Positive electrode active material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode comprising the same, and a lithium secondary battery, the positive electrode active material being capable of not only exhibiting the electrical and chemical characteristics unique to a manganese-rich positive electrode active material, but also inhibiting cracking of particles in the positive electrode and improving the density of the positive electrode.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0108199, filed on August 13, 2024, and Korean Patent Application No. 10-2025-0106778, filed on August 4, 2025, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode containing the same, and a lithium secondary battery. The positive electrode active material not only exhibits the electrical and chemical properties unique to manganese-rich positive electrode active materials, but also inhibits particle cracking in the positive electrode and improves the density of the positive electrode. Background Technology

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

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

[0006] Recently, lithium-rich manganese oxides have attracted much attention as next-generation cathode active materials. Lithium-rich manganese oxides have the advantage of achieving high capacity by increasing the content of relatively inexpensive and abundant manganese (Mn). In particular, even when compared with lithium-nickel-cobalt-manganese composite oxides with high nickel content and known high energy density, these lithium-rich manganese oxides are superior in terms of unit price and energy density.

[0007] However, the compositional limitation of this lithium-rich manganese-rich oxide is its low rate capability. Therefore, to improve this problem, the lithium-rich manganese-rich oxide controls its structure by reducing the size of primary particles and increasing the BET specific surface area of ​​secondary particles.

[0008] However, compared with conventional cathode active materials such as lithium nickel cobalt manganese composite oxides, lithium-rich and manganese-rich oxides have low density and relatively large BET specific surface area, thus having the disadvantage of being prone to cracking.

[0009] In particular, because lithium-rich and manganese-rich oxide particles are prone to cracking during the rolling step in cathode manufacturing processes, their electrical and chemical properties may be reduced, the cathode density may decrease, and the porosity may increase, potentially lowering the overall energy density of the lithium-ion secondary battery. Furthermore, such a low cathode density may inevitably increase the cathode thickness, which could also limit the increase in battery energy density.

[0010] Furthermore, during the activation of the contained rock salt phase lithium manganese oxides, lithium-rich and manganese-rich oxides may release relatively large amounts of gas. Therefore, strategies to reduce this gas release remain necessary. Summary of the Invention

[0011] Technical issues

[0012] One object of the present invention is to provide a positive electrode active material for lithium secondary batteries, which not only exhibits the electrical and chemical properties unique to manganese-rich positive electrode active materials, but also inhibits particle cracking in the positive electrode, improves the density of the positive electrode, and reduces gas release.

[0013] Another object of the present invention is to provide a positive electrode and a lithium secondary battery comprising the aforementioned positive electrode active material and thereby exhibiting high density and excellent electrical, chemical and mechanical properties.

[0014] Technical solution

[0015] According to one embodiment of the present invention, a positive electrode active material for lithium secondary batteries is provided, the positive electrode active material comprising: a lithium-rich manganese-rich oxide, the lithium-rich manganese-rich oxide comprising a layered crystal structure, wherein the molar ratio of lithium is greater than 1 based on the molar number of all metals excluding lithium, and the content of manganese in the total metals excluding lithium is 50 mol% or more. The positive electrode active material comprises: First positive electrode active material particles and second positive electrode active material particles, the first positive electrode active material particles and the second positive electrode active material particles containing lithium-rich and manganese-rich oxides and having different average particle sizes (D50), and The third positive electrode active material particles comprise a lithium transition metal oxide containing manganese, nickel, and cobalt, wherein the lithium transition metal oxide contains less manganese than a lithium-rich, manganese-rich oxide, and When performing volumetric cumulative particle size distribution analysis on the positive electrode active material, the positive electrode active material exhibits a bimodal particle size distribution due to the particle size difference between the first positive electrode active material particles and the second and third positive electrode active material particles.

[0016] In one embodiment, the lithium-rich manganese-rich oxide contained as a main component of the first and second positive electrode active material particles can be represented by the following Chemical Formula 1: [Chemical Formula 1] Li a [Mn b Ni c M d 2-a O2 wherein in Chemical Formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, wherein 0 < c+d ≤ 0.5, and M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0017] According to another embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material according to one embodiment.

[0018] According to yet another embodiment of the present invention, there is provided a lithium secondary battery comprising: the positive electrode according to said another embodiment; a negative electrode; and an electrolyte.

[0019] Advantageous Effects

[0020] As a result of experiments conducted by the present inventors, it has been found that by controlling the particle size distribution of manganese-rich positive electrode active material particles to have different average particle sizes (D50) and using a positive electrode active material having a bimodal particle size distribution based on particle size distribution analysis results, cracking of positive electrode active material particles during calendering can be significantly reduced.

[0021] In addition, since the positive electrode active material further comprises positive electrode active material particles in the form of lithium nickel cobalt manganese composite oxide, cracking of the positive electrode active material particles can be further reduced, and gas release during activation or charge / discharge processes can be further reduced.

[0022] Furthermore, by applying a positive electrode active material having a bimodal particle size distribution, the contact area with the electrolyte in the positive electrode can be improved, and the rate performance can be enhanced. Therefore, the BET specific surface area of each positive electrode active material particle can be kept small, and cracking of the positive electrode active material particles can be further reduced.

[0023] ​Therefore, by using a cathode active material with a bimodal particle size distribution according to one embodiment, an excellent cathode with high density and low porosity, reduced gas release, and no particle cracking can be manufactured. Thus, by using a cathode active material according to one embodiment, a next-generation lithium-ion battery can be provided that not only exhibits the electrical and chemical properties characteristic of manganese-rich cathode active materials, such as high capacity, but also possesses thinness, high density, excellent rate capability, and lifetime characteristics. Attached Figure Description

[0024] Figure 1 The volume cumulative particle size distribution curves of the positive electrode active materials prepared in Example 1 and Examples 1 and 2 are shown.

[0025] Figure 2 The analysis results of gas release from lithium secondary batteries made from the positive electrode active materials of Comparative Example 1 and Examples 1 and 2 are shown.

