Lithium metal secondary battery

Abstract

The present invention relates to a lithium metal secondary battery in which side reactions and generation of by-products at an interface of a lithium metal negative electrode are suppressed and electrochemical properties and lifespan properties are improved. The lithium metal secondary battery comprises: a positive electrode including a positive electrode active material layer; a negative electrode including a lithium metal layer; a separator including a porous separator substrate and an active layer formed only on one surface of the porous separator substrate facing the positive electrode, the active layer including inorganic oxide particles having a dielectric constant of 5 or higher and a polymer binder; and an electrolyte, wherein the active layer of the separator may be in contact with the positive electrode active material layer, and the lithium metal layer may be in contact with the porous separator substrate.

Description

lithium metal secondary battery

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0100663, filed July 30, 2024, and Korean Patent Application No. 10-2025-0093507, filed July 11, 2025, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a lithium metal secondary battery in which side reactions and by-products are suppressed at a lithium metal negative electrode interface and electrochemical characteristics and life characteristics are improved.

[0004] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, long life, and high stability is increasing.

[0005] Lithium metal batteries utilize lithium metal (Li-metal) as the anode active material. Compared to conventional graphite or lithium alloy anodes, lithium metal batteries theoretically offer significantly higher energy density and capacity. Therefore, research and development are ongoing to apply these lithium metal batteries to batteries requiring high energy densities.

[0006] However, lithium metal batteries have disadvantages such as a large volume change of the negative electrode during the charge and discharge process, uneven growth of needle-like lithium metal layers (such as lithium dendrites), and the generation of side reactions and a large amount of by-products at the interface between the lithium metal layer and the electrolyte due to the characteristics of lithium metal with high reactivity, resulting in a large irreversible capacity. In particular, a large amount of by-products at the negative electrode interface can significantly reduce the output and capacity of the secondary battery by increasing the resistance of the battery, and further, can cause a significant deterioration in the electrochemical performance and life characteristics of the lithium metal secondary battery.

[0007] For this reason, various attempts are being made to suppress the generation of large amounts of byproducts at the lithium metal negative electrode interface and to improve the electrochemical characteristics and lifespan characteristics of lithium metal secondary batteries, but the problem has not yet been sufficiently resolved.

[0008] Accordingly, the present invention provides a lithium metal secondary battery that reduces side reactions and by-products at the lithium metal negative electrode interface and exhibits improved electrochemical characteristics and lifespan characteristics.

[0009] According to an embodiment of the invention, a positive electrode comprising a positive electrode active material layer;

[0010] A cathode comprising a lithium metal layer;

[0011] A separator comprising a porous separator substrate and an active layer formed only on one side of the porous separator substrate facing the anode and including inorganic oxide particles having a dielectric constant of 5 or more and a polymer binder; and an electrolyte.

[0012] A lithium metal secondary battery is provided in which the active layer of the separator is in contact with the positive electrode active material layer, and the lithium metal layer is in contact with the porous separator substrate.

[0013] In such a lithium metal secondary battery, the positive electrode active material layer may include a positive electrode active material including lithium iron phosphate of the following chemical formula 1 or a lithium transition metal oxide of the following chemical formula 2:

[0014] [Chemical Formula 1]

[0015] Li 1+a Fe 1-y M y (PO 4-b )X b

[0016] In the above chemical formula 1, M is at least one selected from Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤y≤0.5, 0≤b≤0.1,

[0017] [Chemical Formula 2]

[0018] Li 1+a’ Ni 1-y’-z’-s Co y’ Mn z’ M' s O 2-b’ X b’

[0019] In the above chemical formula 2, M' is at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and -0.5≤a'≤0.5, 0 <y’<1, 0<z’<1, 0≤s<0.2, 0≤b’≤0.1이며,

[0020] In the above chemical formulas 1 and 2, X is at least one selected from F, S, and N.

