Electrode for secondary battery comprising over-lithiated manganese-based oxide, and lithium secondary battery comprising same

Abstract

An embodiment of the present invention provides an electrode for a secondary battery, and a lithium secondary battery, the electrode including an electrode current collector and an electrode layer formed on one surface or both surfaces of the electrode current collector, wherein the electrode layer includes a lithium-based active material including: an over-lithiated manganese-based oxide in which a molar ratio of lithium to transition metals other than lithium is more than 1 and a molar content of manganese in the transition metals is 50 mol % or more; and a coating layer formed on a surface of the over-lithiated manganese-based oxide, and the coating layer includes Co in an amount of 3000 ppm to 8000 ppm on the basis of the total weight of the lithium-based active material.

Description

Electrode for a secondary battery comprising a lithium-rich manganese oxide, 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. 10-2024-0143603 filed October 21, 2024 and Korean Patent Application No. 10-2025-0133260 filed September 17, 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 an electrode for a secondary battery comprising a lithium-rich manganese oxide, 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 lithium-rich manganese oxides, they have a structure in which layered (LiM'O2) and rock salt phases (Li2MnO3) are mixed. During the initial activation process, the rock salt phase is activated to generate an excess amount of lithium ions, and since the irreversible capacity of the anode is compensated by this, it is possible to balance with the silicon-based anode without a separate compensation material such as a sacrificial cathode or a prior lithium compensation process such as pre-lithiation.

[0008] However, compared to lithium nickel cobalt manganese oxide with a high nickel content, the above-mentioned lithium manganese oxide has many internal pores in the active material particles and a low particle density, so there is a lot of particle breakage at the same pressure, which limits the control of porosity.

[0009] Accordingly, the above-mentioned lithium manganese-based oxide requires the development of technology capable of improving rolling characteristics.

[0010] The present invention aims to provide an electrode comprising an active material capable of improving rolling characteristics by improving particle strength and reducing the rate of particle breakage during target rolling at the same porosity, and a lithium secondary battery comprising the same.

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

[0012] An electrode for a secondary battery comprising an electrode current collector and an electrode layer formed on one or both sides of the electrode current collector,

[0013] The electrode layer comprises a lithium-based active material including an over-lithium manganese-based 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 a coating layer formed on the surface of the over-lithium manganese-based oxide.

[0014] The above coating layer provides an electrode containing Co in an amount of 3,000 ppm to 8,000 ppm based on the total weight of the lithium-based active material.

[0015] Here, the content of Co in the coating layer may be 3300 ppm to 6600 ppm based on the total weight of the lithium-based active material.

[0016] Specifically, the coating layer may include one or more materials selected from the group consisting of Co metal, Co oxide, and lithium cobalt oxide.

[0017] The above-mentioned lithium manganese oxide can be represented by the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019] Li a Ni b Co c Mn d M e O 2+f

[0020] In the above formula, 1.12≤a≤1.18, 1.1≤a / (b+c+d)≤1.5, 0.24≤b≤0.36, 0≤c≤0.1, 0.47≤d<0.63, 0≤e≤0.05, 0≤f≤0.05, b+c+d+e=1, and 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.

[0021] In addition, the above-mentioned lithium manganese-based oxide is a secondary particle with a structure in which primary particles are aggregated, and the coating layer may be formed on both the surface of the primary particles and the surface of the secondary particles.

[0022] Specifically, the coating layer may be distributed within a thickness of 20 nm to 100 nm from the surface of the primary particle based on the primary particle, and may be distributed within a thickness of 3 μm or less from the surface of the secondary particle.

[0023] Here, the average diameter (D50) of the secondary particles may be 5 to 10 μm.

[0024] Meanwhile, the content of particles of the lithium-based active material having a diameter of 1 μm or less in the electrode layer may be 2.5 volume% or less based on the total volume of the lithium-based active material.

[0025] Furthermore, the particle fracture strength of the lithium-based active material may be 1.4 mN to 2.0 mN, and the degree of sphericity of the lithium-based active material may be 0.7 to 0.8.

