Electrolyte for lithium metal batteries and lithium metal battery comprising the same

Abstract

The present invention relates to an electrolyte for a lithium metal battery and a lithium metal battery comprising the same. The electrolyte for a lithium metal battery comprises a lithium salt and a non-aqueous organic solvent. The non-aqueous organic solvent comprises a main solvent and a co-solvent. The main solvent includes N,N-dimethylsulfamoyl fluoride, vinyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfamide, or any combination thereof. The co-solvent is represented by Chemical Formula 1, and the co-solvent is included in an amount of more than 1 mol% based on the total amount (100 mol%) of the non-aqueous organic solvent. Chemical Formula 1: In Chemical Formula 1, each substituent is the same as defined in the DETAILED DESCRIPTION.

Description

[0001] Cross-reference to related applications This application claims priority and benefit to Korean Patent Application No. 10-2025-0045986, filed with the Korean Intellectual Property Office on April 9, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to an electrolyte for lithium metal batteries and a lithium metal battery comprising said electrolyte. Background Technology

[0003] With the growth of the electric vehicle market, the demand for high-capacity batteries exceeding those of lithium-ion batteries is increasing. Consequently, the demand for anode and cathode materials with high energy density and long-term stability for lithium metal batteries is also increasing.

[0004] Lithium metal (with its high specific capacity of 3860 mAh / g and low standard electrode potential (-3.04 V compared to a conventional hydrogen electrode)) has attracted considerable attention as a negative electrode material for rechargeable lithium-ion batteries. However, lithium metal is highly reactive and generates an extremely reducing atmosphere during charging, which can lead to irreversible decomposition reactions between the lithium metal and the electrolyte. These decomposition reactions can deplete the electrolyte, and the decomposition products may form a non-uniform film on the lithium metal surface. Furthermore, with repeated charging and discharging, lithium can grow in the form of dendrites. Dendritic lithium can cause electrical short circuits inside the battery, leading to safety issues such as battery fires.

[0005] Therefore, in order to utilize lithium metal, which has high stability and high capacity, it is desirable to develop an electrolyte that reduces the reactivity of lithium metal, prevents the growth of dendritic lithium, and enables uniform lithium deposition (coating).

[0006] The statements in this background section are merely background information related to the present invention and do not constitute prior art. Summary of the Invention

[0007] An embodiment of the present invention provides an electrolyte for lithium metal batteries, which helps to improve the durability of lithium metal batteries by delaying the decomposition of anions constituting lithium salts. At the same time, since the electrolyte is stable to lithium metal and its reaction is limited, the phenomenon of continuous consumption of lithium salts by reacting with lithium metal to form a thin film can be reduced.

[0008] Furthermore, the implementation scheme provides a lithium metal battery with excellent stability.

[0009] According to the implementation scheme, the electrolyte for lithium metal batteries comprises a lithium salt and a non-aqueous organic solvent. The non-aqueous organic solvent comprises a primary solvent and a co-solvent. The primary solvent includes N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof. The co-solvent is represented by chemical formula 1: In chemical formula 1, R 1 It is a substituted or unsubstituted C2 to C20 alkyl group, and R 2 It is a substituted or unsubstituted C1 to C20 alkyl group. R 1 and R 2 They are different from each other, and R 1 More carbon atoms than R 2 Based on the total amount of non-aqueous organic solvents (100 mol%), co-solvents are included in amounts exceeding 1 mol%.

[0010] The main solvent may include N,N-dimethylaminosulfonyl fluoride.

[0011] The cosolvent can be a compound of formula 1, wherein R 1 For ethyl, R 2 It is a methyl group.

[0012] Based on the total amount of non-aqueous organic solvents (100 mol%), cosolvents may be included in an amount of 2.5 mol% or greater.

[0013] Based on the total amount of non-aqueous organic solvent (100 mol%), the cosolvent can be included in an amount ranging from 2.5 mol% to 10 mol%.

[0014] The molar ratio of lithium salt to non-aqueous organic solvent can be in the range of 1:1 to 1:5.

[0015] The lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), or any combination thereof.

[0016] The concentration of lithium salt can range from 1.0 M to 5.0 M.

[0017] The lithium nuclear magnetic resonance (Li-NMR) signal values ​​of electrolytes used in lithium metal batteries can have more positive values ​​than those of electrolytes used in lithium metal batteries that do not contain co-solvents.

[0018] According to another embodiment, a lithium metal battery may include a positive electrode, a lithium metal layer serving as a negative electrode and opposite to the positive electrode, a separator between the positive and negative electrodes, and an electrolyte for the lithium metal battery.

[0019] The thickness of the lithium metal layer can range from 5 μm to 50 μm.

