Electrolytes for lithium secondary batteries and lithium metal secondary batteries

Abstract

The present invention relates to an electrolyte for lithium secondary batteries and a lithium metal secondary battery containing the same, which can improve the initial discharge characteristics, life characteristics, and output characteristics of lithium metal secondary batteries. The electrolyte may contain a lithium salt; a non-aqueous organic solvent; an organic anti-solvent that exhibits solubility 10 times or more less than that of the non-aqueous organic solvent relative to the lithium salt; and an additive containing a fluorine-substituted ether compound.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2023-0110045 dated August 22, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to an electrolyte for lithium secondary batteries and a lithium metal secondary battery containing the same, which can improve the initial discharge characteristics, life characteristics, and output characteristics of lithium metal secondary batteries. [Background technology]

[0003] Recently, as the application areas of lithium-ion batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, communications, and computers to power storage and supply for large-area devices such as automobiles and energy storage devices, the demand for lithium-ion batteries that are high-capacity, high-power, long-life, and highly stable has increased.

[0004] Lithium metal batteries are batteries that use lithium metal (Li-metal) as the negative electrode active material. Compared to conventional batteries that use graphite-based or lithium alloy-based negative electrodes, they have the advantage of theoretically having much higher energy density and capacity. Therefore, research and development of such lithium metal batteries are continuing in order to apply them to batteries that require high energy density.

[0005] However, lithium metal batteries have several drawbacks. During the charge and discharge process, the volume change of the negative electrode is large, and needle-like lithium metal layers (such as lithium dendrites) grow unevenly. Due to the characteristics of lithium metal with high reactivity, side reactions occur between the lithium metal layer and the electrolyte, resulting in a large irreversible capacity. Also, during the process of lithium metal desorption during discharge, the dissolution of lithium ions and the collapse of the interface layer occur, continuously generating inactive lithium (Dead Li), and as a result, the irreversible capacity further increases. This is a major factor that degrades the life characteristics of lithium metal batteries and hinders their practical application.

[0006] Therefore, various attempts have been made to solve the problems of lithium metal batteries, such as forming a protective layer on the surface of the lithium metal layer or developing a new electrolyte that can suppress the electrolyte decomposition reaction on the lithium metal surface.

[0007] As one of such various attempts, recently, so-called Localized High-Concentration Electrolytes (LHCE) have been proposed, which increase the concentration of lithium salts in the electrolyte while adding an anti-solvent with relatively low solubility to the lithium salts (Chem Vol.4, Issue 8, August 9, 2018, p1877-1892). Such localized high-concentration electrolytes can form a high-concentration region of lithium salts to improve the output characteristics of lithium metal batteries and, by surrounding the high-concentration region of lithium salts with the anti-solvent, are expected to suppress the side reaction between the lithium metal layer and the electrolyte and improve the life characteristics of lithium metal batteries.

[0008] However, when applying the local high-concentration electrolyte, not only is the improvement of the life characteristics of the lithium metal battery insufficient, but also the conductivity of the ions in the electrolyte decreases, the viscosity increases, and the performance of the electrolyte itself may deteriorate. In addition, due to the decrease in the activity of the electrolyte itself, the designed capacity of the lithium metal battery cannot be manifested initially, and there is a disadvantage that the initial discharge capacity and the like decrease. In particular, such disadvantages may appear more clearly when applying a cathode active material such as lithium iron phosphate in order to reduce the manufacturing cost of the battery.

Prior Art Documents

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Therefore, an object of the present invention is to provide an electrolyte for a lithium secondary battery that can improve the initial discharge capacity as well as the life characteristics and output characteristics of the lithium metal secondary battery.

[0011] Another object of the present invention is to provide a lithium metal secondary battery that includes the electrolyte for a lithium secondary battery and exhibits excellent electrochemical characteristics.

Means for Solving the Problems

[0012] The present invention provides an electrolyte for a lithium secondary battery including a lithium salt; a non-aqueous organic solvent; an organic anti-solvent that exhibits a solubility 10 times or less than that of the non-aqueous organic solvent with respect to the lithium salt; and an additive including a fluorine-substituted ether compound.

[0013] In such an electrolyte, the additive may further include a nitrate-based compound.

[0014] Furthermore, the present invention provides a lithium metal secondary battery comprising a positive electrode containing a positive electrode active material; a negative electrode containing a lithium metal layer; a separation membrane between the positive and negative electrodes; and the electrolyte of the present invention.

