Positive electrode active material and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material including an overlithiated lithium manganese-based oxide, in which, through surface modification of the lithium manganese-based oxide, the surface resistance of the lithium manganese-based oxide is reduced, thereby improving the lifetime characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material, and a lithium secondary battery including the same.SOLUTION: A positive electrode active material includes a lithium manganese-based oxide in which a phase belonging to a C2 / m space group and a phase belonging to a R3-m space group are dissolved in a solid solution. The lithium manganese-based oxide further includes a spinel phase belonging to a Fd-3 m space group. In X-ray diffraction analysis using Cu-Kα rays for the positive electrode active material, the intensity ratio between the diffraction peaks attributed to the (003) and (104) planes satisfies a specific equation, and the intensity ratio between the diffraction peaks attributed to the (018) and (110) planes satisfies a specific equation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cathode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material including a lithium-excess lithium-manganese-based oxide, which can improve the life characteristics of a lithium secondary battery using the lithium-manganese-based oxide as a cathode active material by reducing the surface resistance of the lithium-manganese-based oxide through surface modification of the lithium-manganese-based oxide, and a lithium secondary battery including the same. [Background technology]

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

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

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and oxides of Ni, Co, Mn, and Al.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but suffer from low capacity and poor high-temperature characteristics. LiNiO2-based positive electrode active materials exhibit high discharge capacity, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, resulting in significant problems with rate characteristics.

[0007] Furthermore, depending on the depth of this cation mixing, a large amount of Li by-products are generated. These Li by-products, mostly consisting of LiOH and Li2CO3, can cause gelation during the preparation of the positive electrode paste or can generate gas during repeated charge / discharge cycles after electrode fabrication. Furthermore, the residual Li2CO3 among these Li by-products can increase cell swelling, thereby reducing the lifespan characteristics.

[0008] Various candidate materials have been proposed to overcome the drawbacks of conventional positive electrode active materials.

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

[0010] While OLO theoretically has the advantage of being able to exhibit high capacity under high-voltage operating conditions, it has the disadvantage of having relatively low electrical conductivity due to the excessive Mn content in the oxide, resulting in poor rate performance of lithium secondary batteries using OLO. This poor rate performance can lead to problems such as reduced charge / discharge capacity and life efficiency (capacity retention) during cycling of the lithium secondary battery.

[0011] To solve the above problems, research has been conducted to change the composition of OLO, but so far, these attempts have not reached a commercial level. Summary of the Invention [Problem to be solved by the invention]

[0012] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is playing a role as a market driver, and as a result, the demand for positive electrode active materials used in lithium secondary batteries is also continuously increasing.

[0013] For example, lithium secondary batteries using lithium iron phosphate (LFP) have been mainly used in the past due to safety reasons, but recently there has been a trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP. Of course, relatively cheap LFP is still sometimes used to save costs.

[0014] In addition, nickel-based lithium composite oxides, which have recently been primarily used as positive electrode active materials for high-capacity lithium secondary batteries, essentially contain ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only unstable in supply and demand but is also excessively expensive compared to other raw materials, so new positive electrode active materials with reduced or eliminated cobalt content are needed.

[0015] Considering these various circumstances, lithium-excess lithium manganese-based oxides can meet the aforementioned market expectations, but they still have limitations in that their electrochemical properties and stability are insufficient to replace commercially available positive electrode active materials such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary lithium composite oxides.

[0016] For example, the present inventors have confirmed that lithium manganese oxides are more likely to release transition metals from the particle surface through repeated charge and discharge than ternary lithium composite oxides, and in particular, there is a high possibility that excess Mn contained in lithium manganese oxides will release from the particle surface.

[0017] When a transition metal is eluted from the lithium manganese-based oxide, the eluted transition metal may react with the electrolyte on the surface of the lithium manganese-based oxide to form impurities, which not only increase the surface resistance of the lithium manganese-based oxide but also act as a cause of a decrease in the intercalation / deintercalation efficiency of lithium ions through the lithium manganese-based oxide.

