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

Abstract

The present disclosure relates to an electrolyte for a lithium metal battery, which includes: a lithium salt; and a non-aqueous organic solvent including a main solvent and a co-solvent different from the main solvent. The electrolyte is capable of improving the durability of the lithium metal battery, for example, by retarding the decomposition of an anion constituting the lithium salt. The present disclosure also relates to a lithium metal battery including the electrolyte.

Description

[0001] Cross-references to related applications This application claims priority and benefit from Korean Patent Application No. 10-2024-0187679, filed with the Korean Intellectual Property Office on December 16, 2024, the entire contents of which are incorporated herein by reference. Technical Field

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

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

[0004] Lithium metal, with its high capacity (up to 3860 mAh / g) and low standard electrode potential (-3.04 V compared to the standard hydrogen electrode), has attracted considerable attention as a negative electrode material for lithium-ion batteries. However, lithium metal exhibits high reactivity, creating a highly reducing environment during charging, which can lead to irreversible decomposition reactions between the lithium metal and the electrolyte. This decomposition consumes the electrolyte, and the decomposition products may form an uneven film on the lithium metal surface. Furthermore, with repeated charge and discharge cycles, lithium can grow in the form of dendrites. Dendritic lithium can cause short circuits within the battery, leading to battery safety issues (such as fires).

[0005] Therefore, in order to utilize lithium metal, which has high stability and high capacity, it is necessary to develop an electrolyte that can reduce the reactivity of lithium metal, prevent lithium dendrite growth, and achieve uniform lithium deposition (lithium plating). Summary of the Invention

[0006] On the one hand, this disclosure provides an electrolyte for lithium metal batteries that can improve the durability of lithium metal batteries, for example, by delaying the decomposition of anions constituting lithium salts.

[0007] In some other embodiments, this disclosure provides a lithium metal battery with excellent stability.

[0008] According to one embodiment, the electrolyte for a lithium metal battery comprises: a lithium salt; and a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises a main solvent and a co-solvent, wherein the main solvent comprises N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamide, or combinations thereof, and the co-solvent comprises a compound of formula 1.

[0009] Chemical Formula 1 In chemical formula 1, R 1 and R 2 Each is independently methyl or ethyl, but R 1 and R 2 Not all of them are ethyl.

[0010] In some embodiments, the main solvent may be N,N-dimethylaminosulfonyl fluoride.

[0011] In some embodiments, the co-solvent may be R in formula 1. 1 and R 2 Compounds that are methyl groups on their own.

[0012] In some embodiments, the content of the cosolvent can be from 24 mol% to 66 mol% based on the total amount of non-aqueous organic solvents (i.e., the total amount of non-aqueous organic solvents is 100 mol%).

[0013] In some embodiments, the molar ratio of lithium salt to non-aqueous organic solvent can be from 1:2 to 1:2.5.

[0014] In some embodiments, the lithium salt may include at least one of LiFSI, LiFNFSI, and LiTFSI.

[0015] In some embodiments, the concentration of the lithium salt can be from 3.0 M to 5.0 M.

[0016] According to another aspect, this disclosure provides a lithium metal battery comprising: a positive electrode; a lithium metal layer serving as a negative electrode and facing the positive electrode; a separator between the positive and negative electrodes; and an electrolyte for the lithium metal battery according to various embodiments of this disclosure.

[0017] In some implementations, the thickness of the lithium metal layer can be from 5 μm to 50 μm.

[0018] In some implementations, the positive electrode may include lithium nickel manganese cobalt-based metal oxide.

[0019] According to the various embodiments described herein, electrolytes for lithium metal batteries can exhibit excellent stability by, for example, introducing co-solvents capable of delaying salt or solvent decomposition through localized overconcentration or reducing overvoltage by improving physical properties such as wettability and volatility, combined with a specific type of main solvent. Therefore, this disclosure provides a lithium metal battery including the electrolyte described herein, which has improved durability. Attached Figure Description

[0020] Figure 1 The results of the durability characteristic evaluation of lithium metal battery cells using each electrolyte according to Example 1 and Comparative Example 1 are shown.

[0021] Figure 2A and Figure 1 The attached diagram is the same. Figure 2B and 2C The results of F-NMR quantitative analysis performed before and after operation of lithium metal battery cells using the electrolytes according to Comparative Example 1 and Example 3 are shown respectively.

