Positive electrode active material and lithium secondary battery including the same

Abstract

To provide a positive electrode active material in which the decrease in stability caused by the presence of excess amounts of lithium and manganese in a lithium-manganese-based oxide is mitigated and / or prevented.SOLUTION: A positive electrode active material includes a lithium-excess lithium manganese-based oxide containing at least lithium, nickel, and manganese, and when the number of moles of all metal elements in the lithium manganese-based oxide is referred to as M1 and the number of moles of nickel is referred to as M2, M2 / M1 calculated from an average composition of all metal elements in a core of the lithium manganese-based oxide and M2 / M1 calculated from an average composition of all metal elements in a shell of the lithium manganese-based oxide are different from each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly to a positive electrode active material including a lithium-excess lithium-manganese-based oxide including at least lithium, nickel, manganese, and a doping metal, in which the concentrations of transition metals in the lithium manganese-based oxide are controlled by region, thereby mitigating and / or preventing a decrease in stability caused by excess lithium and manganese in the lithium manganese-based oxide, and a lithium secondary battery including the same. [Background technology]

[0002] Batteries store electricity by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such batteries is the lithium secondary battery, which stores electrical energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

[0003] The lithium secondary battery is manufactured by using a material 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] Lithium composite oxides are used as the positive electrode active material of lithium secondary batteries. Examples of such oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and composite oxides containing Ni, Co, Mn, Al, etc., as disclosed in 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 because of its excellent life characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, and therefore has limited price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of being thermally safe and inexpensive, but have problems with small capacity and poor high-temperature characteristics. In addition, LiNiO2-based positive electrode active materials show high discharge capacity battery characteristics, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, which causes major problems with rate characteristics.

[0007] In addition, a large amount of Li by-products are generated depending on the depth of this cation mixing, and most of these Li by-products consist of compounds of LiOH and Li2CO3, which cause gelation during the manufacture of the positive electrode paste and gas generation during charge and discharge after the electrode is manufactured. The remaining Li2CO3 not only increases the swelling phenomenon of the cell, reducing the cycle, but also causes the battery to swell.

[0008] Various candidate materials for compensating for the shortcomings of conventional positive electrode active materials are being discussed.

[0009] For example, research is being conducted to use lithium-rich lithium manganese oxides, which contain an excess amount of Mn among transition metals and have a lithium content greater than the total content of the transition metals, as a positive electrode active material for lithium secondary batteries. Such lithium-rich lithium manganese oxides are also called overlithiated layered oxides (OLO).

[0010] Although OLO has an advantage of theoretically being able to exhibit high capacity under a high voltage operating environment, it has a disadvantage in that the rate capability of a lithium secondary battery using OLO is low due to its relatively low electrical conductivity caused by the excessive amount of Mn contained in the oxide. If the rate capability is low, there is a problem in that the charge / discharge capacity and life efficiency (capacity retention) decrease during cycling of the lithium secondary battery.

[0011] In addition, the decrease in charge / discharge capacity or voltage decay during cycling of a lithium secondary battery using OLO may be caused by a phase transition due to the movement of transition metals in the lithium manganese oxide. For example, when a phase transition is induced by the movement of transition metals in an unintended direction in a lithium manganese oxide having a layered crystal structure, a spinel or similar crystal structure may be formed entirely and / or partially in the lithium manganese oxide.

[0012] There have been attempts to solve the above problems with OLO through particle structure and surface modification, such as adjusting the particle size or coating the surface of OLO, but these efforts have not yet reached a commercial level. Summary of the Invention [Problem to be solved by the invention]

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

[0014] For example, lithium secondary batteries using LFP have traditionally been used primarily for safety reasons, but recently there has been a trend toward expanding use of nickel-based lithium composite oxides, which have a larger energy capacity per weight than LFP.

[0015] In addition, many nickel-based lithium composite oxides that are currently used as positive electrode active materials for high-capacity lithium secondary batteries essentially use ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. Among them, cobalt has problems such as unstable supply and demand and is excessively expensive compared to other raw materials, so there is a need for a new positive electrode active material with a reduced cobalt content or that can eliminate cobalt.

[0016] From this perspective, lithium-rich lithium manganese oxide can meet the above market expectations, but the electrochemical properties and stability of lithium manganese oxide are still insufficient to replace the commercially available NCM or NCA type positive electrode active materials.

[0017] However, when compared with other types of commercially available positive electrode active materials, the conventional lithium-excess lithium manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability. However, the present inventors have confirmed that when the concentration of the transition metal in the lithium manganese-based oxide can be controlled by region, the lithium-excess lithium manganese-based oxide can also exhibit electrochemical properties and stability at a level that allows for commercialization.

[0018] Accordingly, the present invention provides a positive electrode active material that includes a lithium-excess lithium-manganese-based oxide that includes at least lithium, nickel, manganese, and a doping metal, and that controls the concentration of a transition metal in the lithium-manganese-based oxide by region, thereby mitigating and / or preventing a decrease in stability caused by the excess lithium and manganese in the lithium-manganese-based oxide.

[0019] Another object of the present invention is to provide a lithium secondary battery in which the low rate characteristics of conventional OLO are improved by using a positive electrode containing the positive electrode active material defined in the present application. [Means for solving the problem]

[0020] According to one aspect of the present invention for solving the above technical problems, there is provided a positive electrode active material comprising a lithium-rich lithium manganese-based oxide containing at least lithium, nickel, and manganese, wherein the mole number of all metal elements in the lithium manganese-based oxide is M 1 The number of moles of nickel is called M 2 In this case, M calculated from the average composition of all metal elements in the core of the lithium manganese oxide 2 / M 1 and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. 2 / M 1 In each of the above-mentioned examples, different positive electrode active materials are provided.

[0021] The lithium manganese-based oxide may be represented by the following Chemical Formula 1.

[0022] [Chemical formula 1] rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2

[0023] Where: M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi; 0 <r≦0.7、0<a≦1、0<x≦1、0≦y<1、0<z<1および0<x+y+z≦1である。

[0024] The lithium manganese-based oxide represented by Chemical Formula 1 may selectively contain cobalt. In addition, when the lithium manganese-based oxide contains cobalt, the ratio of the mole number of the cobalt to the mole number of the total metal elements in the lithium manganese-based oxide may be 10% or less, preferably 5% or less.

[0025] In one embodiment, the lithium manganese-based oxide may be a secondary particle including at least one primary particle. In this case, M calculated from the average composition of all metal elements in the core of the primary particle may be 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of all metal elements in the shell of the primary particle. 2 / M 1 (or M 3 / M 1 ) may be different from each other. In other cases, M calculated from the average composition of all metal elements in the core of the secondary particle 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of all metal elements in the shell of the secondary particle. 2 / M 1 (or M 3 / M 1 ) may be different from each other.

