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

Abstract

According to an embodiment of the present disclosure, provided is a positive electrode active material comprising: a core including a lithium-rich manganese-based oxide in which a molar ratio of lithium to a transition metal excluding lithium is more than 1 and a molar content of manganese in the transition metal is 50 mol% or more, and a surface layer located on the surface of the core, and including a compound in which a ratio of Li / Me (where Me is a metal excluding Li) is less than 1 on a molar basis, 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, a method of manufacturing the same, and a lithium secondary battery comprising the same.

Description

A positive electrode active material comprising a lithium-rich manganese oxide, a method for manufacturing the same, and a lithium secondary battery comprising the same

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0138505 filed October 11, 2024 and Korean Patent Application No. 10-2025-0145195 filed October 2, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

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

[0004] Recently, as the application areas of lithium-ion batteries have rapidly expanded to include not only power supply for electronic devices such as electrical, electronic, telecommunications, and computers, but also power storage for large-area devices such as automobiles and power storage systems, there is a growing demand for high-capacity, high-output, and high-stability secondary batteries.

[0005] The above lithium secondary battery generally consists of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transporting lithium ions, and a separator. In this case, carbon-based active materials, silicon-based active materials, etc., may be used as the negative active material. Additionally, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel-cobalt-manganese composite oxide may be used as the positive active material.

[0006] Meanwhile, lithium-over-manganese oxides have recently been attracting attention as next-generation cathode active materials. Lithium-over-manganese oxides have the advantage of having a high capacity of over 250 mAh / g, as they have a low Co content and a high content of manganese (Mn), which is relatively inexpensive and abundant in reserves, which enables cost reduction and allows for the use of a larger amount of lithium.

[0007] In the case of such over-lithium manganese-based oxides, they have a structure in which layered (LiM'O2) and rock salt phases (Li2MnO3) coexist. During the initial activation process, the rock salt phase is activated, generating an excess amount of lithium ions. Since this compensates for the irreversible capacity of the anode, it is possible to balance the performance 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 above-mentioned over-lithium manganese-based oxides have problems such as a change in the cathode structure due to high driving voltage, oxygen-redox reactions occurring during the activation of the rock salt phase, and the generation of large amounts of gas due to side reactions in the electrolyte. This leads to capacity degradation caused by gas trapping, as well as intensified cathode degradation caused by internal cracking of the active material and crystal structure collapse, resulting in reduced lifespan characteristics and safety. In particular, when Si-based anode active materials are applied together, the degradation of cycle characteristics becomes even more severe.

[0008] Moreover, when used as a power source for automobiles, which are often left unattended while charged, gas generation is a fatal problem.

[0009] Accordingly, research is actively underway to improve the performance of lithium secondary batteries containing such lithium-ion manganese oxides.

[0010] The present invention aims to provide a positive electrode active material and a lithium secondary battery that have an improved gas generation effect in the charged state even when a high-lithium manganese oxide with a high manganese content is used as a positive electrode active material.

[0011] According to one embodiment of the present invention,

[0012] A core comprising a lithium-over-manganese oxide having a molar ratio of lithium to transition metals excluding lithium greater than 1, and a molar content of manganese among the transition metals of 50 mol% or more, and

[0013] It comprises a surface layer located on the surface of the above-mentioned core and containing a compound in which Li / Me (wherein Me is a metal other than Li) is less than 1 based on moles, and

[0014] The above-described core has a structure in which a layered structure and a rock salt structure are mixed, and the above-described surface layer has an olivine structure or an amorphous structure, thereby providing an anode active material.

[0015] The above-mentioned lithium manganese oxide can be represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] xLi2MnO3·(1-x)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0018] In the above formula, M is at least one selected from the group consisting of Al, B, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤x≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.2.

[0019] Specifically, the Li / Me ratio in the surface layer may be 0.8 to 0.98.

[0020] The above surface layer may, in detail, include a compound comprising Li, Fe, and P.

[0021] The above surface layer may not contain Mn, or may contain Mn at a content of 0.1 mole or less relative to 1 mole of Fe.

[0022] The thickness of the surface layer may be 3 nm to 2 µm, and it may be formed with an area of ​​0.03% to 100% of the total surface area of ​​the core.

[0023] Meanwhile, according to another embodiment of the present invention,

[0024] As a method for manufacturing the above positive active material,

[0025] A method for manufacturing an anode active material is provided, comprising the steps of manufacturing the above-mentioned lithium manganese-based oxide powder, mixing it with a solution containing a surface layer precursor, and forming a surface layer together with washing the above-mentioned lithium manganese-based oxide powder.

[0026] The above surface layer precursor may be a compound containing Fe and a compound containing P.

[0027] The above solution may be distilled water.

