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

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a positive electrode and a lithium secondary battery, both comprising same, wherein the positive electrode active material is capable of suppressing particle breakage in a positive electrode and improving the density of the positive electrode while exhibiting unique electrical and chemical properties of a manganese-rich positive electrode active material.

Description

Cathode active material, cathode containing same, and lithium secondary battery

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0108198, filed August 13, 2024, and Korean Patent Application No. 10-2025-0103869, filed July 30, 2025, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a cathode active material for a lithium secondary battery, which exhibits the electrical and chemical properties unique to a manganese-rich cathode active material, while also suppressing particle breakage in the cathode and improving the density of the cathode, and to a cathode and a lithium secondary battery including the same.

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

[0005] The above lithium secondary battery is generally composed of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte that serves as a medium for transferring lithium ions, and a separator. At this time, carbon-based active materials, silicon-based active materials, etc. can be used as the negative electrode active material. In addition, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium nickel-cobalt-manganese composite oxide can be used as the positive electrode active material.

[0006] Recently, lithium manganese-rich oxide (LiMn-rich oxide) has been attracting attention as a next-generation cathode active material. LiMn-rich oxide boasts high capacity due to its high manganese content, which is relatively inexpensive and abundant. However, LiMn-rich oxide has a compositional limitation that leads to low rate characteristics. To improve this, the structure is being controlled by making the primary particles smaller and increasing the BET surface area of ​​the secondary particles.

[0007] However, the above lithium manganese rich oxide has a low density and a relatively large BET surface area compared to existing cathode active materials, such as lithium nickel-cobalt-manganese composite oxide, and thus has the disadvantage of being easily broken.

[0008] In particular, during the rolling process and other processes during the manufacture of the positive electrode, the lithium manganese-rich oxide particles may be easily broken, thereby deteriorating their electrical and chemical properties, lowering the density of the positive electrode and increasing its porosity, which may lower the overall energy density of the lithium secondary battery. In addition, the thickness of the positive electrode may inevitably increase due to such low positive electrode density, which may also act as a limitation in increasing the energy density of the battery.

[0009] Accordingly, the present invention provides a cathode active material for a lithium secondary battery that can suppress particle breakage in the cathode and improve the density of the cathode while exhibiting the electrical and chemical properties unique to a manganese-rich cathode active material.

[0010] In addition, the present invention provides a positive electrode and a lithium secondary battery including the positive electrode active material, which exhibit high density and excellent electrical, chemical and mechanical properties.

[0011] According to one embodiment of the invention, a cathode active material comprising a lithium manganese rich oxide having a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeding 1, and manganese in a content of 50 mol% or more among all metals excluding lithium,

[0012] The above positive electrode active materials have different average particle diameters (D50) and include first positive electrode active material particles and second positive electrode active material particles each including the lithium manganese rich oxide,

[0013] When the volume cumulative particle size distribution of the above positive electrode active material is analyzed, a positive electrode active material for a lithium secondary battery having a bi-modal particle size distribution is provided.

[0014] In these positive electrode active materials, the lithium manganese rich oxide, which is the main component of the first and second positive electrode active material particles, can be represented by the following chemical formula 1:

[0015] [Chemical Formula 1]

[0016] Li a [Mn b Ni c M d ] 2-a O2

[0017] In the above 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, but 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.

[0018] In addition, according to another embodiment of the invention, a positive electrode for a lithium secondary battery is provided, including: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material of one embodiment.

[0019] According to another embodiment of the invention, a lithium secondary battery is provided, including a positive electrode; a negative electrode; and an electrolyte of the other embodiment.

[0020] As a result of the experiments of the present inventors, it was confirmed that by controlling the particle size distribution of manganese-rich positive electrode active material particles, and using positive electrode active materials having different average particle diameters (D50) and having a bi-modal particle size distribution as shown in the particle size distribution analysis results, breakage of positive electrode active material particles during rolling can be significantly reduced.

[0021] In particular, by applying a positive electrode active material using the above bimodal particle size distribution, the contact area with the electrolyte within the positive electrode can be improved, and the rate characteristics can be enhanced. Accordingly, the BET specific surface area of ​​each positive electrode active material particle can be maintained small, and the breakage of the positive electrode active material particles can be further reduced.