[0026] In another embodiment, the lithium manganese oxide may be a secondary particle including at least one primary particle, and the primary particle may include at least one crystallite. In this case, M calculated from the average composition of all metal elements in the core of the crystallite may be 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of all metal elements in the shell of the crystallite. 2 / M 1 (or M 3 / M 1 ) may be different from each other.

[0027] As in the various embodiments described above, when the concentration of any metal element present in the shell and core of a particle (wherein the particle may be any crystallite present in a primary particle, or any primary or secondary particle present in a secondary particle) is different, the particle may be referred to as a core-shell particle. That is, the lithium manganese-based oxide is a core-shell particle, and the average composition of all metal elements constituting the lithium manganese-based oxide in the core and the shell may be different from each other.

[0028] According to another aspect of the present invention, there is provided a positive electrode comprising the above-described positive electrode active material.

[0029] According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-mentioned positive electrode. Effect of the Invention

[0030] According to the present invention, it is possible to improve the limitations of conventional lithium-excess lithium manganese-based oxides, which have various disadvantages in terms of electrochemical properties and / or stability, when compared with other types of commercially available positive electrode active materials.

[0031] Specifically, according to the present invention, the concentration of transition metals (particularly nickel and doping metal) contained in the lithium-excess lithium manganese-based oxide is controlled in each region within the particle, thereby providing an advantage in that it is possible to mitigate and / or prevent a decrease in stability caused by the excess lithium and manganese present in the lithium manganese-based oxide.

[0032] In addition, according to the present invention, the concentration of transition metals (particularly nickel and doping metals) contained in the lithium-excess lithium manganese-based oxide is controlled in each region within the particle, thereby alleviating charge-transfer and / or diffusion of Li ions on the particle surface, which is hindered by excess Mn, and thus improving the low electrical conductivity of the lithium manganese-based oxide to a commercially available level.

[0033] In addition, according to the present invention, a gradient in the concentration of the transition metal is formed between the core and shell of the lithium manganese oxide, and abrupt changes in the concentration of the transition metal within the particles are prevented, thereby improving the stability of the crystal structure of the lithium manganese oxide. [Brief description of the drawings]

[0034] [Figure 1] 3 is a cross-sectional TEM image of the lithium manganese-based oxide contained in the positive electrode active material according to Example 1, showing the distribution of Ni, Mn, and W elements through EDS mapping of the cross section of the lithium manganese-based oxide. FIG. [Diagram 2] 2 is a line sum spectrum showing the change in the content of metal elements (Ni, Mn, W) present in lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of FIG. 1. [Diagram 3] FIG. 4 is a cross-sectional TEM image of the lithium manganese-based oxide contained in the positive electrode active material according to Example 2, showing the distribution of Ni, Co, and Mn elements through EDS mapping of the cross section of the lithium manganese-based oxide. [Figure 4] 4 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn) present in lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of FIG. 3. [Diagram 5] FIG. 11 is a cross-sectional TEM image of the lithium manganese-based oxide contained in the positive electrode active material according to Example 3, showing the distribution of Ni, Co, Mn and W elements through EDS mapping of the cross section of the lithium manganese-based oxide. [Figure 6] 6 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn, W) present in lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of FIG. 5. [Figure 7]FIG. 11 is a cross-sectional TEM image of the lithium manganese-based oxide contained in the positive electrode active material according to Example 8, showing the distribution of Ni, Co, and Mn elements through EDS mapping of the cross section of the lithium manganese-based oxide. [Figure 8] 8 is a graph (line sum spectrum) showing the change in the content of metal elements (Ni, Co, Mn) present in lithium manganese-based oxide through EDS analysis in a direction 1 shown in the cross-sectional TEM image of FIG. 7. [Figure 9] 8 is a graph (line sum spectrum) showing the change in the content of metal elements (Ni, Co, Mn) present in lithium manganese-based oxide through EDS analysis in the direction 2 shown in the cross-sectional TEM image of FIG. 7. [Figure 10] 4 is a cross-sectional TEM image of a lithium manganese-based oxide included in a positive electrode active material according to Comparative Example 1, showing the distribution of Ni and Mn elements through EDS mapping of a cross section of the lithium manganese-based oxide. FIG. [Figure 11] 11 is a graph (line sum spectrum) showing a change in the content of metal elements (Ni, Mn) present in a lithium manganese-based oxide through EDS analysis in the direction shown in the cross-sectional TEM image of FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In order to make the present invention easier to understand, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used in the present invention shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified by the context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0036] Hereinafter, a positive electrode active material including a lithium-rich lithium manganese-based oxide including at least lithium, nickel, manganese, and a doping metal according to the present invention and a lithium secondary battery including the positive electrode active material will be described in more detail.

[0037] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material comprising a lithium-rich lithium manganese-based oxide that contains at least lithium, nickel, manganese, and a doping metal, the lithium manganese-based oxide being a composite metal oxide capable of intercalating and deintercalating lithium ions.

[0038] The lithium manganese-based oxide contained in the positive electrode active material defined herein may be a secondary particle including at least one primary particle.

[0039] Here, "secondary particles containing at least one primary particle" should be interpreted as including both "particles formed by agglomeration of multiple primary particles" and "non-agglomerated particles containing a single primary particle."

[0040] The primary particles and the secondary particles may each independently have a rod-like, elliptical and / or amorphous shape. Therefore, when the average major axis length is used as an index showing the size of the primary particles and the secondary particles, the average major axis length of the primary particles constituting the lithium manganese oxide may be in the range of 0.1 μm to 5 μm, and the average major axis length of the secondary particles may be 1 μm to 30 μm. The average major axis length of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles, and the positive electrode active material may include secondary particles having various average major axis lengths.

[0041] In addition, when the lithium manganese-based oxide is "non-agglomerated particles including a single primary particle" or "particles formed by agglomeration of a relatively small number of primary particles," the size (average particle size) of the primary particles contained in the "non-agglomerated particles including a single primary particle" or "particles formed by agglomeration of a relatively small number of primary particles" may be larger than the size (average particle size) of the primary particles contained in the secondary particles formed by agglomeration of tens to hundreds or more of primary particles.

[0042] For example, when the lithium manganese oxide is "non-agglomerated particles including a single primary particle" or "particles formed by agglomeration of a relatively small number of primary particles," the primary particles may have an average major axis length in the range of 0.5 μm to 20 μm. On the other hand, when the lithium manganese oxide is "particles formed by agglomeration of a plurality of (tens to hundreds or more) primary particles," the primary particles may have an average major axis length in the range of 0.1 μm to 5 μm.

[0043] The primary particles may also include at least one crystallite, i.e., the primary particles may consist of a single crystallite or may exist as particles containing multiple crystallites.

