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

Abstract

The present invention provides an electrolyte composition for a lithium secondary battery and a lithium secondary battery comprising the same. The electrolyte composition includes a lithium salt and a non-aqueous organic solvent composed of a first carbonate-based solvent and a second carbonate-based solvent, wherein the second solvent includes a compound of Chemical Formula 1. By adjusting the volume ratio of these solvents and the content of the compound of Chemical Formula 1, the electrolyte achieves improved flame retardancy, prolonged cycle life and high decomposition voltage stability. A lithium secondary battery using such an electrolyte exhibits strong capacity retention, has excellent durability at high temperatures, and has stable performance during high-voltage operation.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0166125, filed with the Korean Intellectual Property Office on November 20, 2024, 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] Lithium-ion batteries are manufactured by placing a porous polymer separator between the negative and positive electrodes and adding an electrolyte containing a lithium salt (such as LiPF6). During charging, lithium ions are released from the positive electrode active material and then inserted into the carbon layer of the negative electrode. During discharging, lithium ions are released from the carbon layer and then inserted into the positive electrode active material. The electrolyte acts as a medium for the movement of lithium ions between the negative and positive electrodes.

[0006] Existing carbonate-based electrolytes have low flash points and poor flame retardancy, leading to reduced safety in the event of short circuits and fires. To compensate for this, phosphorus (P)-based materials have been used as flame retardant solvents and additives, but this degrades battery life characteristics due to interfacial stability issues with the electrodes. Furthermore, when fluorine (F)-based materials are used as flame retardant solvents and additives, the solubility and ionic conductivity of the salt decrease depending on the degree of fluorine substitution.

[0007] Therefore, it is necessary to research and develop flame-retardant electrolytes to simultaneously provide improved flame-retardant properties and battery performance. Summary of the Invention

[0008] The present invention aims to provide an electrolyte composition for lithium secondary batteries and a lithium secondary battery comprising the electrolyte composition, wherein the electrolyte composition and the lithium secondary battery can ensure improved flame retardant properties while maintaining good battery performance, such as cycle life characteristics, output characteristics and oxidation stability.

[0009] Furthermore, the present invention aims to provide an electrolyte composition for lithium secondary batteries that can be applied in green technology fields using batteries, such as electric vehicles.

[0010] Some embodiments of the present invention can provide an electrolyte composition for a lithium secondary battery, the electrolyte composition comprising a lithium salt and a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises a first carbonate-based solvent and a second carbonate-based solvent, the second carbonate-based solvent comprising a compound represented by chemical formula 1:

[0011]

[0012] In Formula 1, R1 and R2 can each independently represent a C2 to C5 straight-chain alkyl group that is substituted with a halogen or not, and n can be an integer from 1 to 6.

[0013] According to some implementation schemes, the compound represented by chemical formula 1 can be

[0014]

[0015] According to some implementation schemes, the first carbonate-based solvent may include one or more selected from ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, and ethyl propyl carbonate.

[0016] Suitably, the first carbonate-based solvent and the second carbonate-based solvent are different (structurally different) chemical compositions. In some embodiments, the first carbonate-based solvent and the second carbonate-based solvent may be the same chemical composition, although it is generally preferred that the first carbonate-based solvent and the second carbonate-based solvent are different (structurally different) chemical compositions.

[0017] According to some implementation schemes, the lithium salt can be one or more selected from LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiN(SO2F)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI and LiB(C2O4)2.

[0018] According to some implementation schemes, the non-aqueous organic solvent may comprise a first carbonate-based solvent and a second carbonate-based solvent in a volume ratio of 1:0.5 to 1:1.2.

[0019] Some embodiments of the present invention may provide a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte composition for a lithium secondary battery.

[0020] According to some embodiments, the positive electrode may include at least one transition metal and a positive electrode active material, the transition metal including cobalt, manganese and nickel, and the positive electrode active material including a lithium-nickel-cobalt-manganese composite oxide.

[0021] According to some embodiments, the lithium-nickel-cobalt-manganese composite oxide may be Li x (Ni a Co b Mn c )O2 (0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x (Ni a Co b Mn c )O4 (0.5 < x < 1.3, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2) or a mixture thereof.

[0022] According to some embodiments, the negative electrode may include a carbon-based active material, a silicon-based active material or a combination thereof.

[0023] According to some embodiments, the carbon-based active material may include graphite, activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fiber, carbon black or a combination thereof.

