Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. Specifically, the present invention relates to the following non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same, wherein the non-aqueous electrolyte solution for a lithium secondary battery comprises: a lithium salt, an organic solvent containing a carbonate compound and a propionate compound, and an additive, wherein the carbonate compound and the propionate compound are present in a volume ratio of 10:90 to 40:60, and the additive comprises 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile in a weight ratio of 1:1.5 to 1:3.7.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2020-0088217 filed on July 16, 2020, and Korean Patent Application No. 10-2021-0092353 filed on July 14, 2021, the disclosures of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. The non-aqueous electrolyte solution can form a stable film on the surface of an electrode. Background Art

[0005] With the recent development of the information society, personal IT devices and computer networks have been developed, and the dependence of society as a whole on electric energy has increased, and there is a need to develop technologies for efficiently storing and utilizing electric energy.

[0006] Lithium secondary batteries are the most suitable technology for use in various fields, among which lithium secondary batteries have been used as power sources for electric vehicles and power storage devices as well as notebook computers and mobile phones in view of the fact that they can be miniaturized to be suitable for personal IT equipment compared with lead batteries or nickel-cadmium batteries, have high energy density and operating voltage, and can have high capacity.

[0007] In order to achieve high energy density of lithium secondary batteries, a high operating voltage is required.

[0008] However, when a secondary battery is operated under a high voltage environment, the electrolyte solution is depleted due to the continuous oxidative decomposition reaction of the electrolyte solution, or the film formed on the electrode surface is degraded (collapsed) due to the side reaction between the electrolyte solution and the electrode, thereby causing the following problems: transition metal ions dissolve into the non-aqueous electrolyte solution or generate gas. Since this problem may be accelerated by the increase in voltage and storage temperature during battery operation or the generation of heat, the cycle characteristics of the battery may be reduced.

[0009] To solve this problem, it is necessary to develop a non-aqueous electrolyte solution that can prevent the continuous decomposition of the electrolyte solution and can suppress the reduction of the dissolved transition metals on the negative electrode by forming a stable film on the electrode surface at high voltage. Summary of the Invention

[0010] [Technical Issues]

[0011] One aspect of the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, which can form a stable film on the surface of a positive electrode.

[0012] Another aspect of the present invention provides a lithium secondary battery in which high-temperature storage characteristics and cycle characteristics during high-voltage operation are improved by including the non-aqueous electrolyte solution for a lithium secondary battery.

[0013] [Technical solution]

[0014] According to one aspect of the present invention, there is provided a non-aqueous electrolyte solution for a lithium secondary battery, comprising:

[0015] lithium salts,

[0016] An organic solvent containing a carbonate compound and a propionate compound, and

[0017] additive,

[0018] wherein the carbonate compound and the propionate compound are present in a volume ratio of 10:90 to 40:60, and

[0019] The additive includes 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid nitrile ((1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid nitrile) in a weight ratio of 1:1.5 to 1:3.7.

[0020] According to another aspect of the present invention, a lithium secondary battery is provided, comprising: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separator disposed between the negative electrode and the positive electrode; and the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

[0021] [Beneficial effects]

[0022] Since the non-aqueous electrolyte solution of the present invention contains 1,3,5-cyclohexanetricarbonitrile and 1,4-dicyano-2-butene containing two or more nitrile groups (-CN) in its structure, it can form a stable film on the surface of the positive electrode, which can facilitate the movement of lithium ions even during high-voltage operation. Therefore, it can effectively inhibit the dissolution of transition metals by preventing the collapse of the positive electrode caused by HF, and can improve the decomposition reaction of the non-aqueous electrolyte solution by preventing side reactions between the positive electrode and the electrolyte solution.

[0023] The nonaqueous electrolyte solution of the present invention can suppress gas generation at high voltage by reducing the amount of the carbonate compound (which is easily decomposed at high voltage) in the organic solvent component.

[0024] When the nonaqueous electrolyte solution of the present invention is used, a lithium secondary battery having improved high-temperature storage performance and cycle capacity retention during high-voltage operation can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following drawings of the specification illustrate preferred embodiments of the present invention by way of example, and together with the detailed description of the present invention provided below, are used to enable a further understanding of the technical concept of the present invention. Therefore, the present invention should not be interpreted solely by the contents of such drawings.

[0026] Figure 1 This is a graph showing the resistance evaluation results of Experimental Example 9 of the present invention. DETAILED DESCRIPTION

[0027] Hereinafter, the present invention will be described in more detail.

[0028] It will be understood that the words or terms used in the specification and claims should not be interpreted as the meanings defined in commonly used dictionaries, and it will also be understood that the words or terms should be understood to have the following meanings: based on the principle that the inventor can appropriately define the meanings of the words or terms to best explain the present invention, consistent with their meanings in the context of the relevant technology and the technical ideas of the present invention.

[0029] Regarding lithium secondary batteries, a film with passivation ability is formed on the surface of the negative electrode and the positive electrode, and the non-aqueous electrolyte solution decomposes during the initial charge and discharge to improve high temperature storage characteristics. However, since the metal elements are lost due to the degradation of the film during high voltage operation and high temperature storage due to the dissolution of the transition metal elements from the positive electrode, the discharge capacity may be reduced. In addition, since the thus dissolved transition metal ions are not only electrodeposited on the negative electrode (reacting in a strong reduction potential range to consume electrons), but also destroy the solid electrolyte interphase (SEI) on the negative electrode surface, the negative electrode surface is exposed, causing additional electrolyte decomposition reactions. Therefore, the capacity of the battery may continue to decrease while the irreversible capacity increases.

[0030] Therefore, the present invention aims to provide a non-aqueous electrolyte solution for a secondary battery that prevents the dissolution of transition metals by forming a stable film on the positive electrode surface and simultaneously suppresses side reactions between the electrode and the electrolyte solution, thereby reducing the amount of metal impurities in the battery. Furthermore, the present invention aims to provide a lithium secondary battery in which the inclusion of the non-aqueous electrolyte solution improves cycle characteristics during high-voltage operation.

[0031] Non-aqueous electrolyte solutions for lithium secondary batteries

[0032] According to one embodiment, the present invention provides a non-aqueous electrolyte solution for a lithium secondary battery.

