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

Abstract

A lithium metal negative electrode protective film (20) according to one embodiment includes a polymer containing fluorine (F), and the crystallinity of the lithium metal negative electrode protective film is 2% or more. According to one embodiment, it is possible to provide a lithium metal negative electrode protective film which induces a uniform electrodeposition behavior and distribution of lithium ions and which has excellent ionic conductivity and mechanical strength, and a lithium metal negative electrode including the lithium metal negative electrode protective film.

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] Interest in electric vehicles (EVs) that can replace fossil fuel-based vehicles, one of the main causes of air pollution, continues to increase, and in recent years, lithium secondary batteries that have high charging voltage and power stability and are mainly used as power sources for electric vehicles (EVs) are being actively developed.

[0003] In addition, in recent years, lithium metal, which has a relatively high capacity (3860 mAh / g) and a low redox potential (-3.04 V vs. SHE), has attracted much attention as one of the promising negative electrode materials, and research on lithium metal batteries including such lithium metal anodes (Lithium Metal Anode; LMA) is also underway.

[0004] However, when lithium metal is used as the negative electrode, its high reactivity leads to continuous side reactions with the electrolyte, resulting in unstable thin films and poor battery life. In particular, dendrites, the formation of lithium dendrites during battery charge and discharge, not only significantly reduces battery life but also causes sudden internal short circuits, potentially leading to fires and explosions. Therefore, a technology to effectively control these problems is needed. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] The purpose of a specific embodiment is to provide a lithium metal negative electrode protective film, a lithium metal negative electrode and a manufacturing method thereof, wherein the lithium metal negative electrode protective film can inhibit the growth of lithium dendrites by inducing uniform lithium electrodeposition, and can effectively improve the electrochemical performance, efficiency, safety, etc. of the battery.

[0007] Another embodiment aims to provide a lithium metal battery including a lithium metal negative electrode having excellent electrochemical performance, lifespan characteristics, safety, etc.

[0008] (2) Technical solution

[0009] According to a specific embodiment, a lithium metal negative electrode protection film includes a polymer containing fluorine (F), and the lithium metal negative electrode protection film has a crystallinity of 2% or more.

[0010] The polymer may include at least any one selected from polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP).

[0011] Based on the total weight of the lithium metal negative electrode protective film, the content of the polymer may be 5-30 wt %.

[0012] The crystallinity of the lithium metal negative electrode protection film may be 70% or less.

[0013] The lithium metal negative electrode protection film may further include a lithium salt containing fluorine (F).

[0014] The lithium salt may include at least any one selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoride (LiF), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3) and lithium hexafluoroarsenate (LiAsF6).

[0015] Based on the total weight of the lithium metal negative electrode protective film, the content of the lithium salt may be 5-30 wt %.

[0016] The thickness of the lithium metal negative electrode protective film can be 0.1-20 μm.

[0017] According to a specific embodiment, a lithium metal negative electrode includes the lithium metal negative electrode protection film described in any one of the above specific embodiments and a lithium metal layer, wherein the lithium metal negative electrode protection film is formed on at least one side of the lithium metal layer.

[0018] According to a specific embodiment, the manufacturing method of the lithium metal negative electrode includes the following steps: step S1, applying a composition for a lithium metal negative electrode protective film on at least one side of a lithium metal layer; and step S2, drying the applied composition for a lithium metal negative electrode protective film; wherein the composition for a lithium metal negative electrode protective film contains a polymer containing fluorine (F).

[0019] The composition for a lithium metal negative electrode protective film may further include an organic solvent.

[0020] The organic solvent may include a cyclic ether-based solvent.

[0021] In the step S2, the drying temperature may be 10-50°C.

[0022] A lithium metal battery according to one embodiment includes the lithium metal negative electrode described in any one of the above embodiments.

[0023] (3) Beneficial effects

[0024] According to a specific embodiment, a lithium metal negative electrode protection film that induces uniform electrodeposition behavior and distribution of lithium ions and has excellent ionic conductivity and mechanical strength, and a lithium metal negative electrode including the lithium metal negative electrode protection film can be provided.

[0025] According to another specific embodiment, when a protective film is formed on the surface of the lithium metal layer, a one-pot reaction can be performed by a solution process using the composition, and process time and cost can be reduced, thereby manufacturing a lithium metal negative electrode with high productivity.

[0026] According to another specific embodiment, a lithium metal negative electrode can be provided, which includes a protective film that can effectively inhibit the growth of lithium dendrites by inducing uniform distribution and reversible electrodeposition / desorption behavior of lithium ions during electrochemical reactions, and can improve the life characteristics and electrochemical performance of a lithium metal battery including the lithium metal negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1a is a conceptual diagram illustrating a cross section of a lithium metal anode according to one specific embodiment.

