Lithium metal electrode with inhibited dendrite formation, method of making the same, and secondary battery comprising the same

Abstract

The present invention relates to a lithium metal electrode with inhibited dendrite formation, a method of manufacturing the same, and a secondary battery comprising the same. The lithium metal electrode comprises: a current collector; a metal-organic framework coated on the current collector, the metal-organic framework comprising lithiumophilic metal ions and organic linkers; and lithium metal plated on the metal-organic framework.

Description

Technical Field

[0001] The present invention relates to a lithium metal electrode with suppressed dendrite formation, a method for manufacturing the electrode, and a secondary battery including the electrode. Background Technology

[0002] With the increasing demand for portable electronic devices, high-capacity storage devices, and electric vehicles, the need to develop high-capacity rechargeable batteries is also growing.

[0003] Lithium metal electrodes have a theoretical capacity of 3840 mAh / g and a low reduction potential. As a high-capacity anode material for secondary batteries that can replace conventional graphite (372 mAh / g), lithium metal electrodes have recently attracted much attention and are emerging as a next-generation anode material for secondary batteries, alongside lithium-sulfur and lithium-air batteries.

[0004] However, lithium metal electrodes have a short cycle life and cause safety issues such as explosions due to dendrite formation, the formation of an unstable and thick solid electrolyte interphase (SEI) layer, and volume expansion within the electrode. Therefore, these problems must be addressed before lithium metal electrodes can be practically used.

[0005] In particular, in order to suppress dendrite formation, researchers have conducted active studies on optimizing the design of electrodes and current collectors, requiring strategies such as using current collectors with high surface area, improving the lithium affinity of electrodes, and homogenizing lithium-ion flux. Summary of the Invention

[0006] Technical issues The present invention aims to provide a lithium metal electrode with suppressed dendrite formation, which, while suppressing dendrite formation, simultaneously forms a lithium alloy layer with high lithium affinity and a solid electrolyte interface (SEI) layer with high lithium ion conductivity. The lithium metal electrode includes: a current collector; a metal-organic framework coated on the current collector, which contains lithium-loving metal ions and organic linkers; and lithium metal plated on the metal-organic framework.

[0007] However, the technical problems to be solved by the present invention are not limited to the above-mentioned technical problems. Those skilled in the art can clearly understand other technical problems not mentioned herein from the following description.

[0008] Technical solution The present invention provides a lithium metal electrode with suppressed dendrite formation, comprising: a current collector; a metal-organic framework coated on the current collector, comprising lithium-philic metal ions and organic linkers; and lithium metal plated on the metal-organic framework.

[0009] Lithophile metal ions can be selected from the group consisting of silver, gold, magnesium, zinc, and copper.

[0010] Organic linkers may include one or more compounds containing thiol groups.

[0011] The one or more thiol-containing compounds may be trithiocyanate (TCA).

[0012] Within a metal-organic framework, lithium-loving metal ions and organic linkers can be repeatedly stacked via coordination covalent bonds.

[0013] The thickness of metal-organic frameworks can range from 1 nm to 100 nm.

[0014] Metal-organic frameworks can have contact angles of 30° or less relative to mixed solvents containing 1,3-dioxolane (DOL) and dimethoxyethane (DME) and electrolytes containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0015] In another aspect, the present invention provides a method for manufacturing a lithium metal electrode with suppressed dendrite formation, the method comprising the steps of: (a) coating a current collector with a metal-organic framework comprising lithium-philic metal ions and an organic linker; and (b) depositing lithium metal onto the coated metal-organic framework.

[0016] In another aspect, the present invention provides a secondary battery comprising a lithium metal electrode in which dendrite formation is suppressed.

[0017] During the operation of a secondary battery, lithium metal electrodes can form a solid electrolyte interface (SEI) layer containing Li2S or Li3N.

[0018] Invention Effects The dendrite-suppressed lithium metal electrode according to the present invention comprises: a current collector; a metal-organic framework coated on the current collector, comprising lithium-philic metal ions and organic linkers; and lithium metal plated on the metal-organic framework. Therefore, when a secondary battery employing the dendrite-suppressed lithium metal electrode according to the present invention is in operation, the secondary battery provides the following advantages: while suppressing dendrite formation, it simultaneously forms a lithium alloy layer with high lithium affinity and a solid electrolyte interface (SEI) layer with high lithium-ion conductivity.

[0019] Therefore, the present invention can be used in various high-capacity secondary batteries that require excellent operational stability and power density. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating a method for manufacturing a dendrite-free lithium metal electrode according to an embodiment of the present invention.

