Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material including a lithium manganese-based oxide, the positive electrode active material being capable of mitigation and / or prevention of a decrease in charge / discharge capacity or voltage decay during the cycling of a lithium secondary battery using the positive electrode active material.SOLUTION: A positive electrode active material includes a lithium-rich lithium manganese-based oxide containing at least lithium, nickel, manganese and molybdenum. The lithium manganese-based oxide includes at least one primary particle. The average particle diameter of the primary particle in the lithium manganese-based oxide is 0.4 to 3.0 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a positive electrode active material including a lithium-excess lithium manganese-based oxide containing at least lithium, nickel, manganese, and molybdenum, the lithium manganese-based oxide including at least one primary particle, and a lithium secondary battery including the same, in which the stability degradation caused by lithium and manganese present in excess in the lithium manganese-based oxide is alleviated and / or prevented by improving the crystal growth of the primary particle using a flux containing molybdenum.

Background Art

[0002] A battery stores electric power by using substances capable of electrochemical reactions for a positive electrode and a negative electrode. As a typical example of such a battery, there is a lithium secondary battery that stores electric energy due to a difference in chemical potential when lithium ions are intercalated / deintercalated in a positive electrode and a negative electrode.

[0003] The lithium secondary battery is manufactured by using substances capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

[0004] As the positive electrode active material of the lithium secondary battery, a lithium composite oxide is used. Examples thereof include composite oxides in which Ni, Co, Mn, or Al is combined, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015).

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency. However, it has the disadvantage of being expensive due to the resource limitations of cobalt used as a raw material, thus limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages such as excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature performance. On the other hand, LiNiO2-based cathode active materials exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to cation mixing problems between Li and transition metals, which results in significant problems with their rate characteristics.

[0007] Furthermore, depending on the degree of cation mixing, a large amount of Li byproducts are generated. Since the majority of these Li byproducts consist of LiOH and Li2CO3 compounds, they cause gelling problems during the production of the positive electrode paste and gas generation as charging and discharging progresses after the electrode is manufactured. Residual Li2CO3 not only increases the swelling phenomenon of the cell and reduces the number of cycles, but also causes the battery to swell.

[0008] Various candidate materials are being discussed to compensate for the shortcomings of these conventional cathode active materials.

[0009] As an example, research is being conducted to use lithium-rich lithium-manganese oxides, which contain an excess amount of manganese (Mn) among the transition metals, and whose lithium content exceeds the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such lithium-rich lithium-manganese oxides are also called lithium-overlithiated layered oxides (OLOs).

[0010] While the aforementioned OLO has the advantage of theoretically exhibiting high capacity under high-voltage operating conditions, in reality, it has a disadvantage in that its electrical conductivity is relatively low due to the excess amount of Mn contained in the oxide, resulting in a low capacity rate for lithium secondary batteries using OLO. When the capacity rate is low in this way, problems arise in which the charge / discharge capacity and life efficiency (cycle capacity retention rate) of lithium secondary batteries decrease during cycling.

[0011] Furthermore, during the cycling of lithium secondary batteries using OLO, a decrease in charge / discharge capacity or voltage decay can also be induced by phase transitions due to the migration of transition metals in lithium manganese oxides. For example, if a phase transition is induced by the unintended migration of transition metals in a layered crystalline lithium manganese oxide, a spinel or similar crystalline structure may develop throughout and / or partially within the lithium manganese oxide.

[0012] To address the aforementioned problems, there have been attempts to improve the OLO's issues through structural improvements and surface modifications, such as adjusting the particle size or coating the OLO's surface, but these have not yet reached a commercialization level. [Overview of the project] [Problems that the invention aims to solve]

[0013] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is playing a leading role, and the demand for positive electrode active materials used in lithium-ion batteries is also continuously changing.

[0014] For example, conventionally, lithium secondary batteries using LFPs have been primarily used from the perspective of ensuring safety, but recently there has been a growing trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFPs.