[0033] The non-aqueous electrolyte solution for lithium secondary batteries comprises:

[0034] lithium salts,

[0035] An organic solvent containing a carbonate compound and a propionate compound, and

[0036] additive,

[0037] wherein the carbonate compound and the propionate compound are present in a volume ratio of 10:90 to 40:60, and

[0038] The additive includes 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid nitrile ((1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid nitrile) in a weight ratio of 1:1.5 to 1:3.7.

[0039] (1) Lithium salt

[0040] First, the lithium salt will be described as follows.

[0041] Any lithium salt commonly used in electrolyte solutions for lithium secondary batteries may be used as the lithium salt without particular limitation. For example, the lithium salt may include Li + as cations, and may include a compound selected from the group consisting of 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 of the group consisting of is used as an anion.

[0042] Specifically, the lithium salt may include a lithium salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(perfluoroethanesulfonyl)imide, LiBETI) and LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), or a mixture of two or more thereof. In addition to the above-mentioned lithium salts, any lithium salt commonly used in the electrolyte solution of lithium secondary batteries can also be used without limitation. Specifically, the lithium salt may include LiBF6.

[0043] In order to obtain the best effect of forming a film to prevent corrosion of the electrode surface, the lithium salt can be appropriately changed within a commonly used range and can be present in the electrolyte solution at a concentration of 0.8 M to 3.0 M (e.g., 1.0 M to 3.0 M). When the concentration of the lithium salt satisfies the above range, the viscosity of the non-aqueous electrolyte solution can be controlled so that optimal permeability can be achieved, and the capacity characteristics and cycle characteristics of the lithium secondary battery can be improved by improving the mobility of lithium ions.

[0044] (2) Organic solvents

[0045] In addition, the organic solvent will be described as follows.

[0046] The organic solvent may contain a carbonate compound and a propionate compound.

[0047] Specifically, the carbonate compound may include at least one selected from a cyclic carbonate compound and a linear carbonate compound.

[0048] The cyclic carbonate compound is an organic solvent that can well dissociate the lithium salt in the electrolyte due to its high dielectric constant as a highly viscous organic solvent, wherein a specific example thereof can be at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, wherein the cyclic carbonate compound can include at least one selected from ethylene carbonate and propylene carbonate, which can improve the output characteristics by improving the ion conductivity.

[0049] In addition, the linear carbonate compound is an organic solvent having low viscosity and low dielectric constant, wherein a general example thereof 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), methylpropyl carbonate and ethylpropyl carbonate, wherein the linear carbonate compound can include dimethyl carbonate.

[0050] Furthermore, in the present invention, in order to improve the disadvantages of the carbonate compound, a propionate compound having relatively higher stability during high-temperature and high-voltage operation than the carbonate compound may be mixed.

[0051] The propionate compound may include at least one selected from the group consisting of methyl propionate, ethyl propionate (EP), propyl propionate, and butyl propionate, and may specifically include at least one selected from ethyl propionate and propyl propionate.

[0052] The volume ratio of the carbonate compound to the propionate compound in the non-aqueous electrolyte solution may be 10:90 to 40:60, specifically 20:80 to 40:60, and preferably 30:70.

[0053] The volume ratio of the carbonate compound to the propionate compound can have a significant impact on improving the capacity and cycle characteristics at high temperature and room temperature during the preparation of the secondary battery. Therefore, when the volume ratio of the carbonate compound to the propionate compound meets the above range, a synergistic effect caused by the mixed use of the two organic solvents can be achieved. For example, when the carbonate compound and the propionate compound are present in the above range, the high-temperature storage stability can be improved during storage at a high voltage of 4.45V or above and a high temperature of 60°C or above, and at the same time, the cycle characteristics and capacity characteristics can be fully improved by ensuring the high ion conductivity of the electrolyte solution.

[0054] Since carbonate compounds are susceptible to side reactions at high voltages due to their high reactivity, when an excess of carbonate compounds is used as a non-aqueous solvent in high-voltage batteries, gas generation increases, and as a result, battery swelling increases and high-temperature storage stability may decrease. Therefore, when the volume ratio of the carbonate compound to the propionate compound is adjusted within the above range, electrolyte wetting can be improved by suppressing an increase in electrolyte viscosity, the oxidation reaction of the carbonate compound can be reduced to further improve battery stability and swelling suppression performance at high voltages, and battery safety can be improved because the ionic conductivity of lithium ions can be increased when the propionate compound is added at a desired level, and a stable SEI passivation film can be formed.

[0055] (3) Additives

[0056] The non-aqueous electrolyte solution for a lithium secondary battery of the present invention may contain two types of nitrile compounds as additives.

[0057] Specifically, the two types of nitrile compounds may include 1,4-dicyano-2-butene represented by the following Formula 1 and 1,3,5-cyclohexanetricarboxylic acid nitrile ((1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid nitrile) represented by Formula 2.

[0058] [Formula 1]

[0059]

[0060] [Formula 2]

[0061]

[0062] First, since 1,4-dicyano-2-butene contains at least one polar nitrile group (-CN) with a high dipole moment at both ends, it can not only form a stable film by forming a strong bond with the positive electrode active material, but also achieve the effect of suppressing the dissolution of metal ions due to its high binding force with dissolved metal ions. In addition, since 1,4-dicyano-2-butene contains a double bond in the middle of its structure compared to succinonitrile or adiponitrile (conventional nitrile additives), it is easier to form a film in the form of an organic polymer by oxidative decomposition of the double bond, and simultaneously form a composite structure or ligand by strongly binding to the metal ions on the positive electrode surface, so 1,4-dicyano-2-butene can form a very stable ion conductive film. Therefore, side reactions between the electrolyte and the positive electrode can be prevented, and gas generation can be suppressed. In addition, in addition to the metal ion adsorption effect described above, since the unshared electron pair of the nitrogen (N) of the nitrile group in 1,4-dicyano-2-butene stabilizes the anion of the lithium salt, thereby suppressing the generation of HF caused by the decomposition of the lithium salt, 1,4-dicyano-2-butene can further improve the high-temperature storage characteristics of the secondary battery.

[0063] In the non-aqueous electrolyte solution for a lithium secondary battery, 1,4-dicyano-2-butene may be present in an amount of 0.1 wt % to 2.5 wt %.