[0021] In addition, in the lithium metal secondary battery, the porous separator substrate may include a polyolefin resin, and the inorganic oxide particles of the active layer may include at least one selected from the group consisting of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2. In addition, the polymer binder of the active layer is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol. It may include at least one selected from the group consisting of (cyanoethylpolyvinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

[0022] The above-described separator may be an organic / inorganic porous composite separator in which the inorganic oxide particles are connected and fixed by the polymer binder of the active layer, and a pore structure is formed due to the interstitial volume between the inorganic oxide particles, and in a specific embodiment, may have the form of a ceramic coated separator referred to as a so-called Safety Reinforced Separator (SRS) or Ceramic Coated Separator (CCS).

[0023] In such a separator, the active layer in contact with the positive electrode active material layer may have a thickness of, for example, 0.1 μm to 10 μm.

[0024] Meanwhile, in the lithium metal secondary battery, the electrolyte may include a non-aqueous organic solvent and a lithium salt, and in some cases, may further include an organic anti-solvent that exhibits a solubility in the lithium salt that is at least 10 times lower than that in the non-aqueous organic solvent.

[0025] At this time, the organic non-solvent may include an acyclic ether compound substituted with multiple fluorines or an acyclic diether compound substituted with multiple fluorines.

[0026] A lithium metal secondary battery according to an embodiment of the invention may have a form in which an active layer coated on a separator substrate is formed only on one side facing the positive electrode, the active layer is in contact with the positive electrode active material layer, and the lithium metal negative electrode is in contact with the separator substrate.

[0027] As a result, it was confirmed that side reactions and by-product generation at the interface of the lithium metal negative electrode were significantly suppressed. This is expected because when a porous separator substrate exhibiting relatively low reactivity, such as a porous polyolefin substrate, comes into contact with the lithium metal negative electrode, side reactions between the lithium metal negative electrode and the electrolyte are suppressed, and additional side reactions with the active layer are also suppressed. In addition, the active layer of the separator appears to be able to improve ionic conductivity and electrochemical characteristics by coming into contact with the positive electrode active material layer.

[0028] Accordingly, the lithium metal secondary battery can suppress the generation of byproducts on the lithium metal negative electrode and the resulting increase in resistance, and can exhibit improved electrochemical characteristics such as stability and capacity, as well as life characteristics.

[0029] Figure 1 is a graph showing the results of a comparative evaluation of cycle-by-cycle capacity and coulombic efficiency (CE %) for lithium metal secondary batteries of Comparative Examples 2 and 3.

[0030] Figure 2 is a graph showing the results of a comparative evaluation of cycle-by-cycle capacity and coulombic efficiency (CE %) for the lithium metal secondary batteries of Comparative Example 3 and Example 1.

[0031] Figures 3a and 3b are electron microscope photographs of the surface of a lithium metal negative electrode in a lithium metal secondary battery of Example 1 and Comparative Example 2, respectively.

[0032] Figures 4a and 4b show the results of analyzing the surface of the lithium metal negative electrode in the lithium metal secondary battery of Example 1 using an electron microscope (Figure 4a) and elemental analysis using EDS (Energy Dispersive Spectroscopy) based on the analysis (Figure 4b).

[0033] Figures 4c and 4d show the results of analyzing the surface of the lithium metal negative electrode of the lithium metal secondary battery of Comparative Example 2 using an electron microscope (Figure 4c) and elemental analysis using EDS (Energy Dispersive Spectroscopy) based on the analysis (Figure 4d).

[0034] Hereinafter, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0035] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense to those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0036] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0037]

[0038] A lithium metal secondary battery according to one embodiment of the invention comprises: a positive electrode including a positive electrode active material layer; a negative electrode including a lithium metal layer; a porous separator substrate; and a separator including an active layer formed only on one surface of the porous separator substrate facing the positive electrode and including inorganic oxide particles having a dielectric constant of 5 or more and a polymer binder; and an electrolyte, wherein the active layer of the separator may be in contact with the positive electrode active material layer, and the lithium metal layer may be in contact with the porous separator substrate.