[0020] According to another embodiment, a lithium metal battery may include a first electrode, a lithium metal layer serving as a second electrode and opposite to the first electrode, a separator between the first electrode and the second electrode, and an electrolyte for the lithium metal battery.

[0021] According to the implementation scheme, the electrolyte for lithium metal batteries forms a suitable solvation environment to enhance the inhibition of oxidative decomposition of salt, thereby delaying further salt consumption. Furthermore, by introducing a compound as a co-solvent (which is less reactive to the lithium anode than the main solvent and thus can exhibit a sustained effect), the lithium metal battery containing the electrolyte can have improved durability and excellent stability. Attached Figure Description

[0022] Figure 1 This is a view showing whether the oxidative and reductive decomposition of salts is delayed or accelerated depending on the type of co-solvent used with the primary solvent that produces a weak solvation environment.

[0023] Figure 2 The results of durability evaluations of lithium metal battery cells using each electrolyte according to Example 1 and Comparative Example 1 are shown.

[0024] Figure 3 The results of the nuclear magnetic resonance (NMR) quantitative analysis of the electrolyte according to Comparative Example 1 are shown.

[0025] Figure 4 The results of NMR quantitative analysis of the electrolyte according to Example 1 are shown.

[0026] Figure 5 The lithium nuclear magnetic resonance (Li-NMR) analysis results of the electrolytes according to Example 1, Comparative Example 1 and Comparative Example 4 are shown.

[0027] Figure 6 The results of durability evaluations of lithium metal battery cells using each electrolyte according to Examples 1 to 4 and Comparative Example 1 are shown.

[0028] Figure 7 The results of durability evaluations of lithium metal battery cells using each electrolyte according to Comparative Examples 1 and 2 are shown.

[0029] Figure 8The results of durability evaluations of lithium metal battery cells using each electrolyte according to Examples 1, 3 and 4 are shown.

[0030] Figure 9 The results of NMR quantitative analysis of the electrolyte according to Comparative Example 3 are shown.

[0031] Figure 10 The results of NMR quantitative analysis of the electrolyte according to Comparative Example 4 are shown.

[0032] Figure 11 The results of durability evaluations of lithium metal battery cells using each electrolyte according to Comparative Examples 1 and 5 are shown.

[0033] Figure 12 This is a schematic diagram of an implementation scheme for a lithium metal battery.

[0034] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0035] [Symbol Explanation] 11: Lithium metal batteries 12: Lithium metal layer as negative electrode 13: Positive electrode 14: Diaphragm 15: Battery casing. Detailed Implementation

[0036] In this specification, the terms first, second, and third are used to describe various processes, components, regions, layers, and / or portions, but are not limited thereto. These terms are used only to distinguish any part, component, region, layer, or portion from other parts, components, regions, layers, or portions. Therefore, a first part, component, region, layer, or portion described below can be described as a second part, component, region, layer, or portion within the scope of the invention without departing from the scope of the invention.

[0037] The specific terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular form used herein includes the plural form unless there is a clear opposite meaning. The terms “comprising” or “including” as used in the specification mean that a particular feature, region, integer, step, operation, element, and / or component is embodied, and do not exclude other particular features, regions, integers, steps, operations, elements, and / or components.

[0038] When any part is referred to as "on" or "above" another part, it can be directly on or above the other part, or different parts can be involved between them. Conversely, when any part is described as "directly on" another part, no other part is inserted between them.

[0039] Unless otherwise specified, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Commonly used predefined terms are further interpreted as having meanings consistent with relevant technical literature and this invention, and shall not be construed as having ideal or highly formal meanings unless otherwise defined.

[0040] As used herein, the term "combination thereof" as described in the description means one or more mixtures or combinations selected from the components described in the description, and means including at least one selected from said components. In this invention, each of the phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B or C", "at least one of A, B and C", "at least one of A, B or C", and "at least one of A, B or C or a combination thereof" may include any or all possible combinations of the items listed together in the corresponding phrase.

[0041] The invention is described more fully below, with exemplary embodiments of the invention shown. Those skilled in the art will recognize that various modifications can be made to the described embodiments without departing from the spirit or scope of the invention.

[0042] Electrolytes for Lithium Metal Batteries Currently, there is active research and development on the composition of electrolytes (salt type, salt concentration, additives, etc.) to improve the durability of lithium metal batteries. This invention relates to a technique that can improve durability characteristics by introducing novel co-solvents to control the composition of the solvent and thus delay the decomposition of salts and solvents in the electrolyte.

