Lithium metal negative electrode, method for producing the same, and lithium metal battery including the same

Abstract

According to one embodiment, a lithium metal negative electrode includes a lithium metal layer and a protective layer formed on at least one surface of the lithium metal layer, the protective layer including lithium-affinity inorganic particles, and a peak intensity (PTE) of 1750 to 1880 cm during FT-IR analysis of the protective layer. -1 At least one peak appears in the region of The lithium metal anode has excellent ionic conductivity and mechanical strength, includes a protective layer capable of inducing uniform lithium electrodeposition behavior, and can effectively inhibit the growth of lithium dendrites, thereby providing a lithium metal battery with excellent cycle life, capacity characteristics, safety, etc. during electrodeposition / desorption.

Description

[Technical Field]

[0001] The present disclosure relates to lithium metal negative electrodes, methods for making same, and lithium metal batteries including same. [Background technology]

[0002] There has been a steady increase in interest in electric vehicles (EVs) that can replace fossil fuel-based vehicles, which are one of the main causes of air pollution. Recently, there has been active development of lithium secondary batteries, which have high charging voltage and output stability and are mainly used as a power source for electric vehicles (EVs).

[0003] Meanwhile, lithium metal, which has a relatively high capacity (3860 mAh / g) and a low redox potential (-3.04 V vs. SHE), has recently attracted attention as a promising anode material, and research into lithium metal batteries containing such a lithium metal anode (LMA) is also underway.

[0004] However, when lithium metal is used as the anode, it is difficult to ensure the cycle characteristics and stability of the battery due to problems such as (1) low coulombic efficiency during charge / discharge caused by the high reactivity of lithium metal with the electrolyte, and (2) formation of lithium dendrites. Therefore, a technology to effectively control these problems is required. Summary of the Invention [Problem to be solved by the invention]

[0005] The objective of one embodiment is to provide a lithium metal anode that can induce uniform lithium electrodeposition and inhibit the growth of lithium dendrites, thereby effectively improving the electrochemical performance, efficiency, safety, etc. of the battery.

[0006] Another object of the present invention is to provide a lithium metal battery that has excellent electrochemical performance, life characteristics, safety, and the like. [Means for solving the problem]

[0007] A lithium metal negative electrode according to one embodiment includes a lithium metal layer and a protective layer formed on at least one surface of the lithium metal layer, the protective layer including lithium-affinity inorganic particles, and a peak intensity (PTE) of 1750 to 1880 cm upon FT-IR analysis of the protective layer. -1 At least one peak appears in the region of

[0008] The protective layer may contain an organic-inorganic hybrid polymer.

[0009] The organic-inorganic composite polymer may have a structure in which the lithium affinity inorganic particles are three-dimensionally connected to each other by forming chemical bonds between them.

[0010] During FT-IR analysis of the above protective layer, -1 and 1820-1880cm -1 At least one peak may appear in each of the regions.

[0011] When the protective layer is analyzed by FT-IR, the ratio of the peak area according to the following formula 1 may be greater than 1.

[0012] [Formula 1]

[0013] R P =I / A

[0014] In the above formula 1, R P is the ratio of the peak area, and A is the peak area from 1680 to 1750 cm -1 is the area of ​​the peak region that appears in the region of 1750-1800 cm -1 and 1820-1880cm -1 is the total area of ​​each peak area appearing in the region.

[0015] The protective layer may include one or more of LiF and Li3N.

[0016] The lithium-philic inorganic particles can include a metal, a metal oxide, a metal nitride, or a combination thereof.

[0017] The lithium affinity inorganic particles include Au, Ag, Pt, Al, Mg, Zn, Ni, Se, Te, Bi, Pb, Ga, Cd, Hg, Pd, Sc, Y, Ca, Sr, Ba, NiO, ZnO, SnO, and Cu. x O (x is 1 or 2), GeO, Ag x O (x is 1 or 2), SbO y (y is 3, 4 or 5), CuZn or combinations thereof.

[0018] The lithium-affinitive inorganic particles may have a diameter of less than 500 nm.

[0019] The protective layer may have a thickness of 0.1 to 20 μm.

[0020] A method for manufacturing a lithium metal negative electrode according to one embodiment includes step S1 of modifying lithium-affinity inorganic particles to have amino groups on their surfaces, step S2 of imidizing the modified lithium-affinity inorganic particles and a dianhydride to produce an organic-inorganic composite polymer, and step S3 of forming a protective layer on at least one side of the lithium metal layer using a composition including the organic-inorganic composite polymer.

[0021] Step S1 may include dispersing lithium-affinity inorganic particles in an organic solution.

[0022] The organic solution may contain a compound represented by the following Chemical Formula 1:

[0023] [Chemical formula 1]

[0024] [ka]

[0025] In the above chemical formula 1, R 1is at least one organic group selected from an optionally substituted alkylene group, an arylene group, a heterocyclic group, and an alkylene oxide group.

[0026] The organic solution may contain the compound represented by Chemical Formula 1 at 1 to 20 mol / L.

[0027] The dianhydride may contain a fluorine atom.

[0028] A lithium metal battery according to one embodiment includes a lithium metal negative electrode according to any one of the above embodiments. [Effects of the Invention]

[0029] According to one embodiment, it is possible to provide a lithium metal negative electrode that has excellent ionic conductivity and mechanical strength, includes a protective layer that can induce uniform lithium electrodeposition behavior, and can effectively suppress the growth of lithium dendrites.