[0022] Therefore, by using a manganese-rich cathode active material having a bimodal particle size distribution, a good cathode having high density, low porosity, and excellent rate characteristics can be manufactured without particle breakage. Therefore, by using the cathode active material of this embodiment, a next-generation lithium secondary battery can be provided that exhibits electrical and chemical characteristics, such as high capacity characteristics unique to manganese-rich cathode active materials, while also having a thin thickness, high density, and excellent rate characteristics.

[0023] Figure 1 shows the volume cumulative particle size distribution curves for the positive electrode active materials of Example 1, Example 2, and Comparative Example 1.

[0024] Hereinafter, the present invention will be described in more detail.

[0025] In the following specification, “lithium manganese rich oxide” or “manganese rich positive electrode active material” may refer to a lithium metal oxide having a layered crystal structure, a molar ratio of lithium to the molar number of total metals excluding lithium exceeding 1, and containing manganese in an amount of 50 mol% or more among total metals excluding lithium.

[0026] In addition, "primary particle" means a particle unit that has no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope, and "secondary particle" means a particle formed by the aggregation of multiple primary particles.

[0027] In addition, the "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 a laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S-3500), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and finding the particle size at the point where the volume cumulative amount is 50% from the obtained graph.

[0028] In addition, the "BET specific surface area" is measured by the BET (Brunauer-Emmett-Teller) method, and can be specifically calculated from a nitrogen adsorption isotherm obtained under a 77K liquid nitrogen atmosphere using BELSORP-MAX (MicrotracBEL corp.).

[0029]

[0030] Meanwhile, the cathode active material according to one embodiment of the invention may include first and second cathode active material particles having different average particle diameters (D50), and each of the first and second cathode active material particles may include a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeds 1, and a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more among all metals excluding lithium.

[0031] In a specific example, the lithium manganese rich oxide, which is a main component of the first and second positive electrode active material particles, may be a compound represented by the following chemical formula 1:

[0032] [Chemical Formula 1]

[0033] Li a [Mn b Ni c M d ] 2-a O2

[0034] In the above 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, but 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.

[0035] The cathode active material of one embodiment including these first and second cathode active material particles may each have a form of secondary particles in which a plurality of primary particles are aggregated, and when the cathode active material of one embodiment is analyzed for a volume cumulative particle size distribution as a whole, it may exhibit a bimodal particle size distribution including a plurality of, for example, two peaks that are separated from each other. In this case, the bimodal particle size distribution may be defined and confirmed as two separated peaks corresponding to the first and second cathode active material particles, respectively, appearing in the volume cumulative particle size distribution curve of the cathode active material of one embodiment.

[0036] The inventors' experimental results have confirmed that by using an embodiment of a positive electrode active material having the above-described bimodal particle size distribution, breakage of positive electrode active material particles, particularly breakage of particles during rolling, can be suppressed. This is expected to be because the use of a positive electrode active material having the above-described bimodal particle size distribution effectively buffers stress applied to particles during rolling, etc.

[0037] Furthermore, the application of a cathode active material utilizing the above-described bimodal particle size distribution can enhance the contact area with the electrolyte within the cathode, thereby improving the rate characteristics itself. Therefore, the low rate characteristics, a problem of existing lithium manganese-rich oxides, can be resolved, while maintaining a small BET specific surface area of ​​each cathode active material particle. Consequently, the breakage of the cathode active material particles can be further reduced.

[0038] Therefore, when using the cathode active material of one embodiment, a good cathode having high density, low porosity, and thin thickness can be manufactured without particle breakage. Therefore, by using the cathode active material of this embodiment, a next-generation lithium secondary battery can be provided that exhibits electrical and chemical properties, such as high capacity characteristics characteristic of manganese-rich cathode active materials, while also having thin thickness, high density, and excellent rate characteristics.

[0039]

[0040] Meanwhile, in the cathode material of the above embodiment, the 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 metal excluding lithium of greater than 1, or 1.1 to 1.5, or 1.3 to 1.5. In one example, the molar ratio of lithium may be calculated from the equation "a / (2-a)" in the above chemical formula 1. In addition, in the above chemical formula 1, a is a molar ratio of Li in the lithium manganese rich oxide, and a in the above 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.