[0015] In such a lithium metal secondary battery, the positive electrode active material may include a lithium transition metal compound, such as lithium iron phosphate. [Effects of the Invention]

[0016] The electrolyte of the present invention contains an organic non-solvent that exhibits low solubility in relation to lithium salts. Therefore, even when it contains a high concentration of lithium salt, the non-solvent surrounds the high-concentration region of lithium salt, thereby suppressing side reactions between the lithium metal layer and the electrolyte and improving the lifespan and output characteristics of the lithium metal battery.

[0017] Furthermore, the electrolyte contains a fluorine-substituted ether compound as an additive, which can form a film on the lithium metal layer. As a result, side reactions of the electrolyte can be further suppressed, and the lifespan characteristics of the lithium metal battery can be further improved. Moreover, it has been confirmed that such an additive can increase the activity of the electrolyte and suppress the decrease in the initial capacity of the battery caused by the addition of other additives (e.g., nitrate-based additives).

[0018] Therefore, the electrolyte of the present invention can be used in lithium metal secondary batteries to improve not only their lifespan and output characteristics, but also other characteristics such as initial discharge capacity. [Brief explanation of the drawing]

[0019] [Figure 1a] Figure 1a is a graph showing the results of evaluating the discharge capacity of lithium metal secondary batteries containing the electrolytes of Example 1 and Comparative Example 1 at different initial cycles (~20 cycles). [Figure 1b]Figure 1b is a graph showing the results of evaluating the discharge capacity of lithium metal secondary batteries containing the electrolytes of Example 2 and Comparative Example 2 at different initial cycles (~20 cycles). [Figure 2a] Figure 2a is a graph showing the results of evaluating the capacity characteristics and life characteristics of lithium metal secondary batteries containing the electrolytes of Example 1 and Comparative Example 1 over a period of approximately 150 cycles. [Figure 2b] Figure 2b is a graph showing the results of evaluating the capacity characteristics and life characteristics of lithium metal secondary batteries containing the electrolytes of Example 2 and Comparative Example 2 over a period of approximately 150 cycles. [Figure 3] Figure 3 is a graph showing the results of evaluating the discharge resistance for each cycle for lithium metal secondary batteries containing the electrolytes of the examples and comparative examples. [Modes for carrying out the invention]

[0020] The following describes an electrolyte for a lithium secondary battery and a lithium metal secondary battery containing the same, according to specific embodiments of the invention.

[0021] Terms and words used in this specification and claims should not be interpreted restrictively in their usual or dictionary sense, but rather in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0022] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless otherwise clearly stated in the context, singular expressions include plural expressions.

[0023] Throughout the specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of a feature, figure, step, action, component, part, or combination thereof, and should not be understood to preemptively exclude the existence or possibility of adding one or more other features, figures, steps, actions, components, parts, or combination thereof.

[0024] According to one embodiment of the invention, an electrolyte for a lithium secondary battery is provided, comprising a lithium salt; a non-aqueous organic solvent; an organic anti-solvent exhibiting solubility 10 times or more less than that of the non-aqueous organic solvent relative to the lithium salt; and an additive comprising a fluorine-substituted ether compound.

[0025] The electrolyte of the above embodiment includes a non-aqueous organic solvent that dissolves the lithium salt and acts as a transport pathway for lithium ions, as well as an organic non-solvent that exhibits a solubility of 10 times or more, or 10 to 30 times less, than that of the non-aqueous organic solvent, and substantially does not dissolve the lithium salt.

[0026] Such an electrolyte in one embodiment can belong to the category of Localized High-Concentration Electrolytes (LHCE), and can exhibit a configuration in which a high-concentration region in which lithium salt is dissolved at a high concentration in a non-aqueous organic solvent during battery charging and discharging, and the organic non-solvent distributed around this high-concentration region. Therefore, when using such an electrolyte, the output characteristics of the battery can be improved by the high-concentration distribution of lithium salt. Furthermore, the organic non-solvent distribution region can suppress side reactions between the lithium metal layer and the electrolyte, thereby improving the lifespan characteristics of the lithium metal secondary battery.

