Positive electrode active material comprising lithium-rich manganese-based oxide, method for preparing the same, and lithium secondary battery comprising the same

Abstract

According to one embodiment of the present application, there is provided a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery comprising the same, wherein the positive electrode active material comprises: a core comprising a lithium-rich manganese-based oxide in which the molar ratio of lithium to transition metals other than lithium is greater than 1, and the molar content of manganese among the transition metals is 50 mol% or more; and a surface layer located on the surface of the core and comprising a compound having a molar ratio of Li / Me (where Me is a metal other than Li) of less than 1, wherein the core has a structure in which a layered structure and a rock salt structure are mixed, and the surface layer has an olivine structure or an amorphous structure.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2024-0138505, filed on October 11, 2024, and Korean Patent Application No. 10-2025-0145195, filed on October 2, 2025, the entire contents of which are incorporated herein by reference.

[0003] This invention relates to a positive electrode active material comprising lithium-rich manganese-based oxide, a method for manufacturing the same, and a lithium secondary battery comprising the same. Background Technology

[0004] Recently, as the application of lithium secondary batteries has rapidly expanded to provide power not only for electronic devices such as power, electronic components, communications, and computers, but also for power storage and supply for large-scale devices such as automobiles and power storage systems, the demand for secondary batteries with high capacity, high output, and high stability is increasing.

[0005] Lithium-ion rechargeable batteries typically consist of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transferring lithium ions, and a separator. In this case, carbon-based and silicon-based active materials can be used as negative active materials. Furthermore, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel-cobalt-manganese composite oxides can be used as positive active materials.

[0006] Meanwhile, lithium-rich manganese-based oxides have recently attracted attention as next-generation cathode active materials. These oxides have lower cobalt (Co) content and higher manganese (Mn) content (which is relatively inexpensive and readily available), offering advantages such as reduced costs and the ability to utilize larger amounts of lithium, resulting in high capacities exceeding 250 mAh / g.

[0007] In the case of lithium-rich manganese-based oxides, a mixed structure of layered phase (LiM'O2) and rock salt phase (Li2MnO3) is present. During initial activation, the rock salt phase is activated and generates excess lithium ions, which can compensate for the irreversible capacity of the anode. Therefore, it can be balanced with silicon-based anodes without the need for separate compensation materials, such as sacrificial cathode materials, or prior lithium compensation processes, such as pre-lithiation. However, the problem with lithium-rich manganese-based oxides is the high operating voltage, which alters the cathode structure. During the activation of the rock salt phase, not only oxygen-redox reactions occur, but also a large amount of gas is generated through side reactions with the electrolyte. Furthermore, capacity degradation occurs not only due to gas trapping, but also due to the appearance of cracks and crystal structure collapse within the active material, which exacerbates cathode degradation, leading to deterioration in lifetime characteristics and decreased safety. In particular, when silicon-based anode active materials are used together as anode active materials, the degradation of cycle characteristics is more severe.

[0008] Furthermore, when used as a power source for cars that are frequently in a charging state, gas generation can be a fatal problem.

[0009] Therefore, research is actively underway to improve the performance of lithium secondary batteries that include this lithium-rich manganese-based oxide. Summary of the Invention

[0010] Technical issues

[0011] The purpose of this invention is to provide a positive electrode active material and a lithium secondary battery that improves gas generation during charging, even when a lithium-rich manganese-based oxide with high manganese content is used as the positive electrode active material.

[0012] Technical solution

[0013] According to one aspect of the present invention, a positive electrode active material is provided, comprising: The core comprises a lithium-rich manganese-based oxide, wherein the molar ratio of lithium to a transition metal other than lithium is greater than 1, and the molar content of manganese in the transition metal is greater than 50 mol%. A surface layer, located on the surface of the core, comprises a compound having a Li / Me ratio (where Me is a metal other than Li) of less than 1 in molar quantities. The core has a mixed structure of layered and rock salt structures, and the surface layer has an olivine structure or an amorphous structure.

[0014] Lithium-rich manganese-based oxides can be represented by the following formula 1.

[0015] [Formula 1]

[0016] xLi2MnO3 (1-x)Li[Ni 1-y-z-w Mn y Co z M w O2

[0017] Where M is selected from at least one of the group consisting of Al, B, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 0.1≤x≤0.5, 0.4≤y<1, 0≤z≤0.1 and 0≤w≤0.2.

[0018] Specifically, the Li / Me ratio in the surface layer can be between 0.8 and 0.98.

[0019] Specifically, the surface layer may contain compounds including Li, Fe, and P.

[0020] The surface layer does not contain Mn, or may contain less than 0.1 mol of Mn relative to 1 mol of Fe.

[0021] The surface layer can have a thickness of 3 nm to 2 μm and can be formed on an area of ​​0.03% to 100% of the total surface area of ​​the core.

[0022] According to another aspect of the present invention, a method for manufacturing the above-mentioned positive electrode active material is provided, the method comprising: A lithium-rich manganese-based oxide powder is prepared, mixed with a solution containing a surface layer precursor, and washed to form a surface layer.

[0023] The surface layer precursor can be a compound containing Fe or a compound containing P.

[0024] The solution can be distilled water.

[0025] Mixing can be carried out at temperatures ranging from 20°C to 80°C, and can take from 2 minutes to 2 hours.

[0026] Furthermore, the process of forming the surface layer can be specifically carried out by mixing, followed by drying and firing.