[0041] As the molar ratio of lithium to the above-described a and the remaining metal satisfies the above-described range, the chemical and crystallographic stability of the first and second positive electrode active material particles can be maintained, while a higher capacity can be realized and the rate characteristics can be excellent. In addition, if the molar ratio of lithium to the remaining metal is excessively high, the electrical conductivity may decrease and the rock salt phase (Li2MnO3) may increase, which may accelerate the degradation rate, and if it is too low, the effect of improving the energy density may be minimal.

[0042] The above b is the molar ratio of Mn in the lithium manganese rich oxide, and can satisfy 0.5≤b<1, 0.5≤b≤0.9, or 0.55≤b≤0.8 in the above chemical formula 1. As a result, the excellent capacity characteristics unique to the lithium manganese rich oxide can be exhibited.

[0043] The above c is the molar ratio of Ni in the lithium manganese rich oxide, and can satisfy 0≤c≤0.5, 0≤c<0.5, 0.1≤c≤0.5, 0.1≤c≤0.45, or 0.3≤c≤0.4 in the above chemical formula 1.

[0044] The above d is a molar ratio of element M added to the lithium manganese rich oxide or added in the form of doping, etc., and may be 0≤d≤0.5, 0≤d<0.5, 0≤d≤0.2, or 0≤d≤0.1 in the above chemical formula 1. If the content of the additional element M is too high, not only may it have a negative effect on the capacity of the active material, but there is also a concern that the life characteristics may be deteriorated due to the increased oxygen-redox reaction, which may aggravate gas generation and deterioration of the positive electrode active material.

[0045] A more suitable example of the above M may be at least one 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, at least one selected from the group consisting of Co, Zn, Ti, Al, Mg and B may be added to the lithium manganese rich oxide in the form of doping or the like.

[0046] In addition, in a specific embodiment, the lithium manganese-rich oxide may contain additional elements M or the like only on the surface in the form of doping elements, and may contain nickel: manganese in a molar ratio of 25:75 to 50:50, or 25:75 to 45:55, or 30:70 to 40:60. In the above-described range, if the molar ratio of manganese is excessively small, the proportion of the rock salt phase may not be sufficient, resulting in insufficient capacity or deterioration of crystallographic and chemical stability. Conversely, if the molar ratio of manganese is excessively large, the stability of the lithium manganese-rich oxide may be deteriorated.

[0047] 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 greater than or equal to 0.9 and less than 1. The fact that b+c+d is less than 1 may indicate that the above chemical formula 1 further includes an additional metal element in addition to manganese, nickel, and the additional element M. However, it is of course understood that such additional metal elements may be added within the limit of maintaining the crystal structure characteristic of the lithium manganese-rich oxide.

[0048] In a specific embodiment of the positive active material of one embodiment, the lithium manganese rich oxide may be a compound represented by the following chemical formula 1a:

[0049] [Chemical Formula 1a]

[0050] Li a [Mn b Ni c M d ] 2-a O2

[0051] In the above chemical formula 1, 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.

[0052] Meanwhile, in the case of a lithium-rich peroxide containing an excess of lithium, a compound having a rock salt structure, for example, Li2MnO3, and a compound having a layered structure, for example, Li[NiwMnyMz]O2, may be mixed together. Accordingly, the lithium-rich peroxide may be represented by the following chemical formula 2:

[0053] [Chemical Formula 2]

[0054] X*Li2MnO3·(1-X)*Li[NiwMnyMz]O2

[0055] In the above chemical formula 2,

[0056] M is at least one 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, but 0 <w+z≤0.5임.

[0057] The above X represents the ratio of the rock salt phase (Li2MnO3 phase) in the lithium manganese rich 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.

[0058] Meanwhile, if necessary, a coating layer may be further included on the surface of the lithium manganese-rich oxide. In this case, the coating layer suppresses contact between the lithium manganese-rich oxide and the electrolyte, thereby reducing electrolyte side reactions and improving life characteristics.

[0059] The above coating layer comprises a coating element M 1 may include the coating element M 1 For example, the coating element M may be 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 contain two or more kinds, for example, it may contain Al and Co.

[0060] The above coating element is in the form of oxide within the coating layer, i.e., M 1 It can exist as Oz(1≤z≤4).

[0061] 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, formation through atomic layer deposition is preferable because it can form a large coating layer area.

