Positive electrode active material for all-solid-state battery, and all-solid-state battery comprising same

Abstract

According to embodiments of the present invention, by replacing oxygen (O), which is a monoanion included in a coating layer, with a polyanion (P-O) including phosphorus (P), conventional metal materials can be replaced, and the electrochemical safety of an all-solid-state battery can be improved.

Description

Cathode active material for all-solid-state batteries, and all-solid-state batteries containing the same

[0001] This relates to a cathode active material for an all-solid-state battery and an all-solid-state battery containing the same.

[0002] Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as batteries for small devices such as smartphones, tablets, and laptops. Recently, as they have begun to be used as batteries for electric vehicles or energy storage systems (ESS), related research is actively being conducted.

[0003] Lithium secondary batteries currently used in industry use electrolytes containing flammable organic solvents, posing safety concerns that can lead to explosions or fires in the event of collisions or penetrations. Therefore, all-solid-state batteries, which utilize solid electrolytes instead of the electrolyte, are being proposed. All-solid-state batteries are batteries composed entirely of solid materials, specifically those that utilize solid electrolytes. These all-solid-state batteries are safe, eliminating the risk of electrolyte leakage and explosion, and offer the advantage of being easy to manufacture in thin forms.

[0004] Meanwhile, all-solid-state batteries contain sulfide-based solid electrolytes. If the sulfide-based solid electrolyte comes into direct contact with a positive electrode active material, which has a different stable voltage range, it may deteriorate or decompose. As the sulfide-based solid electrolyte deteriorates or decomposes, battery resistance may increase. Therefore, to prevent this, a method of forming a coating layer by coating the surface of the positive electrode active material has been proposed.

[0005] In the case of conventional coating materials, since they contain rare metals, the price of raw materials and precursors is high, which increases the manufacturing cost of all-solid-state batteries, and the density is high, which reduces the energy density of all-solid-state batteries, and the stable voltage range is lower than the maximum stable voltage range of next-generation positive electrode active materials. When charging and discharging in a voltage range outside the maximum stable voltage range, the coating layer collapses, causing decomposition of the solid electrolyte, and the solid electrolyte is oxidized due to the generation of oxygen due to the low bonding force between the coating materials, which has the disadvantage of lowering the electrochemical stability within the battery.

[0006] The problem to be solved by the present invention is to provide a positive electrode active material with improved stability by forming a coating layer.

[0007] Another problem to be solved by the present invention is to provide a method for manufacturing a positive electrode active material with improved stability by forming a coating layer.

[0008] A cathode active material for an all-solid-state battery according to one embodiment of the present invention may include a lithium transition metal oxide; and a coating layer formed by a coating material including a polyvalent anion (PO) on the surface of the lithium transition metal oxide.

[0009] According to one embodiment of the present invention, a cathode active material can replace a rare metal included in an existing coating layer forming material by replacing a single anion, oxygen (O), included in a coating layer with a polyvalent anion (PO) including phosphorus (P), thereby improving the electrochemical safety and lifespan of an all-solid-state battery.

[0010] FIG. 1 is a cross-sectional view of a positive electrode active material for an all-solid-state battery according to one embodiment of the present invention.

[0011] Figure 2 is a graph showing the XRD results of a positive electrode active material manufactured according to Manufacturing Examples 1 and 2, a positive electrode active material without a coating layer formed, and a coating material.

[0012] Figure 3 is a photograph of the surface of a positive electrode active material manufactured according to Manufacturing Example 1, taken using a transmission electron microscope (TEM).

[0013] Figure 4 is a graph comparing the efficiency and lifespan characteristics of the half cells of Example 1 and Comparative Examples.

[0014] According to one aspect of the present invention, a cathode active material for an all-solid-state battery is provided, comprising: a lithium transition metal oxide; and a coating layer formed by a coating material including a polyvalent anion (PO) on the surface of the lithium transition metal oxide.

[0015] According to one embodiment of the present invention, the lithium transition metal oxide is lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, or lithium iron phosphate, which provides a cathode active material for an all-solid-state battery.

[0016] According to one embodiment of the present invention, the coating material is manufactured by a Li precursor and a P precursor, the Li precursor is at least one selected from lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium sulfide (Li2S), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), and lithium hydroxide (LiOH), and the P precursor is at least one selected from phosphoric acid (H3PO4), ammonium phosphate ((NH4)H2P04, (NH4)2HP04), and lithium metaphosphate (LiPO3), thereby providing a cathode active material for an all-solid-state battery.