[0026] In addition, the porosity of the electrode layer may be 20 to 40 volume%.

[0027] According to another embodiment of the present invention,

[0028] A lithium secondary battery comprising the above electrode is provided.

[0029] Figure 1 is an XPS analysis graph showing the coating depth by measuring the Co content of the coating layer according to Experimental Example 1.

[0030] Figure 2 is a graph of particle fracture strength analysis according to Experimental Example 2.

[0031] Figure 3 is an SEM image of the electrode cross-section of Example 1 according to Experimental Example 3.

[0032] Figure 4 is an SEM image of the electrode cross-section of Example 2 according to Experimental Example 3.

[0033] Figure 5 is an SEM image of the electrode cross-section of Comparative Example 1 according to Experimental Example 3.

[0034] Figure 6 is a graph of the active material diameter distribution before electrode layer formation according to Experimental Example 4.

[0035] Figure 7 is a graph of the active material diameter distribution after electrode layer formation according to Experimental Example 4.

[0036] Figure 8 is a graph of the degree of sphericity measurement according to Experimental Example 5.

[0037] Figure 9 is a graph showing the voltage change according to charging and discharging in Experimental Example 6.

[0038] Figure 10 is a graph showing the voltage change according to 0.1C charging and discharging according to Experimental Example 7.

[0039] Figure 11 is a graph showing the voltage change according to 0.33C charging and discharging according to Experimental Example 7.

[0040] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0041] 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.

[0042] 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.

[0043] Furthermore, the “(average) diameter” and “sphericity” defined in the present specification are based on values ​​measured after performing rolling so that the porosity of the electrode layer of the electrode according to the present invention is about 20 volume% to 40 volume%.

[0044]

[0045] electrode

[0046] An electrode for a secondary battery according to one embodiment of the present invention is,

[0047] An electrode for a secondary battery comprising an electrode current collector and an electrode layer formed on one or both sides of the electrode current collector,

[0048] The electrode layer comprises a lithium-based active material including an over-lithium manganese-based 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 a coating layer formed on the surface of the over-lithium manganese-based oxide.

[0049] The coating layer is characterized by containing Co in an amount of 3,000 ppm to 8,000 ppm based on the total weight of the lithium-based active material.

[0050] As explained above, the lithium manganese-based oxide represented by Chemical Formula 1 has a low particle density, which causes particle breakage and consequently limits the ability to increase electrode density. Therefore, after conducting in-depth research, the inventors of the present application confirmed that particle strength can be improved by forming a coating layer containing Co in a specific content on the surface of the lithium manganese-based oxide, and thus completed the present invention.

[0051] Here, as described above, the coating layer may contain Co in an amount of 3,000 ppm to 8,000 ppm based on the total weight of the lithium-based active material, more specifically 3,000 ppm to 7,000 ppm, and even more specifically 3,300 ppm to 6,600 ppm.

[0052] If the above range is exceeded, such as being less than 3000 ppm or exceeding 8000 ppm, the particle strength effect obtainable by forming a coating layer cannot be sufficiently obtained, and it is also undesirable in terms of capacity or energy density.

[0053] This coating layer may include one or more materials selected from the group consisting of Co metal, Co oxide, and lithium cobalt oxide. Specifically, in addition to one or more materials selected from the group consisting of Co metal and Co oxide, the lithium cobalt-based material containing both Li and Co may be an oxide, phosphate, hydroxide, etc., or a salt in the form of a sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide containing Co.

[0054] However, even in this case, one or more materials selected from the group consisting of the above-mentioned Co metal, Co oxide, and lithium cobalt oxide may be included in an amount of 50% or more by weight, specifically 70% or more by weight, and more specifically 80% or more by weight based on the total weight of the coating layer.

[0055] Meanwhile, the above-mentioned lithium manganese oxide can be represented by the following chemical formula 1.