[0039] According to a specific embodiment of such a lithium metal secondary battery, a positive electrode having a positive electrode active material layer formed on a metal current collector and a negative electrode including a lithium metal layer as an negative electrode active material layer face each other with the separator interposed therebetween.

[0040] At this time, the separator includes a porous separator substrate including a polyolefin resin, etc., and an active layer is formed on only one surface of the porous separator substrate. The active layer may include inorganic oxide particles having a dielectric constant of 5 or more and a polymer binder. In a more specific example, the active layer may be an organic / inorganic porous composite separator in which the inorganic oxide particles are connected and fixed by the polymer binder and a pore structure is formed due to the empty space (interstitial volume) between the inorganic oxide particles, and in a specific example, may have the form of a porous ceramic coated separator referred to as a so-called SRS (Safety Reinforced Separator) or CCS (Ceramic Coated Separator).

[0041] In particular, in one embodiment of a lithium metal secondary battery, a separator is included in which the active layer is formed only on one side of a porous separator substrate facing the positive electrode, and is not formed on the other side facing the lithium metal negative electrode. In such a separator, the surface of the active layer may be in contact with the surface of the positive electrode active material layer, and the surface of the lithium metal negative electrode, for example, the lithium metal layer, may be in contact with the porous separator substrate.

[0042] As also supported by the examples below, it was confirmed that the coating form of the separator significantly suppresses side reactions and the generation of by-products at the interface between the lithium metal negative electrode and the electrolyte. This is expected because when a porous separator substrate exhibiting relatively low reactivity, for example, a porous polyolefin substrate such as polyethylene or polypropylene, comes into contact with the lithium metal negative electrode, side reactions between the lithium metal layer and the electrolyte are suppressed, and additional side reactions with the active layer are also suppressed. In addition, the active layer of the separator appears to be able to improve stability, ionic conductivity, and electrochemical characteristics by coming into contact with the positive electrode active material layer.

[0043] Therefore, the lithium metal secondary battery of one embodiment can suppress the generation of byproducts on the lithium metal negative electrode and the increase in resistance caused by them, and can exhibit improved electrochemical characteristics such as stability, capacity, and life characteristics.

[0044]

[0045] anode

[0046] In the lithium metal secondary battery of the above embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one or both sides of the positive electrode current collector.

[0047] Here, the positive electrode current collector may be any conductive material that does not induce chemical changes in the battery, and is not particularly limited. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like.

[0048] The positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance adhesion to the positive electrode active material layer. The positive electrode current collector may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0049] The above positive electrode active material layer includes a positive electrode active material and may further include a conductive material, a binder, and other additives, as needed.

[0050] The above positive electrode active material is not limited to a compound capable of reversible intercalation and deintercalation of lithium, but in a specific example, lithium iron phosphate of the following chemical formula 1 or lithium transition metal oxide of the following chemical formula 2 may be appropriately used:

[0051] [Chemical Formula 1]

[0052] Li 1+a Fe 1-y M y (PO 4-b )X b

[0053] In the above chemical formula 1, M is at least one selected from Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤y≤0.5, 0≤b≤0.1,

[0054] [Chemical Formula 2]

[0055] Li 1+a’ Ni 1-y’-z’-s Co y’ Mn z’ M' s O 2-b’ Xb’

[0056] In the above chemical formula 2, M' is at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and -0.5≤a'≤0.5, 0 <y’<1, 0<z’<1, 0≤s<0.2, 0≤b’≤0.1이며,

[0057] In the above chemical formulas 1 and 2, X is at least one selected from F, S, and N.

[0058] These lithium iron phosphates or lithium transition metal oxides may be included in an amount of 80 wt% or more, specifically 90 wt% to 100 wt%, based on the total weight of the cathode active material. Among these, by using lithium iron phosphates, the manufacturing cost of lithium metal secondary batteries can be lowered, while the stability of the batteries can be further improved.