[0062] The formation area of ​​the above coating layer 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 electrode active material particles including the lithium manganese-rich oxide. When the formation area of ​​the coating layer satisfies the above range, the effect of improving the life characteristics is excellent.

[0063] Meanwhile, in the positive electrode active material of the above embodiment, the first and second positive electrode active material particles may include lithium manganese rich oxide having the same or different compositions, and more specifically, may be represented by chemical formulas that are the same or different from each other within the range of the above-described chemical formula 1 or 2.

[0064] In addition, the first positive electrode active material particles may have an average particle diameter (D50) of, for example, 7 to 20 μm, or 8 to 15 μm, or 8.5 to 11 μm, and the second positive electrode active material particles may have an average particle diameter (D50) smaller than this, for example, 1 to 6 μm, or 2 to 5 μm, or 2.5 to 4.5 μm.

[0065] In this way, the stress applied during processes such as rolling can be more effectively relieved, thereby further reducing breakage of positive electrode active material particles, and providing a positive electrode with higher density and lower porosity becomes possible.

[0066] In addition, in a specific embodiment of the invention, the first cathode active material particle: the second cathode active material particle may be included in the cathode active material at 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. As a result, a cathode having a higher density and lower porosity can be provided while maintaining the electrical and chemical properties unique to lithium manganese-rich oxide.

[0067] Meanwhile, if the average particle diameter (D50) of the first positive electrode active material particles becomes excessively large or the average particle diameter (D50) of the second positive electrode active material particles becomes excessively small, the electrical, chemical or mechanical properties of the positive electrode active material of one embodiment may deteriorate. Conversely, if the average particle diameter (D50) of the first positive electrode active material particles becomes excessively small or the average particle diameter (D50) of the second positive electrode active material particles becomes excessively large, the bimodal particle size distribution characteristic unique to the positive electrode active material of one embodiment may not be properly implemented, and thus, particle breakage may occur during the rolling process, or the density of the positive electrode may not be sufficient.

[0068] Meanwhile, the positive electrode active material of the above embodiment has a total BET specific surface area of ​​0.1 m including the first and second positive electrode 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 / g may be.

[0069] In addition, the BET specific surface area of ​​the first cathode active material particles included in these cathode active materials is 1.2 m 2 / g or more, preferably 1.3m 2 / g or more, which is desirable in that it can realize high capacity and efficiency. However, considering the electrode processability, large surface area, low sphericity, surface side reactions, and increased non-uniformity, 4.0 m 2 / g or less, or 3.0m 2 / g or less, or 2.0m 2 / g or less. In addition, the BET specific surface area of ​​the second positive electrode active material particles may be smaller than that of the first positive electrode active material particles, and specifically, 0.3 m 2 / g to 1.7m 2 / g, or 1.0m 2 / g to 1.5m 2 / g may be.

[0070] The cathode active material of one embodiment has a bimodal particle size distribution including the first and second cathode active materials, thereby securing a reaction area with the electrolyte itself and securing excellent capacity and rate characteristics. As a result, it can have the low specific surface area described above, and particle breakage due to rolling can be further reduced. In addition, as each specific surface area is optimized within the above-described range, the solid content of the slurry for forming the cathode active material layer can be optimized, and the amount of gas generation can be further reduced. However, if the BET specific surface area described above is too low, the reaction area with the electrolyte is insufficient, making it difficult to implement sufficient capacity, 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 life characteristics.

[0071] The cathode active material of the above-described embodiment, specifically, the first and second cathode active material particles, can be manufactured according to a general manufacturing method for lithium manganese-rich oxide. For example, each of the first and second cathode active material particles can be manufactured by mixing a transition metal precursor including manganese and a lithium raw material and then calcining them. Since the types and manufacturing conditions of each precursor and raw material can be in accordance with the manufacturing conditions of a general manganese-rich cathode active material, further description thereof will be omitted.

[0072] However, in the manufacturing process, by controlling the type or particle size of the transition metal precursor, or controlling the firing temperature, etc., the first and second positive electrode active material particles satisfying the above-described average particle size (D50) can be manufactured, and these can be mixed at a certain ratio to obtain the positive electrode active material of one embodiment. However, since the process conditions for manufacturing the positive electrode active material to obtain a certain average particle size (D50) are well known to those skilled in the art, further description thereof will be omitted.