[0021] Figure 2The results of ultraviolet-visible (UV-vis) spectral analysis of a metal-organic framework coated on a planar quartz glass substrate are shown.

[0022] Figure 3 The results of scanning electron microscopy (SEM) analysis of a metal-organic framework coated on a planar Si wafer are shown.

[0023] Figure 4 The results of evaluating the lithiophilicity of a metal-organic framework coated on a planar Ni current collector are shown.

[0024] Figure 5 The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses of the metal-organic framework coated on Ni current collectors in fabric form before and after lithium metal plating are shown.

[0025] Figure 6 Results evaluating the lithiophilicity of a metal-organic framework coated on a Ni current collector in fabric form are shown.

[0026] Figure 7 The results of X-ray photoelectron spectroscopy (XPS) analysis of the composition of the solid electrolyte interface (SEI) layer formed during operation of a secondary cell (half-cell) employing a lithium metal electrode with a Ni current collector in fabric form are shown.

[0027] Figure 8 It shows 1mA cm - ² and 1mA h cm - The results of evaluating the performance of a secondary battery (half-cell) using a Ni current collector based on fabric under the condition of ².

[0028] Figure 9 It shows 3mA cm - ² and 1mA h cm - The results of evaluating the performance of a secondary battery (symmetric full cell) using a Ni current collector based on fabric under the condition of ². Detailed Implementation

[0029] Therefore, in the process of manufacturing lithium metal electrodes with suppressed dendrite formation, the inventors of this application use lithium metal electrodes containing lithium-philic metal ions (e.g., Ag) + Au 3+ Mg 2+ Zn 2+A lithium metal electrode was prepared by coating a current collector with a metal-organic framework (MOF) and an organic linker (e.g., trithiocyanate (TCA)), and then depositing lithium metal onto the MOF. The inventors of this application have demonstrated that the manufactured lithium metal electrode simultaneously suppresses dendrite formation and forms a lithium alloy layer with high lithium affinity and a solid electrolyte interface (SEI) layer with high lithium-ion conductivity, thus completing this invention.

[0030] The present invention will now be described in detail.

[0031] Lithium metal electrode with suppressed dendrite formation The present invention provides a lithium metal electrode with suppressed dendrite formation, comprising: a current collector; a metal-organic framework coated on the current collector, the metal-organic framework comprising lithium-philic metal ions and organic linkers; and lithium metal plated on the metal-organic framework.

[0032] As used herein, the term "dendritic" refers to needle-like or dendritic deposits formed on the anode surface during the charging / discharging of lithium metal, in which lithium crystals act as nuclei and gradually accumulate.

[0033] First, the lithium metal electrode with suppressed dendrite formation according to the present invention includes a current collector.

[0034] A current collector refers to a conductive current collector or support, which can be any of the various known conductive current collectors or supports. For example, a current collector can be a planar conductive current collector or support, or a fabric-like conductive current collector or support. Therefore, conductive metal atoms can be present in the current collector. For example, the current collector can be a planar quartz glass, a Si wafer, or a Ni current collector (Ni 99.9% foil), or it can be a current collector with Ni electroplated onto a fabric.

[0035] Secondly, the dendrite-suppressed lithium metal electrode according to the present invention comprises a metal-organic framework coated on a current collector, the metal-organic framework containing lithium-philic metal ions and organic linkers.

[0036] Lithophile metal ions are characterized by forming coordination covalent bonds with organic linkers and exhibiting high lithium affinity.

[0037] Specifically, the lithium-loving metal ion can be selected from silver (Ag) + ), gold (Au) 3+ Au + ), magnesium (Mg) 2+ ), Zinc (Zn) 2+ ) and copper (Cu 2+ The ions in the group consisting of ) are preferably silver ions, but are not limited thereto.

[0038] The innermost organic linker can form a coordinate covalent bond with the conductive metal atom in the current collector, or it can form a coordinate covalent bond with a lithium-philic metal ion; in addition, the outermost organic linker can bond with lithium metal as described below.

[0039] Specifically, the organic linker may include one or more (preferably two or more, more preferably three or more) thiol-containing compounds, preferably trithiocyanate (TCA), but not limited thereto.

[0040] Within the coated metal-organic framework, lithium-philic metal ions and organic linkers can be repeatedly stacked through coordination covalent bonds, wherein the number of lithium-philic metal ion layers can be regarded as the number of repetitions, which can be 1 to 20, preferably 3 to 10, but not limited thereto, wherein the number of repetitions is used to control the thickness of the coated metal-organic framework.

