Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a cathode active material and a lithium secondary battery including the same, and more specifically to a cathode active material and a lithium secondary battery including the same, which includes a lithium-excess lithium-manganese-based oxide containing at least lithium, nickel, manganese, and a doping metal, and 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 the excess lithium and manganese present in the lithium-manganese-based oxide.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a lithium-rich lithium manganese-based oxide including at least lithium, nickel, manganese, and a doping metal, and by controlling the concentration of transition metals in regions in the lithium manganese-based oxide, a positive electrode active material in which a decrease in stability caused by lithium and manganese present in excess in the lithium manganese-based oxide is alleviated and / or prevented, and a lithium secondary battery including the same.

Background Art

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

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

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

[0005] Among the above-mentioned cathode active materials, LiCoO₂ is excellent in life characteristics and charge-discharge efficiency and is the most widely used. However, due to the resource limitations of cobalt used as a raw material, it is expensive, so it has the disadvantage of limited price competitiveness.

[0006] Lithium manganese oxides such as LiMnO₂ and LiMn₂O₄ have the advantages of excellent thermal safety and low price, but have problems such as small capacity and poor high-temperature characteristics. In addition, LiNiO₂-based cathode active materials exhibit battery characteristics with high discharge capacity, but are difficult to synthesize due to the cation mixing problem between Li and transition metals, and thus have major problems in rate characteristics.

[0007] In addition, a large amount of Li by-products are generated according to the degree of deepening of such cation mixing. Most of these Li by-products consist of compounds of LiOH and Li₂CO₃, so there are problems of gelling during the production of the cathode paste and causing gas generation due to the progress of charge and discharge after the production of the electrode. Residual Li₂CO₃ not only increases the swelling phenomenon of the cell and reduces the cycle, but also causes the battery to swell.

[0008] Various candidate materials have been discussed to complement the disadvantages of such conventional cathode active materials.

[0009] As an example, research has been conducted on using a lithium-rich lithium manganese-based oxide in which Mn among transition metals is excessively contained and at the same time the lithium content is higher than the total content of transition metals as a cathode active material for a lithium secondary battery. Such a lithium-rich lithium manganese-based oxide is also referred to as an overlithiated layered oxide (OLO).

[0010] Although the OLO has the advantage of being able to theoretically exhibit high capacity in a high-voltage operating environment, in practice, due to the excessive amount of Mn contained in the oxide, the electrical conductivity is relatively low. As a result, there is a disadvantage that the capability rate of a lithium secondary battery using OLO is low. Thus, when the rate characteristic is low, problems such as a decrease in charge-discharge capacity and life efficiency (capacity retention) occur during the cycling of the lithium secondary battery.

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

[0012] In order to solve the above problems, there have been attempts to improve the problems of OLO through structural improvement and surface modification of particles, such as adjusting the particle size of OLO or coating the surface of OLO, but it has not reached the commercialization level.

Summary of the Invention

Problems to be Solved by the Invention

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

[0014] For example, conventionally, lithium secondary batteries using LFP have been mainly used from the viewpoint of ensuring safety, etc., but recently, the use of nickel-based lithium composite oxides with a higher energy capacity per unit weight than LFP has been on the rise.

[0015] Recently, many nickel-based lithium composite oxides used as cathode 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, in the case of cobalt, there is a problem that not only the supply and demand is unstable but also it is excessively expensive compared to other raw materials. Therefore, there is a need for a cathode active material with a new composition that can reduce the cobalt content or eliminate cobalt.

[0016] From this perspective, lithium-excess lithium manganese oxides can meet the aforementioned market expectations. However, it can be said that the electrochemical properties and stability of lithium manganese oxides are insufficient as a substitute for commercially available NCM or NCA type cathode active materials.

[0017] However, when compared with other types of commercially available cathode active materials, even if conventional lithium-excess lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability, if it is possible to control the concentration of transition metals in the lithium manganese oxide by region, the present inventors have confirmed that lithium-excess lithium manganese oxides can also exhibit electrochemical properties and stability at a commercially viable level.

[0018] Accordingly, an object of the present invention is to provide a cathode active material including a lithium-excess lithium manganese oxide containing at least lithium, nickel, manganese, and a doping metal, and by controlling the concentration of transition metals in the lithium manganese oxide by region, reducing and / or preventing the decrease in stability caused by excessive lithium and manganese present in the lithium manganese 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 cathode including the cathode active material defined in the present application.

Means for Solving the Problems

[0020] According to one aspect of the present invention for solving the above technical problem, a positive electrode active material containing a lithium-rich lithium manganese-based oxide containing at least lithium, nickel, and manganese, wherein in the lithium manganese-based oxide, the number of moles of the total metal elements is M 1 is referred to as, and the number of moles of nickel is M 2 When it is referred to as, M calculated from the average composition of the total metal elements in the core of the lithium manganese-based oxide 2 / M 1 and M calculated from the average composition of the total metal elements in the shell of the lithium manganese-based oxide 2 / M 1 are different from each other, and 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] Here, 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.