[0027] In addition, the electrolyte contains a fluorine-substituted ether compound as an additive. Such a fluorine-substituted ether compound can form a film containing lithium fluoride on the lithium metal layer, for example. As a result, side reactions of the electrolyte can be further suppressed to improve the life characteristics of the lithium metal battery, while gas generation can be suppressed. Also, it has been confirmed that such an additive can increase the activity of the electrolyte and suppress a decrease in the initial capacity of the battery due to the addition of other additives (for example, nitrate-based additives). Therefore, the electrolyte of the above-described embodiment is used in a lithium metal secondary battery, and can improve not only its life characteristics and output characteristics but also characteristics such as the initial discharge capacity, and can reduce gas generation due to side reactions of the electrolyte.

[0028] On the other hand, in the electrolyte of the above-described embodiment, the lithium salt is used as a mediator for transmitting ions in the lithium secondary battery. The lithium salt contains, for example, Li as a cation. + and contains F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 -(CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - It can also contain anions selected from the group consisting of the following.

[0029] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It can contain one or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (Lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2), and LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), and LiFSI or LiTFSI can be appropriately used considering the output characteristics of the lithium metal secondary battery and the solubility in the non-aqueous organic solvent and non-organic solvent.

[0030] Furthermore, the concentration of the lithium salt may be relatively high, such as 1.0 M or higher, or 1.0 to 2.5 M, or 1.1 to 1.8 M, taking into consideration the output characteristics of the lithium secondary battery. Such a concentration of lithium salt can be defined as the molar concentration considering the total volume of the non-aqueous organic solvent and the organic non-solvent. The high concentration of the lithium salt can further accelerate the desolvation of lithium ions, thereby improving the output characteristics of the lithium secondary battery.

[0031] On the other hand, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent that has been known to be applicable to lithium-ion battery electrolytes and the like can be used. However, considering combinations with appropriate organic non-solvents, the non-aqueous organic solvent can appropriately include carbonate-based solvents or aliphatic ether-based solvents.

[0032] More specifically, the carbonate-based solvent can be dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, or methyl (2,2,2-trifluoroethyl) carbonate, and the aliphatic ether-based solvent can be dimethyl ether, dibutyl ether, tetraglyceride, diglyme, or dimethoxyethane.

[0033] On the other hand, the electrolyte of the above embodiment includes, in addition to the lithium salt and non-aqueous organic solvent described above, an organic non-solvent that exhibits solubility of 10 times or more, or 10 to 30 times less, than that of the non-aqueous organic solvent, and substantially does not dissolve the lithium salt. Such an organic non-solvent can be defined as one that exhibits substantially no solubility for the lithium salt and, for example, can dissolve the lithium salt only at concentrations of 0.1 M or less, or 0 to 0.1 M, or 0 to 0.05 M. Furthermore, the organic non-solvent may be an organic solvent that exhibits low solubility in the lithium salt and is miscible with the non-aqueous organic solvent, for example, an ether-based solvent having a fluorine-substituted alkyl group. More specifically, it may include one or more selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynononafluorobutane (MOFB), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), and ethoxynononafluorobutane (EOFB).

[0034] Such organic non-solvents can be selected considering factors such as miscibility with the non-aqueous organic solvent and solubility depending on the type / concentration of the lithium salt. For example, when an aliphatic ether solvent is used as the non-aqueous organic solvent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) can be appropriately used, and when a carbonate solvent is used as the non-aqueous organic solvent, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE) can be appropriately used.

[0035] The electrolyte of one embodiment further comprising the organic non-solvent may include, as described above, a region in the non-aqueous organic solvent where a locally high concentration of lithium salt exists, as well as a region in which the lithium salt is substantially absent from the organic non-solvent distribution. In this way, the presence of a locally high concentration of lithium salt in a solventized form within the electrolyte can further improve the output characteristics of the lithium secondary battery, while the organic non-solvent distribution region can reduce the increase in viscosity and decrease in fluidity of the electrolyte.

[0036] The amount of the organic non-solvent used can be adjusted according to the type of non-aqueous organic solvent and lithium salt, and the overall concentration of the lithium salt. For example, the organic non-solvent may be included in the electrolyte in a content such that the molar ratio of the organic non-solvent to the non-aqueous organic solvent is 1:0.4 to 1:1, or 1:0.4 to 1:0.67.

[0037] The electrolyte of the above embodiment further comprises a fluorine-substituted ether compound as an additive. Such a fluorine-substituted ether compound can, for example, form a film containing lithium fluoride on the lithium metal layer. Therefore, it is possible to further suppress side reactions of the electrolyte and improve the life characteristics of the lithium metal battery, while suppressing gas generation. Furthermore, as can be confirmed through the examples described later, it has been confirmed that the additive can increase the activity of the electrolyte and suppress the decrease in the initial capacity of the battery. Therefore, a lithium metal secondary battery containing the electrolyte of the above embodiment can exhibit improved initial discharge capacity and the like.