[0059] In addition, the positive electrode active material is a lithium metal oxide, such as a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., Li 1+x1 Ni 1-y1 Mn y1 O2(where, -0.5≤x1≤0.5, 0 <y1<1), Li 1+x2 Mn 2-z2 Ni z2 O4 (where -0.5≤x2≤0.5, 0<z2<2), etc.), lithium-nickel-cobalt oxides (e.g., Li 1+x3 Ni 1-Y1 Co Y1 O2(where, -0.5≤x3≤0.5, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, Li 1+x4 Co 1-Y2 Mn Y2 O2(where, -0.5≤x4≤0.5, 0 <Y2<1), Li 1+x5 Mn 2-Z1 Co Z1O4 (where -0.5≤x5≤0.5, 0<Z1<2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li 1+a2 (Ni p1 Co q1 Mn r1 )O4(wherein, -0.5≤a2≤0.5, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), and one or more compounds among these may be included.

[0060] The above positive electrode active material may be included in an amount of 60 to 98 wt%, preferably 80 to 98 wt%, and more preferably 90 to 98 wt%, based on the total weight of the positive electrode active material layer.

[0061] The conductive agent is a component for further improving the conductivity of the positive electrode active material, and the conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0062] The above-mentioned conductive material may be included in an amount of 0.1 to 20 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0063] The above binder is a component that assists in bonding between the conductive material, the positive electrode active material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0064] Typically, the binder may be included in an amount of 0.5 to 20 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0065] In addition, the additive may further include, for example, a filler as a component that suppresses expansion. The filler is not particularly limited as long as it can suppress expansion of the electrode without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0066] cathode

[0067] The negative electrode includes a lithium metal layer, and may include, for example, a negative electrode current collector and a lithium metal layer formed on one or both sides of the negative electrode current collector.

[0068] Here, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0069] The above-mentioned negative electrode collector may typically have a thickness of 3 μm to 500 μm, and like the positive electrode collector, it may be provided with fine irregularities on the surface of the negative electrode collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0070] The negative electrode including the lithium metal layer can be manufactured by forming lithium metal on the negative electrode current collector by a method such as physically bonding, rolling, or depositing. The deposition method may include a method of forming lithium metal by an electrical deposition method or a chemical vapor deposition method.

[0071] Here, the lithium metal may include an alloy that partially contains, in addition to lithium (Li), at least one metal selected from the group consisting of nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0072] membrane

[0073] In the lithium metal secondary battery described above, the separator may have a form in which an active layer including inorganic oxide particles and a polymer binder is coated on one surface of a porous separator substrate. This active layer faces and contacts the positive electrode active material layer, and the other surface of the porous separator substrate, on which the active layer is not formed, may face and contact a lithium metal negative electrode, for example, a lithium metal layer.

[0074] Such a separator is interposed between the positive and negative electrodes, and can not only separate the negative and positive electrodes and provide a passage for lithium ions to move, but also reduce the generation of byproducts at the negative electrode interface in a lithium metal secondary battery of one embodiment, and improve the stability, electrochemical characteristics, and life characteristics of the battery.

[0075] In such a separator, the type of the porous separator substrate is not particularly limited, but it is preferable that it has relatively low reactivity and excellent mechanical properties, has low resistance to ion movement of the electrolyte, and has excellent electrolyte moisture retention capacity. More specifically, the porous separator substrate may be, for example, a porous polymer film made of a polyolefin resin such as a polyethylene resin or a polypropylene resin, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, the porous separator substrate may have a thickness of, for example, 5 to 30 μm, or 7 to 20 μm, or 8 to 15 μm.

[0076] In addition, the active layer coated on one side of the porous separator may include inorganic oxide particles having a dielectric constant of 5 or more, 10 or more, or 5 to 30, and a polymer binder. By using the inorganic oxide particles having a high dielectric constant, the ionic conductivity and electrochemical properties of the secondary battery can be improved.

[0077] Non-limiting examples of the inorganic oxide particles having the dielectric constant of 5 or more include at least one selected from the group consisting of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2. Among these, alumina (Al2O3) particles can be appropriately used considering the ionic conductivity of the secondary battery, etc.