[0030] According to another embodiment, it is possible to provide a lithium metal battery that is excellent in all aspects, such as cycle life during charge / discharge, capacity characteristics, and safety. [Brief explanation of the drawings]

[0031] [Figure 1a] 1A to 1C are diagrams showing a method for forming an organic-inorganic composite polymer according to an embodiment in a step-by-step manner. [Figure 1b] 1A to 1C are diagrams showing a method for forming an organic-inorganic composite polymer according to an embodiment in a step-by-step manner.

[0032] [Figure 2] FIG. 1 is a conceptual diagram illustrating a cross section of a lithium metal negative electrode according to one implementation.

[0033] [Figure 3] 1A-1C are diagrams illustrating a method for manufacturing a lithium metal anode according to one implementation.

[0034] [Figure 4a] FIG. 1 is a diagram showing the results of FT-IR analysis of lithium metal negative electrodes according to Examples and Comparative Examples. [Figure 4b] FIG. 2 is a diagram showing the results of FT-IR analysis of the lithium metal negative electrode according to Example 1. [Figure 4c] FIG. 10 is a diagram showing the results of FT-IR analysis of the lithium metal negative electrode according to Example 2.

[0035] [Figure 5] FIG. 1 is a diagram showing the results of evaluation of electrodeposition / desorption characteristics of lithium metal batteries including lithium metal negative electrodes according to Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0036] The preferred embodiments will be described below with reference to various examples, however, the embodiments are not limited to the implementations described below and may be embodied in various other forms.

[0037] Hereinafter, unless otherwise defined in this specification, when a part such as a layer, film, thin film, region, or plate is said to be "on" or "above" another part, this may include not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0038] Hereinafter, unless otherwise defined, "combination thereof" may mean a mixture or copolymerization of the previously defined components. Furthermore, "combination thereof" may mean that two or more of the previously defined components may be used or provided together.

[0039] As used herein, the term "polymer" refers to a molecule with a relatively high molecular weight, and the structure of the "polymer" may be a structure in which units derived from low-molecular-weight monomers are repeated multiple times. The "polymer" may include organic polymers composed of organic materials, inorganic polymers composed of inorganic materials, organic-inorganic hybrid polymers containing organic and inorganic materials, or combinations thereof. The term "polymer" may include not only polymers composed of the same type of monomers but also copolymers thereof. The copolymer may also include alternating copolymers, block copolymers, random copolymers, branched copolymers, cross-linked copolymers, or any combination thereof.

[0040] In the present specification, the term "organic-inorganic composite polymer" refers to a polymer in which chemical bonds are formed between inorganic particles by reacting monomers containing inorganic particles with each other or with other compounds. Specifically, the term "organic-inorganic composite polymer" refers to a polymer having a structure in which the inorganic particles are three-dimensionally connected to each other, specifically, a polymer having a network structure in which the inorganic particles are three-dimensionally cross-linked and connected to each other.

[0041] As described above, research is underway into applying lithium metal, which has relatively high capacity and low redox potential characteristics, to the negative electrode. However, due to issues such as lithium dendrite formation, it is difficult to ensure the cycle characteristics and stability of the battery.

[0042] A lithium metal anode according to one embodiment may include a protective layer on at least one surface of the lithium metal layer, which can induce uniform lithium electrodeposition behavior and effectively suppress the growth of lithium dendrites, thereby substantially resolving the above-mentioned problems and contributing to the provision of a lithium metal battery that is excellent in all aspects, such as ionic conductivity, cycle life, capacity characteristics, and safety. Specific details are disclosed below with reference to Figures 1a to 5.

[0043] 1a and 1b are diagrams showing a method for forming an organic-inorganic hybrid polymer according to one embodiment in a step-by-step manner.

[0044] FIG. 2 is a conceptual diagram showing a cross section of a lithium metal negative electrode according to one embodiment.

[0045] FIG. 3 is a flow chart illustrating a method for manufacturing a lithium metal anode according to one implementation.

[0046] 4a to 4c are diagrams showing the results of FT-IR analysis of the lithium metal negative electrodes according to the examples and comparative examples.

[0047] FIG. 5 is a diagram showing the results of evaluation of the electrodeposition / desorption characteristics of lithium metal batteries including lithium metal negative electrodes according to Examples and Comparative Examples.

[0048] Lithium metal anode

[0049] The lithium metal negative electrode 100 according to one embodiment includes a lithium metal layer 10 and a protective layer 20 formed on at least one surface of the lithium metal layer. The protective layer includes lithium-affinity inorganic particles 1. The protective layer 20 has an FT-IR spectrum of 1750 to 1880 cm -1 At least one peak appears in the region of

[0050] As described above, the protective layer 20 can induce uniform lithium electrodeposition behavior on at least one surface of the lithium metal layer 10 and effectively suppress the growth of lithium dendrites.

[0051] The protective layer 20 includes lithium-affinity inorganic particles 1. Here, "lithiophilic" refers to having an affinity for lithium. When a material with low affinity for lithium coexists with lithium, lithium metal is selectively electrodeposited first. In contrast, a lithium-affinity material with high affinity for lithium reduces the initial nucleation resistance of the lithium electrodeposition reaction, thereby inducing uniform electrodeposition of lithium metal and suppressing the growth of lithium dendrites. Therefore, the lithium-affinity inorganic particles 1 can induce uniform electrodeposition of lithium metal and suppress the growth of lithium dendrites, thereby improving the stability and cell performance of lithium metal batteries.

[0052] The lithium-affinity inorganic particles 1 refer to particles containing a lithium-affinity inorganic material, and may include a metal, a metal oxide, a metal nitride, or a combination thereof. Exemplary lithium-affinity inorganic particles 1 include Au, Ag, Pt, Al, Mg, Zn, Ni, Se, Te, Bi, Pb, Ga, Cd, Hg, Pd, Sc, Y, Ca, Sr, Ba, NiO, ZnO, SnO, Cu x O (x is 1 or 2), GeO, Ag x O (x is 1 or 2), SbO y (y is 3, 4, or 5), CuZn, or a combination thereof. The lithium-affinity inorganic particles may consist essentially of the lithium-affinity inorganic material described above.