[0022] Figure 3A The results show the durability characteristics evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1 and Comparative Example 2. Figure 3B The results of F-NMR quantitative analysis performed before and after operation of the lithium metal battery cell using the electrolyte according to Comparative Example 2 are shown. Figure 3C The results show the durability characteristics evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1 and Comparative Example 4.

[0023] Figure 4A The images show Raman spectra of lithium metal battery cells using the electrolytes of Comparative Example 1 and Comparative Example 2. Figure 4B The images show Raman spectra of lithium metal battery cells using the electrolytes of Comparative Example 1 and Example 1.

[0024] Figure 5A and 5B The Tafel analysis plots of lithium metal battery cells using each electrolyte according to Comparative Examples 1 to 3 are shown.

[0025] Figure 6A The results of the durability characteristics evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1 and Example 2 are shown. Figure 6B The results of the durability characteristic evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1, Example 3 and Example 4 are shown. Figure 6C The results of the durability characteristic evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1 and Comparative Example 5 are shown. Figure 6D The results show the durability characteristics evaluation of lithium metal battery cells using each electrolyte according to Comparative Example 1 and Comparative Example 6.

[0026] Figure 7A The results show the durability characteristics evaluation of lithium metal battery cells using the electrolytes according to Examples 1 and 5. Figure 7B The results show the durability characteristics evaluation of lithium metal battery cells using the electrolytes according to Example 1 and Comparative Example 7.

[0027] Figure 8 The results show the durability characteristics evaluation of lithium metal battery cells using the electrolytes of Examples 3, 6, 7 and Comparative Examples 8 to 10. Detailed Implementation

[0028] In this specification, the terms "first," "second," and "third" are used to describe various components, assemblies, regions, layers, and / or portions, but are not limited thereto. These terms are used only to distinguish any component, assembly, region, layer, or portion from other components, assemblies, regions, layers, or portions. Therefore, a first component, assembly, region, layer, or portion described below may be referred to as a second component, assembly, region, layer, or portion without departing from the scope of this embodiment.

[0029] The specific terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit these embodiments. Unless otherwise expressly indicated, the singular forms used herein include the plural forms. The terms “comprising” or “including” as used herein signify 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.

[0030] When any component is described as being "on" or "above" another component, that component may be directly on or above the other component, or there may be different components between them. Conversely, when any component is described as being "directly" on another component, there are no other components between them.

[0031] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the meaning commonly understood by one of ordinary skill in the art to which this embodiment pertains. Commonly used predefined terms shall be further interpreted as having meanings consistent with relevant technical documents and this disclosure, and shall not be construed as having ideal or unformal meanings unless otherwise defined.

[0032] As used herein, the term “combination thereof” (e.g., “comprising” the Markush group or “composed of” the Markush group) as described in the list of components means one or more mixtures or combinations selected from the components described in the description of the components (e.g., the Markush group), and means containing at least one of the components selected from the components.

[0033] The various embodiments will be described in more detail below, and some exemplary embodiments will be illustrated by examples. Those skilled in the art will understand that the described embodiments can be modified in various ways without departing from the spirit or scope of this embodiment.

[0034] Electrolytes for Lithium Metal Batteries Researchers are actively working to develop novel electrolyte compositions (salt types, salt concentrations, additives, etc.) to improve the durability of lithium metal batteries. This disclosure relates to a technique that can improve durability characteristics by controlling solvent composition, for example, by introducing novel co-solvents into the main solvent to delay the decomposition of salts and solvents in the electrolyte.

[0035] According to one embodiment, this disclosure provides a non-aqueous organic solvent for an electrolyte in a lithium metal battery, the solvent comprising a main solvent and a co-solvent. In these embodiments, by adding a co-solvent of a specific type, amount, and molar ratio to the lithium salt to the electrolyte, several advantages can be achieved, such as: i) achieving localized overconcentration to delay the decomposition of the salt or solvent; and ii) improving physical properties such as wettability and volatility to reduce overvoltage.

[0036] In one embodiment, the co-solvent may include a perfluoroether solvent having a wide voltage range. Some representative non-limiting examples may include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (denoted as TTE), bis(2,2,2-trifluoroethyl) ether (denoted as BTFE), and 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoropentyl ether (denoted as TFOFE).

