Lithium metal negative electrode protective film, lithium metal negative electrode and manufacturing method thereof, and lithium metal battery

Abstract

A lithium metal anode protective film according to one specific embodiment includes lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, or a combination thereof. The lithium metal negative electrode protective film can effectively inhibit the growth of lithium dendrites in the battery charging / discharging process by inducing the uniform electro-deposition behavior and distribution of lithium ions.

Description

Technical Field

[0001] The present invention relates to a lithium metal negative electrode protective film, a lithium metal negative electrode, a manufacturing method thereof, and a lithium metal battery. Background Art

[0002] Attention is continuously increasing for electric vehicles (EVs) such as those based on fossil fuel vehicles, which are one of the main causes of air pollution, and recently, lithium secondary batteries, which mainly serve as a power source for electric vehicles (EVs) with high discharge voltage and power stability, are being actively developed.

[0003] In addition, recently, lithium metal, which has a relatively high capacity (3860 mAh / g) and a low redox potential (-3.04 V vs. SHE), has received attention as one of the promising negative electrode materials, and research is being conducted on lithium metal batteries including such lithium metal anodes (Lithium Metal Anode, LMA). Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] An object of one aspect of the present invention is to suppress the growth of lithium dendrites by inducing uniform electrodeposition of lithium.

[0006] Another object of the present invention is to provide a lithium metal negative electrode protective film that can improve the electrochemical performance of a battery.

[0007] Another object of the present invention is to form, by an in-situ reaction on the surface of a lithium metal layer, a substance formed to protect the surface of the lithium metal layer.

[0008] Another object of the present invention is to prevent the unnecessary formation of a separate substance for stabilizing the lithium metal layer.

[0009] (II) Technical Solutions

[0010] The lithium metal negative electrode protective film according to a specific embodiment includes lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, or a combination thereof.

[0011] The lithium metal negative electrode protective film may further include magnesium nitride (Mg3N2) nanoparticles.

[0012] The diameter of the magnesium nitride (Mg3N2) nanoparticles may be larger than the diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles.

[0013] The lithium metal negative electrode protective film may further include lithium fluoride (LiF).

[0014] The lithium metal negative electrode protective film may further comprise a fluorine (F)-containing polymer.

[0015] The fluorine (F)-containing polymer may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), or a combination thereof.

[0016] The lithium metal negative electrode protective film may further comprise magnesium nitride (Mg3N2) nanoparticles and a fluorine (F)-containing polymer, and the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the lithium metal negative electrode protective film may be greater than the weight of the fluorine (F)-containing polymer contained in the lithium metal negative electrode protective film.

[0017] The diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles may each independently be 1-200 nm.

[0018] The diameter of the magnesium nitride (Mg3N2) nanoparticles may be 1-200 nm.

[0019] The thickness of the lithium metal negative electrode protective film may be 500 nm to 10 μm.

[0020] The lithium metal negative electrode according to a specific embodiment includes the lithium metal negative electrode protective film described in any one of the above specific embodiments.

[0021] The manufacturing method of the lithium metal negative electrode according to a specific embodiment includes the following steps: preparing a solution containing magnesium nitride (Mg3N2) nanoparticles; and forming a lithium metal negative electrode protective film on at least one surface of the lithium metal layer by using the solution.

[0022] The solution may further comprise a fluorine (F)-containing polymer.

[0023] The fluorine (F)-containing polymer may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), or a combination thereof.

[0024] The solution may further comprise magnesium nitride (Mg3N2) nanoparticles and a fluorine (F)-containing polymer, and the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the solution may be greater than the weight of the fluorine (F)-containing polymer contained in the solution.

[0025] The lithium metal battery according to a specific embodiment includes the lithium metal negative electrode described in any one of the above specific embodiments.

[0026] (III) Beneficial effects

[0027] According to a specific embodiment of the present invention, a uniform electro-deposition behavior and distribution of lithium ions can be induced.

[0028] According to another specific embodiment of the present invention, the growth of lithium dendrites during battery charging / discharging can be effectively suppressed.

[0029] According to another specific embodiment of the present invention, the performance of a lithium metal battery can be improved.

[0030] According to another specific embodiment of the present invention, a substance formed to protect the surface of the lithium metal layer can be formed through an in-situ reaction on the surface of the lithium metal layer.

[0031] According to another specific embodiment of the present invention, the unnecessary formation of a separate substance for stabilizing the lithium metal layer can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic cross-sectional view showing a lithium metal negative electrode according to a specific embodiment.

[0033] Figure 2a is a diagram showing a scanning electron microscope (SEM) analysis image and an energy dispersive spectroscopy (EDS) analysis image of the surface of a protective film on a negative electrode according to an example.

[0034] Figure 2b is a diagram showing a scanning electron microscope (SEM) analysis image and an energy dispersive spectroscopy (EDS) analysis image of the surface of a protective film on a negative electrode according to Comparative Example 1.

