead of the nonaqueous electrolytic solution of Example 1.

[0215] Comparative Example 7.

[0216] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the lithium secondary battery was prepared by injecting the nonaqueous electrolytic solution of Comparative Example 1 instead of the nonaqueous electrolytic solution of Example 1.

[0217] Comparative Example 8.

[0218] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the nonaqueous electrolyte solution of Comparative Example 2 was injected instead of the nonaqueous electrolyte solution of Example 1 to prepare the lithium secondary battery.

[0219] Comparative Example 9.

[0220] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the nonaqueous electrolyte solution of Comparative Example 3 was injected instead of the nonaqueous electrolyte solution of Example 1 to prepare the lithium secondary battery.

[0221] Comparative Example 10.

[0222] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the nonaqueous electrolyte solution of Comparative Example 4 was injected instead of the nonaqueous electrolyte solution of Example 1 to prepare the lithium secondary battery.

[0223] Comparative Example 11.

[0224] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the nonaqueous electrolyte solution of Comparative Example 5 was injected instead of the nonaqueous electrolyte solution of Example 1 to prepare the lithium secondary battery.

[0225] Comparative Example 12.

[0226] A pouch-type lithium secondary battery was prepared in the same manner as in Example 9, except that the nonaqueous electrolyte solution of Comparative Example 6 was injected instead of the nonaqueous electrolyte solution of Example 1 to prepare the lithium secondary battery.

[0227] Experimental examples

[0228] Experimental Example 1. Evaluation of Flame Retardancy

[0229] Each 1 g of the nonaqueous electrolyte solutions of Examples 1 to 8 and each 1 g of the nonaqueous electrolyte solutions of Comparative Examples 1 to 6 were put into a metal container, and the surface of the electrolyte solution was ignited with a gas lighter to check whether the electrolyte solution caught fire, and the results are listed in Table 2 below.

[0230] In this case, O indicates a case where the electrolyte solution caught fire, and X indicates a case where the electrolyte solution did not catch fire.

[0231] Table 2

[0232] Presence or absence of ignition Comparative example 1 O Comparative example 2 × Comparative example 3 × Comparative example 4 × Comparative example 5 × Comparative example 6 × Example 1 × Example 2 × Example 3 × Example 4 × Example 5 × Example 6 × Example 7 × Example 8 ×

[0233] Referring to Table 2, it can be confirmed that the non-aqueous electrolyte solutions of Comparative Examples 2 to 6 containing the flame retardant additive and the non-aqueous electrolyte solutions of Examples 1 to 8 were not ignited, except for the electrolyte solution of Comparative Example 1 not containing the additive.

[0234] Experimental Example 2. Cycle characteristics evaluation

[0235] After the activation (formation) process was performed on the lithium secondary batteries prepared in Examples 9 to 16 and the lithium secondary batteries prepared in Comparative Examples 7 to 12 at a rate of 0.2C, a degassing process was performed to remove gas in each battery.

[0236] An initial charging and discharging process of 3 cycles was performed using a charge / discharge device, in which each of the lithium secondary batteries in which gas was removed was charged to 4.45V at a rate of 0.2C under constant current / constant voltage conditions at room temperature (25℃), was subjected to cut-off charging at 0.05C, and was discharged to 3.0V at a rate of 0.2C, which was taken as 1 cycle. In this case, a PNE-0506 charge / discharge device (manufacturer: PNE SOLUTION) was used as a charge / discharge device for battery charging and discharging.

[0237] Subsequently, a charging and discharging process of 74 cycles was performed using a charge / discharge device, in which each of the lithium secondary batteries was charged to 4.45V at a rate of 1.0C under constant current / constant voltage conditions at high temperature (45℃), was subjected to cut-off charging at 0.05C, and was discharged to 3.0V at a rate of 1.0C constant current, which was taken as 1 cycle.

