Cathode active material for lithium secondary battery, preparation method therefor, and lithium secondary battery comprising same

Abstract

To provide cathode active material for a secondary battery, which enables increase of charge / discharge capacity and enables resolution of life degradation and voltage drop.SOLUTION: Cathode active material for a secondary battery includes a lithium composite oxide including a lithium-rich layered oxide represented by the formula below. The lithium composite oxide includes secondary particles. The secondary particles include one or more primary particles. The primary particles include one or more crystallites. At least one or more selected from secondary particles, primary particles, and crystallites includes a core and a shell that occupies at least a part of the surface of the core. When the number of moles of at least one or more elements selected from nickel (Ni), cobalt (Co), and manganese (Mn) with respect to the total number of moles of M1 and M2 in the following formula is defined as NCM / M, the NCM / M of the shell and the core of the secondary particles are different. rLi2M1O3.(1-r)LiaM2O2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a secondary battery including a lithium composite oxide containing a lithium-excess oxide having a layered structure.

Background Art

[0002] With the development of portable mobile devices such as smartphones, MP3 players, and tablet PCs, the demand for secondary batteries that store electrical energy has been explosively growing. In particular, with the emergence of electric vehicles, medium and large-sized energy storage systems, and portable devices that require high energy density, the demand for lithium secondary batteries is increasing.

[0003] As a positive electrode active material, in recent years, the most spotlighted material is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z )O2 (where x, y, and z are the atomic fractions of the independent oxide composition elements, respectively, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, and 0 < x + y + z ≤ 1). This material has the advantage of exhibiting a higher voltage than LiCoO2, which has been actively studied and used as a positive electrode active material so far, and thus has the advantage of providing a high capacity. Also, since the Co content is relatively low, it has the advantage of being inexpensive. However, it has the disadvantage of inferior rate capability and life characteristics at high temperatures.

[0004] Therefore, research has been actively conducted to apply a lithium-excess layered oxide that exhibits a higher reversible capacity than existing Li(Ni x Co y Mn z )O2 to a lithium secondary battery.

[0005] However, problems such as a decrease in discharge capacity (cycle life) and a voltage decay that occur during the life cycle are caused by a phase transition to a spinel-like structure due to the migration of transition metals during the life cycle. These problems of a decrease in discharge capacity and a voltage decay must be solved for the commercialization of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to increase the charge / discharge capacity and solve the problems of deterioration in life and voltage drop by suppressing the phase transition during the life cycle of a positive electrode active material for a secondary battery. Another object of the present invention is to increase the lithium ion mobility of a positive electrode active material for a secondary battery and improve the rate characteristics. Another object of the present invention is to improve the surface kinetic and structural stability of a positive electrode active material for a secondary battery. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a positive electrode active material for a secondary battery according to an embodiment of the present invention includes a lithium composite oxide containing a lithium-excess oxide having a layered structure represented by the following [Chemical Formula 1], the lithium composite oxide includes secondary particles, the secondary particles include one or more primary particles, the primary particles include one or more crystallites, and any one or more selected from the secondary particles, the primary particles, and the crystallites each include a core and a shell occupying at least a portion of the surface of the core, and when NCM / M is the number of moles of at least one or more elements selected from nickel (Ni), cobalt (Co), and manganese (Mn) relative to the total number of moles of M1 and M2 in the following [Chemical Formula 1], the NCM / M of the shell and the NCM / M of the core of the secondary particle are different.

[0008] [C1] rLi2M1O3·(1-r)Li a M2O2 In the above [Chemical Formula 1], 0 < r < 1 and 0 < a ≤ 1. M1 is at least one selected from the group consisting of Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. M2 is at least one selected from the group consisting of Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi.

[0009] Also, as a more preferable example, the shell of the secondary particles can include a concentration gradient portion having a gradient in the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

[0010] Also, as a more preferable example, the shell of the primary particles can include a concentration gradient portion having a gradient in the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

[0011] Also, as a more preferable example, the shell of the crystallites can include a concentration gradient portion having a gradient in the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