[0015] Furthermore, many nickel-based lithium composite oxides used as positive electrode active materials in high-capacity lithium secondary batteries recently require ternary metallic elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, in the case of cobalt, not only is the supply and demand unstable, but it is also extremely expensive compared to other raw materials. Therefore, there is a need for new compositions of positive electrode active materials that can reduce or eliminate the cobalt content.

[0016] From this perspective, lithium-rich lithium manganese oxides can meet the aforementioned market expectations, but their electrochemical properties and stability are still insufficient to replace commercially available NCM or NCA type cathode active materials.

[0017] However, even though conventional lithium-rich lithium manganese oxides have some disadvantages in terms of electrochemical properties and / or stability when compared to other commercially available types of cathode active materials, the inventors have confirmed that lithium-rich lithium manganese oxides can also exhibit commercially viable levels of electrochemical properties and stability when the crystal growth of the primary particles constituting the lithium manganese oxide is improved using a molybdenum-containing flux (i.e., when the size of the primary particles is increased).

[0018] Accordingly, the present invention aims to provide a positive electrode active material that includes a lithium-rich lithium-manganese oxide containing at least lithium, nickel, manganese, and molybdenum, and that reduces the phase transition effect due to the movement of interparticle transition metals by growing crystals in the lithium-manganese oxide using a molybdenum-containing flux so that the average particle size of primary particles is 0.4 μm or more, thereby mitigating and / or preventing a decrease in charge / discharge capacity or voltage decay during the cycling of a lithium secondary battery using a positive electrode active material containing the lithium-manganese oxide.

[0019] Furthermore, the present invention aims to provide a positive electrode active material that can mitigate and / or prevent a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles due to an increase in the average particle size of the primary particles in the lithium manganese oxide, by using a flux containing molybdenum to promote crystal growth of primary particles in the lithium manganese oxide, while at the same time allowing some molybdenum to exist on the surface of the primary particles in the form of an oxide.

[0020] Furthermore, the present invention aims to provide a lithium secondary battery in which the conventional low discharge capacity of OLO is improved by using a positive electrode containing the positive electrode active material defined in this application. [Means for solving the problem]

[0021] According to one aspect of the present invention for solving the aforementioned technical problems, a positive electrode active material is provided which comprises a lithium-rich lithium-manganese oxide containing at least lithium, nickel, manganese, and molybdenum, wherein the lithium-manganese oxide contains at least one primary particle, and the average particle size of the primary particle in the lithium-manganese oxide is 0.4 μm to 3.0 μm.

[0022] In this case, the lithium manganese oxide includes primary particles whose crystal growth has been promoted using a molybdenum-containing flux.

[0023] In this case, some of the molybdenum contained in the flux may exist as a dopant within the primary particle.

[0024] In one embodiment, the lithium manganese oxide can be represented by the following chemical formula 1.

[0025] [Chemical formula 1] rLi2Mn 1-a Mo a O3·(1-r)Li bNi x Co y Mn z Mo z′ M1 1-(x+y+z+z′) O2

[0026] Here, M1 is at least one selected from Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi, 0 < r ≤ 0.7, 0 ≤ a < 0.2, 0 < b ≤ 1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z < 1, 0 < z' < 0.2, and 0 < x + y + z + z' ≤ 1.

[0027] As shown in Chemical Formula 1 above, molybdenum present in the lithium manganese oxide corresponds to rLi2Mn in the c2 / m phase and (1 - r)Li 1-a Mo a O3 and / or may be present as a dopant in (1 - r)Li b Ni x Co y Mn z Mo z′ Ml 1-(x+y+z+z′) O2.

[0028] Among the molybdenum used as a flux for crystal growth of primary particles constituting the lithium manganese oxide, a part thereof is present as a dopant in the lithium manganese oxide. Thus, particularly in the lithium manganese oxide, rLi2Mn 1-a Mo a O3 corresponding to the c2 / m phase containing excess lithium and manganese can be induced to be electrochemically activated.

[0029] Furthermore, by having a portion of the molybdenum used as a flux for the crystal growth of the primary particles constituting the lithium manganese oxide present on the surface of the primary particles in the form of an oxide, it is possible to mitigate and / or prevent a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles, which would otherwise occur due to an increase in the average particle size of the primary particles in the lithium manganese oxide.