[0028] The above mixing can be performed at a temperature of 20°C to 80°C and for 2 minutes to 2 hours.

[0029] In addition, the process of forming the surface layer can specifically be carried out through drying and firing after the mixing.

[0030] Here, the drying can be performed at a temperature of 80°C to 150°C for 1 hour to 10 hours, and the firing can be performed at a temperature of 500°C to 1050°C for 1 hour to 10 hours.

[0031] Furthermore, according to another embodiment of the present invention, a lithium secondary battery is provided comprising a positive electrode including the positive active material, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0032] Figure 1 is a graph showing the high-temperature storage characteristics according to Experimental Example 1.

[0033] Figure 2 is a graph showing the XRD analysis results of the active material of Example 1 according to Experimental Example 2.

[0034] Figure 3 is a graph showing the XRD analysis results of the active material of Comparative Example 1 according to Experimental Example 2.

[0035] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0036] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0037] Furthermore, throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0038]

[0039] positive electrode active material

[0040] A lithium secondary battery according to one embodiment of the present invention is,

[0041] A core comprising a lithium-over-manganese oxide having a molar ratio of lithium to transition metals excluding lithium greater than 1, and a molar content of manganese among the transition metals of 50 mol% or more, and

[0042] It includes a surface layer located on the surface of the above core and comprising a compound having a Li / M (metal excluding Li) ratio of less than 1 on a molar basis, and

[0043] The above-mentioned core is characterized by having a structure in which a layered structure and a rock salt structure are mixed, and the above-mentioned surface layer is characterized by having an olivine structure or an amorphous structure.

[0044] Here, the above-mentioned lithium manganese oxide can be represented by the following chemical formula 1.

[0045] [Chemical Formula 1]

[0046] xLi2MnO3·(1-x)Li[Ni 1-y-z-w Mn y Co z M w ]O2

[0047] In the above formula, M is at least one selected from the group consisting of Al, B, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤x≤0.5, 0.4≤y<1, 0≤z≤0.2, and 0≤w≤0.2.

[0048] Here, the lithium-rich manganese oxide included in the core may have a ratio of lithium to metals other than lithium (Li / Metal) of 1.1 to 1.6, specifically 1.2 to 1.6, and more specifically 1.3 to 1.6.

[0049] In addition, in Chemical Formula 1, the above y may be 0.4 to 0.9 in detail, and more specifically 0.4 to 0.8, and the above z and w may each be 0 to 0.1 in detail.

[0050] That is, as explained above, the lithium manganese oxide as the core material is a material containing a compound with a layered structure and a compound with a rock salt structure, and has excellent capacity characteristics due to the high content of Mn and Li.

[0051] However, since an oxygen-redox reaction occurs during the activation process of rock salt and generates a large amount of gas, measures are required to prevent this.

[0052] Accordingly, the inventors of the present application, after conducting in-depth research, confirmed that when the core surface includes a surface layer comprising a compound having an olivine structure or an amorphous structure with a Li / Me ratio of less than 1, these problems can be resolved and cycle characteristics can be improved.

[0053] Accordingly, the surface layer located on the surface of the core comprises a compound in which Li / Me (wherein Me is a metal other than Li) is less than 1 based on moles.

[0054] Here, specifically, Li / Me may be 0.5 to 0.98 based on moles, more specifically 0.8 to 0.98, and most specifically 0.85 to 0.9.

[0055] At this time, the compound included in the surface layer may be a lithium-based phosphate containing various additive metals. For example, the compound may be a lithium-based phosphate containing Ni, Co, Fe, Cr, Cu, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, etc.

[0056] However, the above surface layer may have an olivine structure different from the core or an amorphous structure that does not have complete crystallinity, and may be in a mixed form.

[0057] Among these, in terms of increasing the surface safety of the above-mentioned lithium manganese-based oxide while preventing degradation of output characteristics, etc., specifically, the surface layer may be a compound containing Li, Fe, and P, and more specifically, Li a It may be an FePO4-based compound. Here, a may be 0.5 to 0.98, more specifically 0.8 to 0.98, and most specifically 0.85 to 0.9.

[0058] Here, Li a FePO4-based compounds refer to Li a It may be a material having an olivine structure such as FePO4, or it may be an amorphous material that includes the above materials but does not form a complete crystalline structure. As such, the surface layer may not contain Mn.

[0059] Or, the above Li aThe FePO4-based compound may be in a form in which some Mn of the core is incorporated, but in this case, the incorporated Mn content may be very small, specifically 0.1 mole or less relative to 1 mole of Fe, more specifically 0.05 mole or less, and even more specifically 0.01 mole or less.