Advantages of the Invention

[0012] According to the positive electrode active material for a secondary battery according to an embodiment of the present invention, by suppressing the phase transition during the life cycle, the charge and discharge capacity can be increased, and the problems of life deterioration and voltage drop can be solved. Also, according to the positive electrode active material for a secondary battery according to an embodiment of the present invention, the lithium ion mobility can be increased, and the rate performance can be improved. Furthermore, the positive electrode active material for a secondary battery according to the embodiment of the present invention can improve the kinetic and structural stability of the surface. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 10 is a diagram showing the results of FQ-EDS analysis according to a comparative example and an example. [Figure 2] FIG. 1 is a diagram showing the results of FQ-EDS analysis of positive electrode active materials according to a comparative example and an example. [Figure 3] FIG. 1 is a diagram showing the results of FQ-EDS analysis of positive electrode active materials according to a comparative example and an example. [Figure 4] FIG. 2 is a diagram showing the analysis results of TEM-EDS according to Example 1. [Figure 5] FIG. 2 is a diagram showing the analysis results of TEM-EDS according to Example 1. [Figure 6] 1 is a diagram showing the results of TEM-EDS and concentration gradient analysis according to Example 1. FIG. [Figure 7] 1 is a diagram showing the results of TEM-EDS and concentration gradient analysis according to Example 1. FIG. [Figure 8] FIG. 10 is a diagram showing the results of TEM-EDS and concentration gradient analysis according to Example 5. [Figure 9] FIG. 10 is a diagram showing the results of SEM analysis according to a comparative example and an example. [Figure 10] FIG. 10 is a diagram showing analysis results of initial voltage profiles according to a comparative example and an example. [Figure 11] FIG. 10 is a diagram showing the analysis results of rate characteristics according to a comparative example and an example. [Figure 12] FIG. 10 is a diagram showing the analysis results of rate characteristics according to a comparative example and an example. [Figure 13] FIG. 10 is a diagram showing the analysis results of life characteristics according to a comparative example and an example. [Figure 14] FIG. 10 is a diagram showing the analysis results of life characteristics according to a comparative example and an example. [Figure 15] FIG. 10 is a diagram showing analysis results of voltage characteristics according to a comparative example and an example. [Figure 16]It is a diagram showing the analysis results of voltage characteristics according to Comparative Examples and Examples.

Mode for Carrying Out the Invention

[0014] As used herein, the term "comprising" should be understood as open-ended terms that subsume the possibility of including other technical features. As used in the present invention, the terms "as an example", "as an embodiment", and "preferred" refer to embodiments of the present invention that can provide predetermined advantages under a predetermined environment, and do not intend to exclude other embodiments from the scope of the present invention.

[0015] The positive electrode active material for a secondary battery according to an embodiment of the present invention includes a lithium composite oxide containing a layered lithium peroxide represented by the following [Chemical Formula 1].

[0016] [Chemical Formula 1] rLi2M1O3·(1-r)Li a M2O2 In the above [Chemical Formula 1], 0 < r < 1, 0 < a ≤ 1, M1 and M2 are independent of each other, and M1 is at least one selected from Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi, and M2 is at least one selected from Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi.

[0017] <00As a more preferred example, M1 is at least one selected from Mn, Cr, Fe, Co, Ni, Mo, Ru, W, Ti, Zr, Sn, V, Al, Mg, Ta, B, P, Nb, Cu, La, Ba, Sr, and Ce, and M2 is at least one selected from Ni, Co, Mn, Cr, Fe, Mo, Ru, W, Ti, Zr, Sn, V, Al, Mg, Ta, B, P, Nb, Cu, La, Ba, Sr, and Ce.

[0018] As an example, in the above [Chemical Formula 1], the lithium excess oxide may be a mixture of a monoclinic structure Li2M1O3 and a rhombohedral structure Li a It can be a solid solution phase in which M2O2 is mixed.

[0019] As a more preferred example, the average valence of M1 is 3.5 to 4.5, and may be 4. As a more preferred example, the average valence of M2 is 2.5 to 3.5, and may be 3.

[0020] As a more preferred example, the above [Chemical Formula 1] can be represented by the following [Chemical Formula 1-1]. [Case 1-1] rLi2Mn p Md1 1-p O3·(1-r)Li a Ni x Co y Mn z Md2 1-(x+y+z) O2 In the above [Chemical Formula 1], 0 < r < 1, 0 < p ≤ 1, 0 < a ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 < x + y + z ≤ 1. Md1 and Md2 are independent of each other. Md1 is at least one selected from Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. Md2 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi.

[0021] Md1 and Md2 can each independently be an element forming a lattice, a dopant, or a coating substance, and regardless of the types of Md1 and Md2, the effects intended by the present invention can be obtained.

[0022] As a more preferable example, Md1 is at least one selected from Cr, Fe, Co, Ni, Mo, Ru, W, Ti, Zr, Sn, V, Al, Mg, Ta, B, P, Nb, Cu, La, Ba, Sr, and Ce, and Md2 is at least one selected from Cr, Fe, Mo, Ru, W, Ti, Zr, Sn, V, Al, Mg, Ta, B, P, Nb, Cu, La, Ba, Sr, and Ce.

[0023] As an example, in the above [Chemical Formula 1-1], the lithium peroxide is a solid solution phase in which monoclinic-structured Li2Mn p Md1 1-p O3 and rhombohedral-structured Li a Ni x Co y Mn z Md 1―(x+y+z) O2 are mixed.

