Electrolyte composition for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present invention relates to an electrolyte composition for a lithium secondary battery and a lithium secondary battery comprising the same. According to an embodiment of the present invention, flame retardancy of an electrolyte for a lithium secondary battery may be improved, and according to a further aspect of the present invention, charge / discharge life characteristics of a lithium secondary battery may be improved and battery resistance of the lithium secondary battery may be reduced.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0113469, filed on August 23, 2024, entitled "Electrolyte Composition for Lithium Secondary Batteries and Lithium Secondary Batteries Containing the Electrolyte Composition", the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to an electrolyte composition for lithium secondary batteries and a lithium secondary battery comprising the electrolyte composition. Background Technology

[0004] Generally, due to the use of electroactive materials, lithium-ion batteries have higher operating voltages and greater energy densities than lead-acid or nickel / cadmium batteries. Therefore, lithium-ion batteries are attracting attention as an energy storage solution for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0005] To increase the range of electric vehicles, high battery energy density is crucial. To achieve high battery energy density, it is necessary to increase the capacity of the positive and negative electrode materials, or to increase the battery's operating voltage.

[0006] To improve battery operating voltage, the oxidative stability of the electrolyte is a crucial factor. Typically, carbonates, esters, ethers, or ketones are used alone or in combination as non-aqueous organic solvents. However, carbonate solvents are flammable organic materials that can cause side reactions and form dendrites with lithium metal. Therefore, there are concerns about potentially lower battery safety when using carbonate solvents as electrolytes. Furthermore, due to their low flash point and high volatility, carbonate solvents can react with electrode materials at high temperatures, triggering combustion reactions that rapidly increase battery temperature and potentially lead to thermal runaway. Therefore, developing stable electrolytes may be a key factor in improving the energy density of lithium-ion rechargeable batteries. Summary of the Invention

[0007] One aspect of the present invention is to provide an electrolyte with improved flame retardancy.

[0008] Another aspect of the present invention is to provide a lithium secondary battery with improved lifespan characteristics.

[0009] Another aspect of the present invention is to provide a lithium secondary battery with improved output characteristics.

[0010] One aspect of the present invention is to provide an electrolyte composition for lithium secondary batteries, which can be applied in green technology fields that use batteries, such as electric vehicles.

[0011] To achieve these aspects, the present invention provides an electrolyte composition for lithium secondary batteries comprising a lithium salt and an organic solvent, wherein the organic solvent comprises an ether solvent and an aromatic solvent of the following chemical formula 1.

[0012] [Chemical Formula 1]

[0013]

[0014] In chemical formula 1, R 1 R 2 R 3 R 4 and R 5 It can be hydrogen or fluorine independently, and R 1 R 2 R 3 R 4 and R 5 At least three or more of them can be fluorine.

[0015] In one embodiment of the present invention, the aromatic solvent may include at least one selected from 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 2,4,5-trifluorotoluene, and 2,4,6-trifluorotoluene.

[0016] In one embodiment of the present invention, the ether solvent may include at least one selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0017] In one embodiment of the present invention, the lithium salt may include those selected from Li(CF3SO2)2N (LiTFSI), LiBF2(C2O4) (LIDFOB), Li(SO2F)2N (LiFSI), LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4.

[0018] In one embodiment of the invention, the electrolyte composition for a lithium secondary battery may contain an amount of aromatic solvent ranging from about 30% to 90% by volume, based on the total volume of the electrolyte composition.

[0019] In one embodiment of the invention, the molar concentration of the lithium salt can be from about 0.1 M to 3.0 M.

[0020] Another aspect of the present invention provides a lithium secondary battery comprising an electrolyte composition for lithium secondary batteries.

[0021] Another aspect of the present invention provides a lithium metal secondary battery comprising: a positive electrode containing a positive electrode active material; a negative electrode containing lithium metal; a separator disposed between the positive electrode and the negative electrode; and an electrolyte comprising an electrolyte composition for a lithium secondary battery.