[0017] According to one embodiment of the present invention, the coating material provides a positive electrode active material for an all-solid-state battery, which includes a compound containing a polyvalent anion (PO) and a metal represented by the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019] (Li-M)-(PxOy)b

[0020] In the above chemical formula 1, x:y is 2:5 to 2:10, M is a divalent to pentavalent transition metal, and may be Nb, Ni, Ti, Mo, Al, Zn, Cs, Cr, Ag, Mn, Rb, Sn, Cs, Sr, Hf, Sn, Ir, Rb, Cu, Ca, Ga, Cd, Ta, Re, Fe, Rh, Au, Zr, or a combination of any one or more selected from these.

[0021] According to one embodiment of the present invention, a positive electrode active material for an all-solid-state battery is provided, wherein the thickness of the coating layer is 10 nm to 100 nm.

[0022] According to one embodiment of the present invention, a positive electrode active material for an all-solid-state battery is provided, wherein the content of the coating layer is 0.1 wt% to 10 wt% based on the total weight of the positive electrode active material.

[0023] According to another aspect of the present invention, a method for producing a positive electrode active material for an all-solid-state battery is provided, comprising: a step of preparing a coating solution by dissolving a lithium (Li) precursor and a phosphorus (P) precursor in a solvent; a step of forming a mixed solution by adding a lithium transition metal oxide to the coating solution; a step of obtaining a positive electrode active material including a coating layer by stirring and heat-treating the mixed solution; and a step of drying the positive electrode active material including the coating layer.

[0024] According to another embodiment of the present invention, a method for producing a positive electrode active material for an all-solid-state battery is provided, wherein in the step of obtaining a positive electrode active material including a coating layer by stirring and heat-treating the mixed solution, the heating temperature is 50°C to 200°C.

[0025] According to another aspect of the present invention, an all-solid-state battery is provided, comprising: a positive electrode including the positive electrode active material for the all-solid-state battery; a negative electrode; and a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

[0026] According to another embodiment of the present invention, the sulfide-based solid electrolyte is LGPS (Li 10 GeP2S 12 ) system, LPS(Li7P3S 11 ) system, LPSX(Li x P y S z An all-solid-state battery of type X (where X is a halogen element) is provided.

[0027] The present invention is capable of various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, as well as the methods for achieving them, will become clearer with reference to the embodiments described in detail below, along with the drawings. However, the present invention is not limited to the embodiments disclosed below and can be implemented in various forms.

[0028] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0029] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0030] In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0031] In the following examples, when a part such as a film, region, component, etc. is said to be on or above another part, it includes not only a case where it is directly on top of the other part, but also a case where another film, region, component, etc. is interposed in between.

[0032] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to what is shown.

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, and when describing with reference to the drawings, identical or corresponding components will be given the same drawing reference numerals.

[0034] positive electrode active material

[0035] Figure 1 is a cross-sectional view of a positive electrode active material (100) for an all-solid-state battery according to one embodiment of the present invention.

[0036] Referring to FIG. 1, a cathode active material (100) for an all-solid-state battery according to one embodiment of the present invention may include a lithium transition metal oxide (110); and a coating layer (120) formed by a coating material including a polyvalent anion (PO) on the surface of the lithium transition metal oxide (110).

[0037] The positive electrode active material (100) for an all-solid-state battery may include a lithium transition metal oxide (110) and a coating layer (120).

[0038] Lithium transition metal oxide (110) refers to a substance that accepts electrons and is reduced together with a cation, and may include a combination of one or more selected from, for example, lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, or lithium iron phosphate, but is not necessarily limited thereto, and any lithium transition metal oxide (110) used in the relevant technical field may be used.

[0039] The coating layer (120) is formed evenly over the entire surface of the lithium transition metal oxide (110), thereby improving the electrochemical stability range of the lithium transition metal oxide (110), thereby improving the stability voltage range of the all-solid-state battery, and by blocking contact between the lithium transition metal oxide (110) and the solid electrolyte, it can prevent the solid electrolyte from deteriorating or decomposing.