[0043] According to the implementation scheme, the non-aqueous organic solvent in the electrolyte for lithium metal batteries consists of a main solvent and a co-solvent. Here, by including a co-solvent of controlled type and amount in the electrolyte, i) localized over-concentration is implemented to delay the decomposition of the salt or solvent, and ii) simultaneously, physical properties such as wettability and volatility are improved to reduce overvoltage.

[0044] Commonly used cosolvents may include weak solvating solvents, which are mainly perfluorinated ether solvents with a wide voltage range, and representative examples may include TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether), BTFE (bis(2,2,2-trifluoroethyl) ether), and TFOFE (trifluoromethyltrifluorovinyl ether).

[0045] According to the implementation plan, the main solvent in the non-aqueous organic solvent may include N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof. Electrolytes used in lithium metal batteries containing N,N-dimethylaminosulfonyl fluoride as a solvent suffer from continuous salt degradation, which is a major cause of decreased battery durability. In particular, the easily oxidized environment of anions is an important task that must be addressed in high-voltage batteries.

[0046] Therefore, various additives are being developed to delay the aforementioned degradation. However, a problem exists where the instability of the protective film leads to the continuous consumption of the additives and increases electrode resistance, thereby hindering output characteristics. Attempts have been made to induce salt-solvent aggregation and suppress salt-solvent decomposition by applying perfluorinated ether-based co-solvents; however, aggregation increases the negative electrode reactivity of the lithium salt and accelerates reductive decomposition. It has been confirmed that aggregation is difficult to maintain in the high-temperature environment created by the exothermic reaction during battery discharge, but the continuous consumption of lithium salts that react with lithium metal to form a thin film makes it difficult to use as a commercial strategy.

[0047] Therefore, in the field of lithium metal batteries, there is an increasing demand for a cosolvent that inhibits the reductive decomposition of salts and has a long-lasting effect.

[0048] According to the implementation scheme, by adding a cosolvent represented by Formula 1 to the main solvent (including N,N-dimethylaminosulfonyl fluoride (DMSF), ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamide or any combination thereof) in an amount exceeding 1 mol% (based on the total amount of non-aqueous organic solvent including the main solvent and cosolvent, 100 mol%), the decomposition of bis(fluorosulfonyl)imide (FSI) anion (which is the anion of lithium salt) can be delayed, thereby contributing to improved durability of lithium metal batteries and providing an electrolyte for lithium metal batteries that is stable to lithium metal and thus limits the reaction, thereby exhibiting significantly improved stability.

[0049] Chemical Formula 1: In chemical formula 1, R 1 It is a substituted or unsubstituted C2 to C20 alkyl group, and R 2 It is a substituted or unsubstituted C1 to C20 alkyl group. The premise is that R 1 and R 2 They are different from each other, and R 1 More carbon atoms than R 2.

[0050] The electrolyte for lithium metal batteries according to the embodiments may contain lithium salts and non-aqueous organic solvents. The non-aqueous organic solvents include a main solvent and a co-solvent, wherein the main solvent may include N,N-dimethylaminosulfonyl fluoride (DMSF), ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof, and the co-solvent may include a compound represented by Formula 1. Based on the total amount of the non-aqueous organic solvent (100 mol%), the co-solvent represented by Formula 1 should be included in an amount exceeding 1 mol%. The inclusion of the co-solvent comprising a compound represented by Formula 1 in the aforementioned amount contributes to improving the performance of the lithium metal battery. However, if the co-solvent comprising a compound represented by Formula 1 is included in an amount of 1 mol% or less based on the total amount of the non-aqueous organic solvent (100 mol%), the durability performance of the lithium metal battery may decrease, which may be undesirable.

[0051] When the compound represented by chemical formula 1 is used as a co-solvent in conjunction with the main solvent within the above-mentioned amount range, it is stable to lithium metal, and thus a highly stable electrolyte can be produced.

[0052] For example, the main solvent can be N,N-dimethylaminosulfonyl fluoride (DMSF), and the co-solvent can be R in formula 1. 1 It is ethyl and R 2 The compound with methyl groups is 2-ethoxy-1,1,1-trifluoro-3-methoxypropane (TFEMP).

[0053] This invention distinguishes its composition from the prior art by providing a co-solvent that: i) further delays salt consumption by enhancing the inhibition of salt reductive decomposition; and ii) exhibits lower reactivity to the lithium anode than the main solvent (DMSF solvent), thus demonstrating a sustained effect. In this way, it is expected that durability can be improved by delaying salt depletion without inhibiting the role of the solvent involved in forming the conventional anode film.

[0054] The compound represented by Formula 1 i) has a lower salt dissociation degree than the main solvent DMSF, thereby forming an optimal solvation environment and inhibiting the reductive decomposition of the salt, and ii) has a higher lowest unoccupied molecular orbital (LUMO) energy level than the main solvent DMSF, thereby enabling a sustained effect. Ultimately, when a lithium metal battery containing an electrolyte having the composition according to the embodiment is operated, the improvement in durability can be confirmed.