[0022] In some embodiments, the electrolyte composition for lithium secondary batteries comprises a lithium salt and an organic solvent, said organic solvent including 2,3,4-trifluorotoluene. The organic solvent may further comprise an ether solvent, which may be selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran. The lithium salt may include those selected from Li(CF3SO2)2N (LiTFSI), Li(SO2F)2N (LiFSI), LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 The composition may contain at least one compound selected from the following: LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, and LiB(C6H5)4. The composition may contain 2,3,4-trifluorotoluene in an amount of about 30% to 90% of the total electrolyte volume, and the lithium salt concentration may be in the range of about 0.1 M to 3.0 M.

[0023] In some embodiments, the electrolyte composition for lithium secondary batteries comprises a lithium salt and an organic solvent, said organic solvent including aromatic solvents of the following general formula:

[0024] [Chemical Formula 1]

[0025]

[0026] In this formula, R 1 R 2 R 3 R 4 and R5 Independently hydrogen or fluorine, wherein R 1 R 2 R 3 R 4 and R 5 At least three or more of the components are fluorine. The organic solvent may further include an ether solvent selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran. The aromatic solvent may be selected from 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 2,4,5-trifluorotoluene, and 2,4,6-trifluorotoluene, or combinations thereof. Based on the total volume of the electrolyte, the aromatic solvent may be present in an amount from about 30% to 90% by volume, and the molar concentration of the lithium salt may be in the range of about 0.1 M to 3.0 M.

[0027] According to embodiments of the present invention, the flame retardancy of electrolytes used in lithium secondary batteries can be improved.

[0028] According to another aspect of the present invention, the charge / discharge life characteristics of lithium secondary batteries can be improved.

[0029] According to another aspect of the present invention, the battery resistance of a lithium secondary battery can be reduced.

[0030] As discussed, the method and system appropriately include the use of a controller or processor.

[0031] In another embodiment, a vehicle is provided that includes the device as disclosed herein. Attached Figure Description

[0032] The above and other aspects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0033] Figure 1 This is a schematic diagram showing the measurement results of the lifetime characteristics of a lithium secondary battery comprising the electrolyte composition according to embodiments and comparative embodiments of the present invention; and

[0034] Figure 2 This is a schematic diagram showing the measurement results of the discharge capacity of a lithium secondary battery comprising the electrolyte composition according to embodiments and comparative embodiments of the present invention, based on the C-rate. Detailed Implementation

[0035] The invention will be described in more detail below. However, the specific embodiments or examples described below are merely for the purpose of explaining the invention in detail, and the invention is not limited thereto and can be implemented in various forms.

[0036] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] The terminology used in this specification is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0038] It should be understood that, as used herein, the terms “vehicle” or “of a vehicle” or other similar terms generally include motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources). As mentioned herein, a hybrid vehicle is a vehicle with two or more power sources, such as a vehicle that combines gasoline and electric power.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the / said” are intended to also include the plural forms. These terms are intended only to distinguish one component from another, and the terms do not limit the nature, order, or sequence of these constitutive components. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence of said features, integrals, steps, operations, elements, and / or components. Or, one or more other features, integrals, steps, operations, elements, components, and / or groups thereof may be added. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerations. Throughout the specification, unless expressly stated to the contrary, the words “comprising” and variations such as “including” or “having” are to be understood as including said elements, but not excluding any other elements. Furthermore, the terms “unit,” “component,” “device,” and “module” described in this specification refer to a unit for performing at least one function and operation, and may be implemented by hardware components or software components and combinations thereof.

[0040] While exemplary embodiments are described as using multiple units to perform exemplary processes, it should be understood that exemplary processes can also be performed by one or more modules. Furthermore, it should be understood that the term controller / control unit refers to a hardware device including a memory and a processor, specifically programmed to perform the processes described herein. The memory is configured to store modules, and the processor is specifically configured to execute said modules to perform one or more processes further described below.