[0024] According to some embodiments, the silicon-based active material may be at least one selected from Si, SiO x (0 < x < 2), doped metal or carbon-coated SiO x (0 < x < 2), and Si-C composite materials.

[0025] In some embodiments, an electrolyte composition for a lithium secondary battery includes a lithium salt and a non-aqueous organic solvent, the non-aqueous organic solvent including a first carbonate-based solvent and a second carbonate-based solvent, wherein the second carbonate-based solvent includes a compound represented by Chemical Formula 1:

[0026]

[0027] wherein R1 and R2 each independently represent a C2 to C5 straight-chain alkyl group which may or may not be substituted by a halogen, n is an integer from 1 to 6, and the compound represented by Chemical Formula 1 is present in an amount of about 20% by volume to about 60% by volume of the total volume of the non-aqueous organic solvent.

[0028] The compound represented by Chemical Formula 1 may be

[0029] Lithium salts may include one or a combination of two or more of the following: LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiN(SO2F)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, and LiB(C2O4)2.

[0030] The first carbonate-based solvent may include one or a combination of two or more of the following: ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, and ethyl propyl carbonate.

[0031] In non-aqueous organic solvents, lithium salts can exist at a concentration of approximately 1.0 M.

[0032] The first carbonate-based solvent and the second carbonate-based solvent may be present in a volume ratio of about 1:0.5 to 1:1.2.

[0033] The first carbonate-based solvent may contain ethylene carbonate and ethyl methyl carbonate in a volume ratio ranging from about 1:1 to about 3:2.

[0034] The non-aqueous organic solvent may contain about 30% by volume ethylene carbonate, about 20% by volume methyl ethyl carbonate and about 50% by volume diethyl 2,5-dioxadipic acid (DEDH).

[0035] The non-aqueous organic solvent may contain about 30% by volume ethylene carbonate, about 30% by volume methyl ethyl carbonate and about 40% by volume diethyl 2,5-dioxadipic acid (DEDH).

[0036] According to some embodiments of the present invention, an electrolyte with improved flame retardancy can be provided.

[0037] According to some embodiments of the present invention, a lithium secondary battery with improved cycle life characteristics can be provided.

[0038] According to some embodiments of the present invention, a lithium secondary battery with improved output characteristics can be provided.

[0039] According to some embodiments of the present invention, a lithium secondary battery with improved oxidation stability at high potentials can be provided. Attached Figure Description

[0040] The foregoing and other aspects, features, and advantages, as well as the following detailed description of embodiments, will be better understood when read in conjunction with the accompanying drawings. However, the invention is not intended to be limited to the details shown in the figures, and various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and equivalents of the claims. The same reference numerals and symbols denote the same elements in the various figures.

[0041] Figure 1 Experimental results were conducted to demonstrate the flame-retardant properties of the electrolyte compositions according to embodiments and comparative embodiments of the present invention.

[0042] Figure 2 The results were used to evaluate the output performance of lithium secondary batteries containing electrolyte compositions according to embodiments and comparative embodiments of the present invention.

[0043] Figure 3 The results were used to evaluate the durability performance of lithium secondary batteries comprising electrolyte compositions according to embodiments and comparative embodiments of the present invention.

[0044] Figure 4 The results of linear sweep voltammetry analysis were performed on the electrolyte compositions according to embodiments and comparative embodiments of the present invention to measure the decomposition voltage. Detailed Implementation

[0045] The invention will be described in more detail below. However, the following embodiments are provided only as a reference for describing the invention in detail, and the invention is not limited thereto, but can be implemented in various forms.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] The terminology used herein is intended only to effectively describe particular embodiments and is not intended to limit the invention.

[0048] 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 vehicles powered by alternative fuels (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.

[0049] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. These terms are intended only to distinguish one component from another, and do not limit the nature, order, or sequence of the constituent components. It will be further understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of the stated features, values, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof. 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 terms “comprising” and variations such as “including” or “having” should be understood to imply the inclusion of the stated elements but not to exclude any other elements. Furthermore, the terms “unit,” “component,” “device,” and “module” described in the specification mean a unit for performing at least one function and operation and can be implemented by hardware components or software components and combinations thereof.

[0050] 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.

[0051] Furthermore, the control logic of the present invention can be implemented as a non-transient 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, such that the computer-readable medium is stored and executed in a distributed manner, for example, via a telematics server or a controller area network (CAN).

[0052] 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”.