[0035] Figure 3a is a diagram showing a scanning electron microscope (SEM) analysis image and an energy dispersive spectroscopy (EDS) analysis image of the surface of a protective film after electro-deposition in a lithium metal battery including a negative electrode according to an example.

[0036] Figure 3b and Figure 3c is a diagram showing the results of observing a scanning electron microscope (SEM) observation image and an analysis image according to energy dispersive spectroscopy (EDS) at different analysis positions on the surface of a negative electrode protective film, where the surface of the negative electrode protective film is a surface of a negative electrode protective film on which lithium is electro-deposited by charging a lithium metal battery including a negative electrode according to Comparative Example 1.

[0037] DESCRIPTION OF REFERENCE NUMERALS:

[0038] 10: Lithium metal layer

[0039] 20: Protective film

[0040] 100: Lithium metal anode Detailed implementation manners

[0041] Hereinafter, with reference to various implementation manners, preferred implementation manners will be described. However, the implementation manners are not limited to the specific implementation manners described below, and can be modified into various other implementation manners.

[0042] Hereinafter, in this specification, when describing that a part such as a layer, a film, a thin film, a region, a plate, etc. is "above" or "on" another part, unless otherwise specifically defined, this includes not only the case of being "directly" above another part, but also the case of having other parts in between.

[0043] In the case of the above lithium metal anode, the following problems may occur: Due to the high reactivity of lithium metal, continuous side reactions with the electrolyte occur, thereby forming an unstable thin film and showing poor life characteristics. In particular, the dendritic crystals of lithium, so-called dendrites, generated during battery charging / discharging significantly reduce the life efficiency of the battery and cause a sudden internal short circuit, which may lead to fire and explosion.

[0044] In response to this, according to a specific implementation manner, as a method of forming a separate protective film on the surface of lithium metal, a protective film manufactured by an ex-situ reaction outside the battery cell can be formed on the surface of lithium metal. However, the protective film manufactured as described above has the characteristic of being unstable in the electrochemical reaction occurring inside during the driving process of the battery cell, and there may be a problem of forming a separate unnecessary substance to stabilize lithium metal.

[0045] When lithium metal is applied as the anode as described above, it may be difficult to ensure the life characteristics and stability of the battery due to problems such as the formation of lithium dendrites.

[0046] The protective film of the lithium metal anode according to a specific implementation manner contains lithium-containing particles of nanometer size, so that it can have excellent ionic conductivity and electrochemical stability, and can induce a uniform electrodeposition behavior of lithium ions. See Figures 1 to 3c , and the specific content will be disclosed below.

[0047] Figure 1 is a schematic diagram showing a cross section of a lithium metal anode according to a specific implementation manner.

[0048] Figure 2a is a diagram showing a scanning electron microscope (SEM) analysis image and an energy dispersive spectroscopy (EDS) analysis image of the surface of the protective film on the anode according to an embodiment.

[0049] Figure 2bIt is a diagram showing a scanning electron microscope (SEM) analysis image and an energy-dispersive spectrometry (EDS) analysis image of the surface of the protective film on the negative electrode according to Comparative Example 1.

[0050] Figure 3a It is a diagram showing a scanning electron microscope (SEM) analysis image and an energy-dispersive spectrometry (EDS) analysis image of the surface of the protective film after electrodeposition in a lithium metal battery including a negative electrode according to an embodiment.

[0051] Figure 3b and Figure 3c It is a diagram showing the results of observing a scanning electron microscope (SEM) observation image and an analysis image according to energy-dispersive spectrometry (EDS) at different analysis positions on the surface of the negative electrode protective film, where the surface of the negative electrode protective film is a surface of a negative electrode protective film on which lithium is electrodeposited by charging a lithium metal battery including a negative electrode according to Comparative Example 1.

[0052] Lithium metal negative electrode protective film

[0053] The protective film 20 of a lithium metal negative electrode according to a specific embodiment contains lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, or a combination thereof.

[0054] As described above, the protective film 20 of the lithium metal negative electrode contains lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, or a combination thereof as lithium-containing nanoparticles of nanoscale size, so that it can have excellent ionic conductivity and electrochemical stability, and can induce uniform electrodeposition of lithium ions. The lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles can be formed on the surface of the lithium metal layer during the charge / discharge process of the battery by an electrochemical reaction, and the protective film 20 of the lithium metal negative electrode contains lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, or a combination thereof formed by such a reaction. Hereinafter, the lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles will be described in more detail.

[0055] When a separate protective film 20 is formed on the surface of the lithium metal layer 10 of the lithium metal negative electrode, lithium ions participating in the electrochemical reaction must additionally pass through the separate protective film, so the resistance may increase. In this regard, when the protective film 20 of the lithium metal negative electrode contains lithium nitride (Li3N) nanoparticles as a lithium-containing compound having very excellent ionic conductivity, electrochemical stability, etc., the increase in resistance caused by the protective film can be effectively alleviated, and electrochemical stability can be ensured.