[0026] Figure 3 The evaluation results of the lifetime characteristics of lithium secondary batteries made from the positive electrode active materials of Comparative Example 1 and Examples 1 and 2 are shown. Detailed Implementation

[0027] Specific embodiments of the invention will be described in more detail below.

[0028] As used herein, the term "lithium-rich manganese-rich oxide" or "manganese-rich cathode active material" can refer to a lithium metal oxide having a layered crystal structure, wherein the molar ratio of lithium is greater than 1 based on the total number of moles of all metals excluding lithium, and the content of manganese in the total number of metals excluding lithium is greater than 50 mol%.

[0029] As used herein, the term "single particle" refers to a particle consisting of a single nodule, and the term "quasi-single particle" refers to a particle as a composite of fewer than 30 nodules. However, unless otherwise stated herein, the term "single particle" should be considered as a general term that includes "quasi-single particles."

[0030] As used herein, the term “piece” refers to a particle unit that constitutes a single particle and a quasi-single particle, and a piece can be a single crystal without grain boundaries, or a polycrystalline material that appears to have no grain boundaries when observed using a scanning electron microscope (SEM) at magnifications of 5,000 to 20,000.

[0031] As used herein, the term "primary particle" refers to a particle unit that appears to have no grain boundaries when observed using a scanning electron microscope (SEM) at magnifications of 5,000 to 20,000, and the term "secondary particle" refers to a particle formed by the aggregation of multiple primary particles.

[0032] As used herein, the term "average particle size (D50)" refers to a particle size corresponding to 50% of the cumulative volume particle size distribution of the powder to be tested, and can be measured by laser diffraction. For example, it can be measured by a method comprising the steps of: dispersing the positive electrode active material powder in a dispersion medium, introducing the dispersion into a commercially available laser diffraction particle size measuring apparatus (e.g., Microtrac S-3500), and irradiating the dispersion with ultrasonic waves of about 28 kHz at an output power of 60 W to obtain a cumulative volume particle size distribution diagram, then determining the particle size corresponding to 50% of the cumulative volume.

[0033] As used herein, the "BET specific surface area" is measured by the Brunauer-Emmett-Teller (BET) method, specifically, it can be calculated from a nitrogen adsorption isotherm obtained using BELSORP-MAX (from Microtrac BEL) under a 77 K liquid nitrogen atmosphere.

[0034] On the other hand, the positive electrode active material according to one embodiment of the present invention may comprise first and second positive electrode active material particles having different average particle sizes (D50), wherein each of the first and second positive electrode active material particles may comprise lithium-rich manganese-rich oxide, the lithium-rich manganese-rich oxide comprising a layered crystal structure, wherein based on the total number of moles of metals excluding lithium, the molar ratio of lithium is greater than 1, and the content of manganese in all metals excluding lithium is 50 mol% or more.

[0035] In a specific embodiment, the lithium-rich manganese-rich oxide that serves as the main component of the first and second positive electrode active material particles may be a compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li a [Mn b Ni c M d 2-a O2 wherein, in Chemical Formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, wherein 0 < c+d ≤ 0.5, and M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0036] ​In addition to the first and second positive electrode active material particles, the positive electrode active material in one embodiment may further include a third positive electrode active material particle, which comprises a lithium transition metal oxide containing nickel, cobalt, and manganese. In this case, the lithium transition metal oxide of the third positive electrode active material particle contains less manganese than lithium-rich manganese-rich oxides; for example, the manganese content in all metals excluding lithium is less than 40 mol%, and in this respect, it can be distinguished from lithium-rich manganese-rich oxides.

[0037] In one embodiment of the positive electrode active material, the first and second positive electrode active material particles comprising lithium-rich and manganese-rich oxides can each have the form of secondary particles in which a plurality of primary particles are aggregated. Additionally, the third positive electrode active material particle comprising lithium transition metal oxides containing nickel, cobalt, and manganese can have the form of a single particle composed of individual small pieces or a quasi-single particle as a composite formed of 30 or fewer small pieces.

[0038] More specifically, in one embodiment of the positive electrode active material, the second and third positive electrode active material particles may have similar average particle size (D50) and particle size distribution, and the first positive electrode active material particles may have a larger average particle size (D50) than the second and third positive electrode active material particles and may have a different particle size distribution.

[0039] As a result, when the total volumetric cumulative particle size distribution of the positive electrode active material of one embodiment is analyzed, it can exhibit a bimodal particle size distribution containing multiple peaks, such as two peaks separated from each other. In this case, the bimodal particle size distribution can be defined and confirmed by the appearance of two separate peaks in the volumetric cumulative particle size distribution curve of the positive electrode active material of one embodiment, each of the two separate peaks corresponding to the first positive electrode active material particles and corresponding to the second and third positive electrode active material particles, respectively.

[0040] As a result of experiments conducted by the inventors, it was found that by using a positive electrode active material with a bimodal particle size distribution according to one embodiment, cracking of the positive electrode active material particles, especially particle cracking during calendering, can be suppressed. This is presumably because using a positive electrode active material with a bimodal particle size distribution can effectively buffer the stress applied to the particles during calendering and similar processes.

[0041] Furthermore, by applying cathode active materials with a bimodal particle size distribution, the contact area between the cathode and the electrolyte can be improved, and the rate performance can be enhanced. Therefore, while addressing the low rate performance inherent in conventional lithium-rich and manganese-rich oxides, the BET specific surface area of ​​each cathode active material particle can be maintained. This further reduces cracking of the cathode active material particles.

[0042] In addition, based on the first and second positive electrode active material particles containing lithium-rich and manganese-rich oxides, the positive electrode active material of one embodiment further includes a third positive electrode active material particle in the form of a single particle (or quasi-single particle) containing a certain amount of lithium nickel cobalt manganese composite oxide, such that the positive electrode active material can exhibit reduced gas release during battery activation or charging / discharging.