[0024] The lithium manganese-based oxide represented by Chemical Formula 1 may selectively contain cobalt. Further, when the lithium manganese-based oxide contains cobalt, the ratio of the number of moles of cobalt to the number of moles 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 oxide may be a secondary particle including at least one primary particle. In this case, M calculated from the average composition of the entire metal elements within the core of the primary particle 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of the entire metal elements within 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 the entire metal elements within the core of the secondary particle 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of the entire metal elements within 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 is 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 the entire metal elements within the core of the crystallite 2 / M 1 (or M 3 / M 1 ) and M calculated from the average composition of the entire metal elements within 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 the particles (where the particles may be any crystallites present within the primary particles, any primary particles or secondary particles present within the secondary particles) is different, the particles can be referred to as core-shell particles. That is, the lithium manganese-based oxide is a core-shell particle, and the average composition of the total metal elements constituting the lithium manganese-based oxide in the core and the shell may be different from each other.

[0028] Also, according to another aspect of the present invention, a positive electrode including the above-described positive electrode active material is provided.

[0029] Furthermore, according to still another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

Advantages of the Invention

[0030] According to the present invention, when compared with other types of commercialized positive electrode active materials, it is possible to improve the limitations of conventional lithium-excess lithium manganese-based oxides that have various disadvantages from the viewpoints of electrochemical characteristics and / or stability.

[0031] Specifically, according to the present invention, by controlling the concentration of transition metals (particularly nickel and doping metals) contained in the lithium-excess lithium manganese-based oxide by region within the particles, there is an advantage that it is possible to alleviate and / or prevent a decrease in stability caused by excessive lithium and manganese present in the lithium manganese-based oxide.

[0032] Also, according to the present invention, by controlling the concentration of transition metals (particularly nickel and doping metals) contained in the lithium-excess lithium manganese-based oxide by region within the particles, it is possible to alleviate the charge-transfer and / or diffusion of Li ions on the particle surface hindered by excessive Mn and improve the low electrical conductivity of the lithium manganese-based oxide to a commercially viable level.

[0033] Further, according to the present invention, by forming a gradient in the concentration of the transition metal between the core and the shell of the lithium manganese-based oxide and preventing a sharp change in the concentration change of the transition metal within the particles, the stability of the crystal structure of the lithium manganese-based oxide can be improved.

Brief Description of the Drawings

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BEST MODE FOR CARRYING OUT THE INVENTION

[0035] For easier understanding of the present invention, for convenience, specific terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in the present invention have meanings generally understood by those having ordinary knowledge in the technical field. Also, unless otherwise specified in the context, terms in the singular form are to be understood to include their plural forms, and terms in the plural form are to be understood to include their singular forms.

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

[0037] Positive electrode active material According to one aspect of the present invention, a positive electrode active material containing a lithium-excess lithium manganese-based oxide containing at least lithium, nickel, manganese, and a doping metal is provided. The lithium manganese-based oxide is a composite metal oxide capable of intercalation and deintercalation of lithium ions.

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

[0039] Here, the "secondary particle containing at least one primary particle" should be interpreted to include all of "particles formed by aggregation of a plurality of primary particles" or "non-aggregated particles containing a single primary particle".

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

[0041] Further, when the lithium manganese-based oxide is "non-aggregated particles containing single primary particles" or "particles formed by aggregation of a relatively small number of primary particles", the size (average particle diameter) of the primary particles contained in the "non-aggregated particles containing single primary particles" or "particles formed by aggregation of a relatively small number of primary particles" may be larger than the size (average particle diameter) of the primary particles contained in secondary particles formed by aggregation of dozens to hundreds or more primary particles.

[0042] For example, when the lithium manganese-based oxide is "non-aggregated particles containing single primary particles" or "particles formed by aggregation of a relatively small number of primary particles", the average major axis length of the primary particles may be in the range of 0.5 μm to 20 μm. On the other hand, when the lithium manganese-based oxide is "particles formed by aggregation of a plurality (dozens to hundreds or more) of primary particles", the average major axis length of the primary particles may be in the range of 0.1 μm to 5 μm.

[0043] Further, the primary particles may contain at least one crystallite. That is, the primary particles may exist as particles composed of a single crystallite or particles containing a plurality of crystallites.

[0044] The lithium manganese-based oxide defined in the present application 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] Here, 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. Further, when the lithium manganese oxide contains cobalt, the ratio of the number of moles of cobalt to the number of moles 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 ratio of Li2MnO3, which is an oxide of the C2 / m phase, in the lithium manganese oxide becomes excessively large, and there is a risk that the discharge capacity of the positive electrode active material may decrease.

[0050] In the lithium manganese oxide represented by the chemical formula 1, for Li which is an oxide of the R3-m phase a Ni x Co y Mn z M1 1-(x+y+z) O2, x indicating the content of Ni is more 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)z, which represents the content of Ni in O2, may be more than 0 and not more than 0.6.

[0051] In the lithium manganese oxide represented by the chemical formula 1, Li, which is an oxide of the R3-m phase a Ni x Co y Mn z M1 1-(x+y+z) In O2, z, which represents the content of Mn, is more than 0 and less than 1. Preferably, so that the positive electrode active material containing the lithium manganese oxide defined in the present application can exhibit a higher capacity in a high-voltage operating environment, Li a Ni x Co y MnzM1 1-(x+y+z) z, which represents the content of Mn in O2, may be 0.4 or more and less than 1.

[0052] The positive electrode active material according to the present invention contains a lithium-excess lithium manganese oxide containing at least lithium, nickel, manganese, and a doping metal, as represented by the chemical formula 1. By controlling the concentration of transition metals in different regions in the lithium manganese oxide, it is possible to alleviate and / or prevent the decrease in stability caused by lithium and manganese present in excess in the lithium manganese oxide.