[0064] When the amount of 1,4-dicyano-2-butene is within the above range, a stable film can be formed on the surface of the positive electrode, effectively suppressing the dissolution of metal ions from the positive electrode. Furthermore, a stable film can be formed on the surfaces of both the negative and positive electrodes, effectively suppressing gas generation and resulting battery swelling due to side reactions between the positive electrode and the electrolyte solution. Therefore, when the amount of 1,4-dicyano-2-butene is within the above range, battery stability, battery swelling, and capacity characteristics during high-temperature storage can be further improved.

[0065] In the non-aqueous electrolyte solution, the amount of 1,4-dicyano-2-butene present can be specifically 0.5 wt % to 2 wt %, particularly 0.8 wt % to 1.7 wt %, and more particularly 0.8 wt % to 1.5 wt %. In the case where the amount of 1,4-dicyano-2-butene is 0.5 wt % or more, the metal foreign matter removal effect can be more stably maintained during the battery operation time. In the case where the amount of the compound represented by Formula 1 is 2.0 wt % or less, since the increase in the viscosity of the electrolyte solution caused by the excess compound can be prevented, the decrease in capacity and cycle characteristics can be prevented, the ion mobility in the battery can be improved at the same time, the battery swelling inhibition effect can be significantly improved, and the increase in battery resistance can be effectively prevented by suppressing excessive film formation.

[0066] In addition, since 1,3,5-cyclohexanetricarbonitrile (which contains three or more nitrile groups with high dipole moments) represented by Formula 2 has a very high binding affinity with ions of transition metals (such as cobalt (Co), manganese (Mn) or nickel (Ni)) dissolved from the positive electrode during the repeated charge and discharge process of the battery or the chemical dissolution reaction of the electrolyte solution, the dissolution of the metal ions can be effectively suppressed by forming a stable film on the positive electrode surface by combining with the metal ions. In particular, since 1,3,5-cyclohexanetricarbonitrile has a structure in which nitrile groups form a large volume with each other, it is excellent in the ability to form a complex by combining with the dissolved metal ions, and thus can prevent the precipitation or electrodeposition of the dissolved metal ions on the negative electrode surface, thereby improving thermal safety.

[0067] In the electrolyte solution of the present invention, the mixing ratio of 1,3,5-cyclohexanetricarboxylic acid nitrile to 1,4-dicyano-2-butene can have an important influence on improving the overall performance of the secondary battery, and the amount of 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid nitrile present in the non-aqueous electrolyte solution can be specifically 1:1.5 to 1:3.7.

[0068] When the amount of 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile is within the above range, a stable film is formed during storage at a high voltage of 4.45 V or higher and a high temperature of 60° C or higher, thereby suppressing metal dissolution from the positive electrode and preventing side reactions between the positive electrode and the electrolyte solution, thereby suppressing gas generation and battery swelling. When the amount of 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile is within the above range, the transition metal dissolution suppression effect and the cycle characteristics and capacity characteristics of the secondary battery can be fully improved, while minimizing the capacity reduction and resistance increase caused by side reactions.

[0069] In particular, the weight ratio of 1,3,5-cyclohexanetricarboxylic acid nitrile to 1,4-dicyano-2-butene may be 1:1.5 to 1:3.3, for example, 1:2 to 1:3.0.

[0070] When the weight ratio of 1,3,5-cyclohexanetricarbonitrile to 1,4-dicyano-2-butene is 1.5 or greater, a stable film can be easily formed on the surface, effectively suppressing side reactions and dissolution of transition metals, thereby improving battery capacity and cycle characteristics. When the weight ratio of 1,3,5-cyclohexanetricarbonitrile to 1,4-dicyano-2-butene is 3.3 or less, a film with low resistance is formed on the positive and negative electrodes, thereby reducing resistance, improving lithium mobility, and thus improving cycle characteristics.

[0071] (4) Other additives

[0072] If necessary, the non-aqueous electrolyte solution for lithium secondary batteries of the present invention may further include other additional additives in addition to the two nitrile additives to prevent the negative electrode from collapsing due to decomposition of the non-aqueous electrolyte solution in a high-power environment, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge protection, and the effect of inhibiting battery expansion at high temperatures.

[0073] Examples of other additives may be at least one selected from the group consisting of cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds or phosphite compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

[0074] The cyclic carbonate compound may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0075] The halogenated carbonate compound may include fluoroethylene carbonate (FEC).

[0076] The sultone compound may be, for example, at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethane sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0077] The sulfate compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS).

[0078] The phosphate or phosphite compound can be, for example, at least one compound selected from the group consisting of lithium difluorobis(oxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphite.

[0079] Borate compounds may include tetraphenyl borate and lithium oxalyldifluoroborate (LiODFB) or lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), which can form a film on the negative electrode surface.

[0080] The nitrile compound may include compounds other than 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid nitrile, for example, at least one compound selected from the group consisting of succinonitrile, pimelonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptonitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorobenzonitrile and 4-fluorobenzonitrile.

[0081] The benzene compound may be fluorobenzene, the amine compound may be triethanolamine or ethylenediamine, and the silane compound may be tetravinylsilane.

[0082] The lithium salt compound is a compound other than the lithium salt contained in the non-aqueous electrolyte solution, wherein the lithium salt compound may include LiPO 2 F 2 or LiBF 4 .

[0083] Among these other additives, in order to form a stronger SEI on the surface of the negative electrode, the non-aqueous electrolyte solution may include other additives having an excellent effect of forming a film on the surface of the negative electrode, in particular, at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC) and lithium oxalyldifluoroborate (LiODFB), as well as 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile.

[0084] Two or more compounds may be mixed and used as other additives. In the non-aqueous electrolyte solution, the amount of the other additives present may be 0.01 to 50 wt %, particularly 0.01 to 10 wt %, and preferably 0.05 to 5 wt %. When the amount of the other additives is within the above range, it is ideal because the remaining unreacted material and the occurrence of excessive side reactions due to excessive addition can be prevented, while significantly achieving the effect of improving the cycle characteristics by the other additives.

[0085] lithium secondary batteries

[0086] In another embodiment of the present invention, a lithium secondary battery is provided, comprising the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

[0087] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode, and the non-aqueous electrolyte solution for the lithium secondary battery.