[0043] Therefore, by using the positive electrode active material of one embodiment, an excellent positive electrode with high density, low porosity, and reduced gas release can be manufactured without any particle cracking. Thus, by using the positive electrode active material of one embodiment, a next-generation lithium-ion battery can be provided that not only exhibits the electrical and chemical properties characteristic of manganese-rich positive electrode active materials, such as high capacity and rate capability, but also has thinness and high density.

[0044] On the other hand, in one embodiment of the positive electrode active material, the lithium-rich manganese-rich oxide contained in the first and second positive electrode active material particles may have a lithium molar ratio based on the total number of all metals excluding lithium being greater than 1, or 1.1 to 1.5, or 1.3 to 1.5. In one example, this lithium molar ratio may be calculated by the mathematical formula "a / (2-a)" in Formula 1. Furthermore, in Formula 1, a is the molar ratio of Li in the lithium-rich manganese-rich oxide, and a in Formula 1 may satisfy 1.1 ≤ a ≤ 1.5, 1.1 ≤ a ≤ 1.4, 1.1 ≤ a ≤ 1.3, or 1.14 ≤ a ≤ 1.3.

[0045] When the range of 'a' and the molar ratio of lithium to the remaining metals meet the aforementioned ranges, higher capacity and excellent rate performance can be achieved while maintaining the chemical and crystallographic stability of the first and second cathode active material particles. Furthermore, if the molar ratio of lithium to the remaining metals is too high, conductivity may decrease, the formation of the rock salt phase (Li₂MnO₃) may increase, and the degradation rate may become faster. If the molar ratio is too low, the effect on improving energy density may be minimal.

[0046] b represents the molar ratio of Mn in lithium-rich and manganese-rich oxides. In chemical formula 1, b can satisfy 0.5 ≤ b < 1, 0.5 ≤ b ≤ 0.9, or 0.55 ≤ b ≤ 0.8. Therefore, it can exhibit the excellent capacity characteristics unique to lithium-rich and manganese-rich oxides.

[0047] c is the molar ratio of Ni in lithium-rich and manganese-rich oxides. In chemical formula 1, c can satisfy 0≤c≤0.50, 0≤c<0.5, 0.1≤c≤0.5, 0.1≤c≤0.45, or 0.3≤c≤0.4.

[0048] d represents the molar ratio of the element M added or incorporated into the lithium-rich manganese-rich oxide in the form of doping, wherein in Chemical Formula 1, d can satisfy 0≤d≤0.50, 0≤d<0.5, 0≤d≤0.2 or 0≤d≤0.1. If the content of the additional element M is too high, it will not only negatively affect the capacity of the active material, but also increase the oxygen-redox reaction, thereby aggravating gas release and degradation of the positive electrode active material, and the lifespan characteristics may be reduced.

[0049] More suitable examples of the element M may be one or more elements selected from the group consisting of Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr. In a more specific embodiment, one or more elements selected from the group consisting of Co, Zn, Ti, Al, Mg and B may be added to the lithium-rich manganese-rich oxide in the form of doping or the like.

[0050] Furthermore, in a specific embodiment, the lithium-rich manganese-rich oxide may contain the additional element M only on the surface in the form of doping element, and the molar ratio of nickel:manganese may be 25:75 to 50:50, or 25:75 to 45:55, or 30:70 to 40:60. Within the above range, if the molar ratio of manganese is too low, the proportion of rock salt phase may be insufficient, which may lead to insufficient capacity or reduced crystallinity and chemical stability. Conversely, if the molar ratio of manganese is too high, the stability of the lithium-rich manganese-rich oxide may also be reduced.

[0051] On the other hand, in an example of Chemical Formula 1, b+c+d may satisfy 1, while in other examples, it may have a value of 0.9 or more and less than 1. b+c+d being less than 1 may indicate that on the basis of including manganese, nickel and the additional element M, Chemical Formula 1 further contains an additional metal element. However, it goes without saying that such an additional metal element can be added within a limit that maintains the unique crystal structure of the lithium-rich manganese-rich oxide.

[0052] In a specific embodiment of the positive electrode active material according to one embodiment, the lithium-rich manganese-rich oxide may be a compound represented by the following Chemical Formula 1a: [Chemical Formula 1a] Li a [Mn b Ni c M d 2-a O2 wherein in Chemical Formula 1a, 1.1<a<1.3, 0.5≤b≤0.9, 0.1≤c≤0.5, 0≤d≤0.1, and ​M is selected from one or more of Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr.

[0053] On the other hand, lithium-rich and manganese-rich oxides containing excessive lithium can contain compounds with a rock-salt structure, such as Li₂MnO₃, in a mixed state, and compounds with a layered structure, such as Li[Ni]. w Mn y M z O2. Therefore, lithium-rich and manganese-rich oxides can be represented by the following chemical formula 2: [Chemical Formula 2] X×Li2MnO3·(1-X)×Li[Ni w Mn y M z O2 In chemical formula 2, M is selected from one or more of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, where 0 <w+z≤0.5。

[0054] X refers to the ratio of rock salt phase (Li2MnO3 phase) in lithium-rich and manganese-rich oxides, and w, y, and z refer to the molar ratios of Ni, Mn, and additional element M in layered compounds, respectively.

[0055] In lithium-rich and manganese-rich oxides, additional capacity characteristics can be achieved due to further activation of the rock salt phase Li2MnO3. However, the gas release may increase during the activation process of this rock salt phase. In one embodiment of the cathode active material, a portion of the second cathode active material particles with relatively small particle size can be replaced by third cathode active material particles in single-particle (or quasi-single-particle) form containing lithium nickel cobalt manganese composite oxide, thereby reducing the gas release.

[0056] On the other hand, if desired, a coating can be further incorporated onto the surface of the lithium-rich and manganese-rich oxides contained in the first and second positive electrode active material particles. In this case, the coating can suppress the contact between the lithium-rich and manganese-rich oxides and the electrolyte to reduce electrolyte side reactions, thereby improving lifetime characteristics.