[0040] Specifically, the coating material may include a polyvalent anion (PO), and a specific example may be lithium dihydrogen phosphate (LiH2PO4, LDP). In this case, the surface of a lithium transition metal oxide (110) can be coated without expensive equipment and a complicated process, and the manufacturing cost is greatly reduced compared to coating with a metal oxide containing an expensive metal, so that mass production can be facilitated. In addition, since it has a higher maximum stable voltage range (about 4.6 V) than existing coating materials, it can be used in next-generation high-voltage cathode active materials, and since it has a low density, it can create a thinner and more uniform coating layer (120). In addition, by blocking direct contact between the lithium transition metal oxide (110) and the solid electrolyte, the solid electrolyte can be prevented from being decomposed by the high voltage applied from the lithium transition metal oxide (110) during charge and discharge, oxygen generated from the lithium transition metal oxide (110) can be prevented from directly reacting with the solid electrolyte, and can act as a kind of adhesive that maintains contact between the lithium transition metal oxide (110) and the solid electrolyte. That is, lithium dihydrogen phosphate (LiH2PO4) can act as a new passivation layer that enables the all-solid-state battery to maintain high energy density and lifespan characteristics.

[0041] Meanwhile, the coating material is manufactured using a Li precursor and a P precursor. Specifically, the coating layer (120) can be manufactured by preparing a coating solution by dissolving a lithium (Li) precursor and a phosphorus (P) precursor in a solvent, then adding a lithium transition metal oxide (110) to the coating solution in a desired ratio, followed by heat treatment and drying.

[0042] The Li precursor may be, for example, one or more selected from lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium sulfide (Li2S), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), and lithium hydroxide (LiOH), and the P precursor may be, for example, one or more selected from phosphoric acid (H3PO4), ammonium phosphate ((NH4)H2P04, (NH4)2HP04), and lithium metaphosphate (LiPO3).

[0043] As an optional embodiment, the coating material may include a polyvalent anion (PO) and a metal, for example, the coating material may include a compound including a polyvalent anion (PO) and a metal represented by the following chemical formula 1.

[0044] [Chemical Formula 1]

[0045] Li-M-(PxOy)

[0046]

[0047] In the above chemical formula 1, x:y is 2:5 to 2:10, M is a divalent to pentavalent transition metal, and may be Nb, Ni, Ti, Mo, Al, Zn, Cs, Cr, Ag, Mn, Rb, Sn, Cs, Sr, Hf, Sn, Ir, Rb, Cu, Ca, Ga, Cd, Ta, Re, Fe, Rh, Au, Zr, or a combination of any one or more selected from these. At this time, the value of x:y may be determined depending on the type of metal selected.

[0048] Since the coating material includes a polyvalent anion (PO) and a metal, it can block direct contact between the lithium transition metal oxide (110) and the solid electrolyte, prevent the solid electrolyte from being decomposed by a high voltage applied from the lithium transition metal oxide (110) during charge and discharge, prevent oxygen generated from the lithium transition metal oxide (110) from directly reacting with the solid electrolyte, and can act as a kind of adhesive that maintains contact between the lithium transition metal oxide (110) and the solid electrolyte. That is, the coating material including a polyvalent anion (PO) and a metal can act as a new passivation layer that enables the all-solid-state battery to maintain high energy density and lifespan characteristics.

[0049] As an optional embodiment, the coating layer (120) can be manufactured by preparing a coating solution by dissolving a lithium (Li) precursor, a phosphorus (P) precursor, and a metal (M) precursor in a solvent, then adding a lithium transition metal oxide (110) to the solution in a desired ratio, followed by heat treatment and drying.

[0050] The Li precursor may be, for example, one or more selected from lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium sulfide (LiS), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), and lithium hydroxide (LiOH), the P precursor may be, for example, one or more selected from phosphoric acid (H3PO4), ammonium phosphate (NH4)H2P04, (NH4)2HP04, and LiPO3, and the metal (M) precursor may be, for example, a compound including one selected from Nb, Ni, Ti, Mo, Al, Zn, Cs, Cr, Ag, Mn, Rb, Sn, Cs, Sr, Hf, Sn, Ir, Rb, Cu, Ca, Ga, Cd, Ta, Re, Fe, Rh, Au, and Zr.

[0051] According to one embodiment of the present invention, the positive electrode active material (100) for an all-solid-state battery may have a coating layer (120) having a thickness of 10 nm to 100 nm. Specifically, the lower limit of the thickness of the coating layer (120) may be 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, or 40 nm or more, and the upper limit of the thickness of the coating layer (120) may be 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, or 70 nm or less. When the thickness of the coating layer (120) satisfies the above range, direct contact of the solid electrolyte is blocked without excessively increasing the resistance, and lithium transition metal oxides (110) may be prevented from being arranged in an island shape while being spaced apart from each other on the surface.