[0056] [Chemical Formula 1]

[0057] Li a Ni b Co c Mn d M e O 2+f

[0058] In the above formula, 1.12≤a≤1.18, 1.1≤a / (b+c+d)≤1.5, 0.24≤b≤0.36, 0≤c≤0.1, 0.47≤d<0.63, 0≤e≤0.05, 0≤f≤0.05, b+c+d+e=1, and 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.

[0059] In the above formula, specifically 1.2≤a / (b+c+d)≤1.5 and 0.5≤d<0.63, and more specifically 1.2≤a / (b+c+d)≤1.4 and 0.55≤d<0.6.

[0060] The above-mentioned lithium manganese oxide may be a secondary particle with a structure in which primary particles are aggregated.

[0061] Here, the primary particle may be a single particle of single crystal, and the secondary particle refers to a primary particle that is physically aggregated into hundreds to thousands or more.

[0062] The average diameter (D50) of the above primary particles may be 0.1 to 2 μm, more specifically 0.1 to 1.5 μm, and even more specifically 0.1 to 1.0 μm.

[0063] If the average diameter (D50) of the primary particles is too small outside the above range, the agglomeration may increase, and it is difficult to manufacture them as single particles, which is undesirable.

[0064] The average diameter (D50) of the primary particles can be measured by cutting the electrode cross-section using FIB (Focused in beam), then selecting secondary particles having a diameter of D50, taking a cross-section with FE-SEM, running a DX program, and mapping to obtain the average size of the primary particles.

[0065] The average diameter (D50) of the above secondary particles may be 5 to 20 μm, more specifically 5 to 15 μm, and even more specifically 5 to 10 μm.

[0066] If the average diameter (D50) of the secondary particles is too small, the fine particle content may increase, and if it is too large, the internal porosity of the particles may increase, the particle strength may decrease, and the specific surface area may decrease, which is undesirable.

[0067] Here, the “(average) diameter D10, D50, D90” of the secondary particles refers to the particle size of the active material in the electrode layer after rolling, and represents the particle size at the 10%, 50%, and 90% points of the cumulative particle volume distribution according to particle size. That is, D10, D50, and D90 are the particle sizes at the 10%, 50%, and 90% points of the cumulative particle volume distribution according to particle size.

[0068] The above D10, D50, and D90 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. D10, D50, and D90 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 10%, 50%, and 90%.

[0069] The above measurement target powder can be performed by selecting the active material from the powder after rolling.

[0070] In addition, the above-mentioned lithium manganese-based oxide may have a monomodal structure comprising large particles having an average diameter (D50) of the secondary particles, or may have a bimodal structure in which large particles and small particles having an average diameter (D50) of 3 to 5 μm are mixed. Here, a bimodal structure may be one in which two D50 peaks are formed in the particle size distribution. In this case, the small particles may have single particles or secondary particles.

[0071] When the above-mentioned lithium manganese-based oxide has a bimodal structure, the large particles and small particles may be included in a weight ratio of 50:50 to 90:10, more specifically in a ratio of 60:40 to 80:20, and even more specifically in a ratio of 65:35.

[0072] In this way, when the above-mentioned lithium manganese-based oxide is a secondary particle, the coating layer may be formed on both the surface of the primary particle and the surface of the secondary particle.

[0073] That is, the coating layer may be formed in such a way that it is coated on the surface of the secondary particle and simultaneously inserted into the interior through the internal pores of the particle to coat up to the surface of the primary particle. Accordingly, the coating layer may be distributed within a thickness of 20 nm to 100 nm from the surface of the primary particle based on the primary particle, and more specifically, within a thickness of 30 nm to 80 nm.

[0074] In addition, the coating layer is also formed on the surface of the secondary particle, and based on the secondary particle, it can be distributed within a thickness of 3㎛ or less from the surface of the secondary particle, specifically within a thickness of 1㎛ to 3㎛, and more specifically, can be formed with a thickness of 1.5㎛ to 2.5㎛.