[0044] The lithium manganese-based oxide defined herein may be represented by the following Chemical Formula 1:

[0045] [Chemical formula 1] rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2

[0046] Where: M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi; 0 < r ≤ 0.7, 0 < a ≤ 1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z < 1, and 0 < x + y + z ≤ 1. At this time, preferably, x may be 0.6 or less, and z may be 0.4 or more.

[0047] The lithium manganese oxide represented by the chemical formula 1 may selectively contain cobalt. When the lithium manganese oxide contains cobalt, the ratio of the molar number of cobalt to the molar number of the total 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 the chemical formula 1 may not contain cobalt.

[0048] The lithium manganese oxide represented by the chemical formula 1 is a composite oxide in which an oxide of the C2 / m phase represented by Li2MnO3 and an oxide of the R3-m phase represented by Li a Ni x Co y Mn z M1 1-(x+y+z) O2 coexist. At this time, the oxide of the C2 / m phase and the oxide of the R3-m phase exist in a state of forming a solid solution.

[0049] In the lithium manganese oxide represented by the chemical formula 1, when r exceeds 0.7, the proportion of Li2MnO3, which is an oxide of the C2 / m phase, in the lithium manganese oxide becomes excessively large, and the discharge capacity of the positive electrode active material may decrease.

[0050] In the lithium manganese oxide represented by the chemical formula 1, in Li a Ni x Co y Mn z M1 1-(x+y+z) O2, x indicating the content of Ni is greater than 0 and less than or equal to 1. Preferably, in the lithium manganese oxide defined in the present application, in order to reduce the occurrence of the cation mixing phenomenon, Li a Ni x Co y Mn z M1 1-(x+y+z)The value z, which indicates the content of Ni in O2, may be more than 0 and 0.6 or less.

[0051] Among the lithium manganese oxides represented by the above chemical formula 1, the R3-m phase oxide Li a Ni x Co y Mn z M1 1-(x+y+z) In O2, z, which indicates the Mn content, is more than 0 and less than 1. Preferably, Li a Ni x Co y MnzM1 1-(x+y+z) The content of Mn in O2, z, may be 0.4 or more and less than 1.

[0052] The positive electrode active material according to the present invention includes a lithium-excess lithium-manganese-based oxide including at least lithium, nickel, manganese, and a doping metal, as represented by Chemical Formula 1, and the concentration of the transition metal in the lithium-manganese-based oxide is controlled by region, thereby mitigating and / or preventing a decrease in stability caused by the excess lithium and manganese in the lithium-manganese-based oxide.

[0053] In one embodiment, when the lithium manganese-based oxide is a secondary particle including at least one primary particle, the secondary particle has an average composition of M calculated from the average composition of all metal elements in the core. 2 / M 1 and M calculated from the average composition of all metallic elements in the shell 2 / M 1 may comprise at least one primary particle that is different from one another.

[0054] Here, the lithium manganese-based oxide may be "non-aggregated particles including a single primary particle," "secondary particles formed by agglomeration of a relatively small number of primary particles," and / or "secondary particles formed by agglomeration of a plurality of (several tens to several hundreds or more) primary particles."

[0055] As described above, when the concentration of any metal element present in the shell (or surface portion) and the core (or center portion) of the particle is different, the particle may be referred to as a core-shell particle. That is, the lithium manganese-based oxide may be a core-shell particle, and the average composition of all metal elements constituting the lithium manganese-based oxide in the core and the shell may be different from each other.

[0056] The shell may occupy at least a part of the surface of the core. That is, the shell may be present partially on the surface of the core, or may occupy the entire surface of the core. When the radius of the core-shell particle is r, the thickness of the shell may be 0.001r to 0.5r.

[0057] In the present application, the mole number of all metal elements in the lithium manganese oxide is M 1 The number of moles of nickel is called M 2 When the lithium manganese oxide is defined as above, M calculated from the average composition of all metal elements in the core of the lithium manganese oxide is 2 / M 1 and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. 2 / M 1 may be different from each other.

[0058] It is well known that lithium-excess lithium manganese oxides containing excessive Mn have lower electrical conductivity than LCO or NCM or NCA containing excessive Ni. In addition, there is a problem that the electrical conductivity of general NCM decreases as the Mn content increases.

[0059] Various reactions occur on the surface of the various types of cathode materials mentioned above. The higher the Mn content in the cathode active material, the more the charge-transfer and / or diffusion of Li ions on the surface is hindered, and this phenomenon can be called the surface kinetic or surface reaction kinetic decline.

[0060] As described above, the lithium manganese oxide defined in the present application has M in the shell. 2 / M 1 is in-core M 2 / M 1 By varying the Mn content, the surface kinetics of the lithium manganese oxide can be improved. Such an effect is achieved by the Mn content in the core and shell of the primary particles, secondary particles, crystallites, and / or single crystals described later. 2 / M 1 This effect can also be achieved through the difference in M ​​in the core and shell of the primary particles, secondary particles, crystallites and / or single crystals described below. 3 / M 1 This can also be achieved through differences in

[0061] The core M of the primary particle 2 / M 1 and M in the shell of the primary particle 2 / M 1 are different from each other, M 2 / M 1 is in the core of the primary particle M 2 / M 1 If it is larger, it can further contribute to the improvement of the surface kinetic described above.

[0062] Thus, the M 2 / M 1 is in the core of the primary particle M 2 / M 1 By making it larger, it is possible to mitigate and / or prevent phase transitions caused by migration of transition metals in the lithium manganese-based oxide.

[0063] M in the shell of the primary particle 2 / M 1 is in the core of the primary particle M 2 / M 1 When the M 2 / M 1A gradient of M can be formed from the shell to the core of the primary particle. 2 / M 1 When a gradient is formed in which the concentration of the metal element decreases, the abrupt change in concentration of the metal element between the shell and the core of the primary particle can be reduced.

[0064] That is, M in the lithium manganese oxide defined in the present application 2 / M 1 The gradient of M is not given by any oxide physically bonded to the primary particles and / or secondary particles constituting the lithium manganese-based oxide, but is given through a natural concentration gradient of the metal elements constituting the lithium manganese-based oxide. As a result, M is present in any region of the primary particles and / or secondary particles constituting the lithium manganese-based oxide. 2 / M 1 Thus, the stability of the crystal structure of the lithium manganese-based oxide can be improved.

[0065] When the primary particle is present as a particle containing a plurality of crystallites, the concentration of the transition metal in the crystallites can also be controlled for each region.

[0066] Specifically, the primary particles have a M calculated from the average composition of all metal elements in the core. 2 / M 1 and M calculated from the average composition of all metal elements in the shell of the crystallite. 2 / M 1 may contain at least one crystallite that is different from each other.