[0027] Here, drying can be carried out at a temperature of 80°C to 150°C for 1 to 10 hours, and firing can be carried out at a temperature of 500°C to 1050°C for 1 to 20 hours.

[0028] According to another aspect of the present invention, a lithium secondary battery is provided, comprising: a positive electrode containing the above-described positive electrode active material, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Attached Figure Description

[0029] Figure 1 This is a graph showing the high-temperature storage characteristics in Experiment Example 1.

[0030] Figure 2 This is a graph showing the XRD analysis results of the active material from Example 1 in Experimental Example 2.

[0031] Figure 3 This is a graph showing the XRD analysis results of the active material in Comparative Example 1 of Experimental Example 2. Detailed Implementation

[0032] The present invention will be described in more detail below to provide a better understanding of it.

[0033] The terminology used herein is provided for the purpose of describing exemplary embodiments and is not intended to limit the concepts of the invention. Singular forms include plural forms unless the context clearly indicates otherwise.

[0034] Throughout this description, when a part “includes” a component, it does not mean that the part excludes other components, but rather that the part may further include other components, unless otherwise defined.

[0035] Positive electrode active material

[0036] The positive electrode active material of one embodiment of the present invention comprises: The core comprises a lithium-rich manganese-based oxide, wherein the molar ratio of lithium to a transition metal other than lithium is greater than 1, and the molar content of manganese in the transition metal is greater than 50 mol%. A surface layer, located on the surface of the core, comprises a compound with a Li / Me ratio (where Me is a metal other than Li) of less than 1 in molar quantities. The core has a mixed structure of layered and rock salt structures, and the surface layer has an olivine structure or an amorphous structure.

[0037] Here, lithium-rich manganese-based oxides can be represented by the following formula 1.

[0038] [Formula 1]

[0039] xLi2MnO3 (1-x)Li[Ni 1-y-z-w Mn y Co z M w O2

[0040] Where M is selected from at least one of the group consisting of Al, B, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 0.1≤x≤0.5, 0.4≤y<1, 0≤z≤0.1 and 0≤w≤0.2.

[0041] Here, the molar ratio (Li / metal) of lithium in the lithium-rich manganese-based oxide contained in the core to transition metals other than lithium can be 1.1 to 1.6, specifically 1.2 to 1.6, and more specifically 1.3 to 1.6.

[0042] Furthermore, in Equation 1, y can specifically be 0.4 to 0.9, more specifically 0.4 to 0.8, and z and w can each specifically be 0 to 0.1.

[0043] That is, as described above, lithium-rich manganese-based oxides as nuclear materials are materials containing compounds with layered structures and compounds with rock salt structures, and have high Mn content and high Li content, thus exhibiting excellent capacity characteristics.

[0044] However, during the activation process of the rock salt phase, an oxygen-redox reaction occurs, which generates a large amount of gas. Therefore, measures are needed to prevent this.

[0045] In this regard, the inventors conducted in-depth research and found that when the core surface includes a surface layer containing compounds with an olivine structure or an amorphous structure, and the Li / Me ratio is less than 1, this problem can be solved and the cycling characteristics can be improved.

[0046] Therefore, the surface layer on the surface of the core contains compounds with a molar Li / Me ratio (where Me is a metal other than Li) of less than 1.

[0047] The Li / Me ratio, in molar terms, can be specifically from 0.5 to 0.98, more specifically from 0.8 to 0.98, and most specifically from 0.85 to 0.9.

[0048] In this case, the compound contained in the surface layer can be a lithium-based phosphate containing various doped metals. For example, the compound can be a lithium-based phosphate containing Ni, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, and Sr.

[0049] However, the surface layer may have a different olivine structure from the core, an amorphous structure without complete crystallinity, or a mixture of both.

[0050] From the perspective of preventing the deterioration of output characteristics while improving the surface safety of lithium-rich manganese-based oxides, the surface layer can specifically be a compound containing Li, Fe, and P, and more specifically, it can be Li a FePO4-based compounds. Here, a can be 0.5 to 0.98, more specifically 0.8 to 0.98, and most specifically 0.85 to 0.9.

[0051] Here, Li a FePO4-based compounds can be materials with an olivine structure, such as Li a FePO4, or an amorphous material that includes the above-mentioned materials but does not form a complete crystal structure. Similarly, the surface layer may not include Mn.

[0052] Or, Li a FePO4-based compounds can be in the form of partially doped Mn from the core. However, the amount of Mn incorporated relative to 1 mol of Fe can be very small, specifically less than 0.1 mol, more specifically less than 0.05 mol, or even more specifically less than 0.01 mol.

[0053] This surface layer contains no excess Li, thus preventing side reactions with the electrolyte. This not only reduces gas generation but also improves surface stability. Furthermore, the surface layer's structure, with increased porosity at Li sites and increased space within the crystal structure, increases lithium-ion mobility and enhances secondary battery performance.

[0054] The thickness of the surface layer can be from 3 nm to 2 μm, specifically from 5 nm to 0.5 μm, and more specifically from 5 nm to 0.1 μm.

[0055] If the thickness of the surface layer falls outside the aforementioned range and is too thin, the intended effects of the invention, such as improved surface stability or improved lithium mobility, may not be achieved. If the surface layer is too thick, lithium mobility may decrease, and capacity may decrease due to reduced core content, which is not preferred.