[0060] The above surface layer does not contain an excess amount of Li, so it can prevent adverse reactions with the electrolyte, thereby reducing gas generation and improving surface safety. Additionally, since it has a structure with increased voids in Li sites and increased space within the crystal structure, the mobility of lithium ions can be increased, which can also improve the performance of the secondary battery.

[0061] The thickness of the surface layer may be 3 nm to 2 µm, more specifically 5 nm to 0.5 µm, and even more specifically 5 nm to 0.1 µm.

[0062] If the surface layer thickness is too thin outside the above range, the effects intended by the present invention, such as improved surface safety or improved lithium mobility, cannot be achieved; conversely, if it is too thick, lithium mobility may decrease and capacity may be reduced due to a decrease in core content, which is undesirable.

[0063] In addition, the surface layer may be formed with an area of ​​0.03% to 100% of the total surface area of ​​the core, more specifically, with an area of ​​1% to 100%, more specifically, with an area of ​​1% to 50%, and most specifically, with an area of ​​1% to 30%.

[0064] If formed outside the above range with an area that is too small, the core remains highly exposed, making it difficult to prevent side reactions in the electrolyte and thus unable to reduce gas generation, which is undesirable.

[0065] The above-mentioned lithium manganese oxide may have a monomodal structure composed of large particles with an average diameter (D50) of 5 μm to 20 μm, or a bimodal structure comprising large particles and small particles with an average diameter (D50) of 2 μm to 5 μm.

[0066] Here, in the monomodal structure, a single D50 peak is formed in the particle analysis, and in the bimodal structure, two peaks are formed in the particle analysis.

[0067] In addition, the above-mentioned large particle may be a secondary particle with a structure in which tens or hundreds of single particles of the primary particle are clustered together, and the above-mentioned small particle may be a single particle of the primary particle or a secondary particle.

[0068] The average diameter (D50) of the above-mentioned large particles may be, in detail, 5㎛ to 15㎛, and more specifically, 5㎛ to 14㎛.

[0069] The average diameter (D50) of the above-mentioned small particles may be, in detail, 3㎛ to 5㎛, and more specifically, 3㎛ to 4㎛.

[0070] “Average diameter D50” refers to the particle diameter at the 50th point of the cumulative distribution of particle volume according to particle diameter. That is, D50 is the particle diameter at the 50th point of the cumulative distribution of particle volume according to particle diameter.

[0071] The above D50 can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to particle size as the particles pass through the laser beam, thereby calculating the particle size distribution. D50 can be measured by calculating the particle diameter at the point where the cumulative distribution of particle volume according to particle size in the measuring device reaches 50%.

[0072]

[0073] Method for manufacturing positive electrode active material

[0074] According to another embodiment of the present invention, a method for manufacturing a positive electrode active material is provided, comprising the steps of manufacturing the lithium-over-manganese-based oxide powder and mixing it with a solution containing a surface layer precursor to form a surface layer together with washing the lithium-over-manganese-based oxide powder.

[0075] Here, the above lithium manganese-based oxide powder may be a substance represented by the above chemical formula 1.

[0076] The lithium-over-manganese oxide powder represented by the above chemical formula 1 can be formed by mixing precursor materials for manufacturing the lithium-over-manganese oxide with a lithium compound and heat-treating the mixture.

[0077] At this time, the precursor materials may be compounds or co-precipitates of materials containing elements other than Li among the materials included in the above-mentioned lithium manganese-based oxide, for example, oxides containing elements other than Li, sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides may be used, or co-precipitates of such materials.

[0078] The above lithium compound may also be a lithium-containing oxide, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and specifically, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, but in detail, it may be Li2CO3, LiOH, or Li2O.

[0079] The above heat treatment can be performed in a range of 700°C to 1050°C and can be performed in an inert atmosphere. Outside of this range, if the temperature is too low, the lithium-based manganese oxide may not form well, and if it is too high, there is a problem with lithium volatilization, which is undesirable.

[0080] After preparing the lithium manganese oxide powder in this manner, it is mixed with a solution containing a surface layer precursor.

[0081] Here, the solution containing the surface layer precursor is a solution in which the surface layer precursor is mixed with a solvent, and the surface layer precursor is a precursor containing a metal (Me) included in the surface layer, and may be an oxide, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide. Specifically, since the surface layer contains Fe and P, it may be a compound containing Fe, for example, an oxide containing Fe, a sulfate, a nitrate, an acetate, a carbonate, an oxalate, a citrate, a halide, a hydroxide, or an oxyhydroxide, and a compound containing P such as H3PO4 or (NH4)3PO4.

[0082] In addition, Mn is not included in the surface layer precursor so that the surface layer has a crystal structure different from the core.

[0083] The above solvent may be an aqueous solvent, and more specifically, distilled water.

[0084] After preparing a solution containing such a surface layer precursor, the above-mentioned lithium manganese oxide powder can be mixed into the solution.