[0037] According to one embodiment, 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 combinations thereof. Wherein, when N,N-dimethylaminosulfonyl fluoride is used as the solvent in the electrolyte for lithium metal batteries, continuous salt degradation has been observed to be the main cause of decreased battery durability. These observations indicate that an electrolyte environment prone to anion oxidation is a technical challenge that must be addressed to improve high-voltage batteries.

[0038] Although various additives are being developed to slow down the aforementioned degradation, the instability of the protective film leads to the continuous consumption of these additives and increases electrode resistance, thus affecting output characteristics. Therefore, attempts have been made to induce salt-solvent aggregation and suppress the decomposition of salt and solvent by using perfluoroether cosolvents. However, this aggregation increases the negative electrode reactivity of lithium salts, leading to reductive decomposition. Because perfluorosolvents have a low degree of dissociation from lithium salts, it is difficult to achieve high-concentration electrolytes, which in turn reduces the absolute salt content in the electrolyte. This results in the continuous consumption of the thin film formed by the reaction with lithium metal, making this approach unsuitable for commercial application. Therefore, the lithium metal battery field still needs to develop an additive cosolvent that can: 1) dissociate excess lithium salt to increase the amount of salt dissolved in the electrolyte; 2) suppress salt decomposition; and / or 3) have a lasting effect because it does not decompose during electrode reactions.

[0039] As described in the various aspects and embodiments below, it has been surprisingly found that by adding a co-solvent of Formula 1 to a main solvent comprising N,N-dimethylaminosulfonyl fluoride, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxy ether, dipropyl ether, cyclic sulfonamides, or combinations thereof, the modified solvent allows the introduction of additional salts, delaying the decomposition of FSI anions (the anions of lithium salts), thereby contributing to improved durability of lithium metal batteries. These aspects and embodiments provide an electrolyte for lithium metal batteries that is stable for lithium metal, thereby limiting certain reactions and improving stability.

[0040] In some embodiments, the cosolvent comprises chemical formula 1: In chemical formula 1, R 1 and R 2 Each is independently methyl or ethyl, but R 1 and R 2 Not all of them are ethyl.

[0041] According to one embodiment of this disclosure, the electrolyte for a lithium metal battery comprises: a lithium salt; and a non-aqueous organic solvent. As described herein, the non-aqueous organic solvent may include a primary solvent and a co-solvent, wherein the primary 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 combinations thereof, and the co-solvent may include a compound represented by Formula 1.

[0042] As described in this article, combining the co-solvent shown in Formula 1 with the main solvent results in a non-aqueous organic solvent that is stable to lithium metal and can therefore be used to prepare highly stable electrolytes.

[0043] In some embodiments, the primary solvent may be N,N-dimethylaminosulfonyl fluoride, while the co-solvent may be R in Formula 1. 1 and R 2 Compounds that are each independently methyl, such as 1,2-dimethoxypropane, 1-ethoxy-2-methoxypropane, or 2-ethoxy-1-methoxypropane.

[0044] In some embodiments, the content of the cosolvent can be from 24 mol% to 66 mol% based on the total amount of non-aqueous organic solvent (i.e., 100 mol%).

[0045] In some embodiments, the molar ratio of lithium salt to non-aqueous organic solvent in the electrolyte composition can be from 1:2 to 1:2.5.

[0046] In embodiments where the type and amount of co-solvent and the molar ratio of lithium salt to non-aqueous organic solvent are controlled as described above, the resulting electrolyte can exhibit greatly improved stability and delay the decomposition of lithium salt due to redox reactions.

[0047] Compared to using either the primary solvent or the co-solvent alone, the combined use of the primary solvent and the co-solvent offers significant advantages for non-aqueous organic solvents. For example, when N,N-dimethylaminosulfonyl fluoride, a solvent involved in the formation of the negative electrode film, is used alone as a non-aqueous organic solvent (without any co-solvent), the low electrochemical reduction stability of the salt due to the use of a weakly soluble solvent leads to reduced salt concentration, resulting in reductive decomposition of the salt at the negative electrode. This reduces the film-forming effect of N,N-dimethylaminosulfonyl fluoride, thus requiring strategies to improve its durability to offset the accelerated degradation caused by the decrease in salt concentration. Conversely, when the co-solvent shown in Formula 1 is added to the primary solvent, the resulting solvent inhibits salt decomposition while introducing an absolute excess of salt.

