Positive electrode active material for secondary battery, positive electrode containing the same, secondary battery, and method for manufacturing the same

Abstract

The present invention relates to a positive electrode active material for a secondary battery, a positive electrode including the same, a secondary battery, and a method for manufacturing the same, and more particularly to a positive electrode active material including a core and a nitrogen-containing lithium oxide-containing coating layer.

Description

[Technical Field]

[0001] Cross-reference to related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0170747 filed November 30, 2023 and Korean Patent Application No. 10-2024-0174355 filed November 29, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for a secondary battery, a positive electrode including the same, a secondary battery, and a method for manufacturing the same, and more particularly to a positive electrode active material including a core and a nitrogen-containing lithium oxide-containing coating layer. [Background technology]

[0003] All-solid-state lithium batteries use sulfide-based, oxide-based, or polymer-based solid electrolytes and can directly convert chemical energy into electrical energy by oxidizing or reducing lithium ions through the all-solid-state material. In particular, they offer advantages such as environmental friendliness, safety, and high energy density capacity storage. They are gaining in popularity as sustainable secondary batteries because they can solve the limitations of currently available lithium secondary batteries, such as low energy density, high cost, and toxicity.

[0004] However, all-solid-state batteries have been facing problems such as a decrease in battery capacity due to irreversible side reactions at the interface between the positive electrode active material and the solid electrolyte, which is in direct contact with the positive electrode active material during charge and discharge reactions, and uneven distribution of electrode charge due to interface resistance and space-charge layer formation.

[0005] To solve these problems, a technology has been developed in which a cathode active material is surface-treated with a metal oxide or the like and applied to an all-solid-state battery. However, the metal oxide is only used alone or in combination with other materials, and further research into the metal oxide itself is needed. [Prior art documents]

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide a positive electrode active material for a secondary battery in which a metal oxide coating layer containing nitrogen is formed as a coating layer on the surface of the positive electrode active material, improving the resistance of the battery and extending the battery life.

Means for Solving the Problems

[0008] To solve the above problems, in one embodiment of the present invention, there is provided a positive electrode active material for a secondary battery, including a core containing a lithium metal oxide and a coating layer formed on the surface of the core and containing an oxide represented by the following Chemical Formula 1, wherein the coating layer contains nitrogen: [Chemical Formula 1] Li

[0009] , , 1 , ,

[0011] , ,

[0010] , , M 1 b O c In the Chemical Formula 1, 0 < a ≤ 4, 0 < b ≤ 5, and 0 < c ≤ 12, and M 1 is at least one selected from B, Al, Zr, P, Ti, Nb, and W.

[0009] In one embodiment of the present invention, there is provided a positive electrode active material for a secondary battery, wherein in the oxide represented by the Chemical Formula 1, M 1 is Ti.

[0010] In one embodiment of the present invention, there is provided a positive electrode active material for a secondary battery, wherein the nitrogen is derived from a nitrogen oxide or an aqueous solution containing nitrogen ions.

[0011] In one embodiment of the present invention, the nitrogen is NO2 - , NO3 - The present invention provides a positive electrode active material for a secondary battery, which is contained in at least one form selected from the group consisting of N2O, N2O3, N2O4, N2O5, N3O7, and NH4OH.

[0012] In one embodiment of the present invention, the mole number of Ti element in the coating layer (N Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti ) is 0.5 to 2.0.

[0013] In one embodiment of the present invention, the mole number of Ti element in the coating layer (N Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti ) is 0.6 to 1.0.

[0014] In one embodiment of the present invention, there is provided a positive electrode active material for a secondary battery, wherein the content of the coating layer is 0.1 wt % to 5.0 wt % based on the total weight of the positive electrode active material.

[0015] In one embodiment of the present invention, the lithium metal oxide is a positive electrode active material for a secondary battery represented by the following Chemical Formula 2: [Chemical formula 2] Li x [Ni y Co z Mn w M 2 v ]O2 In the above Chemical Formula 2, M 2 is at least one element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are in the ranges 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, while y+z+w+v=1.

[0016] In one embodiment of the present invention, there is provided a positive electrode for a secondary battery, comprising the positive electrode active material for a secondary battery, a solid electrolyte, a conductive material, and a binder.