[0085] At this time, the above mixing can be performed at a temperature of 20°C to 80°C, specifically at a temperature of 25°C to 40°C, or at room temperature.

[0086] In addition, this mixing can be performed for 2 minutes to 2 hours, more specifically for 5 minutes to 2 hours, and more specifically for 5 minutes to 20 minutes.

[0087] By this mixing, Li impurities located on the surface of the lithium-rich manganese oxide powder can be washed away by mixing with the solution, thereby forming a surface layer with a Li / Me ratio of less than 1, which in turn creates a surface layer with stability and significantly reduces side reactions in the electrolyte.

[0088] Meanwhile, once such mixing is completed, the mixture can be dried and fired to complete the formation of the surface layer.

[0089] Here, the drying and firing may be performed in a vacuum oven, and the drying may be performed at a temperature of 80°C to 150°C for 1 hour to 10 hours, more specifically, at a temperature of 90°C to 140°C for 2 hours to 10 hours, and even more specifically, at a temperature of 100°C to 120°C for 4 hours to 10 hours.

[0090] In addition, the above firing can be performed at a temperature of 300°C to 1050°C for 1 hour to 20 hours, more specifically at a temperature of 500°C to 1050°C for 1 hour to 10 hours, and even more specifically at a temperature of 500°C to 1000°C for 1 hour to 10 hours.

[0091] As such, the surface layer after firing can have an olivine structure, a spinel structure, or an amorphous structure as described above, and accordingly, it is effective for gas reduction and can also increase surface structure stability.

[0092]

[0093] lithium secondary battery

[0094] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery comprising a positive electrode including the positive electrode active material is provided.

[0095] Specifically, the lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0096] The above anode has a structure in which an anode composite layer is formed on one or both sides of an anode current collector.

[0097] The above positive current collector may generally have a thickness of 3 to 500 μm. In addition, the above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the positive active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0098] The above positive composite layer may further include the binder, conductive material, and other additives together with the positive active material.

[0099] The above-mentioned cathode active material, in addition to the above-mentioned lithium manganese-based oxide, is a compound capable of reversible intercalation and deintercalation of lithium, for example, a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni ZO4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4(where, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (Here, M is one or more selected from Al, Mg and Ti, X is one or more selected from F, S and N, and -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1) etc. may be further included.

[0100] When the above positive active material is a mixture of the above lithium manganese-based oxide and other positive active materials, the above lithium manganese-based oxide may be included in an amount of 80% or more by weight and 90% or more by weight based on the total weight of the positive active material.

[0101] The above conductive material is a component for further improving the conductivity of the positive electrode active material. Such conductive material is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. Among these, the above conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers to further lower the resistance of the lithium metal battery and further improve output characteristics.

[0102] Typically, the conductive material may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the anode composite layer.

[0103] The above binder is a component that assists in the bonding of the positive active material and the conductive material, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0104] Typically, the binder may be included in an amount of 1 to 20 weight%, or 1 to 15 weight%, or 1 to 10 weight% based on the total weight of the anode composite layer.

[0105] In addition, the above-mentioned other additives may further include, for example, fillers as components that inhibit expansion. The above-mentioned filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical changes in the battery, and, for example, olifin-based polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. may be used.

[0106] The above cathode has a structure in which a cathode composite layer is formed on one or both sides of a cathode current collector.

[0107] The above negative current collector may generally have a thickness of 3 to 500 μm. In addition, the above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, it may be one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper surface-treated with a dissimilar metal, stainless steel surface-treated with a dissimilar metal, and aluminum-cadmium alloy, and may have fine irregularities formed on its surface to increase the adhesion of the negative active material, and may be in various forms such as film, sheet, foil, net, porous body, foam, nonwoven body, etc.

[0108] The above cathode composite layer may include a cathode active material, a binder, a conductive material, and other additives as described in the anode.

[0109] As the above-mentioned cathode active material, one or more carbon-based materials selected from the group consisting of graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, Si-based materials, 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, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 포함할 수 있지만, 당업계에 알려진 것이라면 이들만으로 한정되는 것은 아니다.

[0110] The above separator may be a Safety Reinforced Separator (SRS) separator made of a polymer substrate, or having a coating layer containing a binder and inorganic particles formed on one or both sides of the polymer substrate.

[0111] The above polymer substrate may be, for example, a polyolefin-based substrate, and the above polyolefin-based substrate may be used in the form of a sheet, a multilayer membrane, a microporous film, a woven fabric, a nonwoven fabric, etc., but is not necessarily limited thereto. The above polyolefin-based substrate may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the separator may generally be in the range of 0.01 to 10 μm, and the thickness may generally be in the range of 5 to 300 μm, but is not limited thereto.