[0055] Based on the total amount of non-aqueous organic solvent (100 mol%), the cosolvent may be included in an amount of 2.5 mol% or greater, for example, from 2.5 mol% to 10 mol%.

[0056] The molar ratio of lithium salt to non-aqueous organic solvent having the above composition can be from 1:1 to 1:5.

[0057] When the type and amount of co-solvent (and, in addition, the molar ratio of lithium salt to non-aqueous organic solvent) are controlled as described above, electrolytes with significantly improved durability and stability can be prepared, while delaying the decomposition of lithium salt due to oxidation and reduction.

[0058] Unlike the implementation scheme, when N,N-dimethylaminosulfonyl fluoride (DMSF) (which is the solvent involved in the formation of the negative electrode film) is used alone as a non-aqueous organic solvent (i.e., when no co-solvent is included), the low electrochemical reduction stability of the salt generated by the use of a weak solvating solvent leads to observed salt reduction decomposition at the negative electrode, thereby reducing the film-forming effect of N,N-dimethylaminosulfonyl fluoride and accelerating degradation due to the decrease in salt concentration, making a strategy to improve durability inevitable. When a compound represented by Formula 1 is introduced as a co-solvent, salt decomposition can be suppressed and an absolute excess of salt can be introduced (see [link to relevant documentation]). Figure 1 wait).

[0059] When the compound represented by Formula 1 is used alone as a co-solvent as the main solvent (i.e., when the compound represented by Formula 1 is used alone as a non-aqueous organic solvent), it has a stronger solvation structure than electrolytes using only existing ether solvents. Due to the low electrochemical oxidation stability of the salt resulting from the stronger solvation structure than the aforementioned N,N-dimethylaminosulfonyl fluoride, salt oxidative decomposition is observed at the anode, inevitably leading to an increase in positive electrode resistance and salt depletion due to the formation of a positive electrode film. To address this problem, it is necessary to suppress salt decomposition and introduce an absolute excess of salt, and this problem can be solved by adjusting the composition of the electrolyte according to the embodiment.

[0060] A non-aqueous organic solvent was also prepared using 1,2-dimethoxyethane (DME) (which is commonly used as an ether-based solvent) as the main solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) (which is the aforementioned commonly used co-solvent). In this case, the advantage lies in its ability to cause structural aggregation of the electrolyte, delay the oxidative decomposition of the electrolyte, and improve the limitations of ionic conductivity and viscosity. However, this composition is intended to simulate a weakly solvated solvent environment and has the following problems: 1) the salt concentration decreases due to the reductive decomposition of the salt, and 2) when added in excess to find the optimal solvation environment, the salt precipitates with low salt dissociation, making it difficult to control the salt amount. Furthermore, the film-forming effect of the solvent containing only N,N-dimethylaminosulfonyl fluoride (DMSF) deteriorates due to the chemical reaction at the negative electrode caused by the low LUMO energy level of the co-solvent, and it is difficult to observe sustained performance improvements.

[0061] In contrast, according to the embodiment, 1) an electrolyte composition is proposed that increases the amount of salt by delaying decomposition, and 2) it exhibits low reactivity to the lithium anode and thus demonstrates a sustained effect. This is expected to improve durability by delaying salt depletion without suppressing the role of the solvent involved in the formation of the anode film in an electrolyte composition containing only N,N-dimethylaminosulfonyl fluoride (DMSF).

[0062] In other words, when the main solvent includes N,N-dimethylaminosulfonyl fluoride (DMSF), the co-solvent represented by Formula 1 should: 1) create an optimal solvation environment to suppress the oxidative / reductive decomposition of the salt; 2) possess excellent salt solubility, allowing it to mix into the solvent to dissociate excess salt; and 3) be stable to lithium metal. Therefore, using 2-ethoxy-1,1,1-trifluoro-3-methoxypropane (TFEMP) as a co-solvent is likely most advantageous.

[0063] The durability of lithium metal batteries using said electrolyte can be improved by using an electrolyte having the composition according to the embodiment.

[0064] According to the implementation scheme, the lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), or any combination thereof. For example, the lithium salt may be LiFSI.

[0065] The concentration of lithium salt contained in the electrolyte for lithium metal batteries according to the implementation scheme can be from 1.0 M to 5.0 M, specifically from 1.0 M to 4.0 M.