[0017] In one embodiment of the present invention, (S1) adding a solution containing positive electrode active material particles to a titanium precursor solution to prepare a first mixed solution; (S2) adding a nitrogen-containing lithium source solution to the first mixed solution to prepare a second mixed solution; (S3) heat-treating the second mixed solution to prepare a cathode active material having a coating layer formed thereon.

[0018] In one embodiment of the present invention, there is provided a method for manufacturing a positive electrode for a secondary battery, wherein the heat treatment temperature in step (S3) is 400° C. or less.

[0019] In one embodiment of the present invention, there is provided a method for manufacturing a positive electrode for a secondary battery, wherein in step (S3), the coating layer contains nitrogen.

[0020] In one embodiment of the present invention, there is provided an all-solid-state lithium secondary battery including the positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0021] The cathode active material for a secondary battery according to the present invention has a nitrogen-containing metal oxide coating layer formed on its surface, which suppresses the reaction between the cathode active material and the solid electrolyte, thereby reducing the interfacial resistance and simultaneously suppressing the increase in electrode resistance due to charge / discharge, thereby improving the life of the battery containing the cathode active material. DETAILED DESCRIPTION OF THE INVENTION

[0022] Because the present invention is susceptible to various modifications and embodiments, a specific embodiment will be described in detail.

[0023] However, it should be understood that this is not to limit the invention to the particular embodiments, but to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0024] In the present invention, the terms "comprise" or "have" and the like are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0025] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "immediately above" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "immediately below" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0026] The present invention will now be described in more detail.

[0027] [Cathode active material for secondary batteries] In one embodiment of the present invention, a positive electrode active material for a secondary battery includes a core containing a lithium metal oxide and a coating layer formed on a surface of the core and containing an oxide represented by the following Chemical Formula 1, wherein the coating layer may contain nitrogen: [Chemical formula 1] Li a M 1 b O c In the above Chemical Formula 1, 0 < a ≤ 4, 0 < b ≤ 5, and 0 < c ≤ 12, M 1 is at least one selected from B, Al, Zr, P, Ti, Nb, and W.

[0028] In one embodiment of the present invention, the secondary battery may be an all-solid-state battery.

[0029] In one embodiment of the present invention, the all-solid-state battery may be a sulfide-based all-solid-state battery.

[0030] The lithium metal oxide contained in the core is not particularly limited as long as it is a lithium metal oxide that reversibly reacts during charging and discharging of the battery to provide lithium ions, and may specifically contain a lithium metal oxide represented by the following Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mn w M 2 v O2 In Chemical Formula 2, M 2 is at least one element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, y, z, w, and v are respectively 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 1, 0 ≤ z ≤ 1, 0 ≤ w ≤ 1, 0 ≤ v ≤ 0.1, while y + z + w + v = 1.

[0031] The lithium metal oxide represented by Chemical Formula 2 is an oxide containing a transition metal together with lithium, and may contain a high content of nickel among the transition metals. As an example, the lithium metal oxide may be LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2, and LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 It may contain at least one selected from, but not limited to, O2. The lithium metal oxide contains nickel in a high content and has an excellent effect of improving the charge and discharge capacity of the battery.

[0032] The positive electrode active material for a secondary battery according to the present invention may include a coating layer formed on the surface of the core and containing an oxide represented by the following Chemical Formula 1: [Chemical Formula 1] Li[[ID= forty-five]] a M 1 b O c In the Chemical Formula 1, 0 < a ≤ 4, 0 < b ≤ 5, and 0 < c ≤ 12, M 1 is at least one selected from B, Al, Zr, P, Ti, Nb, and W.

[0033] The oxide represented by the Chemical Formula 1 is an oxide containing a transition metal (M 1 ) together with lithium, and in particular, it may contain Ti among the transition metals. As an example, the oxide represented by the Chemical Formula 1 may be lithium titanate (LTO), and may be at least one selected from Li4Ti5O 12 ​​The lithium titanium oxide may be preferably used because it has stable life characteristics and safety.

[0034] The positive electrode active material for a secondary battery according to the present invention may include a coating layer containing nitrogen, that is, the positive electrode active material for a secondary battery according to the present invention may include a coating layer of lithium titanium oxide containing nitrogen.

[0035] The nitrogen may be derived from nitrogen oxides or from an aqueous solution containing nitrogen ions. - , NO3 - , N2O, N2O3, N2O4, N2O5, N3O7, and NH4OH.