[0057] The coating may include coating element M 1 The coating element M 1 It can be, for example, one or more selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. Coating element M1 It can contain more than two types, such as Al and Co.

[0058] The coating element can be in the form of an oxide (i.e., M). 1 Oz (1≤z≤4) exists in the coating.

[0059] The coating can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). Among these, atomic layer deposition is preferred because it allows for the formation of a large coating area.

[0060] The coating area can be 10% to 100%, 30% to 100%, or 50% to 100% of the total surface area of ​​the first and / or second positive electrode active material particles containing lithium-rich and manganese-rich oxides. When the coating area meets the above range, the effect of improving lifetime characteristics is excellent.

[0061] Furthermore, in one embodiment of the positive electrode active material, the first and second positive electrode active material particles may comprise lithium-rich and manganese-rich oxides having compositions that are the same as or different from each other. More specifically, they may be represented by chemical formulas that are the same as or different from each other within the range of the aforementioned chemical formula 1 or 2.

[0062] On the other hand, the third positive electrode active material particles may contain lithium transition metal oxides of the following chemical formula 3: [Chemical Formula 3] Li 1+p (Ni q Co r Mn s M 2 t O2 In chemical formula 3, M 2 It is selected from one or more of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 1+p, q, r, s, and t are each the atomic fractions of independent elements, where -0.2 ≤ p ≤ 0.2, 0.50 ≤ q < 1, and 0 <r≤0.40,0<s≤0.40,0≤t≤0.10。

[0063] More specifically, in Chemical Formula 3, q, r, s and t can respectively satisfy 0.50≤q<1, 0<r≤0.30, 0<s≤0.30, and 0≤t≤0.10. In addition, in one specific embodiment, q+r+s+t can satisfy a value of 1, but in another embodiment, the sum of q+r+s+t can be a value greater than or equal to 0.9 and less than 1. The value being less than 1 indicates that in addition to nickel, cobalt, manganese and M 2 , Chemical Formula 3 further includes an additional metal element. However, it goes without saying that such additional metal element can be added within the limit that the layered crystal structure unique to Chemical Formula 3 is maintained.

[0064] That is, in the third positive electrode active material particles, the lithium transition metal oxide may be a lithium nickel cobalt manganese composite oxide, wherein the nickel content based on all transition metals including nickel, cobalt and manganese is 50 mol% or more, 60 mol% or more, or 80 mol% or more. In addition, compared with lithium-rich manganese-rich oxides, the lithium transition metal oxide may contain a smaller amount of manganese, for example, 40 mol% or less, 35 mol% or less, 30 mol% or less, 20 mol% or less, or 15 mol% or less.

[0065] 1+p represents the molar ratio of lithium in the lithium transition metal oxide, and can satisfy -0.1≤p≤0.2 or 0≤p≤0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the third positive electrode active material particles can be stably formed.

[0066] q represents the molar ratio of nickel in all metals excluding lithium in the lithium transition metal oxide, and can satisfy 0.60≤q<1, 0.70≤q<1, or 0.80≤q<1. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, and high capacity can be achieved.

[0067] r represents the molar ratio of cobalt in all metals excluding lithium in the lithium transition metal oxide, and can satisfy 0<r≤0.20, 0<r≤0.15, or 0<r≤0.10. When the molar ratio of cobalt satisfies the above range, excellent resistance characteristics and output characteristics can be achieved.

[0068] s represents the molar ratio of manganese in all metals excluding lithium in the lithium transition metal oxide, and can satisfy 0<s≤0.20, 0<s≤0.15, or 0<s≤0.10. When the molar ratio of manganese satisfies the above range, the positive electrode active material exhibits excellent structural stability.

[0069] Furthermore, the lithium transition metal oxide represented by Formula 3 may contain one or more additional or doped elements selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and in this case, it exhibits the effect of suppressing structural degradation and improving high-temperature durability. Preferably, the lithium transition metal oxide represented by Formula 3 may contain Al as a doping element. The molar ratio of the doping elements, t, may be 0 ≤ t ≤ 0.08, 0 ≤ t ≤ 0.06, or 0 ≤ t ≤ 0.05.

[0070] On the other hand, in the positive electrode active material of the above embodiments, the first positive electrode active material particles may have an average particle size (D50) of, for example, 7 to 20 μm, 8 to 15 μm, or 8.5 to 11 μm, and the second positive electrode active material particles may have a smaller average particle size (D50) of, for example, 1 to 6 μm, 2 to 5 μm, or 2.5 to 4.5 μm. Furthermore, the third positive electrode active material particles may be smaller than the first positive electrode active material particles and may have an average particle size (D50) similar to that of the second positive electrode active material particles, for example, 2 to 5 μm or 2.5 to 4.5 μm.

[0071] This effectively alleviates the stress applied during processes such as calendering, thereby further reducing the cracking of cathode active material particles and enabling the provision of cathodes with higher density and lower porosity.

[0072] Furthermore, in one specific embodiment of the present invention, the first positive electrode active material particles and the second and third positive electrode active material particles may be included in the positive electrode active material in a weight ratio of 50:50 to 95:5, or 55:45 to 95:5, or 60:40 to 90:10, or 65:35 to 70:30. This allows for the provision of a positive electrode with higher density and lower porosity while maintaining the electrical and chemical properties characteristic of lithium-rich and manganese-rich oxides.

[0073] On the other hand, if the average particle size (D50) of the first positive electrode active material particles is too large, or the average particle size (D50) of the second and third positive electrode active material particles is too small, the electrical, chemical, or mechanical properties of the positive electrode active material in one embodiment may be reduced. Conversely, if the average particle size (D50) of the first positive electrode active material particles is too small, or the average particle size (D50) of the second and third positive electrode active material particles is too large, the bimodal particle size distribution characteristic characteristic of the positive electrode active material in one embodiment may not be properly achieved, particle cracking may occur during the calendering process, or the density of the positive electrode may be insufficient.