[0075] Here, "distributed within the thickness" means that the coating layer exists at a thickness less than or equal to a thickness selected within the numerical range. That is, for example, "distributed within the thickness of 1㎛ to 3㎛" means that it may be distributed within one numerical value selected within the range, for example, within a thickness of 1㎛, within a thickness of 2㎛, or within a thickness of 3㎛.

[0076] At this time, the thickness of the coating layer at the primary particle surface can be confirmed through XPS analysis. Specifically, the anode active material powder was prepared in a dry room, loaded onto an Al-core carbon tape, and then placed into an analysis chamber (Nexsa G2, ESCA_04, Thermo Fisher Scientific) using a VTM. While performing a depth profile, a survey scan spectrum and a narrow scan spectrum were obtained.

[0077] At this time, the depth profile was performed for up to 3000 seconds using monoatomic Ar ions. The thickness at the surface of the secondary particle was measured through SEM images.

[0078] In addition, according to the present invention, the particle strength of the lithium-based active material having a coating layer containing Co formed on the surface of the lithium-over-manganese oxide can be expressed as particle breaking strength, wherein the particle breaking strength of the lithium-based active material may be 1.4 mN to 2.0 mN, more specifically 1.4 mN to 1.9 mN, and more specifically 1.5 mN to 1.8 mN.

[0079] That is, according to the present invention, the particle fracture strength of a lithium manganese-based oxide that does not form a coating layer containing Co can be improved compared to having a value within the range of about 1.0 mN to 1.4 mN.

[0080] Here, the particle fracture strength can be measured using a Nano indentation device with a needle based on a single secondary particle. In this case, the fracture strength refers to the maximum particle strength just before particle fracture within the elastic strain region.

[0081] Furthermore, the degree of sphericity of the lithium-based active material may be 0.6 to 0.9, and more specifically, 0.7 to 0.8.

[0082] The above sphericity (roughness, r) refers to a value obtained according to Equation 1 below for a lithium-based active material in an SEM image, and may be a value calculated by setting the particle parameter to 300 to 400 through Clustering analysis of IAM (Image Analysis Management).

[0083] [Equation 1]

[0084] Sphericity: 4 x Area (A) / πD max 2At this time, the standard deviation of the sphericity may be about 0.05 to 0.1.

[0085] Consequently, in the case of an electrode containing the above lithium-based active material, the particle strength can be increased due to the formation of a coating layer containing Co, even though the lithium-based active material contains an over-lithium manganese-based oxide, and thus rolling characteristics can be improved.

[0086] Specifically, the lithium-based active material according to the present invention may have a content of particles of the lithium-based active material having a diameter of 1 μm or less in the electrode layer of 2.5 volume% or less, more specifically 2.47 volume% or less, and even more specifically 0.1 volume% to 2 volume% based on the total volume of the lithium-based active material.

[0087] Here, the content of the lithium-based active material particles having a diameter of 1 μm or less is referred to as the fine amount, and this can also be measured as a value after manufacturing the electrode layer, that is, after forming an electrode slurry on a current collector and drying and rolling it, and at this time, the fine amount is based on the amount after rolling is performed so that the porosity of the electrode layer of the electrode according to the present invention is about 20 volume% to 40 volume%.

[0088] Specifically, the above amount of fine material can be determined by performing rolling so that the porosity of the electrode layer is about 30 volume% when manufacturing the electrode, separating the electrode layer from the electrode current collector, and measuring it using the (average) diameter measurement method described above.

[0089] In other words, according to the present invention, by forming a coating layer containing Co, the particle strength is increased, and it can be seen that the amount of fine particles generated can be reduced compared to the case where it is not.

[0090] That is, the lithium-based active material according to the present invention has improved particle strength, which reduces fine particles caused by breakage and increases the number of secondary particles that maintain the degree of sphericity, thereby enabling the effect of easily obtaining the target porosity of the electrode layer even with a low rolling load.

[0091] Meanwhile, in the electrode according to the present invention, the porosity of the electrode layer may be 20 to 40 volume%, and more specifically, 25 to 35 volume%.