[0036] In the process of coating the surface of the positive electrode active material core with a coating layer, a high-temperature heat treatment is required when synthesizing a lithium source and a titanium source using a liquid, i.e., wet, sol-gel method, but this requires a heat treatment of 400°C or higher in the manufacturing process, which reduces economic efficiency and efficiency.

[0037] Therefore, the present inventors have completed the present invention by alleviating the process conditions and improving the ionic conductivity to improve the life characteristics of the battery.

[0038] That is, by including nitrogen element in the lithium ion supply source, the heat treatment temperature in the manufacturing process can be significantly reduced to 200°C or less, improving economy and efficiency. Furthermore, it was confirmed that the ionic conductivity of the cathode active material coated with the coating layer is significantly superior to that of cathode active materials containing conventional lithium ion supply sources.

[0039] The nitrogen element may be detected without disappearing even after being coated on the core surface and subjected to heat treatment.

[0040] In one embodiment of the present invention, when the positive electrode active material for a secondary battery includes a lithium titanium oxide coating layer containing nitrogen, the mole number of titanium (Ti) element in the coating layer (N Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti ) may be 0.5 to 2.0. More specifically, in the positive electrode active material for a secondary battery, N in the coating layer may be N / N Ti The value may be 0.5 or more, 0.55 or more, 0.6 or more, 0.65 or more, or 2.0 or less, 1.8 or less, 1.6 or less, 1.4 or less, 1.2 or less, 1.0 or less.

[0041] The mole number of titanium (Ti) element in the coating layer (N Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti If the molar ratio (N) of titanium (Ti) in the coating layer is less than 0.5, the content of lithium titanium oxide in the coating layer is relatively higher than the content of nitrogen, which increases the heat treatment temperature required to form the coating layer in the manufacturing process of the positive electrode, resulting in a decrease in economy and efficiency. Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti ) exceeds 2.0, the nitrogen content in the coating layer becomes relatively higher than the titanium content, which causes the generation of impurities of excessively supplied nitrogen compounds, resulting in a problem of reduced ionic conductivity of the positive electrode active material.

[0042] In one embodiment of the present invention, the content of the coating layer may be 0.1 wt % to 5.0 wt % based on the total weight of the positive electrode active material. More specifically, the content of the coating layer may be 0.1 wt % or more, 0.5 wt % or more, 1.0 wt % or more, 1.5 wt % or more, 2.0 wt % or more, 2.5 wt % or more, 3.0 wt % or more, or 5.0 wt % or less, 4.5 wt % or less, 4.0 wt % or less, 3.5 wt % or less based on the total weight of the positive electrode active material.

[0043] [Positive electrodes for secondary batteries] The lithium secondary battery according to the present invention contains the above-described positive electrode active material of the present invention, and thereby side reactions occurring at the interface between the positive electrode active material and the solid electrolyte are suppressed, the resistance inside the positive electrode is reduced, and the battery performance may be characterized by excellent properties.

[0044] In this case, the positive electrode may have a structure in which a positive electrode mixture layer containing the above-described positive electrode active material of the present invention is formed on a positive electrode current collector.

[0045] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may include, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like.

[0046] The positive electrode mixture layer contains a positive electrode active material, a solid electrolyte, a conductive material, and a binder, and may further contain an additive in some cases.

[0047] The solid electrolyte may include at least one selected from a sulfide-based solid electrolyte, a polymer-based solid electrolyte, and an oxide-based solid electrolyte, and preferably includes a sulfide-based solid electrolyte. The solid electrolyte may be in a particulate form.

[0048] The sulfide-based solid electrolyte contains sulfur (S) and has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and may include Li-PS-based glass or Li-PS-based glass ceramic.

[0049] Specifically, the sulfide-based solid electrolyte may contain one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and preferably contains one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, and Li6PS5I. The Li6PS5Cl, Li6PS5Br, and Li6PS5I may be argyrodite-type solid electrolytes. The sulfide-based solid electrolyte may be doped with a trace element, for example, Li6PS5Cl doped with bromine (Br).

[0050] The polymer solid electrolyte is a composite of lithium salt and polymer resin, i.e., a polymer electrolyte material formed by adding polymer resin to solvated lithium salt, and has a capacity of about 1×10 -7 S / cm or more, preferably about 1×10 -5 It may exhibit ionic conductivity of S / cm or more.