[0018] As mentioned above, compared to other commercially available positive electrode active materials, conventional lithium-excess lithium manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability. However, the Mn content of the lithium manganese-based oxide can be reduced by surface modification of the lithium manganese-based oxide. 4+ is Mn 2+ The inventors have confirmed that the anionic redox reaction of the lithium manganese-based oxide can be suppressed, thereby stabilizing the unstable surface of the lithium manganese-based oxide, thereby improving the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0019] The present inventors have confirmed that the surface modification of the lithium manganese-based oxide forms a physical barrier between the lithium manganese-based oxide and an electrolyte, thereby reducing side reactions between the lithium manganese-based oxide and an electrolyte. In addition, when a spinel phase is formed on at least a portion of the surface of the lithium manganese-based oxide through the surface modification, the spinel phase stabilizes the unstable surface of the lithium manganese-based oxide, thereby improving the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0020] Furthermore, the present inventors have confirmed that when the surface resistance of the lithium manganese-based oxide is reduced through surface modification of the lithium manganese-based oxide, early deterioration of the lithium manganese-based oxide can be prevented, and thus the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material can be improved.

[0021] Therefore, the present invention aims to provide a cathode active material that includes a lithium-excess lithium-manganese-based oxide, and that can reduce the surface resistance of the lithium-manganese-based oxide through surface modification using molybdenum, thereby improving the life characteristics of a lithium secondary battery using the lithium-manganese-based oxide as a cathode active material.

[0022] Another object of the present invention is to provide a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material defined in the present application.

[0023] Another object of the present invention is to provide a lithium secondary battery that uses the positive electrode defined in the present application, thereby preventing the shortening of life caused by the excess lithium and manganese that are conventionally present in OLO. [Means for solving the problem]

[0024] According to one aspect of the present invention for solving the above-mentioned technical problems, there is provided a cathode active material including a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-dissolved.

[0025] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions contain a single phase of the R3-m space group, whereas the lithium-rich lithium manganese oxide defined in this application is characterized by a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0026] In one embodiment, the lithium manganese-based oxide may be represented by the following Chemical Formula 1:

[0027] [Chemical formula 1] rLi2MnO 3-c X′ c (1-r)Li a M1 x M2 y O 2-b X b (wherein M1 is at least one selected from Ni and Mn, M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, M2 does not overlap with M1, X and X′ are each independently a halogen capable of substituting at least a portion of oxygen present in the lithium manganese-based oxide, and 0 <r≦0.7、0<a≦1、0≦b≦0.1、0≦c≦0.1、0<x≦1、0≦y<1、0<x+y≦1である) The lithium manganese-based oxide may further include a spinel phase belonging to the Fd-3m space group, and thus may be a solid solution of a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group.

[0028] In one embodiment, the lithium manganese-based oxide may be represented by the following Chemical Formula 2:

[0029] [Chemical formula 2] (1-z){rLi2MnO 3-c X′ c (1-r)Li a M1 x M2 y O 2-b X b}·zLi(Li d Mn 2-d-e M3 e )O4-g X″ g (wherein M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd; M2 does not overlap with M1; M3 is at least one selected from Ni, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd; X, X′, and X″ are each independently a halogen capable of substituting at least a portion of oxygen present in the lithium manganese-based oxide; and <r≦0.7、0<a≦1、0≦b≦0.1、0≦c≦0.1、0<x≦1、0≦y<1、0<x+y≦1、0<z≦0.5、0≦d≦1、0<e≦1、0≦g≦0.1である) The lithium manganese-based oxide may be a core-shell particle including a core portion in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-dissolved, and a shell portion present on at least a portion of the surface of the core portion and containing a spinel phase belonging to the Fd-3m space group. In this case, the core portion and the shell portion are solid-dissolved with each other, so that there is no inter-particle boundary between the core portion and the shell portion.

[0030] A molybdenum-containing coating layer may be present on at least a portion of the surface of the shell portion.

[0031] According to another aspect of the present invention, there is provided a positive electrode including the positive electrode active material defined herein. Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material is present in the positive electrode active material layer.