[0088] More specifically, the lithium secondary battery may include a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the above-mentioned non-aqueous electrolyte solution for the lithium secondary battery.

[0089] After an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially stacked is formed and housed in a battery case, the lithium secondary battery of the present invention may be prepared by injecting the nonaqueous electrolyte solution of the present invention.

[0090] The lithium secondary battery of the present invention can be prepared and used according to conventional methods known in the art. In particular, the method for preparing the lithium secondary battery of the present invention is the same as described below.

[0091] (1) Positive electrode

[0092] The positive electrode may be prepared by coating a positive 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 current collector.

[0093] There is no specific limitation on the positive electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium or silver can be used.

[0094] In addition, the positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, wherein the positive electrode active material may include a lithium transition metal oxide containing lithium and at least one metal selected from cobalt, manganese, nickel, or aluminum.

[0095] Specifically, the positive electrode active material may include lithium cobalt-based oxides (e.g., LiCoO2, etc.), lithium manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium nickel-based oxides (e.g., LiNiO2, etc.), lithium nickel manganese-based oxides (e.g., LiNi 1- Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2)), lithium nickel cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1)), lithium manganese cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2)), lithium nickel manganese cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2 and p1 + q1 + r2 = 2), etc.) or lithium nickel cobalt transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), p2, q2, r3, and s2 are the atomic fractions of each individual element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < S2 < 1, p2 + q2 + r3 + S2 = 1), and may include any one of them or a mixture of two or more of them.

[0096] Among these materials, in terms of improving the capacity characteristics and stability of the battery, the positive electrode active material may include those selected from the group consisting of lithium cobalt oxide, lithium manganese-based oxide, and lithium nickel manganese cobalt-based oxide (e.g., including those selected from the group consisting of Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co0.2 )O2、Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 ) at least one of the group consisting of 2O2) may specifically include at least one selected from lithium cobalt oxide and lithium nickel manganese cobalt-based oxide, and may more specifically include at least one selected from lithium cobalt oxide and lithium nickel manganese cobalt-based oxide wherein the nickel content is 60atm% or more.

[0097] The lithium nickel manganese cobalt-based oxide may include a 0.6 Mn 0.2 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 )At least one of the group consisting of O2.

[0098] When high nickel (Hi-Ni) in which the Ni content is greater than 0.55 is used as the lithium transition metal oxide, due to the +1 Ions and Ni +2 The ions are similar in size, so cation mixing occurs during charge and discharge, where Li +1 ions and Ni +2 The position of the ions is exchanged in the layered structure of the positive electrode active material. In other words, the nickel transition metal having a d orbital in an environment (such as high temperature) should have an octahedral structure during coordination bonding according to the change in the oxidation value of Ni contained in the positive electrode active material, but when a distorted octahedron is formed by a heterogeneous reaction, the crystal structure of the positive electrode active material is deformed and collapsed. In the heterogeneous reaction, the oxidation value changes or the energy level order is reversed due to external energy supply. In addition, due to the side reaction between the positive electrode active material and the electrolyte solution during high temperature storage, another side reaction is caused (in which the transition metal, especially nickel metal, is dissolved from the positive electrode active material). Therefore, due to the structural collapse of the positive electrode active material and the loss of the electrolyte solution, the overall performance of the secondary battery is reduced.

[0099] In the present invention, this problem can be improved by using a non-aqueous electrolyte solution containing a specific configuration of additives and a positive electrode containing a high nickel (Hi-Ni) transition metal oxide as a positive electrode active material. In other words, since a strong ion conductive film is formed on the positive electrode surface by the non-aqueous electrolyte solution of the present invention, Li +1 ions and Ni+2 The ion mixing phenomenon is suppressed, and the side reaction between the positive electrode and the electrolyte solution and the metal dissolution phenomenon are effectively suppressed, thereby reducing the structural instability of the high-capacity electrode. As a result, since a sufficient amount of nickel transition metal can be ensured to ensure the capacity of the lithium secondary battery, the energy density can be increased to improve the output characteristics.

[0100] The positive electrode active material may be present in an amount of 80 wt % to 99 wt %, for example 90 wt % to 99 wt %, based on the total weight of the solids in the positive electrode slurry. When the amount of the positive electrode active material is less than 80 wt %, the capacity may be reduced due to reduced energy density.

[0101] The binder is a component that helps the bonding between the active material and the conductive agent and the bonding with the current collector, wherein the amount of the binder added is generally 1% to 30% by weight based on the total weight of the solids in the positive electrode slurry. Examples of the binder may be fluororesin binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose or regenerated cellulose; polyol binders, such as polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester binders; and silane binders.

[0102] The conductive agent is a material that provides conductivity without causing adverse chemical changes in the battery. The conductive agent may be added in an amount of 1 wt % to 20 wt % based on the total weight of the solids in the positive electrode slurry.

[0103] 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 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 carbon fluoride powder, aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or polyphenylene derivatives.

[0104] In addition, the solvent may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and the amount used may be such that the desired viscosity is obtained when the positive electrode active material and the optional binder and conductive agent are included. For example, the content of the solvent may be such that the solid concentration in the positive electrode slurry containing the positive electrode active material and the optional binder and conductive agent is 10 wt % to 60 wt %, such as 20 wt % to 50 wt %.

[0105] (2) Negative electrode

[0106] The negative electrode may be prepared by coating a negative electrode 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 collector.

[0107] The thickness of the negative electrode current collector is generally 3 to 500 μm. There are no specific limitations on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, or aluminum-cadmium alloys can be used. Similarly to the positive electrode current collector, the negative electrode current collector can have fine surface roughness to enhance bonding strength with the negative electrode active material. The negative electrode current collector can be used in a variety of shapes, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0108] 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 intercalating / deintercalating lithium ions, a metal or an alloy of lithium and the metal, a metal composite oxide, a material that can be doped and dedoped with lithium, and a transition metal oxide.

[0109] As a carbon material capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used without particular limitation, and as a typical example, crystalline carbon and / or amorphous carbon can be used. Examples of crystalline carbon can be graphite, such as random, planar, flaky, spherical or fibrous natural graphite or artificial graphite; examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbide and fired coke.

[0110] 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.

