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

Abstract

An electrolyte for a lithium metal battery includes a lithium salt, a nonaqueous organic solvent, and a metal cation additive. The metal cation additive can include calcium and trifluoromethanesulfonimide.

Description

[0001] Cross-reference of related applications This application claims priority to Korean Patent Application No. 10-2024-0185582, filed with the Korean Intellectual Property Office on December 13, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to electrolytes for lithium metal batteries and lithium metal batteries including the electrolyte. Background Technology

[0003] As the electric vehicle market grows, the demand for high-capacity batteries that improve upon or surpass lithium-ion batteries is increasing. Consequently, the demand for anode and cathode materials with high energy density and providing long-term stability for lithium metal batteries is also growing.

[0004] Lithium metal, with its high capacity per unit weight of 3860 mAh / g and low standard electrode potential (-3.04 V vs. conventional hydrogen electrode), has been used as the anode material in rechargeable lithium-ion batteries. However, lithium metal is highly reactive and can generate an extremely reducing atmosphere during charging, leading to an irreversible decomposition reaction between the lithium metal and the electrolyte. This decomposition depletes the electrolyte, and the decomposition products can form a non-uniform film on the lithium metal surface. Furthermore, with repeated charging and discharging, lithium can form dendrites. Dendritic lithium can cause short circuits inside the battery, potentially leading to battery safety issues such as fires.

[0005] Therefore, in order to utilize lithium metal in a way that provides high stability and high capacity, an electrolyte is needed that can mitigate the reactivity of lithium metal, prevent the growth of dendritic lithium, and / or achieve uniform lithium deposition (plating). Summary of the Invention

[0006] Embodiments of this disclosure provide an electrolyte for lithium metal batteries that can induce uniform electrodeposition and desorption of lithium ions by forming a thin film on a current collector and / or lithium metal surface.

[0007] In another embodiment, this disclosure provides a lithium metal battery, for example, which includes the electrolyte described above and is capable of achieving excellent durability.

[0008] An electrolyte for a lithium metal battery according to an embodiment includes: a lithium salt; a non-aqueous organic solvent; and a metal cation additive, wherein the metal cation additive may include calcium (cationic form) and trifluoromethanesulfonylimide (anionic form).

[0009] In some embodiments, the metal cation additive may include bis(trifluoromethanesulfonylimide)calcium(II).

[0010] In this embodiment, the content of the metal cation additive can be greater than 0.5 wt% and less than 5 wt% based on the total weight of the electrolyte.

[0011] In this embodiment, the non-aqueous organic solvent may include fluorosulfonamide (FSA).

[0012] In embodiments, the lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and / or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0013] In this embodiment, the lithium salt concentration can be from 2.5 M to 4.5 M.

[0014] In this embodiment, the molar ratio of lithium salt to non-aqueous organic solvent can be approximately 1:3 (salt:solvent).

[0015] According to another embodiment, a lithium metal battery may include: a positive electrode; a lithium metal layer serving as a negative electrode, which is oriented (e.g., facing) the positive electrode; a separator located between the positive and negative electrodes; and an electrolyte according to the above aspects and embodiments of this disclosure.

[0016] In this embodiment, the thickness of the lithium metal layer can be from 10 μm to 200 μm.

[0017] In implementation methods, the positive electrode may include LiCoO2, Li(Ni) x Co y Mn z O2 and / or Li(Ni) x Co y Al z At least one of O2, where x+y+z=1.

[0018] As disclosed herein, the electrolyte for lithium metal batteries according to embodiments can improve the durability of lithium metal batteries. Attached Figure Description

[0019] Figure 1 The durability evaluation results of Li / NCM811 button batteries using electrolytes according to Example 1, Comparative Example 1 and Comparative Examples 5-8 are shown under high power (1 C) conditions.

[0020] Figure 2 The results of lithium reversibility evaluation for Cu / NCM811 electrodeless coin cells (1 / 3 C) using electrolytes according to Examples 1 and Comparative Examples 3-7 are shown.

[0021] Figure 3The durability evaluation results of Li / NCM811 button batteries (1 / 3 C) using electrolytes according to Example 1 and Comparative Examples 1-4 are shown.

[0022] Figure 4 The durability evaluation results of Li / NCM811 pouch cells (1 / 3 C) using electrolytes according to Example 1 and Comparative Example 1 are shown.

