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

Abstract

The present application provides an electrolyte composition for a lithium secondary battery and a lithium secondary battery comprising the same. The electrolyte composition for a lithium secondary battery of the present application can ensure high-voltage stability, thereby enabling the lithium secondary battery to operate stably even at a high voltage of 4.5 V or more. In addition, the electrolyte composition for a lithium secondary battery of the present application can prevent the electrolyte from undergoing electrochemical decomposition on the surface of a positive electrode, form a stable electrolyte-positive electrode interface, thereby inhibiting positive electrode deterioration; and stabilize the electrolyte-lithium metal negative electrode interface, inhibit lithium dendrite growth and side reactions, thereby enabling a high-energy density battery. The present application also provides a vehicle comprising the battery.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2025-0015034, filed with the Korean Intellectual Property Office on February 6, 2025, 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] Typically, lithium-ion batteries, due to their inclusion of electroactive materials, exhibit higher operating voltages and higher energy densities than lead-acid or nickel-cadmium batteries. Therefore, lithium-ion batteries are gaining attention as an energy storage solution for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0005] Improving battery energy density is a crucial issue for extending the driving range of electric vehicles. To achieve this, either the capacity of the positive and negative electrode materials used must be increased, or the battery's operating voltage must be increased.

[0006] To improve battery operating voltage, the oxidative stability of the electrolyte is crucial. Typically, non-aqueous organic solvents (such as carbonates, esters, ethers, or ketones) are used alone or in combination. However, carbonate-based organic solvents are flammable organic materials that may react with lithium metal and form dendrites; therefore, there are concerns that their use as electrolytes may jeopardize battery safety. Furthermore, due to the low flash point and high volatility of carbonate-based organic solvents, their use at high temperatures may induce combustion reactions with electrode materials, leading to a rapid increase in battery temperature and ultimately thermal runaway. Therefore, developing a stable electrolyte is a key factor in improving the energy density of lithium-ion rechargeable batteries. Summary of the Invention

[0007] The present invention aims to provide an electrolyte composition for lithium secondary batteries with improved high voltage stability.

[0008] Furthermore, the present invention aims to provide a lithium secondary battery that improves energy density by suppressing lithium dendrite growth and side reactions with lithium metal.

[0009] Furthermore, the present invention aims to provide an electrolyte composition for lithium secondary batteries applicable to green technology fields such as electric vehicle batteries.

[0010] In one aspect, an electrolyte composition for a lithium secondary battery comprises: 1) a lithium salt; 2) a functional additive; and 3) an organic solvent comprising: i) a first organic solvent comprising a fluorinated ether-based solvent; and ii) a second organic solvent comprising a carbonate-based solvent. A suitable first organic solvent has or can exhibit non-dissociative properties of the lithium salt, and the second organic solvent has or can exhibit dissociative properties of the lithium salt, thereby providing an effective electrolyte composition that does not exhibit phase separation, for example, after being placed at room temperature (e.g., 25°C) for an extended period (e.g., at least 3, 6, 12, 24, 48, 72, or 96 hours or longer).

[0011] Some embodiments of the present invention provide an electrolyte composition for a lithium secondary battery, the electrolyte composition comprising a lithium salt, a functional additive, and an organic solvent, wherein the organic solvent comprises a first organic solvent and a second organic solvent, the first organic solvent comprising a fluorinated ether-based solvent having lithium salt non-dissociation properties, and the second organic solvent comprising a carbonate-based solvent having lithium salt dissociation properties.

[0012] The first organic solvent may include at least one fluorinated ether solvent selected from the following: 1,1,2,3,3,3-hexafluoropropyl methyl ether, 2,2,2-trifluoroethyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether.

[0013] According to one embodiment, the second organic solvent may comprise at least one carbonate-based solvent selected from the following: dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, methyl propyl carbonate, and ethyl methyl carbonate.

[0014] According to one embodiment, the organic solvent may include a first organic solvent and a second organic solvent in a volume ratio of 30:70 to 90:10.

[0015] According to one embodiment, the lithium salt may include at least one selected from the following: Li(CF3SO2)2N (LiTFSI), Li(SO2F)2N (LiFSI), LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, LiB 10 Cl 10, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4.