[0053] In one embodiment, when the lithium manganese oxide is a secondary particle containing at least one primary particle, the secondary particle has 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 may include at least one primary particle different from each other.

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

[0055] As described above, when the concentrations of any metal elements present in the shell (or surface portion) and the core (or central portion) of the particles are different, the particles can be referred to as core-shell particles. That is, the lithium manganese oxide is a core-shell particle, and the average compositions of all the metal elements constituting the lithium manganese 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 can be partially present on the surface of the core or can entirely occupy the 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, in the lithium manganese oxide, the number of moles of all the metal elements is denoted as M 1 and the number of moles of nickel is denoted as M 2 When defined in this way, M 2 / M 1 calculated from the average composition of all the metal elements in the core of the lithium manganese oxide and M 2 / M 1 calculated from the average composition of all the metal elements in the shell of the lithium manganese oxide may be different from each other.

[0058] In the case of a lithium-excess type lithium manganese oxide containing an excessive amount of Mn, it is well known that the electrical conductivity is lower than that of LCO or NCM or NCA containing an excessive amount of Ni. Also, in general NCM, there is a problem that the electrical conductivity decreases as the content of Mn increases.

[0059] Although various reactions occur on the surfaces of the above-described various types of cathode materials, as the content of Mn in the cathode active material increases, the charge-transfer and / or diffusion of Li ions on the surface is hindered, and such a phenomenon can be referred to as surface kinetic or surface reaction kinetic reduction.

[0060] As described above, the lithium manganese oxide defined in the present application has M in the shell 2 / M 1 different from M in the core 2 / M 1 to improve the surface kinetics of the lithium manganese oxide. Such an effect can also be achieved through the differences in M 2 / M 1 in the core and shell of the primary particles, secondary particles, crystallites and / or single crystals described later. Also, such an effect can be achieved through the differences in M 3 / M 1 in the core and shell of the primary particles, secondary particles, crystallites and / or single crystals described later.

[0061] When M 2 / M 1 in the core of the primary particle is different from M 2 / M 1 in the shell of the primary particle, and M 2 / M 1 in the shell of the primary particle is larger than M 2 / M 1 in the core of the primary particle, it can further contribute to the improvement of the surface kinetics described above.

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

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

[0064] That is, the M in the lithium manganese oxide defined in the present application 2 / M 1 The gradient is not imparted by any oxide physically bonded to the primary particles and / or secondary particles constituting the lithium manganese oxide, but is imparted through the natural concentration gradient of the metal elements constituting the lithium manganese oxide. Thereby, a sharp change in M 2 / M 1 in any region within the primary particles and / or secondary particles constituting the lithium manganese oxide can be prevented, and through this, the stability of the crystal structure of the lithium manganese oxide can be improved.

[0065] In addition, when the primary particle exists as a particle containing a plurality of crystallites, the concentration of the transition metal among the crystallites can also be controlled by region.

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

[0067] At this time, the M calculated from the average composition of all metal elements in the core of the primary particle 2 / M 1 and the M calculated from the average composition of all metal elements in the shell of the crystallite 2 / M 1 When there are at least one crystallite that is different from each other, a concentration gradient of the transition metal can be formed in the same direction as the above-described primary particle inside the crystallite.

[0068] That is, M within the shell of the crystallite 2 / M 1 is greater than M within the core of the crystallite 2 / M 1 and a gradient in which M 2 / M 1 decreases from the shell to the core of the crystallite can be formed.

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

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

[0071] In this case, M within the shell of the secondary particle 2 / M 1 is greater than M within the core of the secondary particle 2 / M 1 and a gradient in which M 2 / M 1 decreases from the shell to the core of the secondary particle can be formed. When there is a gradient of M 2 / M 1 within the secondary particle, a gradient of M 2 / M 1 within the primary particle constituting the secondary particle may selectively exist. That is, when there is a gradient of M 2 / M 1 within the secondary particle, a gradient of M 2 / M 1Even if there is no gradient, the secondary particles themselves can be stabilized as bulk particles by the gradient of the transition metal described above.

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

[0073] When the lithium manganese oxide is a secondary particle containing at least one primary particle, M calculated from the average composition of the total metal elements in the core of the secondary particle 3 / M 1 and M calculated from the average composition of the total 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 particle may contain at least one primary particle in which M calculated from the average composition of the total metal elements in the core 3 / M 1 and M calculated from the average composition of the total metal elements in the shell 3 / M 1 are different from each other.

[0075] Also, when the primary particles exist as particles containing a plurality of crystallites, the primary particles have an M calculated from the average composition of all the metal elements in the core 3 / M 1 and an M calculated from the average composition of all the metal elements in the shell 3 / M 1 may include at least one crystallite different from each other.

[0076] As in the various cases described above, the M in the core of the crystallite, the primary particle and / or the secondary particle 3 / M 1 and the M in the shell 3 / M 1 are different from each other, and the M in the shell of the particle 3 / M 1 is preferably larger than the M in the core of the particle 3 / M 1 . Also, when the M in the shell of the particle 3 / M 1 is larger than the M in the core of the particle 3 / M 1 , a gradient in which M 3 / M 1 decreases can be formed from the shell to the core of the particle.