[0051] Non-limiting examples of the polymer resin include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives such as polyethylene oxide, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups, and the polymer electrolyte may include one or more of these. Examples of the polymer resin include branched copolymers in which a polyethylene oxide (PEO) main chain is copolymerized with an amorphous polymer such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane (pdms), and / or phosphazene, as a comonomer, comb-like polymer resins, and crosslinked polymer resins, and the polymer electrolyte may include one or more of these.

[0052] In the electrolyte of the present invention, the lithium salt is an ionizable lithium salt, and Li + X - The anion of such a lithium salt is not particularly limited, but may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C- , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - Examples include:

[0053] The oxide-based solid electrolyte may contain oxygen (O) and have the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. For example, an LLTO-based compound, Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (where 0≦x≦1, 0≦y≦1), LiAl x Zr 2-x (PO4)3 (where 0≦x≦1, 0≦y≦1), LiTi x Zr 2-x (PO4)3 (where 0≦x≦1, 0≦y≦1), LISICON-based compounds, LIPON-based compounds, perovskite-based compounds, Nasicon-based compounds, and LLZO-based compounds may be included.

[0054] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. Specifically, graphite, carbon-based materials, metal powder or metal fiber, needle-like or branch-like conductive whiskers, conductive metal oxides, conductive polymers, and any one or a mixture of these may be used. More specifically, examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal 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; conductive metal oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives, and a mixture of any one or more of these may be used.

[0055] The binder for the positive electrode is any 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-styrene butadiene The rubber may be any one selected from the group consisting of conjugated diene rubber latex such as styrene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, or a mixture of two or more thereof.

[0056] Furthermore, the negative electrode may have a structure in which a negative electrode mixture layer containing a negative electrode active material is formed on a negative electrode current collector.

[0057] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may include, for example, stainless steel, copper, nickel, titanium, baked carbon, or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like.

[0058] The negative electrode mixture layer contains a negative electrode active material, a conductive material, a binder, and a solid electrolyte, and may further contain additives in some cases.

[0059] At this time, the negative electrode active material can be one selected from the group consisting of lithium metal, lithium alloy, lithium metal composite oxide, lithium-containing titanium composite oxide (LTO), and combinations thereof. Here, as the lithium alloy, 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 may be used. Further, the lithium metal composite oxide is an oxide (MeO x ) of any one metal (Me) selected from the group consisting of lithium and Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe. As an example, it may be Li x Fe2O3 (0 < x ≦ 1) or Li x WO2 (0 < x ≦ 1).

[0060] Furthermore, as the negative electrode active material, metal composite oxides such as Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5 may be used, and carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon, or carbon composites may be used alone or in combination of two or more.

[0061] In addition, examples of the conductive material include nickel powder, cobalt oxide, titanium oxide, carbon, etc. Examples of carbon include any one selected from the group consisting of ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene, or one or more of these.

[0062] The binder for the negative electrode is any 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), styrene butadiene glycol The rubber may be any one selected from the group consisting of conjugated diene rubber latex such as styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, or a mixture of two or more thereof.

[0063] [Method of manufacturing a positive electrode for a secondary battery] In one embodiment of the present invention, a method for producing a positive electrode for a secondary battery includes the steps of: (S1) adding a solution containing positive electrode active material particles to a titanium precursor solution to prepare a first mixed solution; (S2) adding a nitrogen-containing lithium source solution to the mixed solution to prepare a second mixed solution; (S3) heat-treating the second mixed solution to prepare a cathode active material having a coating layer formed thereon.

[0064] In the method for manufacturing a positive electrode for a secondary battery, in step (S1), a solution containing positive electrode active material particles may be mixed with a titanium precursor solution to prepare a first mixed solution.

[0065] Thereafter, in step (S2), a nitrogen-containing lithium source solution may be added to the first mixed solution to prepare a second mixed solution, which may form a nitrogen-containing lithium cobalt oxide coating layer on the surface of the positive electrode active material.

[0066] Here, the nitrogen-containing lithium supply source may be, but is not limited to, lithium nitroxide or an aqueous solution containing lithium and nitrogen ions.

[0067] The description of the nitrogen is the same as above.

[0068] In addition, the method for manufacturing a positive electrode for a secondary battery according to the present invention may include, in step (S3), heat-treating the second mixed solution to manufacture a positive electrode active material having a coating layer formed thereon.