[0041] Depending on the number of repetitions, the thickness of the coated metal-organic framework can be from 1 nm to 100 nm, preferably from 10 nm to 100 nm, but is not limited thereto.

[0042] The coated metal-organic framework is effective in improving lithium affinity and can have a contact angle of 30° or less, preferably 10° or less, more preferably 0° relative to the electrolyte, but is not limited thereto, the electrolyte comprising a mixed solvent of 1,3-dioxolane (DOL) and dimethoxyethane (DME) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0043] Secondly, the dendrite-suppressed lithium metal electrode according to the present invention comprises lithium metal plated on a metal-organic framework.

[0044] The plated lithium metal can be formed by electroplating using lithium precursors and an electroplating solution.

[0045] Depending on the electroplating conditions, the thickness of the plated lithium metal can range from 1 μm to 10 μm, and this thickness can be adjusted in various ways while suppressing dendrite formation.

[0046] Methods for manufacturing lithium metal electrodes with suppressed dendrite formation The present invention provides a method for manufacturing a lithium metal electrode with suppressed dendrite formation, the method comprising the steps of: (a) coating a current collector with a metal-organic framework comprising lithium-philic metal ions and an organic linker; and (b) depositing lithium metal onto the coated metal-organic framework.

[0047] Figure 1 This is a schematic diagram illustrating a method for manufacturing a dendrite-free lithium metal electrode according to an embodiment of the present invention, wherein a lithium metal containing lithium-philic metal ions (e.g., Ag) is used. + Au3+ Mg 2+ Zn 2+ A dendrite-free lithium metal electrode is fabricated by coating a current collector with a metal-organic framework (such as trithiocyanate (TCA)) and an organic linker (such as trithiocyanate (TCA)).

[0048] First, the method of manufacturing a dendrite-suppressed lithium metal electrode according to the present invention includes the step of coating a current collector with a metal-organic framework comprising lithium-philic metal ions and organic linkers [step (a)].

[0049] Current collectors, lithium-philic metal ions, organic linkers, and coated metal-organic frameworks are described above, and repeated descriptions are omitted.

[0050] The coating is performed using a solution-based, layer-by-layer self-assembly method, in which an organic linker is first deposited on the current collector by forming coordination covalent bonds with conductive metal atoms in the current collector. Then, the organic linker and lithium-loving metal ions are repeatedly layered through mutual coordination covalent bonds. Simultaneously, the thiol groups of the outermost organic linker can bond with lithium metal to form an interface with high lithium affinity. The number of lithium-loving metal ion layers can be considered as the number of repetitions, which can be 1 to 20, preferably 3 to 10, but is not limited to this, wherein the number of repetitions controls the thickness of the coated metal-organic framework.

[0051] Next, the method of manufacturing a dendrite-suppressed lithium metal electrode according to the present invention includes the step of depositing lithium metal on a coated metal-organic framework [step (b)].

[0052] The lithium metal plating is as described above, and repeated descriptions are omitted.

[0053] Electroplating can be performed using lithium precursors and electroplating solutions. Electroplating conditions used to control the thickness of the plated lithium metal can include approximately 100 mA cm⁻¹. - ² to approximately 500mA cm - Electroplating is performed at a current density of approximately 200 mA for about 1 minute to about 60 minutes, preferably including approximately 200 mA cm⁻¹. - ² to approximately 300mA cm - Electroplating is performed at a current density of ² for approximately 10 to 30 minutes, but not limited to this.

[0054] Secondary batteries The present invention provides a secondary battery comprising a lithium metal electrode with dendrite formation suppressed as described above.

[0055] Specifically, the secondary battery of the present invention includes a separator, a positive electrode and a negative electrode, and an electrolyte in contact with the positive electrode and the negative electrode, wherein a lithium metal electrode with suppressed dendrite formation is applied to the negative electrode, and wherein the separator is disposed between the positive electrode and the negative electrode.

[0056] By applying a lithium metal electrode with a theoretical capacity of 3840 mAh / g and a low reduction potential to the negative electrode, the theoretical storage capacity of the secondary battery can be significantly increased.

[0057] Specifically, during the operation of the secondary battery, the lithium metal electrode can form a solid electrolyte interface (SEI) layer comprising Li2S or Li3N, each corresponding to a material with high lithium-ion conductivity. Therefore, the secondary battery according to the present invention provides the advantage of simultaneously forming a lithium alloy layer with high lithium affinity and a solid electrolyte interface (SEI) layer with high lithium-ion conductivity while suppressing dendrite formation.