[0053] As described above, such lithium-affinitive inorganic materials can electrochemically react with lithium to induce uniform electrodeposition of lithium ions. Therefore, when a protective layer 20 containing the lithium-affinitive inorganic particles 1 is formed on at least one surface of the lithium metal layer 10, it can suppress the growth of lithium dendrites during the charge / discharge process of the battery, thereby effectively preventing problems such as a decrease in irreversible capacity and short circuits inside the battery.

[0054] In one embodiment, the lithium affinity inorganic particles 1 are Ag, Ag x O (x is 1 or 2), or a combination thereof. Specifically, the lithium-affinity inorganic particles 1 may be silver nanoparticles (AgNPs) containing silver (Ag). When the lithium-affinity inorganic particles 1 contain silver (Ag), it may be advantageous for forming an alloy with lithium to generate initial lithium nuclei, thereby more effectively reducing the lithium electrodeposition resistance.

[0055] The diameter of the lithium affinity inorganic particles 1 may be less than 500 nm. Specifically, the diameter of the lithium affinity inorganic particles 1 may be 0.1 nm or more, 1 nm or more, 10 nm or more, or 20 nm or more, or 400 nm or less, or 300 nm or less. If the size of the lithium affinity inorganic particles 1 is too small, the specific surface area decreases, which may make it difficult to polymerize functional groups on the surface of the inorganic particles during the particle surface modification step described below. Therefore, if the lithium affinity inorganic particles 1 are nanoparticles with a diameter within the above range, they have excellent dispersibility, allowing functional groups to be appropriately formed on the surface of the inorganic particles during the particle surface modification step described below, and the imidization reaction due to polymerization between functional groups to proceed easily.

[0056] The protective layer 20 may include an organic-inorganic composite polymer, which may have a structure in which the lithium-affinity inorganic particles 1 are three-dimensionally connected to each other through chemical bonds formed between them. When the protective layer includes such an organic-inorganic composite polymer, the lithium-affinity inorganic particles 1 may exist in the protective layer 20 as a network structure in which the particles are cross-linked and connected to each other in a three-dimensional structure through organic chemical bonds. The structure of the organic-inorganic composite polymer is distinct from the structure of a mixture in which a separate organic polymer having the above-mentioned chemical bonds is physically mixed with the lithium-affinity inorganic particles, and specifically, can be distinguished by whether the lithium-affinity inorganic particles are three-dimensionally connected to each other through chemical bonds.

[0057] The chemical bond formed between the lithium affinity inorganic particles 1 may be an imide bond. Specifically, the lithium affinity inorganic particles 1 may form a compound (PI) having an imide bond between particles via an amino group, which is a functional group formed on the particle surface, and may exist in the protective layer 20 as a crosslinked and linked structure (see FIGS. 1b and 2). Therefore, a peak indicating an imide bond may appear when the protective layer 20 is subjected to infrared (IR) analysis.

[0058] Generally, in FT-IR analysis using a Fourier transform infrared (FT-IR) spectrometer, the peak temperature is 1750-1880 cm -1 At least one peak in the region of 1750-1800 cm -1 and 1820-1880cm -1 When at least one peak appears in each of the regions, it means that an imide bond is present in the specific material. -1 At least one peak appears in the region of 1750-1800 cm -1 and 1820-1880cm -1 At least one peak may appear in each of the above regions. -1 The "region" refers to a region that is divided by absorbance according to wavenumbers during FT-IR analysis.

[0059] When the protective layer 20 is analyzed by FT-IR, the ratio of the peak area according to the following formula 1 may exceed 1.

[0060] [Formula 1]

[0061] R P =I / A

[0062] In the above formula 1, R P is the ratio of the peak area, and A is the peak area from 1680 to 1750 cm -1is the area of ​​the peak region that appears in the region of 1750-1800 cm -1 and 1820-1880cm -1 is the total area of ​​each peak area appearing in the region.

[0063] Specifically, during FT-IR analysis of the protective layer 20, the ratio value of the peak area according to the above formula 1 may be 1.1 or more, 3 or more, 6 or more, or 8 or more, and may be less than 30, 20 or less, or 15 or less.

[0064] In the above formula 1, R P means the ratio of the area of ​​the imide C=O peak region (I) to the area of ​​the acid C=O peak region (A) that appears in FT-IR analysis, and A is the area of ​​the acid C=O peak region from 1680 to 1750 cm -1 I means the area of ​​the peak region in the range of 1750 to 1880 cm where the imide C=O peak appears. -1 and 1820-1880cm -1 The area of ​​each peak region refers to the total area of ​​each peak region in the region. In this case, the area of ​​the peak region can be calculated by measuring the infrared absorptivity of the wavenumber region where the peak appears using an FT-IR instrument and integrating the area of ​​each peak using the OriginPro 2021b program. For example, the area (A) of the Acid C=O peak region is calculated by deriving the baseline using the second derivative method and then integrating the area of ​​each peak from 1680 to 1750 cm. -1 The peak corresponding to the wave number can be fitted with a Gaussian curve and the area derived is integrated to calculate the peak.