[0030] Furthermore, according to another aspect of the present invention, a positive electrode containing the aforementioned positive electrode active material is provided.

[0031] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided in which the aforementioned positive electrode is used. [Effects of the Invention]

[0032] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese oxides, which have various disadvantages in terms of electrochemical properties and / or stability when compared with other commercially available types of cathode active materials.

[0033] Specifically, the primary particles constituting the lithium manganese oxide according to the present invention, as crystal growth is promoted using a molybdenum-containing flux, can mitigate or eliminate the decrease in charge / discharge capacity or voltage decay during the cycling of a lithium secondary battery containing the lithium manganese oxide as the positive electrode active material.

[0034] Furthermore, some of the molybdenum used as a flux for the crystal growth of the primary particles constituting the lithium manganese oxide exists as a dopant within the lithium manganese oxide, particularly in the rLi2Mn phase which corresponds to the c2 / m phase containing excess lithium and manganese in the lithium manganese oxide. 1-a Mo aBy inducing the electrical activation of O3, discharge characteristics such as the average discharge voltage maintenance rate and discharge capacity ratio of a lithium secondary battery using the lithium manganese oxide as the positive electrode active material can be improved.

[0035] Furthermore, by having a portion of the molybdenum used as a flux for the crystal growth of the primary particles constituting the lithium manganese oxide present on the surface of the primary particles in the form of an oxide, it is possible to mitigate and / or prevent a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles, which would otherwise occur due to an increase in the average particle size of the primary particles in the lithium manganese oxide. [Brief explanation of the drawing]

[0036] [Figure 1] This is an SEM image of the lithium manganese oxide contained in the positive electrode active material according to Example 1. [Figure 2] This is an SEM image of the lithium manganese oxide contained in the positive electrode active material according to Comparative Example 1. [Figure 3] This is an SEM image of the lithium manganese oxide contained in the positive electrode active material in Comparative Example 2. [Figure 4] This is a cross-sectional SEM image of the lithium manganese oxide contained in the positive electrode active material according to Example 1. [Figure 5] This image shows molybdenum mapped onto the cross-sectional SEM image in Figure 4 via EDX analysis. [Modes for carrying out the invention]

[0037] For the convenience of making the present invention easier to understand, certain terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in this invention have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0038] The following describes in more detail a positive electrode active material containing a lithium-rich lithium-manganese oxide, which includes at least lithium, nickel, manganese, and molybdenum, and a lithium secondary battery containing the said positive electrode active material, according to the present invention.

[0039] positive electrode active material According to one aspect of the present invention, a positive electrode active material is provided which comprises a lithium-rich lithium-manganese oxide containing at least lithium, nickel, manganese, and molybdenum. The lithium-manganese oxide is a composite metal oxide capable of intercalation and deintercalation of lithium ions.

[0040] The lithium manganese-based oxide contained in the positive electrode active material as defined in this application may be a particle containing at least one primary particle. If the lithium manganese-based oxide contains a particle formed by the aggregation of multiple primary particles, the particle formed by the aggregation of multiple primary particles may be referred to as a secondary particle.

[0041] Here, "a particle containing at least one primary particle" should be interpreted as including all "particles formed by the aggregation of multiple primary particles" or "non-aggregated particles containing a single primary particle." In this case, it is preferable that the smaller the number of primary particles constituting the overall particle, the larger the size of the primary particles.

[0042] The primary particles and secondary particles may each independently have a rod-shaped, elliptical, and / or amorphous shape.

[0043] In this case, the average particle size of the primary particles in the lithium manganese oxide, which contains at least one primary particle, is preferably 0.4 μm to 3.0 μm. The average particle size of the primary particles can be measured as the length of the major axis or minor axis of the primary particle, or as the cumulative average particle size.