[0074] Furthermore, based on a total of 100 parts by weight of second and third cathode active material particles, the content of the third cathode active material particles can be 5 to 95 parts by weight, 10 to 90 parts by weight, or 15 to 87 parts by weight. Therefore, the amount of gas released during the activation or charge / discharge process of the cathode active material can be reduced, while maintaining the excellent electrical and chemical properties characteristic of lithium-rich and manganese-rich oxides, such as capacity characteristics.

[0075] On the other hand, in one embodiment, the positive electrode active material, as a whole comprising the first to third positive electrode active material particles, can have a particle size of 0.1 μm. 2 / g to 5.0 m 2 / g, specifically 0.5 m 2 / g to 3.0 m 2 / g, more specifically 1.0m 2 / g to 2.0 m 2 / g BET specific surface area.

[0076] In addition, the BET specific surface area of ​​the first positive electrode active material particles contained in the positive electrode active material can be 1.2 m². 2 / g or more, preferably 1.3 m 2 / g or higher. In this case, it is preferable that this can achieve high capacity and efficiency. However, considering problems such as electrode processability, large surface area and surface side reactions, and increased inhomogeneity due to low sphericity, the BET specific surface area can be 4.0 m². 2 / g or less or 3.0 m 2 / g or less or 2.0 m 2 / g or less. Furthermore, the BET specific surface area of ​​the second and third positive electrode active material particles can be smaller than that of the first positive electrode active material particles, and can be 0.3 m². 2 / g to 1.7 m 2 / g or 1.0 m 2 / g to 1.5 m 2 / g. The BET specific surface area of ​​the third positive electrode active material particles can be 0.5 m². 2 / g to 1.5 m 2 / g.

[0077] One embodiment of the positive electrode active material comprises first to third positive electrode active materials, thus exhibiting a bimodal particle size distribution. This inherently ensures a sufficient reaction area with the electrolyte and effectively guarantees capacity and rate characteristics. Consequently, the positive electrode active material can possess the aforementioned low specific surface area, further reducing particle cracking caused by calendering. Furthermore, by optimizing each specific surface area within the aforementioned range, the solids content of the slurry used to form the positive electrode active material layer can be optimized, further reducing gas release. However, if the BET specific surface area is too low, the reaction area with the electrolyte is insufficient, making it difficult to achieve adequate capacity; conversely, if the specific surface area is too large, rapid moisture absorption and accelerated side reactions with the electrolyte make it difficult to ensure lifetime characteristics.

[0078] The positive electrode active material of the above embodiments, specifically the first and second positive electrode active material particles, can be prepared according to the general preparation method of lithium-rich and manganese-rich oxides. For example, each of the first and second positive electrode active material particles can be prepared by mixing a manganese-containing transition metal precursor with a lithium raw material to form a mixture, and then sintering the mixture. The types of precursors and raw materials and the preparation conditions can follow the general preparation conditions for manganese-rich positive electrode active materials, so further description of them will be omitted.

[0079] However, in this preparation process, the first and second positive electrode active material particles that meet the above-mentioned average particle size (D50) can be prepared by adjusting the type or particle size of the transition metal precursor, or by adjusting the sintering temperature, etc., and these particles can be mixed in a predetermined ratio to obtain a positive electrode active material of one embodiment. However, the process conditions used to prepare the positive electrode active material to achieve the predetermined average particle size (D50) are well known to those skilled in the art, and therefore further description thereof will be omitted.

[0080] On the other hand, the third positive electrode active material particles can be prepared according to conventional methods known for preparing lithium nickel cobalt manganese composite oxides in single-particle form, so further explanation of them will be omitted.

[0081] On the other hand, the positive electrode active material of the above embodiment is mixed with a binder, a conductive material, a solvent, etc. to form a positive electrode slurry, and then the positive electrode slurry is coated onto a positive electrode current collector, dried, and calendered to manufacture a positive electrode. The positive electrode slurry will be described below.

[0082] First, based on the total weight of solids (e.g., positive electrode active material, conductive material, and binder) in the positive electrode slurry, the content of positive electrode active material in the above embodiments can be 90% to 99% by weight, 95% to 99% by weight, or 97% to 98% by weight. If the content of positive electrode active material in the solids is less than 90% by weight, the energy density may be lower, and the capacity may be reduced.

[0083] Furthermore, the adhesive may be selected from one or more of the following substances: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Preferably, the adhesive may be polyvinylidene fluoride (PVDF).

[0084] Based on the total weight of solids in the cathode slurry, the binder content can be from 0.5% to 2.5% by weight, or from 1% to 2% by weight, or from 1.5% to 2% by weight. When the binder content is within the above range, sufficient adhesion to the current collector and bonding between particles are ensured, thereby improving the durability of the cathode while maintaining a low initial resistance.

[0085] The conductive material may be selected from one or more of the following: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or conductive polymers, such as polyphenylene derivatives. Preferably, the conductive material may be carbon nanotubes or carbon black, with carbon nanotubes being the most preferred.

[0086] Based on the total weight of solids in the positive electrode slurry, the content of conductive material can be from 0.1% to 2.5% by weight, 0.3% to 2% by weight, or 0.5% to 1% by weight. When the content of conductive material is within the above range, it is preferable that this can reduce dead volume while maintaining conductivity between active materials.

[0087] Additionally, the cathode slurry may optionally further contain a dispersant, wherein the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0088] On the other hand, the solvent for the positive electrode slurry can be any solvent commonly used in the art, such as: N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropanol, dimethylformamide (DMF), acetone, water, or mixtures of two or more thereof. The solvent can be adjusted to an amount sufficient to achieve the viscosity of the aforementioned positive electrode slurry.

[0089] On the other hand, according to another embodiment of the present invention, a positive electrode comprising the above-described positive active material is provided. This positive electrode can be manufactured from a positive electrode slurry and may include, for example, a positive current collector; and a positive active material layer formed on the positive current collector and comprising the positive active material of one embodiment. In this case, the positive active material layer is formed by processes such as coating, drying, and calendering of the above-described slurry, and may further comprise a binder and a conductive material.