[0067] In this case, M calculated from the average composition of all metal elements in the core of the primary particle 2 / M 1 and M calculated from the average composition of all metal elements in the shell of the crystallite. 2 / M 1 When at least one different crystallite is present, a concentration gradient of the transition metal may be formed in the crystallite in the same direction as the primary particle.

[0068] That is, M in the shell of the crystallite 2 / M 1 is in the core of the crystallite M 2 / M 1 is larger, and M 2 / M 1 A gradient can be formed in which

[0069] When the primary particle is present as a particle containing a plurality of crystallites, M present inside the crystallites 2 / M 1 The gradient of can contribute to stabilizing the crystal structure of the crystallites and primary particles containing the crystallites, while at the same time improving the electrical conductivity.

[0070] When the lithium manganese-based oxide is a "secondary particle formed by agglomeration of a relatively small number of primary particles" and / or a "secondary particle formed by agglomeration of a plurality of (tens to hundreds or more) primary particles," the secondary particle itself may be a core-shell particle in which the average composition of all metal elements constituting the lithium manganese-based oxide in the core and shell is different from each other.

[0071] In this case, the M 2 / M 1 is the core M of the secondary particle 2 / M 1 is larger, and M 2 / M 1 A gradient in which the M in the secondary particles decreases can be formed. 2 / M 1 When a gradient of M exists in the primary particle constituting the secondary particle, 2 / M 1 A gradient of M may be selectively present. 2 / M 1 When a gradient of M exists in the primary particle constituting the secondary particle, 2 / M 1Even if no gradient of transition metal is present, the secondary particles themselves may be stabilized by the aforementioned gradient of transition metal as bulk particles.

[0072] In the present application, the mole number of all metal elements in the lithium manganese oxide is M 1 The number of moles of the doping metal is called M 3 When the lithium manganese oxide is defined as above, M calculated from the average composition of all metal elements in the core of the lithium manganese oxide is 3 / M 1 and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. 3 / M 1 may be different from each other. M calculated from the average composition of all metal elements in the core of the lithium manganese-based oxide 3 / M 1 and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. 3 / M 1 The effect of the difference in M 2 / M 1 is in-core M 2 / M 1 is the same as the difference between the two.

[0073] When the lithium manganese-based oxide is a secondary particle including at least one primary particle, M calculated from the average composition of all metal elements in the core of the secondary particle is 3 / M 1 and M calculated from the average composition of all metal elements in the shell of the primary particle and / or the secondary particle. 3 / M 1 may be different from each other.

[0074] In other cases, the secondary particles have a core-to-core average composition of metallic elements, calculated as M 3 / M 1 and M calculated from the average composition of all metallic elements in the shell 3 / M 1 may include at least one primary particle having different

[0075] In addition, when the primary particle is present as a particle including a plurality of crystallites, the primary particle has a M calculated from the average composition of all metal elements in the core. 3 / M 1 and M calculated from the average composition of all metallic elements in the shell 3 / M 1 may contain at least one crystallite that is different from each other.

[0076] As in the various cases described above, M 3 / M 1 and M in the shell 3 / M 1 are different from each other, M 3 / M 1 is the particle's core M 3 / M 1 It is preferable that the particle shell M 3 / M 1 is the particle's core M 3 / M 1 If it is larger, M 3 / M 1 A gradient can be formed in which

[0077] That is, M formed in the lithium manganese oxide 3 / M 1 The direction of the gradient of M 2 / M 1 The direction of the gradient of the M in the lithium manganese oxide is the same as that of the 2 / M 1 and M. 3 / M 1 By forming a gradient of the above, it is possible to mitigate and / or prevent the decrease in stability caused by the presence of excess lithium and manganese in the lithium manganese-based oxide.

[0078] In addition to the core-shell type lithium manganese oxides mentioned in the present application, in various core-shell type positive electrode active materials (e.g., NCA / NCM, etc.), it is common to synthesize precursors using metal aqueous solutions with different compositions in order to make the composition of metal elements in the core and shell different or to form a concentration gradient of the metal elements between the core and shell.

[0079] However, in the case of the positive electrode active material defined in the present application, in the case of lithium manganese oxide, the hydroxide precursor is coated with Ni and / or Co before roasting (first heat treatment), thereby forming M in the core and shell of the final product (lithium manganese oxide). 2 / M 1 In addition, the difference between M and M along the direction from the core to the shell can be realized. 2 / M 1 It is possible to form a gradient of

[0080] According to another embodiment of the present invention, instead of coating the hydroxide precursor with Ni and / or Co before roasting (first heat treatment), a doping metal is present in the lithium manganese-based oxide, and the concentration of the doping metal (in this application, M 3 / M 1 By forming a gradient of M 2 / M 1 It is possible to embody the difference.

[0081] As a result, the positive electrode active material including the lithium-excess lithium manganese-based oxide according to the various embodiments defined herein can exhibit electrochemical properties and stability at a commercially viable level.

[0082] In another embodiment, at least one metal oxide represented by the following formula 2 may be present on at least a portion of the surface of the lithium manganese-based oxide:

[0083] [Chemical formula 2] Li b M2 c Od

[0084] Where: 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≦b≦8, 0 <c≦8、2≦d≦13である。

[0085] The metal oxide represented by Formula 2 may be formed by reacting at least a portion of the metal elements (nickel, manganese, cobalt and / or doping metal) constituting the lithium manganese-based oxide with Li present on the surface of the lithium manganese-based oxide.

[0086] The metal oxide reduces lithium-containing impurities (or residual lithium) present on the surface of the lithium manganese-based oxide and acts as a diffusion path for lithium ions, thereby improving the electrochemical properties of the lithium manganese-based oxide.

[0087] When the lithium manganese-based oxide is a core-shell particle, the metal oxide may be present integrally with the shell.

[0088] 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 that constitute the lithium manganese-based oxide.

[0089] The metal oxide is an oxide of lithium and an element represented by M2 in a composite form, or an oxide of M2. 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 , Co b O c , Al b O c , W b O c , Zr b O c or Ti b O c However, the above examples are merely given for the sake of convenience in order to facilitate understanding, and the metal oxide defined in the present application is not limited to the above examples.

[0090] The metal oxide may be an oxide in which lithium and at least two elements represented by M2 are combined, or may further include an oxide in which lithium and at least two elements represented by M2 are combined. The oxide in which lithium and at least two elements represented by M2 are combined may be, 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 It may be, but is not necessarily limited to, this.

[0091] Lithium secondary battery According to another aspect of the present invention, there is provided a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include the lithium composite oxide according to any of the various embodiments of the present invention as a positive electrode active material.

[0092] Therefore, a detailed description of the lithium composite oxide will be omitted, and only the remaining components not described above will be described below. Also, for convenience, the lithium composite oxide will be referred to as a positive electrode active material below.