[0111] As the metal composite oxide, 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), Fe, Pb or Ge; Me': Al, boron (B), phosphorus (P), Si, elements of Groups I, II and III of the periodic table, or a halogen, 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), one kind in the group.

[0112] Materials that can be doped and undoped with lithium may include: Si, SiO x (0 < x ≤ 2), 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 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), and mixtures of SiO2 with at least one of them can also be used. Element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, scandium (Sc), yttrium (Y), Ti, zirconium (Zr), hafnium (Hf), (Rf), V, niobium (Nb), Ta, (Db), Cr, Mo, tungsten (W), (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.

[0113] Transition metal oxides may include lithium-containing titanium composite oxides (LTO), vanadium oxides, and lithium vanadium oxides.

[0114] Based on the total weight of the solids in the negative electrode paste, the amount of the negative electrode active material present may be 80% to 99% by weight.

[0115] The binder is a component that helps to bind the conductive agent, active material and current collector, wherein the amount of the binder added is generally 1% to 30% by weight based on the total weight of the solids in the negative electrode slurry. Examples of the binder may be fluororesin binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose or regenerated cellulose; polyol binders, such as polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester binders; and silane binders.

[0116] The conductive agent is a component that further improves the conductivity of the negative electrode active material, wherein the amount of the conductive agent added can be 1% to 20% by weight based on the total weight of the solid content in the negative electrode slurry. Any conductive agent can be used without specific limitation, as long as it has conductivity and does not cause adverse chemical changes 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 black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive fibers, such as carbon fibers or metal fibers; conductive powders, such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or polyphenylene derivatives.

[0117] The solvent may include water or an organic solvent, such as NMP and alcohol, and when the negative electrode active material and optionally a binder and a conductive agent are included, the amount of the solvent may be such that a desired viscosity is obtained. For example, the amount of the solvent may be such that the solids concentration in the negative electrode slurry containing the negative electrode active material and optionally a binder and a conductive agent is 50 wt % to 75 wt %, for example 50 wt % to 65 wt %.

[0118] (3) Diaphragm

[0119] As the separator included in the lithium secondary battery of the present invention, commonly used general porous polymer films (such as porous polymer films prepared from polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers)) can be used alone or as a laminate thereof, and general porous non-woven fabrics can be used, such as non-woven fabrics formed from high-melting point glass fibers or polyethylene terephthalate fibers, but the present invention is not limited thereto.

[0120] The shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical type using a can, a prismatic type, a pouch type, or a coin type may be used.

[0121] Hereinafter, the present invention will be described in more detail based on embodiments. However, the present invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that this description will be thorough and complete and will fully convey the scope of the present invention to those skilled in the art.

[0122] Example

[0123] I. Preparation of non-aqueous electrolyte solution for lithium secondary batteries

[0124] Example 1

[0125] LiPF6 was dissolved in 95.5 g of a non-aqueous organic solvent (in which ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP) and propyl propionate (PP) were mixed in a volume ratio of 2:1:2.5:4.5) so that the concentration of LiPF6 was 1.2 M, and 1.0 g of 1,4-dicyano-2-butene (hereinafter referred to as "DCB"), 1.5 g of 1,3,5-cyclohexanetricarbonitrile (hereinafter referred to as "CHTN") and 1.0 g of vinyl ethylene carbonate (VEC) and 1.0 g of fluoroethylene carbonate (FEC) as other additives were added (see Table 1 below) to prepare a non-aqueous electrolyte solution for a lithium secondary battery.

[0126] Example 2

[0127] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 2.0 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 95.0 g of a non-aqueous organic solvent (see Table 1 below).

[0128] Example 3

[0129] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 3.0 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 94.0 g of a non-aqueous organic solvent (see Table 1 below).

[0130] Example 4

[0131] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 3.5 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 93.5 g of a non-aqueous organic solvent (see Table 1 below).

[0132] Comparative Example 1

[0133] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB as an additive and 1.0 g of VEC, 1.0 g of FEC, and 1.5 g of tricyanoethylamine as other additives were added to 95.5 g of a non-aqueous organic solvent (see Table 1 below).

[0134] Comparative Example 2

[0135] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB as an additive and 1.0 g of VEC, 1.0 g of FEC and 1.5 g of tricyanoethoxypropane as other additives were added to 95.5 g of a non-aqueous organic solvent (see Table 1 below).

[0136] Comparative Example 3

[0137] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB as an additive and 1.0 g of VEC, 1.0 g of FEC, and 1.0 g of 1,3,6-hexanetricarbonitrile (HTCN) as other additives were added to 96.0 g of a non-aqueous organic solvent (see Table 1 below).

[0138] Comparative Example 4

[0139] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.5 g of CHTN as an additive and 1.0 g of VEC, 1.0 g of FEC, and 1.0 g of SN as other additives were added to 95.5 g of a non-aqueous organic solvent (see Table 1 below).

[0140] Comparative Example 5

[0141] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of VEC, 1.0 g of FEC, 1.5 g of SN, and 1.0 g of 1,3,6-hexanetricarbonitrile (HTCN) were added to 95.5 g of the non-aqueous organic solvent as other additives (see Table 1 below).

[0142] Comparative Example 6

[0143] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of CHTN as an additive and 1.0 g of VEC, 1.0 g of FEC, and 1.0 g of SN as other additives were added to 96.0 g of a non-aqueous organic solvent (see Table 1 below).

[0144] Comparative Example 7

[0145] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 3.0 g of CHTN as an additive and 1.0 g of VEC, 1.0 g of FEC, and 2.0 g of pimelonitrile (PN) as other additives were added to 93.0 g of a non-aqueous organic solvent (see Table 1 below).

[0146] Comparative Example 8

[0147] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 1.4 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 95.6 g of a non-aqueous organic solvent (see Table 1 below).

[0148] Comparative Example 9

[0149] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 4.0 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 93.0 g of a non-aqueous organic solvent (see Table 1 below).

[0150] Comparative Example 10

[0151] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 1.0 g of CHTN as additives and 1.0 g of VEC and 1.0 g of FEC as other additives were added to 96.0 g of a non-aqueous organic solvent (see Table 1 below).