[0077] That is, the direction of the gradient of M formed in the lithium manganese oxide 3 / M 1 is formed to be the same as the direction of the gradient of M formed in the lithium manganese oxide 2 / M 1 , and by forming the gradients of M and M in the lithium manganese oxide 2 / M 1 and M 3 / M 1 in the lithium manganese oxide, it is possible to alleviate and / or prevent a decrease in stability caused by an excessive amount of lithium and manganese present in the lithium manganese oxide.

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

[0079] However, for the cathode active material defined in the present application, in the case of lithium manganese oxide, by coating the hydroxide precursor with Ni and / or Co before roasting (the first heat treatment), the difference in M within the core and shell of the final product (lithium manganese oxide) can be realized, and also, a gradient of M 2 / M 1 can be formed along the direction from the core to the shell. 2 / M 1 is possible.

[0080] Also, according to another embodiment of the present invention, instead of coating the hydroxide precursor with Ni and / or Co before roasting (the first heat treatment), a doping metal is present in the lithium manganese oxide, and by forming a gradient of the concentration of the doping metal (represented as M 3 / M 1 in the present application), the difference in M within the core and shell 2 / M 1 can be realized.

[0081] Thereby, the cathode active material containing lithium-rich lithium manganese oxide according to various embodiments defined in the present application can exhibit electrochemical characteristics and stability at a commercially viable level.

[0082] In other embodiments, at least a part of the surface of the lithium manganese oxide may have at least one metal oxide represented by the following Chemical Formula 2.

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

[0084] Here, M2 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, 0 ≦ b ≦ 8, 0 < c ≦ 8, 2 ≦ d ≦ 13.

[0085] The metal oxide represented by Chemical Formula 2 can be formed by reacting at least a part 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 can improve the electrochemical properties of the lithium manganese-based oxide by reducing lithium-containing impurities (or residual lithium) present on the surface of the lithium manganese-based oxide and acting as a diffusion path for lithium ions.

[0087] When the lithium manganese-based oxide is core-shell particles, the metal oxide can also exist integrally with the shell.

[0088] Accordingly, the metal oxide may be present on at least a part of the surfaces of crystallites, primary particles, and / or secondary particles constituting the lithium manganese-based oxide.

[0089] The metal oxide is an oxide in which lithium and the element represented by M2 are complexed, 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 It may be, for example, the above, but the above examples are only described for convenience to aid understanding and the metal oxide defined in the present application is not limited to the above examples.

[0090] In addition, the metal oxide may be an oxide in which at least two elements represented by lithium and M2 are combined, or may further contain an oxide in which at least two elements represented by lithium and M2 are combined. The oxide in which at least two elements represented by lithium and M2 are combined is, for example, Li a (W / Ti) b O c , Li a (W / Zr) b O c , Li a (W / Ti / Zr) b O c , Li a (W / Ti / B) b O c It may be, for example, the above, but is not necessarily limited thereto.

[0091] Lithium secondary battery According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. Here, the positive electrode active material layer may contain a lithium composite oxide according to various embodiments of the present invention described above as a positive electrode active material.

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

[0093] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Also, 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 enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0094] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition containing a conductive material and optionally a binder together with the positive electrode active material to the positive electrode current collector.

[0095] At this time, the positive electrode active material may be contained 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 it is not necessarily limited thereto.

[0096] The conductive material is used to impart conductivity to the electrode, and in the battery to be formed, it can be used without particular limitation as long as it has electron conductivity without causing chemical changes. Specific examples include carbon materials such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used. 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 in improving the adhesion between the positive electrode active material particles and the adhesive force 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. Among these, one kind alone or a mixture of two or more kinds 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 normal positive electrode manufacturing method except that the positive electrode active material is used. Specifically, after applying a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent onto a positive electrode current collector, it may be manufactured 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 of these alone or a mixture of two or more may be used. The amount of the solvent used is sufficient if it can dissolve or disperse the positive electrode active material, conductive material, and binder, and then provide a viscosity that can exhibit excellent thickness uniformity during coating for the production of the positive electrode, considering the coating thickness of the slurry and the production yield.

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

[0101] According to still another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. The electrochemical element may specifically be a battery, a capacitor, etc., and more specifically, it may be a lithium secondary battery.

[0102] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite to 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, for the sake of convenience, a specific description is omitted, and hereinafter, only the remaining configurations not described above will be specifically described.

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

[0104] The negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned 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. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Further, the negative electrode current collector may usually have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

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

[0107] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys, SiO β(0 < β < 2), metal oxides capable of doping and undoping lithium such as SnO2, vanadium oxides, lithium vanadium oxides, or composites containing the metal compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. may be mentioned, and mixtures of any one or two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Further, as the carbon material, all of low-crystalline carbon and highly crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of highly crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0108] The negative electrode active material may be contained at 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0109] The binder is usually added at 0.1 to 10 wt% based on the total weight of the negative electrode active material layer as a component that assists in the bonding between the conductive material, the active material, and the current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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. For example, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0111] In one embodiment, the negative electrode active material layer is manufactured by applying and drying 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, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the support on the negative electrode current collector.

[0112] In another embodiment, the negative electrode active material layer may be manufactured by applying and drying 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, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the support on the negative electrode current collector.

[0113] On the one hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Generally, any separator that can be used in a lithium secondary battery can be used without particular limitation, and it is particularly preferable that it has low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene 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. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it 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, but are not limited to, 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 manufacture of lithium secondary batteries.