[0016] According to one embodiment, the concentration of the lithium salt can be from 0.1 mol to 3.0 mol.

[0017] According to one embodiment, the functional additive may include at least one selected from the following: fluoroethylene carbonate, vinylene carbonate, tris(pentafluorophenyl)borane, propylene sulfite, and 1,3,2-dioxazothiophene 2,2-dioxide.

[0018] Some embodiments of the present invention provide a lithium secondary battery comprising an electrolyte composition for lithium secondary batteries.

[0019] Some embodiments of the present invention also provide 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.

[0020] The electrolyte composition for lithium secondary batteries of the present invention can ensure high voltage stability, thereby enabling the lithium secondary batteries to operate stably even at high voltages of 4.5V or higher.

[0021] The electrolyte composition for lithium secondary batteries of the present invention can prevent electrochemical decomposition of the electrolyte on the positive electrode surface and form a stable electrolyte-positive electrode interface, thereby suppressing positive electrode degradation.

[0022] Furthermore, the electrolyte composition for lithium secondary batteries of the present invention can promote the stabilization of the electrolyte-lithium metal anode interface and suppress the growth of lithium dendrites and side reactions, thereby enabling high energy density batteries.

[0023] The present invention also provides an electrolyte composition for lithium secondary batteries, the electrolyte composition comprising: a lithium salt, fluoroethylene carbonate (FEC), and an organic solvent, wherein the lithium salt comprises LiTFSI at a concentration of about 1.0 mol to 1.5 mol, the fluoroethylene carbonate (FEC) content is about 1 wt% to 10 wt% of the total weight of the electrolyte composition, and the organic solvent comprises 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPMe) and dimethyl carbonate (DMC) mixed in a volume ratio of about 70:30 to 90:10, wherein the electrolyte composition maintains a single liquid phase.

[0024] The volume ratio of HFPMe to DMC can be approximately 90:10.

[0025] The amount of FEC present can be 5% by weight of the total weight of the electrolyte composition.

[0026] At 25°C, at least 2.7 mS cm⁻¹ can be obtained. -1 ionic conductivity.

[0027] When used in lithium metal-lithium metal symmetric batteries, under the same conditions, its charge / discharge overvoltage is lower than that of batteries containing an electrolyte consisting only of dimethyl carbonate.

[0028] A lithium metal secondary battery is provided, 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 about 1.0 mol to 1.5 mol of LiTFSI, about 1 wt% to 10 wt% of FEC, and an organic solvent comprising HFPMe and DMC mixed in a volume ratio of about 70:30 to 90:10.

[0029] The volume ratio of HFPMe to DMC can be approximately 90:10.

[0030] The electrolyte may further contain about 0.1% to 5% by weight of vinylene carbonate.

[0031] The diaphragm may comprise a porous polyolefin membrane selected from polyethylene and polypropylene.

[0032] The battery can be configured as a pouch cell.

[0033] A vehicle comprising the lithium secondary battery is also provided.

[0034] As discussed, the method and system appropriately include the use of a controller or processor. Attached Figure Description

[0035] 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 drawings, and various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope of equivalents of the claims. The same reference numerals and identifiers in the figures denote the same elements.

[0036] Figure 1 The results of lithium salt dissociation performance tests of electrolyte compositions for lithium secondary batteries according to embodiments and comparative embodiments of the present invention are shown.

[0037] Figure 2The results of stability tests on lithium secondary batteries comprising electrolyte compositions for lithium secondary batteries according to embodiments and comparative embodiments of the present invention are shown.

[0038] Figure 3 The results of cycle life characteristic tests for lithium secondary batteries comprising electrolyte compositions for lithium secondary batteries according to embodiments and comparative embodiments of the present invention are shown.

[0039] Figure 4 The results of a discharge capacity evaluation test based on charge / discharge rate are shown for a lithium secondary battery comprising an electrolyte composition for a lithium secondary battery according to embodiments and comparative embodiments of the present invention.

[0040] Figure 5 The results of overvoltage characteristic evaluation tests are shown for a lithium secondary battery comprising an electrolyte composition for a lithium secondary battery according to embodiments and comparative embodiments of the present invention.