[0024] As an example, the excess lithium oxide may have a layered structure in which atomic layers of lithium and atomic layers of nickel, cobalt, manganese, or Md are alternately stacked with an atomic layer of oxygen interposed therebetween.

[0025] As an example, the r value can be 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. As an example, p can be greater than 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or greater, or 1.0.

[0026] As a more preferred example, in the lithium composite oxide of the present invention, the number of moles of lithium relative to the total number of moles of M1 and M2, Li / M, can be 1.01 or more, 1.05 or more, or 1.1 or more, and can be 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, or 1.3 or less.

[0027] As a more preferred example, in the lithium composite oxide, the number of moles of nickel (Ni) relative to the total number of moles of M1 and M2 (Ni / M) may be 0.1, 0.2, or 0.3 or more, and may be 0.7 or less, 0.6 or less, or 0.5 or less.

[0028] As a more preferred example, in the lithium composite oxide, the number of moles of cobalt (Co) relative to the total number of moles of M1 and M2, Co / M, may be 0.0, 0.05, or 0.1 or more, and may be 0.3, 0.2, or 0.1 or less.

[0029] As a more preferred example, the positive electrode active material according to an embodiment of the present invention may be Co-free.

[0030] As a more preferred example, in the lithium composite oxide, the number of moles of manganese (Mn) relative to the total number of moles of M1 and M2, Mn / M, can be 0.1, 0.2, or 0.3 or more, and can be 0.8 or 0.7 or less.

[0031] As a more preferred example, in the lithium composite oxide, the number of moles of Md2 relative to the total number of moles of M1 and M2, Md2 / M, can be 0.0 or more and 0.2 or 0.1 or less.

[0032] The lithium composite oxide includes secondary particles, each of which includes one or more primary particles, and each of which includes one or more crystallites.

[0033] In the present specification, "one or more" means one or more than one. For example, the secondary particle may include one primary particle, or may be formed by agglomeration of two or more primary particles. For example, the primary particle may include one crystallite, or may be formed by agglomeration of two or more crystallites.

[0034] In addition, at least one selected from the secondary particles, primary particles, and crystallites each includes a core and a shell occupying at least a portion of the surface of the core.

[0035] As an example, the secondary particles may be particles having a core-shell structure including a core and a shell occupying at least a portion of the surface of the core.

[0036] In this case, the term "at least a portion" can mean more than 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% or more of the total surface area of ​​the secondary particles.

[0037] The secondary particles may have an average particle size (D50) of 0.5 to 20 μm.

[0038] For example, the shell thickness of the secondary particles may be greater than 0 and less than 10 μm, greater than 0 and less than 1 μm, greater than 0 and less than 500 nm, greater than 0 and less than 400 nm, greater than 0 and less than 300 nm, greater than 0 and less than 200 nm, greater than 0 and less than 150 nm, greater than 0 and less than 100 nm, greater than 0 and less than 90 nm, greater than 0 and less than 80 nm, greater than 0 and less than 70 nm, greater than 0 and less than 60 nm, or greater than 0 and less than 50 nm.

[0039] As an example, the shell thickness of the secondary particles can be more than 0.0%, 1, 10, 20, 30, 40, 50, 60, 70, 80, or 90% or more of the length of the secondary particles, and can be less than 100%, 90, 80, 70, 60, 50, 40, 30, 20, 10, or 1% or less.

[0040] As an example, the primary particle may include a core and a shell occupying at least a portion of the surface of the core.

[0041] In this case, "at least a portion" can mean more than 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% or more of the total surface area of ​​the primary particles.

[0042] For example, the shell thickness of the primary particles may be greater than 0 and less than 10 μm, greater than 0 and less than 1 μm, greater than 0 and less than 500 nm, greater than 0 and less than 400 nm, greater than 0 and less than 300 nm, greater than 0 and less than 200 nm, greater than 0 and less than 150 nm, greater than 0 and less than 100 nm, greater than 0 and less than 90 nm, greater than 0 and less than 80 nm, greater than 0 and less than 70 nm, greater than 0 and less than 60 nm, or greater than 0 and less than 50 nm.

[0043] As an example, the shell thickness of the primary particles can be more than 0.0%, 1, 10, 20, 30, 40, 50, 60, 70, 80, or 90% or more of the length of the primary particles, and can be less than 100%, 90, 80, 70, 60, 50, 40, 30, 20, 10, or 1% or less.

[0044] As an example, the crystallite can include a core and a shell occupying at least a portion of the surface of the core. In this case, "at least a portion" can mean greater than 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% or more of the total surface area of ​​the crystallites.