[0073] Meanwhile, the positive electrode active material of the above-described embodiment is mixed with a binder, a conductive agent, a solvent, etc. to form a positive electrode slurry, and this positive electrode slurry is coated on a positive electrode current collector, dried, and rolled to produce a positive electrode. Hereinafter, this positive electrode slurry will be described.

[0074] First, the positive electrode active material of the above-described embodiment may be included in an amount of 90 wt% to 99 wt%, or 95 wt% to 99 wt%, or 97 wt% to 98 wt%, based on the total weight of the solid content (e.g., positive electrode active material, conductive agent, and binder) in the positive electrode slurry. If the content of the positive electrode active material in the solid content is 90 wt% or less, the energy density may be lowered, resulting in a decrease in capacity.

[0075] In addition, the binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, 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 polyvinylidene fluoride (PVDF).

[0076] The above binder may be included in an amount of 0.5 wt% to 2.5 wt%, or 1 wt% to 2 wt%, or 1.5 wt% to 2 wt%, based on the total weight of the solid content in the positive electrode slurry. When the content of the binder is within the above range, sufficient adhesion to the current collector and bonding between particles can be secured, thereby improving the durability of the positive electrode while maintaining a low initial resistance.

[0077] The conductive material may be at least one 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, and summer black; carbon-based materials such as carbon fibers and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and preferably carbon nanotubes or carbon black, and most preferably carbon nanotubes.

[0078] The conductive agent may be included in an amount of 0.1 wt% to 2.5 wt%, or 0.3 wt% to 2 wt%, or 0.5 wt% to 1 wt%, based on the total weight of the solid content in the positive electrode slurry. When the content of the conductive agent is within the above range, it is preferable in that the dead volume can be reduced while maintaining conductivity between active materials.

[0079] In addition, the above cathode slurry may optionally further include a dispersant, and the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0080] Meanwhile, the solvent of the positive electrode slurry may be a solvent generally used in the relevant technical field, and examples thereof include N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethyl formamide (DMF), acetone, water, or a mixture of two or more thereof. The solvent may be used in an amount adjusted to have the viscosity of the positive electrode slurry described above.

[0081] Meanwhile, according to another embodiment of the invention, a positive electrode comprising the positive electrode active material described above is provided. The positive electrode can 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 is formed by coating, drying, rolling, etc. of the slurry described above, and may further include a binder and a conductive material.

[0082] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and is non-reactive within the voltage range of the battery. The positive electrode 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. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0083] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material of the above-described embodiment is used. Specifically, the positive electrode can be manufactured by applying the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode slurry onto a separate support, then peeling the support, and laminating the resulting film onto a positive electrode current collector.

[0084] At this time, the coating and drying process of the positive electrode slurry can be carried out in a general manner considering the contents of the solvent and solids contained therein, and the rolling process can be carried out in a manner of continuously rolling two or more times, or 2 to 4 times, or 2 to 3 times, for example, by a tandem rolling method. At this time, the first rolling can be carried out to 60% to 90%, or 70% to 90% of the target thickness reduction, and the second rolling can be carried out to 70% to 100%, or 80% to 100% of the target thickness reduction. In addition, when rolling is carried out three or more times, it can be carried out so that 100% of the target thickness reduction is achieved at the final rolling.

[0085] In a more specific example, in order to prevent electrode breakage, etc. from occurring during the rolling, the pressure applied during the rolling may be 1.0 ton / cm to 2.0 ton / cm, and the rolling may be performed by applying a uniform pressure throughout.

[0086] Meanwhile, according to another embodiment of the invention, a lithium secondary battery is provided that includes the positive electrode of the other embodiment described above. Such a lithium secondary battery may include, for example, the positive electrode described above, an anode facing the positive electrode, a separator or 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 described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0087] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0088] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0089] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0090] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloy, Sn alloy, or Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 <β< 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds 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. In addition, a metallic lithium thin film may be used as the negative electrode active material. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0091] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0092] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; 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; and conductive materials such as polyphenylene derivatives.