[0041] Figure 6 The results of interface characteristic evaluation tests for lithium secondary batteries comprising electrolyte compositions for lithium secondary batteries according to embodiments and comparative embodiments of the present invention are shown. Detailed Implementation

[0042] The invention will be described in more detail below. However, the following embodiments are provided for reference only to describe the invention in detail, but the invention is not limited thereto and can be implemented in many forms.

[0043] The term "lithium salt" in this article refers to an ionic lithium compound that can dissociate in a suitable organic solvent to provide lithium ions.

[0044] The term "non-dissociative properties" in this article refers to the ability of a solvent to dissolve and ionize lithium salts, thereby increasing the ionic conductivity of the electrolyte solution.

[0045] The term "functional additive" in this article refers to any additional compound introduced to enhance or alter performance characteristics.

[0046] Unless otherwise specified, 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 a particular embodiment and is not intended to limit the invention.

[0048] Unless the context clearly specifies otherwise, the singular forms “a,” “an,” and “the” used in the specification and appended claims are intended to include plural references.

[0049] All units used in this specification are by weight, unless otherwise specified. 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.

[0050] When a part is described as "including" or "containing" a component, it means that, unless otherwise expressly stated to the contrary, it does not exclude the inclusion of other components, but may also include other components.

[0051] Furthermore, the numerical ranges used in this specification may include all values ​​between the lower and upper limits, all values ​​logically incremented within the shape and width of the defined range, all double-limited values, and all possible combinations of the upper and lower limits of different limited numerical ranges. Unless 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.

[0052] 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.

[0053] 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 constituting components. It should also be understood that the terms “comprising” and / or “including” as used in this specification indicate the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups 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 words “comprising” and variations such as “including” or “having” are to be understood as meaning to include the stated elements, but not excluding any other elements. Furthermore, the terms “unit,” “component,” “device,” and “module” described in this specification mean a unit for performing at least one function and operation, and may be implemented by hardware components or software components and combinations thereof.

[0054] 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.

[0055] 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).

[0056] 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”.

[0057] A more detailed description of the invention is provided below.

[0058] The present invention provides an electrolyte composition for lithium secondary batteries, the electrolyte composition comprising a lithium salt, a functional additive, and an organic solvent, wherein the organic solvent comprises a first organic solvent and a second organic solvent, the first organic solvent comprising a fluorinated ether-based solvent having lithium salt non-dissociation properties, and the second organic solvent comprising a carbonate-based solvent having lithium salt dissociation properties.

[0059] In one embodiment of the present invention, the lithium salt may include at least one selected from the following: Li(CF3SO2)2N (LiTFSI), Li(SO2F)2N (LiFSI), LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, LiB 10 Cl 10 LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3 and LiB(C6H5)4, particularly including Li(CF3SO2)2N (LiTFSI).

[0060] In one embodiment of the invention, the total concentration of lithium salt in the electrolyte composition can be from 0.1 mol to 3.0 mol, specifically from 0.5 mol to 2.5 mol, and more specifically from 1.0 mol to 1.5 mol. When the above range is met, suitable ionic conductivity for battery operation is ensured, and phase separation of the electrolyte does not occur.

[0061] In one embodiment of the invention, the functional additive may include at least one selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, tris(pentafluorophenyl)borane, propylene sulfite, and 1,3,2-dioxazolthiophene 2,2-dioxide, specifically including fluoroethylene carbonate. The functional additive can be used to form a protective film on the negative electrode, but is not limited thereto.

[0062] The organic solvent can be used by mixing a first organic solvent and a second organic solvent, wherein the first organic solvent has low reactivity to impart oxidative stability to the electrolyte, and the second organic solvent has lithium salt dissociation properties.

[0063] In one aspect, the first organic solvent may be a non-polymer and has a molecular weight of less than 600, 500, 400, 350, 300, or 200 Daltons. The molecular weight of the first solvent is suitably at least 50, 100, or 150 Daltons. Suitable first organic solvents include haloethers, which suitably have 2 to 20 carbon atoms, more typically 2 or 3 to 12, 10, or 8 carbon atoms. Fluorinated alkyl oxyethers may be particularly preferred, including such ethers having 1, 2, 3, 4, 5, or 6 or more fluorine atom substituents.