[0023] Figure 5 The durability evaluation results of Li / NCM811 button cells (1 / 3 C) using electrolytes according to Example 1 and Reference Examples 1-3 are shown.

[0024] Figure 6A The image is a scanning electron microscope photograph (top view) of the electrolyte from Comparative Example 1.

[0025] Figure 6B The image is a scanning electron microscope (SEM, top view) photograph of the electrolyte according to Example 1.

[0026] Figure 6C This is a top view of the SEM-energy dispersive X-ray spectroscopy (EDS) mapping analysis of the electrolyte according to Example 1. The white spots on the surface represent calcium.

[0027] Figure 7A The image is a scanning electron microscope photograph (side view) of the electrolyte from Comparative Example 1.

[0028] Figures 7B to 7D The images shown are a scanning electron microscope image (side view) and an energy-dispersive X-ray spectroscopy (EDS) surface distribution analysis diagram (side view) of the electrolyte according to Example 1. Figure 7D In the image, the white dots on the surface represent calcium.

[0029] Figure 8A The images are based on scanning electron microscope (SEM) photographs (left, top view) and EDS surface distribution analysis diagrams (right, top view) of the electrolyte from Reference Example 1. Figure 8A In the image on the right, the white dots on the surface represent calcium.

[0030] Figure 8B The images show scanning electron microscope (SEM) photographs (left, top view) and EDS surface distribution analysis diagrams (right, top view) of the electrolyte according to Example 1. Figure 8B In the image on the right, the white dots on the surface represent calcium.

[0031] Figure 8C The images are based on scanning electron microscope (SEM) photographs (left, top view) and EDS surface distribution analysis diagrams (right, top view) of the electrolyte from Reference Example 2. Figure 8C In the image on the right, the white dots on the surface represent calcium.

[0032] Figure 8D The images are based on scanning electron microscope (SEM) photographs (left, top view) and EDS surface distribution analysis diagrams (right, top view) of the electrolyte from Reference Example 3. Figure 8D In the image on the right, the white dots on the surface represent calcium.

[0033] Figure 9A The images are based on scanning electron microscope (SEM) photographs (the two middle images, cross-sectional views) and EDS surface distribution analysis diagrams (the leftmost and rightmost images, cross-sectional views) of the electrolyte from Reference Example 1. Figure 9A In the leftmost and rightmost images, the black dots on the surface represent calcium.

[0034] Figure 9B The images are scanning electron microscope (SEM) images (the two middle images, cross-sectional views) and EDS surface distribution analysis diagrams (the leftmost and rightmost images, cross-sectional views) of the electrolyte from Example 1. Figure 9B In the leftmost and rightmost images, the white dots on the surface represent calcium.

[0035] Figure 9C The images are based on scanning electron microscope (SEM) photographs (the two middle images, cross-sectional views) and EDS surface distribution analysis diagrams (the leftmost and rightmost images, cross-sectional views) of the electrolyte from Reference Example 2. Figure 9C In the leftmost and rightmost images, the white dots on the surface represent calcium. Detailed Implementation

[0036] Unless otherwise stated, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that, unless expressly defined herein, terms used throughout this disclosure generally have their common meaning in dictionaries and any specific meaning in the context of the relevant field.

[0037] In this application, terms such as “first” and “second” may be used to describe various components, but these components should not be construed as being limited to these terms. These terms are used only to distinguish one component from another. For example, without departing from the scope of this disclosure (i.e., identifying individual components in a certain way), a first component may be named a second component, and a second component may similarly be named a first component.

[0038] The terminology used in this specification is for describing specific exemplary embodiments only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, the singular form includes the plural form. It should be understood that the terms “comprising,” “having,” or “including” as used in this specification refer to the presence of the features, numbers, steps, operations, components, parts, or combinations thereof mentioned in this specification, but do not exclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. These terms should also be understood to include transitional terms such as “consisting of” and “primarily composed of”, which can be used to specify the presence of the stated feature and a small number of other components or features that do not substantially affect the operability of the embodiment, and / or can be used to specify only the presence of the stated feature, excluding any other features.

[0039] As used herein, the term "combination thereof" refers to a mixture or combination of one or more components described in the list of alternatives, and includes at least one selected from the list.

[0040] The following detailed description provides several aspects and implementations for illustrative and exemplary description of the technology. Those skilled in the art will understand that the described aspects and implementations can be modified in various ways without departing from the spirit or scope of this disclosure.