[0093] The above negative electrode active material layer can be manufactured by applying and drying 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 on a negative electrode current collector, or by casting the negative electrode slurry on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0094] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0095] Meanwhile, the lithium secondary battery may include the separator, but may also include an electrolyte layer separately from the separator, or may include a laminate in which an electrolyte layer is laminated on the separator. In a specific example, the electrolyte layer may be a gel electrolyte layer including a gel electrolyte, or a solid electrolyte layer.

[0096] In a more specific example, the electrolyte layer including the gel electrolyte may include a matrix including, for example, a polyurethane-based or polyacrylic-based cross-linked 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 cross-linked polymers, lithium salts, and organic solvents that may be included in the gel electrolyte are apparent to those skilled in the art, further description thereof will be omitted.

[0097] In addition, in another specific example, the solid electrolyte layer may include any solid electrolyte, for example, at least one selected from the group consisting of a polymer-based solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and a halogenated solid electrolyte. However, since the composition of the solid electrolyte layer may be based on a general solid electrolyte layer known in the past, further description is omitted.

[0098] Meanwhile, the lithium secondary battery described above may further include an electrolyte including a lithium salt and a non-aqueous organic solvent.

[0099] The above non-aqueous organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes 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 hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, 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 linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0100] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is 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 selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 4.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0101] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0102] The lithium secondary battery described above exhibits excellent discharge capacity, output characteristics, and stable life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0103] In addition, there is no particular limitation on the external shape of the lithium secondary battery, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0104] In addition, the lithium secondary battery described above can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0105] Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0106]

[0107] Hereinafter, the present invention will be described in more detail through specific examples.

[0108]

[0109] <Example - Manufacturing of positive electrode material>

[0110] The positive electrode active materials A to D used in the following examples and comparative examples each have the characteristics shown in Table 1 below.

[0111] Composition D50 (㎛) Particle shape BET specific surface area (m 2 / g) Anode active material ALi 1.36 [Mn 0.65 Ni 0.35 ]O29.462nd particle 1.56positive electrode active material BLi 1.36 [Mn 0.65 Ni 0.35 ]O29.502 secondary particle 1.53 Cathode active material CLi 1.36 [Mn 0.65 Ni 0.35 ]O23.772nd particle 1.28Cathode active material DLi 1.36 [Mn 0.65 Ni 0.35 ]O23.762nd particle 1.39

[0112] Example 1.

[0113] The positive electrode material was manufactured by mixing the positive electrode active material A and the positive electrode active material C in a weight ratio of 65:35. The overall BET specific surface area of ​​this positive electrode material was approximately 1.46 m 2 / g was confirmed.

[0114]

[0115] Example 2.

[0116] The positive electrode material was manufactured by mixing the positive electrode active material B and the positive electrode active material D in a weight ratio of 50:50. The overall BET specific surface area of ​​this positive electrode material was approximately 1.46 m 2 / g was confirmed.

[0117]

[0118] Comparative Example 1.

[0119] As a cathode material, only the cathode active material A was used alone.

[0120]

[0121] Comparative Example 2.

[0122] The positive electrode material was manufactured by mixing the positive electrode active material A and positive electrode active material B in a weight ratio of 65:35. The overall BET specific surface area of ​​this positive electrode material was approximately 1.55 m 2 / g was confirmed.

[0123]

[0124] Manufacturing example: Manufacturing of cathode and lithium secondary battery

[0125] A cathode slurry was prepared by mixing a cathode material of an example or comparative example: carbon nanotube: PVDF binder: dispersant including HNBR in a weight ratio of 97.46:0.62:1.7:0.22 in N-methylpyrrolidone. The cathode slurry was applied onto an aluminum current collector sheet, dried, and then rolled at a pressure of about 1.5 ton / cm to prepare a cathode.

[0126] Graphite negative electrode active material: single-walled carbon nanotube: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96.2:0.8:2:1 in water to prepare a negative electrode slurry. The negative electrode slurry was applied onto a copper current collector sheet, dried, and then rolled to prepare a negative electrode.

[0127] Meanwhile, the positive and negative electrodes were manufactured by adjusting the loading amount so that the ratio of the negative electrode discharge capacity to the positive electrode discharge capacity (N / P ratio) was 115%.