[0064] In one embodiment of the invention, the first organic solvent may include, for example, at least one fluorinated ether-based solvent selected from the group consisting of: 1,1,2,3,3,3-hexafluoropropyl methyl ether, 2,2,2-trifluoroethyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether. The first solvent may comprise a mixture of two or more different solvent compositions. The fluorinated ether-based solvent may have lithium salt non-dissociation properties. Such lithium salt non-dissociation properties can be determined empirically, for example using Experimental Example 1 and... Figure 1 Phase separation tests were conducted using the scheme described herein.

[0065] Specifically, the preferred first organic solvent may include 1,1,2,3,3,3-hexafluoropropyl methyl ether (hereinafter referred to as "HFPME"), represented by chemical formula 1.

[0066] [Chemical Formula 1]

[0067]

[0068] 1,1,2,3,3,3-Hexafluoropropyl methyl ether (HFPME) exhibits excellent oxidative stability and can improve cycle life and output characteristics when used as a solvent in high-concentration salt electrolytes.

[0069] However, since the first organic solvent has the non-dissociation property of lithium salt, an organic solvent can be prepared by mixing the first organic solvent with a second organic solvent that has the dissociation property of lithium salt, so that the lithium salt constituting the electrolyte can be dissociated.

[0070] In one aspect, the second organic solvent may be a non-polymer and has a molecular weight of less than 600, 500, 400, 350, 300, 200, or 150 Daltons. The second solvent suitably has a molecular weight of at least 40, 50, 60, 70, 80, 90, 100, or 150 Daltons. Suitable second organic solvents include compositions containing one or more ketone (>C=O) groups, such as carbonates or esters, which suitably have 2 to 20 or 30 carbons, more typically 2 or 3 to 16, 14, 12, 10, or 8 carbons.

[0071] In one embodiment of the invention, the second organic solvent may include, for example, at least one carbonate-containing solvent selected from the group consisting of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, methyl propyl carbonate, and methyl ethyl carbonate. The carbonate-based solvent may have lithium salt dissociation properties. These lithium salt dissociation properties can be determined empirically, for example using Experimental Example 1 and... Figure 1 Phase separation tests were conducted using the scheme described herein.

[0072] In a preferred system, the second organic solvent may be dimethyl carbonate, which may exist as the sole solvent or as a component in a mixture to form the second solvent composition.

[0073] Here, in a preferred system, dimethyl carbonate (DMC), used as the second organic solvent, can compensate for the lithium salt non-dissociation properties of 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPME), used as the first organic solvent, and can dissociate the lithium salt.

[0074] However, when dimethyl carbonate (DMC) is used as the second organic solvent, dissociated lithium ions may be electrodeposited on the negative electrode surface. In this case, 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPME), used as the first organic solvent, can suppress this reaction.

[0075] Therefore, it is necessary to limit the mixing ratio of the first organic solvent and the second organic solvent so that they can compensate for each other's shortcomings while maintaining their respective advantages in oxidation stability and lithium salt dissociation performance.

[0076] In one embodiment of the invention, the organic solvent may include a first organic solvent and a second organic solvent with a volume ratio of 30:70 to 90:10, specifically 50:50 to 90:10, and more specifically 70:30 to 90:10. When this range is met, the high voltage stability and cycle life characteristics of the battery can be enhanced, while exhibiting improved output characteristics.

[0077] A suitable first organic solvent has or can exhibit lithium salt non-dissociation properties, and a second organic solvent has or can exhibit lithium salt dissociation properties, thereby providing an effective electrolyte composition that does not exhibit phase separation after being placed at room temperature (e.g., 25°C) for an extended period of time (e.g., at least 3, 6, 12, 24, 48, 72, or 96 hours or longer), as demonstrated by, for example, Experimental Example 1 and... Figure 1 The scheme shown.

[0078] Furthermore, the present invention provides a lithium secondary battery comprising an electrolyte composition for lithium secondary batteries.