[0041] Furthermore, the control logic of the present invention can be implemented as a non-volatile computer-readable medium on a computer-readable medium, which contains executable program instructions that are executed by a processor, controller, etc. Examples of computer-readable media include (but are not limited to) ROM, RAM, optical disc (CD)-ROM, magnetic tape, floppy disk, flash drive, smart card, and optical data storage device. The computer-readable medium can also be distributed across a network-connected computer system, thereby enabling the computer-readable medium to be stored and executed in a distributed manner via, for example, a telematics server or a controller area network (CAN).

[0042] Unless otherwise stated or obvious from the context, the term “about” as used herein is understood to mean within the normal tolerance range in the field, such as within two standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context clearly indicates otherwise, all numerical values ​​provided herein are modified by the term “about”.

[0043] Additionally, as used in the specification and appended claims, the singular form may be intended to include the plural form, unless otherwise expressly indicated in the context.

[0044] In addition, all units used in this specification unless otherwise specified are based on weight. For example, % or proportion refers to weight % or weight ratio, and weight % refers to the weight % of any one component in the whole composition, unless otherwise stated.

[0045] Furthermore, unless explicitly stated otherwise, when any part “includes” any component, it will be understood to further include other components rather than exclude other components.

[0046] Additionally, the numerical ranges used herein may include lower and upper limits, all values ​​within that range, increments logically derived from the shape and width of the defined range, all double-limited values, and all possible combinations of upper and lower limits for numerical ranges defined by different shapes. Unless otherwise specifically defined in this specification, values ​​outside the defined numerical range that may occur due to experimental errors or rounding are also included within the defined numerical range.

[0047] The “dielectric constant” mentioned in this specification refers to the value measured at room temperature (25°C).

[0048] The invention will be described in more detail below.

[0049] This invention relates to an electrolyte composition for lithium secondary batteries comprising a fluorinated aromatic solvent, and a lithium secondary battery comprising the same electrolyte composition. The fluorinated aromatic solvent can provide flame retardancy to the electrolyte while suppressing side reactions between the negative electrode and the electrolyte, thereby improving the safety, lifespan characteristics, and battery performance of the lithium secondary battery.

[0050] The present invention provides an electrolyte composition for lithium secondary batteries, comprising a lithium salt and an organic solvent, wherein the organic solvent comprises an ether solvent and an aromatic solvent of the following chemical formula 1.

[0051] [Chemical Formula 1]

[0052]

[0053] In chemical formula 1, R 1 R 2 R 3 R 4 and R 5 It can be hydrogen or fluorine independently, R 1 R 2 R 3 R 4 and R 5 At least three or more of them, specifically three, can be fluorine.

[0054] Aromatic solvents can be solvents with a lower dissociation ability for lithium salts compared to ether solvents. More specifically, the dissociation ability of aromatic solvents allows for the visual observation of precipitates when used alone in lithium salts. Conversely, the dissociation ability of ether solvents prevents the visual observation of precipitates when used alone in lithium salts. Aromatic solvents can form a stable protective film on the electrode surface to inhibit the continuous decomposition reaction of the bulk electrolyte. Furthermore, aromatic solvents can be used to generate fluorine radicals through a series of reactions to terminate chain reactions during combustion, thereby providing flame retardancy to the electrolyte composition.

[0055] <Propagation (highly exothermic reaction)>

[0056] HO· + CO → CO2 + H·

[0057] Chain reaction

[0058] RH→R·+H·

[0059] R·+O2→ROO·+H·

[0060] <Chain Transfer>

[0061] O·+F-based solvent → RO·+F·

[0062] <Termination>

[0063] RO· + F-based solvent → ROH + F·

[0064] In addition, aromatic solvents can suppress side reactions between ether solvents (used as lithium dissociation solvents) and the negative electrode of lithium secondary batteries. Furthermore, aromatic solvents have low freezing points, thus expanding the usable temperature range of lithium secondary batteries.

[0065] In one embodiment of the present invention, the aromatic solvent of the above-mentioned chemical formula 1 may include at least one selected from 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 2,4,5-trifluorotoluene and 2,4,6-trifluorotoluene, specifically 2,3,4-trifluorotoluene.

[0066] In one embodiment of the present invention, the ether solvent may include at least one selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran and tetrahydrofuran, specifically dimethoxyethane, but not limited thereto.

