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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery that can suppress particle breakage within the cathode and improve the density of the cathode while exhibiting the electrical and chemical properties characteristic of a manganese-rich cathode active material, a cathode including the same, and a lithium secondary battery.

Description

Technology Field

[0001] The present invention relates to a cathode active material for a lithium secondary battery that can suppress particle breakage within the cathode and improve the density of the cathode while exhibiting the electrical and chemical properties characteristic of a manganese-rich cathode active material, a cathode including the same, and a lithium secondary battery. Background Technology

[0002] Recently, as the application areas of lithium-ion batteries have rapidly expanded to include not only power supply for electronic devices such as electrical, electronic, telecommunications, and computers, but also power storage for large-area devices such as automobiles and power storage systems, there is a growing demand for high-capacity, high-output, and high-stability secondary batteries.

[0003] The above lithium secondary battery generally consists of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transporting lithium ions, and a separator. In this case, carbon-based active materials, silicon-based active materials, etc., may be used as the negative active material. Additionally, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel-cobalt-manganese composite oxide may be used as the positive active material.

[0004] Recently, lithium-rich manganese oxides have been attracting attention as next-generation cathode active materials. Lithium-rich manganese oxides have the advantage of high capacity due to their high content of manganese (Mn), which is relatively inexpensive and abundant. In particular, these lithium-rich manganese oxides can have superior competitiveness in terms of unit cost and energy density compared to high-nickel content lithium nickel-cobalt-manganese composite oxides, which are known to have high energy density.

[0005] However, since these lithium-rich manganese oxides have a compositional limitation of low rate characteristics, the structure is being controlled to increase the BET specific surface area of ​​the secondary particles by making the primary particles smaller in order to improve this.

[0006] However, the above-mentioned lithium manganese-rich oxide has a low density and a relatively large BET specific surface area compared to conventional cathode active materials, such as lithium nickel-cobalt-manganese composite oxide, and has the disadvantage of being easily broken.

[0007] In particular, during the process of manufacturing the cathode, such as through rolling, the above-mentioned lithium manganese-rich oxide particles may easily break, which can degrade their electrical and chemical properties, lower the density of the cathode, and increase the porosity, thereby lowering the overall energy density of the lithium secondary battery. Furthermore, since the thickness of the cathode may inevitably increase due to such low cathode density, this can also act as a limit in increasing the energy density of the battery.

[0008] In addition, since the above-mentioned lithium manganese-rich oxide can generate a relatively large amount of gas during the activation process of rock salt-like lithium manganese oxides contained therein, there is also a continuous demand for measures to reduce such gas generation. The problem to be solved

[0009] Accordingly, the present invention provides a cathode active material for a lithium secondary battery that exhibits the characteristic electrical and chemical properties of a manganese-rich cathode active material, while suppressing particle breakage within the cathode, improving cathode density, and reducing gas generation.

[0010] In addition, the present invention provides a positive electrode and a lithium secondary battery comprising the above-mentioned positive electrode active material, which exhibit high density and excellent electrical, chemical, and mechanical properties. means of solving the problem

[0011] According to one embodiment of the invention, a positive electrode active material comprising a lithium manganese-rich oxide having a layered crystal structure, wherein the molar ratio of lithium to the molar amount of all metals excluding lithium exceeds 1, and the manganese content among all metals excluding lithium is 50 mol% or more,

[0012] The above positive electrode active material comprises a lithium-rich manganese oxide and first and second positive electrode active material particles having different average particle sizes (D50), and

[0013] It comprises a third cathode active material particle comprising a lithium transition metal oxide containing nickel and cobalt, and manganese having a content smaller than that of the above-mentioned lithium manganese-rich oxide, and

[0014] When the volume cumulative particle size distribution of the above-mentioned positive active material is analyzed, a positive active material for a lithium secondary battery having a bi-modal particle size distribution due to the difference in particle size between the first positive active material particle and the second and third positive active material particles is provided.

[0015] In a specific example, the lithium-rich oxide included as a main component of the first and second positive electrode active material particles can be represented by the following chemical formula 1:

[0016] [Chemical Formula 1]

[0017] Li a [Mn b Ni c M d ] 2-a O2

[0018] In the above Chemical Formula 1, a is greater than 1, b is 0.5 or more and less than 1, and c and d are each 0 or more and 0.5 or less, provided that 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0019] In addition, according to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, comprising: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising a positive electrode active material of the first embodiment.

[0020] According to another embodiment of the invention, a lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte of the other embodiment is provided. Effects of the invention

[0021] Experimental results by the inventors confirmed that by controlling the particle size distribution of manganese-rich positive active material particles and using a positive active material having different average particle sizes (D50) and a bimodal particle size distribution in the particle size distribution analysis results, the breakage of positive active material particles during rolling can be significantly reduced.

[0022] Additionally, as the above-mentioned positive active material further includes positive active material particles in the form of a lithium nickel-cobalt-manganese composite oxide, the breaking of the positive active material particles can be further reduced, and the generation of gas during the activation process or charging and discharging processes can be further reduced.

[0023] In addition, by applying a positive electrode active material using the above-mentioned bimodal particle size distribution, the contact area with the electrolyte within the positive electrode can be improved and rate characteristics can be improved. Accordingly, the BET specific surface area of ​​each positive electrode active material particle can be kept small, and the breakage of the positive electrode active material particles can be further reduced.