[0078] Meanwhile, the polymer binder is a component that attaches the inorganic oxide particles between the inorganic oxide particles and the porous membrane substrate, and the inorganic oxide particles are connected and fixed by the polymer binder, and a porous structure on the active layer can be defined due to the empty space (interstitial volume) between the inorganic oxide particles.

[0079] Any polymer having the above-described properties can be used as the polymer binder without any special restrictions, but from the perspective of improving the electrochemical properties of a lithium metal secondary battery, a polymer that exhibits ionic conductivity itself can be preferably used.

[0080] Non-limiting examples of such polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, and cyanoethylpolyvinylalcohol. (cyanoethylpolyvinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

[0081] The above-described inorganic oxide particles and polymer binder may be included in the active layer in a volume ratio of, for example, 1:99 to 99:1, or 70:30 to 30:70, or 40:60 to 60:40, so as to form pores of an appropriate size on the active layer. In this range, as the volume of the inorganic oxide particles relative to the polymer binder increases, the porosity of the separator may increase.

[0082] In addition to the above-described inorganic oxide particles and the above-described polymer binder, the above-described active layer may further include additional components or additives that have been previously known to be usable in ceramic-coated separators.

[0083] In addition, the thickness of the active layer may be 0.1 µm to 10 µm, and specifically, may be 0.5 µm or more, 1 µm or more, or 2 µm or more, 8 µm or less, 6 µm or less, 5 µm or less, or 4 µm or less. If the thickness of the active layer is too thin, the stability and electrochemical characteristics of the lithium metal secondary battery may not be sufficient. Conversely, if the thickness of the active layer is too thick, the resistance of the secondary battery may increase.

[0084] Meanwhile, the above-mentioned separator can be manufactured by preparing an organic coating solution containing the inorganic oxide particles and a polymer binder, similar to a typical ceramic-coated separator such as SRS or CCS, and coating and drying the coating solution on a porous separator substrate. However, the coating process is performed only on one side of the porous separator substrate facing the anode.

[0085] electrolyte

[0086] Meanwhile, a lithium metal secondary battery of one embodiment further includes, for example, an electrolyte including a non-aqueous organic solvent and a lithium salt.

[0087] The above lithium salt is used as a medium to transfer ions in a secondary battery. Lithium salt is, for example, Li as a cation. + , and the anion is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one selected from the group consisting of

[0088] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2) may include a single substance or a mixture of two or more substances selected from the group consisting of, but in terms of excellent stability, imide-based lithium salts, i.e., LiFSI (lithium bis(fluorosulfonyl) imide), LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide), LiN(SO2CF2CF3)2 and LiTFSI (lithium bis(trifluoromethanesulfonyl) It is preferable to include at least one selected from the group consisting of LiN(SO2CF3)2).

[0089] In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0090] The above lithium salt can be appropriately changed within a commonly usable range, but considering the output characteristics and stability of the lithium metal secondary battery, it can be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically, at a concentration of 1 M to 2.5 M, and more specifically, at a concentration of 1 M to 2 M.

[0091] The above non-aqueous organic solvent is not limited as long as it minimizes decomposition by oxidation reactions, etc. in the voltage range of the charge / discharge process of a lithium secondary battery, and can exhibit properties together with the material. For example, a carbonate-based organic solvent, an ether-based organic solvent, or an ester-based organic solvent may be used alone or in a mixture of two or more. However, when the organic non-solvent described below is used together, the ether-based organic solvent may be primarily used in consideration of miscibility with the organic non-solvent. At this time, the ether-based organic solvent may be included in an amount of about 50 vol% or more, specifically 60 vol%, 70 vol%, or 80 vol% or more, and may be included in an amount of 100 vol% or less, or 90 vol% or less, based on the total non-aqueous organic solvent.

[0092] Additionally, the non-aqueous organic solvent may be included in an amount of 20 wt% to 70 wt% based on the total weight of the electrolyte.