[0041] Electrolytes for Lithium Metal Batteries The development of electrolytes (including organic electrolytes) for lithium metal batteries has identified salts or solvents containing fluorosulfonyl functional groups. Salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are already used in conventional lithium-ion or lithium metal batteries; therefore, recent research has focused on electrolyte compositions including carbonate and ether solvents containing these salts. Studies have shown that the performance of lithium metal batteries can be improved when bis(fluorosulfonyl)amide (FSA)-based electrolytes are used in conjunction with salts having similar structures (e.g., LiFSI, LiTFSI, etc.).

[0042] However, it has been found that such compositions form a thick, porous SEI interface (or SEI layer) during battery charge and discharge, which leads to side reactions and reduces battery durability and performance. Because these compositions shorten cycle life and have low oxidative stability, there is still a need to develop compositions that can delay salt decomposition and improve antioxidant properties.

[0043] As described herein, the electrolyte compositions provided in this disclosure can significantly improve battery durability by introducing functional additives, including metal ions (e.g., calcium cations), into the composition. In embodiments, metal ions (cations) are included in a specific content or concentration range sufficient to form a thin SEI interface and induce uniform electrodeposition / desorption of lithium metal. Such embodiments avoid problems present in the prior art (e.g., the formation of a thick SEI interface and associated side reactions).

[0044] According to embodiments of this disclosure, electrolytes comprising the compositions described herein (e.g., salts and solvents comprising fluorosulfonyl groups and additives comprising metal ions) can maximize the reversibility of lithium electrodeposition-desorption and significantly improve the durability of lithium metal batteries. In specific embodiments, the amounts of additives include specific operating ranges.

[0045] The electrolyte for lithium metal batteries according to embodiments may include: lithium salt; non-aqueous organic solvent; and metal cation additives. Without limitation on a specific mechanism, the metal cation additives can suppress any side reactions between lithium metal and the electrolyte and / or induce dense electrodeposition of lithium, which can improve the reversibility of the lithium metal electrodeposition / desorption reaction while inhibiting the growth of dendritic lithium, thereby improving the durability of lithium metal batteries including such electrolytes.

[0046] In some embodiments, the metal cation additive may include a metal cation; in some further embodiments, the cation may include a calcium cation (i.e., Ca). 2+ Although calcium is one of the most abundant and inexpensive minerals in nature, offering potential economic benefits, calcium ions have not yet been incorporated as a necessary component of lithium-ion batteries or as an electrolyte component of lithium metal batteries.

[0047] In some embodiments, in addition to calcium cations, metal cation additives may also include trifluoromethanesulfonyl imide as an anion (e.g., metal cation additives may include calcium cations and trifluoromethanesulfonyl imide anions).

[0048] In some further embodiments, the metal cationic additive includes bis(trifluoromethanesulfonylimide)calcium(II).

[0049] In some embodiments, the content of the metal cation additive can be greater than 0.5 wt% and less than 5 wt% based on the total weight of the electrolyte, for example, 1 wt% to 4 wt%, 1 wt% to 3 wt%, or 1 wt% to 2 wt%. In embodiments where the content of the metal cation additive (e.g., bis(trifluoromethanesulfonylimide)calcium(II)) falls within these ranges, the electrolyte can improve battery durability. Conversely, when the content of the metal ion additive exceeds the above ranges (e.g., less than or equal to 0.5 wt% or greater than or equal to 5 wt%), the thickness of the formed SEI interface may be excessive, which can lead to uneven lithium-ion deposition, decreased durability and performance, or a rapid decline.

[0050] In some embodiments, the non-aqueous organic solvent may include fluorosulfonamide (FSA). FSA has excellent compatibility with lithium metal anodes and also with lithium salts (e.g., lithium salts comprising fluorosulfonyl groups). Therefore, when the electrolyte composition according to the embodiments includes FSA as a solvent, the SEI interface characteristics of lithium metal can be improved, and durability can be significantly enhanced.

[0051] In some embodiments, this disclosure relates to electrolytes comprising a complex salt including an FSA and a fluorosulfonyl group, wherein the amount is suitably sufficient to improve the durability of lithium metal batteries. In some embodiments, the fluorosulfonyl-containing complex salt may refer to the aforementioned metal cation additive and the lithium salt described below.

[0052] According to some embodiments, the lithium salt may include a fluorosulfonyl group, and non-limiting examples include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), and / or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In some further embodiments, the lithium salt may be LiFSI.