[0048] Similarly, when only a co-solvent of Formula 1 is used as the solvent (without adding other main solvents), its solubility structure is weaker than that of electrolytes using conventional ether solvents alone, which may limit the reaction between the solvent and the lithium anode. However, due to the lower electrochemical oxidative stability of salts derived from stronger solubility structures (e.g., compared to N,N-dimethylaminosulfonyl fluoride), oxidative decomposition of the salt is observed at the cathode, leading to increased cathode resistance and salt loss due to cathode film formation. One way to address this problem is to suppress salt decomposition and add an absolute excess of salt. The above-mentioned problems can be solved by the electrolyte composition of the embodiments described herein.

[0049] A non-aqueous organic solvent was prepared using 1,2-dimethoxyethane, a commonly used ether solvent, as the main solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), a commonly used co-solvent as described above. In this embodiment, without any mechanistic limitations, it appears to have the following advantages: it can form structural aggregates in the electrolyte, thereby delaying the oxidative decomposition of the electrolyte and improving the limitations of ionic conductivity and viscosity. However, such a composition also presents some technical challenges, such as the reduction and decomposition of the salt leading to a decrease in salt concentration; when excessive amounts are added to find the optimal dissolution environment, the salt will precipitate due to its low degree of dissociation, making it difficult to control the amount of salt used. Furthermore, the film-forming effect of solvents containing only N,N-dimethylaminosulfonyl fluoride is weakened by the lower LUMO energy level of the co-solvent, resulting in a chemical reaction at the negative electrode, making it difficult to observe a sustained performance improvement.

[0050] In contrast to the challenges described above, the electrolyte composition according to the embodiments described herein has the following characteristics: 1) an increased content of salts with decomposition-retarding properties; and 2) low reactivity towards the lithium anode, thereby exhibiting a durable effect. This is expected to improve durability by delaying salt consumption without inhibiting the role of the solvent in forming an anode film with an electrolyte composition (e.g., an electrolyte containing only N,N-dimethylaminosulfonyl fluoride).

[0051] Therefore, in some embodiments, when the main solvent contains N,N-dimethylaminosulfonyl fluoride, the co-solvent represented by Formula 1 should meet the following conditions: 1) forming a favorable dissolution environment to inhibit the oxidative / reductive decomposition of the salt; 2) having excellent salt solubility to mix with the solvent to dissociate excess salt; and 3) being stable to lithium metal. In some preferred embodiments, the non-aqueous organic solvent contains 1,2-dimethoxypropane as a co-solvent.

[0052] Ultimately, by using an electrolyte having a composition that conforms to the aspects and embodiments described herein, the durability of lithium metal batteries using this electrolyte can be improved.

[0053] According to one embodiment, the lithium salt may comprise at least the following lithium salts: lithium bis(fluorosulfonyl)imide (denoted as LiFSI), lithium (fluorosulfonyl)(nonafluorobutanesulfonyl)imide (denoted as LiFNFSI), lithium bis(perfluoroethylsulfonyl)imide (denoted as LiBETI), and lithium bis(trifluoromethanesulfonyl)imide (denoted as LiTFSI). In some specific embodiments, the lithium salt may be LiFSI.

[0054] In one embodiment, the concentration of the lithium salt contained in the electrolyte of the lithium metal battery can be from 3.0 M to 5.0 M, and in some more specific embodiments, the concentration can be from 3.1 M to 4.9 M.

[0055] Conversely, if the lithium salt concentration is below the aforementioned range, the electrolyte conductivity may decrease, leading to a decline in electrolyte performance. If the lithium salt concentration exceeds the aforementioned range, the electrolyte viscosity may increase, resulting in a decrease in lithium-ion mobility and potentially causing overvoltage at the start of cycling. Furthermore, lithium salts outside the aforementioned range may cause the formation of an undesirable SEI layer on the surface of the lithium metal serving as the negative electrode. This SEI layer may not form at all, or it may form an excessively thick film, leading to a decrease in the electrochemical performance of the lithium metal battery.

[0056] Lithium metal batteries Another aspect of this disclosure provides a lithium metal battery comprising an electrolyte for lithium metal batteries as described above.