[0093] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0094] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0095] At this time, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically, 85 to 98.5 wt%, based on the total weight of the positive electrode active material layer. When included in this content range, excellent capacity characteristics can be exhibited, but the amount is not necessarily limited thereto.

[0096] The conductive material is used to impart electrical conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials such as carbon fibers, 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 the like, and one or more of these may be used alone or in combination. The conductive material may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0097] The binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and among these, one type alone or a mixture of two or more types may be used. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0098] The positive electrode may be manufactured by a typical method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0099] The solvent may be a 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 alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when applied to manufacture a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0100] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the positive electrode slurry composition from the support, and laminating the resulting film on a positive electrode current collector.

[0101] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-mentioned positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0102] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0103] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0104] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0105] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0106] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0107] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material 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, and Al alloys, and SiO β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, may be used. A metallic lithium thin film may be used as the negative electrode active material. Low-crystalline carbon and high-crystalline carbon may both be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0108] The negative electrode active material may be included in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer.

[0109] The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and may be added in an amount of usually 0.1 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0110] The conductive material may be added as a component for further improving 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 may be, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives.

[0111] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition 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 and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, and then peeled off from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0112] In another embodiment, 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 optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating, or by casting the negative electrode slurry composition on a separate support and peeling the composition from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0113] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ions to move. Any separator generally used in lithium secondary batteries may be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte humidification ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. In addition, in order to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0114] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0115] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0116] The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. 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, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that may be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based 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 / discharge performance of a 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 performance of the electrolyte may be excellent if the cyclic carbonate and the chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9.

[0117] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. 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. The concentration of the lithium salt is preferably used within a range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

[0118] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine 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 the decrease in battery capacity, improving the discharge capacity of the battery, etc. In this case, the additives may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0119] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0120] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0121] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0122] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (Electric Vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0123] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0124] Production Example 1. Production of positive electrode active material Example 1 (a) Preparation of precursor The reactor was filled with a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, and NaOH and NH4OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was added to the reactor. After the reaction was completed, the reactor was washed and dehydrated to produce Ni with an average particle size of 4 μm. 0.4 Mn 0.6 The (OH)2 precursor was obtained.

[0125] (b) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550° C., and then the furnace was cooled.

[0126] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.25) as a lithium compound and WO3 of 1.0 mol% relative to the metal elements in the precursor to prepare a mixture.

[0127] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0128] Example 2 (a) Preparation of precursor A nickel-manganese hydroxide precursor was prepared in the same manner as in Example 1.

[0129] (b) Precursor coating In the reactor in which the precursor obtained in step (a) was stirred, CoSO4·7H2O aqueous solution, NaOH, and NH4OH were added. At this time, CoSO4·7H2O was weighed out to be 10 mol% and then added. After the reaction was completed, the product was washed and dehydrated, and then dried at 150℃ for 14 hours to obtain the coated precursor.

[0130] (c) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550° C., and then the furnace was cooled.

[0131] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (Li-excluded metal) molar ratio=1.25) as a lithium compound to prepare a mixture.

[0132] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 850°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0133] Example 3 A positive electrode active material was prepared in the same manner as in Example 2, except that step (d) was performed as follows.

[0134] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.25) as a lithium compound and WO3 of 1.0 mol% relative to the metal elements in the precursor to prepare a mixture.

[0135] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 850°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0136] Example 4 (a) Preparation of precursor A nickel-manganese hydroxide precursor was prepared in the same manner as in Example 1.

[0137] (b) Precursor coating In the reactor in which the precursor obtained in step (a) was stirred, NiSO4·6H2O aqueous solution, NaOH, and NH4OH were added. At this time, NiSO4·6H2O was weighed out to be 5mol% and then added. After the reaction was completed, the precursor was washed and dehydrated, and then dried at 150℃ for 14 hours to obtain the coated precursor.

[0138] (c) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (b) was heat-treated for 5 hours while maintaining the temperature at 550° C., and then the furnace was cooled.

[0139] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (Li-excluded metal) molar ratio=1.25) as a lithium compound to prepare a mixture.

[0140] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0141] Example 5 A positive electrode active material was prepared in the same manner as in Example 4, except that step (d) was performed as follows.

[0142] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.25) as a lithium compound and WO3 of 1.0 mol% relative to the metal elements in the precursor to prepare a mixture.

[0143] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0144] Example 6 A positive electrode active material was prepared in the same manner as in Example 2, except that step (d) was performed as follows.

[0145] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.25) as a lithium compound and Nb2O5 of 0.5 mol% relative to the metal elements in the precursor to prepare a mixture.

[0146] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 850°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0147] Example 7 A positive electrode active material was prepared in the same manner as in Example 2, except that step (d) was performed as follows.

[0148] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (metal excluding Li) molar ratio=1.25) as a lithium compound and MoO3 of 0.5 mol% relative to the metal elements in the precursor to prepare a mixture.

[0149] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 850°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0150] Example 8 (a) Preparation of precursor The reactor was filled with a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, and NaOH and NH4OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated to produce Ni with an average particle size of 4 μm. 0.4 Mn0.6 The (OH)2 precursor was obtained.

[0151] (b) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 800° C., and then the furnace was cooled.

[0152] (c) Precursor coating CoSO4·7H2O aqueous solution, NaOH, and NH4OH were added to the reactor in which the oxide precursor obtained in step (b) was stirred. At this time, CoSO4·7H2O was weighed out to be 10 mol% and then added. After the reaction was completed, the product was washed and dehydrated, and then dried at 150℃ for 14 hours to obtain the coated precursor.

[0153] (d) Second heat treatment The precursor obtained in step (c) was mixed with LiOH (Li / (Li-excluded metal) molar ratio=1.25) as a lithium compound to prepare a mixture.

[0154] Next, the mixture was heat-treated for 16 hours while maintaining the temperature at 1,000°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-rich lithium manganese-based oxide having an average particle size of 5μm. At this time, as shown in Fig. 7, it was confirmed that the average particle size of the primary particles constituting the lithium manganese-based oxide contained in the positive electrode active material was larger than that of the primary particles constituting the lithium manganese-based oxide contained in the positive electrode active materials according to Examples 1 to 3.

[0155] Comparative Example 1 (a) Preparation of precursor The reactor was filled with a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, and NaOH and NH4OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated to produce Ni with an average particle size of 4 μm. 0.4 Mn 0.6 The (OH)2 precursor was obtained.

[0156] (b) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550° C., and then the furnace was cooled.

[0157] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (Li-excluded metal) molar ratio=1.25) as a lithium compound to prepare a mixture.

[0158] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material including a lithium-excess lithium manganese-based oxide having an average particle size of 4 μm.