[0044] Generally, in OLOs, which are secondary particle forms formed by the aggregation of multiple primary particles, unlike conventional OLOs where the average particle size of the primary particles is only a few to tens of nanometers, in the lithium manganese oxide defined in the present invention, the primary particles have an average particle size of at least 0.4 μm, thereby reducing the phase transition effect due to the movement of interparticle transition metals, and making it possible to mitigate and / or prevent a decrease in charge / discharge capacity or voltage decay during the cycling of a lithium secondary battery using a positive electrode active material containing the lithium manganese oxide.

[0045] While various methods are possible for promoting the crystal growth of primary particles in the lithium manganese oxide, according to the present invention, the average particle size of the primary particles constituting the lithium manganese oxide may be obtained by promoting crystal growth using a flux containing molybdenum. When promoting the crystal growth of primary particles using a flux containing molybdenum, a portion of the molybdenum used as the flux may exist as a dopant within the primary particles.

[0046] On the other hand, if the average particle size of the primary particles in the lithium manganese oxide is increased by raising the roasting or firing temperature during the manufacturing process to promote particle crystal growth, the phase transition effect due to the movement of interparticle transition metals may not be sufficiently prevented, or conversely, the size of the primary particles may become unnecessarily large, which can lead to a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the particle surface.

[0047] If the average particle size of the primary particles is less than 0.4 μm, it is difficult to adequately mitigate or eliminate the decrease in charge / discharge capacity or voltage decay during the cycling of a lithium secondary battery containing the lithium manganese oxide as the positive electrode active material. On the other hand, if the average particle size of the primary particles is greater than 3.0 μm, the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles decreases due to the excessively large average particle size, which can cause a rapid decrease in the initial charge / discharge capacity.

[0048] The average particle size of the secondary particles can vary depending on the number of primary particles that make up the secondary particles, but is generally between 1 μm and 30 μm.

[0049] The lithium manganese oxide as defined in this application can be represented by the following chemical formula 1.

[0050] [Chemical formula 1] rLi2Mn 1-a Mo a O3·(1-r)Li b Ni x Co y Mn z Mo z′ M1 1-(x+y+z+z′) O2

[0051] Here, M1 is at least one selected from Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. 0 <r≦0.7、0≦a<0.2、0<b≦1、0<x≦1、0≦y<1、0<z<1、0<z′<0.2および0<x+y+z+z′≦1である。

[0052] The lithium manganese oxide represented by chemical formula 1 may selectively contain cobalt. Furthermore, if the lithium manganese oxide contains cobalt, the ratio of the number of moles of cobalt to the total number of moles of metal elements in the lithium manganese oxide may be 10% or less, preferably 5% or less. On the other hand, the lithium manganese oxide represented by chemical formula 1 does not have to contain cobalt.

[0053] The lithium manganese oxide represented by the above chemical formula 1 is rLi2Mn 1-a Mo a Oxides of phases belonging to the C2 / m space group represented by O3 (hereinafter referred to as "C2 / m phase") and (1-r)Li b Ni x Co y Mn z Mo z′ M1 1-(x+y+z+z′) This is a composite oxide in which oxides of a phase belonging to the R3-m space group represented by O2 (hereinafter referred to as the "R3-m phase") coexist. In this case, the oxides of the C2 / m phase and the oxides of the R3-m phase exist in a solid solution state.

[0054] In the lithium manganese oxide represented by the chemical formula 1, if r exceeds 0.8, the proportion of Li2MnO3, which is the C2 / m phase oxide, in the lithium manganese oxide becomes excessively high, which may reduce the discharge capacity of the positive electrode active material. In other words, in order to sufficiently activate the C2 / m phase oxide, which has relatively high resistance, in the lithium manganese oxide and improve the surface kinetics, it is preferable that the R3-m phase oxide be present in a predetermined proportion or higher.

[0055] In the lithium manganese oxide represented by the chemical formula 1, it is preferable that molybdenum is present in a range of 0.02 mol% to 5.0 mol% based on the total metallic elements excluding lithium.