[0112] The polymer substrate of the above SRS separator may be the above polyolefin substrate.

[0113] The inorganic particles in the coating layer enable the formation of empty spaces between the inorganic particles, thereby serving the role of forming micropores and acting as a kind of spacer that maintains a physical shape. In addition, since the inorganic particles generally have the characteristic that their physical properties do not change even at high temperatures of 200°C or higher, the formed organic-inorganic mixed layer has excellent heat resistance.

[0114] The above-mentioned inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied battery. In particular, when using inorganic particles with ion-transfer capabilities, it is desirable to have as high an ion conductivity as possible, as this can improve performance by increasing the ion conductivity within the electrochemical device. Furthermore, if the inorganic particles have a high density, it is desirable to have as low a density as possible, as this not only makes it difficult to disperse them during manufacturing but also causes problems with weight increase during the production of secondary batteries. Additionally, in the case of inorganic materials with high dielectric constant, they can improve the ion conductivity of the electrolyte by contributing to an increased degree of dissociation of electrolyte salts, such as lithium salts, within the liquid electrolyte. Finally, in the case of inorganic particles with thermal conductivity, it is even more desirable because their excellent heat-endoscopy ability suppresses the phenomenon where heat is concentrated locally to form heat points, which leads to thermal runaway.

[0115] For the reasons stated above, the inorganic particles are preferably one or more selected from the group consisting of (a) high dielectric constant inorganic particles having a dielectric constant of 1 or more, 5 or more, preferably 10 or more, (b) inorganic particles having piezoelectricity, (c) thermally conductive inorganic particles, and (d) inorganic particles having lithium ion transfer ability.

[0116] The above-mentioned piezoelectric inorganic particles refer to materials that are insulators at atmospheric pressure but possess the property of conducting electricity due to changes in their internal structure when a certain pressure is applied. In addition to exhibiting high dielectric constant characteristics with a dielectric constant of 100 or more, when subjected to tension or compression by applying a certain pressure, electric charge is generated, causing one side to become positively charged and the opposite side to become negatively charged, thereby creating a potential difference between the two sides.

[0117] Examples of the above-mentioned inorganic particles having piezoelectric properties include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT) hafnia (HfO2) or mixtures thereof, but are not limited thereto.

[0118] The inorganic particles having the above lithium ion transfer capability refer to inorganic particles that contain lithium elements but do not store lithium and have the function of moving lithium ions. Since the inorganic particles having the lithium ion transfer capability can transfer and move lithium ions due to a type of defect existing within the particle structure, a decrease in lithium mobility can be prevented, thereby preventing a decrease in battery capacity.

[0119] Examples of inorganic particles having the above-mentioned lithium ion transfer ability include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O5등과 같은 (LiAlTiP) x Oy Series glass (0 <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4, etc. x Ge y P z S w , 0 <x<4, 0<y<1, 0<z<1, 0<w<5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS2등과 같은 SiS2계열 glass (Li x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass (Li x P y S z , 0 <x<3, 0<y<3, 0<z<7), 또는 이들의 혼합물 등이 있으나, 이에 한정되는 것은 아니다.

[0120] In addition, examples of inorganic particles with a dielectric constant of 1 or greater include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, or mixtures thereof, but are not limited thereto.

[0121] The above thermally conductive inorganic particles are materials that provide low thermal resistance but do not provide electrical conductivity, thus having insulating properties, and may be one or more selected from the group consisting of, for example, aluminum nitride (AlN), boron nitride (BN), alumina (Al2O3), silicon carbide (SiC), and beryllium oxide (BeO), but are not limited thereto.

[0122] When the aforementioned high dielectric constant inorganic particles, piezoelectric inorganic particles, thermally conductive inorganic particles, and inorganic particles capable of transporting lithium ions are mixed, their synergistic effect can be doubled.

[0123] There is no limit to the size of the inorganic particles, but it is preferable that they be in the range of 0.001 to 10 μm to ensure an appropriate porosity between the inorganic particles. If the size is less than 0.001 μm, dispersibility is reduced, making it difficult to control physical properties; if the size exceeds 10 μm, the thickness increases, leading to a decrease in mechanical properties, and furthermore, due to the excessively large pore size, it fails to perform the function of a sufficient coating layer, increasing the probability of an internal short circuit occurring during battery charging and discharging.

[0124] There are no specific limitations on the content of the above inorganic particles, but a range of 1 to 99 weight% per 100 weight% of the mixture of inorganic particles and binder is preferred, and particularly 10 to 95 weight% is more preferred. If it is less than 1 weight%, the content of the binder becomes excessively high, which may reduce the pore size and porosity due to a decrease in the empty space formed between the inorganic particles, thereby reducing the mobility of lithium ions. Conversely, if it exceeds 99 weight%, the mechanical properties of the coating layer deteriorate due to weakened adhesion between the inorganic particles because the binder content is too low.