[0024] Accordingly, by using a positive electrode active material of one embodiment having a bimodal particle size distribution, it is possible to manufacture a good positive electrode having high density and low porosity without particle breakage and reduced gas generation. Accordingly, by using a positive electrode active material of this one embodiment, it is possible to provide a next-generation lithium secondary battery having thin thickness, high density, excellent rate characteristics, and lifespan characteristics while exhibiting electrical and chemical properties such as the high capacity characteristic of manganese-rich positive electrode active materials. Brief explanation of the drawing

[0025] Figure 1 shows the volume cumulative particle size distribution curves for the cathode active materials of Preparation Example 1, Examples 1 and 2. Figure 2 shows the results of analyzing the amount of active gas generated for lithium secondary batteries prepared with the positive active materials of Comparative Example 1, Examples 1 and 2. Figure 3 shows the results of evaluating the lifespan characteristics of lithium secondary batteries prepared with the positive active materials of Comparative Example 1, Examples 1 and 2. Specific details for implementing the invention

[0026] The present invention will be described in more detail below.

[0027] In the following specifications, "lithium manganese-rich oxide" or "manganese-rich cathode active material" may refer to a lithium metal oxide having a layered crystal structure, wherein the molar ratio of lithium to the molar amount of all metals excluding lithium exceeds 1, and the manganese content among all metals excluding lithium is 50 mol% or more.

[0028] Additionally, "single particle" refers to a particle composed of a single nodule, and "pseudo-single particle" refers to a particle that is a composite formed of 30 or fewer nodules. However, unless otherwise noted in the present invention, "single particle" should be regarded as a comprehensive term that includes "pseudo-single particle."

[0029] In addition, "nodule" refers to a particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not apparent when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM).

[0030] Also, "primary particle" refers to a particle unit in which no grain boundaries appear when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope, and "secondary particle" refers to a particle formed by the aggregation of multiple primary particles.

[0031] In addition, "average particle size (D50)" refers to the particle size corresponding to 50% of the volume cumulative particle size distribution of the powder to be measured, and can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S-3500), irradiated with ultrasound of about 28 kHz at an output of 60 W, and then a volume cumulative particle size distribution graph is obtained, and the particle size at the point where the volume cumulative amount is 50% is determined from the obtained graph.

[0032] In addition, the "BET specific surface area" is measured by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the nitrogen adsorption isotherm obtained under a 77K liquid nitrogen atmosphere using BELSORP-MAX (MicrotracBEL corp.).

[0034] Meanwhile, the positive active material according to one embodiment of the invention may include first and second positive active material particles having different average particle sizes (D50), and the first and second positive active material particles each include a layered crystal structure, and may include a lithium manganese-rich oxide in which the molar ratio of lithium to the molar amount of all metals excluding lithium exceeds 1, and the manganese content among all metals excluding lithium is 50 mol% or more.

[0035] In a specific example, the lithium-over-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:

[0036] [Chemical Formula 1]

[0037] Li a [Mn b Ni c M d ] 2-a O2

[0038] In the above Chemical Formula 1, a is greater than 1, b is 0.5 or more and less than 1, and c and d are each 0 or more and 0.5 or less, provided that 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0039] In addition, the positive electrode active material of the above embodiment may further include a third positive electrode active material particle comprising a lithium transition metal oxide including nickel, cobalt, and manganese, together with the first and second positive electrode active material particles. In this case, the lithium transition metal oxide of the third positive electrode active material particle may be distinguished from the lithium manganese-rich oxide in that it contains a small amount of manganese compared to the lithium manganese-rich oxide, and, for example, the manganese is included in an amount of 40 mol% or less of the total metal excluding lithium.

[0040] In the positive electrode active material of this embodiment, the first and second positive electrode active material particles comprising the lithium-rich manganese oxide may each have the form of a secondary particle in which a plurality of primary particles are aggregated. Additionally, the third positive electrode active material particle comprising the lithium transition metal oxide including nickel, cobalt, and manganese may have the form of a single particle consisting of one nodule or a pseudo-single particle consisting of a complex of 30 or fewer nodules.

[0041] More specifically, in the positive active material of the above embodiment, the second and third positive active material particles may have similar average particle size (D50) and particle size distribution, and the first positive active material particle may have a larger average particle size (D50) than the second and third positive active material particles and a particle size distribution distinct from them.

[0042] As a result, when the volume cumulative particle size distribution of the positive active material of one embodiment is analyzed overall, a bimodal particle size distribution including multiple, for example, two peaks separated from each other may be exhibited. At this time, the bimodal particle size distribution can be defined and confirmed by the appearance of two separated peaks corresponding to the first positive active material particle and the second and third positive active material particles, respectively, in the volume cumulative particle size distribution curve of the positive active material of one embodiment.

[0043] Experimental results by the inventors confirmed that using the positive active material of one embodiment having the bimodal particle size distribution can suppress the breakage of the positive active material particles, particularly the breakage of particles during rolling. This is predicted to be because the stress applied to the particles during rolling, etc., can be effectively buffered by using the positive active material having the bimodal particle size distribution.

[0044] In addition, by applying a positive electrode active material using the above-mentioned bimodal particle size distribution, the contact area with the electrolyte within the positive electrode can be improved, and the rate characteristics can be improved in itself. Therefore, while solving the problem of low rate characteristics of existing lithium-rich manganese oxides, the BET specific surface area of ​​each positive electrode active material particle can be maintained small. For this reason, the breakage of the positive electrode active material particles can be further reduced.

[0045] Additionally, as the positive active material of the above embodiment further comprises a third positive active material particle in the form of a single particle (or similar-single particle) comprising a certain amount of lithium nickel-cobalt-manganese composite oxide together with the first and second positive active material particles comprising the lithium-manganese-rich oxide, the positive active material may exhibit a reduced amount of gas generation during the activation or charging and discharging process of the battery.