[0032] According to yet another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode defined herein. Specifically, the lithium secondary battery may include the positive electrode defined herein, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0033] According to the present invention, it is possible to improve upon the limitations of conventional lithium-excess lithium manganese-based oxides, which have various disadvantages in terms of electrochemical properties and / or stability, compared to commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[0034] Specifically, according to the present invention, Mn in the lithium manganese-based oxide is removed by surface modification of the lithium manganese-based oxide. 4+ is Mn 2+ Therefore, the anionic redox reaction of the lithium manganese-based oxide can be suppressed, thereby stabilizing the unstable surface of the lithium manganese-based oxide.

[0035] The OLO, such as the lithium manganese-based oxide, has an advantage of exhibiting high capacity under a high-voltage operating environment. However, since the possibility of side reactions occurring between the lithium manganese-based oxide and the electrolyte increases as the operating voltage increases, it is important to reduce the side reactions between the lithium manganese-based oxide and the electrolyte.

[0036] Therefore, as the side reaction between the lithium manganese-based oxide and the electrolyte is reduced, the stability and lifespan of a lithium secondary battery using the lithium manganese-based oxide as a cathode active material can be improved. In particular, a cathode active material with reduced side reaction with the electrolyte can operate a lithium secondary battery at a higher voltage. In this case, a spinel phase can be formed on at least a portion of the surface of the lithium manganese-based oxide during surface modification of the lithium manganese-based oxide.

[0037] Furthermore, according to the present invention, the surface resistance of the lithium manganese-based oxide can be reduced by modifying the surface of the lithium manganese-based oxide, thereby preventing early deterioration of the lithium manganese-based oxide and thereby improving the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0038] In addition to the above-mentioned effects, specific effects of the present invention will be described together with the following description of the preferred embodiments of the present invention. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 shows a surface SEM image and surface EDS analysis results (target element: Mo) of the lithium manganese-based oxide (secondary particles) according to Example 3. [Figure 2] FIG. 2 is a diagram showing the line scan direction of a cross-sectional SEM image of the lithium manganese-based oxide according to Example 3. [Figure 3] FIG. 3 shows a surface SEM image and surface EDS analysis results (target element: Mo) of the lithium manganese-based oxide (secondary particles) according to Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0040] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0041] Hereinafter, a cathode active material including a lithium-excess lithium manganese-based oxide and a lithium secondary battery including the cathode active material according to some embodiments of the present invention will be described in more detail.

[0042] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material containing a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved.

[0043] The phases belonging to the C2 / m space group and the R3-m space group can be distinguished not only by the composition of each phase but also by the peaks specific to each phase during XRD analysis. For example, the peak specific to the phase belonging to the C2 / m space group may appear in the 2θ=20.8±1° region, and the peak specific to the phase belonging to the R3-m space group may appear in the 2θ=18.6±1° region.

[0044] The lithium manganese-based oxide is a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved, and the phases belonging to the C2 / m space group and the R3-m space group coexist within the lithium manganese-based oxide. Furthermore, the lithium manganese-based oxide is different from composite oxides having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn2O4 or oxides having a similar composition).

[0045] The lithium manganese-based oxide contains at least lithium, manganese, and a transition metal. The transition metal may include at least one selected from nickel, cobalt, and aluminum. The lithium manganese-based oxide may contain lithium, nickel, and manganese, or may optionally further contain a transition metal other than nickel.

[0046] The lithium manganese-based oxide is also called an overlithiated layered oxide (OLO) because the lithium content in the lithium manganese-based oxide is greater than the total content of other transition metals (generally, when the molar ratio of lithium to all metal elements other than lithium in the lithium manganese-based oxide (Li / Metal molar ratio) is greater than 1).

[0047] The lithium manganese-based oxide is also called a lithium- and manganese-excess layered oxide because the manganese content in the lithium manganese-based oxide is higher than the content of other transition metals.