[0052] And, the content of the coating layer (120) of the positive electrode active material (100) for an all-solid-state battery according to one embodiment of the present invention may be 0.1 wt% to 10 wt% based on the total weight of the positive electrode active material (100). Specifically, the lower limit of the content of the coating layer (120) may be 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 1.5 wt% or more, 2 wt% or more, or 2.5 wt% or more, and the upper limit of the content of the coating layer (120) may be 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4 wt% or less, or 3 wt% or less. When the content of the coating layer (120) satisfies the above range, a thin yet dense coating layer (120) can be created to maximize the energy density of the positive electrode active material (100).

[0053]

[0054] Method for manufacturing positive electrode active material

[0055] A method for manufacturing a positive electrode active material (100) for an all-solid-state battery according to one embodiment of the present invention may include the steps of: preparing a coating solution by dissolving a lithium (Li) precursor and a phosphorus (P) precursor in a solvent; forming a mixed solution by adding a lithium transition metal oxide (110) to the coating solution; obtaining a positive electrode active material (100) including a coating layer (120) by stirring and heat-treating the mixed solution; and drying the positive electrode active material (100) including the coating layer (120).

[0056] For example, a coating material prepared by dissolving a lithium (Li) precursor and a phosphorus (P) precursor in a solvent can be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the positive electrode active material (100). The mixed solution prepared in this way is heat-treated using a spray dryer at 50°C to 200°C, and then dried at 80°C to less than 150°C to remove any residual solvent that may be present on the surface, thereby preparing a positive electrode active material (100) having a coating layer (120) formed thereon.

[0057] As an optional embodiment, a coating material prepared by dissolving a lithium (Li) precursor, a phosphorus (P) precursor, and a metal (M) precursor in a solvent may be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the positive electrode active material (100).

[0058] The mixed solution thus manufactured is heat-treated using a spray dryer at 50°C to 200°C, and then dried at 80°C to less than 150°C to remove any residual solvent that may be present on the surface, thereby manufacturing a positive electrode active material (100) having a coating layer (120) formed thereon.

[0059] In the step of obtaining a positive electrode active material (100) including a coating layer (120) by stirring and heat-treating the above-mentioned mixed solution, the heating temperature may be 50°C to 200°C. Specifically, the heating temperature may be 50°C or higher, 55°C or higher, 60°C or higher, 65°C or higher, 70°C or higher, 75°C or lower, or 80°C or lower, and may be 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, 160°C or lower, 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, 110°C or lower, or 100°C or lower. Even when the heating temperature satisfies the above range, the coating material can form crystallinity to form a thin yet dense coating layer (120).

[0060]

[0061] All-solid-state battery

[0062] An all-solid-state battery according to one embodiment of the present invention may include a positive electrode including the positive electrode active material (100) for the all-solid-state battery; a negative electrode; and a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

[0063] The above positive electrode can be used in next-generation high-voltage positive electrode active materials because the positive electrode active material (100) for an all-solid-state battery according to the present invention includes a coating layer (120) having a higher maximum stable voltage range (about 4.6 V) than existing coating materials, and by blocking direct contact between the lithium transition metal oxide (110) and the solid electrolyte, the solid electrolyte can be prevented from being decomposed by the high voltage applied from the lithium transition metal oxide (110) during charge and discharge.

[0064] At this time, the positive electrode may have a structure in which a positive electrode composite layer containing the positive electrode of the present invention is formed on a positive electrode current collector. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode composite layer contains a positive electrode active material (100), a conductive agent, a binder, and a solid electrolyte, and may further contain additives as needed.

[0065] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, but specifically, graphite, a carbon-based material, a metal powder or metal fiber, a needle-shaped or branch-shaped conductive whisker, a conductive metal oxide, a conductive polymer, and any one or a mixture thereof may be used. More specifically, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; needle-shaped or branch-shaped conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers; Examples include conductive metal oxides such as titanium dioxide, or conductive polymers such as polyphenylene derivatives, and one or a mixture of two or more of these may be used.