[0053] Unless otherwise stated, all units used in this specification are based on weight. For example, units such as “%” or “ratio” refer to weight percentage (weight %) or weight ratio, respectively. Unless otherwise defined, weight percentage (weight %) refers to the proportion of a particular component in the total composition, expressed as a weight percentage.

[0054] Furthermore, the numerical ranges used in this specification may include all values ​​between the lower and upper limits, all values ​​logically derived within the form and breadth of the defined range, all double-limited values, and all possible combinations of the upper and lower limits of different defined numerical ranges. Unless specifically defined in the specification of this invention, values ​​that may exceed the defined numerical range due to experimental errors or rounding are also included within the defined numerical range.

[0055] As used herein, the term “substituted” means that all or some of the hydrogen atoms of the substituted portion (e.g., alkyl) are replaced by substituents, while “unsubstituted” means that none of the hydrogen atoms of the alkyl group are replaced by substituents.

[0056] The term "non-aqueous organic solvent" as used herein refers to an organic solvent or mixture of solvents that is substantially free of water, capable of dissolving lithium salts, and suitable for use in electrochemical cells. In some respects, the electrolyte composition is preferably substantially free of water, for example, containing less than 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, 0.5 wt%, or 0.1 wt% water by weight of the total electrolyte composition.

[0057] The term "carbonate-based solvent" in this article refers to organic solvents containing carbonate functional groups.

[0058] The term "lithium secondary battery" in this article refers to a rechargeable electrochemical battery cell or battery that uses lithium-containing materials for its electrodes and can be repeatedly charged and discharged while maintaining its capacity over multiple cycles.

[0059] A more detailed description of the invention is provided below.

[0060] This invention relates to an electrolyte composition for lithium secondary batteries and a lithium secondary battery comprising the electrolyte composition, said electrolyte composition containing a compound represented by Chemical Formula 1. The compound represented by Chemical Formula 1 has a high flash point and low volatility, resulting in improved flame-retardant properties in the electrolyte composition containing this compound. Furthermore, the lithium secondary battery containing this electrolyte composition can exhibit battery performance equivalent to or better than that of lithium secondary batteries using existing commercial electrolytes.

[0061] This invention provides an electrolyte composition for lithium secondary batteries, the electrolyte composition comprising a lithium salt and a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises a first carbonate-based solvent and a second carbonate-based solvent, and the second carbonate-based solvent comprises a compound represented by the following chemical formula 1:

[0062]

[0063] In Formula 1, R1 and R2 can be independently C2 to C5 straight-chain alkyl groups, specifically C2 to C3 straight-chain alkyl groups, more specifically C2 alkyl groups, and n can be an integer from 1 to 6, specifically an integer from 2 to 4, more specifically 2.

[0064] According to some implementation schemes, the halogen can be -F, -Cl, -Br, or -I, specifically -F or -Cl, but is not limited to these, as long as the purpose of the present invention can be achieved.

[0065] According to embodiments of the present invention, the lithium salt may include one or a combination of two or more of the following: LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiN(SO2F)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, and LiB(C2O4)2, specifically LiPF6, but is not limited thereto.

[0066] According to some implementation schemes, the first carbonate-based solvent may include one or a combination of two or more of the following: ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, and ethyl propyl carbonate, specifically including ethylene carbonate and methyl ethyl carbonate.

[0067] The compound represented by Chemical Formula 1 has a high flash point and low volatility, providing flame retardant properties to the electrolyte composition. In addition, it does not excessively increase the viscosity of the electrolyte composition, making the battery performance equivalent to or better than that of batteries containing existing commercial carbonate-based solvents.

[0068] According to some embodiments, the compound represented by Chemical Formula 1 can be diethyl 2,5-dioxohexanedioate, which can be represented by the following Structural Formula 1.

[0069]

[0070] According to some embodiments, the non-aqueous organic solvent can include a first carbonate-based solvent and a second carbonate-based solvent in a volume ratio of 1:0.5 to 1:1.2 (specifically 1:0.6 to 1:1). When this range is met, an increase in the viscosity of the electrolyte composition caused by the inclusion of the compound represented by Chemical Formula 1 in the second carbonate-based solvent and the resulting decrease in battery performance can be suppressed.

[0071] In addition, the present invention also provides a lithium secondary battery, which includes a positive electrode, a negative electrode, and the above electrolyte composition for a lithium secondary battery.

[0072] The description of the electrolyte composition for a lithium secondary battery is the same as above, and thus is omitted here.