[0238] Subsequently, the discharge capacity after 74 cycles was measured, the cycle characteristics were obtained by comparing the discharge capacity after 74 cycles with the initial capacity, and the results thereof are shown in Table 3 below.

[0239] Experimental Example 3. Rate performance evaluation

[0240] After the formation process was performed by charging the lithium secondary batteries prepared in Examples 9 to 16 and the lithium secondary batteries prepared in Comparative Examples 7 to 12 to a state of charge (SOC) of 100% at a rate of 0.2C, a degassing process was performed after aging for 4 hours. Each of the lithium secondary batteries after degassing was charged to 4.2V at a rate of 0.5C at 25℃, was subjected to cut-off charging at 0.05C, was initially charged under constant current-constant voltage (CC-CV) conditions, and was discharged to 3.0V at a rate of 0.5C under CC conditions, and the initial discharge capacity value was checked.

[0241] Then, after each lithium secondary battery was charged to 4.2 V at 25℃ at 0.5C rate, cut off at 0.05C, charged under constant current-constant voltage (CC-CV) conditions, and discharged to 3.0 V at 2C rate and 4C rate, respectively, the discharge capacity at 2C and 4C relative to the initial discharge capacity was evaluated and shown in Table 3 below.

[0242] Table 3

[0243]

[0244] Referring to Table 3, the secondary batteries of Examples 9 to 16 had a discharge capacity retention rate of about 93% or more after 74 cycles, wherein it can be appreciated that the discharge capacity retention rate after 74 cycles was improved compared to the secondary batteries of Comparative Examples 7 to 12.

[0245] Further, referring to Table 3, the secondary batteries of Examples 9 to 16 had a rate performance at 2C of 97.5% or more and a rate performance at 4C of 90.0% or more, wherein it can be appreciated that the rate performance at 2C and the rate performance at 4C were improved compared to the secondary batteries of Comparative Examples 7 to 12, respectively.

Claims

1. A nonaqueous electrolyte solution for a lithium secondary battery, the nonaqueous electrolyte solution comprising: a lithium salt; a nonaqueous solvent; a compound represented by Formula 1; and a compound represented by Formula 2, wherein a volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included is 1:0.1 to 1:1.5: [Formula 1] wherein, in Formula 1, R1 to R3 are each independently an alkyl group having 1 to 6 carbon atoms substituted with at least one fluorine element; [Formula 2] wherein, in Formula 2, R4 and R5 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, R6 to R8 are each independently hydrogen, fluorine, or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, and R9 is an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine.

2. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein, In Formula 1, R1 to R3 are each independently an alkyl group having 1 to 4 carbon atoms substituted with at least one fluorine element.

3. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein, In Formula 1, R1 to R3 are each independently an alkyl group having 1 to 3 carbon atoms substituted with at least one fluorine element.

4. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein, The compound represented by Formula 1 is a compound represented by Formula 1-1: [Formula 1-1] 5. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein, In Formula 2, R4 and R5 are each independently hydrogen or an alkyl group having 1 to 3 carbon atoms, R6 is fluorine or an alkyl group having 1 to 7 carbon atoms substituted with at least one fluorine, R7 and R8 are each independently hydrogen or fluorine, and R9 is an alkyl group having 1 to 5 carbon atoms substituted with at least one fluorine.

6. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein The compound represented by Formula 2 includes at least one of compounds represented by Formula 2-1 and Formula 2-2: [Formula 2-1] [Formula 2-2] 7. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, wherein, A volume ratio of the compound represented by Formula 1 and the compound represented by Formula 2 included is 1:0.2 to 1:

1.

8. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 1, further comprising at least one additive selected from the group consisting of butanedinitrile, trimethyl phosphate, and di-(2,2,2-trifluoroethyl) carbonate.

9. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 8, wherein, A volume ratio of the compound represented by Formula 1 and the additive included is 1:0.1 to 1:

5.

10. A lithium secondary battery containing the nonaqueous electrolyte solution for a lithium secondary battery according to claim 1.

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