[0092] If the porosity is too low outside the above range, it is undesirable as it may cause the active material to break due to high pressure, and if the porosity is too high, it is undesirable as it results in a low electrode density, leading to problems such as a reduction in capacity relative to volume.

[0093] The above porosity can be calculated by measuring the total volume of the electrode layer from the density and weight values ​​of each material included in the electrode layer and determining the difference in volume obtained from the density and weight of the materials relative to the volume of the electrode layer.

[0094] As described above, when the electrode layer of the electrode is rolled to a target porosity, the particle fracture strength is high, and particle breakage caused by rolling is significantly reduced, thereby improving rolling characteristics. Additionally, the inclusion of a specific content has the effect of improving battery performance, such as capacity and energy density.

[0095]

[0096] lithium secondary battery

[0097] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery including the electrode is provided.

[0098] 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.

[0099] The electrode according to the present invention may specifically be an anode, and may have a structure in which the electrode layer is formed on one or both sides of an anode current collector.

[0100] Accordingly, the electrode layer may further include other positive electrode active materials in addition to the lithium-based active material, and furthermore, may further include a conductive material, a binder, or other additives as needed.

[0101] 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.

[0102] The above positive electrode active material, in addition to the above lithium-based active material, is a compound capable of reversible intercalation and deintercalation of lithium, for example, a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (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), LiMn2-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.

[0103] When the above active material is a mixture of other positive active materials in addition to the lithium-based active material, the lithium-based active material 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 active material.

[0104] The above conductive material is a component for further improving the conductivity of the active material, and 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 secondary battery and further improve output characteristics.

[0105] 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 electrode layer.

[0106] The above binder is a component that assists in the bonding of the active material and the conductive material, etc., 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-based rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0107] 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 electrode layer.

[0108] 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.

[0109] The above cathode has a structure in which a cathode layer is formed on one or both sides of a cathode current collector.

[0110] 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.

[0111] The above cathode layer may include a cathode active material, a binder, a conductive material, and other additives as described in the above anode.

[0112] 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, Lix 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.

[0113] 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.

[0114] 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.

[0115] The polymer substrate of the above SRS separator may be the above polyolefin substrate.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] In addition to these, lithium salts commonly used in the electrolytes of lithium secondary batteries can be used without restriction.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] Two or more of the above functional additives may be mixed 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 secondary battery may occur.

[0160]

[0161] Hereinafter, an example according to the present invention is described with reference to an example to demonstrate the effects according to the present invention.

[0162]

[0163] <Example 1> (Co content: 6600 ppm)

[0164] Synthesis of lithium-over-manganese oxides

[0165] Transition metal precursor (Ni 0.304 Mn 0.565 (OH)2) and a lithium precursor are mixed such that the molar ratio of the transition metal (Ni+Mn) to Li is 1:1.13, and calcined at 850°C in an oxygen atmosphere (oxygen content 50%) to obtain a lithium-over-manganese oxide (Li 1.13 Ni 0.304 Mn 0.565 O2) was manufactured.

[0166]

[0167] Surface layer formation

[0168] The above-described lithium-rich manganese oxide (Li 1.13 Ni 0.304 Mn 0.565After preparing O2), Co metal was coated on its surface. Specifically, the above lithium manganese oxide and Co3O4 were mixed, and the lithium manganese oxide with a Co-containing coating layer was heat-treated at 500°C for 8 hours to prepare the lithium manganese oxide as a positive electrode active material.

[0169]

[0170] <Example 2> (Co content: 3300 ppm)

[0171] A positive electrode active material was prepared as in Example 1 above, except that the Co content was 3300 ppm.

[0172]

[0173] <Comparative Example 1>

[0174] The lithium manganese oxide prepared in Example 1 above was used as the positive electrode active material without coating with Co.

[0175]

[0176] <Comparative Example 2> (Co content: 9900 ppm)

[0177] A positive electrode active material was prepared as in Example 1 above, except that the Co content was 9900 ppm.