[0046] Accordingly, when using the cathode active material of one embodiment, a good cathode can be manufactured that exhibits high density, low porosity, thin thickness, and reduced gas generation without particle breakage. Therefore, by using the cathode active material of this embodiment, it is possible to provide a next-generation lithium secondary battery that has a thin thickness and high density while exhibiting electrical and chemical properties, such as high capacity and rate characteristics characteristic of manganese-rich cathode active materials.

[0048] Meanwhile, in the cathode material of the above embodiment, the over-lithium manganese-rich oxide included in the first and second cathode active material particles may have a molar ratio of lithium to the total number of moles of metals excluding lithium greater than 1, or 1.1 to 1.5, or 1.3 to 1.5. In one example, such a molar ratio of lithium may be calculated from the formula "a / (2-a)" in Chemical Formula 1. Additionally, in Chemical Formula 1, a is the molar ratio of Li in the over-lithium manganese-rich oxide, and a in Chemical 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.

[0049] As the range of a and the molar ratio of lithium to the remaining metal satisfy the range described above, the chemical and crystallographic stability of the first and second cathode active material particles can be maintained, while a higher capacity can be realized and excellent rate characteristics can be achieved. In addition, if the molar ratio of lithium to the remaining metal is excessively high, electrical conductivity may decrease and the rock salt phase (Li2MnO3) may increase, accelerating the degradation rate, and if it is too low, the effect of improving energy density may be negligible.

[0050] The above b is the molar ratio of Mn in the lithium-over-manganese-rich oxide, and in Chemical Formula 1, it can satisfy 0.5≤b<1, 0.5≤b≤0.9, or 0.55≤b≤0.8. As a result, excellent capacity characteristics unique to lithium-over-manganese-rich oxide can be exhibited.

[0051] The above c is the molar ratio of Ni in the lithium manganese-rich oxide, and 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 in the above formula 1.

[0052] The above d is the molar ratio of element M added to the lithium manganese-rich oxide or added in the form of doping, and in the above Chemical Formula 1, it may be 0≤d≤0.50, 0≤d<0.5, 0≤d≤0.2, or 0≤d≤0.1. If the content of the added element M is too high, it may not only adversely affect the capacity of the active material, but also increase the oxygen-redox reaction, which may lead to gas generation and intensify the degradation of the cathode active material, thereby potentially degrading the lifespan characteristics.

[0053] More suitable examples of the above M may be 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, and in a more specific embodiment, one or more selected from the group consisting of Co, Zn, Ti, Al, Mg, and B may be added to the above lithium manganese-rich oxide in the form of doping, etc.

[0054] In addition, in a specific embodiment, the lithium-rich manganese oxide may contain additional element M as a doping element only on the surface, and may contain a molar ratio of nickel to manganese of 25:75 to 50:50, or 25:75 to 45:55, or 30:70 to 40:60. Within the above ranges, if the molar ratio of manganese becomes excessively small, the proportion of rock salt phase may be insufficient, resulting in insufficient capacity or reduced crystallographic and chemical stability. Conversely, if the molar ratio of manganese becomes excessively large, the stability of the lithium-rich manganese oxide may also be reduced.

[0055] Meanwhile, in one example of the above chemical formula 1, b+c+d may satisfy 1, but in another example, it may have a value of 0.9 or higher and less than 1. The fact that b+c+d is less than 1 may indicate that the above chemical formula 1 contains additional metal elements in addition to manganese, nickel, and additional element M. However, it goes without saying that such additional metal elements may be added to the extent that they maintain the crystal structure characteristic of lithium-rich manganese oxide.

[0056] In a specific embodiment of the positive electrode active material of one embodiment, the lithium-over-manganese-rich oxide may be a compound represented by the following chemical formula 1a:

[0057] [Chemical Formula 1a]

[0058] Li a [Mn b Ni c M d ] 2-a O2

[0059] In the above chemical formula 1a, 1.1 <a<1.3이고, 0.5≤b≤0.9, 0.1≤c≤0.5이고, 0≤d≤0.1이고, 이고, M은 Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다.

[0060] Meanwhile, in the case of an over-lithium manganese-rich oxide containing an excess of lithium, it may contain a compound having a rock salt structure, e.g., Li2MnO3, and a compound having a layered structure, e.g., Li[NiwMnyMz]O2, in a mixed state. Accordingly, the over-lithium manganese-rich oxide may also be represented by the following chemical formula 2:

[0061] [Chemical Formula 2]

[0062] X*Li2MnO3·(1-X)*Li[NiwMnyMz]O2

[0063] In the above chemical formula 2,

[0064] 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, and 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, wherein 0 <w+z≤0.5임.

[0065] The above X represents the ratio of the rock salt phase (Li2MnO3 phase) in the lithium-rich manganese oxide, and the above w, y, and z represent the molar ratios of Ni, Mn, and additional element M in the layered structure compound, respectively.

[0066] In the above-mentioned lithium manganese-rich oxide, additional capacity characteristics may be exhibited due to the additional activation of the rock salt phase Li2MnO3. However, while the amount of gas generated may increase during this rock salt phase activation process, in one embodiment, the amount of gas generated may be reduced by replacing a portion of the second cathode active material particles having a relatively small particle size with third cathode active material particles in the form of single particles (or pseudo-single particles) containing lithium nickel-cobalt-manganese composite oxide.