[0028] Figure 1b is a conceptual diagram illustrating a cross section of a lithium metal anode according to another specific embodiment.

[0029] Figure 2 Graphs showing overvoltage evaluation results according to time (number of cycles) of lithium metal batteries including lithium metal negative electrodes according to Comparative Examples and Examples. Best Practice

[0030] Hereinafter, preferred embodiments will be described with reference to various embodiments. However, the embodiments are not limited to the specific embodiments described below, but can be modified into various other forms.

[0031] Hereinafter, in this specification, unless otherwise specifically defined, when describing a layer, membrane, film, region, plate or the like as being “above” or “on” another part, this may include not only the case where it is “directly” “above” the other part, but also the case where there is another part in between.

[0032] As mentioned above, research is underway on using lithium metal, which has relatively high capacity and low redox potential characteristics, as the negative electrode. However, due to problems such as the formation of lithium dendrites, it is difficult to ensure the life characteristics and stability of the battery.

[0033] According to a specific embodiment, a lithium metal negative electrode can be provided, in which a protective film that can induce uniform electrodeposition behavior and distribution of lithium ions is formed on the surface of the lithium metal layer, thereby effectively suppressing the occurrence of the above-mentioned problems and improving the ion conductivity and life characteristics of a lithium metal battery including the negative electrode as described above. Figures 1a to 2 , and make the specific content public.

[0034] Figure 1a is a conceptual diagram illustrating a cross section of a lithium metal anode according to one specific embodiment.

[0035] Figure 1b is a conceptual diagram illustrating a cross section of a lithium metal anode according to another specific embodiment.

[0036] Figure 2 Graphs showing overvoltage evaluation results according to time (number of cycles) of lithium metal batteries including lithium metal negative electrodes according to Comparative Examples and Examples.

[0037] Lithium metal anode protective film

[0038] The lithium metal negative electrode protection film 20 according to one embodiment includes a polymer containing fluorine (F), and the crystallinity of the lithium metal negative electrode protection film is 2% or more.

[0039] The lithium metal negative electrode protection film 20 is a protection film containing a polymer containing fluorine (F) and having a certain level of crystallinity or higher. The lithium metal negative electrode protection film 20 can induce uniform electrodeposition behavior and distribution of lithium ions and can have excellent ionic conductivity and mechanical strength.

[0040] The polymer contains fluorine (F). Specifically, the polymer can be a fluorine-rich (F-Rich) organic polymer containing a large amount of fluorine (F). When the lithium metal negative electrode protective film 20 contains the above-mentioned polymer, a thin film containing a large amount of fluorine (F) (fluorine-rich SEI) can be formed inside or on the surface of the protective film during the battery charge / discharge process. The fluorine-rich SEI can induce a uniform distribution of lithium ions during the electrochemical reaction and inhibit the growth of lithium dendrites, thereby further improving the performance of the lithium battery.

[0041] The polymer can be a semi-crystalline structure comprising a crystalline portion and a partially amorphous portion, and the polymer can include at least any one selected from polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP). Specifically, the polymer can include a copolymer formed by copolymerizing two or more monomers containing fluorine (F), more specifically, the polymer can be a copolymer comprising a crystalline structural unit and an amorphous structural unit. For example, the polymer can include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP). Wherein, the copolymer can include an alternating polymer, a block copolymer, a random copolymer, a graft copolymer, a cross-linked copolymer, or all of the above copolymers.

[0042] Although not bound by a particular theory, the PVDF-co-HFP is a copolymer having a semi-crystalline structure comprising both a crystalline portion (PVDF) and a partially amorphous portion (HFP). When the lithium metal negative electrode protective film comprises the PVDF-co-HFP, an excellent level of mechanical strength can be ensured by the crystalline portion, and lithium ion conductivity can be improved by the amorphous portion.

[0043] The polymer content may be 5-30 wt % based on the total weight of the lithium metal negative electrode protection film 20. Specifically, the polymer content may be 7 wt % or 9 wt % or more, and 20 wt % or 15 wt % or less, based on the total weight of the lithium metal negative electrode protection film 20.

[0044] When the polymer content is too low, it is difficult to form a fluorine-rich SEI, thus limiting the substantial benefits of the polymer addition. When the polymer content is too high, the viscosity of the polymer solution increases, and when the polymer solution is applied to the lithium surface, the thickness of the protective film may increase. This may increase the resistance during lithium migration, leading to increased overvoltage during battery charge / discharge and reduced battery performance. Therefore, by appropriately adjusting the polymer content within the above range, while maintaining the viscosity of the polymer solution within a range that does not excessively increase, the ionic conductivity and mechanical strength of the protective film can be improved.