[0073] According to some embodiments, the positive electrode can include at least one transition metal and a positive electrode active material. The at least one transition metal is selected from cobalt, manganese, nickel, or a combination of two or more thereof, and the positive electrode active material is a lithium-nickel-cobalt-manganese composite oxide. The unshared electron pairs contained in the compound represented by Chemical Formula 1 can coordinate with the transition metal of the positive electrode, thereby stabilizing the positive electrode structure, suppressing side reactions on the surface of the positive electrode during high-temperature storage, and thus improving the high-temperature storage stability of the lithium secondary battery.

[0074] According to some embodiments, the lithium-nickel-cobalt-manganese composite oxide can be Li x (Ni a Co b Mn c )O2(0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), Li x (Ni a Co b Mn c )O4(0.5 < x < 1.3, 0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), or a mixture thereof. Specifically, Li x (Ni a Co b Mn c)O2, where 0.90 ≤ x ≤ 1.10, 0.3 ≤ a ≤ 0.8, 0.1 ≤ b < 0.5, 0.1 ≤ c < 0.5 and a + b + c = 1.

[0075] According to some embodiments, the negative electrode may include a carbon-based active material, a silicon-based active material, or a combination thereof.

[0076] According to some embodiments, the carbon-based active material may include graphite, activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fiber, carbon black, or a combination thereof, specifically including graphite. According to some embodiments, the silicon-based active material may include Si, SiO x (0 < x < 2), doped metal, or carbon-coated SiO x (0 < x < 2), one of Si-C composite materials, or a combination of two or more thereof. Accordingly, the negative electrode may include graphite and an Si-C composite material, or may include SiO x (0 < x < 2).

[0077] According to some embodiments, the lithium secondary battery may further include a separator interposed between the negative electrode and the positive electrode.

[0078] The separator material is not particularly limited in the present invention and may be selected from materials known in the art. Some detailed examples are as follows.

[0079] In some embodiments of the present invention, the separator may be a separator having micropores through which ions can pass, and as a non-limiting example, the separator may be a combination of one or more selected from glass fiber, polyester, polyethylene, polypropylene, and polytetrafluoroethylene, and may be in the form of a non-woven fabric or a woven fabric. Specifically, polyolefin-based polymer separators such as polyethylene and polypropylene may be mainly used in the lithium secondary battery, but the present invention is not limited thereto. In addition, in order to enhance heat resistance or mechanical strength, a separator coated with a composition containing a ceramic component or a polymer material may also be used, and the separator may optionally have a single-layer or multi-layer structure, and separators known in the art may be used, but the present invention is not limited thereto.

[0080] In some embodiments of the present invention, the external shape of the lithium secondary battery is not particularly limited, but may be selected from, for example, a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can.

[0081] Various embodiments and comparative examples of the present invention will be described below. However, the following examples are only various embodiments of the present invention, and the present invention is not intended to be limited thereto.

[0082] Example 1

[0083] An electrolyte composition for lithium secondary batteries is obtained by mixing a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent comprises 30 vol% ethylene carbonate (EC), 20 vol% ethyl methyl carbonate (EMC), and 50 vol% diethyl 2,5-dioxadipic acid (DEDH) by volume of the total solvent, and the lithium salt is 1.0 M LiPF6.

[0084] By using the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, binder polyvinylidene fluoride (PVdF), and conductive agent carbon were mixed in a weight ratio of 98:1:1 and dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. This slurry was coated onto an aluminum foil with a thickness of 20 μm, then dried and rolled to manufacture the positive electrode.

[0085] A negative electrode slurry was prepared by mixing the negative electrode active material graphite / Si-C composite, the binder styrene-butadiene rubber (SBR), and the thickener carboxymethyl cellulose (CMC) in a weight ratio of 97:1:2 and dispersing them in water. This slurry was then coated onto a 15 μm thick copper foil, followed by drying and rolling to manufacture the negative electrode.

[0086] A 25 μm thick polyethylene (PE) membrane separator is stacked between the electrodes to form a pouch cell with dimensions of 6 mm thickness × 60 mm width × 90 mm length, and then an electrolyte composition for lithium secondary batteries is injected to manufacture a lithium secondary battery.

[0087] Example 2

[0088] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous organic solvent contained 30% by volume ethylene carbonate (EC), 30% by volume ethyl methyl carbonate (EMC), and 40% by volume diethyl 2,5-dioxadipic acid (DEDH).

[0089] Comparative Example 1

[0090] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous organic solvent contained 30% by volume ethylene carbonate (EC) and 70% by volume ethyl methyl carbonate (EMC) of the total solvent volume.