[0093] Among the organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC), and specifically, may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0094] In addition, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically, may include dimethyl carbonate.

[0095] The above ether organic solvent may be any one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more thereof, but is not limited thereto.

[0096] The above ester organic solvent may include at least one selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0097] Specific examples of the linear ester organic solvent include, but are not limited to, one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more thereof.

[0098] The above cyclic ester organic solvent may be, as a specific example, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0099] Among the above ester solvents, cyclic carbonate compounds are preferably used as high-viscosity organic solvents with high dielectric constants, which facilitate the dissociation of lithium salts in the electrolyte. When low-viscosity, low-dielectric constant linear carbonate compounds and linear ester compounds, such as dimethyl carbonate and diethyl carbonate, are mixed and used in an appropriate ratio with these cyclic carbonate compounds, an electrolyte with high electrical conductivity can be produced, and thus the compounds can be used more preferably.

[0100] Meanwhile, the electrolyte may further comprise an organic non-solvent that exhibits a solubility in the lithium salt that is at least 10 times lower than that in the non-aqueous organic solvent. The electrolyte further comprising such an organic non-solvent may include a region where a high-concentration lithium salt is locally solvated by the non-aqueous organic solvent and an organic non-solvent region surrounding the solvated region. As a result, the output of the secondary battery can be further improved by the solvation of the high-concentration lithium salt, while side reactions, such as those between the lithium metal negative electrode and the electrolyte, can be suppressed.

[0101] As the organic non-solvent, an organic solvent that does not substantially exhibit solubility in the lithium salt and is miscible with the non-aqueous organic solvent may be used, for example, an acyclic ether compound substituted with multiple fluorines or an acyclic diether compound substituted with multiple fluorines, and more specific examples thereof include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), ethoxynonafluorobutane (EOFB), At least one selected from the group consisting of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE) and bis(2,2,2-trifluoroethoxy)ethane.

[0102] The amount of the organic non-solvent used can be adjusted depending on the type of non-aqueous organic solvent and lithium salt, or the overall concentration of the lithium salt, and for example, the organic non-solvent: non-aqueous organic solvent can be included in the electrolyte in a molar ratio of 1:0.2 to 1:5, or 1:0.5 to 1:2.

[0103] Meanwhile, the lithium metal secondary battery of the above embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator can be housed in a case, and manufactured by injecting and impregnating the electrolyte described above.

[0104] These lithium metal secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

[0105]

[0106] The invention will be described in more detail below through specific examples. However, the following examples are provided solely to aid understanding of the invention and do not limit the scope of the invention.

[0107]

[0108] Example 1: Manufacturing of a lithium metal secondary battery

[0109] First, a polyethylene substrate (width*length*thickness: 40mm*60mm*9um, porosity: 55-60%) was prepared for the manufacture of the membrane.

[0110] Al2O3 powder with a D50 of 500 nm was used as the inorganic oxide particle, and PVdF was used as the polymer binder. The inorganic particles (Al2O3) and binder (PVdF) were mixed in a volume ratio of 1:1 in NMP (N-Methyl-2-pyrrolidone) as a solvent to prepare a coating solution. The solid content of the total amount (100 wt%) of the coating solution including the inorganic particles (Al2O3) and the binder (PVdF) was set to 50 wt%.

[0111] After applying the coating solution to one side of the polyethylene substrate, the solution was dried at 80°C for 180 minutes to produce a single-sided coated separator. At this time, the thickness of the coated active layer was approximately 2.5 μm.

[0112] Meanwhile, a 15 μm thick aluminum (Al) metal film was prepared as a positive electrode current collector, and a positive electrode slurry was prepared by dispersing LiFePO4 / C as a positive electrode active material, carbon black as a conductive material, and PVDF as a binder in a weight ratio of 96 1:3 in an NMP solvent on one surface of the aluminum metal film, and coating, drying, and rolling to a thickness of 60 μm to prepare a positive electrode.