[0045] For example, the shell thickness of the crystallite may be greater than 0 and less than 10 μm, greater than 0 and less than 1 μm, greater than 0 and less than 500 nm, greater than 0 and less than 400 nm, greater than 0 and less than 300 nm, greater than 0 and less than 200 nm, greater than 0 and less than 150 nm, greater than 0 and less than 100 nm, greater than 0 and less than 90 nm, greater than 0 and less than 80 nm, greater than 0 and less than 70 nm, greater than 0 and less than 60 nm, or greater than 0 and less than 50 nm.

[0046] As an example, the thickness of the shell of the crystallite can be more than 0.0%, 1, 10, 20, 30, 40, 50, 60, 70, 80, or 90% or more of the length of the crystallite, and can be less than 100%, 90, 80, 70, 60, 50, 40, 30, 20, 10, or 1% or less.

[0047] Here, in the secondary particle, primary particle, or crystallite, the "core" refers to a region present inside the secondary particle, primary particle, or crystallite and close to the center of the particle, excluding the surface of the particle, and the "shell" refers to a region close to the surface, excluding the center or interior of the particle.

[0048] The "core" and "shell" of a secondary particle, primary particle, or crystallite of the present invention may be distinguished by the points at which the mole fraction or concentration of the contained elements changes. For example, the "core" and "shell" of a secondary particle, primary particle, or crystallite may refer to the points at which the Ni concentration in the shell of the secondary particle, primary particle, or crystallite decreases sharply from the surface to the center, and then at the core, the gradient becomes gentler, or the core maintains a constant level, or the shell increases. For example, the "core" and "shell" of a secondary particle, primary particle, or crystallite may refer to the points at which the Co concentration in the shell of the secondary particle, primary particle, or crystallite decreases sharply from the surface to the center, and then at the core, the gradient becomes gentler, or the shell increases. For example, the "shell" of a secondary particle, primary particle, or crystallite may refer to the points at which the Mn concentration in the shell of the secondary particle, primary particle, or crystallite increases sharply from the surface to the center, and then at the core, the gradient becomes gentler, or the shell increases, or the shell increases.

[0049] In the positive electrode active material according to an embodiment of the present invention, a transition metal such as nickel, cobalt, and / or manganese may be dispersed within secondary particles, primary particles, and / or crystallites to form a shell distinct from the core.

[0050] In addition, in the cathode active material according to an embodiment of the present invention, when the mole number of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn) relative to the total mole number of M1 and M2 is defined as NCM / M, the NCM / M of the shell and core of the secondary particles may be different.

[0051] This may mean that when a cross section is taken across the interior of the secondary particle, the NCM / M of the shell and core of the secondary particle are different.

[0052] For example, when the number of moles of nickel (Ni) relative to the total number of moles of M1 and M2 is Ni / M, the Ni / M of the shell and core of the secondary particle may be different. For example, when the number of moles of cobalt (Co) relative to the total number of moles of M1 and M2 is Co / M, the Co / M of the shell and core of the secondary particle may be different.

[0053] For example, when the number of moles of manganese (Mn) relative to the total number of moles of M1 and M2 is defined as Mn / M, the Mn / M of the shell and core of the secondary particle may be different.

[0054] As a more preferred example, the shell of the secondary particle may include a concentration gradient portion having a gradient in concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

[0055] This may mean that when a cross section of the secondary particle is observed across the interior thereof, the shell of the secondary particle includes a concentration gradient portion in which the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn) is gradient.

[0056] In addition, in the positive electrode active material according to an embodiment of the present invention, the NCM / M of the shell and the core of the primary particles may be different.

[0057] This may mean that when a cross section is viewed across the interior of the primary particle, the NCM / M of the shell and core of the primary particle are different.

[0058] For example, the Ni / M ratio of the shell and the core of the primary particle may be different. As an example, the Co / M ratio of the shell and the core of the primary particle may be different. For example, the Mn / M of the shell and core of the primary particle may be different.

[0059] Here, the primary particles may be primary particles in contact with the surface of the secondary particles, or may include all primary particles present in the core of the secondary particles.

[0060] As a more preferred example, the shell of the primary particle may include a concentration gradient portion having a gradient in concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

[0061] This may mean that when a cross section of the primary particle is examined across the interior thereof, the shell of the primary particle includes a concentration gradient portion in which the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn) is gradient.

[0062] In addition, in the positive electrode active material according to an embodiment of the present invention, the NCM / M of the shell and the core of the crystallite may be different.

[0063] This can mean that when a cross section is taken across the interior of the crystallite, the NCM / M of the shell and core of the crystallite are different.

[0064] As an example, the Ni / M ratio of the shell and the core of the crystallite may be different. As an example, the Co / M ratio of the shell and the core of the crystallite may be different. As an example, the Mn / M of the shell and core of the crystallite may be different.