[0090] The positive electrode current collector can contain a highly conductive metal, and the positive electrode active material layer should adhere easily, but there are no particular limitations, as long as it is non-reactive within the battery's voltage range. Examples of materials that can be used as the positive electrode current collector include: stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector can typically have a thickness from 3 μm to 500 μm, and it can have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0091] In addition to using the aforementioned cathode materials, the cathode can be manufactured according to conventional cathode manufacturing methods. Specifically, the cathode can be manufactured by coating a cathode slurry onto a cathode current collector, then drying and calendering it, or by casting a cathode slurry onto a separate carrier and then pressing the film layer obtained by peeling it off from the carrier onto the cathode current collector.

[0092] In this case, considering the solvent and solids content, the coating and drying processes of the cathode slurry can be performed using conventional methods. The calendering process can be carried out, for example, by tandem calendering, in which calendering is performed two or more times consecutively, or two to four times, or two to three times. In this case, during the first calendering period, a target thickness reduction of up to 60% to 90% or 70% to 90% can be achieved, and during the second calendering period, a target thickness reduction of up to 70% to 100% or 80% to 100% can be achieved. Furthermore, if calendering is performed three or more times, this process can be carried out to achieve a 100% target thickness reduction during the final calendering period.

[0093] In more specific instances, to prevent electrode breakage during calendering, the pressure applied during calendering can be from 1.0 ton / cm to 3.0 ton / cm or from 1.5 ton / cm to 2.8 ton / cm, and uniform pressure can be applied throughout the process.

[0094] On the other hand, according to yet another embodiment of the present invention, the lithium secondary battery includes the positive electrode of the other embodiments described above. This lithium secondary battery may include, for example, the aforementioned positive electrode, a negative electrode facing the positive electrode, and a separator or electrolyte layer between the positive and negative electrodes, and optionally an electrolyte. In this case, since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0095] In a lithium secondary battery, the negative electrode consists of a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0096] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and will not cause any chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can typically have a thickness from 3µm to 500µm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0097] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0098] Compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples of anode active materials can be: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides that can be doped and de-doped with lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or a composite containing (semi-)metallic materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used. Additionally, a thin film of metallic lithium may be used as the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be from 80% to 99% by weight.

[0099] Adhesives are components that facilitate bonding between conductive materials, active materials, and current collectors. Typically, the amount of adhesive added can range from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM, styrene-butadiene rubber, fluororubber, or various copolymers thereof.

[0100] Conductive materials are components used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the amount of conductive material added can be less than 10% by weight, preferably less than 5% by weight. There are no particular restrictions on this conductive material, as long as it is conductive and will not cause any chemical changes in the battery. Examples of materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; and conductive materials, such as polyphenylene derivatives, etc.

[0101] The negative electrode active material layer can be prepared by coating a negative electrode slurry, which is prepared by dissolving or dispersing the negative electrode active material, along with optional binders and conductive materials, in a solvent, onto a negative electrode current collector and then drying the coated current collector, or by casting the negative electrode slurry onto a separate carrier and then pressing the film layer obtained by peeling it off from the carrier onto the negative electrode current collector.

[0102] On the other hand, in lithium-ion secondary batteries, the separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular restriction, as long as it is commonly used as a separator in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to the movement of electrolyte ions are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0103] On the other hand, a lithium secondary battery may include a separator, but it may also include an electrolyte layer separate from the separator, or it may include a stack in which the electrolyte layer is stacked on the separator. In specific examples, the electrolyte layer may be a gel electrolyte layer containing a gel electrolyte or a solid electrolyte layer.

[0104] In a more specific example, the electrolyte layer comprising a gel electrolyte comprises a matrix containing, for example, a polyurethane or polyacrylic acid crosslinked polymer, a lithium salt, and a non-aqueous organic solvent, and may have a form in which the lithium salt and the non-aqueous organic solvent are dispersed or encapsulated within the matrix. However, the types of crosslinked polymers, lithium salts, and organic solvents that may be included in the gel electrolyte will be apparent to those skilled in the art, and therefore further description thereof will be omitted.

[0105] In another specific example, the solid electrolyte layer may contain any solid electrolyte, for example, one or more selected from polymer-based solid electrolytes, oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes. However, the composition of such a solid electrolyte layer can follow the known composition of conventional solid electrolyte layers, and therefore further description therein will be omitted.

[0106] On the other hand, the aforementioned lithium secondary battery may further include an electrolyte containing lithium salt and non-aqueous organic solvent.

[0107] Non-aqueous organic solvents can be used without particular restrictions, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; sulfolane, etc. Among these solvents, carbonate solvents are preferred, and more preferably, mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can increase the charge / discharge performance of the battery and linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity are preferred.

[0108] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F...- Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of the following can be used as a lithium salt: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4), etc. The lithium salt can be used in a concentration range from 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent performance because it can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0109] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, at least one additive can be added to the electrolyte in addition to the electrolyte components. Examples of additives include: alkylene carbonate halocarbonates such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted alkyl ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content can be from 0.1 to 5% by weight, based on the total weight of the electrolyte.

[0110] Because the aforementioned lithium secondary batteries consistently exhibit excellent discharge capacity, output characteristics, and lifespan, they are suitable for portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0111] Lithium secondary batteries can be of various types, but are not specifically limited to cylindrical, prismatic, pouch-shaped, or coin-shaped containers.

[0112] The lithium secondary battery according to the present invention can be used not only in battery cells as power sources for small devices, but also as unit cells in medium and large battery modules comprising multiple battery cells.

[0113] Examples of medium to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0114] The present invention will now be described in detail with reference to embodiments.

[0115] <Preparation of cathode materials>

[0116] The positive electrode active materials A to C used in the following preparation examples, embodiments and comparative examples each have the properties shown in Table 1 below.

[0117] [Table 1]

[0118] Preparation Example 1.