[0079] The description of the electrolyte composition for lithium secondary batteries is the same as that described above, and therefore omitted.

[0080] In one embodiment of the present invention, in addition to the electrolyte composition for lithium secondary batteries described above, the lithium secondary battery may also include a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode.

[0081] This invention does not impose any particular limitations on the materials used for the negative electrode, positive electrode, and separator; they can be selected from materials known in the art. Some detailed embodiments are as follows.

[0082] In one embodiment of the invention, both the positive and negative electrodes can be prepared by mixing and stirring the positive and negative active materials with a solvent and, if necessary, a binder, a conductive material and a dispersant, thereby preparing a mixture, then coating the mixture onto a metal current collector, drying the mixture and pressing it.

[0083] The positive electrode active material can be any active material commonly used in the positive electrode of lithium secondary batteries. For example, the positive electrode 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.

[0084] The negative electrode active material can be any active material commonly used in lithium secondary batteries. 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 include one or more materials 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, Li4Ti5O). 12 ).

[0085] In one embodiment of the present invention, common conductive carbon materials can be used as conductive materials without any particular limitations.

[0086] In one embodiment of the invention, the metal current collector can be any highly conductive metal, which allows the mixture of positive or negative electrode active materials to adhere easily and is non-reactive 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 include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0087] In one embodiment of the invention, the separator may be a separator having micropores that allow ions to pass through. As a non-limiting example, it may be one or more combinations selected from glass fiber, polyester, polyethylene, polypropylene, and polytetrafluoroethylene, and may be in the form of a nonwoven or woven fabric. Specifically, lithium secondary batteries may primarily use polyolefin-based polymer separators, such as polyethylene and polypropylene, but the invention is not limited thereto. Furthermore, to enhance heat resistance or mechanical strength, separators coated with compositions comprising ceramic components or polymer materials may be used. These separators may optionally have a single-layer or multi-layer structure, and separators known in the art may be used, but the invention is not limited thereto.

[0088] There are no particular restrictions on the external shape of lithium secondary batteries, but they can be selected from, for example, cylindrical, square, pouch-shaped or coin-shaped containers.

[0089] Furthermore, the present invention provides a lithium metal secondary battery, the 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.

[0090] The above description of the electrolyte composition for lithium secondary batteries and the lithium secondary batteries also applies to lithium metal secondary batteries to the extent that they overlap.

[0091] Preferred embodiments and comparative embodiments of the present invention will be described below. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not intended to be limited thereto.

[0092] Example 1

[0093] An electrolyte composition for lithium secondary batteries was prepared by adding 1.5 M LiTFSI lithium salt and 5 wt% fluoroethylene carbonate (FEC) to an organic solvent comprising dimethyl carbonate (DMC) and 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPME) in a volume ratio of 1:9.

[0094] Examples 2 and 3

[0095] Electrolyte compositions for lithium secondary batteries were prepared according to the compositions shown in Table 1 below.

[0096] Comparative Example 1

[0097] An electrolyte composition for lithium secondary batteries was prepared in the same manner as in Example 1, except that an organic solvent comprising dimethyl carbonate (DMC) and 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPME) in a volume ratio of 5:95 was used.

[0098] Comparative Examples 2 to 4

[0099] Electrolyte compositions for lithium secondary batteries are prepared according to the compositions shown in Table 1 below.

[0100] [Table 1]

[0101]

[0102]

[0103] Experimental Example 1: Lithium Salt Dissociation Performance Test

[0104] To determine whether lithium salt dissociation occurred based on the mixing ratio of a solvent (DMC) with lithium salt dissociation properties to compensate for the lithium salt non-dissociation properties of HFPME, phase separation was examined in Example 1 and Comparative Example 1. The results showed... Figure 1 As shown in the image.

[0105] from Figure 1 As can be seen, for Comparative Example 1, it was confirmed that the lithium salt did not dissociate and phase separation occurred. However, for Example 1, it was confirmed that mixing occurred without phase separation.

[0106] Experimental Example 2: Ionic Conductivity Test Based on Organic Solvents

[0107] To determine the ionic conductivity based on the mixing ratio of the first and second organic solvents, the ionic conductivity of the electrolyte compositions according to Examples 1 to 3 was measured. The results are shown in Table 2.