[0067] In one embodiment of the present invention, the lithium salt may include those selected from Li(CF3SO2)2N (LiTFSI), LiBF2(C2O4) (LIDFOB), Li(SO2F)2N (LiFSI), LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4, specifically Li(CF3SO2)2N and LiBF2(C2O4), but not limited thereto, as long as the purpose of the present invention can be achieved.

[0068] In one embodiment of the invention, the molar concentration of the lithium salt can be from 0.1M to 3.0M, specifically from 0.5M to 2.0M, and more specifically from 1.0M to 1.5M. When this range is met, it is easy to ensure ionic conductivity suitable for battery operation, excellent lithium ion mobility, and suppression of the decomposition reaction of the lithium salt itself.

[0069] In one embodiment of the invention, the electrolyte composition for a lithium secondary battery may contain 30 vol% to 90 vol%, specifically 40 vol% to 80 vol%, more specifically 50 vol% to 70 vol% of an aromatic solvent, based on the total volume of the electrolyte composition. When this range is met, excellent output characteristics can be exhibited while improving the flame retardancy and lifespan characteristics of the battery.

[0070] Furthermore, the present invention provides a lithium secondary battery comprising an electrolyte composition for lithium secondary batteries.

[0071] The description of the electrolyte composition for lithium secondary batteries is the same as above, and therefore will be omitted.

[0072] In one embodiment of the present invention, in addition to the electrolyte composition for lithium secondary batteries described above, the lithium secondary battery may further include a negative electrode, a positive electrode, and a separator inserted between the negative electrode and the positive electrode.

[0073] This invention does not impose any particular limitations on the materials used for the negative electrode, positive electrode, and separator; materials known in the art can be used. Specific embodiments are as follows.

[0074] In one embodiment of the present invention, the positive and negative electrodes can be manufactured as follows: the desired solvent, binder, conductive agent, dispersant, etc. are mixed with the positive electrode active material and the negative electrode active material respectively and stirred to prepare a mixture, then the mixture is applied to a current collector made of a metal material, and then the mixture is dried and pressed.

[0075] In one embodiment of the present invention, any active material commonly used in the positive electrode of a lithium secondary battery can be used as the positive electrode active material. For example, the positive electrode active material may include lithium metal oxide particles, which include one or more metals selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B, and combinations thereof.

[0076] As the negative electrode active material, any active material commonly used for lithium secondary battery negative electrodes can be used. Preferably, the negative electrode active material for lithium secondary batteries is a material capable of intercalating lithium. In one embodiment of the invention, the negative electrode active material may be selected from lithium (metallic lithium), graphitizable carbon, non-graphitizable carbon, graphite, silicon, Sn alloys, Si alloys, Sn oxides, Si oxides, Ti oxides, Ni oxides, Fe oxides (FeO), and lithium titanium oxides (LiTiO2 and Li4Ti5O). 12 One or two or more of the materials in ).

[0077] In one embodiment of the present invention, conventional conductive carbon materials can be used as conductive materials, without any specific limitations.

[0078] In one embodiment of the invention, the current collector of the metallic material can be any metal with high conductivity and to which a mixture of positive or negative electrode active materials can easily adhere, as long as no reaction occurs within the voltage range of the battery. Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of the negative electrode current collector can be foils made of copper, gold, nickel, or copper alloys or combinations thereof.

[0079] In one embodiment of the invention, the separator is a membrane having micropores through which ions can pass. Non-limiting examples may include one or a combination of two or more selected from glass fiber, polyester, polyethylene, polypropylene, and polytetrafluoroethylene, and may be in the form of a nonwoven or woven fabric. Specifically, in lithium secondary batteries, polyolefin polymer separators such as polyethylene and polypropylene may be used primarily, but are not limited thereto. Additionally, separators coated with compositions comprising ceramic components or polymer materials may also be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures, and may use separators known in the art, but are not limited thereto.

[0080] In one embodiment of the invention, the appearance of the lithium secondary battery is not particularly limited, but can be selected from cylindrical, square, pouch-shaped or coin-shaped containers.