[0066] In addition, the binder for the positive electrode is one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), or a mixture of two or more thereof, N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), acrylonitrile-based styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl butadiene methacrylate rubber (MBR), butadiene rubber (BR), and the like, conjugated diene rubber latex, It may be one selected from the group consisting of carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dienther polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluoroelastomer, various copolymers, etc., or a mixture of two or more thereof.

[0067] The above-described negative electrode may have a structure in which a negative electrode composite layer containing a negative electrode active material is formed on a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and may include, for example, stainless steel, copper, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the negative electrode composite layer contains a negative electrode active material, a conductive material, a binder, and a solid electrolyte, and may further contain an additive if necessary. At this time, the negative electrode active material may be one selected from the group consisting of lithium metal, a lithium alloy, a lithium metal composite oxide, a lithium-containing titanium composite oxide (LTO), and combinations thereof. Here, the lithium alloy may be an alloy composed of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. In addition, the lithium metal composite oxide is an oxide (MeOx) of any one metal (Me) selected from the group consisting of lithium and Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe, and may be, for example, LixFe2O3(0≤x≤1) or LixWO2(0≤x≤1).

[0068] In addition, the negative electrode active material may be a metal composite oxide such as SnxMe1-xMe'yOz (where Me is Mn, Fe, Pb, or Ge, and Me' is Al, B, P, Si, an element of group 1, group 2, or group 3 of the periodic table, or a halogen; 0≤x≤1; 1≤y≤3; 1≤z≤8); an oxide such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and a carbon-based negative electrode active material such as crystalline carbon, amorphous carbon, or a carbon composite may be used alone or in a mixture of two or more thereof.

[0069] Examples of the above-mentioned conductive material include nickel powder, cobalt oxide, titanium oxide, carbon, etc. As for the carbon, any one or more selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene may be mentioned.

[0070] In addition, the binder for the negative electrode is one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), or a mixture of two or more thereof, N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), conjugated diene rubber latex such as styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), and butadiene rubber (BR), It may be any one selected from the group consisting of carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ether polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluoroelastomer, various copolymers, etc., or a mixture of two or more thereof.

[0071] Meanwhile, the solid electrolyte may include a sulfide-based solid electrolyte. Specifically, the sulfide-based solid electrolyte may be LGPS (Li 10 GeP2S 12 ) system, LPS(Li7P3S 11 ) system, or LPSX(Li x P y S z X) system (X is a halogen element) solid electrolyte, and may include, for example, Li6PS5Cl.

[0072] A sulfide-based solid electrolyte containing Li6PS5Cl may begin to decompose at 2.5 V or higher as shown in the following chemical formula 2, and thus, when it comes into direct contact with a lithium transition metal oxide (110) that undergoes charging and discharging in a high voltage range, decomposition may occur.

[0073]

[0074] [Chemical Formula 2]

[0075] 2Li6PS5Cl-(4Li+) → 2Li4PS5Cl (2.0 - 2.5 V)

[0076] → 2LiCl+2S+2Li3PS4-(6Li+) (2.5 - 2.9 V)

[0077] → 2LiCl+P2S7 4- + S (2.9 V ~)

[0078]

[0079] Therefore, when using the cathode active material (100) according to the present invention, it can be used in next-generation high-voltage cathode active materials by including a coating layer (120) having a high maximum stable voltage range (about 4.6 V), and by blocking direct contact between the lithium transition metal oxide (110) and the solid electrolyte, it is possible to prevent the solid electrolyte from being decomposed by the high voltage applied from the lithium transition metal oxide (110) during charge and discharge.

[0080] Hereinafter, examples are presented to help understand the present invention, but the examples are only illustrative of the present disclosure, and the scope of the present application is not construed as being limited to the examples described below, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0081]

[0082] Manufacturing Example 1: Manufacturing of positive electrode active material

[0083] Lithium hydroxide monohydrate (LiOH·H2O) (Sigma Aldrich; >98%) 0.0095 g and phosphoric acid (H3PO 4) (Sigma Aldrich; ≥ 5 wt. % in H2O) was dissolved in 200 ml of ethanol solvent to form a coating solution, and 1.98 g of NCM622 (polycrystalline; D50 5.5 μm, Thermofisher Scientific Korea) powder as a lithium transition metal oxide was added to the solution, stirred and ultrasonically treated at 60 °C for 1 h, and ethanol was dried and evaporated using a spray dryer at 80 °C. The dried powder was dried in a vacuum at 60 °C for one day to obtain a cathode active material (LDP@NCM622) coated with 1 wt% lithium dihydrogen phosphate (LiH2PO4).