[0108] Among them, LiNi 83 Co 11Mn6O2 was used as the positive electrode active material, polyvinylidene fluoride (PVdF) as the positive electrode binder, and Super-P carbon as the conductive agent, all mixed in a weight ratio of 93:3:4. This mixture was then dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The slurry was then coated onto aluminum foil to a thickness of 30 micrometers and dried at 80°C, thereby producing a loading level of approximately 10.0 mg / cm³. 2 The positive electrode is used. For the negative electrode, lithium metal foil is cut into 14π dimensions and used. Button batteries are assembled using the positive and negative electrodes according to existing methods, and corresponding experiments are conducted.

[0109] [Table 2]

[0110]

[0111]

[0112] As can be seen from Table 2, it has been confirmed that the ionic conductivity increases with the increase of the proportion of dimethyl carbonate (DMC), the dissociation solvent of lithium salt.

[0113] Experimental Example 3: Stability Test

[0114] The electrochemical stability of the battery comprising the electrolyte composition according to embodiments of the present invention was evaluated, and the results are as follows: Figure 2 As shown in the image.

[0115] from Figure 2 As can be seen, it has been confirmed that when using an electrolyte containing 1,1,2,3,3,3-hexafluoropropyl methyl ether (HFPME) solvent, the battery can operate stably without side reactions even at a high voltage of 5.0V.

[0116] Experimental Example 4: Cyclic Life Characteristics Test

[0117] The discharge capacity and cycle life characteristics of lithium secondary batteries using the electrolyte compositions of the examples and comparative examples were measured. The results are shown in Table 3 and... Figure 3 As shown in the image.

[0118] [Table 3]

[0119]

[0120] From Table 3 and Figure 3 As can be seen, it has been confirmed that when using the electrolyte composition according to embodiments of the present invention, the discharge capacity and cycle life characteristics are significantly improved compared with comparative embodiments using different electrolyte compositions.

[0121] Experimental Example 5: Discharge Capacity Test Based on Charge / Discharge Rate

[0122] To determine the impact of the electrolyte compositions of the examples and comparative examples on the battery electrochemical performance, the discharge capacity was evaluated according to the charge / discharge rate. The results are shown in Table 4 and... Figure 4 As shown in the image.

[0123] [Table 4]

[0124]

[0125] From Table 4 and Figure 4 It can be seen that, in most cases, the discharge capacity is improved when using the electrolyte composition for lithium secondary batteries according to the embodiments. Specifically, the battery including Example 1 exhibits the best performance. This is because a higher HFPME content results in a more stable electrode-electrolyte interface and enhanced electrochemical stability of the electrolyte.

[0126] Experimental Example 6: Overvoltage Characteristic Evaluation Test

[0127] To measure the overvoltage caused by side reactions occurring during charging and discharging, the overvoltage of a lithium metal-lithium metal symmetric electrode battery was measured at room temperature (25.0 °C). The results are shown in... Figure 5 .

[0128] from Figure 5 As can be seen, it has been confirmed that, compared with Comparative Example 2 which uses a commercially available electrolyte composition under the same conditions, the interface characteristics between the lithium metal anode and the electrolyte are stabilized and the overvoltage characteristics are improved when using the electrolyte composition according to Example 1.

[0129] Experimental Example 7: Interface Characteristic Evaluation Test

[0130] To evaluate the interfacial characteristics between the lithium metal anode and the electrolyte, the overvoltage of a lithium metal-copper current collector asymmetric electrode cell was measured at room temperature (25°C). The results are shown in... Figure 6 .

[0131] from Figure 6 As can be seen, it has been confirmed that, compared with Comparative Example 2 which uses a commercially available electrolyte composition under the same conditions, the interfacial characteristics between the lithium metal anode and the electrolyte are stabilized when using the electrolyte composition according to Example 1, thereby reducing the formation of lithium dendrites and improving coulombic efficiency.