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

[0116] As the organic solvent, any solvent may be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge-discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0117] The lithium salt may be used without 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, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0118] In addition to the above-described electrolyte constituent components, the electrolyte may further contain one or more additives such as haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc., for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. At this time, the additive 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 containing the positive electrode active material according to the present invention is useful in portable devices such as mobile phones, notebook personal computers, digital cameras, etc., and the field of electric vehicles such as hybrid electric vehicles (HEV) because it stably exhibits excellent discharge capacity, output characteristics, and life characteristics.

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

[0121] According to still another aspect of the present invention, there can 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 any one or more medium- to large-sized devices including a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV).

[0123] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and it should not be construed that the scope of the present invention is limited by these examples.

[0124] Production Example 1. Production of positive electrode active material Example 1 (a) Production of precursor While stirring, NaOH and NH4OH were added to a mixed aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60 in a reactor. The temperature inside the reactor was maintained at 45°C, and while introducing N2 gas into the reactor, a precursor synthesis reaction was carried out. After completion of the reaction, washing and dehydration were performed to obtain a Ni 0.4 Mn 0.6 (OH)2 precursor having an average particle size of 4 μm.

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

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

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

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

[0129] (b) Precursor coating An aqueous solution of CoSO₄·7H₂O, NaOH, and NH₄OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, after weighing so that CoSO₄·7H₂O became 10 mol%, it was added. After completion of the reaction, after washing and dehydration, it was dried at 150 °C for 14 hours to obtain a coated precursor.

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

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

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

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

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

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

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

[0137] (b) Precursor coating An aqueous solution of NiSO4·6H2O, NaOH, and NH4OH were added to a reactor in which the precursor obtained in step (a) was being stirred. At this time, after weighing so that NiSO4·6H2O became 5 mol%, it was added. After completion of the reaction, it was washed and dehydrated, and then dried at 150 °C for 14 hours to obtain a coated precursor.

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

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

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

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

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

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

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

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

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

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

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

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

[0150] Example 8 (a) Production of precursor While stirring, NaOH and NH4OH were introduced into a mixed aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60 in a reactor. The temperature inside the reactor was maintained at 45 °C, and a precursor synthesis reaction was carried out while introducing N2 gas into the reactor. After completion of the reaction, washing and dehydration were performed to obtain Ni with an average particle size of 4 μm 0.4 Mn0.6 The (OH)₂ precursor was obtained.

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

[0152] (c) Precursor coating An aqueous solution of CoSO₄·7H₂O, NaOH, and NH₄OH were added to a reactor in which the oxide-state precursor obtained in step (b) was being stirred. At this time, after weighing so that CoSO₄·7H₂O was 10 mol%, it was added. After completion of the reaction, after washing and dehydration, it was dried at 150 °C for 14 hours to obtain a coated precursor.

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

[0154] Next, after raising the temperature of the firing furnace in an O₂ atmosphere at a rate of 2 °C / min, while maintaining 1,000 °C, the mixture was heat-treated for 16 hours and then furnace cooled to finally obtain a positive electrode active material containing a lithium-excess lithium manganese-based oxide with an average particle size of 5 μm. 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) Production of precursor While stirring, NaOH and NH4OH were introduced into a mixed aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60 in a reactor. The temperature inside the reactor was maintained at 45 °C, and while introducing N2 gas into the reactor, a precursor synthesis reaction was carried out. After the reaction was completed, washing and dehydration were performed to obtain a Ni 0.4 Mn 0.6 (OH)2 precursor with an average particle size of 4 μm.

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

[0157] (c) Second heat treatment The precursor in the oxide state obtained in step (b) and LiOH (Li / (Li-except metal) mol ratio = 1.25) as a lithium compound were mixed to prepare a mixture.

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

[0159] Comparative Example 2 (a) Production of precursor While stirring, NaOH and NH4OH were introduced into a mixed aqueous solution in which NiSO4·6H2O and MnSO4·H2O were mixed at a molar ratio of 40:60 in a reactor. The temperature inside the reactor was maintained at 45 °C, and while introducing N2 gas into the reactor, a precursor synthesis reaction was carried out. After the reaction was completed, washing and dehydration were performed to obtain a Ni 0.4 Mn 0.6 (OH)2 precursor with an average particle size of 4 μm.

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

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

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

[0163] Production Example 2. Production of lithium secondary battery 90 wt% of each of the positive electrode active materials produced by Production Example 1, 5.5 wt% of carbon black, and 4.5 wt% of a PVDF binder were dispersed in 30 g of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum thin film with a thickness of 15 μm and vacuum-dried at 135 °C to produce a positive electrode for a lithium secondary battery.

[0164] A lithium foil was used as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and an electrolytic solution in which LiPF6 was present at a concentration of 1.15 M in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7 was used to manufacture a coin cell.

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

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

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

[0168] The concentration gradients of Ni, Mn, and W formed in a direction substantially perpendicular to the direction from the shell to the core of the secondary particles in this way are M calculated from the average composition of all metal elements in the core of the primary particles 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 particles 2 / M 1 and M 3 / M 1 It can be confirmed that they occurred because they are different from each other.

[0169] Also, it can be confirmed that the concentrations of Ni and W in the secondary particles are higher the closer they are to the grain boundary between the primary particles.