[0081] Furthermore, the present invention provides a lithium metal secondary battery comprising: a positive electrode containing a positive electrode active material; a negative electrode containing lithium metal; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the electrolyte comprises an electrolyte composition for a lithium secondary battery.

[0082] The electrolyte composition and lithium secondary battery content described above can also be applied equally to lithium metal secondary batteries within a repeatable range.

[0083] Preferred embodiments and comparative embodiments of the present invention will now be described. However, the following embodiments are merely preferred implementations of the present invention, and the present invention is not limited to these embodiments.

[0084] Experimental Example 1: Evaluation of Ionic Conductivity and Degree of Dissociation

[0085] First, the ionic conductivity and degree of dissociation were evaluated based on the lithium salt content and solvent mixing amount in the electrolyte composition. For this purpose, an electrolyte composition for lithium secondary batteries with the composition shown in Table 1 was prepared.

[0086] Ionic conductivity was measured using a three-electrode impedance technique, with two 0.5 × 0.5 cm Pt plates as working / counter electrodes and a 0.5 mm diameter Pt wire as a reference electrode. The measurement was performed in a glove box with moisture and oxygen concentrations of 0.1 ppm or lower, and a calibration curve was prepared using a KCl aqueous solution for impedance measurement.

[0087] The presence of undissociated material can be assessed by visually inspecting for the presence of sediment.

[0088] The evaluation results of ionic conductivity and degree of dissociation are as follows.

[0089] [Table 1]

[0090]

[0091]

[0092] Referring to Table 1, when 100% by volume of an aromatic solvent was included, as in Comparative Example 4, the lithium salt did not dissociate. Therefore, the number of dissociated free ions was small, resulting in a very low ionic conductivity of 1.8. Thus, it can be seen that using only an aromatic solvent as the solvent is disadvantageous.

[0093] Meanwhile, when 100% by volume of ether solvent was included, as in Comparative Example 3, very high ionic conductivity was observed. However, when only ether solvent was used, electrode performance was adversely affected due to reaction with the lithium metal anode.

[0094] As in Examples 1 to 5 and Comparative Example 5, the ionic conductivity and undissociation properties of the electrolyte compositions were evaluated by varying the molar concentration of the lithium salt. As a result, when the total molar concentration of the lithium salt was 1.5 M, LiTFSI and LiDFOB exhibited optimal ionic conductivity at 1.2 M and 0.3 M, respectively. Furthermore, as in Comparative Example 5, when 1.5 M of LiTFSI was included, it was observed that the lithium salt did not dissociate, making the use of LiTFSI as a solvent disadvantageous. Therefore, in Experimental Example 2 below, the molar concentration of the lithium salt was kept constant as in Example 5, and various property tests were performed based on the mixing ratio of aromatic solvent to ether solvent.

[0095] Experimental Example 2: Evaluation of the ionic conductivity, flame retardancy, and lifespan characteristics of the electrolyte composition

[0096] Evaluation of ionic conductivity

[0097] Electrolyte compositions for lithium secondary batteries were prepared using the compositions shown in Table 2 below. The methods for evaluating the ionic conductivity of the electrolyte compositions were performed in the same manner as in Experimental Example 1.

[0098] Flame retardancy evaluation

[0099] Meanwhile, to evaluate flame retardancy, the electrolyte compositions listed in Table 2 were immersed in glass fiber, and the self-extinguishing time (SET) was measured. The results are shown in Table 2. SET represents the time it takes for the electrolyte to ignite and then extinguish. Considering that the combustion time varies with the weight of the electrolyte, the combustion time per unit weight (unit: seconds / gram) is introduced in this invention.

[0100] Evaluation of lifespan characteristics

[0101] The following evaluations include the life characteristics of lithium secondary batteries having electrolyte compositions as shown in Table 2 below.

[0102] A negative electrode slurry was prepared by mixing 96 wt% graphite as the negative electrode active material, 2 wt% styrene-butadiene rubber (SBR) as a binder, and 2 wt% carboxymethyl cellulose (CMC). The prepared negative electrode slurry was applied to both sides of a lithium metal foil, dried, and then laminated to manufacture the negative electrode.