[0038] As the fluorine-substituted ether compound, a dialkoxyalkane compound with a total of 4 to 10 carbon atoms substituted with multiple fluorines, for example, 3 or more, or 3 to 5 fluorines, can be used. Specific examples include one or more selected from the group consisting of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB) and 2,2,3,3-tetrafluoro-1,4-diethoxybutane (FDEB).

[0039] Furthermore, the electrolyte of the above embodiment may optionally contain additional additives, such as nitrate compounds, and the addition of such nitrate compounds can further improve the capacity characteristics and lifespan characteristics of the lithium metal secondary battery. When only the nitrate compound is added, the initial discharge capacity of the battery may decrease, but it has been confirmed that this disadvantage can be overcome by combining it with the aforementioned fluorine-substituted ether compounds.

[0040] As the nitrate compound, for example, one or more metal nitrates selected from the group consisting of lithium nitrate (LiNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), magnesium nitrate (MgNO3), barium nitrate (BaNO3), lithium nitrite (LiNO2), potassium nitrite (KNO2), and cesium nitrite (CsNO2) can be used.

[0041] In addition, considering the effects of adding the fluorine-substituted ether compound and nitrate compound on improving initial discharge capacity, lifetime characteristics, and capacity characteristics, the additive may contain 1 to 10% by weight, or 3 to 9% by weight, of the fluorine-substituted ether compound and 0.2 to 5% by weight, or 0.2 to 2% by weight, of the nitrate compound, based on the total weight of the electrolyte.

[0042] On the other hand, according to another embodiment of the invention, a lithium metal secondary battery is provided that includes the electrolyte of the above-described embodiment. Such a lithium metal secondary battery may include a positive electrode containing a positive electrode active material; a negative electrode containing a lithium metal layer; a separator membrane between the positive and negative electrodes; and the electrolyte of the above-described embodiment.

[0043] First, in the lithium metal secondary battery of the other embodiment described above, the negative electrode may be a lithium metal layer formed on one or both sides of a planar negative electrode current collector, in accordance with the general configuration of a lithium metal secondary battery, and can be manufactured by depositing lithium metal onto the negative electrode current collector or by rolling lithium foil.

[0044] The negative electrode current collector can be formed using any metal that does not induce chemical changes in the battery, has high conductivity, and has been known to be usable as a negative electrode current collector.

[0045] Specific examples include metals such as stainless steel, aluminum, nickel, titanium, or copper, or copper, aluminum, or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Such negative electrode current collectors can be formed in a variety of forms, such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0046] Furthermore, the negative electrode current collector may have a thickness of 3 to 100 μm, and the lithium metal layer may have a thickness of, for example, 1 to 300 μm.

[0047] On the other hand, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0048] Such a positive electrode can be manufactured by mixing an active material and a binder, and optionally a conductive material, filler, etc., in a solvent to produce a positive electrode slurry composition, and then coating a positive electrode current collector with this slurry.

[0049] The positive electrode current collector can generally have a thickness of 3 to 500 μm. Furthermore, the positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used. The current collector can also have fine irregularities formed on its surface to increase the adhesion strength of the positive electrode active material, and can take various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0050] And in the case of the positive electrode active material, it can be a compound capable of reversible intercalation and deintercalation of lithium, specifically, it can include a lithium metal compound containing one or more metals such as iron, cobalt, manganese, nickel or aluminum and lithium.

[0051] Specifically, the lithium metal compound includes lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2)O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), etc. may be mentioned, and one or two or more of these compounds may be included.

[0052] Among these, the positive electrode active material can include lithium iron phosphate. For reference, although the use of lithium iron phosphate has been considered for expansion due to its low unit price, etc., a lithium metal secondary battery including a positive electrode containing this shows more clearly a decrease in life characteristics and capacity characteristics, particularly a decrease in initial capacity, etc. However, the lithium metal secondary battery of the other embodiments can solve the decrease in the capacity and initial discharge capacity, etc. by combining the electrolyte of one embodiment with such a positive electrode containing lithium iron phosphate, and can contribute to the application to lithium metal secondary batteries at a lower unit price.