[0069] In this case, the heat treatment temperature may be 400° C. or less, more specifically, 400° C. or less, 350° C. or less, 300° C. or less, 250° C. or less, or 200° C. or less. By coating the surface of the positive electrode active material with a nitrogen-containing lithium cobalt oxide coating layer, the present invention significantly reduces the heat treatment temperature compared to conventional methods, which may improve the economy and efficiency of the manufacturing process.

[0070] The positive electrode active material having the coating layer formed in step (S3) may contain nitrogen in the coating layer even after heat treatment, which means that the nitrogen element can be detected without disappearing even after heat treatment after being coated on the core surface. [Example]

[0071] The present invention will be described in more detail below with reference to examples and experimental examples.

[0072] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0073] [Production Example 1: Production of nitrogen-containing lithium oxide film] A lithium nitrate (LiNO3) solution was prepared by adding 2 g of lithium nitrate to 100 ml of water (H2O). A titanium precursor solution was prepared by adding 10.3 g of titanium (IV) propoxide and 2.9 g of acetylacetone to 100 ml of 2-propanol.

[0074] The lithium nitrate solution was slowly added to the titanium precursor solution and mixed for 2 hours. A thin layer was applied to a Petri dish and dried in a fume hood for 100 hours. The thin film thus obtained was heat-treated at 200°C for 4 hours to form a Li4Ti5O3 film containing nitrogen (N). 12 The molar ratio of nitrogen (N) to titanium (Ti) was N / N Ti The molar ratio of nitrogen (N) to titanium (Ti) was confirmed to be 0.83. N / N Ti ) was measured by ICP-MS analysis.

[0075] [Production Example 2: Production of nitrogen-containing lithium oxide film] A mixed solution of 10 g of TiO2 and 100 ml of KOH was added to 50 ml of distilled water, and a small amount of acetic acid was added to prepare a TiO2·nH2O solution. LiOH was added to the mixed solution in a stoichiometric ratio, and NH3·H2O was dissolved in [Li + ]:[N]=1:1 to prepare a mixed solution.

[0076] The thin film was thinly coated in a Petri dish and dried in a fume hood for 100 hours. The thin film thus obtained was heat-treated at 200 °C for 72 hours to form a Li4Ti5O 12 The molar ratio of nitrogen (N) to titanium (Ti) was N / N Ti The element molar ratio of nitrogen (N) to titanium (Ti) (N N / N Ti ) was measured by ICP-MS analysis.

[0077] [Production Example 3: Production of nitrogen-containing lithium oxide film] A mixed solution was prepared by adding 1 g of lithium nitrate and 1 g of lithium hydroxide to 100 ml of water (HO). A titanium precursor solution was prepared by adding 10.3 g of titanium (IV) propoxide and 2.9 g of acetylacetone to 100 ml of 2-propanol.

[0078] The mixed solution was slowly added to the titanium precursor solution and mixed for 2 hours, after which it was thinly coated on a Petri dish and dried in a fume hood for 100 hours. The thin film thus obtained was heat-treated at 200°C for 4 hours to form a Li4Ti5O3 film containing nitrogen (N). 12 The molar ratio of nitrogen (N) to titanium (Ti) was N / N Ti The molar ratio of nitrogen (N) to titanium (Ti) was confirmed to be 0.39. N / N Ti ) was measured by ICP-MS analysis.

[0079] [Production Example 4: Production of nitrogen-containing lithium oxide film] A lithium nitrate solution was prepared by adding 6 g of lithium nitrate to 100 ml of water (HO). A titanium precursor solution was prepared by adding 10.3 g of titanium (IV) propoxide and 2.9 g of acetylacetone to 100 ml of 2-propanol.

[0080] The lithium nitrate solution was slowly added to the titanium precursor solution and mixed for 2 hours, after which it was thinly coated on a Petri dish and dried in a fume hood for 100 hours. The thin film thus obtained was heat-treated at 200°C for 4 hours to form Li4Ti5O containing nitrogen (N). 12 The molar ratio of nitrogen (N) to titanium (Ti) was N / N Ti ) was confirmed to be 2.21.