[0056] In the aforementioned lithium manganese oxide, a molybdenum content less than 0.02 mol% relative to the total metal elements excluding lithium means that the amount of molybdenum-containing flux used for the crystal growth of the primary particles constituting the lithium manganese oxide is insufficient, and that the effect of the molybdenum-containing flux on the crystal growth of the primary particles is minimal.

[0057] Furthermore, if the molybdenum content in the lithium manganese oxide becomes excessively high, the content of active metal elements in the lithium manganese oxide may decrease, potentially leading to a reduction in the discharge capacity of the positive electrode active material.

[0058] If the amount of molybdenum-containing flux used for crystal growth of primary particles constituting the lithium manganese oxide is insufficient, the average particle size of the primary particles constituting the lithium manganese oxide may become smaller than 0.4 μm, or the proportion of primary particles with a particle size smaller than 0.4 μm in the lithium manganese oxide may increase.

[0059] This can induce a phase transition in the lithium manganese oxide due to unintended movement of interparticle transition metals, which can lead to the formation of spinel or similar crystalline structures throughout and / or partially within the lithium manganese oxide.

[0060] The occurrence of such an internal phase transition of lithium manganese oxide acts as a major cause of a decrease in charge / discharge capacity or voltage decay during the cycling of lithium secondary batteries using positive electrode active materials containing the lithium manganese oxide.

[0061] In the aforementioned lithium manganese oxide, a molybdenum content greater than 5.0 mol% relative to the total metal elements excluding lithium means that an excessive amount of molybdenum-containing flux was used for the crystal growth of the primary particles constituting the lithium manganese oxide.

[0062] In this case, excessive use of the molybdenum-containing flux can unnecessarily increase the crystal growth of primary particles, which may reduce the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles.

[0063] Furthermore, by increasing the molybdenum content in the lithium manganese oxide, the proportion of active metal elements that can contribute to improving the initial charge and discharge capacity of lithium secondary batteries using the lithium manganese oxide as the positive electrode active material can be reduced.

[0064] Even when the crystal growth of primary particles is promoted using the molybdenum-containing flux, the compressive density of the positive electrode active material under a pressure of 4.5 tons may be 2.8 g / cc or higher.

[0065] If the size of the primary particles in the lithium manganese oxide is too small or too large, the structural stability of the positive electrode active material may decrease. Also, if the size of the primary particles in the lithium manganese oxide increases, which increases the porosity within the secondary particles, the structural stability of the positive electrode active material may decrease.

[0066] However, as mentioned above, the positive electrode active material according to the present invention can prevent a decrease in the structural stability of the positive electrode active material by ensuring that the average particle size of the primary particles, whose crystal growth is promoted using a flux containing molybdenum, is in the range of 0.4 μm to 3.0 μm.

[0067] In other embodiments, at least a portion of the surface of the lithium manganese-based oxide may contain at least one metal oxide represented by the following chemical formula 2. In this case, the region containing the metal oxide may be at least a portion of the surface of the primary particles and / or the secondary particles.

[0068] [Chemical formula 2] Li d M2 e O f

[0069] Here, M2 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd. 0≦d≦8, 0 <e≦8、2≦f≦13である。

[0070] The metal oxide represented by chemical formula 2 can be formed when at least some of the metal elements (nickel, manganese, cobalt, and / or doping metals) constituting the lithium manganese oxide react with Li present on the surface of the lithium manganese oxide.

[0071] The metal oxide can improve the electrochemical properties of the lithium manganese oxide by reducing lithium-containing impurities (or residual lithium) present on the surface of the lithium manganese oxide and by acting as a diffusion path for lithium ions.

[0072] Furthermore, the metal oxide may include at least one selected from molybdenum oxide and lithium molybdenum oxide.

[0073] By having a portion of the molybdenum used as a flux for the crystal growth of the primary particles constituting the lithium manganese oxide present on the surface of the primary particles in the form of an oxide, it is possible to mitigate and / or prevent a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles, which would otherwise occur due to an increase in the average particle size of the primary particles in the lithium manganese oxide.

[0074] If the lithium manganese-based oxide is a core-shell particle, the metal oxide may also exist integrally with the shell.