[0125] Meanwhile, the above-mentioned binder is not limited as long as it does not cause adverse reactions with the electrolyte, but in particular, one with a glass transition temperature (Tg) as low as possible can be used, preferably in the range of -200 to 200°C. This is because it can improve the mechanical properties of the final insulating film.

[0126] In addition, the above-mentioned binder does not necessarily have to possess ion conductivity, but it is more preferable to use a polymer that possesses ion conductivity.

[0127] Therefore, it is desirable for the above-mentioned binder to have a high possible dielectric constant, and since the degree of dissociation of the salt in the electrolyte actually depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the above-mentioned polymer, the higher the degree of dissociation of the salt in the electrolyte can be improved. The dielectric constant of the above-mentioned polymer can be 1 or higher, specifically in the range of 1.0 to 100 (measurement frequency = 1 kHz), and it is particularly desirable that it be 10 or higher.

[0128] In addition to the aforementioned functions, the binder may have the characteristic of gelling upon liquid electrolyte impregnation to exhibit a high degree of swelling. In practice, if the binder is a polymer with excellent electrolyte impregnation, the electrolyte injected after battery assembly permeates into the polymer, and the polymer retaining the absorbed electrolyte acquires electrolyte ion conductivity. Therefore, if possible, the solubility index is 15 to 45 MPa 1 / 2 A phosphorus polymer is preferred, with a value of 15 to 25 MPa 1 / 2 and 30 to 45 MPa 1 / 2 The range is more desirable. The solubility index is 15 MPa 1 / 2 Less than and 45 MPa 1 / 2 If it exceeds, it becomes difficult to swell with a conventional liquid electrolyte for batteries.

[0129] Examples of such binders include polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethylpullulan. It may be one or more selected from the group consisting of cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinyl alcohol.

[0130] The total thickness of the separator may be 5 micrometers to 20 micrometers, more specifically 5 micrometers to 15 micrometers, and even more specifically 6 micrometers to 13 micrometers. When the thickness of the separator satisfies the above range, it is possible to effectively prevent a short circuit between the positive and negative electrodes while minimizing the resistance value of the lithium secondary battery. As a result, it is possible to prevent a decrease in the energy density of the lithium secondary battery and improve its lifespan characteristics.

[0131] The above electrolyte may be a lithium non-aqueous electrolyte, and the lithium non-aqueous electrolyte may include a lithium salt and a non-aqueous organic solvent.

[0132] In this case, the lithium salt is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 -, (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one selected from the group consisting of can be cited.

[0133] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It may include a single substance or a mixture of two or more substances selected from the group consisting of 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)2 and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2), but it is preferable to include Li(N(SO2CF3)2 for excellent stability.

[0134] In addition to these, lithium salts commonly used in the electrolytes of lithium secondary batteries can be used without restriction.

[0135] The above lithium salt can be appropriately modified within a range that is typically usable, but in order to obtain the effect of forming a corrosion-preventing film on the optimal electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically at a concentration of 1 M to 2.5 M, and more specifically at a concentration of 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so the electrolyte impregnation can be improved.

[0136] The above-mentioned non-aqueous organic solvent is not limited to any type that can minimize decomposition due to oxidation reactions, etc., during the charging and discharging process of a lithium secondary battery and can exhibit the desired characteristics together with the additive. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used individually or in a mixture of two or more types, and specifically, carbonate-based organic solvents can be used.

[0137] Among the above organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively low melting point compared to ethylene carbonate.

[0138] In addition, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically may include dimethyl carbonate.

[0139] The above ether-based organic solvent may be any one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited thereto.

[0140] The above ester-based organic solvent may include at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0141] The above linear ester-based organic solvent may be represented by any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more of these, but is not limited thereto.

[0142] The above-mentioned cyclic ester-based organic solvent may be 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 of these, but is not limited thereto.

[0143] Among the above ester-based solvents, cyclic carbonate compounds can be preferably used as high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte. Furthermore, if low-viscosity, low-dielectric constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate, and linear ester compounds are mixed with such cyclic carbonate compounds in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0144] Furthermore, the above lithium non-aqueous electrolyte may further include a functional additive, and the functional additive may be included to prevent cathode decay from occurring in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and swelling improvement effects during high-temperature storage.

[0145] Specifically, the functional additive may include one or more functional additives selected from the group consisting of sulfonate compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds as representative examples.