[0065] As a more preferred example, the shell of the crystallite may include a concentration gradient portion having a gradient in the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

[0066] This may mean that when a cross section of the crystallite is viewed across the interior thereof, the shell of the crystallite includes a concentration gradient portion in which the concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn) is gradient.

[0067] In a more preferred example of the present invention, not only the secondary particles and primary particles but also the shells of the crystallites may have a concentration gradient portion of the transition metal.

[0068] As a more preferred example, the Ni / M of one or more shells selected from the secondary particles, primary particles, and crystallites may be higher than that of the core.

[0069] As a more preferred example, the shell of the secondary particle may include a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the secondary particle.

[0070] As a more preferred example, the shell of the primary particle may include a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the primary particle.

[0071] As a more preferred example, the shell of the crystallite may include a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the crystallite.

[0072] As a more preferred example, the Co / M of one or more shells selected from the secondary particles, primary particles, and crystallites may be higher than that of the core.

[0073] As a more preferred example, the shell of the secondary particle may include a concentration gradient portion in which the concentration of cobalt (Co) decreases from the surface toward the center of the secondary particle.

[0074] As a more preferred example, the shell of the primary particle may include a concentration gradient portion in which the concentration of cobalt (Co) decreases from the surface toward the center of the primary particle.

[0075] As a more preferred example, the shell of the crystallite may include a concentration gradient portion in which the concentration of cobalt (Co) decreases from the surface toward the center of the crystallite.

[0076] In another preferred embodiment, the positive electrode active material according to the present invention may be free of cobalt (Co).

[0077] In this case, by including a concentration gradient portion of nickel or manganese in the shell within the secondary particles, primary particles, or crystallites, without using expensive cobalt, it is possible to suppress phase transition during the life cycle of the positive electrode active material for a secondary battery, thereby increasing the charge / discharge capacity and solving the problems of life deterioration and voltage drop.

[0078] As a more preferred example, the Mn / M of one or more shells selected from the secondary particles, primary particles, and crystallites may be lower than that of the core.

[0079] As a more preferred example, the shell of the secondary particle may include a concentration gradient portion in which the concentration of manganese (Mn) increases from the surface toward the center of the secondary particle.

[0080] As a more preferred example, the shell of the primary particle may include a concentration gradient portion in which the concentration of manganese (Mn) increases from the surface toward the center of the primary particle.

[0081] As a more preferred example, the shell of the crystallite may include a concentration gradient portion in which the concentration of manganese (Mn) increases from the surface toward the center of the crystallite.

[0082] In addition, as a more preferred example of the present invention, the gradient of the concentration gradient portion of nickel (Ni) may be greatest compared to that of manganese (Mn) or cobalt (Co) in the shell of the secondary particles, primary particles, and / or crystallites.

[0083] As a more preferred example, the gradient of the concentration gradient portion of manganese (Mn) may be greatest compared to nickel (Ni) or cobalt (Co) in the shell of the secondary particles, primary particles, and / or crystallites.

[0084] As a more preferred example, the gradient of the concentration gradient portion of cobalt (Co) may be the smallest compared to nickel (Ni) or manganese (Mn) in the shell of the secondary particles, primary particles, and / or crystallites.

[0085] In addition, as a preferred example of the present invention, in the shell of the secondary particles, primary particles, and / or crystallites, the maximum value of Ni / M may be greater than the minimum value of Mn / M.

[0086] As a more preferred example, in the shell of the secondary particles, primary particles, and / or crystallites, the maximum value of Co / M may be smaller than the minimum value of Mn / M.

[0087] As a more preferred example, the relationship may be Mn / M>Ni / M>Co / M in the core of the secondary particles, primary particles, and / or crystallites.

[0088] As a more preferred example, in the core of the secondary particles, primary particles, and / or crystallites, Ni / M may be 0.1, 0.2, or 0.3 or more, and 1.0, 0.9, or 0.8 or less.

[0089] As a more preferred example, in the core of the secondary particles, primary particles, and / or crystallites, Co / M can be 0.3, 0.2, 0.1, or 0.05 or less, and can be 0.0 or more.

[0090] As a more preferred example, in the core of the secondary particles, primary particles, and / or crystallites, Mn / M may be 0.4, 0.5, or 0.6 or more, and 1.0, 0.9, or 0.8 or less.

[0091] In addition, in a more preferred example of the present invention, in the shell of the secondary particles, primary particles, and / or crystallites, the maximum value of Ni / M may be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 mol% or more, and may be 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 mol% or less.