[0128] An electrode assembly was manufactured by interposing a polyethylene separator between the positive and negative electrodes manufactured as described above, inserting the electrode assembly into a battery case, injecting an electrolyte, charging it to 4.6 V at a constant current of 0.1 C at 45°C, and then discharging it to 2.0 V at a constant current of 0.1 C to perform an activation process, thereby manufacturing a lithium secondary battery.

[0129]

[0130] Experimental Example 1: Analysis of the volume-cumulative particle size distribution and average particle diameter (D50) of the positive electrode active material.

[0131] First, for the powder of the positive electrode material included in the examples or comparative examples, the volume cumulative particle size distribution (PSD) was obtained using Microtrac's S-3500. This volume cumulative particle size distribution curve is shown in Fig. 1. From this volume cumulative particle size distribution curve, it was confirmed that the positive electrode materials of Examples 1 and 2 had a bimodal particle size distribution. In addition, from the volume cumulative particle size distribution curve, the average particle diameter (50) of each positive electrode active material included in the positive electrode material was analyzed, and the analysis results were as described in Table 1 above.

[0132] In addition, the PSD of the entire cathode material contained in each cathode slurry manufactured in the manufacturing example was analyzed identically 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 the counteractive material (e.g., cathode active material A or B) contained in the cathode slurry were evaluated, respectively.

[0133]

[0134] Experimental Example 2: Evaluation of the cumulative volumetric particle size distribution and particle breakage rate of the anode

[0135] The cathodes manufactured in the manufacturing examples using the cathode materials of the examples or comparative examples were heat-treated in a furnace at a temperature of 700°C for 10 hours to collect the cathode materials, which were then finely ground using a mortar and pestle and then classified using a 250 mesh sieve to obtain cathode material powder contained in each cathode. For the obtained powders, a volumetric cumulative particle size distribution (PSD) was obtained using Microtrac's S-3500.

[0136] From this, the volume ratio of particles having a particle size of 1 μm or less and the volume ratio of the counter material (e.g., the cathode active material A or B) included in the cathode were evaluated, respectively. The volume ratio of particles having a particle size of 1 μm or less and the volume ratio of the counter material included in the cathode after such rolling are shown in Table 2 below.

[0137] In addition, compared to 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 the opposing particles changed in the anode manufactured through rolling was evaluated, and is shown together in Table 2 below.

[0138]

[0139] Classification Example 1 Example 2 Comparative Example 2 Particle breakage rate evaluation Volume ratio of particles (fine powder) of 1 ㎛ or less (positive electrode after rolling; %) 8.4 13.0 7.2 Change in fine powder volume ratio before / after rolling (%) 0 4.6% increase 1.2% decrease Volume ratio of opposing particles (positive electrode after rolling; %) 18.6 23.9 28.5 Change in opposing particle volume ratio before / after rolling (%) 0 5.3% decrease 9.9% decrease

[0140] Referring to Table 2 above, when using the cathode material of Example 1, it was confirmed that even when manufacturing an anode through rolling, there was no substantial change in the volume ratio of particles having a particle diameter of 1 μm or less and the volume ratio of the opposing particles. From this, it can be confirmed that particle breakage can be suppressed during the anode manufacturing process through rolling.

[0141] When the cathode material of Example 2 was used, it was confirmed that particle breakage occurred more than in Example 1, but compared to Comparative Example 2 which only included the cathode active material, it was confirmed that the change in the volume ratio of the cathode before and after rolling was small, so that particle breakage could be relatively suppressed.

[0142]

[0143] Experimental Example 3: Gas Emission Evaluation

[0144] For the lithium secondary batteries manufactured in the manufacturing examples using the positive electrode materials of the above examples or comparative examples, the gases generated during an additional 100 charge and discharge cycles (charge and discharge cycles performed under conditions of 2.0 to 4.6 V and 45°C) were captured, and the amount of gas generated was quantitatively analyzed using GC-FID / TCD. The results of the analysis of the amount of active gas generated are compared and presented in Table 3 below.

[0145] Gas generation amount (μl) Total H2COCO2CH4C2H4C2H6Example 14746710469152127Example 247664102103151857Comparative example 149964117130141686

[0146] Referring to Table 3 above, it was confirmed that the lithium secondary battery manufactured using the positive electrode materials of Examples 1 and 2 exhibited a reduced amount of gas generation compared to Comparative Example 1.