[0113] The ceramic coating separator was interposed between the positive electrode and the negative electrode, a lithium foil (thickness: 45 μm), such that the coated surface of the separator faced and contacted the active material layer of the positive electrode, and the non-coated surface of the separator substrate faced and contacted the lithium foil of the negative electrode.

[0114] In the electrode assembly manufactured as above, a lithium salt of LiFSI was dissolved in an ethylene glycol dimethyl ether solvent at a concentration of 1.2 M, and an electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), an organic nonsolvent, was added at 70 wt% based on the total electrolyte, and the electrolyte was injected into the electrode assembly to manufacture a coin half-cell.

[0115]

[0116] Comparative Example 1: Manufacturing of a Lithium Metal Secondary Battery

[0117] A coin half-cell type lithium metal secondary battery was manufactured in the same manner as Example 1, except that the polyethylene substrate (width*length*thickness: 40 mm*60 mm*9 um, porosity: 55-60%) without a separate ceramic coating was used as a separator.

[0118]

[0119] Comparative Example 2: Manufacturing of a Lithium Metal Secondary Battery

[0120] The separator, anode, cathode, and electrolyte were manufactured using the same method as in Example 1.

[0121] However, when the ceramic coating separator is interposed between the positive electrode and the negative electrode, the lithium foil (thickness: 45 μm), the coated surface of the separator is made to face and contact the lithium foil of the negative electrode, and the non-coated surface of the separator substrate is made to face and contact the active material layer of the positive electrode, and a lithium metal secondary battery in the form of a coin half-cell is manufactured in the same manner as Example 1.

[0122]

[0123] Comparative Example 3: Manufacturing of Lithium Metal Secondary Battery

[0124] In manufacturing a separator, a coating solution containing the inorganic particles (Al2O3) and the binder (PVdF) was applied to both sides of a polyethylene substrate and dried to manufacture a double-coated separator. At this time, the thicknesses of the coated active layers were approximately 2.5 μm and 2.5 μm, respectively.

[0125] A coin half-cell type lithium metal secondary battery was manufactured in the same manner as Example 1, except that the double-coated separator was interposed between the positive and negative electrodes so that the two coated surfaces of the separator faced and contacted the active material layer of the positive electrode and the lithium foil of the negative electrode, respectively.

[0126]

[0127] Experimental Example 1

[0128] The coin half-cells manufactured in the above examples and comparative examples were aged at 25°C for 12 hours, charged at the same temperature at a constant current of 0.1C until 3.7 V, and activated for 2 cycles by completely discharging at a constant current of 0.1C at 25°C. Afterwards, the process of charging at 25°C at a constant current of 0.5C until 3.7 V and discharging at 0.5C was repeated.

[0129] As these charge-discharge cycles progressed, the capacity and coulombic efficiency (CE %) per cycle were evaluated, and the results are shown in Figures 1 and 2. For reference, Figure 1 shows the comparative evaluation results of Comparative Examples 2 and 3, and Figure 2 shows the comparative evaluation results of Comparative Example 3 and Example 1.

[0130] Referring to FIGS. 1 and 2, it was confirmed that the lithium metal secondary battery of Example 1 exhibited superior capacity, coulombic efficiency, and lifespan characteristics compared to the lithium metal secondary battery of the comparative example, as the ceramic coating surface of the separator faced and contacted only the positive electrode active material layer.

[0131]

[0132] Experimental Example 2

[0133] In the lithium metal secondary batteries of Example 1 and Comparative Example 2, the surface of the lithium metal negative electrode was analyzed by electron microscopy, and the results are shown in FIGS. 3a and 3b, respectively. In addition, in the lithium metal secondary batteries of Example 1 and Comparative Example 2, the surface of the lithium metal negative electrode was analyzed by electron microscopy, and the results of elemental analysis using EDS (Energy Dispersive Spectroscopy) based on the analysis are shown in FIGS. 4a to 4d, respectively.