[0075] As a result, the metal oxide may be present on at least a portion of the surface of the crystallites, primary particles, and / or secondary particles constituting the lithium manganese-based oxide.

[0076] The metal oxide is an oxide in which lithium and an element represented by M2 are combined, or an oxide of M3, and the metal oxide is, for example, Li a W b O c Li a Zr b O c Li a Ti b O c Li a Ni b O c Li a Co b O c Li a Al b O c Li a Mo b O c Co b O c , Al b O c , W b O c , Zr b O c or action b O c Other examples are also acceptable, but the aforementioned examples are merely provided for convenience to aid understanding, and the metal oxides as defined in this application are not limited to the aforementioned examples.

[0077] Furthermore, the metal oxide may be an oxide in which lithium and at least two elements represented by M2 are combined, or may further contain an oxide in which lithium and at least two elements represented by M2 are combined. An oxide in which lithium and at least two elements represented by M2 is, for example, Li a (W / Ti)b O c Li a (W / Zr) b O c Li a (W / Ti / Zr) b O c Li a (W / Ti / B) b O c Other options are also acceptable, but the system is not necessarily limited to these.

[0078] Lithium-ion battery According to another aspect of the present invention, a positive electrode can be provided that includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may contain a lithium composite oxide according to the various embodiments of the present invention described above as the positive electrode active material.

[0079] Therefore, a detailed explanation of the lithium composite oxide will be omitted, and only the remaining components not mentioned above will be described below. Also, for convenience, the aforementioned lithium composite oxide will be referred to as the positive electrode active material below.

[0080] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0081] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0082] In this case, the positive electrode active material may be present in an amount of 80 to 99 wt%, more specifically, 85 to 98.5 wt%, relative to the total weight of the positive electrode active material layer. While excellent capacity characteristics can be observed when the material is within this content range, it is not necessarily limited to this range.

[0083] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, 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, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0084] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0085] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0086] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0087] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0088] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0089] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0090] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0091] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0092] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. 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. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0093] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0094] As the 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; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0095] The aforementioned negative electrode active material may be present in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0096] The binder may be added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0097] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, 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 a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change 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, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0098] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0099] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0100] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any membrane commonly used as a separation membrane in lithium secondary batteries can be used without particular limitations, and it is especially preferable that the membrane has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0101] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0102] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0103] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0104] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0105] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0106] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0107] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0108] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0109] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0110] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0111] Manufacturing Example 1. Manufacturing of positive electrode active material Example 1 (a) Production of precursors In the reactor, a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60 was added, and NaOH and NH4OH were added while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn 0.6 Hydroxide precursors with (OH)2 composition were obtained.

[0112] (b) First heat treatment After heating an O2 atmosphere furnace at a rate of 2°C / min, the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C, and then furnace-cooled to obtain the oxide precursor.

[0113] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b) with a lithium compound, LiOH (Li / (Li-excluded metal) mol ratio = 1.3), and 0.5 mol% MoO3 relative to the total metal elements in the precursor.

[0114] Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 1,000°C. After furnace cooling, a cathode active material containing lithium manganese oxide was finally obtained.

[0115] Example 2 The cathode active material was prepared in the same manner as in Example 1, except that 6.0 mol% MoO3 was used in step (c).

[0116] Example 3 The cathode active material was prepared in the same manner as in Example 1, except that 0.01 mol% of MoO3 was used in step (c).

[0117] Comparative Example 1 The positive electrode active material was manufactured in the same manner as in Example 1, except that MoO3 was not used in step (c).

[0118] Comparative Example 2 (a) Production of precursors In the reactor, a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60 was added, and NaOH and NH4OH were added while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn0.6 Hydroxide precursors with (OH)2 composition were obtained.

[0119] (b) First heat treatment After heating an O2 atmosphere furnace at a rate of 2°C / min, the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining a temperature of 800°C, and then furnace-cooled to obtain the oxide precursor.

[0120] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (Li-excluded metal) mol ratio = 1.3) as a lithium compound to prepare a mixture. Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 1,000°C. After furnace cooling, a cathode active material containing lithium manganese oxide was finally obtained.