[0053] The above-mentioned positive electrode active material may be included at 60 to 99% by weight, or 70 to 99% by weight, or 80 to 98% by weight based on the total weight of the positive electrode active material layer.

[0054] On the other hand, the conductive material contained in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material, and such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. Among these, the conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium metal secondary battery and further improve output characteristics.

[0055] Typically, the conductive material may be included in an amount of 1 to 20% by weight, 1 to 15% by weight, or 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0056] The binder selectively included in the positive electrode active material layer is a component that assists in the bonding of the positive electrode active material to conductive materials and to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more of these can also be used.

[0057] Typically, the binder may be present in an amount of 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0058] Furthermore, a filler may be selectively added to the positive electrode as a component to suppress its expansion.

[0059] Such fillers are not particularly limited as long as they can suppress electrode expansion without inducing chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0060] The aforementioned positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying this slurry to a metal current collector, and then drying and rolling it. In this process, the dispersion medium can be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof.

[0061] On the other hand, the lithium metal secondary battery described above may further include a porous separator membrane interposed between the positive electrode and the negative electrode.

[0062] Such porous separation membranes can be made from polyethylene, polypropylene or other olefin polymers, glass fibers, etc., in the form of sheets, multilayer membranes, fine porous films, woven fabrics, and nonwoven fabrics, but are not necessarily limited thereto. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the separation membrane, and it may be even more preferable to use porous glass fiber nonwoven fabric (glass filter) as the separation membrane. The separation membrane may be a thin insulating film with high ion permeability and mechanical strength, and the pore diameter of the separation membrane may generally be in the range of 0.01 to 10 μm, and the thickness may generally be in the range of 5 to 300 μm, but are not limited thereto.

[0063] On the other hand, the aforementioned lithium metal secondary battery may be manufactured by conventional methods in this field.

[0064] For example, an electrode assembly including a positive electrode, a negative electrode, and a separator membrane may be housed in a case and manufactured by injecting and impregnating it with the aforementioned electrolyte.

[0065] Such lithium metal secondary batteries can be applied not only to battery cells used as power sources for small devices, but are also particularly suitable as unit batteries in battery modules that power medium- and large-sized devices. The batteries of one embodiment or other embodiments can be selectively used, taking into consideration the appropriate discharge rate for each application.

[0066] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0067] Example 1: Electrolyte Production Dimethyl ether (DME), a non-aqueous organic solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), an organic non-solvent, and LiFSI (99.9%, Sigma-Aldrich), a lithium salt, were mixed in a molar ratio of 1.2:3:1 to prepare the electrolyte of Example 1. To this electrolyte, 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB) was added as an additive at a content of 3% by weight relative to the total electrolyte, and then the mixture was prepared.

[0068] Example 2: Electrolyte Production Dimethyl ether (DME), a non-aqueous organic solvent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as an organic non-solvent, and LiFSI (99.9%, Sigma-Aldrich) as a lithium salt were mixed in a molar ratio of 2:3:1 to prepare the electrolyte of Example 2. To this electrolyte, 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB) and lithium nitrate were added as additives at concentrations of 3.5% by weight and 0.2% by weight, respectively, relative to the total electrolyte, and then mixed.

[0069] Comparative Example 1: Electrolyte Production An electrolyte was prepared as Comparative Example 1 by mixing dimethyl ether (DME), a non-aqueous organic solvent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), as an organic non-solvent, and LiFSI (99.9%, Sigma-Aldrich), a lithium salt, in a molar ratio of 1.2:3:1.

[0070] Comparative Example 2: Electrolyte Production To prepare the electrolyte of Comparative Example 2, lithium nitrate was added as an additive at a concentration of 0.35% by weight relative to the total electrolyte content. This mixture consisted of a non-aqueous organic solvent dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as an organic non-solvent, and LiFSI (99.9%, Sigma-Aldrich) as a lithium salt, in a molar ratio of 2:3:1. These were then mixed to produce the electrolyte of Comparative Example 2.

[0071] Manufacturing example: Fabrication of pouch cells A prototype pouch cell was fabricated as follows: A Li anode (20 μm, Honjo Metal) and a double-sided coated LFP cathode (provided by LG Energy Solutions, active material: Super P C65:PVDF=96:2:2) were punched to 40 mm × 60 mm and 30 mm × 50 mm, respectively. The anode and cathode were welded to Ni and Al tabs using an ultrasonic welding machine. All electrodes and separation membranes were stacked and packaged in an aluminum pouch bag, and 3.2 g (3.2 gAh) of the electrolyte of the example or comparative example was added. -1 The pouch cells were fabricated by injection, and all cell assembly processes were carried out in a dry room where the moisture content could be controlled.