[0056] In addition, the lithium-magnesium (Li-Mg) alloy nanoparticles are a material in the form of an alloy formed by the reaction of magnesium (Mg), which corresponds to a lithio-philic metal, with lithium ions. The lithio-philic metal can act as a seed that reduces the lithium nucleation barrier through an electrochemical reaction with lithium ions. Therefore, the lithium-magnesium (Li-Mg) alloy nanoparticles can reduce the nucleation polarization overpotential during the electrodeposition of lithium ions, thereby inducing a uniform electrodeposition behavior of lithium ions. Therefore, when the protective film 20 of the lithium metal negative electrode contains the lithium-magnesium (Li-Mg) alloy nanoparticles, a uniform electrodeposition behavior of lithium ions can be induced, thereby effectively suppressing the growth of lithium dendrites and effectively preventing problems such as a decrease in irreversible capacity and internal short circuit of the battery.

[0057] The protective film 20 of the lithium metal negative electrode may contain only the above-mentioned lithium nitride (Li3N) nanoparticles, may contain only lithium-magnesium (Li-Mg) alloy nanoparticles, or may contain both lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles.

[0058] Both the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles are lithium-containing particles of nanoscale size. The diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles can be independently 1-200 nm. Exemplarily, the diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles can be independently 200 nm or less, 150 nm or less, or 100 nm or less, and can be 1 nm or more or 10 nm or more.

[0059] When the sizes of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles are as large as the micron scale or more, the thickness of the protective film 20 containing one or more of them becomes too thick, so there may be limitations in terms of improving the energy density of the negative electrode, and it is not easy to occur an electrochemical reaction, so it may be difficult to form a uniform protective film. In addition, when the sizes of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles are too small, it is difficult to remain in the form of a single particle, so the effect of improving the performance of the protective film may not be substantially obtained. Therefore, when the sizes of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles are adjusted as described above, a protective film with excellent performance can be uniformly formed with an appropriate thickness, so the energy density, stability, etc. of the negative electrode can be effectively improved.

[0060] The protective film 20 of the lithium metal anode may further include magnesium nitride (Mg3N2) nanoparticles. The magnesium nitride (Mg3N2) nanoparticles are materials that can be used in manufacturing the protective film 20. During the electrochemical reaction that occurs during the operation of the battery cell, the magnesium nitride (Mg3N2) nanoparticles can be converted into the above-mentioned lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles. That is, in the protective film 20 of the lithium metal anode according to one specific embodiment, not all of the magnesium nitride (Mg3N2) nanoparticles are converted into lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles during the electrochemical reaction, but rather they exist in the protective film 20. On the other hand, in the protective film 20 of the lithium metal anode according to another specific embodiment, the magnesium nitride (Mg3N2) nanoparticles can be completely converted into lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles, such that the magnesium nitride (Mg3N2) nanoparticles are substantially absent from the protective film 20.

[0061] The magnesium nitride (Mg3N2) nanoparticles are also nanoparticles of nanoscale size. The diameter of the magnesium nitride (Mg3N2) nanoparticles can be 1 - 200 nm. Exemplarily, the diameter of the magnesium nitride (Mg3N2) nanoparticles can be 200 nm or less, 150 nm or less, or 100 nm or less, and can be 1 nm or more or 10 nm or more.

[0062] As described above, when forming the protective film 20 of the lithium metal anode, the materials that substantially contribute to the stabilization of the lithium metal, etc. are the lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles converted from the magnesium nitride (Mg3N2) nanoparticles. When the size of the magnesium nitride (Mg3N2) nanoparticles is as large as micron size or more, the conversion reaction into lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles is not likely to occur easily. Therefore, an uneven protective film may be formed, and it may not make a substantial contribution to improving the performance of the protective film.

[0063] In addition, when the size of the magnesium nitride (Mg3N2) nanoparticles is too small, the effect of improving the performance of the protective film may not be substantially obtained thereby. Therefore, when adjusting the size of the magnesium nitride (Mg3N2) nanoparticles as described above, the conversion reaction into lithium nitride (Li3N) nanoparticles or lithium-magnesium (Li-Mg) alloy nanoparticles is likely to occur easily, thereby effectively improving the performance of the protective film containing the magnesium nitride (Mg3N2) nanoparticles.

[0064] The diameter of the magnesium nitride (Mg3N2) nanoparticles can be greater than the diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles. Specifically, within the range where the magnesium nitride (Mg3N2) nanoparticles, the lithium nitride (Li3N) nanoparticles, and the lithium-magnesium (Li-Mg) alloy nanoparticles each satisfy the above diameter conditions, the diameter of the magnesium nitride (Mg3N2) nanoparticles can be greater than the diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles. In this case, the magnesium nitride (Mg3N2) nanoparticles can act as a stable substance without additional side reactions, so the protective film can have more excellent stability.