[0159] Comparative Example 2 (a) Preparation of precursor The reactor was filled with a mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, and NaOH and NH4OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated to produce Ni with an average particle size of 4 μm. 0.4 Mn 0.6 The (OH)2 precursor was obtained.

[0160] (b) First heat treatment The temperature of the sintering furnace in an O2 atmosphere was increased at a rate of 2° C. / min, and the precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 800° C., and then the furnace was cooled.

[0161] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (Li-excluded metal) molar ratio=1.25) as a lithium compound to prepare a mixture.

[0162] Next, the mixture was heat-treated for 16 hours while maintaining the temperature at 1,000°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then the furnace was cooled to finally obtain a positive electrode active material containing a lithium-rich lithium manganese-based oxide having an average particle size of 5 μm. It was confirmed that the average particle size of the primary particles constituting the lithium manganese-based oxide contained in the positive electrode active material was large, similar to Example 8.

[0163] Manufacturing Example 2. Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation 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 positive electrode slurry was uniformly applied to a thin aluminum film having a thickness of 15 μm and dried in a vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0164] A coin battery was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte of LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0165] Experimental example 1. Analysis of metal elements in lithium manganese oxide TEM / EDS analysis was carried out to confirm the change in the content of metal elements in the lithium manganese-based oxide produced by Production Example 1. The TEM image of the lithium manganese-based oxide was obtained after cross-sectioning the lithium manganese-based oxide with FIB.

[0166] Fig. 1 is a cross-sectional TEM image of the lithium manganese oxide included in the positive electrode active material according to Example 1, and shows the distribution of Ni, Mn, and W elements through EDS mapping of the cross section of the lithium manganese oxide. Also, Fig. 2 is a line sum spectrum showing the change in the content of metal elements (Ni, Mn, W) present in the lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of Fig. 1.

[0167] 1 and 2, it can be seen that the lithium manganese-based oxide included in the positive electrode active material according to Example 1 is a secondary particle including a plurality of primary particles, and a concentration gradient of Ni, Mn, and W is formed in a direction that is approximately perpendicular to the direction from the shell to the core of the secondary particle.

[0168] The concentration gradients of Ni, Mn, and W formed in the direction almost perpendicular to the direction from the shell to the core of the secondary particle were calculated from the average composition of all metal elements in the core of the primary particle. 2 / M 1 and M. 3 / M 1 and M calculated from the average composition of all metal elements in the shell of the primary particle. 2 / M 1 and M. 3 / M 1 are different from each other, so it can be confirmed that this has occurred.

[0169] It can also be seen that the concentrations of Ni and W in the secondary particles are higher near the grain boundary between the primary particles.

[0170] Table 1 below shows the concentrations (mol%) of Ni, Mn, and W in the core and shells (shell 1, shell 2) of primary particles. The concentrations (mol%) of Ni, Mn, and W in the core and shells (shell 1, shell 2) of primary particles were calculated from the line EDS spectrum, and the concentrations of Ni, Mn, and W in the bulk particles were calculated through ICP analysis. Here, shell 1 corresponds to the shell of the primary particle located on one side of the region corresponding to the core of the primary particle based on the direction shown in the cross-sectional TEM image of Figure 1, and shell 2 corresponds to the shell of the primary particle located on the other side of the region corresponding to the core of the primary particle based on the direction shown in the cross-sectional TEM image of Figure 1.

[0171] [Table 1]

[0172] Referring to the results of FIG. 2 and Table 1, M calculated from the average composition of all metal elements in the core of the primary particle 2 / M 1 is 39.1, calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particles. 2 / M 1 are 64.7 and 71.6. As a result, the lithium manganese oxide has a M 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the gradient of decrease in the particle size indicates that the aggregates of primary particles (secondary particles) are formed.

[0173] In addition, M calculated from the average composition of all metal elements in the core of the primary particle 3 / M 1 is 0.2, calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particle.3 / M 1 are 2.6 and 2.1. As a result, the lithium manganese oxide has a M 3 / M 1 is in-core M 3 / M 1 Larger, from shell to core, M 3 / M 1 It can be seen that the decreasing gradient of β contains the formed primary particles.

[0174] Fig. 3 is a cross-sectional TEM image of the lithium manganese oxide included in the positive electrode active material according to Example 2, and shows the distribution of Ni, Co, and Mn elements through EDS mapping of the cross section of the lithium manganese oxide. Also, Fig. 4 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn) present in the lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of Fig. 3.

[0175] 3 and 4, it can be seen that the lithium manganese-based oxide included in the positive electrode active material according to Example 2 is a secondary particle including a plurality of primary particles, and a concentration gradient of Ni, Co, and Mn is formed in the direction from the shell to the core of the secondary particle.

[0176] Thus, the concentration gradients of Ni, Co, and Mn formed in the direction from the shell to the core of the secondary particle were calculated from the average composition of all metal elements in the core of the secondary particle. 2 / M 1 and M. 3 / M 1 and M calculated from the average composition of the entire metal elements in the shell of the secondary particle. 2 / M 1 and M. 3 / M 1 are different from each other, so it can be confirmed that this has occurred.

[0177] It can also be confirmed that the Ni concentration in the secondary particles is higher the closer to the outermost periphery of the secondary particles.

[0178] Table 2 below shows the concentrations (mol%) of Ni, Co, and Mn in the core and shell of secondary particles. The concentrations (mol%) of Ni, Co, and Mn in the core and shell of secondary particles were calculated from the line EDS spectrum, and the concentrations of Ni, Co, and Mn in the bulk of the particle were calculated through ICP analysis. Here, the shell corresponds to the shell of the secondary particle located on the outer periphery of the area corresponding to the core of the secondary particle based on the direction shown in the cross-sectional TEM image of Figure 3.

[0179] [Table 2]

[0180] Referring to the results of FIG. 4 and Table 2, M calculated from the average composition of all metal elements in the core of the secondary particle 2 / M 1 is 33.7, which is calculated from the average composition of all metal elements in the shell of the secondary particle. 2 / M 1 is 67.9. As a result, the lithium manganese oxide has a M 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the decreasing gradient of is the secondary particle formed.

[0181] Fig. 5 is a cross-sectional TEM image of the lithium manganese oxide included in the positive active material according to Example 3, and shows the distribution of Ni, Co, Mn, and W elements through EDS mapping of the cross section of the lithium manganese oxide. Also, Fig. 6 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn, W) present in the lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of Fig. 5.

[0182] 5 and 6, it can be seen that the lithium manganese-based oxide included in the positive electrode active material according to Example 3 is a secondary particle including a plurality of primary particles, and a concentration gradient of Ni, Co, Mn, and W is formed in a direction that is approximately perpendicular to the direction from the shell to the core of the secondary particle.