[0067] Meanwhile, if necessary, a coating layer may be further included on the surface of the lithium-rich manganese oxide contained in the first and second positive electrode active material particles. In this case, contact between the lithium-rich manganese oxide and the electrolyte is suppressed by the coating layer, thereby reducing side reactions in the electrolyte and improving lifespan characteristics.

[0068] The above coating layer is, coating element M 1 It may include, and the coating element M 1 The coating element M may be, for example, at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. 1It may include two or more types, for example, Al and Co.

[0069] The above coating element is in the form of an oxide within the coating layer, i.e., M 1 It can exist as Oz (1 ≤ z ≤ 4).

[0070] The above coating layer can be formed through methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, it is preferable to form it through atomic layer deposition in that it can form a large coating layer area.

[0071] The area of ​​the coating layer formed above may be 10% to 100%, 30% to 100%, or 50% to 100% based on the total surface area of ​​the first and / or second positive active material particles containing the lithium-over-manganese-rich oxide. When the area of ​​the coating layer formed satisfies the above range, the effect of improving lifespan characteristics is excellent.

[0072] In addition, in the positive active material of the above embodiment, the first and second positive active material particles may include lithium manganese-rich oxides having the same or different compositions, and more specifically, may be represented by the same or different chemical formulas within the range of the above-described chemical formula 1 or 2.

[0073] Meanwhile, the third positive electrode active material particle may include a lithium transition metal oxide of the following chemical formula 3:

[0074] [Chemical Formula 3]

[0075] Li 1+p (Ni q Co r Mn s M 2 t )O2

[0076] In the above chemical formula 3, M 2is one or more selected from the group consisting 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, where 1+p, q, r, s, and t are the atomic fractions of independent elements, -0.2≤p≤0.2, 0.50≤q<1, 0 <r≤0.40, 0<s≤0.40, 0≤t≤0.10이다.

[0077] More specifically, in the above chemical formula 3, q, r, s, and t are respectively 0.50≤q<1, 0 <r≤0.30, 0<s≤0.30, 0≤t≤0.10을 만족할 수 있다. 또한, 구체적인 일 예에서, 상기 q+r+s+t=1의 값을 충족할 수 있지만, 다른 예에서 상기 q+r+s+t의 합이 0.9 이상 1 미만의 값을 가질 수도 있다. 상기 값이 1 미만으로 된다 함은 상기 화학식 3이 니켈, 코발트, 망간 및 M 2 In addition, it may be indicated that additional metal elements are included. However, it goes without saying that such additional metal elements may be added to the extent that the layered crystal structure characteristic of the above chemical formula 3 is maintained.

[0078] That is, in the third positive electrode active material particle, the lithium transition metal oxide may be a lithium nickel-cobalt-manganese composite oxide in which the nickel content among the total transition metals including nickel, cobalt, and manganese is 50 mol% or more, 60 mol% or more, or 80 mol% or more. In addition, the lithium transition metal oxide may contain manganese in a smaller amount than the over-lithium manganese-rich oxide, for example, 40 mol% or less, 35 mol% or less, 30 mol% or less, 20 mol% or less, or 15 mol% or less of manganese.

[0079] The above 1+p represents the molar ratio of lithium in the lithium transition metal oxide, which may be -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 particle can be stably formed.

[0080] The above q represents the molar ratio of nickel among the total metals excluding lithium in the lithium transition metal oxide, and may be 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, making it possible to realize high capacity.

[0081] The above r represents the molar ratio of cobalt among the total metals excluding lithium in the lithium transition metal oxide, where 0 <r≤0.20, 0<r≤0.15, 또는 0<r≤0.10일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0082] The above s represents the molar ratio of manganese among the total metals excluding lithium in the lithium transition metal oxide, where 0 <s≤0.20, 0<s≤0.15, 또는 0<s≤0.10 일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0083] In addition, the lithium transition metal oxide represented by Chemical Formula 3 may include one or more additional or doping elements selected from the group consisting 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, in which case it has the effect of suppressing structural degradation and improving high-temperature durability. Preferably, the lithium transition metal oxide represented by Chemical Formula 3 may include Al as a doping element. The t representing the molar ratio of such doping elements may be 0≤t≤0.08, 0≤t≤0.06, or 0≤t≤0.05.

[0084] Meanwhile, in the positive active material of the above-described embodiment, the first positive active material particle may have an average particle size (D50) of, for example, 7 to 20 μm, or 8 to 15 μm, or 8.5 to 11 μm, and the second positive active material particle may have an average particle size (D50) smaller than that, for example, 1 to 6 μm, or 2 to 5 μm, or 2.5 to 4.5 μm. In addition, the third positive active material particle may be smaller than the first positive active material particle and may have an average particle size (D50) in a range similar to that of the second positive active material particle, for example, 2 to 5 μm, or 2.5 to 4.5 μm.

[0085] As a result, stress applied during processes such as rolling can be more effectively relieved, further reducing breakage of the positive active material particles, and it becomes possible to provide a positive electrode with higher density and lower porosity.

[0086] In addition, in a specific embodiment of the invention, the first positive active material particle : the second and third positive active material particles may be included in the positive 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. By doing so, a positive electrode having a higher density and a lower porosity can be provided while maintaining the electrical and chemical properties characteristic of lithium-rich manganese oxide.

[0087] Meanwhile, if the average particle size (D50) of the first positive active material particle becomes excessively large, or if the average particle size (D50) of the second and third positive active material particles becomes excessively small, the electrical, chemical properties or mechanical properties of the positive active material of one embodiment may be degraded. Conversely, if the average particle size (D50) of the first positive active material particle becomes excessively small, or if the average particle size (D50) of the second and third positive active material particles becomes excessively large, the bimodal particle size distribution characteristics unique to the positive active material of one embodiment are not properly realized, and thus, particle breakage may occur during the rolling process, etc., or the density of the positive may not be sufficient.