[0056] Furthermore, the surface layer can be formed on an area of ​​0.03% to 100% of the total surface area of ​​the core, specifically 1% to 100%, more specifically 1% to 50%, and most specifically 1% to 30%.

[0057] If the area of ​​the surface layer is outside the above range and too small, a large amount of the nucleus will be exposed, the possibility of electrolyte side reactions will be too high, it will be difficult to prevent redox reactions, and therefore gas production cannot be reduced, which is not preferred.

[0058] Lithium-rich manganese-based oxides can have a single-peak structure consisting of large particles with an average diameter (D50) of 5 μm to 20 μm, or they can have a double-peak structure consisting of the aforementioned large particles and small particles with an average diameter (D50) of 5 μm to 20 μm.

[0059] Here, the characteristic of a single-peak structure is the formation of a D50 peak in particle analysis, while the characteristic of a double-peak structure is the formation of two peaks in particle analysis.

[0060] Furthermore, large particles can be secondary particles with structures consisting of dozens or hundreds of primary single particles aggregated together, and small particles can be single particles or secondary particles of primary particles.

[0061] Specifically, the average diameter (D50) of the large particles can be from 5 μm to 15 μm, and more specifically from 5 μm to 14 μm.

[0062] Specifically, the average diameter (D50) of the small particles can be from 3 μm to 5 μm, and more specifically from 3 μm to 4 μm.

[0063] "Average diameter D50" refers to the particle diameter at 50% of the cumulative particle volume distribution based on particle diameter. In other words, D50 is the particle size at 50% of the cumulative particle volume distribution based on particle diameter.

[0064] D50 can be measured using laser diffraction. Specifically, the particle size distribution can be determined by a method comprising the following steps: dispersing the powder to be measured in a dispersion medium, then introducing it into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S 3500), and measuring the difference in the diffraction pattern based on the particle diameter as the particles pass through the laser beam. D50 can be measured by calculating the particle diameter at the point corresponding to 50% of the cumulative particle volume distribution based on the particle diameter in the measurement device.

[0065] Methods for manufacturing positive electrode active materials

[0066] According to another aspect of the present invention, a method for manufacturing a positive electrode active material is provided, the method comprising: preparing a lithium-rich manganese-based oxide powder, mixing it with a solution containing a surface layer precursor, and washing the lithium-rich manganese-based oxide powder to form a surface layer.

[0067] Here, the lithium-rich manganese-based oxide powder can be a material represented by Formula 1.

[0068] The lithium-rich manganese-based oxide powder represented by Formula 1 can be formed by mixing a precursor material for preparing the lithium-rich manganese-based oxide with a lithium compound and then heat-treating the mixture.

[0069] In this case, the precursor material can be a compound or coprecipitate of a material containing elements other than Li, which is included in lithium-rich manganese-based oxides. For example, oxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides containing elements other than Li can be used, or coprecipitates of these materials can be used.

[0070] Lithium compounds may also include lithium-containing oxides, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specific examples include Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇, but preferably Li₂CO₃, LiOH, or Li₂O.

[0071] The heat treatment can be carried out at temperatures ranging from 700°C to 1050°C, and can be performed in an inert atmosphere. If the temperature falls outside the above range and is too low, lithium-rich manganese-based oxides may not form properly, and if the temperature is too high, there is a problem that lithium may volatilize, which is not preferred.

[0072] After preparing lithium-rich manganese-based oxide powder in this manner, it is mixed with a solution containing a surface layer precursor.

[0073] Here, a solution containing a surface layer precursor is prepared by mixing the surface layer precursor with a solvent. The surface layer precursor is a precursor containing a metal (Me) included in the surface layer, and can be an oxide, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or hydroxyoxide. Specifically, since the surface layer includes Fe and P, it can be an Fe-containing compound, such as an Fe-containing oxide, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or hydroxyoxide, and a P-containing compound such as H3PO4 or (NH4)3PO4.

[0074] In addition, to ensure that the surface layer has a different crystal structure from the core, the surface layer precursor does not contain Mn.

[0075] The solvent can be an aqueous solvent, especially distilled water.

[0076] After preparing a solution containing the surface layer precursor, lithium-rich manganese-based oxide powder can be mixed with the solution.

[0077] In this case, mixing can be carried out at temperatures ranging from 20°C to 80°C, specifically from 25°C to 40°C, or at room temperature.

[0078] In addition, mixing can be carried out for 2 minutes to 2 hours, specifically 5 minutes to 2 hours, or more specifically 5 minutes to 20 minutes.

[0079] Through this mixing process, Li impurities on the surface of lithium-rich manganese-based oxide powder can be washed away by mixing them with the solution, thereby forming a surface layer with a Li / Me ratio of less than 1. This improves the safety of the surface layer and significantly reduces electrolyte side reactions.

[0080] Meanwhile, once mixing is complete, the mixture can be dried and fired to complete the formation of the surface layer.

[0081] Here, drying and firing can be carried out in a vacuum oven. Drying can be carried out at a temperature of 80°C to 150°C for 1 to 10 hours, specifically at a temperature of 90°C to 140°C for 2 to 10 hours, and more specifically at a temperature of 100°C to 120°C for 4 to 10 hours.

[0082] Furthermore, firing can be carried out at a temperature of 300°C to 1050°C for 1 to 20 hours, specifically at a temperature of 500°C to 1050°C for 1 to 10 hours, and more specifically at a temperature of 500°C to 1000°C for 1 to 10 hours.