[0119] A cathode material was prepared by mixing cathode active materials A, B, and C in a weight ratio of 65:5:30. The total BET specific surface area of ​​this cathode material was confirmed to be approximately 1.34 m². 2 / g.

[0120] Comparative preparation example 1.

[0121] A cathode material was prepared by mixing cathode active material A and cathode active material B at a weight ratio of 65:35. The total BET specific surface area of ​​this cathode material was confirmed to be approximately 1.46 m². 2 / g.

[0122] Examples and Comparative Examples: Manufacturing of Positive Electrode and Lithium-ion Secondary Battery

[0123] A cathode slurry was prepared by mixing the cathode material, carbon nanotubes, PVDF binder, and HNBR-containing dispersant in N-methylpyrrolidone at a weight ratio of 97.46:0.62:1.7:0.22. The cathode slurry was coated onto an aluminum current collector sheet, dried, and then calendered to manufacture the cathode. The calendering was performed twice using a tandem calendering method. The linear pressure between calendering cycles was set differently for various conditions: 1.19 t / cm + 1.14 t / cm (Comparative Example 1; Cathode material: Comparative Preparation Example 1), 1.19 t / cm + 2.59 t / cm (Comparative Example 2; Cathode material: Comparative Preparation Example 1), 2.18 t / cm + 2.28 t / cm (Example 1; Cathode material: Preparation Example 1), and 2.96 t / cm + 2.96 t / cm (Example 2; Cathode material: Preparation Example 1).

[0124] A negative electrode slurry was prepared by mixing graphite anode active material, single-walled carbon nanotubes, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 96.2:0.8:2:1. The negative electrode slurry was coated onto a copper current collector sheet, dried, and then calendered to manufacture the negative electrode.

[0125] On the other hand, the positive and negative electrodes are manufactured by adjusting the load so that the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity (N / P ratio) is 115%.

[0126] A polyethylene separator is inserted between the positive and negative electrodes manufactured as described above to prepare an electrode assembly. The electrode assembly is inserted into a battery case, an electrolyte is injected into it, and an activation process is performed by charging at 5°C with a constant current of 0.1C until 4.6 V, and then discharging at a constant current of 0.1C until 2.0 V, thereby manufacturing a lithium secondary battery.

[0127] Experimental Example 1: Analysis of the volumetric cumulative particle size distribution and average particle size (D50) of positive electrode active materials

[0128] First, the volumetric cumulative particle size distribution (PSD) of the cathode powders included in the examples and comparative examples was determined using a Microtrac S-3500 size analyzer. For reference, the volumetric cumulative particle size distribution curve of the cathode material obtained in Preparation Example 1 is shown below. Figure 1 The volumetric cumulative particle size distribution curve confirmed that the cathode material of Preparation Example 1 has a bimodal particle size distribution. Furthermore, the average particle size (D50) of each cathode active material contained in the cathode material was analyzed using the volumetric cumulative particle size distribution curve, and the results were the same as those shown in Table 1 below.

[0129] Furthermore, the PSD of all cathode materials contained in each cathode slurry prepared in the preparation examples and comparison examples was analyzed in the same manner, and the data was exported as pre-calendering data. Thus, the volume ratio of particles with a particle size of 1 μm or less and the volume ratio of large particles (e.g., cathode active material A) in the cathode materials contained in the cathode slurry were evaluated respectively.

[0130] Experimental Example 2: Evaluation of Cumulative Particle Size Distribution and Particle Cracking Rate of the Positive Electrode

[0131] The cathodes manufactured using the cathode materials from the preparation examples or comparative examples were heat-treated in a furnace at 700°C for 10 hours to recover the cathode material. The cathode material was finely crushed using a mortar and pestle, and then sieved using a 250-mesh sieve to obtain the cathode powder contained in each cathode. The obtained powders were analyzed using a Microtrac S-3500 to obtain the volumetric cumulative particle size distribution (PSD). For reference, the volumetric cumulative particle size distribution of the cathode material contained in the cathodes of Examples 1 and 2 is shown below. Figure 1 This confirms that the cathode material maintains a bimodal particle size distribution.

[0132] Therefore, the volume ratio of particles smaller than 1 μm and the volume ratio of large particles (e.g., cathode active material A) in the cathode material were evaluated. These data were compared with the data obtained in Experimental Example 1, and the changes in the volume ratio of particles smaller than 1 μm and the volume ratio of large particles in the cathode manufactured by calendering before and after calendering were evaluated, as shown in Table 2 below.

[0133] [Table 2]

[0134] Referring to Table 2, it was confirmed that, despite having lower porosity and higher density compared to Comparative Examples 1 and 2 due to the application of much higher pressure during calendering, the cathodes of Examples 1 and 2 using the cathode material of Preparation Example 1 were essentially free of particles smaller than 1 μm. This indicates that no small particle cracking occurred in the cathode material. Furthermore, it was confirmed that, despite the application of high pressure during calendering, the cracking rate of large particles also exhibited similar large particle cracking characteristics.

[0135] Experiment Example 3: Evaluation of Gas Release Amount

[0136] For the lithium secondary batteries manufactured using the cathode materials of the preparation examples or comparative examples, the gases released after the activation process were captured and quantitatively analyzed using GC-FID / TCD. The analytical results of gas release amounts in Comparative Example 1 are compared with those in Examples 1 and 2 and are shown below. Figure 2 middle.

[0137] refer to Figure 2 It was confirmed that, compared with Comparative Example 1, the lithium secondary batteries of Examples 1 and 2 exhibited reduced gas release.

[0138] Experiment Example 4: Evaluation of Lifetime Characteristics

[0139] The lithium secondary batteries manufactured using the cathode materials of the preparation examples or comparative examples were subjected to 100 to 150 charge / discharge cycles at 45°C and 2.5 to 4.35 V. During these charge-discharge cycles, the energy retention rates of Comparative Example 1 and Examples 1 and 2 were evaluated and are shown below. Figure 3 middle.