[0084]

[0085] Manufacturing Example 2: Manufacturing of positive electrode active material

[0086] A cathode active material (LDP@NCM622) coated with 10 wt% lithium dihydrogen phosphate (LiH2PO4) was obtained using the same method as in Manufacturing Example 1.

[0087]

[0088] Example 1: Half-cell manufacturing

[0089] A positive electrode composite was manufactured by mixing the positive electrode active material (LDP@NCM622), solid electrolyte (Li6PS5Cl), and conductive material (Super P) manufactured according to Manufacturing Example 1 in a weight ratio of 70:30:2, and a half-cell with an inner diameter of 13 mm was manufactured using the same sulfide-based solid electrolyte as a separator and Li-In powder as a negative electrode.

[0090]

[0091] Example 2: Half-cell manufacturing

[0092] A half cell was manufactured in the same manner as in Example 1, except that the positive electrode active material (LDP@NCM622) manufactured according to Manufacturing Example 2 was used.

[0093]

[0094] Comparative Example 1: Half-cell manufacturing

[0095] A half cell was manufactured in the same manner as in Example 1, except that a cathode active material (Bare NCM622) without a coating layer was used.

[0096]

[0097] Comparative Example 2: Half-cell manufacturing

[0098] A half-cell was manufactured in the same manner as in Example 1, except that a positive electrode active material (LNO@NCM622) coated with lithium niobate (LiNbO3) was used.

[0099]

[0100] Experimental Example 1: X-ray diffraction (XRD) analysis

[0101] X-ray diffraction (XRD) analysis was performed using Aeris from Marvern on the positive electrode active material (LDP@NCM622) manufactured according to Manufacturing Examples 1 and 2 and the positive electrode active material without a coating layer formed (Bare NCM622). Cu K α radiation was used for the X-ray diffraction (XRD) analysis. The results of the X-ray diffraction (XRD) analysis are shown in Fig. 2.

[0102] Referring to FIG. 2, it can be confirmed that the positive electrode active materials (LDP@NCM622) manufactured according to Manufacturing Examples 1 and 2 have the same pattern of peaks as the positive electrode active material (Bare NCM622) on which a coating layer is not formed. However, in the case of the positive electrode active material (LDP@NCM622) manufactured according to Manufacturing Example 2, it can be confirmed that multiple small peaks showing a different pattern from the positive electrode active material (Bare NCM622) on which a coating layer is not formed are observed, and since these small peaks have the same pattern as the peaks observed in the graph of lithium dihydrogen phosphate (LiH2PO4), it can be seen that the positive electrode active material (LDP@NCM622) manufactured according to Manufacturing Example 2 has a coating layer formed. In addition, in the case of the positive electrode active material (LDP@NCM622) manufactured according to Manufacturing Example 1, there is no change in crystal phase as seen in XRD compared to the positive electrode active material (Bare NCM622) in which a coating layer is not formed, but since no crystallinity for other impurities is detected, it can be assumed that a coating layer was formed even when the content of lithium dihydrogen phosphate (LiH2PO4) is 1 wt%.

[0103]

[0104] Experimental Example 2: Transmission Electron Microscopy (TEM) Measurements

[0105] The surface of the positive electrode active material manufactured according to Manufacturing Example 1 was measured using Titan cubed G2 60-300 from FEI. The results of the transmission electron microscope (TEM) measurement are shown in Fig. 3.

[0106] Referring to FIG. 3, a thin layer was observed on the surface of the positive electrode active material manufactured according to Manufacturing Example 1, and this was observed to be a substance including phosphorus (P), i.e. lithium dihydrogen phosphate (LiH2PO4), so it can be confirmed that the surface of the positive electrode active material manufactured according to Manufacturing Example 1 was uniformly coated with lithium dihydrogen phosphate (LiH2PO4).

[0107]

[0108] Experimental Example 3: Evaluation of Charge-Discharge Characteristics

[0109] Galvanostatic charge / discharge was performed at 30°C and a rate of 0.2C (1C = 200 mA·g-1) in a voltage range of 2.38–3.68 V vs. Li-In / Li+, which corresponds to 3.0–4.3 V vs. Li / Li+, using the WonAtech charge / discharge cycle. The results are shown in Fig. 4.