[0048] Generally, in commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, the manganese content of the total metal elements excluding lithium is 20 mol% or less. Considering this, the lithium-manganese-based oxide has a relatively high ratio of manganese to the total metal elements (e.g., 50 mol% or more, 52 mol% or more, 53 mol% or more, or 55 mol% or more) compared to commercially available ternary lithium composite oxides.

[0049] In addition, considering that commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a nickel content of 60 mol% or more (80 mol% or more in the case of high-Ni types) of all metal elements excluding lithium, the lithium-manganese-based oxide has a relatively low proportion of nickel in all metal elements (e.g., less than 50 mol%, 48 mol% or less, 46 mol% or less, 45 mol% or less, 44 mol% or less, 42 mol% or less, or 40 mol% or less) compared to commercially available ternary lithium composite oxides.

[0050] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined herein is larger than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese-based oxide defined herein is larger than 1, preferably 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0051] Therefore, in the present application, a lithium manganese-based oxide can be defined as a composite oxide in which the manganese content of all metal elements excluding lithium is 50 mol% or more, or as a composite oxide in which the manganese content of all metal elements excluding lithium is 50 mol% or more and the nickel content is less than 50 mol%.

[0052] In addition, in the present application, a lithium manganese-based oxide can be defined as a composite oxide in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or is a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, and the manganese content of all metal elements excluding lithium is 50 mol% or more; or as a composite oxide in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or is a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, and the manganese content of all metal elements excluding lithium is 50 mol% or more, and the nickel content is less than 50 mol%.

[0053] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0054] The lithium manganese-based oxide contained in the positive electrode active material defined herein may exist as particles including at least one primary particle.

[0055] When the lithium manganese-based oxide exists as a single primary particle, the lithium manganese-based oxide may be referred to as a single particle, whereas when the lithium manganese-based oxide exists as an aggregate of a plurality of primary particles, the lithium manganese-based oxide may be referred to as a secondary particle.

[0056] The positive electrode active material may contain at least one selected from a lithium manganese-based oxide that exists as a single particle and a lithium manganese-based oxide that exists as a secondary particle formed by aggregation of a plurality of primary particles.

[0057] The primary particles constituting the lithium manganese-based oxide may have a rod shape, an elliptical shape, and / or an irregular shape. Furthermore, unless otherwise intended in the manufacturing process, primary particles of various shapes exist within the same positive electrode active material. Furthermore, the primary particles refer to particle units that do not appear to have grain boundaries when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0058] The primary particles constituting the lithium manganese-based oxide defined herein may have an average particle size of 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated by the average value of the length of the major axis and the length of the minor axis of the primary particles ([major axis length + minor axis length] / 2).

[0059] If the average particle size of the primary particles is less than 0.05 μm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles is relatively large, which increases the possibility of side reactions occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0060] On the other hand, when the average particle size of the primary particles is larger than 5 μm, excessive growth of the primary particles is induced, and the diffusion path of the lithium ions within the primary particles also becomes longer. When the diffusion path of the lithium ions within the primary particles is excessively long, the mobility of the lithium ions within the primary particles and the diffusibility of the lithium ions through the primary particles decrease, which causes an increase in the resistance of the lithium manganese-based oxide (secondary particles) composed of the primary particles.

[0061] In order to reduce the specific surface area of ​​the lithium manganese oxide and prevent a decrease in the mobility of lithium ions within the primary particles and the diffusibility of lithium ions through the primary particles, the average particle size of the primary particles may be 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm.

[0062] When the lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, the average particle size of the secondary particles may be 0.5 μm to 15 μm, 1.0 μm to 15 μm, 2.0 μm to 15 μm, 3.0 μm to 15 μm, 4.0 μm to 15 μm, or 5.0 μm to 15 μm. The average particle size of the secondary particles may vary depending on the number of primary particles constituting the secondary particles. The average particle size (D50) of the secondary particles can be measured using a laser diffraction method. For example, the secondary particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. A volume-accumulated particle size distribution graph can then be obtained, and the particle size corresponding to 50% of the volume-accumulated amount can be determined.