[0083] The surface layer fired in this way can have an olivine structure, spinel structure or amorphous structure as described above, thus being effective in reducing gas and increasing the stability of the surface structure.

[0084] Lithium secondary batteries

[0085] On the other hand, according to yet another aspect of the present invention, a lithium secondary battery is provided, comprising a positive electrode containing a positive electrode active material.

[0086] Specifically, a lithium secondary battery may include an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0087] The positive electrode has a structure in which a layer of positive electrode mixture is formed on one or both surfaces of the positive electrode current collector.

[0088] The positive electrode current collector can generally have a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surfaces are treated with carbon, nickel, titanium, silver, etc. can be used. The current collector can have fine protrusions and depressions formed on its surface to enhance the adhesion of the positive electrode active material. For example, the current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric structures.

[0089] In addition to the positive electrode active material, the positive electrode mixture layer may further contain a binder, a conductive material, and other additives.

[0090] In addition to the lithium-rich manganese-based oxide, the positive electrode active material is, for example, a compound capable of reversibly intercalating and deintercalating lithium, and it may further include: lithium manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (such as LiNiO2, etc.), lithium nickel-based oxides (such as LiNiO2, etc.), lithium nickel manganese-based oxides (such as, LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), lithium manganese cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium nickel manganese cobalt-based oxides (such as Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1 and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2 and p1 + q1 + r1 = 2), etc.), or lithium nickel cobalt transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r2 M s2)O2 (where M is selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), etc.

[0091] When the positive electrode active material is a mixture of a lithium-rich manganese-based oxide and other positive electrode active materials, based on the total weight of the active material, the content of the lithium-rich manganese-based oxide can be 80% by weight or more, or 90% by weight or more.

[0092] The conductive material is a component used to further improve the conductivity of the positive electrode active material, and there is no particular limitation as long as it has conductivity without causing chemical changes in the battery. For example, the following conductive materials can be used, including: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive nanomaterials, such as carbon nanofibers or carbon nanotubes; carbon fluoride powder; conductive powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives. Among these materials, the conductive material includes conductive nanomaterials, such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium metal battery and further enhance the output characteristics.

[0093] Generally, based on the total weight of the positive electrode mixture layer, the content of the conductive material can be 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight.

[0094] The binder is a component that helps the combination of the positive electrode active material and the conductive material and the combination with the current collector. Examples of the binder can include: polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, fluororubber, etc. Mixtures or copolymers of two or more selected from these can also be used.

[0095] Typically, based on the total weight of the cathode mixture layer, the binder content can be 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight.

[0096] In addition, other additives may further include, for example, fillers as components for suppressing expansion. Fillers are not particularly limited, as long as they can suppress electrode expansion without causing chemical changes in the corresponding battery, and examples may include: olefin polymers, such as polyethylene and polypropylene; fibrous materials, such as glass fiber and carbon fiber, etc.

[0097] The negative electrode has a structure in which a layer of negative electrode mixture is formed on one or both surfaces of the negative electrode current collector.

[0098] The negative electrode current collector typically has a thickness ranging from 3 μm to 500 μm. Furthermore, there are no particular limitations on the negative electrode current collector, as long as it does not cause chemical changes in the corresponding battery and is conductive. Examples of such current collectors can be selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper with a dissimilar metal surface treatment, stainless steel with a dissimilar metal surface treatment, and aluminum-cadmium alloys. The current collector can have fine protrusions and depressions formed on its surface to enhance the adhesion of the negative electrode active material and can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven structures.

[0099] In addition to the negative electrode active material, the negative electrode mixture layer may include a binder, a conductive material, and other additives as described for the positive electrode.

[0100] Negative electrode active materials may include: at least one carbon-based material selected from the group consisting of graphite, amorphous hard carbon, low-crystallinity soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, and fibrous carbon; Si-based materials; and metal composite oxides, such as Li. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), Sn x Me 1-x Me' y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 elements in the periodic table, halogens; \(0 < x\leq1\); \(1\leq y\leq3\); \(1\leq z\leq8\)); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SiO, SiO₂, SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄ and Bi₂O₅; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; lithium titanium oxide, etc., but not limited thereto, as long as they are known in the art.)

[0101] The separator can be composed of a polymer substrate or can be a safety enhanced separator (SRS), where a coating containing a binder material and inorganic particles is formed on one or both surfaces of the polymer substrate.

[0102] The polymer substrate can be, for example, a polyolefin-based substrate. The polyolefin-based substrate can be used in the form of a sheet, multilayer film, microporous membrane, textile cloth or non-woven fabric, but not necessarily limited thereto. The polyolefin-based substrate can be a thin insulating film with high ion permeability and mechanical strength. The pore size of the separator can generally be in the range of 0.01 μm to 10 μm, and the thickness can generally be in the range of 5 μm to 300 μm, but not limited thereto.

[0103] The polymer substrate of the SRS separator can be a polyolefin substrate.

[0104] The inorganic particles of the coating can form void spaces between the inorganic particles and serve to form fine pores, and also act as spacers capable of maintaining a physical form. In addition, the inorganic particles generally have the characteristic of not changing physical properties even at high temperatures above 200 °C, so the formed organic-inorganic hybrid layer has excellent heat resistance.