[0065] In this specification, when the protective layer 20 is analyzed by FT-IR, -1 and 1820-1880cm -1When at least one peak appears in each of the above regions and the ratio characteristics of the peak regions according to Equation 1 are as described above, it can be determined that the protective layer contains an organic-inorganic composite polymer having a structure in which chemical bonds are formed between the lithium affinity inorganic particles 1 and they are three-dimensionally connected to each other. The lithium affinity inorganic particles 1 contained in the protective layer 20 of the lithium metal anode 100 exist in a state in which they are cross-linked and connected to each other in a three-dimensional structure through organic bonds, which can result in the lithium metal anode having excellent mechanical / electrochemical performance and charge / discharge characteristics.

[0066] According to one implementation example, during FT-IR analysis of the protective layer 20, the ratio value of the imide peak area according to the following formula 2 may be greater than 1.

[0067] [Formula 2]

[0068] R I =I1 / I2

[0069] In the above formula 2, R I is the ratio of the imide peak area, and I1 is from 1750 to 1800 cm -1 is the area of ​​the peak region that appears in the region of 1820-1880 cm -1 is the area of ​​the peak region appearing in the region

[0070] Specifically, in the FT-IR analysis of the protective layer 20, the ratio of the imide peak area according to the formula 2 may be 2 or more, or 2.5 or more, and may be 10 or less, or 5 or less.

[0071] When the FT-IR analysis of the protective layer 20 reveals the ratio characteristics of the imide peak region according to Equation 2 as described above, the structure of the organic-inorganic composite polymer contained in the protective layer is more excellent, thereby further improving the performance of the lithium metal negative electrode.

[0072] The protective layer 20 may include one or more of LiF and Li3N. Lithium fluoride (LiF) and lithium nitride (Li3N) are inorganic compounds that can be formed when fluorine and nitrogen elements in the protective layer 20 react with lithium ions during the charge / discharge process of the battery, and can further improve the uniform electrodeposition characteristics and mechanical strength of lithium metal during the charge / discharge of the battery. When the protective layer 20 includes one or more of LiF and Li3N, the mechanical strength, life characteristics, electrochemical performance, ion conductivity, etc. of the lithium metal anode 100 can be further improved.

[0073] The thickness of the protective layer 20 may be 0.1 to 20 μm. Specifically, the thickness of the protective layer 20 may be 1 μm or more, or 10 μm or less, or 2 μm or less. When the thickness of the protective layer 20 is within the above range, both the mechanical strength and electrochemical performance of the lithium metal negative electrode can be favorably improved.

[0074] The lithium metal negative electrode 100 can be manufactured by the method for manufacturing a negative electrode described below.

[0075] Negative electrode manufacturing method

[0076] A method for manufacturing a lithium metal negative electrode 100 according to one embodiment includes step S1 of modifying lithium affinity inorganic particles 1 so that they have amino groups on their surfaces, step S2 of imidizing the modified lithium affinity inorganic particles and a dianhydride to produce an organic-inorganic composite polymer, and step S3 of forming a protective layer 20 on at least one side of the lithium metal layer 10 using a composition containing the organic-inorganic composite polymer.

[0077] The method for manufacturing the lithium metal anode 100 includes step S1 of modifying the lithium affinity inorganic particles 1 to have one or more amino groups as functional groups on the surface thereof, so that imide bonds are formed between the lithium affinity inorganic particles 1 contained in the protective layer 20 formed on at least one surface of the lithium metal layer 10, thereby allowing the particles to exist in the protective layer 20 as a cross-linked structure.

[0078] The step S1 may include dispersing the lithium affinity inorganic particles 1 in an organic solution, and the organic solution may include a compound represented by the following Chemical Formula 1:

[0079] [Chemical formula 1]

[0080] [ka]

[0081] In the above chemical formula 1, R 1 is at least one organic group selected from an alkylene group, an arylene group, a heterocyclic group, and an alkylene oxide group, each of which may be substituted.

[0082] The number of carbon atoms in the alkylene group is not particularly limited. For example, the alkylene group may be an alkylene group having 1 to 20 carbon atoms, 1 to 15 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. When the alkylene group is an alkylene group having 2 carbon atoms, the compound represented by Chemical Formula 1 may correspond to 2-aminoethanethiol.

[0083] The arylene group refers to a monovalent or divalent residue derived from an aromatic compound or a derivative thereof that contains a benzene ring or a structure in which two or more benzene rings are fused or bonded while sharing two or one carbon atom. The arylene group may be optionally substituted with one or more substituents, and the number of carbon atoms is not particularly limited, but may be an arylene group having 6 to 30, 6 to 25, 6 to 22, 6 to 18, 6 to 14, or 6 to 12 carbon atoms.

[0084] For example, the arylene group may be a phenyl group, a naphthyl group, an anthracenyl group, a phenanthryl group, a pyrenyl group, a perylenyl group, a chrysenyl group, a fluorenyl group, or a combination thereof. When the arylene group is a phenyl group having 6 carbon atoms, the compound represented by Chemical Formula 1 may be 2-aminobenzenethiol or 4-aminobenzenethiol.

[0085] The heterocyclic group refers to a ring containing one or more heteroatoms other than carbon, and the heteroatoms may be, for example, O, N, Se, S, etc. The heterocyclic group may be optionally substituted with one or more substituents, and the number of carbon atoms is not particularly limited, but may be a heterocyclic group having 2 to 60 carbon atoms.

[0086] Exemplary heterocyclic groups may be pyridyl, pyridine-N-oxide, pyrimidinyl, pyridazyl, furyl, tetrahydrofuryl, thienyl, tetrahydrothienyl, tetrahydropyranyl, oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, isothiazolyl, thiadiazolyl, pyrrole, imidazolyl, triazolyl, pyrazolyl, tetrazolyl, or a combination thereof.