[0058] Therefore, this invention can be applied to various high-capacity secondary batteries that require excellent operational stability and power density, such as portable electronic devices, large-capacity storage devices, and electric vehicles.

[0059] Hereinafter, preferred embodiments are provided for ease of understanding of the present invention. However, the following embodiments are provided merely to facilitate a better understanding of the present invention, and the present invention is not limited to these embodiments.

[0060] [Example] Example 1: Coating a metal-organic framework onto a planar current collector A 10-minute soaking process removes lithium-philic metal ions (Ag). + Au 3+ Mg 2+ Zn 2+ or Cu 2+ An aqueous solution of a compound (i.e., 30 mM silver acetate, 30 mM gold chloride trihydrate, 30 mM magnesium acetate, 30 mM zinc acetate, or 30 mM copper acetate) and an ethanol-based solution of 10 mM trithiocyanate (TCA) as an organic linker are repeatedly layered (n = 1 to 10) onto a planar quartz glass, Si wafer, or Ni current collector (Ni 99.9% foil) to form a metal-organic framework. In this case, lithium-philic metal ions and TCA form coordinate covalent bonds within the coated metal-organic framework.

[0061] Figure 2 The results of ultraviolet-visible (UV-vis) spectral analysis of a metal-organic framework coated on a planar quartz glass are shown.

[0062] like Figure 2As shown, UV-Vis spectral analysis confirmed that as the repetition count increased from 1 to 10, various lithium-loving metal ions (Ag)... + Au + or Cu 2+ The TCA is qualitatively and uniformly layered.

[0063] also, Figure 3 The results of scanning electron microscopy (SEM) analysis of a metal-organic framework coated on a planar Si wafer are shown.

[0064] like Figure 3 As shown, SEM analysis confirmed the presence of lithium-loving metal ions (Ag). + The metal-organic framework is formed by combining TCA with each other in the form of nanoparticles. The thickness of the metal-organic framework increases uniformly with the number of repetitions (n=1, 3, 5, 10).

[0065] in addition, Figure 4 The results of evaluating the lithiophilicity of a metal-organic framework coated on a planar Ni current collector are shown.

[0066] Specifically, an electrolyte containing 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a 1:1 (v / v) mixed solvent of 1,3-dioxolane (DOL) and dimethoxyethane (DME) (hereinafter referred to as "LiTFSI electrolyte in DOL / DME (1:1)") was dropped onto the surface of a metal-organic framework coated on a planar Ni current collector, and its contact angle was measured.

[0067] like Figure 4 As shown, based on the contact angle measurements, the surface of the bare planar Ni current collector exhibits a contact angle of approximately 45.2° relative to the LiTFSI electrolyte in DOL / DME (1:1), while the surface of the metal-organic framework coated on the planar Ni current collector exhibits a contact angle of approximately 0° relative to the LiTFSI electrolyte in DOL / DME (1:1). This confirms that the metal-organic framework coating is effective in improving lithium affinity.

[0068] Example 2: Manufacturing of lithium metal electrode (in fabric form) The lithium metal electrode was manufactured in the same manner as in Example 1, except that a Ni current collector in the form of a fabric (Ni electroplated fabric) was used instead of a planar Ni current collector.

[0069] Figure 5 The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses of the metal-organic framework coated on Ni current collectors in fabric form before and after lithium metal plating are shown.

[0070] like Figure 5 As shown, SEM analysis confirmed that the metal-organic framework coated on the fabric-like Ni current collector is similar to that coated on the planar Ni current collector, and is in the form of lithium-philic metal ions (Ag). + The combination of nanoparticles with TCA also confirmed that subsequent lithium metal plating proceeded uniformly without dendrite formation.

[0071] In addition, XRD analysis confirmed that the metal-organic framework coated on the Ni current collector in fabric form was well formed, thus possessing a specific crystal structure.

[0072] also, Figure 6 Results evaluating the lithiophilicity of a metal-organic framework coated on a Ni current collector in fabric form are shown.

[0073] Specifically, the nucleation overpotential of a metal-organic framework coated on a Ni current collector in the form of a fabric was measured using a constant current charge / discharge method.

[0074] like Figure 6 As shown, the nucleation overpotential measurement results confirm that, compared to the bare fabric Ni current collector, the nucleation overpotential increases uniformly with increasing repetition count (n=1, 3, 5). This indicates that the metal-organic framework coating is effective in improving lithium affinity, and that lithium affinity can be tuned according to the number of repetitions.