[0088] Additionally, the third positive electrode active material particles may be included in an amount of 5 to 95 parts by weight, or 10 to 90 parts by weight, or 15 to 87 parts by weight, based on 100 parts by weight of the total of the second and third positive electrode active material particles. This allows for a reduction in the amount of gas generated during the activation or charging and discharging processes of the positive electrode active material, while maintaining electrical and chemical properties, such as the excellent capacity characteristics characteristic of lithium-rich manganese oxide.

[0089] Meanwhile, the positive active material of the above-described embodiment has an overall BET specific surface area of ​​0.1 m² while containing the first to third positive active material particles described above. 2 / g to 5.0m 2 / g, specifically 0.5m 2 / g to 3.0m 2 / g, more specifically 1.0m 2 / g to 2.0m 2 It can be / g.

[0090] In addition, the BET specific surface area of ​​the first cathode active material particle included in this cathode active material is 1.2 m 2 / g or more, preferably 1.3m 2 It may be greater than / g, which is desirable in that it enables the realization of high capacity and efficiency. However, considering electrode processability, large surface area, and issues such as increased surface side reactions and non-uniformity due to low sphericity, 4.0m 2 / g or less, or 3.0m 2 / g or less, or 2.0m 2 It may be less than / g. In addition, the BET specific surface area of ​​the second and third cathode active material particles may be smaller than that of the first cathode active material particle, and 0.3m 2 / g to 1.7m 2 / g, or 1.0m 2 / g to 1.5m 2 It may be / g, and the BET specific surface area of ​​the third cathode active material particle is 0.5m 2 / g to 1.5m 2 It can be / g.

[0091] The cathode active material of one embodiment includes first to third cathode active materials and has a bimodal particle size distribution, thereby securing a reaction area with the electrolyte and ensuring excellent capacity and rate characteristics. As a result, it can have the aforementioned low specific surface area, and particle breakage caused by rolling can be further reduced. In addition, as each specific surface area is optimized within the aforementioned range, the solid content of the slurry for forming the cathode active material layer can be optimized, and the amount of gas generated can be further reduced. However, if the aforementioned BET specific surface area is too low, it is difficult to achieve sufficient capacity due to insufficient reaction area with the electrolyte, and if the specific surface area is too high, moisture absorption is rapid and side reactions with the electrolyte are accelerated, making it difficult to secure lifespan characteristics.

[0092] The positive active material of the above-described embodiment, specifically the first and second positive active material particles, can be manufactured according to a general method for manufacturing lithium-rich manganese oxide. For example, each of the first and second positive active material particles can be manufactured by mixing a transition metal precursor containing manganese with a lithium raw material and then calcining it. Since the types of each precursor and raw material and the manufacturing conditions can follow the general manufacturing conditions for manganese-rich positive active materials, further explanation regarding this is omitted.

[0093] However, in this manufacturing process, the type or particle size of the transition metal precursor or the calcination temperature can be controlled to produce first and second positive active material particles that satisfy the average particle size (D50) described above, and the positive active material of one embodiment can be obtained by mixing them in a certain ratio. However, since the process conditions for manufacturing the positive active material to obtain a certain average particle size (D50) are obvious to those skilled in the art, further explanation regarding this is omitted.

[0094] Meanwhile, since the above-mentioned third cathode active material particles can be manufactured according to a general method for manufacturing single-particle lithium nickel-cobalt-manganese composite oxides that has been well known for some time, further explanation regarding this will be omitted.

[0095] Meanwhile, the positive active material of the above-described embodiment is mixed with a binder, a conductive material, a solvent, etc., to form a positive slurry, and this positive slurry is coated onto a positive current collector, dried, and rolled to produce a positive electrode. The positive slurry is described below.

[0096] First, the positive active material of the above-described embodiment may be included in an amount of 90% to 99% by weight, or 95% to 99% by weight, or 97% to 98% by weight, based on the total weight of the solids (e.g., positive active material, conductive material, and binder) in the positive slurry. If the content of the positive active material in the solids is 90% by weight or less, the energy density may be lowered, and the capacity may be reduced.

[0097] Additionally, the binder may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof, and preferably may be polyvinylidene fluoride (PVDF).

[0098] The binder may be included in an amount of 0.5% to 2.5% by weight, or 1% to 2% by weight, or 1.5% to 2% by weight, based on the total weight of the solid content in the anode slurry. When the content of the binder is within the above range, sufficient adhesion to the current collector and inter-particle bonding are secured, thereby improving the durability of the anode while maintaining a low initial resistance.

[0099] The conductive material may be one or more selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; carbon-based materials such as carbon fibers or carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and preferably carbon nanotubes or carbon black, most preferably carbon nanotubes.

[0100] The conductive material may be included in an amount of 0.1% to 2.5% by weight, or 0.3% to 2% by weight, or 0.5% to 1% by weight, based on the total weight of the solid content in the anode slurry. It is preferable that the content of the conductive material be within the above range in that it can reduce the dead volume while maintaining conductivity between active materials.

[0101] In addition, the anode slurry may optionally further include a dispersant, and the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0102] Meanwhile, the solvent of the anode slurry may be a solvent commonly used in the relevant technical field, for example, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethyl formamide (DMF), acetone, water, or a mixture of two or more of these may be used. The solvent may be used in an amount adjusted to achieve the viscosity of the anode slurry described above.