[0045] According to a specific embodiment, the lithium metal negative electrode protective film 20 includes a polymer having the above-mentioned properties. By controlling the crystallinity of the protective film to an appropriate level, properties such as mechanical strength and ionic conductivity can be more effectively improved. The crystallinity of the protective film is described in detail below.

[0046] The crystallinity of the lithium metal negative electrode protective film 20 refers to the crystallinity of the protective film itself, which can be measured using differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), wide-angle X-ray scattering analysis (SAXS), etc. Specifically, the crystallinity value can be a value calculated by performing XRD analysis on the lithium metal negative electrode protective film 20 according to the following formula 1.

[0047] [Formula 1]

[0048] Crystallinity (%) = (Ac × 100) / At

[0049] In the above formula 1, Ac is the peak area of the region showing crystallinity in XRD analysis, and At is the total peak area in XRD analysis.

[0050] The XRD analysis can be performed according to the following conditions.

[0051] - Measurement method: After placing the measurement object in the sample holder, perform spectrum analysis at 0° to 90°.

[0052] - Measurement equipment: XRD analyzer (Empyrean)

[0053] - X-ray Source Anode: Cu

[0054] - Generator Voltage: 45kV, Tube Current: 40mA

[0055] - Incidence Beam: BBHD

[0056] - Divergence Slit: 1 / 4°

[0057] - Anti-scatter slit: 1°

[0058] - Detector: Pixel Detector

[0059] - Sample Stage: Reflection Transmission Spinner

[0060] - Use Zero Background Holder

[0061] The lithium metal negative electrode protection film 20 has a crystallinity of 2% or more. In this case, the crystallinity of the lithium metal negative electrode protection film 20 may be 70% or less. Specifically, the crystallinity of the lithium metal negative electrode protection film 20 may be 5% or more, 10% or more, or 20% or more, and may be 60% or less, 40% or less, or 30% or less.

[0062] When the crystallinity of the lithium metal negative electrode protective film 20 is too low, the mechanical strength of the protective film is insufficient, which may substantially limit the ability to suppress the growth of lithium dendrites. When the crystallinity of the lithium metal negative electrode protective film 20 is too high, resistance is generated during the movement of lithium ions, which may lead to a decrease in ionic conductivity, etc. Therefore, when the crystallinity of the lithium metal negative electrode protective film 20 is adjusted to the above-mentioned appropriate range, mechanical strength can be ensured, thereby effectively suppressing the growth of lithium dendrites, while also improving the lithium ion conductivity to an excellent level.

[0063] The lithium metal negative electrode protective film 20 may further include a lithium salt. Specifically, the lithium metal negative electrode protective film 20 may further include a lithium salt containing fluorine (F). The lithium salt is not particularly limited as long as it is an inorganic salt containing lithium (Li) and fluorine (F). However, the lithium salt may include at least one selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoride (LiF), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium hexafluoroarsenate (LiAsF6).

[0064] When the lithium metal negative electrode protection film 20 further includes a lithium salt containing fluorine (F), a thin film (fluorine-rich SEI) containing a large amount of fluorine (F) can be more effectively formed inside or on the surface of the finally manufactured lithium metal negative electrode protection film.

[0065] When the lithium metal negative electrode protection film 20 further includes a lithium salt, the content of the lithium salt may be 5-30% by weight based on the total weight of the lithium metal negative electrode protection film. Specifically, the content of the lithium salt may be 7% by weight or more or 9% by weight or more, and may be 20% by weight or less or 15% by weight or less, based on the total weight of the lithium metal negative electrode protection film.

[0066] The lithium metal negative electrode protective film 20 may further include lithium-philic inorganic particles. The lithium-philic inorganic particles are inorganic particles containing lithium-philic metals, which can be prepared by dissolving metals in nitric acid, i.e., inorganic nitrates (NO3 -) in the protective film. Lithiophilic refers to an affinity for lithium. When a substance with a low affinity for lithium coexists with lithium, lithium metal will selectively be deposited first. On the other hand, a lithiophilic substance with a high affinity for lithium reduces the initial nucleation resistance of the lithium electrodeposition reaction, thereby inducing uniform electrodeposition of lithium metal, thereby suppressing the growth of lithium dendrites.

[0067] The lithiophilic metal is a metal having a lithiophilic property, such as silver (Ag), gold (Au), zinc (Zn), or magnesium (Mg). The lithiophilic metal undergoes an electrochemical reaction with lithium, acting as a seed that reduces the lithium nucleation barrier, and the lithiophilic metal forms an alloy with lithium ions, thereby inducing uniform electrodeposition of lithium ions. Exemplarily, the lithiophilic metal can be Au, Ag, Pt, Al, Mg, Zn, Ni, Te, Bi, Pb, Ga, Cd, Hg, Pd, Sc, Y, Ca, Sr, Ba, Ni, Sn, Cu, Ge, or a combination thereof.