[0057] In some embodiments, a lithium metal battery may include a positive electrode, a lithium metal layer facing the positive electrode as a negative electrode, a separator between the positive and negative electrodes, and an electrolyte for the lithium metal battery.

[0058] In some implementations, the negative electrode of a lithium metal battery can be a lithium metal layer, and the lithium metal layer itself can be used as the negative electrode of the battery.

[0059] In this respect, a battery containing a negative electrode allows lithium ions to move from the positive electrode to the negative electrode during charging to form a lithium metal layer. Charging and discharging of the battery can be achieved by forming or removing this lithium metal layer.

[0060] In some implementations, the negative electrode may be formed on a negative electrode current collector (e.g., copper).

[0061] In some embodiments, 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-mentioned thickness.

[0062] In some embodiments, when the lithium metal layer meets the above-mentioned thickness, side reactions between the lithium metal layer and the electrolyte can be suppressed, thereby improving the electrochemical performance of the lithium metal battery.

[0063] In another implementation, the positive and negative electrodes are arranged opposite each other.

[0064] In some embodiments, the positive electrode may include a positive current collector and a layer of positive active material formed on the positive current collector.

[0065] In some embodiments, the positive current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, silver, etc.

[0066] In some implementations, the thickness of the positive current collector can be from 3 μm to 500 μm.

[0067] In some embodiments, the positive electrode active material layer comprises a positive electrode active material.

[0068] In some embodiments, the positive electrode active material can be a compound capable of reversibly inserting and deintercalating lithium, and in some specific embodiments, it may include lithium iron phosphate. In embodiments where the positive electrode active material comprises lithium iron phosphate, compatibility with the aforementioned electrolyte may be optimal, thereby maximizing battery performance.

[0069] In some embodiments, the positive electrode active material can be a compound capable of reversibly inserting and deintercalating lithium, and in some specific embodiments, it can include a lithium metal oxide comprising at least one of cobalt, manganese, nickel, and aluminum. In some specific embodiments, the lithium metal oxide can include at least one of the following: 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, lithium manganese cobalt-based oxide, or lithium nickel cobalt-transition metal (M) oxide.

[0070] In some embodiments, the positive electrode active material can be a lithium nickel manganese cobalt-based oxide, which can significantly improve the capacity characteristics and stability of the battery. In some specific embodiments, the lithium nickel manganese cobalt-based oxide can be represented by chemical formula 2.

[0071] 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.

[0072] In some embodiments, the positive electrode active material layer may also include a binder and / or a conductive material.

[0073] In some implementations, the separator separates the negative and positive electrodes and provides a channel for the movement of lithium ions. There are no particular restrictions on the specific type of separator, as long as it is a commonly used separator in lithium secondary batteries.

[0074] The following embodiments will illustrate this implementation in more detail. However, the following embodiments are merely exemplary implementations and do not limit the scope of this disclosure or the claims.

[0075] Example: Preparation of electrolytes for lithium metal batteries LiFSI salt is added to a non-aqueous organic solvent to dissociate it and prepare an electrolyte. Then, calcium hydride (CaH2) is added, with the amount being 1% or more of the total weight of the sample. After 30 minutes, the sample is removed to obtain the electrolyte for lithium metal batteries.

[0076] Tables 1 and 2 list the compositions of electrolytes for lithium metal batteries according to the examples and comparative examples, respectively.

[0077] Table 1 Table 2 Performance Verification of Lithium Metal Battery Cells Containing Solvents for Controlling the Dissolution Environment - 1 (1) Experiments confirmed that the Li / NMC lithium metal battery cell containing the electrolyte of Example 1 showed an 18% improvement in durability (197 cycles) compared to the lithium metal battery cell containing the electrolyte of Comparative Example 1 (167 cycles) without a cosolvent. This can be seen from... Figure 1 and Figure 2A This can be seen from the text.