[0170] Table 1 below shows the concentrations (mol%) of Ni, Mn, and W in the core of the primary particles and in the shells (shell 1, shell 2). The concentrations (mol%) of Ni, Mn, and W in the core of the primary particles and in the shells (shell 1, shell 2) 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 (shell 1) corresponds to the shell of the primary particles located on one side of the region corresponding to the core of the primary particles based on the direction shown in the cross-sectional TEM image of Figure 1, and shell (shell 2) corresponds to the shell of the primary particles located on the other side of the region corresponding to the core of the primary particles based on the direction shown in the cross-sectional TEM image of Figure 1.

[0171] [Table 1]

[0172] Referring to the results of Figure 2 and Table 1, M calculated from the average composition of all metal elements in the core of the primary particles 2 / M 1 is 39.1, and M calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particles 2 / M 1 is 64.7 and 71.6. Thus, it can be seen that the lithium manganese-based oxide is an aggregate of primary particles (secondary particles) in which M 2 / M 1 in the shell is larger than M 2 / M 1 in the core, and a gradient is formed in which M 2 / M 1 decreases from the shell towards the core.

[0173] Also, M calculated from the average composition of all metal elements in the core of the primary particles 3 / M 1 is 0.2, and M calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particles3 / M 1 is 2.6 and 2.1. Accordingly, the lithium manganese oxide has M in the shell 3 / M 1 greater than M in the core, and it can be seen that the primary particles include a gradient in which M 3 / M 1 decreases from the shell toward the core. 3 / M 1

[0174] Figure 3 is a cross-sectional TEM image of the lithium manganese oxide contained in the positive electrode active material according to Example 2, and is a diagram showing the distribution of each of the Ni, Co, and Mn elements through EDS mapping of the cross section of the lithium manganese oxide. Further, Figure 4 is a graph (line sum spectrum) showing the change in the content of the 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 Figure 3.

[0175] Referring to Figures 3 and 4, it can be confirmed that the lithium manganese oxide contained in the positive electrode active material according to Example 2 is a secondary particle including a plurality of primary particles, and a gradient of the concentrations of Ni, Co, and Mn is formed from the shell toward the core of the secondary particle.

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

[0177] It can also be confirmed that the concentration of Ni in the secondary particle is higher the closer it is to the outermost shell of the secondary particle. ​

[0178] Table 2 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 particles were calculated through ICP analysis. Here, the shell corresponds to the shell of the secondary particles located on the outer contour of the region corresponding to the core of the secondary particles based on the direction shown in the cross-sectional TEM image of FIG. 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 particles 2 / M 1 is 33.7, and M calculated from the average composition of all metal elements in the shell of the secondary particles 2 / M 1 is 67.9. Thus, it can be seen that the lithium manganese-based oxide is a secondary particle in which M 2 / M 1 in the shell is larger than M 2 / M 1 in the core, and a gradient is formed in which M 2 / M 1 decreases from the shell toward the core.

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

[0182] Referring to FIGS. 5 and 6, it can be confirmed that the lithium manganese oxide contained in the positive electrode active material according to Example 3 is secondary particles containing a plurality of primary particles, and a concentration gradient of Ni, Co, Mn, and W is formed in a direction substantially perpendicular to the direction from the shell to the core of the secondary particles.

[0183] The concentration gradient of Ni, Co, Mn, and W formed in a direction substantially perpendicular to the direction from the shell to the core of the secondary particles is M calculated from the average composition of the whole 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 the whole metal elements in the shell of the primary particle 2 / M 1 and M 3 / M 1 are different from each other, and it can be confirmed that this has occurred.

[0184] It can also be confirmed that the concentrations of Ni and W in the secondary particles are higher the closer they are to 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 the primary particles. The concentrations (mol%) of Ni, Co, Mn, and W in the core and shells (shell 1, shell 2) of the 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 (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 (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 particles 2 / M 1 is 36.6, and M calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particles 2 / M 1 is 49.4 and 46.3. Thus, it can be seen that the lithium manganese oxide contains primary particles in which M 2 / M 1 in the shell is greater than M 2 / M 1 in the core, and a gradient is formed in which M 2 / M 1 decreases from the shell toward the core.

[0188] Also, M calculated from the average composition of all metal elements in the core of the primary particles 3 / M 1 is 0.7, and M calculated from the average composition of all metal elements in the shells (shell 1, shell 2) of the primary particles 3 / M 1 is 4.8 and 4.0. Thus, it can be seen that the lithium manganese oxide contains primary particles in which M 3 / M 1 in the shell is greater than M 3 / M 1 in the core, and a gradient is formed in which M 3 / M 1 decreases from the shell toward the core.

[0189] Furthermore, referring to FIG. 6, between the core and the shell (shell 2) (in the region of 0.15 μm to 0.25 μm based on the line EDS spectrum), M 2 / M 1It can be confirmed that the gradient repeatedly exists. The above results show that the lithium manganese oxide contained in the positive electrode active material according to Example 3 includes secondary particles containing a plurality of primary particles, and at the same time, the primary particles contain a plurality of crystallites, and from the shell to the core of the crystallites, M 2 / M 1 is due to the gradient of decrease.