[0068] Therefore, when the lithium metal negative electrode protection film 20 further contains a lithium-philic metal, the growth of lithium dendrites during the battery charge / discharge process can be more effectively inhibited, thereby effectively preventing the occurrence of problems such as irreversible capacity loss and internal short circuit of the battery.

[0069] In addition, when the lithium metal negative electrode protective film 20 further includes lithium-philic inorganic particles in the form of inorganic nitrates, a thin film containing a large amount of nitrogen (N) (nitrogen-rich (N-Rich) SEI) can be formed inside or on the surface of the protective film, thereby further improving lithium ion conductivity and mechanical strength.

[0070] When the lithium metal negative electrode protection film 20 further comprises lithium-philic inorganic particles, the content of the lithium-philic inorganic particles may be 4-17 wt %, specifically 5-15 wt %, based on the total weight of the lithium metal negative electrode protection film.

[0071] The lithium metal negative electrode protective film 20 may include lithium fluoride (LiF). Lithium fluoride (LiF) is an inorganic compound formed by the reaction of fluorine elements in the lithium metal negative electrode protective film 20 with lithium ions during the battery charge / discharge process. Lithium fluoride (LiF) can further improve the uniform electrodeposition characteristics and mechanical strength of lithium metal during battery charge / discharge. Therefore, when the lithium metal negative electrode protective film 20 includes lithium fluoride (LiF), the mechanical strength, lifespan characteristics, electrochemical performance, ionic conductivity, etc. of the lithium metal negative electrode 100 can be further improved.

[0072] The thickness of the lithium metal negative electrode protective film 20 may be 0.1-20 μm. Specifically, the thickness of the lithium metal negative electrode protective film 20 may be 15 μm or less or 10 μm or less. When the thickness of the lithium metal negative electrode protective film 20 is within the above range, the mechanical strength and electrochemical performance of the lithium metal negative electrode can be significantly improved.

[0073] Hereinafter, the lithium metal negative electrode 100 including the lithium metal negative electrode protection film 20 will be described in detail.

[0074] Lithium metal anode

[0075] According to a specific embodiment, a lithium metal negative electrode 100 includes the lithium metal negative electrode protection film 20 described in any one of the above specific embodiments and a lithium metal layer 10 , wherein the lithium metal negative electrode protection film 20 is formed on at least one side of the lithium metal layer 10 .

[0076] The lithium metal negative electrode 100 includes a lithium metal negative electrode protective film 20 located on at least one side of the lithium metal layer 10. The lithium metal negative electrode protective film 20 can effectively suppress the growth of lithium dendrites by inducing uniform lithium electrodeposition. A detailed description of the lithium metal negative electrode protective film 20 is omitted as it overlaps with the above description.

[0077] The lithium metal layer 10 includes lithium metal or its alloy, and may be a metal layer consisting essentially of lithium metal. The thickness of the lithium metal layer 10 is not particularly limited. For example, the thickness of the lithium metal layer 10 may be 1-200 μm.

[0078] The lithium metal negative electrode 100 may further include an intermediate layer 30 located between the lithium metal layer 10 and the lithium metal negative electrode protection film 20 (see Figure 1b The intermediate layer 30 may be formed during the manufacturing process of the lithium metal negative electrode 100 including the lithium metal layer 10 and the lithium metal negative electrode protective film 20, or may be formed during the charge / discharge process of a lithium metal battery including the lithium metal negative electrode 100. The intermediate layer 30 may induce uniform electrodeposition of lithium ions between the lithium metal layer 10 and the lithium metal negative electrode protective film 20, and may improve the mechanical strength of the lithium metal negative electrode 100.

[0079] The intermediate layer 30 may include lithium fluoride (LiF) and may have a thickness of 0.5-1 μm.

[0080] The lithium metal negative electrode 100 can be manufactured by the following negative electrode manufacturing method.

[0081] Negative electrode manufacturing method

[0082] According to a specific embodiment, a method for manufacturing a lithium metal negative electrode 100 includes the following steps: step S1, applying a lithium metal negative electrode protective film composition on at least one side of a lithium metal layer; and step S2, drying the applied lithium metal negative electrode protective film composition; wherein the lithium metal negative electrode protective film composition contains a polymer containing fluorine (F).

[0083] Existing methods for manufacturing lithium metal anodes include (1) deposition methods such as atomic layer deposition (ALD) and pulsed laser deposition (PLD), and (2) photopolymerization methods such as irradiating a coated polymer solution with ultraviolet light. However, deposition methods require separate equipment and have limitations in reducing process costs and time, making it difficult to ensure productivity. Photopolymerization methods require raw materials such as photopolymerizers and photoinitiators, as well as a separate light irradiation device, resulting in increased costs.