[0066] If the lithium salt concentration is below the aforementioned range, the electrolyte conductivity may decrease, potentially leading to poor electrolyte performance. Conversely, if the lithium salt concentration exceeds the aforementioned range, the electrolyte viscosity may increase, potentially resulting in reduced lithium-ion mobility and overvoltage issues starting from the beginning of cycling. Furthermore, the undesirable SEI layer on the lithium metal (as the negative electrode) surface may not form at all or may form an excessively thick film, which could degrade the electrochemical performance of the lithium metal battery.

[0067] Since the electrolyte for lithium metal batteries according to the embodiment is closer to a strong solvation environment than the weak solvation solvents used in conventional applications, the lithium nuclear magnetic resonance (Li-NMR) signal value of the electrolyte for lithium metal batteries according to the embodiment can have a more positive value than the Li-NMR signal value of electrolytes for lithium metal batteries that do not contain a co-solvent (and electrolytes for lithium metal batteries that contain a compound not represented by chemical formula 1 as a co-solvent).

[0068] Lithium metal batteries Another embodiment provides a lithium metal battery comprising the electrolyte described above for lithium metal batteries.

[0069] Specifically, the lithium metal battery (11) may include a positive electrode (13), a lithium metal layer (12) serving as a negative electrode and opposite to the positive electrode, a separator (14) between the positive electrode (13) and the negative electrode (12), and an electrolyte for the lithium metal battery (see reference). Figure 12 ).

[0070] The negative electrode for lithium metal batteries can be a lithium metal layer, and the lithium metal layer itself can be used as the negative electrode of the battery.

[0071] During charging, the battery, including the negative electrode, allows lithium ions from the positive electrode to move to the negative electrode to form a lithium metal layer. Charging and discharging of the battery can be performed by forming or removing this lithium metal layer.

[0072] The negative electrode can be formed on a negative current collector such as copper.

[0073] A lithium metal layer can be formed on the negative electrode current collector through the charging and discharging of a lithium metal battery.

[0074] The thickness of the lithium metal layer can be from 5 μm to 50 μm, for example, from 10 μm to 50 μm, or it can be formed to have the above thickness.

[0075] When the lithium metal layer meets the above thickness, side reactions between the lithium metal layer and the electrolyte can be suppressed, thereby improving the electrochemical performance of the lithium metal battery.

[0076] In another implementation, the positive and negative electrodes are arranged opposite each other.

[0077] The positive electrode may include a positive current collector and a layer of positive active material formed on the positive current collector.

[0078] The positive current collector can be made of at least one of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, and silver, or any combination thereof.

[0079] The thickness of the positive current collector can range from 3 μm to 500 μm.

[0080] The positive electrode active material layer contains positive electrode active material.

[0081] The positive electrode active material can be a compound capable of reversibly inserting and deintercalating lithium, and specifically can include lithium iron phosphate. When the positive electrode active material includes lithium iron phosphate, the compatibility with the electrolyte is optimal, maximizing the improvement in battery performance.

[0082] The positive electrode active material may include lithium metal oxide (which is a compound capable of inserting and deintercalating lithium), and specifically includes at least one selected from cobalt, manganese, nickel, and aluminum. More specifically, the lithium metal oxide may include at least one selected from lithium manganese-based oxide, lithium cobalt-based oxide, lithium nickel-based oxide, lithium nickel manganese-based oxide, lithium nickel cobalt-based oxide, lithium manganese cobalt-based oxide, or lithium nickel cobalt transition metal (M) oxide.

[0083] The positive electrode active material can be a lithium nickel manganese cobalt-based oxide, which can specifically improve the capacity characteristics and stability of the battery, and can be more specifically represented by chemical formula 2: Li(Ni x Co y Mn z O2 In chemical formula 2, 0≤x≤1, 0≤y≤1, 0≤z≤1 and x+y+z=1.

[0084] The positive electrode active material layer may further include adhesives and / or conductive materials.

[0085] The separator separates the negative electrode from the positive electrode and provides a channel for lithium ion movement. There are no particular restrictions on the separator, as long as it is a separator commonly used in rechargeable lithium batteries.

[0086] The following embodiments illustrate the present invention in more detail. However, the following embodiments are merely exemplary implementations, and the present invention is not limited to the following embodiments.

[0087] (Example) Preparation of electrolyte for lithium metal batteries LiFSI salt was added to a non-aqueous organic solvent to dissociate and form an electrolyte. Then, 1% or more of calcium hydride (CaH2) of the total weight of the sample was added and removed after 30 minutes to finally prepare the electrolyte for lithium metal batteries.

[0088] Table 1 shows the composition of the electrolyte for lithium metal battery cells according to the embodiments and comparative embodiments.