[0134] Referring to FIGS. 3a, 4a, and 4b, in the lithium metal secondary battery of Example 1, it was confirmed that no by-products were generated on the surface of the lithium metal negative electrode and that clean surface characteristics were maintained. In contrast, referring to FIGS. 3b, 4c, and 4d, in the lithium metal secondary battery of Comparative Example 2, it was confirmed that a large amount of by-products were generated on the surface of the lithium metal negative electrode (see carbon and oxygen peaks in FIG. 4d, etc.), and in particular, the generation of a large amount of by-products, including aluminum and copper, which appear to have originated from the coating layer (active layer) of the separator, the electrolyte, and / or the current collector, was confirmed.

[0135] From this, it was confirmed that in the case of the lithium metal secondary battery of Comparative Example 2, in which the coating layer (active layer) of the separator faces the lithium metal negative electrode, a large amount of by-products and side reactions were generated on the surface of the negative electrode, resulting in poor electrochemical characteristics and lifespan characteristics. In addition, this tendency can be equally estimated in the lithium metal secondary battery of Comparative Example 3, in which the coating layer (active layer) of the separator faces both the negative electrode and the positive electrode.

Claims

1. A cathode including a cathode active material layer; A cathode comprising a lithium metal layer; A separator comprising a porous separator substrate and an active layer formed only on one side of the porous separator substrate facing the anode and including inorganic oxide particles having a dielectric constant of 5 or more and a polymer binder; and Contains electrolytes, A lithium metal secondary battery, wherein the active layer of the separator is in contact with the positive electrode active material layer, and the lithium metal layer is in contact with the porous separator substrate.

2. In the first paragraph, the positive electrode active material layer is a lithium metal secondary battery including a positive electrode active material including lithium iron phosphate of the following chemical formula 1 or a lithium transition metal oxide of the following chemical formula 2: [Chemical Formula 1] Li 1+a Fe 1-y M y (PO 4-b )X b In the above chemical formula 1, M is at least one selected from Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤y≤0.5, 0≤b≤0.1, [Chemical Formula 2] Li 1+a’ Ni 1-y’-z’-s Co y’ Mr z’ m' s O 2-b’ X b’ In the above chemical formula 2, M' is at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and -0.5≤a'≤0.5, 0 <y’<1, 0<z’<1, 0≤s<0.2, 0≤b’≤0.1이며, In the above chemical formulas 1 and 2, X is at least one selected from F, S, and N.

3. A lithium metal secondary battery according to claim 1, wherein the porous separator substrate comprises a polyolefin resin.

4. A lithium metal secondary battery according to claim 1, wherein the inorganic oxide particles include at least one selected from the group consisting of SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2.

5. In the first paragraph, the polymer binder is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, A lithium metal secondary battery comprising at least one selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

6. A lithium metal secondary battery in accordance with claim 1, wherein the separator is an organic / inorganic porous composite separator in which the inorganic oxide particles are connected and fixed by a polymer binder of the active layer, and a porous structure is formed due to the interstitial volume between the inorganic oxide particles.

7. A lithium metal secondary battery according to claim 1, wherein the thickness of the active layer is 0.1 µm to 10 µm.

8. A lithium metal secondary battery according to claim 1, wherein the electrolyte comprises a non-aqueous organic solvent and a lithium salt.

9. A lithium metal secondary battery in accordance with claim 8, wherein the electrolyte further comprises an organic anti-solvent having a solubility in the lithium salt that is at least 10 times lower than that in the non-aqueous organic solvent.

10. A lithium metal secondary battery in claim 8, wherein the organic non-solvent comprises an acyclic ether compound substituted with multiple fluorines or an acyclic diether compound substituted with multiple fluorines.

11. In the 8th paragraph, the organic non-solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), ethoxynonafluorobutane (EOFB), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (1,2-Bis(1,1,2,2-tetrafluoroethoxy)ethane; TFEE) and bis(2,2,2-trifluoroethoxy)ethane. A lithium metal secondary battery comprising at least one selected from the group consisting of:

Images