[0084] On the other hand, when using the manufacturing method of the lithium metal negative electrode according to a specific embodiment, when a protective film is formed on the surface of the lithium metal layer, a one-pot reaction can be carried out by utilizing a solution process of the composition, and the process time and cost can be reduced, so that the lithium metal negative electrode can be manufactured with high productivity.

[0085] The lithium metal negative electrode protective film composition may further include a fluorine (F)-containing lithium salt in addition to a fluorine (F)-containing polymer. Detailed descriptions of the fluorine (F)-containing polymer, lithium salt, etc. are omitted because they overlap with the above description.

[0086] The lithium metal negative electrode protective film composition may further include an organic solvent, and the organic solvent may include a cyclic ether-based solvent. The cyclic ether-based solvent may include a cyclic ether-based solvent that is not a dioxolane, methyldioxolane, dimethyldioxolane, vinyldioxolane, methoxydioxolane, ethylmethyldioxolane, or other dioxolane-based solvents. Specifically, the cyclic ether-based solvent may include at least one selected from dioxane, trioxane, tetrahydrofuran, methyltetrahydrofuran, dimethyltetrahydrofuran, dimethoxytetrahydrofuran, ethoxytetrahydrofuran, and tetrahydropyran, more specifically, the cyclic ether-based solvent may include tetrahydrofuran (THF).

[0087] When the composition for a lithium metal negative electrode protective film further comprises an organic solvent, illustratively, the content of the organic solvent in the composition may be 50-99 wt % or 60-90 wt %.

[0088] The lithium metal negative electrode protective film composition can be prepared by adding a fluorine (F)-containing polymer to the above-mentioned organic solvent and stirring the solution at room temperature for 3-48 hours. At this time, the stirring speed (RPM) can be 100-400 RPM.

[0089] When the lithium metal negative electrode protective film composition further comprises a lithium salt, the lithium metal negative electrode protective film composition can be prepared by adding a fluorine (F)-containing polymer to an organic solvent to prepare a first solution, adding the lithium salt to the first solution to prepare a second solution, and stirring the second solution at room temperature for 3-24 hours. In this case, the stirring speed (RPM) can be 100-400 RPM.

[0090] The step S1 of coating the lithium metal negative electrode protective film composition on at least one side of the lithium metal layer can be performed by methods such as doctor blade coating, dip coating, bar coating, and casting, but is not limited thereto.

[0091] In the S2 step of drying the applied lithium metal negative electrode protective film composition, the drying temperature may be 10-50°C. Specifically, in the S2 step, the drying temperature may be room temperature (20-25°C). In the existing manufacturing method, since the temperature of the drying process is carried out in a relatively high temperature region (above 100°C), additional heat treatment process costs are incurred, and there is a problem that operational safety issues may occur due to high temperatures. Therefore, in the manufacturing method of a lithium metal negative electrode according to a specific embodiment, when the drying temperature of the S2 step is within the above range, the convenience, economy, safety, etc. of the process may be relatively excellent.

[0092] lithium metal batteries

[0093] A lithium metal battery according to one embodiment includes the lithium metal negative electrode 100 described in any one of the above embodiments. Specifically, the lithium metal battery may include the lithium metal negative electrode 100 described in any one of the above embodiments, a positive electrode, and an electrolyte, and may optionally further include or exclude a separator.

[0094] The positive electrode is not particularly limited as long as it is a positive electrode commonly used in secondary batteries. The positive electrode may contain a lithium-transition metal oxide as a positive electrode active material. For example, it may contain a lithium-transition metal oxide such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4) or lithium nickel oxide (LiNiO2), or a lithium-transition metal composite oxide in which a portion of these transition metals is replaced by other transition metals. Specifically, the positive electrode active material may be an NCM-based positive electrode active material represented by the following chemical formula 1; or an LLO (Li rich layered oxides, over-lithiated oxides, over-lithiated layered oxides, OLO, LLOs)-based positive electrode active material represented by the following chemical formula 2.

[0095] [Chemical Formula 1]

[0096] Li a Ni b M 1-b O2

[0097] In Chemical Formula 1, 0.9≤a≤1.2, b≥0.5, and M is at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0098] Specifically, in Chemical Formula 1, 0.95≤a≤1.08, and b may be 0.6 or greater, 0.8 or greater, more than 0.8, 0.9 or greater, or 0.98 or greater.

[0099] Specifically, in Chemical Formula 1, M may include Co, Mn, or Al. More specifically, M may include Co and Mn, and may optionally further include Al.

[0100] [Chemical Formula 2]

[0101] Li 1+x M 1-x O2

[0102] In the chemical formula 2, 0≤x≤0.4, and M is at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0103] Specifically, in Chemical Formula 2, M may include Ni, Co, Mn, or Al. More specifically, M may include Ni, Co, and Mn, and may optionally further include Al.