[0091] Comparative Example 2

[0092] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous organic solvent contained 30% by volume ethylene carbonate (EC) and 70% by volume diethyl 2,5-dioxadipic acid (DEDH).

[0093] Comparative Example 3

[0094] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous organic solvent contained 30% by volume ethylene carbonate (EC), 10% by volume ethyl methyl carbonate (EMC), and 60% by volume diethyl 2,5-dioxadipic acid (DEDH).

[0095] Comparative Example 4

[0096] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the non-aqueous organic solvent contained 30% by volume ethylene carbonate (EC), 40% by volume ethyl methyl carbonate (EMC), and 30% by volume diethyl 2,5-dioxadipic acid (DEDH) of the total solvent volume.

[0097] Experimental Example 1: Evaluation of Flame Retardancy

[0098] To evaluate flame retardancy, the electrolyte compositions from Examples 1 and 2, as well as Comparative Examples 3 and 4, were placed in a chamber with an air-exposed surface, and the self-extinguishing time (SET) was measured. The results are shown below. Figure 1 SET represents the time from ignition to extinguishing of the electrolyte. Considering that the combustion time varies with the weight of the electrolyte, this invention introduces the combustion time per unit weight (unit: seconds / gram).

[0099] like Figure 1 As shown, the SET of the electrolyte composition in Comparative Example 4 was 44.54 seconds / gram, indicating that flame retardancy was not ensured. In contrast, the remaining electrolyte compositions did not ignite, demonstrating that improved flame retardancy can be ensured when the non-aqueous organic solvent contains 40% or more of DEDH by volume of the total solvent volume.

[0100] Experiment Example 2: Evaluation of Output Performance

[0101] To investigate the output performance characteristics at room temperature based on the amount of the second carbonate-based solvent added to the electrolyte composition, the output performance of the lithium secondary batteries of the examples and comparative examples was measured at room temperature (25°C), and the results are shown in Table 1 and... Figure 2 .

[0102] The experiment was conducted under the following conditions: cutoff: 2.5-4.2V, C-rate: 0.5C charging / 5.0C discharging, temperature: 25℃.

[0103] [Table 1]

[0104]

[0105] As from Figure 2 As can be seen from Table 1, Examples 1 and 2, containing 50 vol% and 40 vol% of DEDH respectively as a percentage of the total volume of the non-aqueous organic solvent, exhibit output performance comparable to Comparative Example 1 using a conventional commercial carbonate solvent. Meanwhile, Comparative Examples 2 and 3, containing 60 vol% or more of DEDH, show a significant decrease in output performance due to reduced ionic conductivity resulting from increased viscosity of the electrolyte composition.

[0106] Experimental Example 3: Evaluation of Durability

[0107] To examine capacity retention characteristics based on the amount of second carbonate-based solvent added to the electrolyte composition, capacity retention after 100 cycles was measured at room temperature (25°C) and high temperature (45°C), and the results are shown in Table 2 and... Figure 3 Meanwhile, comparative examples 2 and 3 were excluded from the evaluation due to their poor output characteristics.

[0108] The experiments were conducted as follows: Each manufactured lithium-ion secondary battery was charged at a rate of 0.1C at both room temperature (25°C) and high temperature (45°C) until the voltage reached 4.2V (relative to Li). Then, it was charged at a constant voltage of 0.02C at 4.2V until discharge was complete. The battery was then discharged at a constant current of 0.1C until the voltage reached 2.5V (relative to Li). This charge-discharge cycle constituted one cycle. After one more cycle, the applied current for charging and discharging was changed to 0.5C, and this was repeated for 100 cycles, with a 10-minute rest period between cycles. The capacity retention rate was calculated using the following formula:

[0109] Capacity retention rate (%) = [Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle] × 100 [Formula 1].

[0110] [Table 2]

[0111]

[0112]

[0113] As from Figure 3 As can be seen from Table 2, Examples 1 and 2, which contain DEDH at 50% and 40% of the total volume of non-aqueous organic solvent, respectively, exhibit comparable or better durability at room temperature and high temperature than Comparative Example 1, which uses existing commercial carbonate solvents.

[0114] Experimental Example 4: Linear Scan Voltammetry (LSV) Analysis

[0115] To measure the decomposition voltage of the electrolyte compositions according to the examples and comparative examples by linear sweep voltammetry, experiments were conducted as follows. Specifically, an SUS electrode was used as the working electrode, and lithium metal was used as both the reference and counter electrode. Measurements were performed in a voltage range of 3V to 7V at a scan rate of 0.1mV / s. A multichannel potentiostat (Ametek Co.) PMC-100 was used as the LSV measurement device. The results are shown below. Figure 4 And Table 3.