[0110] At this time, 100 th The coulombic efficiency (CCE) and cycle retention in the cycle were derived using the following formulas. The results are shown in Table 1.

[0111] Coulomb efficiency (%) = {100 th Discharge capacity in cycles (mAh / g) / 100 th Charging capacity in cycles (mAh / g)}Х100

[0112] Cycle capacity retention rate (%) = (100 th Discharge capacity in cycles / 3 rd Discharge capacity in cycles)Х100

[0113]

[0114] 1 st Discharge capacity (mAh / g)3 rd Discharge capacity (mAh / g) 100 th Discharge capacity (mAh / g) Coulombic efficiency (%) Capacity retention rate (%) Example 1127.98134.23125.0299.16%94.10 Comparative example 1139.95140.48103.87100.77%73.88 Comparative example 2116.78123.18118.6098.03%96.95

[0115]

[0116] Referring to Table 1 and FIG. 4, Comparative Example 1, which used a cathode active material without a coating layer (Bare NCM622), showed higher capacity and higher coulombic efficiency than Example 1 and Comparative Example 2, which used a cathode active material with a coating layer, but the capacity continuously decreased, and from the 15th cycle onward, Example 1 and Comparative Example 2 showed higher capacity, confirming that the coating layer prevented decomposition of the electrolyte and thus improved capacity retention.

[0117] In addition, it can be confirmed that Example 1 using a positive electrode active material (LDP@NCM622) coated with lithium dihydrogen phosphate (LiH2PO4) shows a more stable Coulombic efficiency than Comparative Example 2 using a positive electrode active material (LNO@NCM622) coated with lithium niobate (LiNbO3).

[0118] Consequently, by coating the cathode active material with lithium dihydrogen phosphate (LiH2PO4), the surface of the cathode active material can be coated without expensive devices and complex processes, metals can be replaced, solid electrolytes can be prevented from decomposing, and the battery can maintain high energy density and life characteristics.

Claims

1. Lithium transition metal oxide; and A cathode active material for an all-solid-state battery, comprising a coating layer formed by a coating material containing a polyvalent anion (PO) on the surface of the lithium transition metal oxide.

2. In paragraph 1, The above lithium transition metal oxide is a cathode active material for an all-solid-state battery, wherein the cathode active material is lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, or lithium iron phosphate.

3. In paragraph 1, The above coating material is manufactured by a Li precursor and a P precursor, A cathode active material for an all-solid-state battery, wherein the Li precursor is at least one selected from lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium chloride (LiCl), lithium sulfide (Li2S), lithium nitrate (LiNO3), lithium phosphate (Li3PO4), and lithium hydroxide (LiOH), and the P precursor is at least one selected from phosphoric acid (H3PO4), ammonium phosphate ((NH4)H2P04, (NH4)2HP04), and lithium metaphosphate (LiPO3).

4. In paragraph 1, The above coating material is a cathode active material for an all-solid-state battery, lithium dihydrogen phosphate (LiH2PO4, LDP).

5. In paragraph 1, A cathode active material for an all-solid-state battery, wherein the thickness of the coating layer is 10 nm to 100 nm.

6. In paragraph 1, A cathode active material for an all-solid-state battery, wherein the content of the coating layer is 0.1 wt% to 10 wt% based on the total weight of the cathode active material.

7. A step of preparing a coating solution by dissolving a lithium (Li) precursor and a phosphorus (P) precursor in a solvent; A step of forming a mixed solution by adding lithium transition metal oxide to the above coating solution; A step of obtaining a positive electrode active material including a coating layer by stirring and heat-treating the above mixed solution; and A method for producing a cathode active material for an all-solid-state battery, comprising: a step of drying a cathode active material including the coating layer.

8. In paragraph 7, A method for producing a cathode active material for an all-solid-state battery, wherein in the step of stirring and heat-treating the above-mentioned mixed solution to obtain a cathode active material including a coating layer, the heating temperature is 50°C to 200°C.

9. A cathode comprising a cathode active material for an all-solid-state battery according to Article 1; cathode; and An all-solid-state battery comprising a sulfide-based solid electrolyte disposed between the positive electrode and the negative electrode.

10. In paragraph 9, The above sulfide-based solid electrolyte is LGPS (Li 10 GeP2S 12 ) system, LPS(Li7P3S 11 ) system, LPSX(Li x P y S z An all-solid-state battery of the X system (X is a halogen element).

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