[0065] The protective film 20 of the lithium metal anode can further contain lithium fluoride (LiF). The lithium fluoride (LiF) is a lithium-containing compound with excellent mechanical strength, etc. When the protective film 20 contains the lithium fluoride (LiF), the mechanical strength of the protective film can be further improved. The lithium fluoride (LiF) can be formed from a fluorine (F)-containing polymer. Specifically, the fluorine (F) contained in the polymer can combine with lithium ions through an electrochemical reaction occurring during the driving process of the battery cell to form lithium fluoride (LiF). The fluorine (F)-containing polymer can act as an adhesive when manufacturing the protective film 20 of the lithium metal anode. According to a specific embodiment, the fluorine (F)-containing polymer can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), or a combination thereof.

[0066] According to another specific embodiment, the fluorine (F)-containing polymer can be a semi-crystalline structure that simultaneously contains a crystallized part and a partially amorphous part. The fluorine (F)-containing polymer is a copolymer formed by copolymerizing two or more monomers each containing fluorine (F), and can be a copolymer containing a crystallized structural unit and an amorphous structural unit. Exemplarily, the fluorine (F)-containing polymer can contain polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP). Among them, the copolymer can be an alternating copolymer, a block copolymer, a random copolymer, a graft copolymer, a crosslinked copolymer, or a combination of all of them.

[0067] Although not bound by a specific theory, the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) is a copolymer with a semi-crystalline structure that simultaneously contains a crystallized part (PVDF) and a partially amorphous part (HFP). When the protective film of the lithium metal anode contains the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), the mechanical strength of the protective film can be ensured through the crystallized part, and the lithium ion conductivity can be further improved through the amorphous part.

[0068] The protective film 20 of the lithium metal anode may further include a fluorine (F)-containing polymer. The fluorine (F) contained in the fluorine (F)-containing polymer may react with lithium ions during the electrochemical reaction that occurs during the driving of the battery cell to form lithium fluoride (LiF). In the protective film 20 of the lithium metal anode, the fluorine (F)-containing polymer may form lithium fluoride (LiF) during the electrochemical reaction, and the fluorine (F)-containing polymer may exist as it is in the protective film 20 of the lithium metal anode. Exemplarily, the fluorine (F)-containing polymer may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), or a combination thereof.

[0069] The protective film 20 of the lithium metal anode may simultaneously include magnesium nitride (Mg3N2) nanoparticles and a fluorine (F)-containing polymer. According to a specific embodiment, the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the protective film 20 of the lithium metal anode may be greater than the weight of the fluorine (F)-containing polymer contained in the protective film of the lithium metal anode.

[0070] The thickness of the protective film 20 of the lithium metal anode may be 10 μm or less. In addition, the thickness of the protective film 20 of the lithium metal anode may be 500 nm or more. Exemplarily, the thickness of the protective film 20 of the lithium metal anode may be 6 μm or less or 2 μm or less, and may be 1 μm or more. The thinner the thickness of the protective film 20 of the lithium metal anode, the more the energy density of the anode can be further improved. However, when the thickness of the protective film 20 of the lithium metal anode is too thin, the mechanical strength decreases, and it may not substantially contribute to improving the anode performance by forming the protective film. Therefore, when the thickness of the protective film is adjusted within the above range, the energy density of the anode can be improved to an excellent level within the range that does not affect the mechanical strength of the protective film, etc.

[0071] Lithium Metal Anode and Method for Manufacturing the Same

[0072] The lithium metal anode 100 according to a specific embodiment includes the protective film 20 of the lithium metal anode according to any one of the above specific embodiments. Specifically, the lithium metal anode 100 may include: a lithium metal layer 10; and a protective film 20 of the lithium metal anode, the protective film 20 of the lithium metal anode being formed on at least one surface of the lithium metal layer. The detailed description of the protective film 20 of the lithium metal anode is repeated with the above content, and thus the description is omitted.

[0073] The lithium metal layer 10 may comprise lithium metal or an alloy thereof, and may be a metal layer consisting essentially of only lithium metal. The thickness of the lithium metal layer 10 is not particularly limited. Exemplarily, the thickness of the lithium metal layer 10 may be 1 - 200 μm.

[0074] The lithium metal negative electrode 100 may optionally further include a separate negative electrode current collector. Specifically, according to one specific embodiment, the lithium metal negative electrode 100 may be a structure that does not include a separate negative electrode current collector, and may be a structure including a lithium foil that includes a lithium metal layer in a free-standing form. According to another specific embodiment, the lithium metal negative electrode 100 may be a structure that further includes a separate negative electrode current collector, and may include: a negative electrode current collector; a lithium metal layer 10 formed on at least one surface of the negative electrode current collector; and a protective film 20 of the lithium metal negative electrode formed on one surface of the lithium metal layer.

[0075] The negative electrode current collector is a current collector having appropriate and excellent electrical conductivity and adhesion to the lithium metal layer, etc. The type, thickness, etc. of the negative electrode current collector are not particularly limited. Exemplarily, the negative electrode current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foam nickel, a foam copper, a polymer substrate coated with a conductive metal, or a combination thereof, and the negative electrode current collector may have a thickness of 10 - 100 μm.

[0076] The lithium metal negative electrode 100 may be manufactured by the method for manufacturing a negative electrode described below.