[0178]

[0179] <Experimental Example 1>

[0180] XPS evaluation was performed on the cathode active materials prepared in Examples 1 and 2 above to examine the tendency of the Co coating layer formation. Specifically, the cathode active material powder was prepared in a dry room, loaded onto an Al-core carbon tape, and then placed into an analysis chamber (Nexsa G2, ESCA_04, Thermo Fisher Scientific) using a VTM. While performing a depth profile, a survey scan spectrum and a narrow scan spectrum were obtained.

[0181] At this time, the depth profile was performed for up to 3000 seconds using monoatomic Ar ions.

[0182] And, the results are shown in Figure 1 below, where % is the at% of the element that Co occupies relative to the total elements.

[0183] -X-ray source: monochromatic Al Ka ​​(1486.6eV)

[0184] - X-ray spot size: 400㎛

[0185] -Sputtering: Ar monatomic (ion energy: 1kV, current: low, raster width: 2mm)

[0186] - Etching rate: 0.13 nm / sec based on Ta2O5

[0187] -Survey scan: pass energy 200eV, energy step 1eV

[0188] -Narrow scan: scanned mode, pass energy 50eV, energy step 0.1eV

[0189] Referring to Fig. 1, it can be seen that Co is coated into the interior of the particles in both the cathode active materials of Example 1 and Example 2. However, it was observed that the content gradually increased as the etching time increased, and then gradually decreased after 1000 seconds in Example 1, while it remained constant in Example 2. It was also observed that the maximum content was higher in Example 1, which has a higher content than Example 2, and the point at which the maximum content appears was later. However, it can be seen that the Co element has partially diffused deeper into the interior of the active material in the thickness direction than the thickness of the coating layer that is generally coated.

[0190]

[0191] <Experimental Example 2>

[0192] The particle fracture strength of the positive electrode active materials prepared in Example 1, Example 2, and Comparative Example 1 was measured, and the results are shown in Fig. 2 below.

[0193] The above particle fracture strength was measured using a Nano indentation device with a needle based on one secondary particle. In this case, fracture strength refers to the maximum particle strength just before particle fracture within the elastic strain region.

[0194] Referring to Figure 2 below, it can be seen that when a Co coating layer is formed according to the present invention, the particle fracture strength increases. Meanwhile, it can be seen that as the content of Co in the coating layer increases, the particle fracture strength increases further, and when it is 6000 ppm or more, it increases significantly.

[0195]

[0196] <Experimental Example 3>

[0197] Using the positive active materials prepared in Example 1, Example 2, and Comparative Example 1, respectively, a positive active material, a binder (PVdF), and a conductive material (FX35, Denka) were mixed in NMP (N-methylpyrrolidone) in a weight ratio of 96.25:2.1:1.65 to prepare a positive slurry. The positive slurry was coated to a thickness of 50 μm onto a 20 μm thick Al foil, dried at 130°C, and then rolled to achieve a porosity of approximately 30 volume% to produce a positive electrode. Here, the porosity was measured in real time while performing the rolling.

[0198] SEM images of the surface of the anode manufactured above were taken and are shown in Figures 3 to 5 below.

[0199] Referring to FIGS. 3 to 5, in Comparative Example 1, in which a Co coating layer was not formed, a large amount of active material particle breakage occurred, whereas in Examples 1 and 2, in which a Co coating layer was formed, particle breakage was reduced, and in Example 1, in which the Co content was 6000 ppm or more, particle breakage was almost non-existent and significantly reduced.

[0200]

[0201] <Experimental Example 4>

[0202] For the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 above, the particle distribution was measured, and after preparing the positive electrode as in Experimental Example 3 above, the current collector was removed from the positive electrode to crush the electrode layer and the positive electrode active material was selected and the particle distribution was measured again. The results are shown in Figures 6 and 7 below, and the results are shown in Table 1.

[0203] Specifically, the particle distribution was measured using the laser diffraction method. Specifically, the powder to be measured was dispersed in a dispersion medium, then 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 passed through the laser beam, thereby calculating the particle size distribution.