[0152] Comparative Example 11

[0153] A non-aqueous electrolyte solution for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1.0 g of DCB and 1.0 g of CHTN as additives and 1.0 g of VEC, 1.0 g of FEC, and 1.0 g of SN as other additives were added to 95.0 g of a non-aqueous organic solvent (see Table 1 below).

[0154] Table 1

[0155]

[0156] In Table 1, the abbreviations of the compounds have the following meanings.

[0157] DCB: 1,4-dicyano-2-butene

[0158] CHTN:1,3,5-cyclohexanetricarbonitrile

[0159] HTCN: 1,3,6-hexanetricarbonitrile

[0160] SN: Succinonitrile

[0161] PN: Pimelonitrile

[0162] FEC: Fluoroethylene carbonate

[0163] VEC: vinyl ethylene carbonate

[0164] II. Preparation of lithium secondary batteries

[0165] Example 5

[0166] The positive electrode active material (LiCoO2), conductive agent (carbon black), and binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) at 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 as a positive electrode current collector was coated with the positive electrode slurry, dried, and then roll-pressed to prepare a positive electrode.

[0167] A negative electrode slurry (solid content: 60 wt%) was prepared by adding the negative electrode active material (artificial graphite), a binder (SBR-CMC), and a conductive agent (carbon black) to water at a weight ratio of 95:3.5:1.5. A 6 μm thick copper (Cu) film, serving as a negative electrode current collector, was coated with the negative electrode slurry, dried, and then roll-pressed to prepare a negative electrode.

[0168] The positive electrode, the polyolefin porous separator coated with inorganic particles (Al2O3) and the negative electrode are stacked in sequence to prepare an electrode assembly.

[0169] The electrode assembly was installed in a pouch-type battery case, and the non-aqueous electrolyte solution for the lithium secondary battery was injected therein, thereby preparing a pouch-type lithium secondary battery having an operating voltage of 4.45 V or higher.

[0170] Example 6

[0171] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Example 2 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0172] Example 7

[0173] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Example 3 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0174] Example 8

[0175] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Example 4 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0176] Example 9

[0177] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 as the positive electrode active material.

[0178] Example 10

[0179] A pouch-type lithium secondary battery was prepared in the same manner as in Example 6, except that Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 as the positive electrode active material.

[0180] Example 11

[0181] A pouch-type lithium secondary battery was prepared in the same manner as in Example 8, except that Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 as the positive electrode active material.

[0182] Comparative Example 12

[0183] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 1 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0184] Comparative Example 13

[0185] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 2 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0186] Comparative Example 14

[0187] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 3 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0188] Comparative Example 15

[0189] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 4 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0190] Comparative Example 16

[0191] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 5 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0192] Comparative Example 17

[0193] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 6 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0194] Comparative Example 18

[0195] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 7 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0196] Comparative Example 19

[0197] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 8 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0198] Comparative Example 20

[0199] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 9 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0200] Comparative Example 21

[0201] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 10 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0202] Comparative Example 22

[0203] A pouch-type lithium secondary battery was prepared in the same manner as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 11 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0204] Comparative Example 23

[0205] 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.

[0206] Comparative Example 24

[0207] 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 8 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0208] Comparative Example 25

[0209] 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 9 was injected instead of the nonaqueous electrolyte solution of Example 1.

[0210] Experimental example

[0211] Experimental Example 1. Evaluation of initial discharge capacity (1)

[0212] The pouch-type secondary batteries prepared in Examples 5 to 8 and the pouch-type secondary batteries prepared in Comparative Examples 12 to 20 and 22 were placed in a drying chamber and respectively formed at room temperature (25°C) by charging to a state of charge (SOC) of 1 / 6 (17.6 mAh) at a 0.2C rate (21.2 mA), followed by a degassing process.

[0213] Each secondary battery was then discharged at 0.2C, charged at a rate of 0.7C under 0.2C constant current / constant voltage conditions, and discharged at a rate of 0.2C, after which the initial discharge capacity was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNE SOLUTION Co., Ltd.). The results are presented in Table 2 below.

[0214] Table 2

[0215] Example Non-aqueous electrolyte solution Positive electrode type Initial discharge capacity (mAh) Example 5 Example 1 LCO 105.8 Example 6 Example 2 LCO 103.7 Example 7 Example 3 LCO 101.3 Example 8 Example 4 LCO 99.8 Comparative Example 12 Comparative Example 1 LCO 80.7 Comparative Example 13 Comparative Example 2 LCO 81.6 Comparative Example 14 Comparative Example 3 LCO 77.8 Comparative Example 15 Comparative Example 4 LCO 77.6 Comparative Example 16 Comparative Example 5 LCO 73.5 Comparative Example 17 Comparative Example 6 LCO 72.6 Comparative Example 18 Comparative Example 7 LCO 77.8 Comparative Example 19 Comparative Example 8 LCO 75.7 Comparative Example 20 Comparative Example 9 LCO 73.6 Comparative Example 22 Comparative Example 11 LCO 97.0

[0216] Referring to Table 2, it can be seen that the initial discharge capacity of the lithium secondary batteries of Examples 5 to 8 is improved compared to the secondary batteries of Comparative Examples 12 to 20 and 22. Specifically, it can be seen that the initial discharge capacity of the lithium secondary battery of Comparative Example 20 (which contains a non-aqueous electrolyte solution containing a considerable amount of 3,5-cyclohexanetricarboxylate) is relatively lower than that of the secondary batteries of Examples 5 to 8 due to the increase in membrane resistance in the battery. In addition, for the secondary batteries of Comparative Examples 19 and 22 containing a small amount of 1,3,5-cyclohexanetricarboxylate, it can be seen that the initial discharge capacity is relatively reduced compared to the secondary batteries of Examples 5 to 8 due to insufficient membrane formation and the dissolution of metal ions on the electrode surface.

[0217] Experimental Example 2. Evaluation of Capacity Retention Rate (%) after Charge and Discharge at Room Temperature (1)

[0218] The pouch-type secondary batteries prepared in Examples 5 to 8 and the pouch-type secondary batteries prepared in Comparative Examples 12 to 17 and 19 to 21 were charged at a 1.0C rate (106 mA) at room temperature (25°C) and discharged at a 1.0C rate (106 mA). The above charge and discharge was set as 1 cycle and performed 200 cycles, after which the capacity retention rate (%) was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNESOLUTION Co., Ltd., 5V, 6A), the results of which are presented in Table 3 below. The capacity retention rate (%) was calculated according to the following [Equation 1].