[0053] In some embodiments, the concentration of the lithium salt included in the lithium metal battery electrolyte can be in the range of 2.5 M to 4.5 M, and in some specific embodiments, it can be 2.6 M to 4.4 M, 2.7 M to 4.3 M, 2.8 M to 4.2 M, 2.9 M to 4.1 M, or 3.0 M to 4.0 M.

[0054] In embodiments where the lithium salt concentration is below the aforementioned range, the electrolyte conductivity may decrease, leading to poor electrolyte performance. Furthermore, in embodiments where the lithium salt concentration exceeds the aforementioned range, the electrolyte viscosity may increase, resulting in reduced lithium-ion mobility and potentially causing overvoltage from the start of cycling. Additionally, exceeding the aforementioned range can lead to poor SEI layer formation (i.e., on the lithium metal surface serving as the negative electrode), where the SEI layer may not form at all or may be excessively thick; both of these conditions degrade the electrochemical performance of the lithium metal battery.

[0055] In some embodiments, the molar ratio of lithium salt to non-aqueous organic solvent can be from 1:2.7 to 1:3.3, for example, 1:3 (salt:solvent). In embodiments in which a cationic metal additive is introduced into the composition of lithium salt and non-aqueous organic solvent mixed in the above molar ratio, the improvement in cycle performance and durability of lithium metal batteries can be maximized.

[0056] Lithium metal batteries In other aspects and embodiments, this disclosure provides a lithium metal battery including an electrolyte for a lithium metal battery according to the aspects and embodiments described herein.

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

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

[0059] In these embodiments, the battery, including the negative electrode, allows lithium ions to move from the positive electrode to the negative electrode during charging to form a lithium metal layer. The battery can be charged and discharged 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 implementations, the lithium metal layer can be formed on the negative electrode current collector through the charging and discharging of the lithium metal battery.

[0062] In some embodiments, the thickness of the lithium metal layer can be from 10 μm to 200 μm.

[0063] In embodiments where the lithium metal layer meets the aforementioned thickness, side reactions between the lithium metal layer and the electrolyte are suppressed, thereby improving the electrochemical performance of the lithium metal battery.

[0064] In another embodiment, the positive electrode is positioned relative to the negative electrode.

[0065] 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.

[0066] 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.

[0067] In some implementations, the thickness of the positive current collector can be from 3 μm to 500 μm.

[0068] The positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material can be a compound capable of lithium intercalation and deintercalation. In some specific embodiments, the electrode active material may include a lithium metal oxide, which includes at least one of cobalt, manganese, nickel, and / or aluminum. In some specific embodiments, the lithium metal oxide may include at least one of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium manganese cobalt oxide, or lithium nickel cobalt transition metal (M) oxide.

[0069] In some embodiments, the positive electrode active material can be lithium nickel manganese cobalt oxide, which can improve the battery's capacity characteristics and stability. In some further embodiments, the lithium nickel manganese cobalt oxide may include Li(Ni) x Co y Mn z O2, where x+y+z=1. In a further embodiment, lithium nickel manganese cobalt oxide may include Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2 and / or Li(Ni) 0.8 Mn 0.1 Co 0.1 )O2.

[0070] In some embodiments, in addition to lithium nickel manganese cobalt oxide, the positive electrode active material may also include LiCoO2, Li(Ni) x Co y Al z O2 (where x+y+z=1) or a combination thereof.

[0071] In some embodiments, the positive electrode active material layer may also include an adhesive and / or a conductive material.

[0072] In this implementation, the separator is used to separate (i.e., physically separate) the negative and positive electrodes and to provide a channel for the movement (migration) of lithium ions. There are no particular limitations on the separator; it can include separators commonly used in rechargeable lithium batteries.

[0073] The following embodiments illustrate only some implementations according to this disclosure in more detail. Therefore, it should be understood that the following embodiments represent only some selected implementations and do not constitute a limitation on the scope of the technology disclosed herein.

[0074] (Example) Preparation of an electrolyte for lithium metal batteries LiFSI salt was added to FSA solvent at a concentration of 3.4 M and mixed to form a solution. Then, calcium hydride (CaH2) at a concentration greater than or equal to 1% by weight of the solution was added, and the mixture was stirred for 30 minutes to separate the liquid and solid phases, yielding a liquid solution. Subsequently, a metal cation additive was mixed with the solution to prepare an electrolyte composition for rechargeable lithium batteries. In this embodiment, the amounts of LiFSI salt and FSA solvent added were such that the molar ratio of salt to solvent in all electrolytes was 1:3.