[0077] The method for manufacturing a lithium metal negative electrode according to one specific embodiment includes the following steps: preparing a solution containing magnesium nitride (Mg3N2) nanoparticles; and forming a protective film 20 of the lithium metal negative electrode on at least one surface of the lithium metal layer 10 using the solution.

[0078] In the method for manufacturing the lithium metal negative electrode, the substance formed to protect the surface of the lithium metal layer 10 may be formed by an in-situ reaction on the surface of the lithium metal layer, thereby further improving the electrochemical stability of the protective film and preventing the unnecessary formation of a separate substance for stabilizing the lithium metal layer.

[0079] The magnesium nitride (Mg3N2) nanoparticles are materials that can be converted into lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles through the electrochemical reactions occurring during the battery cell driving process. The manufacturing method of the lithium metal anode can shorten the process time and reduce costs through a solution process using a solution containing nanoscale magnesium nitride (Mg3N2) nanoparticles, and can manufacture a lithium metal anode including a protective film with excellent performance with high productivity. Detailed descriptions of the magnesium nitride (Mg3N2) nanoparticles, lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles, etc. are repeated in the above content, so the description is omitted here.

[0080] The solution can be prepared by adding magnesium nitride (Mg3N2) nanoparticles to an organic solvent. At this time, the type of the organic solvent is not particularly limited as long as it does not substantially react with lithium metal and magnesium nitride (Mg3N2) and can appropriately dissolve substances used as binders (exemplarily, fluorine (F)-containing polymers, etc.). Exemplarily, the organic solvent can be at least one selected from tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and acetonitrile.

[0081] The step of preparing the solution may further include a step of ultrasonically treating the organic solvent added with magnesium nitride (Mg3N2) nanoparticles. When the step of preparing the solution further includes a step of ultrasonically treating the organic solvent added with magnesium nitride (Mg3N2) nanoparticles, the magnesium nitride (Mg3N2) nanoparticles can be more uniformly dispersed in the organic solvent. The ultrasonication can be carried out for 10 minutes to 100 minutes. Specifically, the ultrasonication can be carried out for 20 minutes to 60 minutes.

[0082] The solution may further contain a fluorine (F)-containing polymer. The fluorine (F)-containing polymer can form lithium fluoride (LiF) with excellent mechanical strength, etc. Specifically, the fluorine (F) contained in the polymer can combine with lithium ions through the electrochemical reactions occurring during the battery cell driving process to form lithium fluoride (LiF). Therefore, when the solution further contains a fluorine (F)-containing polymer, a protective film 20 of the lithium metal anode with further improved mechanical strength, etc. can be manufactured.

[0083] When the solution further contains a fluorine (F)-containing polymer, the order of adding the magnesium nitride (Mg3N2) nanoparticles and the fluorine (F)-containing polymer is not particularly limited, and the two components can also be added simultaneously. Exemplarily, the step of preparing the solution may include the following steps: adding magnesium nitride (Mg3N2) nanoparticles with a diameter of 500 nm or less to an organic solvent to prepare a first solution; and adding a fluorine (F)-containing polymer to the first solution to prepare a second solution. The method for manufacturing the lithium metal negative electrode may form a protective film on at least one surface of the lithium metal layer 10 using the second solution prepared as described above.

[0084] The step of preparing the first solution may further include a step of ultrasonically treating the organic solvent added with magnesium nitride (Mg3N2) nanoparticles, and the step of preparing the second solution may further include a step of stirring after ultrasonically treating the first solution added with a fluorine (F)-containing polymer. In this case, the magnesium nitride (Mg3N2) nanoparticles and the fluorine (F)-containing polymer can be more uniformly dispersed in the organic solvent. The ultrasonication can be performed for 10 minutes to 100 minutes. Specifically, the ultrasonication can be performed for 20 minutes to 60 minutes, and the stirring process can be performed for 12 hours to 48 hours.

[0085] The fluorine (F)-containing polymer may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), or a combination thereof. A detailed description of the fluorine (F)-containing polymer is repeated with the above content, and thus the description is omitted.

[0086] The solution may contain magnesium nitride (Mg3N2) nanoparticles and a fluorine (F)-containing polymer simultaneously. According to a specific embodiment, the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the solution may be greater than the weight of the fluorine (F)-containing polymer contained in the solution. Exemplarily, the weight ratio of the magnesium nitride (Mg3N2) nanoparticles and the fluorine (F)-containing polymer contained in the solution may be 1:1 to 10:1 or 1.5:1 to 4:1. When the weight ratio of the magnesium nitride (Mg3N2) nanoparticles and the fluorine (F)-containing polymer contained in the solution is as described above, a lithium metal negative electrode including a protective film having excellent performance can be manufactured, wherein the protective film is a protective film that appropriately contains at least any one of lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles and lithium fluoride (LiF).

[0087] The step of forming the protective film 20 of the lithium metal negative electrode on at least one surface of the lithium metal layer 10 using the solution may be carried out by a process of coating the solution on at least one surface of the lithium metal layer and then drying.