[0190] Tables 4 to 7 below respectively show the measurement results of the concentrations of metal elements in the core and shell of the primary particles constituting the lithium manganese oxide contained in the positive electrode active material according to Examples 4 to 7 through Line EDS analysis and ICP analysis. Similar to the positive electrode active materials according to the various examples described above, it can be confirmed that a concentration difference of metal elements is realized between the shell and the core. Here, based on the line scanning direction that horizontally cuts the core of the primary particle in a straight line, the shell (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 the shell (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 contained in the positive electrode active material according to Example 8, and is a diagram showing the distribution of each of the Ni, Co, and Mn elements through EDS mapping of the cross-section of the lithium manganese oxide. Further, FIG. 8 is a graph (line sum spectrum) showing the change in the content of the metal elements (Ni, Co, Mn) present in the lithium manganese oxide through EDS analysis with respect to direction 1 shown in the cross-sectional TEM image of FIG. 7, and FIG. 9 is a graph (line sum spectrum) showing the change in the content of the metal elements (Ni, Co, Mn) present in the lithium manganese oxide through EDS analysis with respect to direction 2 shown in the cross-sectional TEM image of FIG. 7.

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

[0197] Direction 1 shown in the cross-sectional TEM image of FIG. 7 is for confirming the change in the concentration of the metal elements (Ni, Co, Mn) within the primary particle. Table 8 below shows the concentrations (mol%) of Ni, Co, and Mn in the core and shell of the primary particle. The concentrations (mol%) of Ni, Co, and Mn in the core and shell of the primary particle were calculated from the Line EDS spectrum, and the concentrations of Ni, Co, and Mn within the entire particle (bulk) were calculated through ICP analysis. Here, the shell corresponds to the shell of the primary particle located at the outer periphery of the region corresponding to the core of the primary particle with respect to direction 1 shown in the cross-sectional TEM image of FIG. 7.

[0198]

Table 8

[0199] Referring to the results in FIG. 8 and Table 8, M calculated from the average composition of all metal elements in the core of the primary particles 2 / M 1 is 41.7, and M calculated from the average composition of all metal elements in the shell of the primary particles 2 / M 1 is 57.3. Thus, it can be seen that the lithium manganese oxide contains primary particles in which M 2 / M 1 in the shell is larger than M 2 / M 1 in the core, and a gradient is formed in which M 2 / M 1 decreases from the shell toward the core.

[0200] Direction 2 shown in the cross-sectional TEM image of FIG. 7 is for confirming the change in the concentration of metal elements (Ni, Co, Mn) in the secondary particles. 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 whole particles were calculated through ICP analysis. Here, the shell corresponds to the shell of the secondary particles located at the outer contour of the region corresponding to the core of the secondary particles based on direction 2 shown in the cross-sectional TEM image of FIG. 7.

[0201]

Table 9

[0202] Referring to the results in FIG. 9 and Table 9, M calculated from the average composition of all metal elements in the core of the secondary particles 2 / M 1is 41.4 and is M calculated from the average composition of all metal elements within the shell of the secondary particles 2 / M 1 is 55.3. Thus, it can be seen that the lithium manganese oxide contains secondary particles in which M 2 / M 1 within the shell is greater than M 2 / M 1 within the core, and a gradient is formed in which M 2 / M 1 decreases from the shell towards the core

[0203] Referring to the results in FIGS. 7 to 9, the lithium manganese oxide may be secondary particles containing primary particles in which M 2 / M 1 within the shell is greater than M 2 / M 1 within the core, and a gradient is formed in which M 2 / M 1 decreases from the shell towards the core, or may itself be secondary particles in which M 2 / M 1 within the shell is greater than M 2 / M 1 within the core, and a gradient is formed in which M 2 / M 1 decreases from the shell towards the core. It can be confirmed

[0204] That is, in the lithium manganese oxide, the unit of particles in which M 2 / M1 within the shell is greater than M 2 / M1 within the core, and a gradient is formed in which M 2 / M1 decreases from the shell towards the core may be primary particles and / or secondary particles, or may be crystallite units constituting the primary particles

[0205] FIG. 10 is a cross-sectional TEM image of the lithium manganese oxide contained in the positive electrode active material according to Comparative Example 1, and is a diagram showing the distribution of each of the Ni and Mn elements through EDS mapping of the cross-section of the lithium manganese oxide. Further, FIG. 11 is a graph (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] Further, Table 10 below shows the concentrations (mol%) of Ni and Mn in the core and shell of the primary particles. The concentrations (mol%) of Ni and Mn in the core and shell of the primary particles were calculated from the Line EDS spectrum, and the concentrations of Ni and Mn in the entire particle (bulk) were calculated through ICP analysis.

[0207]

Table 10

[0208] Referring to FIGS. 10 and 11, it can be confirmed that the lithium manganese oxide contained in the positive electrode active material according to Comparative Example 1 is a secondary particle containing a plurality of primary particles, and no concentration gradient of Ni and Mn is formed between the core and shell of the primary particles existing on the outermost contour of the secondary particle.

[0209] Table 11 below shows the measurement results of the concentrations of metal elements in the core and shell of the primary particles and secondary particles constituting the lithium manganese oxide contained in the positive electrode active material according to Comparative Example 2 through Line EDS analysis and ICP analysis. Different from the positive electrode active material according to Example 8 described above, it can be confirmed that almost no concentration difference of metal elements is realized between the shell and the core.