[0063] Unless otherwise defined, the term "surface of the primary particle" used herein refers to the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" used herein refers to the outer surface of the secondary particle exposed to the outside. In this regard, the "surface of the secondary particle" formed by aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0064] Unless otherwise defined, the term "surface portion of a particle" used herein refers to a region relatively closer to the "outermost surface" of a particle, and the term "center portion of a particle" refers to a region relatively closer to the "middle" of a particle than the "surface portion." Accordingly, the term "surface portion of a primary particle" refers to a region relatively closer to the "outermost surface" of a primary particle, and the term "center portion of a primary particle" refers to a region relatively closer to the "middle" of a primary particle than the "surface portion." Similarly, the term "surface portion of a secondary particle" refers to a region relatively closer to the "outermost surface" of a secondary particle, and the term "center portion of a secondary particle" refers to a region relatively closer to the "middle" of a secondary particle than the "surface portion."

[0065] In this case, the region of any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0066] For example, when the semidiameter of the primary particle is referred to as r, the region that is a distance of 0 to 0.5r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region that is a distance of 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle. When the semidiameter of the primary particle is 0.5 μm, the surface portion of the primary particle can be defined as the region that is a distance of 0 to 0.25 μm from the surface of the primary particle, and the center portion of the primary particle can be defined as the region that is a distance of 0 to 0.25 μm from the center of the primary particle.

[0067] Furthermore, if necessary, when the semidiameter of the primary particle is referred to as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle.

[0068] Similarly, when the semidiameter of the secondary particle is referred to as r, the region that is a distance of 0 to 0.5r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region that is a distance of 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle. When the semidiameter of the secondary particle is 2.0 μm, the surface portion of the secondary particle can be defined as the region that is a distance of 0 to 1.0 μm from the surface of the secondary particle, and the center portion of the secondary particle can be defined as the region that is a distance of 0 to 1.0 μm from the center of the secondary particle.

[0069] Furthermore, if necessary, when the semidiameter of the secondary particle is referred to as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle.

[0070] The lithium manganese-based oxide defined herein may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1:

[0071] [Chemical formula 1] rLi2MnO 3-c X′ c (1-r)Li a M1 x M2 y O 2-b X b (0 <r≦0.7、0≦c≦0.1、0<a≦1、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1) Here, M1 is at least one selected from Ni and Mn, M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and M2 does not overlap with M1.

[0072] X and X' are each independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide. The halogens usable as X and X' can be F, Cl, Br, and / or I, etc., as seen in the periodic table, and preferably F.

[0073] In Chemical Formula 1, when M1 is Ni, M2 may contain Mn, and when M1 is Mn, M2 may contain Ni. Also, when M1 is Ni and Mn, M2 may be absent, or, if present, may be an element other than Ni and Mn.

[0074] That is, when M1 is Ni, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd (preferably, at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably, at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably, at least one selected from P, B, and Si), and Mn.

[0075] When M1 is Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd (preferably, at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably, at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably, at least one selected from P, B, and Si), and Ni.

[0076] When M1 is Ni and Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, preferably at least one selected from Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, and W, more preferably at least one selected from Co, P, B, Si, Ti, Zr, and W, and even more preferably at least one selected from P, B, and Si.

[0077] The lithium manganese-based oxide represented by Chemical Formula 1 may optionally contain cobalt. When the lithium manganese-based oxide contains cobalt, the molar fraction of cobalt relative to the total moles of metal elements in the lithium manganese-based oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese-based oxide represented by Chemical Formula 1 may have a cobalt-free composition.