[0089] Table 1 Performance Verification of Lithium Metal Battery Cells Using Electrolytes with Cosolvents to Control the Solvation Environment - 1 (1) After manufacturing the button cell using the composition shown in Table 2, its durability was confirmed.

[0090] Table 2 (2) It can be confirmed that Example 1 is the electrolyte with the highest observed durability, and is the electrolyte with a TFEMP content of 5.0 mol%, and exhibits a 23% delay in cycle life degradation compared to Comparative Example 1 (143 cycles) without cosolvent, with a Li / NMC durability of 177 cycles (see Figure 2 ).

[0091] (3) Fluorine nuclear magnetic resonance (F-NMR) analysis was performed to identify the degradation factors in the electrolyte, and the results are shown in Table 3. Specifically, after injecting 2.5 g / Ah of electrolyte into a 0.169 Ah dual cell, in Figure 2 Samples were collected after 50 and 100 charge / discharge cycles under the evaluation conditions shown, and F-NMR measurements were performed. During sampling, the top of the pouch cell was cut open, 1 mL of DME was injected to wash away residual electrolyte, and 900 μL of 30 g d... 6 A mixture of dimethyl sulfoxide (DMSO) (as a nuclear magnetic resonance (NMR) solvent) and 5 g of fluorobenzene (as an internal standard solution) was injected into equal aliquots of the sample solution, followed by F-NMR measurements (500 MHz, Unity Inova, Varian Technology). Based on the F-NMR measurements, the areas of the DMSF, FSI, and fluorobenzene signals were read, and the DMSF / FSI (moles) and FSI / fluorobenzene (moles) ratios were calculated. The DMSF / fluorobenzene (moles) ratio was then calculated by multiplying these two ratios. The amount of solvent and salt remaining in the bag was calculated as the residual amount, with the initial volume of the solution in the bag taken as 100%.

[0092] Table 3 *DMSF: N,N-Dimethylaminosulfonyl fluoride FSI: Bis(fluorosulfonyl)imide fBz: Fluorinated benzene (4) Through the above (3), the residual solvent and salt remaining in the electrolyte after the battery reaction can be quantified. According to Table 3 above, Figure 3 and Figure 4 It can be confirmed that the NMR quantitative analysis results of Comparative Example 1 show a rapid decrease in the concentration of FSI salt (which is characteristic of the previously predicted weakly solvated solvent), and it can be seen that the main reason is the reductive decomposition of the salt. The NMR quantitative analysis results of Example 1 show that even after 100 charge / discharge cycles, the amount of FSI salt in the residual electrolyte is definitely greater than the initial amount. This shows that the introduction of the co-solvent delays the degradation of FSI salt.

[0093] (5) Finally, it can be confirmed experimentally that the durability of lithium metal battery cells can be improved by increasing the amount of salt and delaying decomposition.

[0094] Performance Verification of Lithium Metal Battery Cells Using Electrolytes with Cosolvents to Control the Solvation Environment - 2 (1) To determine the structure of a suitable solvation environment for the present invention, Li-NMR was measured to analyze the charge state of the lithium cation. In a weakly solvated environment, the degree of dissociation of the salt decreases, the distance between the cation and anion becomes closer, and electrons are provided from FSI to Li. This is because the nuclear magnetic field received by Li is blocked by the charge of Li, and a signal value is observed in a high magnetic field.

[0095] (2) DMSF is a weak solvation electrolyte that dissociates salts to a limited extent.

[0096] (3) In a high magnetic field of -1.78 ppm, the difference in performance between Comparative Example 1 prepared using DMSF as the sole solvent was clearly observed. 7 The Li-NMR signal value indicates a weakly solvated environment (see [reference]). Figure 5 ).

[0097] (4) The charge density concentrated on the FSI will decrease as much as the electrons provided from the FSI to Li, thus the oxidative decomposition of the salt can be limited to a lower energy level. However, as the charge density decreases, it becomes easier to approach the negative electrode, and a reduction reaction can occur, in which additional electrons are provided by the negative electrode and decomposition takes place. This is the main reason for the degradation of the electrolyte for the lithium metal battery according to Comparative Example 1.

[0098] (5) In Example 1, it can be confirmed that 7 The Li-NMR signal value shifts to -1.74 ppm at lower magnetic fields (see [reference]). Figure 5 ).

[0099] (6) In other words, it can be seen that in the electrolyte composition of Comparative Example 1 (which is a weakly solvated electrolyte), the weak solvation environment is alleviated when TFEMP is used as a co-solvent. Therefore, it is believed that creating a suitable solvation environment further enhances the inhibition of salt oxidative decomposition.