[0078] (2) Perform battery cell testing 19 F-NMR analysis was used to determine the factors contributing to electrolyte degradation. Specifically, in relation to... Figure 1 Under the same evaluation conditions, 2.5 g / Ah of each electrolyte was injected into a 0.169 Ah dual-cell unit, and the cell was subjected to 50 and 100 charge-discharge cycles, respectively, to collect samples for further evaluation. 19 F-NMR analysis was performed. A 100 μL sample was taken by cutting off the top of each pouch cell. 1 mL of dimethyl ether (DME) was injected into the pouch cell to wash away residual electrolyte. Then, 900 μL of a mixed solution consisting of 30 g d6-DMSO (as NMR solvent) and 5 g fluorobenzene (as internal standard solution) was injected into the sample for further analysis. 19 Measured by F-NMR (500 MHz, Unity Inova, Varian Technology). 19 The 1 / 2 ppm F-NMR measurements were used to calculate DMSF / FSI (mol) and FSI / fluorobenzene (mol) by reading the areas of the DMSF, FSI, and fluorobenzene signals. These values ​​were then multiplied to obtain DMSF / fluorobenzene (mol). This method allows for the quantitative analysis of residual solvents and salts in the electrolyte after the battery reaction.

[0079] (3) As a comparative example 1, the NMR quantitative analysis showed a rapid decrease in the concentration of FSI salt. This can be seen from... Figure 2B It was observed that the main cause is believed to be the reductive decomposition of salts, which had previously been predicted to be a characteristic of weakly soluble solvents.

[0080] (4) NMR analysis of Example 3, which contained 1,2-dimethoxypropane (DMP) as a co-solvent, confirmed the presence of a large amount of FSI salt in the electrolyte, even after 100 charge-discharge cycles, indicating the presence of excess FSI. This can be seen from... Figure 2C The results were observed in Table 3. Table 3 shows the NMR quantitative analysis results of Comparative Example 1 and Example 3.

[0081] Table 3 *DMSF: N,N-Dimethylaminosulfonyl fluoride *FSI: Bis(fluorosulfonyl)imide *fBz: Fluorobenzene (5) Finally, experiments have shown that increasing the amount of salt and delaying the decomposition of salt can improve the durability of lithium metal batteries.

[0082] Performance Verification of Lithium Metal Battery Cells Containing Solvents for Controlling the Dissolution Environment - 2 (1) Comparative Example 2 uses an electrolyte with the co-solvent of Example 1 as the solvent, which is a highly soluble solvent electrolyte. Compared to the durability of the lithium metal battery cell using the electrolyte of Comparative Example 1 (167 cycles), the durability of the Li / NMC lithium metal battery cell using the electrolyte of Comparative Example 2 is 137 cycles, a decrease of 18%. This can be seen from... Figure 3A This has been confirmed. Data shows that when a highly soluble solvent electrolyte is used as the solvent, the degree of dissociation of the salt is higher, the distance between Li-FSI is longer, and the anionicity of the salt is stronger, thus making it easier for electrochemical oxidative decomposition to occur.

[0083] (2) When the residual components were quantitatively analyzed by NMR, a rapid decrease in FSI was observed, such as Figure 3B As shown in the figure. The NMR quantitative analysis results of Comparative Example 2 are shown in Table 4.

[0084] Table 4 *DMP: 1,2-Dimethoxypropane *FSI: Bis(fluorosulfonyl)imide *dfBz: Difluorobenzene (3) The data also show that using excessively strong solvents does not improve durability, but using moderately strong solvents in combination with co-solvents (rather than using them alone) can effectively improve durability.

[0085] (4) The electrolyte of Comparative Example 4, prepared by adding a perfluorinated co-solvent (which weakens the dissolution environment), showed improved durability compared to Comparative Example 1 without the co-solvent, but its durability level remained comparable to that of Comparative Example 1. This can be seen from... Figure 3C This can be seen from the text.

[0086] (5) Experimental data confirm that the combination of solvent and cosolvent can create a suitable dissolution environment.

[0087] Performance Verification of Lithium Metal Battery Cells Containing Solvents for Controlling the Dissolution Environment - 3 (1) Raman spectroscopy was used to analyze the dissolution state of FSI anions to confirm the dissolution environment of the examples.

[0088] (2) Comparative Example 1, using a weakly soluble solvent, exhibited prominent aggregated ion pairs (AGG) and contact ion pairs (CIP), which may be due to the low degree of salt dissociation. In contrast, Comparative Example 2, using a strongly soluble solvent, exhibited mainly CIP due to the high degree of salt dissociation. Figure 4A The data confirms this.

[0089] (3) In contrast, CIP was reduced and AGG was increased in Example 1. Figure 4B The data confirms this.