[0146] The above sulfone-based compound may be at least one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone, and may be included in an amount of 0.3% to 5% by weight, specifically 1% to 5% by weight, based on the total weight of the electrolyte. If the content of the sulfone-based compound in the electrolyte exceeds 5% by weight, an excessively thick film may be formed on the electrode surface, causing an increase in resistance and output degradation, and the resistance may also increase due to the excess amount of additive, which may lead to a deterioration in output characteristics.

[0147] The above sulfite-based compounds may include one or more compounds 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-butylene glycol sulfite, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0148] The above sulfone-based compounds may include one or more compounds selected from the group consisting of divinylsulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methylvinyl sulfone, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0149] The above sulfate-based compounds may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0150] In addition, the above halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC), and may be included in an amount of 5% by weight or less based on the total weight of the electrolyte. If the content of the halogen-substituted carbonate compound in the electrolyte exceeds 5% by weight, the cell swelling performance may deteriorate.

[0151] In addition, the nitrile-based compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0152] The above-mentioned cyclic carbonate-based compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte. If the content of the cyclic carbonate-based compound in the electrolyte exceeds 3% by weight, the cell swelling inhibition performance may deteriorate.

[0153] The above phosphate-based compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0154] The above borate-based compound may be lithium oxalyl difluoroborate, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0155] The above lithium salt-based compound is a compound different from the lithium salt included in the above lithium non-aqueous electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate toborate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0156] The above functional additives may be mixed in two or more types and included in an amount of 20% by weight or less, specifically 0.1% to 10% by weight, based on the total weight of the lithium non-aqueous electrolyte. If the content of the above functional additives exceeds 20% by weight, there is a possibility that excessive side reactions may occur within the lithium non-aqueous electrolyte during the charging and discharging of the battery. In particular, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitates within the lithium non-aqueous electrolyte at room temperature. Consequently, side reactions that degrade the lifespan or resistance characteristics of the lithium metal battery may occur.

[0157]

[0158] Hereinafter, an example according to the present invention is described with reference to an example to demonstrate the effects according to the present invention.

[0159]

[0160] <Example 1>

[0161] Core Synthesis

[0162] Transition metal precursor (Ni 0.35 Mn 0.65 (OH)2) and a lithium precursor are mixed such that the molar ratio of transition metal to Li is 1:1.25, and calcined at 850°C in an oxygen atmosphere (oxygen content 50%) to obtain a lithium-rich manganese oxide (0.37Li2MnO3·0.63Li[Ni 0.563 Mn 0.437 ]O2) was manufactured.

[0163] Surface layer formation

[0164] The above-described lithium manganese-based oxide (0.37Li2MnO3·0.63Li[Ni 0.563 Mn 0.437After preparing [O2], a mixture of Fe(NO3)3·H2O and H3PO4 was added in a molar ratio of 1:1, and a mixture of Fe(NO3)3·H2O and citric acid was mixed in a molar ratio of about 1:2. 5 g of the above lithium manganese oxide was added to the mixture mixed in 10 mL of distilled water, 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 an anode active material with a surface layer formed.

[0165]

[0166] <Comparative Example 1>

[0167] A lithium manganese-based oxide that did not form the above surface layer was used as the positive active material.

[0168]

[0169] <Experimental Example 1>

[0170] Using the positive active materials prepared in Example 1 and Comparative Example 1, respectively, a positive active material, a binder (PVdF), and a conductive material (CNT) were mixed in NMP (N-methylpyrrolidone) in a weight ratio of 96:3:1 to prepare a positive slurry, the positive slurry was coated to a thickness of 40 μm on a 20 μm thick Al foil, dried at 130°C, and then rolled to produce a positive.

[0171] Artificial graphite was used as the cathode active material, and a cathode slurry was prepared by mixing the cathode active material, the conductive material (CNT), the binder (styrene-butadiene rubber (SBR)), and the additive (carboxymethyl cellulose (CMC) in water in a weight ratio of 96.2:0.8:2:1. The slurry was then coated to a thickness of 30 μm on an 8 μm thick Cu foil, dried at 130°C, and rolled to produce a cathode.

[0172] An electrode assembly was manufactured by interposing a separator, which has organic-inorganic coating layers (mixed in a weight ratio of 90:10 of Al2O3 and PVDF) formed on both sides of a polypropylene (PP) substrate between the anode and the cathode.

[0173] A pouch-type lithium secondary battery was manufactured using the above electrode assembly and an electrolyte (100 mL) containing 1 M LiPF6 in a solvent with EC : EMC = 3 : 7.

[0174] A lithium secondary battery was manufactured by performing one charge and discharge cycle of charging to 4.6V at 0.1C at 25℃ (CC / CV mode) and discharging to 2.0V at a constant current of 0.1C (CC mode).