[0105] There are no particular limitations on the inorganic particles, as long as they are electrochemically stable. In other words, the inorganic particles that can be used in this invention are not particularly limited unless they cause oxidation and / or reduction reactions within the range of the battery operating voltage to be applied. In particular, when using inorganic particles with ion transfer capabilities, the ionic conductivity in the electrochemical element can be increased to improve performance; therefore, inorganic particles with high ionic conductivity are preferred. Furthermore, if the inorganic particles have a high density, it is difficult to disperse such particles during manufacturing, and there is a problem of weight increase when manufacturing the battery. Therefore, materials with low density are preferred if possible. In addition, inorganic materials with high dielectric constants help to increase the degree of dissociation of electrolyte salts (e.g., lithium salts) in liquid electrolytes, thereby increasing the ionic conductivity of the electrolyte. Finally, inorganic particles with thermal conductivity are more preferred because they have excellent endothermic capabilities and thus suppress the phenomenon of local heat concentration leading to the formation of hot spots and thermal runaway.

[0106] For the reasons mentioned above, the inorganic particles are preferably selected from one or more of the following: (a) inorganic particles with a high dielectric constant of 1 or more, 5 or more, preferably 10 or more; (b) inorganic particles with piezoelectricity; (c) inorganic particles with thermal conductivity; and (d) inorganic particles with lithium-ion transfer capability.

[0107] Piezoelectric inorganic particles are materials that are non-conductive under atmospheric pressure but acquire electrical properties due to changes in their internal structure when pressure is applied. Such inorganic particles exhibit high dielectric properties, with a dielectric constant exceeding 100. If these inorganic particles are stretched or compressed under pressure, charges are generated, making one side positively charged and the other negatively charged. Therefore, such particles are materials capable of generating a potential difference between their two sides.

[0108] Examples of piezoelectric inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg3Nb) 2 / 3 Hafnium oxide (HfO2), mixtures thereof, etc., but not limited to these.

[0109] Inorganic particles with lithium-ion transfer capability refer to inorganic particles that contain lithium elements but do not store lithium, yet enable the movement of lithium ions. These particles can facilitate lithium-ion transfer and movement due to certain defects present within their particle structure. Therefore, such particles can prevent a decrease in lithium mobility, thereby preventing a reduction in battery capacity.

[0110] Examples of inorganic particles having the ability to transfer lithium ions include: (LiAlTiP) x O y -based glasses (0 < x < 4, 0 < y < 13), such as lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, etc.; lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as lanthanum lithium titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4, etc.; lithium nitrides (Li x N y , 0 < x < 4, 0 < y < 2), such as Li3N, etc.; SiS2 - based glasses (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), such as Li3PO4 - Li2S - SiS2, etc.; P2S5 - based glasses (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), such as LiI - Li2S - P2S5, etc.; mixtures thereof; and so on, but not limited thereto.

[0111] In addition, examples of inorganic particles having a dielectric constant of 1 or more include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, mixtures thereof, and so on, but not limited thereto.

[0112] Thermally conductive inorganic particles are materials that provide low thermal resistance but do not have electrical conductivity and thus have insulating properties, and may be, for example, at least one selected from the group consisting of aluminum nitride (AlN), boron nitride (BN), aluminum oxide (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but not limited thereto.

[0113] When the above-mentioned high-dielectric inorganic particles, piezoelectric inorganic particles, thermally conductive inorganic particles, and inorganic particles with lithium-ion transfer capabilities are used together, their synergistic effect can be doubled.

[0114] The size of the inorganic particles is not limited, but preferably between 0.001 μm and 10 μm, if possible, to create appropriate porosity between the inorganic particles. If the size is less than 0.001 μm, the dispersibility deteriorates, making it difficult to control the physical properties. If the size is greater than 10 μm, the increased thickness degrades the mechanical properties, and the coating becomes ineffective due to the excessively large pore size, but increases the chance of internal short circuits during battery charging and discharging.

[0115] The content of inorganic particles is not particularly limited, but preferably it is from 1% to 99% by weight, more preferably from 10% to 95% by weight, relative to 100% by weight of the mixture of inorganic particles and binder material. If the content is less than 1% by weight, the content of binder material becomes too large, resulting in a decrease in pore size and porosity due to the reduced blank space formed between inorganic particles, which may degrade lithium-ion mobility. Conversely, if the content is greater than 99% by weight, the content of binder material becomes too small, resulting in a deterioration in the mechanical properties of the coating due to weakened adhesion between the inorganic materials.

[0116] On the other hand, there are no restrictions on the adhesive material unless it causes a side reaction with the electrolyte. In particular, the adhesive material can be one with the lowest possible glass transition temperature (Tg), preferably between -200°C and 200°C. This is because such an adhesive material can improve the mechanical properties of the final insulating film.

[0117] Furthermore, the adhesive material does not need to have ion conductivity, but it is more preferable to use a polymer with ion conductivity.

[0118] Therefore, it is preferable that the adhesive material has a high dielectric constant. In fact, the degree of dissociation of salts in an electrolyte depends on the dielectric constant of the electrolyte solvent. When the dielectric constant of the polymer increases, the degree of dissociation of salts in the electrolyte can be improved. The dielectric constant of the polymer used can be 1 or higher, particularly 1.0 to 100 (measurement frequency = 1 kHz), and preferably 10 or higher.