[0078] The Li / Metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 may be greater than 1, 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5. When the Li / Metal molar ratio measured from the lithium manganese-based oxide is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide. In addition, in order for the lithium manganese-based oxide to properly form a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and to exhibit high capacity under high-voltage operating conditions, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0079] In addition, in order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved, the content of manganese among all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 is preferably 50 mol% or more. In order for the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under a high-voltage operating environment, the content of manganese among all metal elements excluding lithium present in the lithium manganese-based oxide may be 50 mol% to less than 80 mol%, 51 mol% to less than 80 mol%, 52 mol% to less than 80 mol%, 53 mol% to less than 80 mol%, 54 mol% to less than 80 mol%, 55 mol% to less than 80 mol%, 50 mol% to 75 mol%, 51 mol% to less than 75 mol%, 52 mol% to less than 75 mol%, 53 mol% to less than 75 mol%, 54 mol% to less than 75 mol%, or 55 mol% to 75 mol%. If the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the migration of transition metals (especially manganese) within the lithium manganese-based oxide during the formation and / or operation of the lithium secondary battery. Such phase transitions may occur at random locations within the lithium manganese-based oxide, resulting in a decrease in charge / discharge capacity or voltage decay during cycling of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. Furthermore, if the manganese content in the lithium manganese-based oxide exceeds 80 mol%, it may be difficult to sufficiently form phases belonging to the R3-m space group.

[0080] In order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved, the content of nickel in all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 may be less than 50 mol%, 48 mol% or less, 46 mol% or less, 45 mol% or less, 44 mol% or less, 42 mol% or less, or 40 mol% or less.

[0081] When the nickel content in the lithium manganese-based oxide is 50 mol% or more, the C2 / m phase may not be sufficiently formed, and the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group may not form a sufficient solid solution, which may cause phase separation during the formation and / or operation of the lithium secondary battery.

[0082] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions exist as a single phase belonging to the R3-m space group.

[0083] Meanwhile, the lithium-excess lithium manganese oxide represented by the formula 1 is rLi2MnO 3-c X′ c The oxides of the phase belonging to the C2 / m space group (hereinafter referred to as "C2 / m phase") and (1-r)Li a M1 x M2 y O 2-b X b In this application, the term "a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved" means that oxides of the C2 / m phase and oxides of the R3-m phase are present in a state of forming a solid solution.

[0084] In this case, a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are simply physically and / or chemically bonded or attached does not fall under the category of a solid solution as defined in this application.

[0085] For example, a composite oxide having a phase belonging to the C2 / m space group, which is formed by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R3-m space group and whose surface is coated with a metal oxide having a phase belonging to the R3-m space group, does not fall under the category of a solid solution as defined in the present application.

[0086] In the lithium manganese-based oxide represented by the chemical formula 1, when r is greater than 0.7, the lithium manganese-based oxide is a C2 / m phase oxide, Li2MnO 3-c X′ c The proportion of R3-m phase oxide is preferably present in a certain proportion or more in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance among the lithium manganese-based oxides, and improve the surface kinetics.

[0087] The lithium manganese-based oxide may further include a spinel phase belonging to the Fd-3m space group, in which case the lithium manganese-based oxide exists as a solid solution of a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group.

[0088] The spinel phase can be formed by surface modification of the lithium manganese-based oxide. By forming the spinel phase on at least a portion of the surface of the lithium manganese-based oxide (i.e., a portion or the entire surface of the lithium manganese-based oxide) through surface modification of the lithium manganese-based oxide, Mn in the lithium manganese-based oxide can be easily obtained. 4+ is Mn 2+ Therefore, the anionic redox reaction of the lithium manganese-based oxide can be suppressed, thereby stabilizing the unstable surface of the lithium manganese-based oxide.

[0089] Furthermore, since the spinel phase is formed on the surface of the lithium manganese-based oxide, it is different from a phase formed by a phase transition that occurs at random positions within the lithium manganese-based oxide due to the movement of transition metals (especially manganese) within the lithium manganese-based oxide.

[0090] The lithium manganese-based oxide in which a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group are dissolved can be represented by the following Chemical Formula 2.

[0091] [Chemical formula 2] (1-z){rLi2MnO 3-c X′ c (1-r)Li a M1 x M2 y O 2-b X b}·zLi(Li d Mn 2-d-e M3 e )O 4-g X″ g (0 <r≦0.7、0≦c≦0.1、0<a≦1、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1、0<z≦0.5、0≦d≦1、0<e≦1、0≦g≦0.1) Here, M1 is at least one selected from Ni and Mn, M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and M2 does not overlap with M1.