[0075] Table 1 lists the electrolyte compositions according to the above-described examples, reference examples, and comparative examples. In Comparative Example 1, no metal cation additive was added.

[0076] (Table 1) In Evaluation Examples 1-3 and 5, all coin cells were assembled in an argon glove box, where the concentrations of H2O and O2 were maintained at 1 ppm or lower. A 20 µm thick lithium metal foil was placed as the negative electrode in a 2032-type coin cell, with a 16 mm diameter polyolefin separator (W-scope) placed in the middle, and an NCM811 positive electrode stacked on top. A 1.5 mm thick gasket was used to ensure good upper contact. 15 µL of the electrolyte described in Table 1 above was dispensed into each cell. After assembly and sealing, the cells were thoroughly immersed at room temperature, then subjected to low-rate formation at 25 °C, and charge-discharge durability was evaluated at 1 C.

[0077] In Evaluation Example 4, the pouch cell assembly was performed in an argon glove box, where the concentrations of H2O and O2 were maintained at 1 ppm or lower. A single-layer pouch cell (Al-laminated pouch) with a nominal capacity of 0.2 Ah was fabricated by stacking a 20 µm thick lithium metal anode and an NCM811 cathode, with a polyolefin separator (W-scope) inserted between them. The separator was cut to protrude 1-2 mm beyond the electrode edges on all sides. The anode (Al tab) and cathode (Ni tab) tabs were ultrasonically welded to their respective current collectors. The electrolyte described in Table 1 above was used; injection was performed under vacuum, and the volume was controlled at 2-4 mL·Ah. -1 (Based on E / C (electrolyte / rated capacity)) (For a 0.2 Ah battery: approximately 0.6 mL). After sealing, immerse the battery at room temperature and perform low-rate formation at 25°C (e.g., 0.1 C, 1-2 cycles, 2.8-4.3V, charge CV cutoff current C / 20), followed by charge-discharge durability testing at 1 C within the same voltage window.

[0078] (Evaluation Example 1: 1C evaluation of composite salt Li / NMC based on salt type (high power durability evaluation)) This evaluation example includes the following elements: Battery type: 20 μm Li / W-scope separator (16 pi) / NCM811 cathode, 1.5 T pad, button cell (2032). Electrolyte injection volume: 15 μl The Li / NMC 1C durability of composite salts with other salts added to conventional LiFSI salts was evaluated using a multi-channel battery cycling tester (Arbin Instruments). The results are as follows: Figure 1 As shown in Table 2.

[0079] (Table 2) refer to Figure 1 As shown in Table 2, the electrolyte of Example 1 exhibited excellent durability in the 1 C high-power durability test.

[0080] (Evaluation Example 2: 1 / 3 C evaluation of lithium deposition reversibility) This evaluation example includes the following elements: Battery type: Cu / W-scope separator (16 pi) / NCM811 cathode, 1.5 T pad, button cell (2032) Electrolyte injection volume: 15 μl To evaluate the molecular types and structures in the electrolyte, an electrolyte was prepared with the lithium salt (LiFSI) and solvent (FSA) ratios as described above, and then lithium reversibility was evaluated. The results are as follows: Figure 2 As shown in Table 3. Since lithium-free Cu foil was used as the negative electrode for lithium reversibility evaluation, and only lithium from the positive electrode was used during charge and discharge, the reversible lithium deposition was quantitatively measured by the decrease in discharge capacity during charge and discharge. The charge and discharge measurement device and the coulombic efficiency measurement device were the same multi-channel battery cycle tester (Arbin Instruments) used in Evaluation Example 1.

[0081] (Table 3) refer to Figure 2 Table 3, along with the evaluation results of lithium reversibility during charge-discharge as a function of electrolyte in different composite salt electrolyte compositions, confirms that Example 1 exhibits the highest reversibility. Without being limited to a specific mechanism, calcium cations (Ca...) 2+ The presence of appears to induce uniform internal deposition of lithium and improve the reversibility of lithium deposition.