[0119] In addition to the functions mentioned above, the adhesive material can possess gel-like properties, thus exhibiting a high degree of swelling in the liquid electrolyte solution when immersed in it. In fact, if the adhesive material is a polymer with excellent electrolyte swelling properties, the polymer, after battery assembly, will permeate with the absorbed electrolyte solution and retain the ionic conductivity of the electrolyte. Therefore, if possible, the solubility index of the polymer is preferably 15 MPa. 1 / 2 up to 45 MPa 1 / 2 More preferably 15 MPa 1 / 2 Up to 25 MPa 1 / 2 and 30 MPa 1 / 2 up to 45 MPa 1 / 2 If the solubility index is less than 15 MPa 1 / 2 or greater than 45 MPa 1 / 2 It is difficult to swell using the liquid electrolyte solution of conventional batteries.

[0120] Examples of adhesive materials may be one or more selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trichloroethylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-vinyl acetate copolymer, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, and polyvinyl alcohol.

[0121] The total thickness of the separator can range from 5 micrometers to 20 micrometers, particularly 5 micrometers to 15 micrometers, and even more particularly 6 micrometers to 13 micrometers. When the separator thickness meets the above range, short circuits between the positive and negative electrodes can be effectively prevented, while minimizing the resistance of the lithium secondary battery. As a result, the energy density of the lithium secondary battery can be prevented from decreasing and its lifespan characteristics can be improved.

[0122] The electrolyte can be a lithium non-aqueous electrolyte, and the lithium non-aqueous electrolyte can include lithium salts and non-aqueous organic solvents.

[0123] In this context, lithium salts serve as a medium for transferring ions within the lithium secondary battery. Lithium salts may include Li + As a cation, and selected from 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 of the groups constitutes an anion.

[0124] Specifically, lithium salts may include one selected from the group consisting of: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 The following are considered as a mixture of lithium: 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(trifluoroethanesulfonyl)imide, LiN(SO2CF3)2), or a mixture of two or more thereof. However, for the sake of excellent stability, it preferably contains Li(N(SO2CF3)2.

[0125] In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries can be used without restriction.

[0126] The concentration of lithium salt can be appropriately varied within the generally available range, but the concentration of lithium salt in the electrolyte can be from 0.5 M to 3 M, particularly from 1 M to 2.5 M, and even more particularly from 1 M to 2 M, in order to obtain the best effect of forming a film on the electrode surface to prevent corrosion. When the concentration of lithium salt meets the above range, the effect of improving cycle characteristics during the high-temperature storage of lithium secondary batteries is sufficient, and the viscosity of the electrolyte is appropriate, thereby improving electrolyte wettability.

[0127] Non-aqueous organic solvents are not limited, as long as they minimize decomposition caused by oxidation reactions within the voltage range of the lithium secondary battery's charging / discharging process and can exhibit their properties together with the material. For example, carbonate-based organic solvents, ether-based organic solvents, and ester-based organic solvents can be used alone or in mixtures of two or more thereof, and specifically, carbonate-based organic solvents can be used.

[0128] The carbonate-based organic solvent in the organic solvent can include at least one selected from the group consisting of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents. Specifically, the cyclic carbonate-based organic solvent can 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-pentene carbonate, 2,3-pentene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it can 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.

[0129] In addition, the linear carbonate-based organic solvent is a solvent with 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, methyl ethyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, more specifically, it may include dimethyl carbonate.

[0130] Ether-based organic solvents may include, but are not limited to, 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.

[0131] Ester-based organic solvents may include at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0132] Specific examples of linear ester-based organic solvents may include, but are not limited to, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, or mixtures of two or more thereof.

[0133] Specific examples of cyclic ester-based organic solvents may include, but are not limited to, any 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.

[0134] In ester-based solvents, cyclic carbonate compounds, due to their high dielectric constant as high-viscosity organic solvents, facilitate the excellent dissociation of lithium salts in the electrolyte, thus making them a preferred choice. When cyclic carbonate compounds are mixed in appropriate proportions with low-viscosity, low-dielectric-constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate, and linear ester compounds, electrolytes with high conductivity can be prepared, which are even more preferable.

[0135] In addition, lithium non-aqueous electrolytes also contain functional additives. These additives may be included to prevent negative electrode breakage induced in high-power environments, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and expansion during high-temperature storage.

[0136] Specifically, representative examples of functional additives may include at least one functional additive selected from the group consisting of sulfonyl lactone compounds, sulfite / base compounds, sulfone compounds, sulfate / base compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate / base compounds, borate / base compounds, and lithium-based compounds.

[0137] The sulfonyl group compound may include at least one compound selected from the group consisting of 1,3-propanesulfonyl (PS), 1,4-butanesulfonyl, ethanesulfonyl, 1,3-propenylsulfonyl (PRS), 1,4-butenesulfonyl, and 1-methyl-1,3-propenylsulfonyl, and its content may be from 0.3% to 5% by weight, and particularly from 1% to 5% by weight, based on the total weight of the electrolyte. When the amount of the sulfonyl group compound in the electrolyte is greater than 5% by weight, an excessively thick layer may form on the electrode surface, resulting in increased resistance and output degradation. Furthermore, the resistance may also increase due to excessive additives, thereby degrading the output characteristics.

[0138] The sulfite / base compound may include at least one compound selected from the group consisting of: ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butanediol sulfite, and its content may be less than 3% by weight based on the total weight of the electrolyte.