[0081] Comparative Example 1: Production of Nitrogen-Free Lithium Oxide Film A lithium ethoxide solution was prepared by adding 2 g of lithium ethoxide to 100 ml of 2-propanol, and a titanium precursor solution was prepared by adding 13.7 g of titanium (IV) propoxide to 100 ml of 2-propanol.

[0082] The lithium ethoxide solution was slowly added to the titanium precursor solution, and then mixed for 24 hours.

[0083] [Experimental Example 1: Measurement of ionic conductivity] The ionic conductivities of the lithium oxide films of Preparation Examples 1 to 4 and Comparative Example 1 were measured by electrochemical impedance spectroscopy (EIS) in a frequency range of 5.0 mHz to 7.0 mHz with an applied alternating current (AC) voltage of 10 mV, by fabricating symmetrical cells having a solid electrolyte / ion conductor / solid electrolyte structure. The results are shown in Table 1 below.

[0084] [Table 1] [Table 1]

[0085] As shown in Table 1, it was confirmed that the ionic conductivities of Production Examples 1 and 2, which contain nitrogen element, are significantly higher than that of Comparative Example 1, which does not contain nitrogen. Production Examples 3 and 4 contain nitrogen, but the element molar ratio of nitrogen (N) to titanium (Ti) (N N / N Ti ) is either too high or too low, resulting in poor structural stability and significantly low ionic conductivity.

[0086] [Example 1: Production of positive electrode] The positive electrode active material is LiNi with a particle size (D50) of 5 μm. 0.8 Co 0.1 Mn 0.1100 g of O2 was added to 500 ml of 2-propanol and mixed for 2 hours. The titanium precursor solution prepared in Preparation Example 1 was added to the mixed solution and mixed for 2 hours, after which the lithium nitrate solution was slowly added and mixed for 24 hours. The mixed solution was vacuum dried at 60°C and then heat-treated at 200°C for 4 hours to obtain Li4Ti5O containing N. 12 A positive electrode active material coated with ZnO was prepared.

[0087] The prepared cathode active material composite (81.9 wt%), solid electrolyte LPS (15.6 wt%), carbon black powder (1.5 wt%), and PTFE (1 wt%) were mixed without solvent using a wrap blender (Waring) at 5000 rpm for 1 minute (primary mixing). Next, a shear force of 100 N was applied to the mixture, and high-shear mixing (using PBV-0.1L, Irie Shokai) was performed (secondary mixing) to produce a dough. Next, the dough was milled using a two-roll mill (MR-3, Inoue) to produce a free-standing electrode layer.

[0088] The electrode layer was placed on one side of an aluminum current collector having a thickness of 15 μm and pressed to prepare a positive electrode.

[0089] Comparative Example 2 The positive electrode active material is LiNi with a particle size (D50) of 5 μm. 0.8 Co 0.1 Mn 0.1 100 g of O2 was added to 500 ml of 2-propanol and mixed for 2 hours. The titanium precursor solution prepared in Comparative Example 1 was added to the mixed solution and mixed for 2 hours, after which the lithium ethoxide solution was slowly added and mixed for 24 hours. The mixed solution was vacuum dried at 50°C and then heat-treated at 400°C for 4 hours to obtain nitrogen-free Li4Ti5O 12 A positive electrode was prepared in the same manner as in Example 1, except for the method for preparing the positive electrode active material.

[0090] [Experimental Example 2: Evaluation of all-solid-state batteries] All-solid-state batteries were manufactured including the cathodes prepared in Example 1 and Comparative Example 2. The all-solid-state batteries used lithium metal with a thickness of 40 μm as the anode, and a solid electrolyte membrane of Li6PS5Cl with a thickness of 50 μm was interposed between the cathode and anode prepared in the above examples, and then pressurized at a pressure of 500 MPa to form a jig cell with a capacity of 5 mAh at a driving pressure of 3 MPa.

[0091] (1) Evaluation of initial discharge capacity and efficiency of all-solid-state batteries The battery was charged at a rate of 0.1 C (C-rate) until the voltage reached 4.25 V (vs. Li), and then cut off at a rate of 0.05 C while maintaining this voltage at 4.25 V (vs. Li). Subsequently, the battery was discharged at a rate of 0.1 C (C-rate) until the voltage reached 3.0 V (vs. Li) (1 st The initial efficiency was calculated by discharging capacity / charging capacity x 100 (%).