[0088] The coating process is not particularly limited. Exemplarily, it can be carried out by methods such as doctor blade coating, dip coating, bar coating, casting, etc.

[0089] The drying process can be carried out at 10 - 50 °C. Specifically, the drying process can be carried out at room temperature (20 - 25 °C), and the drying process can be carried out for 12 hours to 48 hours.

[0090] Lithium metal battery

[0091] The lithium metal battery according to a specific embodiment includes the lithium metal negative electrode described in any one of the above specific embodiments. Specifically, the lithium metal battery can include the lithium metal negative electrode 100, a positive electrode, and an electrolyte described in any one of the above specific embodiments, and can further include a separator or not include a separator according to choice.

[0092] The positive electrode is not particularly limited as long as it is a positive electrode commonly used in secondary batteries. The positive electrode active material can include lithium-transition metal oxides. For example, it can include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2) and other lithium-transition metal oxides, or lithium-transition metal composite oxides in which a part of these transition metals is replaced by other transition metals. Specifically, the positive electrode active material can be an NCM-based positive electrode active material represented by the following Chemical Formula 1; or an LLO (Li rich layered oxides, LLOs, Over Lithiated Oxides, Over-lithiated layered oxide, OLO)-based positive electrode active material represented by the following Chemical Formula 2.

[0093] [Chemical Formula 1]

[0094] Li a Ni b M 1-b O2

[0095] In Chemical Formula 1, 0.9 ≤ a ≤ 1.2, b ≥ 0.5, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0096] Specifically, in Formula 1, 0.95 ≤ a ≤ 1.08, and b can be 0.6 or more, 0.8 or more, more than 0.8, 0.9 or more, or 0.98 or more.

[0097] Specifically, in Formula 1, M can include Co, Mn, or Al. More specifically, M can include Co and Mn, and can further include Al according to selection.

[0098] [Formula 2]

[0099] Li 1+x M 1-x O2

[0100] In Formula 2, 0 ≤ x ≤ 0.4, and M is at least one of Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0101] Specifically, in Formula 2, M can include Ni, Co, Mn, or Al. More specifically, M can include Ni, Co, and Mn, and can further include Al according to selection.

[0102] In addition, the positive electrode active material can also be a lithium iron phosphate (LFP)-based positive electrode active material represented by the chemical formula LiFePO4.

[0103] In addition, the lithium-transition metal oxide can also be a secondary particle formed by assembling or aggregating a plurality of primary particles and substantially forming one particle, and can also be in the form of a single particle. The form of a single particle can, for example, exclude the meaning of a secondary particle formed by assembling or aggregating a plurality of primary particles (e.g., more than 10). However, the form of a single particle does not exclude the case where single particles in the range of 2 - 10 are attached or adhered to each other to have an integral form. In some embodiments, the positive electrode active material can also include both the secondary particle form and the single particle form at the same time.

[0104] The lithium metal battery can further include a separator or not include a separator. When the lithium metal battery further includes a separator, the separator is not particularly limited as long as it is a separator applicable to a conventional lithium secondary battery. Exemplarily, the separator can include a porous substrate, and the porous substrate can be a polyolefin-based porous substrate. The polyolefin-based porous substrate can be a substrate having a large number of pores and commonly used in electrochemical devices. The polyolefin-based porous substrate can be exemplarily selected from a polyethylene single layer film, a polypropylene single layer film, a polyethylene / polypropylene bilayer film, a polypropylene / polyethylene / polypropylene trilayer film, and a polyethylene / polypropylene / polyethylene trilayer film, but is not limited thereto.

[0105] The lithium metal battery may be in a form that is housed together with an electrolyte in a separate case. At this time, the electrolyte may be a liquid electrolyte containing a lithium salt and an organic solvent, and the lithium salt may be represented by the chemical formula Li + X - wherein the anion (X - ) may include F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - and the like, and is not limited thereto. In addition, the organic solvent may exemplarily include one or more of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), and is not limited thereto.

[0106] In addition, the lithium metal battery may be an all-solid-state battery including the lithium metal negative electrode 100, the positive electrode, and a solid electrolyte layer located between the negative electrode and the positive electrode described in any one of the above specific embodiments.

[0107] The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and may include at least one of conventional solid electrolytes. Exemplarily, the solid electrolyte may be an oxide-based solid electrolyte such as Li7La3Zr2O 12 (LLZO); a sulfide-based solid electrolyte such as thio-lithium superionic conductor (Thio-LISICON), β-Li3PS4, Li7P3S 11 , Li2S-P2S5, LGPS, and argyrodite-based compounds; or a polymer-based solid electrolyte such as (1) a solid polymer electrolyte formed by adding a polymer resin such as a polyether-based polymer to a lithium salt, and (2) a polymer gel electrolyte obtained by impregnating a polymer resin with an organic electrolyte solution containing an organic solvent and a lithium salt.

[0108] The argyrodite-based compound may be represented by the following Chemical Formula 3.