[0132] The features, structures, effects, etc., described in the above exemplary embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to a single embodiment. Furthermore, the features, structures, effects, etc., exemplified in the various exemplary embodiments can be combined or modified by those skilled in the art in other embodiments. Therefore, such combinations and modifications should be understood to be within the scope of the present invention.

Claims

1. An electrolyte composition for use in a lithium secondary battery, the electrolyte composition comprising: Lithium salts; Functional additives; and Organic solvent, said organic solvent comprising: First organic solvents including fluorinated ether-based solvents; and A second organic solvent, including carbonate-based solvents.

2. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The first organic solvent includes one or more fluorinated ether solvents selected from the following: 1,1,2,3,3,3-hexafluoropropyl methyl ether, 2,2,2-trifluoroethyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether.

3. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The second organic solvent includes one or more carbonate-based solvents selected from the following: dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate, methyl propyl carbonate, and methyl ethyl carbonate.

4. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The organic solvent includes the first organic solvent and the second organic solvent in a volume ratio of 30:70 to 90:

10.

5. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The lithium salt includes those selected from Li(CF3SO2)2N, Li(SO2F)2N, LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 One or more of the following, and any combination thereof: LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, and LiB(C6H5)4.

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

7. The electrolyte composition for lithium secondary batteries according to claim 1, wherein, The functional additives include one or more of fluoroethylene carbonate, vinylene carbonate, tris(pentafluorophenyl)borane, propylene sulfite, and 1,3,2-dioxazolthiophene 2,2-dioxide, and any combination thereof.

8. A lithium secondary battery comprising the electrolyte composition for a lithium secondary battery as described in any one of claims 1 to 7.

9. A lithium metal secondary battery, comprising: Including the positive electrode, which is a 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 an electrolyte composition for lithium secondary batteries according to any one of claims 1 to 7.

10. An electrolyte composition for a lithium secondary battery, the electrolyte composition comprising: This includes lithium salts of LiTFSI with concentrations ranging from 1.0 mol to 1.5 mol; Based on the total weight of the electrolyte composition, 1% to 10% by weight of fluoroethylene carbonate; and An organic solvent comprising 1,1,2,3,3,3-hexafluoropropyl methyl ether and dimethyl carbonate in a volume ratio of 70:30 to 90:

10. in, The electrolyte composition remains in a single liquid phase.

11. The electrolyte composition according to claim 10, wherein, The volume ratio of 1,1,2,3,3,3-hexafluoropropyl methyl ether to dimethyl carbonate is 90:

10.

12. The electrolyte composition according to claim 10, wherein, The amount of fluoroethylene carbonate present is 5% by weight of the total weight of the electrolyte composition.

13. The electrolyte composition according to claim 10, wherein, The ionic conductivity obtained at 25°C is at least 2.7 mS / cm. -1 .

14. The electrolyte composition according to claim 10, wherein, When used in lithium metal-lithium metal symmetric batteries, under the same conditions, its charge / discharge overvoltage is lower than that of batteries containing an electrolyte consisting only of dimethyl carbonate.

15. A lithium metal secondary battery, comprising: Including the positive electrode, which is a positive electrode active material; Including lithium metal anodes; A diaphragm is disposed between the positive electrode and the negative electrode; and Electrolyte, the electrolyte comprising: 1.0 mol to 1.5 mol of LiTFSI; 1% to 10% by weight of fluoroethylene carbonate; and An organic solvent comprising 1,1,2,3,3,3-hexafluoropropyl methyl ether methyl ether and dimethyl carbonate in a volume ratio of 70:30 to 90:

10.

16. The lithium metal secondary battery according to claim 15, wherein, The volume ratio of 1,1,2,3,3,3-hexafluoropropyl methyl ether to dimethyl carbonate is 90:

10.

17. The lithium metal secondary battery according to claim 15, wherein, The electrolyte also contains 0.1% to 5% by weight of vinylene carbonate.

18. The lithium metal secondary battery according to claim 15, wherein, The diaphragm comprises a porous polyolefin membrane selected from polyethylene and / or polypropylene.

19. The lithium metal secondary battery according to claim 15, wherein, The battery is configured as a pouch cell.

20. A vehicle comprising a lithium secondary battery according to claim 8.

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