[0219] [Equation 1]

[0220] Capacity retention (%) = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) × 100

[0221] Table 3

[0222] Example Non-aqueous electrolyte solution Positive electrode type Capacity retention after cycling at 25°C (%) Example 5 Example 1 LCO 82.4 Example 6 Example 2 LCO 80.5 Example 7 Example 3 LCO 79.3 Example 8 Example 4 LCO 79.1 Comparative Example 12 Comparative Example 1 LCO 75.5 Comparative Example 13 Comparative Example 2 LCO 77.1 Comparative Example 14 Comparative Example 3 LCO 78.5 Comparative Example 15 Comparative Example 4 LCO 73.3 Comparative Example 16 Comparative Example 5 LCO 72.0 Comparative Example 17 Comparative Example 6 LCO 70.7 Comparative Example 19 Comparative Example 8 LCO 65.3 Comparative Example 20 Comparative Example 9 LCO 64.8 Comparative Example 21 Comparative Example 10 LCO 78.2

[0223] Referring to Table 3, it can be seen that the capacity retention rate after charging and discharging at room temperature of the lithium secondary batteries of Examples 5 to 8, which contain the non-aqueous electrolyte solution containing the additive of the present invention, is improved compared to the lithium secondary batteries of Comparative Examples 12 to 17 and 19 to 21. In particular, it can be seen that the capacity retention rate (%) of the lithium secondary battery of Comparative Example 20, which contains the non-aqueous electrolyte solution containing a relatively large amount of 1,3,5-cyclohexanetricarboxylic acid, is relatively lower than that of the lithium secondary batteries of Examples 5 to 8 due to the membrane resistance in the battery. In addition, for the secondary battery of Comparative Example 21 containing a relatively small amount of 1,3,5-cyclohexanetricarboxylic acid, it seems that the capacity retention rate is lower than that of the secondary batteries of Examples 5 to 8 due to insufficient membrane formation and the dissolution of metal ions on the electrode surface.

[0224] Experimental Example 3. Evaluation of Capacity Retention Rate (%) after Charging and Discharging at High Temperature (1)

[0225] The pouch-type secondary batteries prepared in Examples 5 to 7 and the pouch-type secondary batteries prepared in Comparative Examples 12, 13, 15 to 17, and 19 to 22 were charged at a 1.0C rate (106 mA) at a high temperature (45°C) and discharged at a 1.0C rate (106 mA). The above charge and discharge was set as 1 cycle and performed 200 cycles, after which the capacity retention rate (%) was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNE SOLUTION Co., Ltd., 5V, 6A). The results are presented in Table 4 below. The capacity retention rate (%) was calculated according to [Equation 1].

[0226] Table 4

[0227] Example Non-aqueous electrolyte solution Positive electrode type Capacity retention after cycling at 45°C (%) Example 5 Example 1 LCO 80.5 Example 6 Example 2 LCO 78.1 Example 7 Example 3 LCO 77.5 Comparative Example 12 Comparative Example 1 LCO 73.8 Comparative Example 13 Comparative Example 2 LCO 73.0 Comparative Example 15 Comparative Example 4 LCO 61.4 Comparative Example 16 Comparative Example 5 LCO 55.6 Comparative Example 17 Comparative Example 6 LCO 59.1 Comparative Example 19 Comparative Example 8 LCO 55.3 Comparative Example 20 Comparative Example 9 LCO 57.5 Comparative Example 21 Comparative Example 10 LCO 76.5 Comparative Example 22 Comparative Example 11 LCO 75.5

[0228] Referring to Table 4, for the lithium secondary batteries of Examples 5 to 7 comprising the non-aqueous electrolyte solution containing the additive of the present invention, it can be seen that the high temperature cycle capacity retention is improved compared to the lithium secondary batteries of Comparative Examples 12, 13, 15 to 17 and 19 to 22.

[0229] Experimental Example 4. Characteristics evaluation after high temperature storage (1)

[0230] The pouch-type secondary batteries prepared in Examples 5 to 7 and the pouch-type secondary batteries prepared in Comparative Examples 13, 14, and 16 to 22 were formed by charging to an SOC of 1 / 6 (17.6 mAh) at a 0.2C rate (21.2 mA) in a dry room at room temperature (25°C). Afterwards, each secondary battery was fully discharged at a 0.2C rate and then charged / discharged again at 0.2C. Thereafter, each secondary battery was fully discharged at a 0.2C rate and stored at a high temperature of 85°C for 8 hours.

[0231] Then, each secondary battery was charged and discharged at a 1.0 C rate (106 mA) and then at a 1.0 C rate (106 mA), and the discharge capacity was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNE SOLUTION Co., Ltd., 5 V, 6 A). The results are presented in Table 5 below.

[0232] Table 5

[0233] Example Non-aqueous electrolyte solution Positive electrode type Discharge capacity after storage at 85℃ (%) Example 5 Example 1 LCO 91.1 Example 6 Example 2 LCO 89.5 Example 7 Example 3 LCO 85.3 Comparative Example 13 Comparative Example 2 LCO 78.3 Comparative Example 14 Comparative Example 3 LCO 83.5 Comparative Example 16 Comparative Example 5 LCO 75.6 Comparative Example 17 Comparative Example 6 LCO 70.5 Comparative Example 18 Comparative Example 7 LCO 71.0 Comparative Example 19 Comparative Example 8 LCO 69.4 Comparative Example 20 Comparative Example 9 LCO 67.3 Comparative Example 21 Comparative Example 10 LCO 82.9 Comparative Example 22 Comparative Example 11 LCO 82.1

[0234] Referring to Table 5, it can be seen that the lithium secondary batteries of Examples 5 to 7 including the nonaqueous electrolyte solutions of the present invention have improved discharge capacities after high-temperature storage compared to the lithium secondary batteries of Comparative Examples 13, 14, and 16 to 22.