[0204] Example 1 Example 2 Comparative Example 1 Comparative Example 2 PSD (bare) D10 (㎛) 7.1 7.1 7.1 7.1 D50 (㎛) 8.7 8.7 8.7 8.7 D90 (㎛) 10.8 10.8 10.8 10.8 PSD (after rolling) D10 (㎛) 6.3 4 6.7 2 6.3 8 6.35 D50 (㎛) 9.2 3 9.3 6 9.2 3 9.23 D90 (㎛) 13.1 12.6 12.7 13.0 Fine amount (<1㎛) Volume % 0 2.4 7 2.9 50

[0205] Referring to Table 1 along with Figures 6 and 7 below, the cathode active materials of Examples 1 and 2 and Comparative Examples 1 and 2 have similar particle size distributions before cathode formation, but when examining the cathode after manufacturing, it can be confirmed that the content of fine particles of 1 μm or less is significantly reduced by Co coating.

[0206]

[0207] <Experimental Example 5>

[0208] The degree of sphericity of the positive electrode active material in the electrode layer was measured for Examples 1 and 2 and Comparative Example 1 in the positive electrode prepared according to Experimental Example 3 above, and the results are shown in Table 2 and Figure 8 below.

[0209] Here, the sphericity is a value obtained according to the following Equation 1 for the positive active material in the electrode layer SEM image, and is a value calculated by setting the particle parameter to 300 to 400 using Clustering analysis of IAM (Image Analysis Management).

[0210] [Equation 1]

[0211] Sphericity: 4 x Area (A) / πD max 2

[0212] In addition, to show that the rolling load is substantially reduced in accordance with the present invention, rolling was performed on the cathode active material powder prepared in Examples 1 and 2 and Comparative Example 1 until the porosity reached 30%, and the rolling load at which the porosity was reached was measured and shown in Table 2 below.

[0213] The above rolling load was evaluated by taking a sample of 3g of active material powder and setting the internal porosity of the powder to a constant condition (30%). Based on the true density information of the active material, a target density was set for the porosity, and a gap gauge was set at the top of a cylindrical mold to achieve a target volume based on the weight (3g) of the active material powder. The load was measured by setting the target so that the volume no longer decreases when the target height is reached after the active material powder is placed in the mold.

[0214] Sphericity Standard Deviation Load (ton) reaching active material powder porosity of approximately 30% Example 10.79 80.08 4.7 Example 20.78 60.07 5.2 Comparative Example 10.79 30.07 6.0

[0215] Referring to Table 2 above and Figure 8 below, it can be seen that the degree of sphericity is similar, approximately 0.7-0.8, in both cases where a Co coating layer is formed and where it is not. On the other hand, even if active materials have similar degrees of sphericity, when rolled to have the same porosity, it can be seen that the rolling load decreases when using the anode active material according to the present invention. This is expected to be because the particle fracture strength is improved.

[0216]

[0217] <Experimental Example 6>

[0218] Lithium secondary batteries were manufactured using the positive active materials of Examples 1 to 2 and Comparative Examples 1 to 2.

[0219] Specifically, an anode slurry was prepared by mixing an anode active material, a binder (PVdF), and a conductive material (CNT) in a weight ratio of 96:3:1 with NMP (N-methylpyrrolidone), and the anode 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 an anode.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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). At this time, the charge capacity, discharge capacity, and discharge efficiency (discharge capacity relative to charge capacity) were measured, and the results are shown in Figure 9 and Table 3 below.

[0224] Charge (mAh / g) Discharge (mAh / g) Efficiency (%) Example 1 295.3 276.1 93.5 Example 2 295.3 277.4 93.9 Comparative Example 1 296.1 275.3 93.0 Comparative Example 2 294.8 274.8 93.2

[0225] Referring to Figure 9 and Table 3, it can be seen that the discharge efficiency is high when the Co coating amount is 3300 ppm and 6600 ppm.

[0226]

[0227] <Experimental Example 7>

[0228] For the lithium secondary batteries that were activated in Experimental Example 6 above, charging and discharging were performed by 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), and charging and discharging were performed at a constant current of 0.33C within the above range, respectively, and the results are shown in Figures 10 and 11 and Table 4 below.