[0082] (Evaluation Example 3: 1 / 3C evaluation of the durability of lithium metal batteries based on metal cation salts) This evaluation example includes the following elements: Battery type: 20 μm Li / W-scope separator (16 pi) / NCM811 cathode, 1.5 T pad, button cell (2032). Electrolyte injection volume: 15 μl This evaluation example assessed the battery (Li / NMC 1 / 3 C) durability as a function of the composite salt composition, in which other salts were added to the conventional LiFSI salt. The results are as follows: Figure 3 As shown in Table 4. Evaluation Example 3 was to verify whether the above-mentioned composite salt formed a denser SEI interface that could induce uniform lithium deposition, thereby improving durability, compared to the SEI interface typically formed by conventional electrolyte compositions. The charge-discharge measurement apparatus used was the same multichannel battery cycle tester (Arbin Instruments) as in Evaluation Example 1.

[0083] (Table 4) refer to Figure 3 As shown in Table 4, the electrolyte of Example 1 exhibited the best durability in the 1 / 3 C evaluation.

[0084] (Evaluation Example 4: 1 / 3 C evaluation of the durability of Li / NMC pouch cells) The durability of composite salts, incorporating additional salts into conventional LiFSI salts, was evaluated in Li / NMC 1 / 3C batteries by replacing button cells with pouch cells (0.2 Ah) for commercialization assessment. The durability evaluation results of the composite salts are as follows: Figure 4 As shown in Table 5. This evaluation example 4 aims to determine whether scaled-up pouch cells manufactured on a commercial scale can exhibit improved durability compared to coin cells. The charge / discharge measurement apparatus used was the same multichannel battery cycle tester (Arbin Instruments) as in evaluation example 1.

[0085] (Table 5) like Figure 4 As shown in Table 5, the battery exhibits excellent durability at 1 / 3 C when using the electrolyte of Example 1.

[0086] (Evaluation Example 5: 1 / 3 C evaluation of lithium metal battery durability based on additive (Ca(TFSI)2) content) This evaluation example includes the following elements: Battery type: 20 μm Li / W-scope separator (16 pi) / NCM811 cathode, 1.5 T pad, button cell (2032). Electrolyte injection volume: 15 μl The results of evaluation examples 1 to 4 confirm that Ca(TFSI)₂ is a very effective metal cation additive. Performance evaluations based on different concentrations of calcium cation additives yielded the following results: Figure 5 As shown in Table 6. Evaluation Example 5 also helps determine whether the density of the SEI interface varies based on the Ca(TFSI)2 content and can help induce uniform lithium deposition, thereby improving durability. The charge / discharge measurement apparatus used was the same multichannel battery cycling tester (Arbin Instruments) as in Evaluation Example 1.

[0087] (Table 6) Referring to Tables 5 and 6, when the electrolyte of Example 1 was used and the content of Ca(TFSI)2 additive was 1.5 wt%, the data showed that this embodiment had the best durability in the 1 / 3 C durability evaluation.

[0088] (Evaluation Example 6: Electrolyte SEM (JSM-7610F Plus, JEOL)-EDS (UltimMax 65, Oxford Instruments) Analysis) (1) At 0.1 C x 2, at 1.33 mAcm-2 4 mAhcm -2 Under conditions of x 5 cycles and Ch, the electrolytes of Example 1 and Comparative Example 1 were examined using SEM images to observe their surfaces (top view), and SEM-EDS analysis was performed on the microscopic images to observe the distribution of various elements (including calcium). The results are as follows: Figures 6A to 6C As shown.

[0089] Figure 6A SEM images of the electrolyte in Comparative Example 1 are shown. Figure 6B and Figure 6C SEM images of the electrolyte of Example 1 are shown. These images confirm that the SEM images of Example 1 have a smoother top view compared to Comparative Example 1. Furthermore, Figure 6C Ca atoms were observed on the surface.

[0090] (2) At 0.1 C x 2, at 1.33 mAcm -2 4 mAhcm -2 Under conditions of x 5 cycles and Ch, the electrolytes of Example 1 and Comparative Example 1 were examined using SEM images to observe their surfaces (side views), and SEM-EDS analysis was performed on the microscopic images to observe the distribution of various elements (including calcium). The results are as follows: Figures 7A to 7D As shown.