[0103] Meanwhile, according to another embodiment of the invention, a positive electrode comprising the positive electrode active material described above is provided. Such a positive electrode may be manufactured from the positive electrode slurry and may include, for example, 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 of one embodiment. In this case, the positive electrode active material layer may further include a binder and a conductive material by being formed by coating, drying, and rolling, etc., of the slurry described above.

[0104] The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0105] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the anode active material of the above-described embodiment. Specifically, it may be manufactured by applying the anode slurry onto an anode current collector and then drying and rolling it, or by casting the anode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto an anode current collector.

[0106] At this time, the coating and drying process of the anode slurry may be carried out in a general manner, taking into account the content of the solvent and solids contained therein, and the rolling process may be carried out, for example, by a tandem rolling method, by rolling continuously two or more times, or two to four times, or two to three times. At this time, during the first rolling, the process may proceed to 60% to 90% or 70% to 90% of the target thickness reduction, and during the second rolling, the process may proceed to 70% to 100% or 80% to 100% of the target thickness reduction. In addition, if rolling is carried out three or more times, the process may be carried out so that 100% of the target thickness reduction is achieved during the final rolling.

[0107] In a more specific example, to prevent electrode breakage or the like from occurring during the above rolling, the applied pressure during rolling can be 1.0 ton / cm to 3.0 ton / cm or 1.5 ton / cm to 2.8 ton / cm, and the process can be carried out by applying a uniform pressure overall.

[0108] Meanwhile, according to another embodiment of the invention, a lithium secondary battery comprising a positive electrode of the other embodiment described above is provided. Such a lithium secondary battery may include, for example, the positive electrode described above, a negative electrode facing the positive electrode, a separator or an electrolyte layer interposed between the positive electrode and the negative electrode, and optionally an electrolyte. In this case, since the positive electrode is the same as previously described, a detailed description is omitted, and only the remaining components are described in detail below.

[0109] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0110] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0111] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0112] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0113] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0114] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0115] The above-mentioned negative electrode active material layer may be manufactured by applying a negative electrode slurry, prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative electrode current collector.

[0116] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0117] Meanwhile, the lithium secondary battery may include the separator, but may also include an electrolyte layer separately from the separator, or include a laminate in which an electrolyte layer is laminated on the separator. In addition, in a specific example, the electrolyte layer may be a gel electrolyte layer containing a gel electrolyte or a solid electrolyte layer.

[0118] In a more specific example, the electrolyte layer including the gel electrolyte comprises, for example, a matrix including a polyurethane-based or polyacrylic-based 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, since the types of crosslinked polymers, lithium salts, and organic solvents that may be included in the gel electrolyte are obvious to those skilled in the art, further explanation regarding this is omitted.

[0119] In addition, in another specific example, the solid electrolyte layer may include one or more selected from the group consisting of any solid electrolyte, for example, polymer-based solid electrolytes, oxide-based solid electrolytes, sulfide-based solid electrolytes, and halogenated solid electrolytes. However, since the composition of such solid electrolyte layer may follow that of a general solid electrolyte layer known previously, further explanation is omitted.

[0120] Meanwhile, the above-described lithium secondary battery may further include an electrolyte comprising a lithium salt and a non-aqueous organic solvent.

[0121] The above-mentioned non-aqueous organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above-mentioned organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0122] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, as the anion of the above lithium salt, 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 - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt within the range of 0.1 to 4.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0123] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0124] Since the aforementioned lithium secondary battery stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0125] In addition, there are no special restrictions on the external shape of the above lithium secondary battery, but it may be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0126] In addition, the above-described lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also preferably be used as a unit cell in a medium-to-large battery module containing a plurality of battery cells.

[0127] Examples of the above-mentioned medium-to-large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but are not limited to these.

[0129] The present invention will be explained in more detail below through specific embodiments.

[0131] Manufacturing of cathode materials

[0132] The positive active materials A to C used in the following manufacturing examples, examples, and comparative examples each have the characteristics shown in Table 1 below.

[0133] Cho Seong-sik D50 (㎛) Particle form BET specific surface area (m 2 / g) Positive active material A Li 1.36 [Mr 0.65 Ni 0.35 ]O2 9.46 secondary particles 1.56 Positive active material B Li 1.36 [Mr 0.65 Ni 0.35 ]O2 3.77 secondary particles 1.28 Positive active material C Li 1.03 [Ni 0.60 Co 0.10 Mr 0.30 ]O2 3.74 single particle 0.87

[0134] Preparation Example 1.

[0135] A cathode material was prepared by mixing the above-mentioned cathode active material A, cathode active material B, and cathode active material C in a weight ratio of 65:5:30. The total BET specific surface area of ​​this cathode material is approximately 1.34 m². 2 It was confirmed as / g.

[0137] Comparative Manufacturing Example 1.

[0138] A cathode material was prepared by mixing the above-mentioned cathode active material A and cathode active material B in a weight ratio of 65:35. The total BET specific surface area of ​​this cathode material is approximately 1.46 m². 2 It was confirmed as / g.