[0229] In addition, the energy density was calculated, and the results are shown in Figures 10 and 11 and Table 4 below.

[0230] The above energy density was calculated as follows.

[0231] -Energy density: Calculated as the product of the 0.33C discharge capacity and the 0.33C average discharge voltage.

[0232] 0.1C Discharge Capacity (mAh / g) 0.33 Discharge Capacity (mAh / g) Energy Density (Wh / Kg) Example 1 218.0 206.0 757.9 Example 2 219.0 206.2 759.0 Comparative Example 1 217.5 204.3 754.1 Comparative Example 2 217.3 205.8 756.5

[0233] Referring to Figure 10 and Table 4 above, it can be seen that when the Co coating amount is 3300 ppm to 6600 ppm, the discharge capacity and energy density are high.

[0234] 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.

[0235] According to the present invention, by forming a coating layer containing Co in a specific amount on a lithium manganese-based oxide with a high manganese (Mn) content, the fracture strength of active material particles can be increased, thereby preventing breakage of active material particles even when rolling an electrode containing the same. Consequently, the amount of fine particles with a diameter of 1 μm or less is reduced, and thus the rolling load can be reduced when rolling with the same porosity, thereby improving rolling characteristics.

[0236] In addition, if rolling characteristics are improved in this way, not only is the processability of the electrode improved, but if a specific Co content is satisfied, the performance of the lithium secondary battery, such as capacity and energy density, can also be improved along with the improvement of rolling characteristics.

Claims

1. An electrode for a secondary battery comprising an electrode current collector and an electrode layer formed on one or both sides of the electrode current collector, The electrode layer comprises a lithium-based active material including an over-lithium manganese-based 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 a coating layer formed on the surface of the over-lithium manganese-based oxide. The above coating layer is an electrode containing Co at a concentration of 3,000 ppm to 8,000 ppm based on the total weight of the lithium-based active material.

2. In Paragraph 1, An electrode in which the Co content of the coating layer is 3300 ppm to 6600 ppm based on the total weight of the lithium-based active material.

3. In Paragraph 1, The electrode comprising one or more materials selected from the group consisting of Co metal, Co oxide, and lithium cobalt oxide in the coating layer.

4. In Paragraph 1, The above-mentioned lithium-ion manganese-based oxide is an electrode represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c Mr d M e O 2+f In the above formula, 1.12≤a≤1.18, 1.1≤a / (b+c+d)≤1.5, 0.24≤b≤0.36, 0≤c≤0.1, 0.47≤d<0.63, 0≤e≤0.05, 0≤f≤0.05, b+c+d+e=1, and 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.

5. In Paragraph 1, The above-mentioned lithium manganese-based oxide is a secondary particle having a structure in which primary particles are aggregated, and the coating layer is an electrode formed on both the surface of the primary particles and the surface of the secondary particles.

6. In Paragraph 5, The above coating layer is an electrode distributed within a thickness of 20 nm to 100 nm from the surface of the primary particle, based on the primary particle.

7. In Paragraph 5, The above coating layer is an electrode distributed within a thickness of 3㎛ or less on the surface of the secondary particle based on the secondary particle.

8. In Paragraph 5, An electrode in which the average diameter (D50) of the secondary particles is 5 to 10 μm.

9. In Paragraph 1, An electrode in which the content of particles of the lithium-based active material having a diameter of 1 μm or less in the electrode layer is 2.5 volume% or less based on the total volume of the lithium-based active material.

10. In Paragraph 1, An electrode having a particle fracture strength of the above lithium-based active material of 1.4 mN to 2.0 mN.

11. In Paragraph 1, An electrode having a sphericity of 0.7 to 0.8 of the above lithium-based active material.

12. In Paragraph 1, An electrode having a porosity of 20 to 40 volume% of the electrode layer.

13. A lithium secondary battery comprising an electrode according to paragraph 1.

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