[0090] (4) Therefore, the data shows that even when a strongly soluble solvent is added as a co-solvent to a weakly soluble electrolyte, a third characteristic is observed, rather than any intermediate characteristic, thus creating a favorable dissolution environment. Therefore, the implementation in this example is a novel composition with new characteristics, rather than simply using solvents and mixing them to obtain intermediate mixed characteristics.

[0091] Lithium stability of cosolvents (1) The durability of lithium metal batteries mainly decreases when the highly reactive lithium anode undergoes chemical side reactions with the electrolyte, which leads to electrolyte consumption and increased resistance. In Comparative Example 1, the solvent N,N-dimethylaminosulfonyl fluoride (DMSF) in the electrolyte is known to react with lithium, and this reaction usually forms a high ionic conductivity SEI film, thereby extending the cycle life of the battery. However, since this electrolyte is a weakly soluble electrolyte, the salt reacts with the anode, inhibiting the formation of a high ionic conductivity film by DMSF. In addition, the electrolyte is consumed during long-term operation, leading to an increase in solution resistance.

[0092] (2) Therefore, experiments were conducted to verify whether the addition of 1,2-dimethoxypropane (DMP) as a co-solvent could reduce the side reactions of the FSI salt. This co-solvent may also react with lithium, reducing the effect of DMSF and being consumed; therefore, this reaction was investigated and Tafel analysis was performed*. The results are as follows: Figure 5A As shown. In the experiment, we constructed a lithium-symmetric battery cell and measured the current generated when a voltage of ±0.1 V was applied using cyclic voltammetry. Lithium foil, electrodeposited on Cu to a thickness of 20 μm and punched into 16 pi and 14 pi sheets, was used, along with a PE separator (18 pi) coated with alumina on both sides. 10 μL of electrolyte was injected using a micropipette. The cyclic voltammetry method involved applying a voltage of 0 V relative to the open circuit potential (OCP) and cycling it between -0.1 V and +0.1 V at a rate of 1 mV / s. Starting from the 50th cyclic voltammetric scan, the overpotential and the resulting current density were read and plotted on a Tafel plot, where the x-intercept was defined as the exchange current density.

[0093] (3) The increase in surface area caused by chemical side reactions and dendrite growth on the electrode surface is quantified as the exchange current density J0, such as Figure 5B As shown. See also Figure 5B The electrolyte of Comparative Example 2, containing only a co-solvent, exhibited an exchange current density of -6.97, which is more negative than the -6.46 of the electrolyte of Comparative Example 1, using only DMSF. Furthermore, this value (-6.97) is more negative than the -6.75 of the electrolyte of Comparative Example 3, using 1,2-dimethoxyethane as a solvent, which is generally considered stable for lithium metal. This demonstrates that a low lithium surface area and low interfacial resistance are achieved under ultra-concentrated solution conditions, and confirms the excellent lithium stability of 1,2-dimethoxypropane (DMP).

[0094] (4) Finally, the data confirmed that when 1,2-dimethoxypropane (DMP) is used as a cosolvent, it has very little side reaction with lithium and continues to act as a cosolvent, while it does not inhibit the reactivity of N,N-dimethylaminosulfonyl fluoride (DMSF).

[0095] Confirmation of cosolvent dosage (1) The electrolytes of Examples 2 to 4 contain 1,2-dimethoxypropane (DMP) in an amount sufficient to ensure improved durability (i.e., based on the total solvent content of 66 mol%, 49 mol%, and 24 mol%, respectively), representing improvements in durability of 7%, 12%, and 3% compared to Comparative Example 1. This can be seen from... Figure 6A and 6B This was observed in [the context].

[0096] The electrolyte of Comparative Example 5 contained a small amount (5 mol%) of 1,2-dimethoxypropane (DMP), and its durability was reduced by 7% compared to Comparative Example 1. Figure 6C As shown.

[0097] The electrolyte of Comparative Example 6 contained a large amount (76 mol%) of 1,2-dimethoxypropane (DMP), resulting in a 7% decrease in durability compared to Comparative Example 1. Figure 6D As shown.

[0098] (4) The data also confirm that when the amount of 1,2-dimethoxypropane (DMP) cosolvent added is 24 mol% to 66 mol% of the total solvent, durability can be continuously improved.