[0140] Examples and Comparative Examples: Preparation of Anodes and Lithium Secondary Batteries

[0141] An anode slurry was prepared by mixing the anode material of the preparation example or comparative preparation example, carbon nanotube, PVDF binder, and HNBR-containing dispersant in N-methylpyrrolidone in a weight ratio of 97.46:0.62:1.7:0.22. The anode slurry was applied onto an aluminum current collector sheet, dried, and then rolled to produce an anode. Rolling was performed twice using a tandem rolling method. At this time, the linear pressure during rolling was varied as follows: 1.19 ton / cm + 1.14 ton / cm (Comparative Example 1; Cathode material: Comparative Manufacturing Example 1), 1.19 ton / cm + 2.59 ton / cm (Comparative Example 2; Cathode material: Comparative Manufacturing Example 1), 2.18 ton / cm + 2.28 ton / cm (Example 1; Cathode material: Manufacturing Example 1), and 2.96 ton / cm + 2.96 ton / cm (Example 2; Cathode material: Manufacturing Example 1).

[0142] A cathode slurry was prepared by mixing graphite cathode active material, single-walled carbon nanotube, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 96.2:0.8:2:1. The cathode slurry was applied onto a copper current collector sheet, dried, and then rolled to produce a cathode.

[0143] Meanwhile, the above anode and cathode were manufactured such that the ratio of the cathode discharge capacity to the anode discharge capacity (N / P ratio) was 115% by adjusting the loading amount.

[0144] An electrode assembly was manufactured by interposing a polyethylene separator between the anode and cathode manufactured as described above, and after inserting the electrode assembly into a battery case, an electrolyte was injected, and an activation process was performed by charging at 45°C with a constant current of 0.1C until the voltage reached 4.6V, and then discharging at a constant current of 0.1C until the voltage reached 2.0V to manufacture a lithium secondary battery.

[0146] Experimental Example 1: Analysis of Volume Cumulative Particle Size Distribution and Average Particle Size (D50) of Anode Active Material

[0147] First, regarding the powder of the cathode material included in the example or comparative example, a Particle Size Distribution (PSD) was obtained using Microtrac's S-3500. For reference, the PDS curve of the cathode material obtained in Preparation Example 1 is shown in FIG. 1. From this PDS curve, it was confirmed that the cathode material of Preparation Example 1 has a bimodal particle size distribution. In addition, the average particle size (50) of each cathode active material included in the cathode material was analyzed from the PDS curve, and the analysis results were as described in Table 1 above.

[0148] In addition, the PSD of the total cathode material contained in each cathode slurry prepared in the preparation example and comparative preparation example was analyzed in the same way and derived as pre-rolling data. From this, the volume ratio of particles having a particle size of 1 μm or less and the volume ratio of coarse particles (e.g., cathode active material A) among the cathode materials contained in the cathode slurry were evaluated, respectively.

[0150] Experimental Example 2: Evaluation of Volume Cumulative Particle Size Distribution and Particle Breakage Rate of Anode

[0151] The cathodes prepared in the above examples and comparative examples using the cathode material of the preparation example or comparative preparation example were heat-treated in a furnace at a temperature of 700°C for 10 hours to collect the cathode material, and then finely ground using a mortar and pestle, and classified using a 250 mesh sieve to obtain the cathode material powder contained in each cathode. For the obtained powder, the Particle Size Distribution (PSD) was obtained using a Microtrac S-3500. For reference, the Particle Size Distribution of the cathode material contained in the cathodes of Examples 1 and 2 is shown in Fig. 1, respectively. Through this, it was confirmed that the cathode material maintains a bimodal particle size distribution.

[0152] From this, the volume ratio of particles having a particle size of 1 μm or less and the volume ratio of large particles (e.g., cathode active material A) among the cathode materials included in the above cathode were evaluated, respectively. By comparing these data with the data obtained in Experimental Example 1, the extent to which the volume ratio of particles having a particle size of 1 μm or less and the volume ratio of large particles changed before and after rolling in the cathode manufactured through rolling was evaluated and is shown together in Table 2 below.

[0154] division Comparative Example 1 Comparative Example 2 Example 1 Example 2 Anode porosity (%) 30.8 27.5 26.0 23.5 Evaluation of particle breakage rate Volume ratio of particles smaller than 1㎛ (Anode after rolling; %) 9.6 13.7 0 0 Rate of change in alliteration volume ratio before / after rolling (%) 27.4% decrease 29.8% decrease 30.8% decrease 32.4% decrease

[0155] Referring to Table 2 above, it was confirmed that the cathodes of Examples 1 and 2, which used the cathode material of Manufacturing Example 1, did not substantially contain particles smaller than 1 μm, even though they were manufactured to have low porosity and high density by applying a very high pressure during rolling compared to Comparative Examples 1 and 2. This indicates that no breakage of small particles occurred in the cathode material. Furthermore, regarding the breakage ratio of large particles, it was confirmed that similar large particle breakage characteristics were exhibited despite the high pressure during rolling.

[0157] Experimental Example 3: Evaluation of Gas Generation Amount

[0158] For the lithium secondary batteries prepared in the Examples and Comparative Examples using the cathode materials of the above Manufacturing Example or Comparative Manufacturing Example, the gas generated after the activation process was collected, and the amount of gas generated was quantitatively analyzed using GC-FID / TCD. The analysis results of the amount of active gas generated for Comparative Example 1, Examples 1 and 2 are shown for comparison in Figure 2.

[0159] Referring to Figure 2 above, it was confirmed that the lithium secondary batteries of Examples 1 and 2 exhibited a reduced amount of gas generation compared to Comparative Example 1.

[0161] Experimental Example 4: Evaluation of Life Characteristics

[0162] For the lithium secondary batteries prepared in the Examples and Comparative Examples using the cathode materials of the above Preparation Example or Comparative Preparation Example, charge and discharge tests of 100 to 150 cycles were conducted at 45°C and a voltage of 2.5 to 4.35 V. While performing these charge and discharge cycles, the energy retention rates of Comparative Example 1, Examples 1 and 2 were evaluated and are shown in FIG. 3.