[0100] Amount of cosolvent (1) Examples 1 to 4 are electrolytes with different amounts of TFEMP, in which improved durability was observed, and each had an amount of total solvent (non-aqueous organic solvent) of 2.5 mol%, 5.0 mol%, 7.5 mol%, and 10.0 mol%, respectively. It can be confirmed that, compared with Comparative Example 1, improvements in durability of 5%, 4%, 10%, and 6% were observed, respectively (see Comparative Example 1). Figure 6 ).

[0101] (2) Comparative Example 2 is a low TFEMP (1.0 mol%) electrolyte, and it can be confirmed that it shows a 2% decrease in durability compared to Comparative Example 1 (see Comparative Example 1). Figure 7 ).

[0102] (3) Due to early short circuits, electrolytes with high TFEMP content (12.0 mol%) may not be evaluated.

[0103] (4) Therefore, it can be seen that the optimal amount of TFEMP is 2.5 mol% to 10 mol% based on the total amount of non-aqueous organic solvent (100 mol%).

[0104] Cosolvent structure (1) Comparative Example 3 is an electrolyte prepared using DMP (1,2-dimethoxypropane) as a co-solvent. It is a comparative example, intended to confirm the role of the -CF3 functional group by comparing the structure of the co-solvent used in the comparative examples. When containing the same amount of co-solvent as in Example 1, the cycle life was 74 cycles, which is 10% shorter than the cycle life of Comparative Example 1 (82 cycles) without the co-solvent (see [link to Comparative Example 1]). Figure 8 Furthermore, since NMR analysis results indicate that the FSI salt and DMSF solvent in the electrolyte of Comparative Example 3 were rapidly reduced, it can be concluded that the co-solvent had no effect on delaying salt decomposition (see [link]). Figure 9 Therefore, it can be seen that cosolvents essentially require the -CF3 functional group.

[0105] (2) Comparative Example 4 is an electrolyte prepared using TFDMP (1,1,1-trifluoro-2,3-dimethoxypropane) as a cosolvent, and compared with the structure of the cosolvent used in the examples, it has a symmetrical structure with methoxy groups on both sides of the structure that does not contain the -CF3 functional group. It can be seen that the cycle life ends at 81 cycles, which is similar to the cycle life (82 cycles) of Comparative Example 1 without the cosolvent (see Figure 10 Meanwhile, as a result of NMR analysis, it can be observed that the FSI salt and DMSF solvent in the electrolyte of Comparative Example 4 decreased rapidly, which can be considered as having no effect on delaying the salt decomposition of the co-solvent (see...). Figure 10 ).

[0106] (3) Li-NMR of Comparative Example 4 was also observed at a low magnetic field (-1.76 ppm) compared to Comparative Example 1, but was observed at a high magnetic field compared to Example 1. This indicates that an optimal solvation structure is required, and according to the embodiment, TFEMP alone creates this environment (see Figure 5Therefore, it can be seen that the ether moiety in the cosolvent, which does not contain the -CF3 functional group, should have an asymmetric structure.

[0107] (4) Comparative Example 5 is an electrolyte prepared using TFMEP (2-methoxy-1,1,1-trifluoro-3-ethoxypropane) as a cosolvent. Compared to the structure of the cosolvent used in the examples, it has an asymmetric structure in the opposite direction to the asymmetric structure that does not contain the CF3 functional group. In other words, TFEMP and TFMEP according to the embodiments have asymmetric ether structures, but TFEMP has a -CF3 functional group located on the ethoxy group (which is a longer aliphatic chain), while TFMEP has a structure where the -CF3 functional group is located on the methoxy group (which is a shorter chain). When the same amount of cosolvent as in Example 1 is included, the cycle life is 83 cycles, which is similar to the cycle life (82 cycles) of Comparative Example 1 without the cosolvent (see [link]). Figure 11 ).

[0108] (5) Therefore, it can be seen that the -CF3 functional group in the cosolvent should be located on the side of the longer chain (with more carbon atoms) of the asymmetric ether structure.

[0109] (6) In other words, in the asymmetric structure, it can be seen that the improvement in durability can only be expected when the use of a compound with the -CF3 functional group located on a longer (more carbon) alkoxy group as a cosolvent in an electrolyte containing 2.5 mol% to 10 mol% of cosolvent in the total amount (100 mol%) of non-aqueous organic solvent.

[0110] Although exemplary embodiments have been described above, the present invention is not limited thereto, and various modifications may be made within the scope of the patent claims, the detailed description of the invention and the accompanying drawings, which also fall within the scope of the present invention.