[0087] The alkylene oxide group may be optionally substituted with one or more substituents, and the number of carbon atoms is not particularly limited. For example, the alkylene oxide group may be an alkylene oxide group having 2 to 20 carbon atoms, such as ethylene oxide or propylene oxide.

[0088] The compound represented by the above formula 1 is a compound having a thiol group and an amino group at both ends. Specifically, in the above formula 1, R 1is an alkylene group, more specifically, 2-aminoethanethiol. When the lithium affinity inorganic particles 1 are dispersed in an organic solution containing the above-mentioned compound, the lithium affinity inorganic particles 1 can be modified to easily form a structure in which thiol groups are attached to the particle surface and amino groups are present in the outermost shell (see FIG. 1a).

[0089] The organic solution may contain the compound represented by Chemical Formula 1 at 1 to 20 mol / L. Specifically, the organic solution may contain the compound represented by Chemical Formula 1 at 5 to 15 mol / L. If the concentration of the compound represented by Chemical Formula 1 is too low, it may be difficult to form amino groups on the surfaces of the lithium affinity inorganic particles, and if the concentration is too high, it may be difficult to uniformly disperse the lithium affinity inorganic particles in the solution. Therefore, when the organic solution contains the compound represented by Chemical Formula 1 within the above range, amino groups can be successfully formed on the surfaces of the lithium affinity inorganic particles without problems such as dispersibility in the solution.

[0090] The organic solution may further contain a commonly used organic solvent. For example, the organic solution may contain tetrahydrofuran (THF) as the organic solvent, but the type of the organic solvent is not particularly limited. The organic solution can disperse the compound represented by Formula 1 in such an organic solvent.

[0091] Step S1 may further include a process of stirring the organic solution in which the lithium affinity inorganic particles 1 are dispersed, a process of filtering the stirred organic solution, and a process of drying the filtrate. The process of stirring the organic solution may be performed for 1 to 5 hours, the process of filtering the organic solution may be performed by washing the solid matter with an organic solvent such as tetrahydrofuran (THF), and the process of drying the filtrate may be performed at room temperature for 12 to 48 hours.

[0092] The method for manufacturing the lithium metal anode 100 includes step S2, in which the lithium affinity inorganic particles modified in step S1 are imidized with a dianhydride to produce a polymer. Specifically, the imidization reaction can be performed by reacting amino groups formed on the surface of the modified lithium affinity inorganic particles with a dianhydride to form polyamic acid (PAA), and then heat-treating the polyamic acid to form imide bonds.

[0093] The step of forming the polyamic acid can be carried out by adding a dianhydride to a solution of the modified lithium affinity inorganic particles dispersed in an organic solvent such as diethylformamide (DEF), and stirring the mixture at room temperature for 12 to 48 hours.

[0094] In step S2, the weight ratio of the modified lithium-affinity inorganic particles to the dianhydride may be 1:50 to 1:200. If the content of the modified lithium-affinity inorganic particles is too high, the degree of polymerization of the polymer may be low, and if the content of the dianhydride is too high, the polymer may have a low degree of polymerization, and problems may occur due to the presence of unreacted materials. Therefore, when the weight ratio of the modified lithium-affinity inorganic particles to the dianhydride is appropriately adjusted within the above range, the polymer can be formed with substantially no unreacted materials remaining, and a polyimide polymer with a degree of polymerization adjusted higher than the appropriate level can be obtained.

[0095] The dianhydride may contain a fluorine atom. Exemplary dianhydrides include, but are not limited to, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMN). When the fluorine-containing dianhydride reacts with the modified lithium-affinity inorganic particles, a fluorine-containing imide-linked compound (F-PI) may be formed. Exemplary dianhydride compounds include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and the fluorine-containing imide-linked compound (F-PI) may include a compound represented by the following Formula 2:

[0096] [Chemical formula 2]

[0097] [ka]

[0098] By using a dianhydride containing fluorine, a fluorine-containing imide-bonded compound (F-PI) can be formed in the protective layer 20. The fluorine reacts with lithium ions to form LiF in the protective layer 20, which further improves the uniform electrodeposition characteristics of lithium metal during charging / discharging of the battery, thereby further improving the life characteristics, electrochemical performance, ion conductivity, etc. of the lithium metal anode 100.

[0099] In the step of forming the imide bond, the heat treatment process may be carried out in a vacuum, the heat treatment time may be 0.5 to 3 hours, and the heat treatment temperature may be 100 to 300°C.

[0100] The method for manufacturing the lithium metal anode 100 includes step S3 of forming a protective layer 20 on at least one surface of the lithium metal layer 10 using a composition containing the polymer prepared in step S2. Specifically, step S3 can be performed by adding the polymer to an organic solvent such as tetrahydrofuran (THF) and stirring to prepare a composition, and coating the composition on at least one surface of the lithium metal layer 10 and then drying it.

[0101] In the process of preparing the composition, the polymer content in the composition may be 5 to 20 wt %. If the polymer content in the composition is too high, the viscosity may increase, which may cause problems in preparing a protective layer of appropriate thickness. If the polymer content is too low, the concentration may be too low, which may cause problems in preparing a uniform protective layer. Therefore, by appropriately adjusting the polymer content in the composition within the above range, a uniform protective layer whose thickness can be controlled within an appropriate range can be prepared. Furthermore, when preparing the composition, the stirring process can be carried out for 12 to 48 hours.

[0102] In the process of coating the composition on at least one surface of the lithium metal layer 10 and then drying, the coating process can be performed by, but is not limited to, bar coating, casting, etc. In addition, the drying process can be performed at room temperature.

[0103] Lithium metal battery

[0104] A lithium metal battery according to one embodiment may include the above-described lithium metal negative electrode 100. Specifically, the lithium metal battery may include the above-described lithium metal negative electrode 100, a positive electrode, and an electrolyte layer located between the negative electrode and the positive electrode.