[0121] Comparative Example 3 The cathode active material was prepared in the same manner as in Example 1, except that 0.5 mol% Nb2O3 was used instead of 0.5 mol% MoO3 in step (c).

[0122] Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced according to Production Example 1, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0123] A coin cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and an electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.15 M.

[0124] Experimental Example 1. Physical property analysis of positive electrode active material After selecting lithium manganese oxides from each cathode active material produced according to Production Example 1, scanning electron microscope (SEM) images were obtained. Figures 1 to 3 show SEM images of lithium manganese oxides contained in the cathode active materials from Example 1, Comparative Example 1, and Comparative Example 2.

[0125] Using an image analyzer program, 100 primary particles were selected from SEM images of lithium manganese oxides contained in the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 3. The average particle size of each primary particle was then measured, and the average values ​​were calculated.

[0126] Next, 3g of each cathode active material produced according to Production Example 1 was weighed into a pelletizer, then pressurized at 4.5 tons for 5 seconds, and the compressed density was measured.

[0127] The measurement results are shown in Table 1 below.

[0128] [Table 1]

[0129] Experimental Example 2. Compositional Analysis of Cathode Active Material After selecting lithium manganese-based oxides from the positive electrode active material according to Example 1, the lithium composite oxides were cross-sectionally treated using a FIB (Ga-ion source), and cross-sectional SEM images were taken using a scanning electron microscope.

[0130] Next, molybdenum, the target transition metal present inside and on the surface of the primary particles, was mapped through EDX analysis of the lithium manganese oxide confirmed from the cross-sectional SEM image.

[0131] Figure 4 is a cross-sectional SEM image of the lithium manganese oxide contained in the positive electrode active material according to Example 1, and Figure 5 is an image of the cross-sectional SEM image of Figure 4 with molybdenum mapped (areas with high density of shading) via EDX analysis.

[0132] Referring to Figure 5, it can be confirmed that molybdenum is present on at least a portion of the surface of the primary particles constituting the lithium manganese oxide. This result means that a portion of the MoO3 used as flux for the crystal growth of the primary particles is present on the surface of the primary particles as molybdenum oxide and / or lithium molybdenum oxide.

[0133] Furthermore, within the region corresponding to the interior of the primary particles constituting the lithium manganese oxide, there are areas that are partially mapped in red. This indicates that molybdenum derived from MoO3, which was used as a flux for the crystal growth of the primary particles, exists as an intraparticle dopant.

[0134] Experimental Example 3. Evaluation of the electrochemical properties of lithium secondary batteries For the lithium secondary battery (coin cell) manufactured in Manufacturing Example 2, the initial charge capacity, initial discharge capacity, initial reversibility efficiency, and rate characteristics (rate capability (C-rate)) were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 2.0V to 4.6V and a discharge rate of 0.1C to 5.0C.

[0135] Furthermore, the same lithium secondary battery underwent 50 charge-discharge cycles at 25°C and within a driving voltage range of 2.0V to 4.6V under 1C / 1C conditions. The cycle capacity retention rate (the ratio of the discharged capacity at the 50th cycle to the initial capacity) and the retention rate of the average discharge voltage at the 50th cycle relative to the average discharge voltage at the 1st cycle were then measured.

[0136] The measurement results are shown in Tables 2 and 3 below.

[0137] [Table 2]

[0138] [Table 3]

[0139] Referring to the results in Tables 2 and 3, it can be confirmed that the discharge characteristics, such as initial discharge capacity and discharge capacity ratio, of the positive electrode active materials of Examples 1 to 3 improved compared to the positive electrode active material of Comparative Example 1 as the crystal growth of primary particles was promoted using a flux containing molybdenum.

[0140] Comparing the positive electrode active materials of Examples 1 to 3, in Example 3, which used a relatively small amount of molybdenum-containing flux, the degree of primary particle crystal growth was lower compared to the positive electrode active material of Example 1. As a result, the discharge capacity (1C-rate) and the discharge capacity ratio (5C / 0.1C) were slightly lower than those of the lithium secondary battery using the positive electrode active material of Example 1.