[0109] [Chemical Formula 3]

[0110] Li + a A + b Q c X - d

[0111] In the chemical formula 3, 1 ≤ a ≤ 12, 0 ≤ b ≤ 5, 0 ≤ c ≤ 10, 0 ≤ d ≤ 2, A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, Q is at least one of S, Se or Te, and X is at least one of Cl, Br, I, F, CN, OCN, SCN or N3.

[0112] Specifically, the argyrodite-based compound may be a compound represented by the chemical formula Li 7-x PS 6-x Cl x (0 ≤ x ≤ 2), Li 7- x PS 6-x Br x (0 ≤ x ≤ 2) or Li 7-x PS 6-x I x (0 ≤ x ≤ 2).

[0113] More specifically, the argyrodite-based compound may be a compound represented by the chemical formula Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 6.5 Sb 0.5 Ge 0.5 S5I, Li 5.7 PS 4.7 Cl 1.3 、Li 6.6 Sb 0.5 Si 0.6 S5I, etc.

[0114] When the lithium metal battery includes the above lithium metal negative electrode 100, the protective film 20 that can induce uniform lithium electro-deposition behavior can effectively inhibit the growth of lithium dendrites, so the life characteristics, electrochemical performance, safety, etc. can all be excellent.

[0115] Examples

[0116] 1. Lithium metal negative electrode protective film

[0117] 1) Example

[0118] 30 mg of nano-sized (diameter: 100 nm) magnesium nitride (Mg3N2) powder was added to 0.5 ml of tetrahydrofuran (THF) as an organic solvent, and then ultrasonic treatment was carried out for 30 minutes using an ultrasonic disperser to obtain a first solution in which the magnesium nitride powder was uniformly dispersed in the organic solvent.

[0119] Thereafter, 15 mg of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) as a fluorine (F)-containing polymer was added to the first solution, and ultrasonic treatment was performed for 30 minutes using an ultrasonic disperser to uniformly disperse the components in the solution, and then stirred for 24 hours to obtain a second solution.

[0120] Using the doctor blade method, the second solution was coated on the surface of the lithium metal layer (thickness: 20 μm), and dried for 24 hours under vacuum conditions and at room temperature to obtain the lithium metal negative electrode of the example. A protective film with a thickness of about 2 μm was formed on the surface of the lithium metal layer in the lithium metal negative electrode of the example.

[0121] In this regard, Figure 2a The left image of is the scanning electron microscope (SEM) analysis image of the surface of the protective film on the negative electrode according to the example. Figure 2a The middle image of is the magnesium (Mg) element distribution (Mg Kα) image according to energy dispersive spectroscopy (EDS) of the surface of the protective film on the negative electrode according to the example. Figure 2a The right image of is the nitrogen (N) element (N Kα) distribution image according to energy dispersive spectroscopy (EDS) of the surface of the protective film on the negative electrode according to the example.

[0122] See Figure 2a , it can be confirmed that a protective film of the example containing magnesium nitride (Mg3N2) nanoparticles was formed.

[0123] 2) Comparative Example 1

[0124] The lithium metal negative electrode of Comparative Example 1 was manufactured by the same method as in the example, except that magnesium nitride (Mg3N2) powder with a micron size (diameter: over 45 μm) was applied as the magnesium nitride (Mg3N2) powder.

[0125] In this regard, Figure 2b The left image of is the scanning electron microscope (SEM) analysis image of the surface of the protective film on the negative electrode according to Comparative Example 1. Figure 2b The middle image of is the magnesium (Mg) element distribution (Mg Kα) image according to energy dispersive spectroscopy (EDS) of the surface of the protective film on the negative electrode according to Comparative Example 1. Figure 2b The right image of is the nitrogen (N) element (N Kα) distribution image according to energy dispersive spectroscopy (EDS) of the surface of the protective film on the negative electrode according to Comparative Example 1.

[0126] See Figure 2b , it can be confirmed that a protective film of Comparative Example 1 containing magnesium nitride (Mg3N2) micron particles was formed.

[0127] 3) Comparative Example 2

[0128] As the lithium metal negative electrode of Comparative Example 2, a negative electrode in which a separate protective film was not formed on the surface of the lithium metal layer (thickness: 20 μm) was used.

[0129] 2. Lithium metal battery

[0130] Lithium metal batteries according to the examples and comparative examples were manufactured using Li / NCM cells, wherein the Li / NCM cells included the negative electrodes and positive electrodes prepared as described above, and the positive electrodes contained NCM-based active materials and had an areal capacity of 3 mAh / cm 2 of.

[0131] 3. Evaluation of capacity retention rate

[0132] At room temperature, the lithium metal batteries prepared as described above were repeatedly cycled 50 times with charging at 0.5C and discharging at 0.5C within the range of state of charge (SOC) 0 - 100%, and the capacity retention rate according to the number of cycles (discharge capacity at the 50th cycle / initial discharge capacity) was measured as a percentage (%) and the results are shown in Table 1 below.