[0105] The above-mentioned positive electrode is not particularly limited, and may include lithium-transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2) as the positive electrode active material, or lithium-transition metal composite oxides in which a part of these transition metals is substituted with other transition metals. Specifically, the above lithium-transition metal composite oxide may be an NCM-based positive electrode active material represented by the chemical formula of Li x Ni a Co b Mn c Al d O y (0 < x ≤ 1.1, 2 ≤ y ≤ 2.02, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 < a + b + c + d ≤ 1). Also, the above positive electrode active material may be a lithium iron phosphate (LFP)-based positive electrode active material represented by the chemical formula of LiFePO4. Further, the above positive electrode may be (1) a positive electrode for a lithium-sulfur battery using lithium polysulfide or the like containing sulfur (S) element as the active material, or (2) a positive electrode for a lithium-air battery using oxygen (O2) in the air as the active material.

[0106] The electrolyte contained in the above electrolyte layer is not particularly limited, and may include at least one of ordinary liquid electrolytes and solid electrolytes. Exemplarily, the above liquid electrolyte may include lithium salts such as LiPF6, LiTFSI (Lithium-(bis)-trifluoromethanesulfonimide); and organic solvents such as ether-based solvents and carbonate-based solvents. Also, the above solid electrolyte may be an oxide-based solid electrolyte such as Li7La3Zr2O 12 (LLZO); a sulfide-based solid electrolyte such as Li2S-P2S5; or (1) a solid polymer electrolyte formed by adding a polymer resin such as a polyether-based polymer to a lithium salt, (2) a polymer-based solid electrolyte such as a polymer gel electrolyte obtained by impregnating a polymer resin with an organic electrolyte solution containing an organic solvent and a lithium salt.

[0107] When the lithium metal battery includes the lithium metal anode 100, the protective layer 20, which can induce uniform lithium electrodeposition behavior, effectively suppresses the growth of lithium dendrites, thereby providing excellent cycle life, capacity characteristics, safety, etc. during charge / discharge. [Example]

[0108] Example

[0109] 1. Lithium metal anode

[0110] 1) Manufacturing of negative electrodes

[0111] (1) Example 1

[0112] A) Modification of lithium-affinic inorganic particles

[0113] 2-aminoethanethiol, a compound containing thiol and amino groups, was dispersed in tetrahydrofuran (THF) at 10 mol / L to prepare an organic solution. 3 g of silver nanoparticles (AgNPs; Sigma-Aldrich), which are lithium-compatible inorganic particles with a diameter of less than 150 nm, was dispersed in 4.5 mL of the organic solution and stirred for 2 hours to form a solid. The solid was then washed with tetrahydrofuran (THF) and filtered. The final filtrate was dried at room temperature for 24 hours to produce silver nanoparticles (Ag-NH2) bearing amino groups on their surfaces.

[0114] B) Preparation of the composition

[0115] 0.04 g of the prepared silver nanoparticles was added to 18 g of diethylformamide (DEF) to prepare a solution, to which 4.44 g of a dianhydride containing fluorine (F) (6FDA; 4,4'-(hexafluoroisopropylidene)diphthalic anhydride) was added and stirred at room temperature for 18 hours to prepare a polyamic acid solution containing silver nanoparticles. The weight ratio of the silver nanoparticles to the dianhydride (6FDA) in the solution was 1:100, and the solid content in the solution was 20 wt%.

[0116] The solution was then heat-treated at 200°C in vacuum for 1 hour for an imidization reaction to produce a polymer (F-Ag-PI) containing silver nanoparticles and having imide bonds. The polymer was then added to tetrahydrofuran (THF) solvent so that the content of the polymer was 10 wt% based on the total content of the composition, and stirred for 24 hours to produce a composition containing a polymer containing silver nanoparticles and having imide bonds.

[0117] C) Formation of a protective layer

[0118] The composition was coated on the surface of a 100 μm-thick lithium metal layer by casting, and then dried at room temperature to prepare a lithium metal anode of Example 1 having a protective layer formed on one side of the lithium metal layer.

[0119] (2) Example 2

[0120] A lithium metal negative electrode of Example 2 was prepared in the same manner as in Example 1, except that the heat treatment temperature for the imidization reaction was 120°C.

[0121] (3) Comparative Examples 1 to 3

[0122] A) Comparative example 1

[0123] A lithium metal anode of Comparative Example 1 was prepared in the same manner as in Example 1, except that an organic solution prepared by dispersing 2-aminoethanethiol in tetrahydrofuran (THF) solvent at 0.01 mol / L was used.

[0124] B) Comparative example 2

[0125] Unlike Example 1, a polyamic acid solution not containing silver nanoparticles was prepared by adding 4.44 g of dianhydride (6FDA; 4,4'-(hexafluoroisopropylidene)diphthalic anhydride) to a solution prepared by adding 3.36 g of diamine (2,2'-bis(trifluoromethyl)benzidine; TFDB) to 31 g of diethylformamide (DEF) and stirring the mixture at room temperature for 18 hours. The molar ratio of diamine (TFDB) to dianhydride (6FDA) was 1.05:1, and the solid content of the solution was 20 wt%.

[0126] The solution was then heat-treated at 200°C in vacuum for 1 hour for imidization to produce a polymer (F-PI) having imide bonds. The polymer was added to tetrahydrofuran (THF) solvent to a concentration of 10 wt% and stirred for 24 hours to produce a composition containing a polymer having imide bonds but not containing silver nanoparticles. The composition was coated on the surface of a 100 μm-thick lithium metal layer and then dried at room temperature to produce a lithium metal anode of Comparative Example 2, in which a protective layer was formed on one side of the lithium metal layer.