[0116] [Table 3]

[0117]

[0118] As from Figure 4 As can be seen in Table 3, the electrolyte compositions manufactured in Examples 1 and 2 decompose later than the commercial electrolyte composition of Comparative Example 1. Therefore, the electrolyte compositions according to the examples have improved oxidative stability and can extend the life of lithium secondary batteries.

[0119] The features, structures, effects, etc., described in the above exemplary embodiments are included in at least one embodiment of the present invention, but are not necessarily limited to a single embodiment. Furthermore, the features, structures, effects, etc., exemplified in each exemplary embodiment can be combined or modified by those skilled in the art in other embodiments. Therefore, such combinations and modifications should be interpreted as being within the scope of the present invention.

Claims

1. An electrolyte composition for a lithium secondary battery, the electrolyte composition comprising: a lithium salt; and a non-aqueous organic solvent, in, the non-aqueous organic solvent comprising a first carbonate-based solvent and a second carbonate-based solvent, the second carbonate-based solvent comprising a compound represented by the following Chemical Formula 1: wherein, R1 and R2 each independently represent a C2 to C5 straight-chain alkyl group which may or may not be substituted by a halogen, and n is an integer from 1 to 6.

2. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The compound represented by chemical formula 1 is 3. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The first carbonate-based solvent includes one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, ethylene ethyl carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, or a combination of two or more thereof.

4. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The lithium salt includes one of LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiN(SO2F)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiCl, LiI, LiB(C2O4)2, or a combination of two or more thereof.

5. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The first carbonate-based solvent and the second carbonate-based solvent are present in a volume ratio of 1:0.5 to 1:1.

2.

6. A lithium secondary battery, comprising: a positive electrode; a negative electrode; and the electrolyte composition according to any one of claims 1 to 5.

7. The lithium secondary battery according to claim 6, wherein, The positive electrode comprises: at least one transition metal, which includes cobalt, manganese, nickel, or a combination of two or more thereof; and a positive electrode active material including a lithium-nickel-cobalt-manganese composite oxide.

8. The lithium secondary battery according to claim 7, wherein, The lithium-nickel-cobalt-manganese composite oxide is: Li x (Ni a Co b Mn c )O2, where 0.5 < x < 1.3, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1; Li x (Ni a Co b Mn c )O4, where 0.5 < x < 1.3, 0 < a < 2, 0 < b < 2, 0 < c < 2, and a + b + c = 2; or a mixture thereof.

9. The lithium secondary battery according to claim 6, wherein, The negative electrode comprises a carbon-based active material, a silicon-based active material, or a combination thereof.

10. The lithium secondary battery according to claim 9, wherein, The carbon-based active material includes graphite, activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fiber, carbon black, or a combination thereof.

11. The lithium secondary battery according to claim 9, wherein, The silicon-based active material includes Si, SiO with 0 < x < 2 x , doped metal or carbon-coated SiO with 0 < x < 2 x , one of Si-C composites, or a combination of two or more of them.

12. An electrolyte composition for a lithium secondary battery, the electrolyte composition comprising: a lithium salt; and a non-aqueous organic solvent, the non-aqueous organic solvent comprising a first carbonate-based solvent and a second carbonate-based solvent, in, the second carbonate-based solvent comprising a compound represented by the following Chemical Formula 1: R1 and R2 each independently represent a C2 to C5 straight-chain alkyl group which may or may not be substituted by a halogen, and n is an integer from 1 to 6, the compound represented by Chemical Formula 1 is present in an amount of 20% by volume to 60% by volume of the total volume of the non-aqueous organic solvent.

13. The electrolyte composition for a lithium secondary battery according to claim 12, wherein, The first carbonate-based solvent includes one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, ethylene ethyl carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, or a combination of two or more thereof.

14. The electrolyte composition for a lithium secondary battery according to claim 12, wherein, The first carbonate-based solvent and the second carbonate-based solvent are present in a volume ratio of 1:0.5 to 1:1.

2.

15. The electrolyte composition for a lithium secondary battery according to claim 12, wherein, The first carbonate-based solvent comprises ethylene carbonate and ethyl methyl carbonate in a volume ratio ranging from 1:1 to 3:2.

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