[0104] In addition, the positive electrode active material may also be a lithium iron phosphate (LFP)-based positive electrode active material represented by the chemical formula LiFePO 4 .

[0105] In addition, the lithium-transition metal oxide can be a secondary particle in which a plurality of primary particles are combined or aggregated to form a particle, or can be a single particle form. The single particle form can mean, for example, a secondary particle in which a plurality of primary particles (for example, more than 10) are combined or aggregated to form a particle. However, the single particle form does not exclude the situation in which single particles in the range of 2-10 are attached to each other or closely adhered to each other and have an overall form. In some embodiments, the positive active material can include both a secondary particle form and a single particle form.

[0106] The lithium metal battery may further include a diaphragm or may not include a diaphragm. When the lithium metal battery further includes a diaphragm, the diaphragm is not particularly limited as long as it is a diaphragm applicable to conventional lithium secondary batteries. Exemplarily, the diaphragm may include a porous substrate, and the porous substrate may be a polyolefin-based porous substrate. The polyolefin-based porous substrate may be a substrate having multiple pores and commonly used in electrochemical devices. Exemplarily, the polyolefin-based porous substrate may be selected from a polyethylene monolayer film, a polypropylene monolayer film, a polyethylene / polypropylene double-layer film, a polypropylene / polyethylene / polypropylene three-layer film, and a polyethylene / polypropylene / polyethylene three-layer film, but is not limited thereto.

[0107] The lithium metal battery may be in a form housed in a separate housing together with an electrolyte. In this case, 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 - Indicates that as anion (X - ), which may include F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 -In addition, illustratively, the organic solvent may include one or more of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), etc., but is not limited thereto.

[0108] In addition, the lithium metal battery may be an all-solid-state battery including the lithium metal negative electrode 100 described in any one of the above specific embodiments, a positive electrode, and a solid electrolyte layer located between the negative electrode and the positive electrode.

[0109] The solid electrolyte contained in the solid electrolyte layer is not particularly limited and may include at least one of conventional solid electrolytes. For example, the solid electrolyte may be Li7La3Zr2O 12 (LLZO) and other oxide-based solid electrolytes; lithium-sulfur superion conductors (Thio-LISICON), β-Li3PS4, Li7P3S 11 , Li2S-P2S5, LGPS, argyrodite-based compounds and other sulfide-based solid electrolytes; or (1) solid polymer electrolytes formed by adding polymer resins such as polyether-based polymers to lithium salts, (2) polymer-based solid electrolytes such as polymer gel electrolytes in which an organic electrolyte containing an organic solvent and a lithium salt is impregnated into a polymer resin.

[0110] The argyrodite-based compound may be represented by the following Chemical Formula 3.

[0111] [Chemical Formula 3]

[0112] Li- + a A + b Q c X -d

[0113] 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.

[0114] Specifically, the argyrodite-based compound may be a compound of the chemical formula Li 7-x PS 6-x Cl x (0≤x≤2), Li 7- x PS 6-x Brx (0≤x≤2) or Li 7-x PS 6-x I x A compound represented by (0≤x≤2).

[0115] More specifically, the argyrodite-based compound may be a compound of 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 or Li 6.6 Sb 0.5 Si 0.6 Compound represented by S5I.

[0116] When the lithium metal battery includes the above-mentioned lithium metal negative electrode 100, the growth of lithium dendrites can be effectively suppressed by the lithium metal negative electrode protective film 20 that can induce uniform lithium electrodeposition behavior, thereby having excellent life characteristics, electrochemical performance, safety, etc. DETAILED DESCRIPTION

[0117] Example

[0118] 1. Lithium metal anode protective film and lithium metal anode

[0119] 1) Manufacturing of protective film and negative electrode

[0120] (1) Example 1

[0121] A solution of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) powder with a crystallinity of 32.4% in tetrahydrofuran (THF) as an organic solvent was stirred at room temperature for 12 to 24 hours to prepare the protective film composition of Example 1 in which PVDF-co-HFP was well dispersed. The PVDF-co-HFP content was 10% by weight based on the total solution.

[0122] Using a dip coating method, the protective film composition is coated on the surface of the lithium metal layer (thickness: 100 μm) with a thickness of 10 μm, and then dried at room temperature for more than 30 minutes to obtain the lithium metal negative electrode of Example 1 having a protective film formed on the lithium metal layer.

[0123] (2) Example 2

[0124] To the protective film composition of Example 1, lithium bis(fluorosulfonyl)imide (LiFSI) was further added as a lithium salt, and stirred at room temperature for 3 to 24 hours to obtain a protective film composition of Example 2 in which the content ratio of LiFSI in the solution was the same as that of PVDF-co-HFP (weight ratio = 1:1). Except for this, the lithium metal negative electrode of Example 2 was manufactured by the same method as Example 1. At this time, the contents of PVDF-co-HFP and LiFSI in the protective film composition were both 9.09% by weight.