[0127] C) Comparative example 3

[0128] A lithium metal anode of Comparative Example 3 was prepared in which no additional protective layer was formed on one side of the lithium metal layer.

[0129] 2) Analysis of negative electrode material (FT-IR)

[0130] The protective layers included in the negative electrode samples of Examples 1 and 2 and Comparative Example 1 prepared as described above were subjected to material analysis using a Fourier transform infrared (FT-IR) spectrometer (Thermo Scientific; Nicolet 6700) with the Resolution Pro S / W program, and the results are shown in Figures 4a to 4c.

[0131] Specifically, (1) the measurement mode was selected as Attenuated Total Reflection (ATR), (2) the instrument configuration conditions were set as follows: IR Source: [MIR Source], Beam Splitter: [KBr], Beam Path: [Internal], Detector: [DTGS], Aperture / Source: [Open], etc., and (3) the method settings were set as Resolution: [8cm -1 ], No.of Scan:[16scans], Scan Range:[4000~650cm -1 ], Speed:[5kHz], Sampling Interval:[2], etc. were set, (4) the background spectrum was measured, and then (5) the sample was loaded onto the ATR crystal and the FT-IR spectrum was measured.

[0132] The area of ​​the peak region was calculated by measuring the infrared absorptivity of the wavenumber region where the peak appears using an FT-IR instrument and integrating the area of ​​each peak. Specifically, the OriginPro 2021b program was used to calculate the area from 1500 to 2000 cm -1 The calculation was performed for the area of ​​the imide peak. The baseline was derived using the second derivative method, and each peak was fitted with a Gaussian curve and the derived area was integrated to calculate the area. Based on the area of ​​each peak calculated as described above, the peak area ratio and the imide peak area ratio were calculated using the following Equations 1 and 2.

[0133] [Formula 1]

[0134] R P =I / A

[0135] In the above formula 1, R P is the ratio of the peak area, and A is the peak area from 1680 to 1750 cm -1 is the area of ​​the peak region that appears in the region of 1750-1800 cm -1 and 1820-1880cm -1 is the total area of ​​each peak area appearing in the region.

[0136] [Formula 2]

[0137] R I =I1 / I2

[0138] In the above formula 2, R I is the ratio of the imide peak area, and I1 is from 1750 to 1800 cm -1 is the area of ​​the peak region that appears in the region of 1820-1880 cm -1 is the area of ​​the peak region appearing in the region

[0139] 2. Lithium metal batteries

[0140] 1) Battery manufacturing

[0141] A lithium metal battery sample was fabricated using the lithium metal negative electrode fabricated as described above. The lithium metal battery sample was a symmetric cell in which lithium metal was used as the working electrode and the counter electrode, and the electrodes were arranged on either side of each other. The electrolyte between the electrodes contained ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (3:7 v / v) containing 1 M LiPF6 and 2 wt% fluoroethylene carbonate (FEC).

[0142] 2) Battery evaluation (life characteristics)

[0143] Among the samples manufactured as described above, the overvoltage characteristics due to lithium electrodeposition / desorption were evaluated for the lithium metal symmetric batteries of Example 1 and Comparative Examples 1 to 3. Specifically, the lithium metal battery samples were evaluated at 25°C under conditions of a capacity per area of ​​2 mAh and a current density per area of ​​1 mA, and the battery overpotential generated during the oxidation / reduction of lithium was measured.

[0144] Referring to FIGS. 4a to 4c, in Examples 1 and 2, an organic solution prepared by dispersing 2-aminoethanethiol in tetrahydrofuran (THF) solvent at 10 mol / L was used. In the FT-IR analysis, a peak was observed at 1750 to 1880 cm -1 Two peaks in the peak region of imide C=O, specifically, 1750~1880cm -1 One peak in the region of 1820-1880 cm -1 In addition, FT-IR analysis of the protective layer revealed that the ratio of the peak area according to the above formula 1 exceeded 1 in both Example 1 and Example 2 (Example 1: 9.44, Example 2: 5.97), and the ratio of the imide peak area according to the above formula 2 also exceeded 1 in both Example 1 and Example 2 (Example 1: 2.57, Example 2: 2.60) (Figures 4b and 4c).

[0145] In contrast, in Comparative Example 1, an organic solution prepared by dispersing 2-aminoethanethiol in tetrahydrofuran (THF) solvent at 0.01 mol / L was used, and the FT-IR analysis showed a peak at 1680 to 1750 cm -1 One peak appears in the peak region of Acid C=O, and the other peak appears in the range of 1750-1880 cm -1No peak appears in the imide C=O peak region (Figure 4a). This is thought to be because, in the silver nanoparticles of Examples 1 and 2, which were modified with an organic solution containing 10 mol / L of 2-aminoethanethiol, amino groups were easily formed on the surface, and the particles were linked to each other by imide bonds, whereas in the silver nanoparticles of Comparative Example 1, which were modified with an organic solution containing a relatively small amount (0.01 mol / L) of 2-aminoethanethiol, amino groups were not easily formed on the surface, and the particles were not linked to each other by imide bonds, and the added dianhydride was not used in the imidization reaction but was decomposed to form an acid.