[0075] Example 3: Fabrication of secondary batteries (half-cell and symmetrical full-cell) using lithium metal electrodes (in fabric form) Secondary batteries (half-cells and symmetrical full cells) are fabricated using the Ni current collector and lithium metal electrode (n=1, 3 or 5) prepared in Example 2.

[0076] Figure 7 The results of X-ray photoelectron spectroscopy (XPS) analysis of the composition of the solid electrolyte interface (SEI) layer formed during operation of a secondary cell (half-cell) employing a lithium metal electrode with a Ni current collector in fabric form are shown.

[0077] like Figure 7 As shown, when a secondary battery (half-cell) employing a Ni current collector-based lithium metal electrode (n=5) operates at 1 mA / cm² and 6 mAh / cm², Li₂S and Li₃N are identified as components of the formed SEI layer. These components correspond to approximately 10⁻⁶ mAh / cm² at room temperature. -3 S / cm and approximately 10 -5 Materials with high lithium-ion conductivity (S / cm).

[0078] also, Figure 8 It shows 1mA cm- ² and 1mA h cm - The results of evaluating the performance of a secondary battery (half-cell) using a Ni current collector based on fabric under the condition of ².

[0079] like Figure 8 As shown, unstable cycling stability was observed when using a lithium metal electrode with a Ni current collector based on a bare fabric; in contrast, when using a lithium metal electrode with a Ni current collector based on a fabric according to the present invention (n=1, 3 or 5), high stability of about 99% or higher was demonstrated even after 400 cycles due to the metal-organic framework coating.

[0080] also, Figure 9 It shows 3mA cm - ² and 1mA h cm - The results of evaluating the performance of a secondary battery (symmetric full cell) using a Ni current collector based on fabric under the condition of ².

[0081] like Figure 9 As shown, unstable cycling stability was observed when using a lithium metal electrode with a Ni current collector based on a bare fabric; in contrast, high stability was achieved when using a lithium metal electrode with a Ni current collector based on a fabric according to the present invention (n=1, 3, or 5) due to the metal-organic framework coating. In particular, it was confirmed that the stability tended to further improve with increasing number of repetitions (n=1, 3, 5).

[0082] The foregoing description of this invention is provided for illustrative purposes only, and those skilled in the art will understand that the invention can be readily modified into other specific forms without departing from its technical spirit or essential characteristics. Therefore, the above embodiments should be understood in all respects as illustrative and not restrictive.

Claims

1. A lithium metal electrode with suppressed dendrite formation, comprising: current collector; A metal-organic framework coated on the current collector, the metal-organic framework comprising lithium-philic metal ions and organic linkers; and Lithium metal plated on the metal-organic framework.

2. The lithium metal electrode with suppressed dendrite formation according to claim 1, wherein, The lithiophilic metal ion is selected from the group consisting of silver, gold, magnesium, zinc, and copper.

3. The lithium metal electrode with suppressed dendrite formation according to claim 1, wherein, The organic linker includes one or more compounds containing thiol groups.

4. The lithium metal electrode with suppressed dendrite formation according to claim 3, wherein, The one or more thiol-containing compounds are trithiocyanic acid (TCA).

5. The lithium metal electrode with suppressed dendrite formation according to claim 1, wherein, Within the metal-organic framework, the lithium-philic metal ions and the organic linkers are repeatedly stacked via coordination covalent bonds.

6. The lithium metal electrode with suppressed dendrite formation according to claim 1, wherein, The thickness of the metal-organic framework is from 1 nm to 100 nm.

7. The lithium metal electrode with suppressed dendrite formation according to claim 1, wherein, The metal-organic framework has a contact angle of 30° or less relative to the electrolyte, which comprises a mixed solvent of 1,3-dioxolane (DOL) and dimethoxyethane (DME) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

8. A method for manufacturing a lithium metal electrode with suppressed dendrite formation, the method comprising the following steps: (a) Coating the current collector with a metal-organic framework containing lithium-philic metal ions and organic linkers; and (b) Plate lithium metal onto a coated metal-organic framework.

9. A secondary battery comprising a lithium metal electrode with dendrite formation suppressed according to claim 1.

10. The secondary battery according to claim 9, wherein, During operation of the secondary battery, the lithium metal electrode forms a solid electrolyte interface (SEI) layer comprising Li2S or Li3N.

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