[0099] Confirmation of salt dosage in electrolytes (1) In Example 5, the amount of 1,2-dimethoxypropane (DMP) in the electrolyte was the same as in Example 1, but the molar ratio of salt to solvent was changed from 1:2.5 to 1:2.0 to increase the salt concentration in the electrolyte. The excess salt resulted in a salt concentration of 4.8 M in the electrolyte, which was higher than that in Example 1 (3.9 M) and Example 2 (3.4 M); however, the salt precipitated at the high concentration.

[0100] (2) Compared to Example 1 (128 times), the durability of Example 5 was improved by 8.6%. This can be seen from... Figure 7A This indicates that the introduction of 1,2-dimethoxypropane (DMP) as a co-solvent dissolved the excess salt, which could explain the improvement in battery durability.

[0101] (3) The electrolyte of Comparative Example 7 contained the same amount of 1,2-dimethoxypropane (DMP) as in Example 1, but the molar ratio of solvent to salt was increased (from 2.5 to 3.0) to reduce the salt concentration in the electrolyte. The salt concentration was 3.2 M, which was lower than the salt concentration of Example 1 (3.9 M) and Example 2 (3.4 M). Therefore, the salt content of Comparative Example 7 was lower than that of Examples 1 and 2.

[0102] (4) The durability of Comparative Example 7 decreased by 14% compared to Example 1 (128 cycles). Figure 7B As shown.

[0103] (5) The data also confirm that battery durability is improved when the molar ratio of lithium salt to non-aqueous organic solvent in the electrolyte used for lithium metal batteries is maintained in the range of 1:2 to 1:2.5.

[0104] Confirmation of cosolvent composition (1) The electrolyte compositions of Examples 6 and 7 and Comparative Examples 8 to 10 were prepared by adding an ether solvent (49 mol%), the structure of which is similar to that of 1,2-dimethoxypropane (DMP), a representative cosolvent that falls within the scope of the Examples and Embodiments.

[0105] (2) Durability assessments showed that the long-term cycle life characteristics of Examples 6 and 7 were similar to those of Example 3, but the durability degradation of Comparative Examples 8 to 10 occurred relatively early. This can be seen from... Figure 8 The durability of lithium metal battery cells prepared using the electrolytes of Examples 3, 6, and 7, and Comparative Examples 8 to 10, was evaluated, and the results are shown in Table 5.

[0106] Table 5 (3) The above results can be explained by the good properties of 1,2-dimethoxypropane (DMP), which generally has a good solubility environment and lithium stability. Therefore, the data show that when either of the two methoxy groups is replaced by an ethoxy group, the durability remains as good as expected.

[0107] (4) The data also confirm that when N,N-dimethylaminosulfonyl fluoride (DMSF) is used as the main solvent, the addition of a cosolvent of formula 1 is particularly advantageous.

[0108] Although some preferred embodiments have been described above, this disclosure is not limited thereto, and various modifications may be made within the scope of the detailed description, the claims and their equivalents, and the drawings.

Claims

1. An electrolyte for lithium metal batteries, 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 combinations thereof. The co-solvent has the structure shown in Formula 1: Chemical Formula 1 in, R 1 and R 2 Each is independently methyl or ethyl, but R 1 and R 2 Not all of them are ethyl.

2. The electrolyte according to claim 1, wherein, The main solvent is N,N-dimethylaminosulfonyl fluoride, and R 1 and R 2 Each is independently a methyl group.

3. The electrolyte according to claim 1, wherein, Based on the total amount of the non-aqueous organic solvent, the content of the co-solvent is from 24 mol% to 66 mol%.

4. The electrolyte according to claim 1, wherein, The molar ratio of the lithium salt to the non-aqueous organic solvent is 1:2 to 1:2.

5.

5. The electrolyte according to claim 1, wherein, The lithium salt includes at least one of LiFSI, LiFNFSI, and LiTFSI.

6. The electrolyte according to claim 1, wherein, The concentration range of the lithium salt is 3.0 M to 5.0 M.

7. A lithium metal battery, comprising: positive electrode; The lithium metal layer facing the positive electrode serves as the negative electrode; A membrane located between the positive electrode and the negative electrode; as well as An electrolyte for lithium metal batteries according to any one of claims 1-6.

8. The lithium metal battery according to claim 7, wherein, The thickness of the lithium metal layer is 5 μm to 50 μm.

9. The lithium metal battery according to claim 7, wherein, The positive electrode contains lithium nickel manganese cobalt-based metal oxide.

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