[0141] Furthermore, in Example 2, which used a relatively large amount of flux containing molybdenum, there was no significant difference in the degree of crystal growth compared to the positive electrode active material in Example 1. On the contrary, as the amount of flux used increased, it was confirmed that the discharge capacity (1C-rate) and the ratio of discharge capacity (5C / 0.1C) were slightly lower than those of the lithium secondary battery using the positive electrode active material in Example 1. This result is presumed to be because, as the residual molybdenum content in the lithium manganese-based oxide increased, the content of the active metal element in the lithium manganese-based oxide decreased.

[0142] Furthermore, in the case of a lithium secondary battery using the positive electrode active material according to Comparative Example 2, which includes primary particles whose crystal growth was promoted by increasing the second heat treatment temperature instead of using a separate flux, it can be confirmed that it exhibits an initial discharge capacity and initial heating efficiency similar to that of the positive electrode active materials of Examples 1 to 3. However, it can be confirmed that the cycle capacity retention rate and discharge capacity ratio of the lithium secondary battery using the positive electrode active material of Comparative Example 2 are lower than those of the lithium secondary batteries using the positive electrode active materials of Examples 1 to 3.

[0143] Furthermore, in the case of a lithium secondary battery using the positive electrode active material according to Comparative Example 3, in which crystal growth of primary particles was promoted by using a flux containing niobium instead of molybdenum, it can be confirmed that the initial charge / discharge capacity and discharge capacity ratio are lower compared to the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 3.

[0144] In other words, the above results indicate that using a molybdenum-containing flux promotes the crystal growth of primary particles constituting lithium manganese oxides, and at the same time, some of the molybdenum used as flux exists as a dopant within the lithium manganese oxide or as an oxide on the surface of the primary particles, thereby forming rLi2Mn corresponding to the c2 / m phase. 1-a Mo aIt can be confirmed that this is achieved by inducing the electrical activation of O3, thereby mitigating and / or preventing a decrease in the charge-transfer and / or diffusion (i.e., surface kinetics) of Li ions on the surface of the primary particles.

[0145] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A positive electrode active material comprising a lithium-rich lithium-manganese oxide containing at least lithium, nickel, manganese, and molybdenum, The aforementioned lithium manganese oxide is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group. The lithium manganese oxide comprises at least one primary particle, In the lithium manganese oxide, the average particle size of the primary particles is 0.4 μm to 3.0 μm. The lithium manganese oxide is a positive electrode active material containing the molybdenum as a dopant.

2. The positive electrode active material according to claim 1, wherein the lithium manganese oxide contains 0.02 mol% to 5.0 mol% of molybdenum based on the total metallic elements excluding lithium.

3. The lithium manganese oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1. [Chemical formula 1] rLi ２ Mn １－ａ Mo ａ O ３ ・(1-r)- ｂ Ni ｘ Co ｙ Mn ｚ Mo ｚ′ M1 １－（ｘ＋ｙ＋ｚ＋ｚ′） O ２ Here, M1 is at least one selected from Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. 0 < r ≤ 0.7, 0 ≤ a < 0.2, 0 < b ≤ 1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z < 1, 0 < z' < 0.2, and 0 < x + y + z + z' ≤ 1.

4. The positive electrode active material according to claim 1, wherein the compressive density of the positive electrode active material under a pressure of 4.5 tons is 2.8 g / cc or more.

5. The positive electrode active material according to claim 1, wherein at least a portion of the surface of the lithium manganese-based oxide has at least one metal oxide selected from molybdenum oxide and lithium molybdenum oxide present on it.

6. The positive electrode active material according to claim 1, wherein at least a portion of the surface of the lithium manganese-based oxide contains at least one metal oxide represented by the following chemical formula 2. [Chemical formula 2] Li d M2 e O f Here, M2 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd. 0 ≤ d ≤ 8, 0 < e ≤ 8, and 2 ≤ f ≤ 13.

7. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 6.

8. A lithium secondary battery using the positive electrode described in claim 7.

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