[0163] Referring to Fig. 3, it was confirmed that the lithium secondary battery of the example exhibits a higher energy retention rate after 100 to 150 charge and discharge cycles compared to the comparative example, and shows improved lifespan characteristics.

Claims

Claim 1 A positive electrode active material comprising a lithium manganese-rich oxide having a layered crystal structure, wherein the molar ratio of lithium to the total number of moles of metals excluding lithium exceeds 1, and wherein manganese is included in an amount of 50 mol% or more among the total metals excluding lithium; wherein the positive electrode active material comprises first and second positive electrode active material particles having different average particle sizes (D50) and a lithium transition metal oxide containing a manganese content smaller than that of the lithium manganese-rich oxide, nickel, and cobalt; wherein when the positive electrode active material is analyzed for volume cumulative particle size distribution, it has a bi-modal particle size distribution due to the difference in particle size between the first positive electrode active material particle and the second and third positive electrode active material particles; wherein the first and second positive electrode active material particles have a secondary particle form in which a plurality of primary particles are aggregated; and the third positive electrode active material particle is composed of a single nodule A positive electrode active material for a lithium secondary battery having a quasi-monopole form, which is a single particle or a complex of 30 or fewer nodules. Claim 2 In claim 1, the lithium-over-manganese-rich oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1]Li a [Mn b Ni c M d ] 2-a O2 In the above chemical formula 1, a is greater than 1, b is 0.5 or more and less than 1, and c and d are each 0 or more and 0.5 or less, wherein 0 <c+d≤0.5이고, M은 Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다. Claim 3 In claim 1, the above-mentioned lithium manganese-rich oxide is a positive electrode active material for a lithium secondary battery having a molar ratio of lithium to the total number of moles of metals excluding lithium of 1.3 to 1.

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

50. Claim 5 In claim 1, the lithium-over-manganese-rich oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1a: [Chemical Formula 1a]Li a [Mn b Ni c M d ] 2-a O2 In the above chemical formula 1a, 1.1 <a<1.3이고, 0.5≤b≤0.9, 0.1≤c≤0.5이고, 0≤d≤0.1이고, 이고, M은 Co, Cr, V, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr 및 Zr로 이루어진 군에서 선택된 하나 이상이다. Claim 6 In claim 1, the lithium-rich manganese-rich oxide is a positive electrode active material for a lithium secondary battery comprising a rock salt structure compound and a layered structure compound in a mixed state. Claim 7 In claim 5, the above-mentioned lithium manganese-rich oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 2: [Chemical Formula 2]X*Li2MnO3·(1-X)*Li[NiwMnyMz]O2, wherein 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, and 0.2≤X≤0.5, 0≤w≤0.5, 0.4≤y<1, 0≤z≤0.2, and 0 <w+z≤0.5임. Claim 8 In claim 1, the third positive electrode active material particle is a positive electrode active material for a lithium secondary battery comprising a lithium transition metal oxide of the following chemical formula 3: [Chemical Formula 3]Li 1+p (Ni q Co r Mn s M 2 t )O2 In the above chemical formula 3, M 2 is one or more selected from the group consisting 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 -0.2≤p≤0.2, 0.30≤q<1, 0 <r≤0.40, 0<s≤0.40, 0≤t≤0.10이다. Claim 9 delete Claim 10 delete Claim 11 A positive active material for a lithium secondary battery according to claim 1, wherein the first positive active material particle has an average particle size (D50) of 7 to 20 μm and has an average particle size (D50) larger than that of the second and third positive active material particles. Claim 12 In claim 11, the second positive active material particle is a positive active material for a lithium secondary battery having an average particle size (D50) of 1 to 6 μm. Claim 13 In claim 11, the third positive active material particle is a positive active material for a lithium secondary battery having an average particle size (D50) of 2 to 5 μm. Claim 14 A positive active material for a lithium secondary battery according to claim 1, wherein the first positive active material particle : the second and third positive active material particles are included in a weight ratio of 55 : 45 to 95 :

5. Claim 15 In claim 14, the third positive active material particle is a positive active material for a lithium secondary battery, comprising an amount of 5 to 95 parts by weight per 100 parts by weight of the total of the second and third positive active material particles. Claim 16 In claim 1, the first positive electrode active material particle is 1.2 m 2 / g to 4.0m 2 A positive electrode active material for a lithium secondary battery having a BET specific surface area of ​​ / g. Claim 17 In claim 1, the second positive active material particle is 0.3m 2 / g to 1.7m 2 A positive electrode active material for a lithium secondary battery having a BET specific surface area of ​​ / g. Claim 18 In claim 1, the third positive electrode active material particle is 0.5m 2 / g to 1.5m 2 A positive electrode active material for a lithium secondary battery having a BET specific surface area of ​​ / g. Claim 19 In claim 1, the positive active material including the first to third positive active material particles is 0.1 m in total. 2 / g to 5.0m 2 A positive electrode active material for a lithium secondary battery having a BET specific surface area of ​​ / g. Claim 20 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 a positive electrode active material according to any one of claims 1 to 8 and claims 11 to 19. Claim 21 In claim 20, the positive active material layer further comprises a binder and a conductive material, a positive electrode for a lithium secondary battery. Claim 22 A lithium secondary battery comprising: a positive electrode according to claim 20; a negative electrode facing the positive electrode; and a separator or electrolyte layer interposed between the positive electrode and the negative electrode. Claim 23 A lithium secondary battery according to claim 22, further comprising an electrolyte including a lithium salt and a non-aqueous organic solvent.

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