[0072] Experimental example Using the pouch cells manufactured in the above manufacturing example, charging and discharging were performed under 0.33C / 0.33C conditions, and the discharge capacity for each initial cycle (~20 cycles) was measured. The measurement results are shown in Figures 1a and 1b.

[0073] Referring to Figures 1a and 1b, it was confirmed that the batteries manufactured using the electrolytes of Examples 1 and 2 exhibited superior initial capacity characteristics compared to Comparative Examples 1 and 2.

[0074] Furthermore, the capacity characteristics and life characteristics were confirmed over approximately 150 cycles using the aforementioned pouch cell, and the measurement results are shown in Figures 2a and 2b.

[0075] Referring to Figures 2a and 2b, it was confirmed that the batteries manufactured using the electrolytes of Examples 1 and 2 exhibited superior capacity characteristics and cycle life characteristics compared to Comparative Examples 1 and 2.

[0076] In addition, the discharge resistance for each cycle was measured using the aforementioned pouch cell, and the measurement results are shown in Figure 3.

[0077] Referring to Figure 3, it was confirmed that the batteries manufactured using the electrolytes of Examples 1 and 2 showed a lower rate of increase in discharge resistance compared to Comparative Examples 1 and 2.

Claims

1. Lithium salt; Non-aqueous organic solvents; An organic anti-solvent that exhibits solubility in the lithium salt that is 10 times or less than that of the non-aqueous organic solvent; and An electrolyte for lithium secondary batteries, comprising an additive containing a fluorine-substituted ether compound.

2. The lithium salt is LiCl, LiBr, LiI, LiBF ４ , LiClO ４ , LiB １０ Cl １０ , LiAlCl ４ , LiAlO ２ , LiPF ６ , LiCF ３ SO ３ , LiCH ３ CO ２ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiCH ３ SO ３ , LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO ２ F) ２ ), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO ２ CF ２ CF ３ ) ２ ), and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO ２ CF ３ ) ２ ), and the electrolyte for a lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium salt is contained in the electrolyte at a concentration of 1.0 M to 2.5 M.

4. The non-aqueous organic solvent is one or more aliphatic ether solvents selected from the group consisting of dimethyl ether, dibutyl ether, tetraglyceride, diglyme, and dimethoxyethane; or The electrolyte for a lithium secondary battery according to claim 1, comprising one or more carbonate-based solvents selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, and methyl (2,2,2-trifluoroethyl) carbonate.

5. The electrolyte for a lithium secondary battery according to claim 1, wherein the organic nonsolvent comprises one or more selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonanafluorobutane (MOFB), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), and ethoxynonanafluorobutane (EOFB).

6. The electrolyte for a lithium secondary battery according to claim 1, wherein the organic non-solvent: the non-aqueous organic solvent is contained in a molar ratio of 1:0.4 to 1:

1.

7. The electrolyte for a lithium secondary battery according to claim 1, wherein the fluorine-substituted ether compound comprises one or more fluorine-substituted dialkoxyalkanes selected from the group consisting of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB) and 2,2,3,3-tetrafluoro-1,4-diethoxybutane (FDEB).

8. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive further comprises a nitrate compound.

9. The nitrate compound is lithium nitrate (LiNO). ３ ), potassium nitrate (KNO ３ ), cesium nitrate (CsNO) ３ ), magnesium nitrate (MgNO ３ ), barium nitrate (BaNO) ３ ), lithium nitrite (LiNO) ２ ), potassium nitrite (KNO ２ ) and cesium nitrite (CsNO) ２ The electrolyte for a lithium secondary battery according to claim 8, comprising one or more selected from the group consisting of ).

10. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive comprises 1% to 10% by weight of the fluorine-substituted ether compound and 0.2% to 5% by weight of the nitrate compound, based on the total weight of the electrolyte.

11. Positive electrode containing positive electrode active material; A negative electrode containing a lithium metal layer; Separation membrane between the positive and negative electrodes; and A lithium metal secondary battery comprising the electrolyte described in any one of claims 1 to 10.

12. The lithium metal secondary battery according to claim 11, wherein the positive electrode active material comprises lithium iron phosphate.

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