[0092] As a more preferred example, in the shell of the secondary particles, primary particles, and / or crystallites, the maximum value of Co / M may be 1, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 mol% or more, and may be 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 mol% or less.

[0093] As a more preferred example, in the shells of the secondary particles, primary particles, and / or crystallites, the minimum value of Mn / M may be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 mol% or more, and may be 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 mol% or less.

[0094] As another example, the ratio of the R-3m space group to the C2 / m space group may be different in the core and shell of the secondary particles, primary particles, and / or crystallites.

[0095] Also, as an example, Ni in the core and shell of the secondary particles, primary particles, and / or crystallites 3+ and Ni 2+ The ratio may be different.

[0096] Also, as an example, Mn in the core and shell of the secondary particles, primary particles, and / or crystallites3+ and Mn 4+ The ratio may be different.

[0097] The cathode active material according to an embodiment of the present invention may further include another coating layer, which may include at least one coating material selected from, but not limited to, P, Nb, Si, Sn, Al, Pr, Al, Ti, Zr, Fe, Al, Fe, Co, Ca, Mn, Ti, Sm, Zr, Fe, La, Ce, Pr, Mg, Bi, Li, W, Co, Zr, B, Ba, F, K, Na, V, Ge, Ga, As, Sr, Y, Ta, Cr, Mo, W, Mn, Ir, Ni, Zn, In, Na, K, Rb, Cs, Fr, Sc, Cu, Ru, Rh, Pd, Ag, Cd, Sb, Hf, Ta, Re, Os, Pt, Au, Pb, Bi, and Po.

[0098] The coating layer can improve the life characteristics and increase the packing density by blocking contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery and suppressing the occurrence of side reactions, and the coating layer can act as a lithium ion conductor.

[0099] The coating layer may be formed on the entire surface of the positive electrode active material, or on the entire surface of the primary particles, or may be formed partially or entirely, and may be in the form of a single-layer coating, a double-layer coating, a grain boundary coating, a uniform coating, or an island coating.

[0100] In the positive electrode active material according to an embodiment of the present invention, lithium ion diffusion paths may be formed inside the primary particles.

[0101] In the positive electrode active material according to the embodiment of the present invention, the surfaces forming the layers of the layered structure have a crystal orientation in a direction perpendicular to the C axis within the primary particle, and can form a lithium ion migration path toward the center of the positive electrode active material particle inside or outside the primary particle.

[0102] Hereinafter, a method for manufacturing a positive electrode active material for a secondary battery according to an embodiment of the present invention will be described. First, a step of forming precursor particles is carried out. As a more preferred example, the precursor particles can be produced by a coprecipitation method, and can be produced by adding a complexing agent.

[0103] Next, the precursor particles obtained above are subjected to a first heat treatment at 300 to 1000° C., followed by a step of cooling.

[0104] Next, after the first heat treatment and subsequent cooling step, a wet coating step with a compound containing at least one element selected from cobalt, nickel, and manganese may be performed.

[0105] Next, the particles cooled after the first heat treatment or the wet-coated particles are mixed with the first lithium compound, and the mixture is subjected to a second heat treatment at 800 to 1000°C, followed by cooling.

[0106] Next, after the second heat treatment and subsequent cooling step, a wet coating step with a compound containing at least one element selected from cobalt, nickel, and manganese may be performed.

[0107] Next, the particles cooled after the second heat treatment or the wet-coated particles are mixed with a second lithium compound, and a third heat treatment is performed at 300 to 1000°C, followed by cooling.

[0108] In one embodiment of the present invention, after the step of forming the precursor particles, a step of wet coating with a compound containing at least one element selected from cobalt, nickel, and manganese may be included before the step of performing a first heat treatment and then cooling, between the step of performing the first heat treatment and then cooling and the step of performing the second heat treatment and then cooling, or between the step of performing the second heat treatment and then cooling and the step of performing the third heat treatment and then cooling.

[0109] As a more preferred example, the wet coating step may be performed by a co-precipitation method, and a complexing agent may be added to the wet coating step.

[0110] A secondary battery according to an embodiment of the present invention includes the above positive electrode active material. The positive electrode active material is as described above, and the binder, conductive material, and solvent are not particularly limited as long as they can be used on the positive electrode current collector of a secondary battery.

[0111] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and an electrolyte between the positive electrode and the negative electrode, but is not particularly limited as long as it can be used as a secondary battery. [Example]

[0112] Positive electrode active materials according to examples of the present invention will be described in detail below. <Examples 1 to 5> Precursor preparation Using the coprecipitation method, spherical Ni x Co y Mn zThe (OH) precursor was synthesized. In a 90L reactor, 25 wt% NaOH and 28 wt% NH4OH were added to a 2.5M composite transition metal sulfate solution prepared by mixing NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O in a molar ratio of Ni:Co:Mn. The pH in the reactor was maintained at 9.0-12.0, and the temperature was maintained at 45-50°C. N2, an inert gas, was added to the reactor to prevent oxidation of the precursor. After synthesis and stirring, the mixture was washed and dehydrated using a filter press (F / P) device. Finally, the dehydrated product was dried at 120°C for 2 days and filtered through a 75μm (200 mesh) sieve to obtain a 4μm Ni sieve. x Co y Mn z (OH) precursor was obtained.