[0183] Thus, the concentration gradients of Ni, Co, Mn, and W formed in a direction almost perpendicular to the direction from the shell to the core of the secondary particle were calculated from the average composition of all metal elements in the core of the primary particle. 2 / M 1 and M. 3 / M 1 and M calculated from the average composition of all metal elements in the shell of the primary particle. 2 / M 1 and M. 3 / M 1 are different from each other, so it can be confirmed that this has occurred.

[0184] It can also be seen that the concentrations of Ni and W in the secondary particles are higher near the grain boundary between the primary particles.

[0185] Table 3 below shows the concentrations (mol%) of Ni, Co, Mn, and W in the core and shells (shell 1, shell 2) of primary particles. The concentrations (mol%) of Ni, Co, Mn, and W in the core and shells (shell 1, shell 2) of primary particles were calculated from the line EDS spectrum, and the concentrations of Ni, Co, Mn, and W in the bulk particles were calculated through ICP analysis. Here, shell 1 corresponds to the shell of the primary particle located on one side of the region corresponding to the core of the primary particle based on the direction shown in the cross-sectional TEM image of FIG. 5, and shell 2 corresponds to the shell of the primary particle located on the other side of the region corresponding to the core of the primary particle based on the direction shown in the cross-sectional TEM image of FIG. 5.

[0186] [Table 3]

[0187] Referring to the results of FIG. 6 and Table 3, M calculated from the average composition of all metal elements in the core of the primary particle 2 / M 1 is 36.6, calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particle. 2 / M 1 are 49.4 and 46.3. As a result, the lithium manganese oxide has M in the shell. 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the decreasing gradient of β contains the formed primary particles.

[0188] In addition, M calculated from the average composition of all metal elements in the core of the primary particle 3 / M 1 is 0.7, calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particle. 3 / M 1 are 4.8 and 4.0. As a result, the lithium manganese oxide has a M 3 / M 1 is in-core M 3 / M 1 Larger, from shell to core, M 3 / M 1 It can be seen that the decreasing gradient of β contains the formed primary particles.

[0189] Furthermore, referring to FIG. 6, there is a M between the core and shell 2 (line EDS spectrum reference 0.15 μm to 0.25 μm region). 2 / M 1The results show that the lithium manganese-based oxide contained in the positive electrode active material according to Example 3 is a secondary particle including a plurality of primary particles, and the primary particles include a plurality of crystallites, and the gradient of M from the shell to the core of the crystallites is observed. 2 / M 1 This is due to the decreasing gradient.

[0190] Tables 4 to 7 below show the results of measuring the concentration of metal elements in the core and shell of the primary particles constituting the lithium manganese-based oxide contained in the positive electrode active materials according to Examples 4 to 7 through line EDS analysis and ICP analysis, respectively, and it can be seen that the concentration difference of metal elements was realized between the shell and the core, the same as in the positive electrode active materials according to the various examples described above. Here, based on the line scanning direction that crosses the core of the primary particle in a straight line, shell 1 corresponds to the shell of the primary particle located on one side of the region corresponding to the core of the primary particle, and shell 2 corresponds to the shell of the primary particle located on the other side of the region corresponding to the core of the primary particle.

[0191] [Table 4]

[0192] [Table 5]

[0193] [Table 6]

[0194] [Table 7]

[0195] Fig. 7 is a cross-sectional TEM image of the lithium manganese oxide included in the positive electrode active material of Example 8, and a diagram showing the distribution of Ni, Co, and Mn elements through EDS mapping of the cross section of the lithium manganese oxide. Fig. 8 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn) present in the lithium manganese oxide through EDS analysis in the direction 1 shown in the cross-sectional TEM image of Fig. 7, and Fig. 9 is a line sum spectrum showing the change in the content of metal elements (Ni, Co, Mn) present in the lithium manganese oxide through EDS analysis in the direction 2 shown in the cross-sectional TEM image of Fig. 7.

[0196] 7 to 9, it can be seen that the crystal size of the particles constituting the lithium manganese-based oxide contained in the positive electrode active material according to Example 8 is larger than the particles constituting the lithium manganese-based oxide shown in Figures 1, 3, and 5. It is believed that this difference is due to the first heat treatment conditions, and it can be seen that the crystal growth of the particles constituting the lithium manganese-based oxide contained in the positive electrode active material according to Example 8 is promoted by heat treating the hydroxide precursor at a higher temperature for a longer period of time.

[0197] Direction 1 shown in the cross-sectional TEM image of Figure 7 is used to confirm the change in concentration of metal elements (Ni, Co, Mn) in the primary particles, and Table 8 below shows the concentrations (mol%) of Ni, Co, and Mn in the core and shell of the primary particles. The concentrations (mol%) of Ni, Co, and Mn in the core and shell of the primary particles were calculated from the line EDS spectrum, and the concentrations of Ni, Co, and Mn in the bulk of the particles were calculated through ICP analysis. Here, the shell corresponds to the shell of the primary particle located on the outer periphery of the area corresponding to the core of the primary particle based on direction 1 shown in the cross-sectional TEM image of Figure 7.

[0198] [Table 8]

[0199] Referring to the results of FIG. 8 and Table 8, M calculated from the average composition of all metal elements in the core of the primary particle 2 / M 1 is 41.7, which is calculated from the average composition of all metal elements in the shell of the primary particle. 2 / M 1 is 57.3. As a result, the lithium manganese oxide has a M 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the decreasing gradient of β contains the formed primary particles.

[0200] Direction 2 shown in the cross-sectional TEM image of Figure 7 is used to confirm the change in concentration of metal elements (Ni, Co, Mn) in the secondary particles, and Table 9 below shows the concentrations (mol%) of Ni, Co, and Mn in the core and shell of the secondary particles. The concentrations (mol%) of Ni, Co, and Mn in the core and shell of the secondary particles were calculated from the line EDS spectrum, and the concentrations of Ni, Co, and Mn in the bulk of the particle were calculated through ICP analysis. Here, the shell corresponds to the shell of the secondary particle located on the outer periphery of the region corresponding to the core of the secondary particle based on direction 2 shown in the cross-sectional TEM image of Figure 7.

[0201] [Table 9]

[0202] Referring to the results of FIG. 9 and Table 9, M calculated from the average composition of all metal elements in the core of the secondary particle 2 / M 1is 41.4, which is calculated from the average composition of all metal elements in the shell of the secondary particle. 2 / M 1 is 55.3. As a result, the lithium manganese oxide has a M 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the decreasing gradient of β contains the formed secondary particles.

[0203] 7 to 9, the lithium manganese oxide has M in the shell. 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 The primary particles may have a secondary particle containing a primary particle in which a gradient of decreasing M 2 / M 1 is in-core M 2 / M 1 Larger, from shell to core, M 2 / M 1 It can be seen that the decreasing gradient may be the formed secondary particles themselves.