[0125] (3) Comparative Example 1

[0126] Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) was added to N-methyl-2-pyrrolidone (NMP) as an organic solvent to obtain a protective film composition, wherein the content of PVDF-co-HFP was 1% by weight based on the entire solution. The protective film composition was coated on the surface of the lithium metal layer and dried at 90°C for 1 hour. Except for this, the lithium metal negative electrode of Comparative Example 1 was manufactured by the same method as Example 1.

[0127] (4) Comparative Example 2

[0128] 0.031 g of lithium fluoride and 1.5 g of lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in 0.75 g of acetone to prepare a first solution, and 0.5 g of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) was dissolved in N,N-dimethylformamide (1.75 g) and stirred at 40 ° C to prepare a second solution. Thereafter, the solution formed by mixing the first solution and the second solution was stirred at 40 ° C to prepare a protective film composition, which was applied to the surface of the lithium metal layer and dried for more than 12 hours after heating to 120 ° C. In addition, the lithium metal negative electrode of Comparative Example 2 was manufactured by the same method as Example 1.

[0129] (5) Comparative Example 3

[0130] To a mixture containing polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP) and ethoxylated trimethylolpropane triacrylate (ETPTA) in a ratio of 1:3 (0.5 g and 1.5 g, respectively) and containing about 0.7 wt % (0.015 g) of 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), a solution 1.5 times the mass of the mixture, which is a dioxolane (DOL) / dimethoxyethane (DME) solution containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt % of lithium nitrate (LiNO 3 ), was added, to prepare a composition for a protective film as a photopolymerization precursor solution.

[0131] Using a doctor blade coating method, the photopolymerization precursor solution was coated on the surface of the lithium metal layer with a thickness of 30 μm, and then irradiated with light with a wavelength in the ultraviolet region (365 nm) for 20 seconds to photocure the photopolymerization precursor solution to form a gel polymer layer on the surface of the lithium metal layer, thereby preparing the lithium metal negative electrode of Comparative Example 3 including the gel polymer layer as a protective film.

[0132] (6) Comparative Example 4

[0133] As the lithium metal negative electrode of Comparative Example 4, a negative electrode in which a separate lithium metal negative electrode protection film was not formed on the surface of the lithium metal layer (thickness: 100 μm) was used.

[0134] 2) Evaluation of protective film (crystallinity)

[0135] For the lithium metal negative electrodes of Examples and Comparative Examples prepared as described above, the crystallinity of the protective film formed on the lithium metal layer was measured (except for Comparative Example 4 which did not include a protective film).

[0136] At this time, the crystallinity value of the protective film was analyzed using an XRD analyzer (Empyrean) according to the following conditions and method, and then the crystallinity value of the protective film was calculated according to the following formula 1. The results are shown in the following Table 1.

[0137] [Formula 1]

[0138] Crystallinity (%) = (Ac × 100) / At

[0139] In the above formula 1, Ac is the peak area of the region showing crystallinity in XRD analysis, and At is the total peak area in XRD analysis.

[0140] - Measurement method: After placing the measurement object in the sample holder, perform spectrum analysis at 0° to 90°.

[0141] - X-ray source cathode: Cu

[0142] - Generator voltage: 45kV, tube current: 40mA

[0143] - Incident beam: BBHD

[0144] - Divergence slit: 1 / 4°

[0145] - Anti-scatter slit: 1°

[0146] - Detector: Pixel detector

[0147] - Sample stage: reflection and transmission rotator

[0148] - Use a zero-background sample holder

[0149] 2. Lithium Metal Batteries

[0150] 1) Battery Manufacturing

[0151] A 2032 coin-type lithium metal symmetrical battery of each embodiment and comparative example was manufactured, wherein the lithium metal symmetrical battery comprises: a negative electrode prepared as described above; a polyolefin-based separator coated on a ceramic-based inorganic material; and 1.0 M LiPF6 - An electrolyte solution of EC / EMC (3 / 7, volume %) + 2 wt % FEC was used. At this time, a protective film was applied only to the lithium electrode corresponding to the working electrode. In Comparative Example 4, the negative electrode and battery were manufactured without applying a separate protective film.

[0152] 2) Battery evaluation

[0153] At room temperature, the 2032 coin-type lithium metal symmetrical battery prepared as described above was evaluated for overvoltage according to the number of cycles. The evaluation conditions used were a current density of 1 mA / cm 2 、Deposition amount 2mAh / cm 2 The overvoltage level generated by the lithium oxidation / reduction reaction of the battery at a limited capacity and current density is measured over time, and the battery's life characteristics based on the number of cycles are evaluated.