[0111] Therefore, the basic scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An electrolyte for lithium metal batteries, the electrolyte comprising: Lithium salts; and Non-aqueous organic solvents; in, The non-aqueous organic solvent comprises a main solvent and a co-solvent. The main solvent includes N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof. The co-solvent is represented by chemical formula 1: ， In chemical formula 1: R 1 It is a substituted or unsubstituted C2 to C20 alkyl group, and R 2 It is a substituted or unsubstituted C1 to C20 alkyl group. R 1 and R 2 They are different, and R 1 More carbon atoms than R 2 ,and Based on the total amount of non-aqueous organic solvents, co-solvents are included in an amount exceeding 1 mol%.

2. The electrolyte for lithium metal batteries according to claim 1, wherein, The main solvent includes N,N-dimethylaminosulfonyl fluoride.

3. The electrolyte for lithium metal batteries according to claim 1, wherein, R 1 It is ethyl, and R 2 It is a methyl group.

4. The electrolyte for lithium metal batteries according to claim 1, wherein, Based on the total amount of non-aqueous organic solvents, the co-solvent is included in an amount ranging from 2.5 mol% to 10 mol%.

5. The electrolyte for lithium metal batteries according to claim 1, wherein, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, or any combination thereof.

6. The electrolyte for lithium metal batteries according to claim 1, wherein, The concentration of the lithium salt is in the range of 1.0 M to 5.0 M.

7. The electrolyte for lithium metal batteries according to claim 1, wherein, The lithium nuclear magnetic resonance (Li-NMR) signal values ​​of the electrolyte used in lithium metal batteries have more positive values ​​than those of the electrolyte used in lithium metal batteries that do not contain a co-solvent.

8. The electrolyte for lithium metal batteries according to claim 1, wherein, The molar ratio of the lithium salt to the non-aqueous organic solvent is in the range of 1:1 to 1:

5.

9. A lithium metal battery, the lithium metal battery comprising: positive electrode; The lithium metal layer serves as the negative electrode and is opposite to the positive electrode; The membrane between the positive and negative electrodes; as well as Electrolytes, The electrolyte comprises: Lithium salts; and Non-aqueous organic solvents; in: The non-aqueous organic solvent comprises a main solvent and a co-solvent. The main solvent includes N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof. The co-solvent is represented by chemical formula 1: ， In chemical formula 1, R 1 It is a substituted or unsubstituted C2 to C20 alkyl group. R 2 It is a substituted or unsubstituted C1 to C20 alkyl group, and R 1 and R 2 They are different, and R 1 More carbon atoms than R 2 Furthermore, based on the total amount of non-aqueous organic solvents, it contains co-solvents in an amount exceeding 1 mol%.

10. The lithium metal battery according to claim 9, wherein, The lithium metal layer is formed to have a thickness in the range of 5 μm to 50 μm.

11. The lithium metal battery according to claim 9, wherein, The main solvent includes N,N-dimethylaminosulfonyl fluoride.

12. The lithium metal battery according to claim 9, wherein, R 1 It is ethyl, and R 2 It is a methyl group.

13. The lithium metal battery according to claim 9, wherein, Based on the total amount of non-aqueous organic solvents, the co-solvent is included in an amount ranging from 2.5 mol% to 10 mol%.

14. The lithium metal battery according to claim 9, wherein, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, or any combination thereof.

15. The lithium metal battery according to claim 9, wherein, The concentration of the lithium salt is in the range of 1.0 M to 5.0 M.

16. The lithium metal battery according to claim 9, wherein, The lithium nuclear magnetic resonance (Li-NMR) signal values ​​of the electrolyte used in lithium metal batteries have more positive values ​​than those of the electrolyte used in lithium metal batteries that do not contain a co-solvent.

17. The lithium metal battery according to claim 9, wherein, The molar ratio of the lithium salt to the non-aqueous organic solvent is in the range of 1:1 to 1:

5.

18. A lithium metal battery, the lithium metal battery comprising: First electrode; A lithium metal layer that serves as the second electrode and is opposite to the first electrode; A diaphragm between the first electrode and the second electrode; as well as Electrolytes, The electrolyte comprises: Lithium salts, and Non-aqueous organic solvents in: The non-aqueous organic solvent comprises a main solvent and a co-solvent. The main solvent includes N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or any combination thereof. The co-solvent is represented by chemical formula 1: ， In chemical formula 1, R 1 It is a substituted or unsubstituted C2 to C20 alkyl group. R 2 It is a substituted or unsubstituted C1 to C20 alkyl group, and R 1 and R 2 They are different, and R 1 More carbon atoms than R 2 Furthermore, based on the total amount of non-aqueous organic solvents, it contains co-solvents in an amount exceeding 1 mol%.

19. The lithium metal battery according to claim 18, wherein, The main solvent includes N,N-dimethylaminosulfonyl fluoride.

20. The lithium metal battery according to claim 18, wherein: The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, or any combination thereof.

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