[0113] First heat treatment and cooling The precursor was heated at a rate of 2°C per minute in a box firing furnace while maintaining an atmosphere of O2 or air (50 L / min), and was maintained at 300 to 1000°C for 1 to 10 hours, after which furnace cooling was carried out.

[0114] Wet coating (if performed after the first heat treatment and cooling described above) The precursor was wet-coated using the coprecipitation method. A composite transition metal sulfate solution, prepared by mixing distilled water with the appropriate molar ratio of CoSO4·7H2O, NiSO4·6H2O, or MnSO4·H2O, along with 25 wt% NaOH and 28 wt% NH4OH, was added to the reactor where the precursor was being stirred. The coating amount of the transition metal was 1-10 mol% relative to the total moles of nickel (Ni), cobalt (Co), and manganese (Mn). The pH in the reactor was maintained at 9.0-12.0. After the synthesis and stirring were completed, the product was washed and dehydrated using a filter plus (F / P) device. Finally, the dehydrated product was dried at 150°C for 14 hours to obtain a precursor with a concentration gradient.

[0115] Second heat treatment and cooling The precursors were mixed with LiOH or Li2CO3 weighed according to the Li / M ratio using a manual mixer (MM). The mixture was heated at a rate of 2°C per minute in a box furnace while maintaining an O2 or air (50 L / min) atmosphere, and maintained at a firing temperature of 800-1000°C for 7-12 hours, after which the furnace was cooled.

[0116] Wet coating (if performed after the second heat treatment and cooling) The lithium composite oxide was wet-coated using the coprecipitation method. A composite transition metal sulfate solution, prepared by mixing distilled water with the molar ratio of CoSO4·7H2O, NiSO4·6H2O, or MnSO4·H2O, along with 25 wt% NaOH and 28 wt% NH4OH, was added to a reactor where the particles were being stirred. The coating amount of the transition metal was 1-10 mol% relative to the total number of moles of nickel (Ni), cobalt (Co), and manganese (Mn). The pH in the reactor was maintained at 9.0-12.0. After the synthesis and stirring were completed, the particles were washed and dehydrated using a filter plus (F / P) device. Finally, the dehydrated product was dried at 150°C for 14 hours to obtain a lithium composite oxide with a concentration gradient.

[0117] Third heat treatment and cooling LiOH or Li2CO3 was weighed out to match the Li / M ratio and mixed with the coated product using a manual mixer (MM). The mixture was heated at a rate of 4.4°C per minute in a box furnace while maintaining an atmosphere of O2 or air (50 L / min), and maintained at a temperature of 300-1000°C for 7-12 hours, after which the furnace was cooled.

[0118] <Comparative Examples 1 and 2> A positive electrode active material was produced in the same manner as in Examples 1 to 5, except that the step of wet coating with a transition metal was not carried out in the production steps of Examples 1 to 5. The following Table 1 relates to the manufacturing methods of Examples 1 to 5 and Comparative Examples 1 and 2.

[0119] [Table 1]

[0120] <Manufacturing example> Manufacturing of lithium secondary batteries 90 wt% of the positive electrode active materials according to the Examples and Comparative Examples, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder were dispersed in 30 g of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was applied to a 15 μm-thick aluminum (Al) thin film as a positive electrode current collector, dried, and roll-pressed to prepare a positive electrode. Metallic lithium was used as a counter electrode for the positive electrode, and 1.15M LiPF6 in EC / DMC / EMC=2 / 4 / 4 (vol %) was used as the electrolyte. A battery assembly was formed by placing a separator made of a porous polyethylene (PE) film between the positive electrode and the negative electrode, and the electrolyte was injected to prepare a lithium secondary battery (coin cell).

[0121] <Experimental Example 1> Table 2 below shows the characteristics of the lithium secondary batteries according to the above examples and comparative examples.

[0122] [Table 2]

[0123] From the results of the EP-EDX analysis shown in FIGS. 1 to 3, the metal concentration gradient of the positive electrode active material according to the example can be confirmed. In addition, in Example 5, in which the positive electrode active material did not contain cobalt and was wet-coated with nickel (Ni), it was confirmed that a concentration gradient similar to that of the positive electrode active material wet-coated with cobalt (Co) was formed.