[0204] That is, in the lithium manganese oxide, M in the shell 2 / M1 is M in the core 2 / M1, and M from the shell to the core 2 The particle units in which a gradient of decreasing / M1 is formed may be primary particles and / or secondary particles, or may be crystallite units constituting primary particles.

[0205] Fig. 10 is a cross-sectional TEM image of the lithium manganese oxide included in the positive active material according to Comparative Example 1, and shows the distribution of Ni and Mn elements through EDS mapping of the cross section of the lithium manganese oxide. Also, Fig. 11 is a line sum spectrum showing the change in the content of metal elements (Ni, Mn) present in the lithium manganese oxide through EDS analysis in the direction shown in the cross-sectional TEM image of Fig. 10.

[0206] The following Table 10 shows the Ni and Mn concentrations (mol%) in the core and shell of the primary particles. The Ni and Mn concentrations (mol%) in the core and shell of the primary particles were calculated from the Line EDS spectrum, and the Ni and Mn concentrations in the bulk were calculated through ICP analysis.

[0207] [Table 10]

[0208] 10 and 11, it can be seen that the lithium manganese-based oxide included in the positive electrode active material according to Comparative Example 1 is a secondary particle including a plurality of primary particles, and no concentration gradient of Ni and Mn is formed between the core and shell of the primary particle present at the outermost part of the secondary particle.

[0209] Table 11 below shows the results of measuring the concentrations of metal elements in the core and shell of primary particles and secondary particles constituting a lithium manganese-based oxide contained in the cathode active material according to Comparative Example 2 through Line EDS analysis and ICP analysis. It can be seen that, unlike the cathode active material according to Example 8, there is almost no difference in the concentration of metal elements between the shell and the core.

[0210] [Table 11]

[0211] Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries The lithium secondary battery (coin cell) manufactured in Manufacturing Example 2 was subjected to a charge-discharge experiment at 25° C., voltage range of 2.0 V to 4.6 V, and discharge rate of 0.1 C to 5.0 C using an electrochemical analyzer (Toyo, Toscat-3100) to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and rate capability (rate capability (C-rate)).

[0212] In addition, the same lithium secondary battery was charged and discharged 50 times at 25°C and within a driving voltage range of 2.0 V to 4.6 V at 1 C / 1 C, and then the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0213] The measurement results are shown in Tables 12 and 13 below.

[0214] [Table 12]

[0215] [Table 13]

[0216] Referring to the results of Tables 12 and 13, it can be seen that the discharge capacity of the lithium secondary batteries using the positive electrode active materials of Examples 1 to 8 is increased compared to the lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 and 2, and thus the reversible efficiency is improved and the cycle capacity retention rate and the discharge capacity rate are increased.

[0217] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding elements without departing from the concept of the present invention described in the claims, and this may also be considered to be within the scope of the claims of the present invention.

Claims

1. A positive electrode active material comprising a lithium-excess lithium-manganese-based oxide containing at least lithium, nickel, and manganese, In the lithium manganese oxide, the mole number of all metal elements is M １ The number of moles of nickel is M ２ When I say, M calculated from the average composition of all metal elements in the core of the lithium manganese-based oxide ２ / M １ and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. ２ / M １ are different positive electrode active materials.

2. The lithium manganese oxide is a secondary particle including at least one primary particle, The secondary particles have a M calculated from the average composition of all metal elements in the core. ２ / M １ and M calculated from the average composition of all metal elements in the shell ２ / M １ 2. The positive electrode active material of claim 1 , comprising at least one primary particle having a diameter greater than or equal to 100 nm.

3. The lithium manganese oxide is a secondary particle including at least one primary particle, M calculated from the average composition of all metal elements in the core of the secondary particle ２ / M １ and M calculated from the average composition of all metal elements in the shell of the secondary particle. ２ / M １ The positive electrode active material according to claim 1 , wherein

4. The lithium manganese oxide is a secondary particle including at least one primary particle, The primary particle comprises at least one crystallite, The primary particles have a M calculated from the average composition of all metal elements in the core. ２ / M １ and M calculated from the average composition of all metal elements in the shell ２ / M １ The positive electrode active material according to claim 1 , wherein each of the first and second crystallites is different from each other.

5. The lithium manganese oxide shell M ２ / M １ is the M in the core of the lithium manganese oxide ２ / M １ The positive electrode active material of claim 1 .

6. The lithium manganese oxide is M from the shell to the core. ２ / M １ The positive electrode active material according to claim 5 , wherein a gradient is formed in which

7. The lithium manganese-based oxide further comprises a doping metal; In the lithium manganese oxide, the mole number of all metal elements is M １ The number of moles of the doping metal is called M ３ When I say, M calculated from the average composition of all metal elements in the core of the lithium manganese-based oxide ３ / M １ and M calculated from the average composition of all metal elements in the shell of the lithium manganese oxide. ３ / M １ The positive electrode active material according to claim 1 , wherein

8. The lithium manganese oxide is a secondary particle including at least one primary particle, The secondary particles have a M calculated from the average composition of all metal elements in the core. ３ / M １ and M calculated from the average composition of all metal elements in the shell ３ / M １ 8. The positive electrode active material of claim 7, comprising at least one primary particle that is different from one another.

9. The lithium manganese oxide is a secondary particle including at least one primary particle, M calculated from the average composition of all metal elements in the core of the secondary particle ３ / M １ and M calculated from the average composition of all metal elements in the shell of the secondary particle. ３ / M １ The positive electrode active material according to claim 7 , wherein:

10. The lithium manganese oxide is a secondary particle including at least one primary particle, The primary particle comprises at least one crystallite, The primary particles have a M calculated from the average composition of all metal elements in the core. ３ / M １ and M calculated from the average composition of all metal elements in the shell ３ / M １ The positive electrode active material according to claim 7 , wherein each of the crystallites includes at least one crystallite that is different from the other crystallites.

11. The lithium manganese oxide shell M ３ / M １ is the M in the core of the lithium manganese oxide ３ / M １ The positive electrode active material of claim 7 .

12. The lithium manganese oxide is M from the shell to the core. ３ / M １ The positive electrode active material according to claim 11 , wherein a gradient is formed in which

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

14. The positive electrode active material according to claim 1 , wherein at least one metal oxide represented by the following chemical formula 2 is present on at least a portion of the surface of the lithium manganese-based oxide: [Chemical formula 2] <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> ｂ <h2 style=";text-align:left;direction:ltr"> 12<h2 style=";text-align:left;direction:ltr"> ｃ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ｄ Where: 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≦b≦8, 0<c≦8, and 2≦d≦13.

15. A positive electrode comprising the positive electrode active material according to claim 1 .

16. A lithium secondary battery using the positive electrode according to claim 15.

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