[0146] 5, unlike Example 1, FT-IR analysis showed that in the lithium metal batteries including the anodes of Comparative Example 1, which includes a protective layer that does not have a peak in the imide C=O peak region, Comparative Example 2, which does not include silver nanoparticles, and Comparative Example 3, which does not include a protective layer, a relatively large overvoltage appeared at a specific point after a certain number of electrodeposition / desorption cycles. Specifically, Comparative Example 1 showed a large overvoltage after 71 electrodeposition / desorption cycles (284 hours), Comparative Examples 2 and 3 began to show overvoltage at an early stage of the electrodeposition / desorption cycle, and Comparative Example 2 showed a voltage of several mV after 66 electrodeposition / desorption cycles (284 hours) and Comparative Example 3 after 99 electrodeposition / desorption cycles (395 hours). This is believed to be because if the lithium metal layer contains (1) an improperly formed protective layer with imide bonds not properly formed, (2) an improperly formed protective layer without silver nanoparticles, or (3) an anode without a protective layer, the growth of dendrites cannot be effectively suppressed during the electrodeposition / deposition process of the battery, resulting in excessive resistance inside the battery, and during long-term electrodeposition / deposition, the dendrites grow larger, causing a short circuit inside the battery.

[0147] On the other hand, the battery of Example 1, which includes an anode with a protective layer properly formed on a lithium metal layer, was found to undergo stable electrodeposition / desorption cycles without significant overvoltage even after long-term charge / discharge cycles. This is believed to be because, in the case of Example 1, the lithium affinity inorganic material (Ag) contained in the protective layer induces uniform lithium electrodeposition behavior, suppressing the growth of dendrites, etc., and the large amount of LiF, etc. contained in the protective layer provides the protective layer with excellent mechanical strength.

[0148] Therefore, it is believed that when a protective layer containing 1) lithium-affinity inorganic particles and 2) imide bonds, etc. is appropriately formed on at least one side of a lithium metal layer, the electrochemical performance of a lithium metal anode and a lithium metal battery including the same can be improved, and the efficiency and safety of the lithium metal anode and the lithium metal battery including the same can be effectively improved.

[0149] As described above, the embodiments of the present disclosure have been described in detail, but the scope of the present disclosure is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope that does not deviate from the technical idea of ​​the present disclosure described in the claims.

[0150] [Explanation of symbols]

[0151] 1: Lithophilic inorganic particles

[0152] 10: Lithium metal layer

[0153] 20:Protective layer

[0154] 100: Lithium metal anode

[0155] PI:imide bonded compounds

[0156] I: Imide C=O peak area

[0157] A: Acid C=O peak area [Industrial Applicability]

[0158] As noted above, the features of the present invention may be applied in whole or in part to lithium metal anodes, methods for making same, and lithium metal batteries containing same.

Claims

1. a lithium metal layer; and a protective layer formed on at least one surface of the lithium metal layer, the protective layer comprises lithium-affinity inorganic particles; During FT-IR analysis of the protective layer, －１ A lithium metal anode, wherein at least one peak appears in the region of

2. the protective layer comprises an organic-inorganic composite polymer, 2. The lithium metal negative electrode according to claim 1, wherein the organic-inorganic composite polymer has a structure in which the lithium affinity inorganic particles are three-dimensionally connected to each other by chemical bonds formed between the particles.

3. During FT-IR analysis of the protective layer, －１ and 1820-1880 cm －１ 2. The lithium metal negative electrode of claim 1, wherein at least one peak appears in each of the regions.

4. The lithium metal negative electrode of claim 3, wherein the ratio of the peak area according to the following formula 1 is greater than 1 when the protective layer is analyzed by FT-IR: [Formula 1] R Ｐ =I / A In the formula 1, R Ｐ is the ratio of the peak area, and A is the peak area from 1680 to 1750 cm －１ is the area of ​​the peak region appearing in the region of 1750 to 1800 cm －１ and 1820-1880 cm －１ is the total area of ​​each peak area appearing in the region.

5. The protective layer is made of LiF and Li ３ 10. The lithium metal anode of claim 1, comprising one or more of the following materials:

6. 10. The lithium metal anode of claim 1, wherein the lithiophilic inorganic particles comprise a metal, a metal oxide, a metal nitride, or a combination thereof.

7. The lithium affinity inorganic particles include Au, Ag, Pt, Al, Mg, Zn, Ni, Se, Te, Bi, Pb, Ga, Cd, Hg, Pd, Sc, Y, Ca, Sr, Ba, NiO, ZnO, SnO, Cu ｘ O (x is 1 or 2), GeO, Ag ｘ O (x is 1 or 2), Sb ２ O ｙ (y is 3, 4, or 5), CuZn, or a combination thereof.

8. 10. The lithium metal anode of claim 1, wherein the lithiophilic inorganic particles have a diameter of less than 500 nm.

9. 2. The lithium metal negative electrode of claim 1, wherein the protective layer has a thickness of 0.1 to 20 μm.

10. Step S1: modifying the lithium affinity inorganic particles to have amino groups on the surface; Step S2 of preparing an organic-inorganic hybrid polymer by imidizing the modified lithium affinity inorganic particles and dianhydride; and forming a protective layer on at least one surface of the lithium metal layer using a composition including the organic-inorganic composite polymer.

11. Step S1 includes dispersing lithium affinity inorganic particles in an organic solution, The method of claim 10 , wherein the organic solution contains a compound represented by the following Chemical Formula 1: [Chemical formula 1] 【Chemistry 1】 In the above formula 1, R １ represents at least one organic group selected from an optionally substituted alkylene group, an arylene group, a heterocyclic group, and an alkylene oxide group.

12. 12. The method of claim 11, wherein the organic solution contains the compound represented by Formula 1 in an amount of 1 to 20 mol / L.

13. The method for producing a lithium metal negative electrode according to claim 10, wherein the dianhydride contains elemental fluorine.

14. A lithium metal battery comprising the lithium metal negative electrode of any one of claims 1 to 9.

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