[0124] From the results of the TEM-EDS analysis shown in FIGS. 4 to 7, a metal concentration gradient can be confirmed in the shell of the primary particle of the positive electrode active material according to the example. From the results of the TEM-EDS analysis shown in FIG. 8, a metal concentration gradient in the shell of the primary particles of the positive electrode active material according to Example 5 can be confirmed.

[0125] FIG. 9 shows the results of SEM analysis of the comparative example and the example. As shown in Figure 10 and Table 2 above, the charge / discharge capacity and efficiency of the Example are improved compared to the Comparative Example. This is because the surface kinetics due to the shell concentration gradient increases the lithium mobility on the surface, reducing the irreversible reaction of Li2MnO3 on the surface, and improving efficiency.

[0126] 11 and 12 and Table 2 above, it can be seen that the high rate characteristics are improved in the examples compared to the comparative examples. This is due to the improvement in surface motion caused by the concentration gradient of the shell.

[0127] 13 and 14 and Table 2 above, it can be seen that the life characteristics of the Examples are improved compared to the Comparative Examples, as a result of solving the problems of cycle life and voltage decay due to phase transition during cycling of the lithium-excess layered oxide.

[0128] 15 and 16 and Table 2 above, it can be seen that the voltage drop is suppressed in the example compared to the comparative example, which is a result of improving the movement of the particle surface and the structural stability.

[0129] 10 to 16 and Table 2 above, the performance of the lithium secondary battery is also significantly improved in Example 5, in which the positive electrode active material does not contain cobalt and is wet-coated with nickel (Ni).

Claims

1. The lithium composite oxide includes a lithium excess oxide having a layered structure represented by the following [Chemical Formula 1], the lithium composite oxide includes secondary particles, the secondary particles include one or more primary particles, and the primary particles include one or more crystallites; At least one selected from the secondary particles, the primary particles, and the crystallites includes a core and a shell occupying at least a portion of a surface of the core; When the number of moles of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn) relative to the total number of moles of M1 and M2 in the following [Chemical Formula 1] is defined as NCM / M, the shell and core of the secondary particles have different NCM / M. [Chemical formula 1] rpai ２ M1O ３ ・(1-r)i ａ M2O ２ (In the above [Chemical Formula 1], 0<r<1, 0<a≦1, and M1 is selected from the group consisting of Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. At least one element is selected from the group consisting of Mo, Nb, Fe, Cr, V, Co, Cu, Zn, Sn, Mg, Ni, Ru, Al, Ti, Zr, B, Mn, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi.

2. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the shell of the secondary particle includes a concentration gradient portion having a gradient in concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

3. The positive electrode active material for a secondary battery according to claim 1 , wherein the shell and the core of the primary particles have different NCM / M.

4. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the shell of the primary particle includes a concentration gradient portion having a gradient in concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

5. The positive electrode active material for a secondary battery according to claim 1 , wherein the shell and core of the crystallite have different NCM / M.

6. 2. The positive electrode active material for a secondary battery according to claim 1, wherein the shell of the crystallite includes a concentration gradient portion having a gradient in concentration of at least one element selected from nickel (Ni), cobalt (Co), and manganese (Mn).

7. 2. The positive electrode active material for a secondary battery according to claim 1, wherein when the number of moles of nickel (Ni) relative to the total number of moles of M1 and M2 is Ni / M, the Ni / M of any one or more shells selected from the secondary particles, the primary particles, and the crystallites is higher than that of the core.

8. 2 . The positive electrode active material for a secondary battery according to claim 1 , wherein the shell of the secondary particle includes a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the secondary particle.

9. 2 . The positive electrode active material for a secondary battery according to claim 1 , wherein the shell of the primary particle includes a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the primary particle.

10. The positive electrode active material for a secondary battery according to claim 1 , wherein the shell of the crystallite includes a concentration gradient portion in which the concentration of nickel (Ni) decreases from the surface toward the center of the crystallite.

11. 2. The positive electrode active material for a secondary battery according to claim 1, wherein when the number of moles of cobalt (Co) relative to the total number of moles of M1 and M2 is Co / M, the Co / M of any one or more shells selected from the secondary particles, the primary particles, and the crystallites is higher than that of the core.

12. The positive electrode active material for a secondary battery according to claim 1 , wherein the positive electrode active material does not contain cobalt (Co).

13. 2. The positive electrode active material for a secondary battery according to claim 1, wherein Mn / M is the number of moles of manganese (Mn) relative to the total number of moles of M1 and M2, and Mn / M of any one or more shells selected from the secondary particles, the primary particles, and the crystallites is lower than that of the core.

14. A secondary battery comprising the positive electrode active material according to claim 1.

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