[0103] LiNi was mixed in a weight ratio of 93:3:4 as the positive electrode active material. 83 Co 11 Mn6O2, poly(vinylidene fluoride) (PVdF) as the positive electrode binder, and super P-carbon as the conductive material were mixed and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. This slurry was then coated onto an aluminum foil with a thickness of 30 micrometers and dried at 80°C to produce a loading level of approximately 10.0 mg / cm². 2 The positive electrode is then used to manufacture a button cell using conventional methods.

[0104] A 20-micrometer-thick polypropylene membrane was inserted between the prepared negative and positive electrodes to form an electrode assembly, and then 40 μl of the electrolyte composition according to the examples and comparative examples was injected to manufacture a pouch-shaped lithium secondary battery. All electrodes were prepared in a drying chamber, and the batteries were manufactured in a glove box under an argon atmosphere.

[0105] The prepared lithium secondary battery was charged at a constant current rate of 0.1C at room temperature (25°C) until the voltage reached 4.3V (relative to Li), and then the current was cut off at a rate of 0.01C while maintaining 4.3V in constant voltage mode, thus charging at a constant voltage. The lithium secondary battery was discharged at a constant current rate of 0.1C until the voltage reached 2.75V (relative to Li). One charge-discharge cycle was defined as one cycle, and another charge-discharge cycle was performed in the same manner. Then, the applied current during charge-discharge was changed to 1.0C, and 100 cycles were performed with a 5-minute rest period between cycles. The lifetime characteristics were calculated by dividing the discharge capacity of 100 cycles by the discharge capacity of one cycle, and the results are shown in Table 2 below.

[0106] [Table 2]

[0107]

[0108]

[0109] As can be seen from Table 2 above, it is confirmed that the electrolyte composition according to the present invention has a shorter self-extinguishing time as the content of aromatic solvent in the composition increases, thereby improving the safety of lithium secondary batteries. In particular, it exhibits significantly superior flame retardancy compared to Comparative Example 1 and Comparative Example 6.

[0110] Furthermore, compared with lithium secondary batteries comprising electrolyte compositions according to Comparative Example 1 and Comparative Example 6, it can be confirmed that lithium secondary batteries using electrolyte compositions according to embodiments of the present invention have relatively superior lifespan characteristics, retaining approximately 81% or more of their initial capacity even after 100 cycles.

[0111] Specifically, refer to Figure 1 When comparing Example 8 with Comparative Example 1 and Comparative Example 6, it can be confirmed that the lifetime characteristics of Example 8 are significantly higher.

[0112] Experimental Example 3: Evaluation of the Output Characteristics of Lithium Secondary Batteries

[0113] To evaluate the charge / discharge behavior of lithium secondary batteries comprising the electrolyte compositions according to Example 8 and Comparative Example 6, five charge-discharge cycles were performed each at C rates of 0.1C, 0.33C, 0.5C, 1.0C, 2.0C, and 0.1C within a voltage range of 2.75 to 4.3V at room temperature (25°C). The battery capacity was then measured, and the results are shown in Table 3. Figure 2 middle.

[0114] [Table 3]

[0115]

[0116] Reference Figure 2 In the embodiments, similar discharge capacity values ​​are maintained at each C-rate. Furthermore, in the embodiments, the discharge capacity measured at each C-rate is superior to that of the comparative embodiments. That is, it is confirmed that the lithium secondary battery of the embodiments including the electrolyte composition according to the embodiments of the present invention can achieve excellent capacity and output characteristics.

[0117] The features, structures, effects, etc., described in the above embodiments are included in at least one embodiment of the present invention, but are not necessarily limited to one embodiment. Furthermore, the features, structures, effects, etc., shown in the various embodiments can even be combined or modified by those skilled in the art in other embodiments. Therefore, the content related to these combinations and modifications should be interpreted as covering the scope of the present invention.