[0139] The sulfone compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and its content may be less than 3% by weight based on the total weight of the electrolyte.

[0140] The sulfate ester / base compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethyl sulfate (MTMS), and its content may be less than 3% by weight based on the total weight of the electrolyte.

[0141] Furthermore, the halogen-substituted carbonate compounds may include fluoroethylene carbonate (FEC), and their content may be less than 5% by weight based on the total weight of the electrolyte. When the amount of halogen-substituted carbonate compounds in the electrolyte exceeds 5% by weight, the cell swelling performance may decrease.

[0142] In addition, the nitrile compound may include at least one compound selected from the group consisting of succinate, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclopentanoic acid, cyclohexanoic acid, 2-fluorobenzyl nitrile, 4-fluorobenzyl nitrile, difluorobenzyl nitrile, trifluorobenzyl nitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0143] The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinyl ethylene carbonate, and its content may be less than 3% by weight based on the total weight of the electrolyte. When the content of the cyclic carbonate-based compound in the electrolyte exceeds 3% by weight, the cell swelling suppression performance may deteriorate.

[0144] The phosphate ester / base compound may include at least one compound selected from the group consisting of lithium difluoro(bis(oxalato)phosphate), lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(2,2,2-trifluoroethyl) phosphite, and its content may be less than 3% by weight based on the total weight of the electrolyte.

[0145] The borate ester / base compound may include lithium oxaloyl difluoroborate, and its content may be less than 3% by weight based on the total weight of the electrolyte.

[0146] Lithium-based compounds are compounds that differ from lithium salts contained in lithium non-aqueous electrolytes. Lithium-based compounds may include at least one compound selected from the group consisting of LiPO₂F₂, LiODFB, LiBOB (lithium bis(oxalatoborate) (LiB(C₂O₄)₂), and LiBF₄), and their content may be less than 3% by weight based on the total weight of the electrolyte.

[0147] Two or more functional additives can be mixed, and their content can be less than 20% by weight, particularly from 0.1% to 10% by weight, based on the total weight of the lithium non-aqueous electrolyte. When the content of the functional additives is greater than 20% by weight, excessive side reactions may occur in the lithium non-aqueous electrolyte during battery charging and discharging. In particular, it cannot be fully decomposed at high temperatures and may exist as unreacted material or in a precipitated state in the electrolyte at room temperature. Therefore, side reactions may occur, resulting in a decrease in the lifespan or resistivity characteristics of the lithium metal battery.

[0148] In the following description, embodiments of the present invention will be presented with reference to examples to reveal the beneficial effects of the present invention.

[0149] <Example 1>

[0150] Nucleosynthesis

[0151] Transition metal precursor (Ni) 0.35 Mn 0.65 (OH)₂) and a lithium precursor were mixed to achieve a molar ratio of transition metal to Li of 1:1.25. The mixture was then calcined at 850°C in an oxygen atmosphere (50% oxygen content) to prepare a lithium-rich manganese-based oxide (0.37Li₂MnO₃). 0.63Li[Ni 0.563 Mn 0.437 O2).

[0152] Surface layer formation

[0153] In the preparation of lithium-rich manganese-based oxides (0.37Li2MnO3) 0.63Li[Ni 0.563 Mn 0.437 After adding O2), Fe(NO3)3 is added at a molar ratio of 1:1. H2O :H3PO4, Fe(NO3)3 mixed in a molar ratio of approximately 1:2. H2O: Citric acid, and mixed with 10 mL of distilled water to prepare a mixture. Then, 5 g of lithium-rich manganese-based oxide was added to the resulting mixture, stirred at 25°C for 5 minutes, dried in an oven at 120°C for 5 hours, and then heat-treated at 600°C for 5 hours to prepare a positive electrode material with a surface layer formed thereon.

[0154] <Comparative Example 1>

[0155] Lithium-rich manganese-based oxides without a surface layer are used as positive electrode active materials.

[0156] <Experimental Example 1>

[0157] Using the positive electrode active materials prepared in Example 1 and Comparative Example 1, respectively, the positive electrode active material, binder (PVdF), and conductive material (CNT) were mixed in NMP (N-methylpyrrolidone) at a weight ratio of 96:3:1 to prepare a positive electrode slurry. The positive electrode slurry was applied to an aluminum foil with a thickness of 20 μm to 40 μm, dried at 130°C, and rolled to prepare the positive electrode.

[0158] Artificial graphite was used as the positive electrode active material, and the negative electrode active material, conductive material (CNT), styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as an additive were mixed in water at a weight ratio of 96.2:0.8:2:1 to prepare the negative electrode slurry. The negative electrode slurry was then coated onto an 8 μm thick Cu foil to a thickness of 30 μm, dried at 130°C, and rolled to prepare the negative electrode.

[0159] An electrode assembly is prepared by inserting a separator with an organic / inorganic coating (Al2O3 and PVDF mixed in a weight ratio of 90:10) formed on both surfaces of a polypropylene (PP) substrate between the positive and negative electrodes.

[0160] A pouch-type lithium secondary battery was manufactured using an electrode assembly and an electrolyte (100 mL) containing 1 M LiPF6 in a solvent with an EC:EMC ratio of 3:7.