[0147]

[0148] Experimental Example 4: Life Characteristics Evaluation

[0149] For the lithium secondary batteries manufactured in the manufacturing examples using the positive electrode materials of the above examples or comparative examples, 100 cycles of charge and discharge tests were conducted at 25°C and a voltage of 2.5 to 4.35 V. While performing these charge and discharge cycles for 100 cycles, the energy retention rate and capacity retention rate were evaluated, and are shown in Table 4 below.

[0150] @100 cycles Example 1 Example 2 Comparative Example 3 Average voltage (V) 3.482 3.489 3.488 Energy retention rate (%) 90.189 1.368 9.71 Capacity retention rate (%) 92.069 3.46 9.143

[0151] Referring to Table 4 above, it was confirmed that the lithium secondary battery including the cathode material of the example exhibited higher energy retention and capacity retention after 100 cycles of charge and discharge testing, and exhibited improved life characteristics, compared to the comparative example.

Claims

1. A cathode active material comprising a lithium manganese rich oxide having a layered crystal structure, a molar ratio of lithium to the molar number of all metals excluding lithium exceeding 1, and manganese in a content of 50 mol% or more among all metals excluding lithium, The above positive electrode active materials have different average particle diameters (D50) and include first positive electrode active material particles and second positive electrode active material particles each including the lithium manganese rich oxide, A positive electrode active material for a lithium secondary battery having a bimodal particle size distribution when the above positive electrode active material is subjected to volume cumulative particle size distribution analysis.

2. In the first paragraph, the lithium 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 [Mr 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, c and d are each 0 or more and 0.5 or less, but 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.

3. In the first paragraph, the lithium manganese rich oxide is a positive electrode active material for a lithium secondary battery having a molar ratio of lithium to the total molar number of metals excluding lithium of 1.3 to 1.

5.

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

50.

5. In the first paragraph, the lithium 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 [Mr b Ni c M d ] 2-a O2 In the above chemical formula 1, 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.

6. In the first paragraph, the lithium 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.

7. In the 6th paragraph, the 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 In the above chemical formula 2, M is at least one 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, but 0 <w+z≤0.5임.

8. A positive electrode active material for a lithium secondary battery, wherein in the first paragraph, the first positive electrode active material particles have an average particle diameter (D50) of 7 to 20 μm, and the second positive electrode active material particles have an average particle diameter (D50) smaller than that of the first positive electrode active material particles.

9. In the 8th paragraph, a positive electrode active material for a lithium secondary battery, wherein the second positive electrode active material particles have an average particle diameter (D50) of 1 to 6 ㎛.

10. A positive electrode active material for a lithium secondary battery, wherein the first and second positive electrode active material particles each have a secondary particle form in which a plurality of primary particles are aggregated.

11. A positive electrode active material for a lithium secondary battery, wherein the first positive electrode active material particle and the second positive electrode active material particle are included in a weight ratio of 50:40 to 95:5 in the first paragraph.

12. In the first paragraph, the first positive electrode active material particle is 1.2 m 2 / g to 4.0m 2 A cathode active material for a lithium secondary battery having a BET surface area of ​​ / g.

13. A positive electrode active material for a lithium secondary battery, wherein the second positive electrode active material particle has a smaller BET specific surface area than the first positive electrode active material particle in the 12th paragraph.

14. In the first paragraph, the second positive electrode active material particles are 0.3 m 2 / g to 1.7m 2 A cathode active material for a lithium secondary battery having a BET surface area of ​​ / g.

15. In the first paragraph, the positive electrode active material including the first and second positive electrode active material particles has a total diameter of 0.1 m 2 / g to 5.0m 2 A cathode active material for a lithium secondary battery having a BET surface area of ​​ / g.

16. Anode current collector; and A positive electrode for a lithium secondary battery, comprising a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material according to any one of claims 1 to 15.

17. A positive electrode for a lithium secondary battery, wherein the positive electrode active material layer further comprises a binder and a conductive material in the 16th paragraph.

18. The anode according to Article 16; a cathode facing the anode; and A lithium secondary battery comprising a separator or electrolyte layer interposed between the positive and negative electrodes.

19. A lithium secondary battery further comprising an electrolyte including a lithium salt and a non-aqueous organic solvent in accordance with claim 18.

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