[0092] (2) Evaluation of the lifespan characteristics of all-solid-state batteries The battery was charged at a 0.33 C rate until the voltage reached 4.25 V (vs. Li), and then cut off at a 0.1 C rate while maintaining 4.25 V (vs. Li). It was then discharged at a 0.33 C rate until the voltage reached 3.0 V (vs. Li). This charge-discharge test was repeated 50 times, and the capacity retention rate of the discharge capacity was measured.

[0093] (3) The content of each element in the coated positive electrode active material was measured by ICP-MS analysis, and the content ratio of the coating layer to the active material and the ratio of N element to Ti element were measured.

[0094] Table 2 below shows the results of the content of the positive electrode active material surface coating layer, the ratio of N element to Ti element, the 0.1C initial capacity and initial efficiency, and the 50 cycle capacity retention rate.

[0095] [Table 2] [Table 2]

[0096] As shown in Table 2, the mole number of Ti element in the coating layer of the positive electrode active material (N Ti ) to the mole number of the nitrogen element (N N ) ratio (N N / N Ti It was confirmed that the battery of Example 1, in which the ratio of the positive electrode active material to the positive electrode active material is 2.0 or less, has a significantly higher capacity retention rate than the battery of Comparative Example 2, which uses a nitrogen-free positive electrode active material. In other words, it was found that the battery of Example 1 has improved life characteristics compared to the battery of Comparative Example 2.

Claims

1. a core containing lithium metal oxide; a coating layer formed on the surface of the core and containing an oxide represented by the following Chemical Formula 1: The coating layer comprises a positive electrode active material for a secondary battery containing nitrogen: [Chemical formula 1] Li ａ M １ ｂ O ｃ In the above Chemical Formula 1, 0<a≦4, 0<b≦5, and 0<c≦12; M １ is at least one selected from B, Al, Zr, P, Ti, Nb, and W.

2. The oxide represented by the formula 1 is M １ The positive electrode active material for a secondary battery according to claim 1 , wherein is Ti.

3. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the nitrogen is derived from a nitrogen oxide or a nitrogen ion-containing aqueous solution.

4. The nitrogen is NO ２ － , NO ３ － , N ２ O, N ２ O ３ , N ２ O ４ , N ２ O ５ , N ３ O ７ , and N.H. ４ 2. The positive electrode active material for a secondary battery according to claim 1, wherein the positive electrode active material is contained in at least one form selected from the group consisting of aryl, aryl, aryl- ...

5. The number of moles of Ti element in the coating layer (N Ｔｉ ) to the moles of nitrogen element (N Ｎ ) ratio (N Ｎ / N Ｔｉ 2. The positive electrode active material for a secondary battery according to claim 1, wherein the value of (a) is 0.5 or more and 2.0 or less.

6. The number of moles of the Ti element in the coating layer (N Ｔｉ ) to the mole number of the nitrogen element (N Ｎ ) ratio (N Ｎ / N Ｔｉ 6. The positive electrode active material for a secondary battery according to claim 5, wherein the value of (a) is 0.6 or more and 1.0 or less.

7. The positive electrode active material for a secondary battery according to claim 1 , wherein the content of the coating layer is from 0.1 wt % to 5.0 wt % based on the total weight of the positive electrode active material for a secondary battery.

8. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the lithium metal oxide is represented by the following chemical formula 2: [Chemical formula 2] Li ｘ [Ni ｙ Co ｚ Mn ｗ M ２ ｖ ]O ２ In the above Chemical Formula 2, M ２ is at least one element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are such that 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, while y+z+w+v=1.

9. A positive electrode for a secondary battery, comprising the positive electrode active material for a secondary battery according to any one of claims 1 to 8, a solid electrolyte, a conductive material, and a binder.

10. (S1) adding a solution containing positive electrode active material particles to a titanium precursor solution to prepare a first mixed solution; (S2) adding a nitrogen-containing lithium source solution to the first mixed solution to prepare a second mixed solution; (S3) heat-treating the second mixed solution to prepare a cathode active material having a coating layer formed thereon.

11. The method of claim 10, wherein in step (S3), the heat treatment temperature is 400° C. or less.

12. The method of claim 10, wherein in step (S3), the coating layer contains nitrogen.

13. The positive electrode according to claim 9 ; a negative electrode; and a solid electrolyte disposed between the positive electrode and the negative electrode.

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