[0091] Figure 7A SEM images of the electrolyte in Comparative Example 1 are shown. Figures 7B to 7D SEM images of the electrolyte of Example 1 are shown. These images confirm that, compared to Comparative Example 1 (37.7 μm, see e.g., see...) Figure 7A The thickness of the electrodeposited lithium observed in the SEM image of Example 1 (23.2 μm, see, for example, see...) Figure 7C The electrodeposited lithium thickness of Example 1 is thinner, and calcium atoms are distributed on the lithium metal surface. Based on the above results, compared with Comparative Example 1, the electrolyte of Example 1 appears to induce more uniform lithium electrodeposition by forming an SEI interface, indicating that uniform lithium electrodeposition will continue to occur with subsequent cycling.

[0092] (3) At 0.1 C x 2, at 1.33 mAcm -2 4 mAhcm -2 Under the conditions of x 5 cycles and Ch, the electrolytes of Examples 1 and Reference Examples 1-3 were examined using SEM images to observe their surface (top view), and SEM-EDS analysis was performed on the microscopic images to observe the distribution of various elements (including calcium). The results are as follows: Figures 8A to 8D As shown.

[0093] Figure 8AThe SEM image of the electrolyte in Reference Example 1 is shown. Figure 8B The image shows an SEM image of the electrolyte from Example 1. Figure 8C SEM images of the electrolyte in Reference Example 2 are shown. Figure 8D SEM images of the electrolyte of Reference Example 3 are shown. These results confirm that, compared to References 1-3, the SEM images of Example 1 show a smoother surface (top view), and furthermore, a large and uniform Ca particle size distribution is observed on the surface. The large and uniform Ca particle size distribution confirms that dead Li (unusable lithium) is minimized during the stripping process. Furthermore, since the relatively small surface area distributes the current uniformly to a lower current density, the results indicate that this structure will induce dense and uniform lithium electrodeposition when lithium is deposited in subsequent cycles, thereby reducing any side reactions between lithium and the electrolyte.

[0094] (4) At 0.1 C x 2, at 1.33 mAcm -2 4 mAhcm -2 Under the conditions of x 5 cycles and Ch, the electrolytes of Example 1 and Reference Examples 1 and 2 were examined using SEM images to observe their surface (cross-sectional view), and SEM-EDS analysis was performed on the SEM images to observe the distribution of various elements (including calcium). The results are as follows: Figures 9A to 9C As shown.

[0095] Figure 9A SEM images of the electrolyte in Reference Example 1 are shown. Figure 9B The image shows an SEM image of the electrolyte from Example 1. Figure 9C SEM images of the electrolyte of Reference Example 2 are shown. The data confirm that the SEM image of Example 1 has the smallest electrodeposited layer thickness compared to Reference Examples 1 and 2. Therefore, the results show that the electrolyte of Example 1 induces uniform lithium deposition by forming an SEI interface, and will lead to uniform lithium deposition with subsequent cycling.

[0096] Although several embodiments of the present disclosure have been described in detail above, the present disclosure is not limited thereto, and various modifications may be made within the scope of the present disclosure and the appended claims.

Claims

1. An electrolyte for lithium metal batteries, comprising: Lithium salts; Non-aqueous organic solvents; and Metal cationic additives; The metal cation additives include calcium and trifluoromethanesulfonylimide.

2. The electrolyte according to claim 1, wherein the metal cation additive comprises bis(trifluoromethanesulfonylimide)calcium(II).

3. The electrolyte according to claim 1, wherein the content of the metal cation additive is greater than 0.5 wt% and less than 5 wt% based on the total weight of the electrolyte.

4. The electrolyte according to claim 1, wherein, The non-aqueous organic solvent includes fluorosulfonamide (FSA).

5. The electrolyte according to claim 1, wherein, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide LiFSI and / or lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

6. The electrolyte according to claim 1, wherein the concentration of the lithium salt is from 2.5 M to 4.5 M.

7. The electrolyte according to claim 1, wherein the molar ratio of the lithium salt to the non-aqueous organic solvent is 1:(3±10%).

8. A rechargeable lithium metal battery, comprising: positive electrode; The lithium metal layer, serving as the negative electrode, faces the positive electrode; The membrane located between the positive electrode and the negative electrode; and The electrolyte according to claim 1.

9. The rechargeable lithium metal battery according to claim 8, wherein the thickness of the lithium metal layer is from 10 μm to 200 μm.

10. The rechargeable lithium metal battery according to claim 8, wherein the positive electrode comprises LiCoO2, Li(Ni) x Co y Mn z O2 and / or Li(Ni) x Co y Al z At least one of O2, where x+y+z=1.

Images