[0154] Specifically, the time and number of cycles at which the overvoltage (1) rose to a value close to 0.1V or (2) fell to a value close to 0V were measured, and the corresponding time point was determined to be the end-of-life time point of the battery. The number of cycles until the end-of-life time point was measured for each battery, and the results are shown in Table 1 below.

[0155] [Table 1]

[0156]

[0157] See Table 1 and Figure 2 The batteries of Comparative Examples 1 to 3 in which an amorphous protective film with a crystallinity of 0% (crystallinity less than 2%) is formed on the lithium metal layer, and the battery of Comparative Example 4 in which no protective film is formed on the lithium metal layer, all exhibit an end-of-life time point of less than 100 cycles (i.e., the number of cycles at which the overvoltage sharply rises to 0.1 V or sharply drops to 0 V). On the other hand, the batteries of Example 1 and Example 2 in which a protective film with a crystallinity of more than 2% is formed on the lithium metal layer, respectively, exhibit an end-of-life time point of more than 150 cycles, showing better life characteristics than those of Comparative Examples 1 to 3.

[0158] Taking the above results into consideration, it is judged that depending on the manufacturing method of the negative electrode including the lithium metal negative electrode protective film, the crystallinity of the protective film may vary. In the case of a protective film that is essentially amorphous due to low crystallinity, there are substantial limitations in improving the life characteristics of the lithium metal negative electrode and the lithium metal battery including the lithium metal negative electrode.

[0159] On the other hand, as shown in Examples 1 and 2, when a protective film containing a polymer containing fluorine (F) and having a crystallinity of 2% or more is formed on the lithium metal layer, it is judged that the life characteristics of the lithium metal negative electrode and the lithium metal battery including the lithium metal negative electrode can be excellently improved. In addition, as shown in Example 2, when the protective film further contains a lithium salt containing fluorine (F), it is judged that the life characteristics of the lithium metal battery can be further improved.

[0160] The embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto, and it is obvious to those skilled in the art that various modifications and variations can be made without departing from the technical concept of the present invention described in the claims.

[0161] [Explanation of Reference Signs]

[0162] 10: Lithium metal layer

[0163] 20: Protective film

[0164] 30: Middle layer

[0165] 100: Lithium metal anode

[0166] Industrial Applicability

[0167] As described above, the features of the present invention can be applied in whole or in part to a lithium metal negative electrode protective film, a lithium metal negative electrode, a method for manufacturing the same, and a lithium metal battery.

Claims

1. A lithium metal negative electrode protective film, comprising a polymer containing fluorine (F), wherein the crystallinity of the lithium metal negative electrode protective film is greater than 2%.

2. The lithium metal negative electrode protective film according to claim 1, wherein The polymer includes at least any one selected from polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP).

3. The lithium metal negative electrode protective film according to claim 1, wherein Based on the total weight of the lithium metal negative electrode protective film, the content of the polymer is 5-30% by weight.

4. The lithium metal negative electrode protective film according to claim 1, wherein The crystallinity of the lithium metal negative electrode protection film is less than 70%.

5. The lithium metal negative electrode protective film according to claim 1, wherein The lithium metal negative electrode protection film further includes a lithium salt containing fluorine (F).

6. The lithium metal negative electrode protective film according to claim 5, wherein The lithium salt comprises at least any one selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoride (LiF), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3) and lithium hexafluoroarsenate (LiAsF6).

7. The lithium metal negative electrode protective film according to claim 5, wherein Based on the total weight of the lithium metal negative electrode protective film, the content of the lithium salt is 5-30% by weight.

8. The lithium metal negative electrode protective film according to claim 1, wherein The thickness of the lithium metal negative electrode protective film is 0.1-20 μm.

9. A lithium metal negative electrode comprising: The lithium metal negative electrode protective film according to any one of claims 1 to 8; as well as Lithium metal layer, Wherein, the lithium metal negative electrode protection film is formed on at least one side of the lithium metal layer.

10. A method for manufacturing a lithium metal negative electrode, comprising the following steps: Step S1, coating the lithium metal negative electrode protective film composition on at least one side of the lithium metal layer; as well as Step S2, drying the coated lithium metal negative electrode protective film composition; The lithium metal negative electrode protective film composition includes a polymer containing fluorine (F).

11. The method for manufacturing a lithium metal negative electrode according to claim 10, wherein: The composition for a lithium metal negative electrode protective film further comprises an organic solvent, and the organic solvent comprises a cyclic ether-based solvent.

12. The method for manufacturing a lithium metal negative electrode according to claim 10, wherein: In the step S2, the drying temperature is 10-50°C.

13. A lithium metal battery comprising the lithium metal negative electrode according to claim 9.

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