[0235] Experimental Example 5. Evaluation of Initial Discharge Capacity (2)

[0236] The pouch-type secondary batteries prepared in Examples 9 to 11 and the pouch-type secondary batteries prepared in Comparative Examples 23 to 25 were formed by charging to an SOC of 1 / 6 (17.6 mAh) at a 0.2 C rate (21.2 mA) at room temperature (25° C.) in a dry room, followed by a degassing process.

[0237] Each secondary battery was then discharged at 0.2C, then charged at a rate of 0.7C under 0.2C constant current / constant voltage conditions, and discharged at a rate of 0.2C, after which the initial discharge capacity was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNE SOLUTION Co., Ltd.). The results are presented in Table 6 below.

[0238] Experimental Example 6. Evaluation of Capacity Retention Rate (%) after Charge and Discharge at Room Temperature (2)

[0239] The pouch-type secondary batteries prepared in Examples 9 to 11 and the pouch-type secondary batteries prepared in Comparative Examples 23 to 25 were charged at a 1.0C rate (106 mA) and discharged at a 1.0C rate (106 mA) at room temperature (25°C). The charge and discharge cycle was set as 1 cycle and was performed 200 times. After that, the capacity retention (%) was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNESOLUTION Co., Ltd., 5V, 6A). The results are presented in Table 6 below. The capacity retention (%) was calculated according to [Equation 1].

[0240] Experimental Example 7. Evaluation of Capacity Retention Rate (%) after Charging and Discharging at High Temperature (2)

[0241] The pouch-type secondary batteries prepared in Examples 9 to 11 and the pouch-type secondary batteries prepared in Comparative Examples 23 to 25 were charged at a 1.0C rate (106 mA) at a high temperature (45°C) and discharged at a 1.0C rate (106 mA). The above charge and discharge was set as 1 cycle and performed 200 cycles. After that, the capacity retention (%) was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNESOLUTION Co., Ltd., 5V, 6A). The results are presented in Table 6 below. The capacity retention (%) was calculated according to [Equation 1].

[0242] Experimental Example 8. Characteristics evaluation after high-temperature storage (2)

[0243] The pouch-type secondary batteries prepared in Examples 9 to 11 and the pouch-type secondary batteries prepared in Comparative Examples 22 to 25 were formed by charging to a SOC of 1 / 6 (17.6 mAh) at a 0.2C rate (21.2 mA) at room temperature (25°C) in a dry room. Afterwards, each secondary battery was fully discharged at a 0.2C rate and then charged / discharged again at 0.2C. Thereafter, each secondary battery was fully discharged at a 0.2C rate and stored at a high temperature of 85°C for 8 hours.

[0244] Then, each secondary battery was charged and discharged at a 1.0 C rate (106 mA), and then the discharge capacity was measured using a PNE-0506 charge / discharge instrument (manufacturer: PNE SOLUTION Co., Ltd., 5 V, 6 A). The results are presented in Table 6 below.

[0245] Table 6

[0246]

[0247] Referring to the initial discharge capacity evaluation results in Table 6, it can be seen that for the lithium secondary batteries of Examples 9 to 11, the initial discharge capacity, the capacity retention rate (%) after room temperature and high temperature cycles, and the discharge capacity after high temperature storage are all improved compared to the lithium secondary batteries of Comparative Examples 23 to 25.

[0248] Experimental Example 9. Resistance Evaluation

[0249] The lithium secondary batteries prepared in Example 5 and Comparative Example 21 were charged to 50% SOC at a rate of 0.5C at room temperature (25°C). Electrochemical impedance spectroscopy (EIS) was used to measure the change in battery impedance with the amount of additive by applying alternating current (AC) signals of different frequencies to the battery. The results are shown below. Figure 1 middle.

[0250] See also Figure 1 The secondary battery of Example 5, which included the non-aqueous electrolyte solution of Example 1 (containing 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid at a ratio of 1:1.5), showed a minimum AC resistance and improved charge and discharge performance. In contrast, the secondary battery of Comparative Example 21, which included a non-aqueous electrolyte solution containing 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid at a ratio of 1:1, showed a higher resistance than that of the secondary battery of Example 5.

[0251] From these results, it can be seen that when the amount of 1,4-dicyano-2-butene is slightly higher than that of 1,3,5-cyclohexanetricarboxylic acid, the film resistance on the electrode surface increases. Therefore, it can be seen that the weight ratio of 1,3,5-cyclohexanetricarboxylic acid to 1,4-dicyano-2-butene is preferably 1.5 or more.

Claims

1. A non-aqueous electrolyte solution for a lithium secondary battery, comprising: lithium salts, An organic solvent containing a carbonate compound and a propionate compound, and additive, in, The carbonate compound and the propionate compound are present in a volume ratio of 10:90 to 40:60, and The additive comprises 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarbonitrile in a weight ratio of 1:1.5 to 1:3.7, and The 1,4-dicyano-2-butene is present in the non-aqueous electrolyte solution in an amount of 0.1 wt % to 2.5 wt %.

2. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein The carbonate compound and the propionate compound are present in a volume ratio of 20:80 to 40:

60.

3. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein The carbonate compound includes at least one selected from a cyclic carbonate compound and a linear carbonate compound.

4. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 3, wherein The cyclic carbonate compound is at least one selected from ethylene carbonate and propylene carbonate.

5. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein The propionate compound is at least one selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

6. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein The 1,4-dicyano-2-butene is present in the non-aqueous electrolyte solution in an amount of 0.5 wt % to 2 wt %.

7. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein 1,4-dicyano-2-butene and 1,3,5-cyclohexanetricarboxylic acid nitrile are present in the non-aqueous electrolyte solution at a weight ratio of 1:1.5 to 1:3.

3.

8. A lithium secondary battery comprising: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; a separator disposed between the negative electrode and the positive electrode; and The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1.

9. The lithium secondary battery according to claim 8, wherein The positive electrode active material includes at least one selected from lithium cobalt oxide, lithium manganese-based oxide, and lithium nickel manganese cobalt-based oxide.

10. The lithium secondary battery according to claim 8, wherein The positive electrode active material includes at least one selected from lithium cobalt oxide and lithium nickel manganese cobalt-based oxide.

11. The lithium secondary battery according to claim 10, wherein The lithium nickel manganese cobalt-based oxide comprises a compound selected from the group consisting of Li(Ni 0.6 Mn 0.2 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 )At least one of the group consisting of O2.

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