[0140] refer to Figure 3 It was confirmed that, compared with the comparative example, the lithium secondary battery of the embodiment exhibited higher energy retention and improved life characteristics after 100 to 150 cycles of charge / discharge testing.

Claims

1. A cathode active material for a lithium secondary battery, the cathode active material comprising: lithium-rich manganese-rich oxide, wherein the lithium-rich manganese-rich oxide has a layered crystal structure, and the molar ratio of lithium is greater than 1 based on the number of moles of all metals excluding lithium, and the content of manganese in all metals excluding lithium is 50 mol% or more, wherein the cathode active material comprises: first cathode active material particles and second cathode active material particles, wherein the first cathode active material particles and the second cathode active material particles comprise lithium-rich manganese-rich oxide and have different average particle sizes (D50), and third cathode active material particles, wherein the third cathode active material particles comprise a lithium transition metal oxide containing manganese, nickel and cobalt, and the lithium transition metal oxide contains a smaller amount of manganese compared with the lithium-rich manganese-rich oxide, and wherein when volume cumulative particle size distribution analysis is performed on the cathode active material, the cathode active material has a bimodal particle size distribution due to the particle size difference between the first cathode active material particles, the second cathode active material particles and the third cathode active material particles.

2. The cathode active material for a lithium secondary battery according to claim 1, wherein the lithium-rich manganese-rich oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li a [Mn b Ni c M d ] 2-a O2 wherein in chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, c and d are each 0 or more and 0.5 or less, wherein 0 < c+d ≤ 0.5, and M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr.

3. The cathode active material for a lithium secondary battery according to claim 1, wherein the lithium-rich manganese-rich oxide has a lithium molar ratio of 1.3 to 1.5 based on the number of moles of all metals excluding lithium.

4. The cathode active material for a lithium secondary battery according to claim 1, wherein the molar ratio of nickel to manganese contained in the lithium-rich manganese-rich oxide is 25:75 to 50:

50.

5. The cathode active material for a lithium secondary battery according to claim 1, wherein the lithium-rich manganese-rich oxide is represented by the following chemical formula 1a: [Chemical Formula 1a] Li a [Mr b Ni c M d ] 2-a O2 wherein in chemical formula 1a, 1.1 < a < 1.3, 0.5 ≤ b ≤ 0.9, 0.1 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.1, and M is one or more selected from the group consisting of Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr.

6. The cathode active material for a lithium secondary battery according to claim 1, wherein the lithium-rich manganese-rich oxide comprises a rock salt structure compound and a layered structure compound in a mixed state.

7. The cathode active material for a lithium secondary battery according to claim 5, wherein the lithium-rich manganese-rich oxide is represented by the following chemical formula 2: [Chemical Formula 2] X×Li2MnO3·(1-X)×Li[Ni w Mn y M z O2 wherein in chemical formula 2, M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr, 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, where 0 <w+z≤0.5。 8. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the third positive electrode active material particles comprise a lithium transition metal oxide of the following chemical formula 3: [Chemical Formula 3] Li 1+p (Ni q Co r Mr s M 2 t )O2 In chemical formula 3, M 2 It is selected from one or more of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. -0.2≤p≤0.2,0.30≤q<1,0 <r≤0.40,0<s≤0.40,0≤t≤0.10。 9. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the first positive electrode active material particles and the second positive electrode active material particles have the form of secondary particles in which a plurality of primary particles are aggregated.

10. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the third positive electrode active material particles are in the form of a single particle consisting of a small piece or a quasi-single particle as a composite of 30 or fewer small pieces.

11. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the first positive electrode active material particles have an average particle size (D50) of 7 μm to 20 μm, and have a larger average particle size (D50) compared with the second positive electrode active material particles and the third positive electrode active material particles.

12. The positive electrode active material for lithium secondary batteries according to claim 11, wherein the second positive electrode active material particles have an average particle size (D50) of 1 μm to 6 μm.

13. The positive electrode active material for lithium secondary batteries according to claim 11, wherein the third positive electrode active material particles have an average particle size (D50) of 2 μm to 5 μm.

14. The positive electrode active material for lithium secondary batteries according to claim 1, wherein it contains the first positive electrode active material particles, the second positive electrode active material particles, and the third positive electrode active material particles in a weight ratio of 55:45 to 95:

5.

15. The positive electrode active material for lithium secondary batteries according to claim 14, wherein the content of the third positive electrode active material particles is from 5 parts by weight to 95 parts by weight, based on a total of 100 parts by weight of the second positive electrode active material particles and the third positive electrode active material particles.

16. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the first positive electrode active material particles have a particle size of 1.2 μm. 2 / g to 4.0 m 2 / g BET specific surface area.

17. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the second positive electrode active material particles have a particle size of 0.3 μm. 2 / g to 1.7 m 2 / g BET specific surface area.

18. The positive electrode active material for lithium secondary batteries according to claim 1, wherein the third positive electrode active material particles have a particle size of 0.5 μm. 2 / g to 1.5 m 2 / g BET specific surface area.

19. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material comprising the first positive electrode active material particles to the third positive electrode active material particles as a whole has a particle size of 0.1 μm. 2 / g to 5.0m 2 / g BET specific surface area.

20. A positive electrode for a lithium secondary battery, the positive electrode for the lithium secondary battery comprising: Positive current collector; and A positive electrode active material layer is formed on the positive electrode current collector and comprises the positive electrode active material according to any one of claims 1 to 19.

21. The positive electrode for a lithium secondary battery according to claim 20, wherein the positive electrode active material layer further comprises a binder and a conductive material.

22. A lithium secondary battery, the lithium secondary battery comprising: The positive electrode as described in claim 20; The negative electrode facing the positive electrode; and A membrane or electrolyte layer located between the positive electrode and the negative electrode.

23. The lithium secondary battery according to claim 22, wherein the lithium secondary battery further comprises an electrolyte including a lithium salt and a non-aqueous organic solvent.

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