[0210]

Table 11

[0211] Experimental Example 2. Evaluation of Electrochemical Characteristics of Lithium Secondary Battery For the lithium secondary battery (coin cell) manufactured in Production Example 2, an electrochemical analyzer (Toyo, Toscat-3100) was used to conduct charge and discharge experiments at 25°C with a voltage range of 2.0 V to 4.6 V and a discharge rate of 0.1C to 5.0C to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and rate characteristics (ratio of discharge capacity; rate capability (C-rate)).

[0212] Also, for the same lithium secondary battery, after performing 50 charge and discharges under the condition of 1C / 1C within the driving voltage range of 2.0 V to 4.6 V at 25°C, the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention; 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 in Tables 12 and 13, when comparing with the lithium secondary batteries using the cathode active materials according to Comparative Example 1 and Comparative Example 2, it can be confirmed that the discharge capacity of the lithium secondary batteries using the cathode active materials according to Examples 1 to 8 increased, thereby improving the reversible efficiency and increasing the cycle capacity retention and the ratio of discharge capacity.

[0217] As described above, the embodiments of the present invention have been explained. However, those having ordinary knowledge in the art can make various modifications and changes to the present invention by adding, changing, deleting, or adding components, etc., without departing from the idea of the present invention described in the claims, and it can be said that this is also included within the scope of the rights of the present invention.

Claims

1. A positive electrode active material containing a lithium-rich lithium manganese-based oxide containing at least lithium, nickel, manganese, and a doping metal, In the lithium manganese-based oxide, the number of moles of the total metal elements excluding lithium is denoted as M １ and the number of moles of nickel is denoted as M ２ and when the number of moles of the doping metal is denoted as M3, M calculated from the average composition of all metal elements excluding lithium in the core of the lithium manganese oxide ２ / M １ is smaller than M ２ / M １ calculated from the average composition of all metal elements excluding lithium in the shell of the lithium manganese oxide, wherein M3 / M1 calculated from the average composition of all metal elements within the core of the lithium manganese-based oxide is smaller than M3 / M1 calculated from the average composition of all metal elements within the shell of the lithium manganese-based oxide, M calculated from the average composition of the total metal elements within the core of the lithium manganese-based oxide ２ / M １ is 33.7 mol% or more and 41.7 mol% or less, a positive electrode active material.

2. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, The secondary particles have an M calculated from the average composition of all metal elements excluding lithium in the core ２ / M １ that is smaller than the M calculated from the average composition of all metal elements excluding lithium in the shell ２ / M １ The positive electrode active material according to claim 1, comprising at least one primary particle.

3. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, M calculated from the average composition of all metal elements excluding lithium in the core of the secondary particles ２ / M １ is smaller than M ２ / M １ calculated from the average composition of all metal elements excluding lithium in the shell of the secondary particles, the positive electrode active material according to claim 1

4. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, The primary particle contains at least one crystallite, The primary particles have an M calculated from the average composition of all metal elements excluding lithium in the core ２ / M １ that is smaller than the M calculated from the average composition of all metal elements excluding lithium in the shell ２ / M １ The cathode active material according to claim 1, comprising at least one crystallite

5. The gradient in which M decreases from the shell to the core of the lithium manganese-based oxide is formed, and the positive electrode active material according to claim 4. ２ / M １ The positive electrode active material according to claim 4, in which a gradient in which M decreases from the shell to the core of the lithium manganese-based oxide is formed.

6. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, The secondary particles have an M calculated from the average composition of all metal elements excluding lithium in the core, ３ / M １ which is smaller than the M calculated from the average composition of all metal elements excluding lithium in the shell, ３ / M １ The positive electrode active material according to claim 1, comprising at least one primary particle.

7. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, M calculated from the average composition of all metal elements excluding lithium in the core of the secondary particles ３ / M １ is smaller than M ３ / M １ calculated from the average composition of all metal elements excluding lithium in the shell of the secondary particles, the positive electrode active material according to claim 1

8. The lithium manganese-based oxide is a secondary particle containing at least one primary particle, The primary particle contains at least one crystallite, The primary particles have an M calculated from the average composition of all metal elements excluding lithium in the core, ３ / M １ which is smaller than the M calculated from the average composition of all metal elements excluding lithium in the shell, and contain at least one crystallite. The positive electrode active material according to claim 1. ３ / M １ ​

9. The gradient in which M decreases from the shell to the core of the lithium manganese-based oxide is formed, and the cathode active material according to claim 1. ３ / M １ The cathode active material according to claim 1, in which a gradient in which M decreases from the shell to the core of the lithium manganese-based oxide is formed.

10. The lithium manganese-based oxide is the positive electrode active material according to Claim 1, represented by the following Chemical Formula 1. [Chemical Formula 1] rLi ２ MnO ３ ・(1 - r)Li ａ Ni ｘ Co ｙ Mn ｚ M1 １－（ｘ＋ｙ＋ｚ） O ２ Here, 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.

11. 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 part of the surface of the lithium manganese-based oxide. [Chemical Formula 2] Li ｂ M2 ｃ O ｄ Here, M2 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd, 0 ≦ b ≦ 8, 0 < c ≦ 8, 2 ≦ d ≦ 13.

12. M calculated from the average composition of all metal elements excluding lithium in the shell of the lithium manganese-based oxide ２ / M １ is 42.9 mol% or more and 71.6 mol% or less, and the positive electrode active material according to claim 1.

13. A positive electrode containing the positive electrode active material according to any one of Claims 1 to 12.

14. A lithium secondary battery using the positive electrode according to claim 13.

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