[0133] The lithium metal batteries were charged to deposit lithium on the negative electrodes, and then scanning electron microscope (SEM) analysis images and energy dispersive spectroscopy (EDS) analysis images of the surfaces of the protective films according to the examples and Comparative Example 1 were observed and are shown respectively in Figures 3a to 3c respectively.

[0134] In Table 1 below, "O" indicates the presence of a protective film, and "X" indicates the absence of a protective film.

[0135] [Table 1]

[0136]

[0137] See Figure 3a , upon analysis, in the negative electrode according to the example, lithium (Li) was electrodeposited around the nanosized magnesium nitride (Mg3N2) nanoparticles contained in the protective film, and thus lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles formed by the reaction of the magnesium nitride (Mg3N2) nanoparticles contained in the protective film with lithium (Li) were included in the protective film.

[0138] On the other hand, see Figure 3b and Figure 3c , in the negative electrode according to Comparative Example 1, magnesium (Mg) was not detected at the position where lithium (Li) was electrodeposited. That is, upon analysis, lithium (Li) was not electrodeposited around the micron-sized magnesium nitride (Mg3N2) particles, and thus the magnesium nitride (Mg3N2) particles did not react with lithium (Li) and remained as they were.

[0139] In addition, referring to Table 1, the negative electrode of the example in which a protective film containing nano-sized magnesium nitride (Mg3N2) nanoparticles is formed not only exhibits excellent capacity retention compared to the negative electrode of Comparative Example 2 in which no protective film is formed, but also exhibits excellent capacity retention compared to the negative electrode of Comparative Example 1 in which a protective film containing micron-sized magnesium nitride (Mg3N2) particles is formed.

[0140] Referring to the above results, it is judged that the protective film formed using micron-sized magnesium nitride (Mg3N2) particles cannot function properly as a protective film, and it is judged that in the case of a protective film formed using nano-sized magnesium nitride (Mg3N2) nanoparticles as in the example, uniform lithium electrodeposition is induced, thereby suppressing the growth of lithium dendrites and effectively improving the electrochemical performance, efficiency, and safety of the battery.

Claims

1. A lithium metal negative electrode protective film comprising lithium nitride (Li3N) nanoparticles, lithium-magnesium (Li-Mg) alloy nanoparticles or a combination thereof.

2. The lithium metal negative electrode protective film according to claim 1, wherein: The lithium metal negative electrode protection film further comprises magnesium nitride (Mg3N2) nanoparticles.

3. The lithium metal negative electrode protective film according to claim 2, wherein: The diameter of the magnesium nitride (Mg3N2) nanoparticles is greater than that of lithium nitride (Li3N) nanoparticles and lithium-magnesium (Li-Mg) alloy nanoparticles.

4. The lithium metal negative electrode protective film according to claim 1, wherein: The lithium metal negative electrode protection film further comprises lithium fluoride (LiF).

5. The lithium metal negative electrode protective film according to claim 1, wherein: The lithium metal negative electrode protection film further comprises a fluorine (F)-containing polymer.

6. The lithium metal negative electrode protective film according to claim 5, wherein: The fluorine (F)-containing polymer is polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer or a combination thereof.

7. The lithium metal negative electrode protective film according to claim 1, wherein: The lithium metal negative electrode protection film further comprises magnesium nitride (Mg3N2) nanoparticles and fluorine (F)-containing polymers, and the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the lithium metal negative electrode protection film is greater than the weight of the fluorine (F)-containing polymer contained in the lithium metal negative electrode protection film.

8. The lithium metal negative electrode protective film according to claim 1, wherein: The diameters of the lithium nitride (Li3N) nanoparticles and the lithium-magnesium (Li-Mg) alloy nanoparticles are each independently 1-200 nm.

9. The lithium metal negative electrode protective film according to claim 2, wherein: The diameter of the magnesium nitride (Mg3N2) nanoparticles is 1-200 nm.

10. The lithium metal negative electrode protective film according to claim 1, wherein: The thickness of the lithium metal negative electrode protection film is 500nm to 10μm. 11 . A lithium metal negative electrode, comprising the lithium metal negative electrode protective film according to any one of claims 1 to 10.

12. A method for manufacturing a lithium metal negative electrode, comprising the following steps: preparing a solution comprising magnesium nitride (Mg3N2) nanoparticles; and The solution is used to form a lithium metal negative electrode protection film on at least one side of the lithium metal layer.

13. The method for producing a lithium metal negative electrode according to claim 12, wherein: The solution further comprises a fluorine (F)-containing polymer.

14. The method for producing a lithium metal negative electrode according to claim 13, wherein: The fluorine (F)-containing polymer is polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer or a combination thereof.

15. The method for manufacturing a lithium metal negative electrode according to claim 12, wherein: The solution further comprises magnesium nitride (Mg3N2) nanoparticles and a fluorine (F)-containing polymer, and the weight of the magnesium nitride (Mg3N2) nanoparticles contained in the solution is greater than the weight of the fluorine (F)-containing polymer contained in the solution.

16. A lithium metal battery comprising the lithium metal negative electrode according to claim 11.

Images