[0161] The lithium secondary battery is charged to 4.6 V at 0.1 C at 25°C (CC / CV mode) and then discharged to 2.0 V at a constant current of 0.1 C (CC mode). This method performs a single charge-discharge cycle and activates the battery to manufacture a lithium secondary battery.

[0162] The lithium-ion secondary battery was stored in a chamber at 60°C for 12 weeks, and the volume change of the lithium-ion secondary battery was measured. The results are shown in... Figure 1 For lithium secondary batteries using the positive electrode active materials of Example 1 and Comparative Example 1, measurements were repeated 2 to 3 times.

[0163] Reference Figure 1 As can be seen, when the positive electrode active material of the present invention is included, the volume change is smaller and the gas generation is reduced compared with the case of using the positive electrode active material of Comparative Example 1 which does not have a surface layer.

[0164] <Experimental Example 2>

[0165] For the lithium secondary battery prepared in Experimental Example 1, a process was performed of charging to 4.6 V at 0.1 C (CC / CV mode) and discharging to 2.0 V at a constant current of 0.1 C. This was followed by another process of charging to 4.35 V at 0.1 C (CC / CV mode) and discharging to 2.0 V at a constant current of 0.1 C, and then charging to 4.35 V at 0.33 C (CC / CV mode). After high-temperature storage in a chamber at 60°C for 12 weeks under these charging conditions, the secondary battery was disassembled, and the changes in the crystal structure of the positive electrode active material were measured by XRD. The results are shown in... Figure 2 and 3 The XRD measurement conditions are as follows: Instrument: Brucker D2 phaser X-ray wavelength: 1.5406 Å Scanning speed: 1 second / 0.01° exposure Measurement time: 150 minutes Reference Figure 2 and Figure 3 It can be confirmed that the positive electrode active material of the present invention maintains its crystal structure, while the crystal structure of the positive electrode active material of Comparative Example 1 collapses due to oxygen-redox reaction.

[0166] Based on the above disclosure, those skilled in the art can make various applications and modifications without departing from the spirit and scope of this invention.

[0167] [Industrial Applications]

[0168] According to the present invention, a coating with a Li / M ratio of less than 1 and a structure different from that of a lithium-rich manganese-based oxide is formed on a core comprising a lithium-rich manganese (Mn)-based oxide with a high manganese (Mn) content, thereby improving the surface safety of the positive electrode active material comprising the coating. As a result, side reactions in the electrolyte of lithium secondary batteries can be reduced, gas generation can be minimized, and an improved effect on gas generation can be shown even in the charging state.

Claims

1. A positive electrode active material, comprising: The core comprises a lithium-rich manganese-based oxide, wherein the molar ratio of lithium to a transition metal other than lithium is greater than 1, and the molar content of manganese in the transition metal is greater than 50 mol%. A surface layer, situated on the surface of the core, comprises a compound having a Li / Me ratio of less than 1 in molar quantities, wherein Me is a metal other than Li. in, The core has a mixed structure of layered and rock salt structures, and the surface layer has an olivine structure or an amorphous structure.

2. The positive electrode active material according to claim 1, in, The lithium-rich manganese-based oxide is represented by the following formula 1: [Formula 1] xLi2MnO3 (1-x)Li[Ni 1-y-z-w Mr y Co z M w ]O2 Where M is selected from at least one of the group consisting of Al, B, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr and Zr, 0.1≤x≤0.5, 0.4≤y<1, 0≤z≤0.1 and 0≤w≤0.

2.

3. The positive electrode active material according to claim 1, in, The Li / Me ratio in the surface layer is between 0.8 and 0.

98.

4. The positive electrode active material according to claim 1, in, The surface layer contains compounds including Li, Fe, and P.

5. The positive electrode active material according to claim 1, in, The surface layer does not contain Mn, or contains Mn in an amount of less than 0.1 mol relative to 1 mol Fe.

6. The positive electrode active material according to claim 1, in, The thickness of the surface layer is 3 nm to 2 μm.

7. The positive electrode active material according to claim 1, in, The surface layer is formed over an area of ​​0.03% to 100% of the total surface area of ​​the core.

8. A method for manufacturing the positive electrode active material according to claim 1, the method comprising: A lithium-rich manganese-based oxide powder is prepared, mixed with a solution containing a surface layer precursor, and washed to form a surface layer.

9. The method for manufacturing a positive electrode active material according to claim 8, in, The surface layer precursor is a compound containing Fe and a compound containing P.

10. The method for manufacturing a positive electrode active material according to claim 8, in, The solution is distilled water.

11. The method for manufacturing a positive electrode active material according to claim 8, in, The mixing is carried out at a temperature between 20°C and 80°C.

12. The method for manufacturing the positive electrode active material according to claim 8, in, The mixing process takes 2 minutes to 2 hours.

13. The method for manufacturing a positive electrode active material according to claim 8, in, The process of forming the surface layer involves mixing, followed by drying and firing.

14. The method for manufacturing a positive electrode active material according to claim 13, in, The drying process is carried out at a temperature of 80°C to 150°C for 1 to 10 hours.

15. The method for manufacturing a positive electrode active material according to claim 13, in, The firing process is carried out at a temperature of 500°C to 1050°C for 1 to 20 hours.

16. A lithium secondary battery, comprising: The positive electrode comprises the positive electrode active material according to any one of claims 1 to 7; Negative electrode; and A diaphragm is disposed between the positive electrode and the negative electrode.

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