[0175] After storing the above lithium secondary battery in a 60°C chamber for 12 weeks, the volume change of the lithium secondary battery was measured, and the results are shown in Fig. 1 below. The measurement was repeated 2-3 times for lithium secondary batteries using the positive electrode active materials of Example 1 and Comparative Example 1.

[0176] Referring to FIG. 1, it can be seen that when the positive electrode active material according to the present invention is included, the volume change is small compared to the positive electrode active material of Comparative Example 1, which does not form a surface layer, and thus gas generation is reduced.

[0177]

[0178] <Experimental Example 2>

[0179] The lithium secondary battery prepared in Experimental Example 1 above was charged to 4.6V at 0.1C (CC / CV mode) and discharged to 2.0V at a constant current of 0.1C once. Then, the process of charging to 4.35V at 0.1C (CC / CV mode) and discharging to 2.0V at a constant current of 0.1C was performed once, and then charging to 4.35V at 0.33C (CC / CV mode) was performed again. After high-temperature storage in a 60℃ chamber for 12 weeks in this charged state, the changes in the crystal structure of the cathode active materials were confirmed through XRD measurement after disassembling the secondary battery, and the results are shown in Figures 2 and 3.

[0180] The XRD measurement conditions are as follows.

[0181] * Equipment: Brucker D2 phaser

[0182] * X-ray wavelength: 1.5406 Å

[0183] * Scan speed: Exposure 1 second / 0.01 degrees

[0184] * Measurement time: 150 minutes

[0185] Referring to FIGS. 2 and FIGS. 3, it can be seen that the crystal structure of the positive active material according to the present invention is maintained, whereas the crystal structure of the positive active material according to Comparative Example 1 collapses according to the oxygen-redox reaction.

[0186]

[0187] A person skilled in the art to which this invention pertains will be able to make various applications and modifications within the scope of this invention based on the above content.

[0188] According to the present invention, by forming a coating layer having a structure different from that of the lithium manganese oxide and having a Li / M ratio of less than 1 on a core containing a high manganese (Mn) content, the surface safety of the positive electrode active material containing the same can be increased, thereby reducing side reactions of the electrolyte of the lithium secondary battery and minimizing gas generation, so that the gas generation improvement effect can be exhibited even in the charged state.

Claims

1. A core comprising a lithium-over-manganese oxide in which the molar ratio of lithium to transition metals excluding lithium is greater than 1 and the molar content of manganese among the transition metals is 50 mol% or more, and It comprises a surface layer located on the surface of the above-mentioned core and containing a compound in which Li / Me (wherein Me is a metal other than Li) is less than 1 based on moles, and The above core has a structure in which a layered structure and a rock salt structure are mixed, and the above surface layer has an olivine structure or an amorphous structure, forming an anode active material.

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

2.

3. In Paragraph 1, A positive active material having a Li / Me ratio of 0.8 to 0.98 in the above surface layer.

4. In Paragraph 1, The above surface layer is a positive active material comprising a compound including Li, Fe, and P.

5. In Paragraph 1, The above surface layer is a positive active material that does not contain Mn or contains Mn at a content of 0.1 mole or less relative to 1 mole of Fe.

6. In Paragraph 1, A positive active material having a surface layer thickness of 3 nm to 2 µm.

7. In Paragraph 1, The above surface layer is an anode active material formed with an area of ​​0.03% to 100% of the total surface area of ​​the core.

8. A method for manufacturing a positive electrode active material according to paragraph 1, A method for manufacturing an anode active material comprising the steps of: manufacturing the above-mentioned lithium manganese-based oxide powder; mixing the powder with a solution containing a surface layer precursor; and forming a surface layer together with washing the above-mentioned lithium manganese-based oxide powder.

9. In Paragraph 8, A method for manufacturing an anode active material in which the above surface layer precursor is a compound containing Fe and a compound containing P.

10. In Paragraph 8, A method for manufacturing an anode active material in which the above solution is distilled water.

11. In Paragraph 8, A method for manufacturing a positive electrode active material in which the above mixing is performed at a temperature of 20℃ to 80℃.

12. In Paragraph 8, A method for manufacturing an anode active material in which the above mixing is performed for 2 minutes to 2 hours.

13. In Paragraph 8, A method for manufacturing an anode active material in which the process of forming the above surface layer is carried out through drying and calcination after the above mixing.

14. In Paragraph 13, A method for manufacturing an anode active material in which the above drying is performed at a temperature of 80°C to 150°C for 1 hour to 10 hours.

15. In Paragraph 13, A method for manufacturing an anode active material in which the above calcination is performed at a temperature of 500℃ to 1050℃ for 1 hour to 20 hours.

16. A positive electrode comprising a positive electrode active material according to paragraphs 1 to 7, A lithium secondary battery comprising a negative electrode and a separator interposed between the positive electrode and the negative electrode.