[0118] As described above, embodiments have been primarily presented; however, they are merely examples and do not limit the invention. Those skilled in the art will understand that various modifications and applications not shown above can be made without departing from the essential characteristics of the embodiments. For example, modifications and implementations can be made to each component specifically shown in the embodiments. Furthermore, differences related to these modifications and applications should be interpreted as including within the scope of the invention as defined in the appended claims.

Claims

1. An electrolyte composition for use in a lithium secondary battery, the electrolyte composition comprising: Lithium salts; and Organic solvents, in, The organic solvents include ether solvents and aromatic solvents of the following chemical formula 1: [Chemical Formula 1] In chemical formula 1, R 1 R 2 R 3 R 4 and R 5 Independently hydrogen or fluorine; and R 1 R 2 R 3 R 4 and R 5 At least three or more of them are fluorine.

2. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The aromatic solvent includes at least one selected from 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 2,4,5-trifluorotoluene, and 2,4,6-trifluorotoluene.

3. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The ether solvent includes at least one selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

4. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The lithium salt includes those selected from Li(CF3SO2)2N, LiBF2(C2O4), Li(SO2F)2N, LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4.

5. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The content of the aromatic solvent is from 30% to 90% by volume, based on the total volume of the electrolyte composition.

6. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The molar concentration of the lithium salt is from 0.1 M to 3.0 M.

7. A lithium secondary battery comprising the electrolyte composition for a lithium secondary battery as described in claim 1.

8. A lithium metal secondary battery, comprising: A positive electrode containing positive electrode active material; Anode containing lithium metal; A diaphragm is disposed between the positive electrode and the negative electrode; and Electrolytes, The electrolyte comprises the electrolyte composition for lithium secondary batteries as described in claim 1.

9. An electrolyte composition for a lithium secondary battery, the electrolyte composition comprising: Lithium salts; and An organic solvent, including 2,3,4-trifluorotoluene.

10. The electrolyte composition for a lithium secondary battery according to claim 9, wherein, The organic solvent also includes ether solvents.

11. The electrolyte composition for a lithium secondary battery according to claim 10, wherein, The ether solvent includes at least one selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

12. The electrolyte composition for a lithium secondary battery according to claim 9, wherein, The lithium salt includes those selected from Li(CF3SO2)2N, Li(SO2F)2N, LiPF6, LiBF4, and LiClO. 4、 LiCl, LiBr, LiI, LiB 10 Cl 10 At least one of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4.

13. The electrolyte composition for a lithium secondary battery according to claim 9, wherein, The content of 2,3-difluorotoluene is from 30% to 90% by volume, based on the total volume of the electrolyte composition.

14. The electrolyte composition for a lithium secondary battery according to claim 9, wherein, The molar concentration of the lithium salt is from 0.1 M to 3.0 M.

15. An electrolyte composition for a lithium secondary battery, said electrolyte composition comprising: Lithium salts, including those selected from Li(CF3SO2)2N, Li(SO2F)2N, LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 At least one of the following: LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and CF3SO3Li; and Organic solvents, including aromatic solvents of Formula 1: [Chemical Formula 1] In chemical formula 1, R 1 R 2 R 3 R 4 and R 5 Independently hydrogen or fluorine; and R 1 R 2 R 3 R 4 and R 5 At least three or more of them are fluorine.

16. The electrolyte composition for a lithium secondary battery according to claim 15, wherein, The organic solvent also includes ether solvents.

17. The electrolyte composition for a lithium secondary battery according to claim 16, wherein, The ether solvent includes at least one selected from dimethoxyethane, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethyl ether, 2-methyltetrahydrofuran, and tetrahydrofuran.

18. The electrolyte composition for a lithium secondary battery according to claim 15, wherein, The aromatic solvents include 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 2,4,5-trifluorotoluene, and 2,4,6-trifluorotoluene or combinations thereof.

19. The electrolyte composition for a lithium secondary battery according to claim 15, wherein, The content of the aromatic solvent is from 30% to 90% by volume, based on the total volume of the electrolyte composition.

20. The electrolyte composition for a lithium secondary battery according to claim 15, wherein, The molar concentration of the lithium salt is from 0.1 M to 3.0 M.

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