[0092] X, X', and X" are each independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide. The types of halogen usable as X and X' refer to the periodic table, and include F, Cl, Br, and / or I, and preferably F.

[0093] The explanation regarding the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group of the lithium manganese-based oxide represented by Chemical Formula 2 is the same as that of the lithium manganese-based oxide represented by Chemical Formula 1.

[0094] M3 is at least one selected from Ni, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. Preferably, M3 is Ni, and may selectively contain at least one element selected from Ni, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd.

[0095] In the chemical formula 2, the composition of the spinel phase belonging to the Fd-3m space group is zLi(Li d Mn 2-d-e M3 e )O 4-g X″ g For example, the spinel phase is represented by LiMn 1.5 Ni 0.5 Can be displayed at O4.

[0096] In the lithium manganese-based oxide represented by Chemical Formula 2, if z exceeds 0.5, the proportion of the spinel phase in the lithium manganese-based oxide becomes excessively high, which may ultimately increase the irreversible capacity and resistance of the positive electrode active material, resulting in a decrease in discharge capacity.

[0097] In one embodiment, the lithium manganese-based oxide may be a core-shell particle including a core portion in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-dissolved, and a shell portion present on at least a portion of the surface of the core portion and containing a spinel phase belonging to the Fd-3m space group. In this case, the core portion and the shell portion are solid-dissolved with each other, so that there is no grain boundary between the core portion and the shell portion.

[0098] When the lithium manganese oxide is a core-shell particle, the ratio of the core portion to the total volume of the lithium manganese oxide may be 1% to 99%, preferably 30% to 99%, and more preferably 50% to 99%.

[0099] When the core portion is a secondary particle formed by aggregating a plurality of primary particles, the shell portion in which the spinel phase is present may be present on at least a portion of the surface of the primary particle. That is, the primary particle may exist as an independent particle in which a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group are solid-dissolved.

[0100] Furthermore, when the core portion is a secondary particle formed by aggregating a plurality of primary particles, the shell portion in which the spinel phase is present may be present on at least a portion of the surface of the secondary particle. That is, the primary particles present inside and / or at the center of the secondary particle may exist as particles in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved, whereas the primary particles present on the outermost surface of the secondary particle and / or in a region close to the outermost surface of the secondary particle (surface portion of the secondary particle) may exist as particles in which a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group are solid-solved.

[0101] Furthermore, the shell portion containing the spinel phase may be present in a diffused form along the boundaries between the primary particles from the surface of the secondary particles toward the center of the secondary particles. Thus, the proportion of the spinel phase in the lithium manganese-based oxide may be higher in the surface portion of the secondary particles than in the center of the secondary particles. Similarly, the proportion of primary particles in which a phase belonging to the C2 / m space group, a phase belonging to the R3-m space group, and a spinel phase belonging to the Fd-3m space group are solid-dissolved may be higher in the surface portion of the secondary particles than in the center of the secondary particles.

[0102] In the present application, the spinel phase may be formed by surface modification of the lithium manganese-based oxide using molybdenum, and the surface modification may form a molybdenum-containing coating layer on at least a portion of the surface of the lithium manganese-based oxide.

[0103] The molybdenum-containing coating layer can reduce the surface resistance of the lithium manganese-based oxide, thereby preventing early degradation of the lithium manganese-based oxide and thereby improving the lifespan of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. Furthermore, the molybdenum-containing coating layer can induce the formation of a spinel phase on the surface of the lithium manganese-based oxide.

[0104] The molybdenum-containing coating layer may include at least one selected from MoO3 and Li2MoO4.

[0105] When the lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, the molybdenum may be present at a higher concentration on the surface of the secondary particles than inside the secondary particles.

[0106] When the lithium manganese-based oxide is a core-shell particle including a core portion in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-dissolved, and a shell portion present on at least a portion of the surface of the core portion and containing a spinel phase belonging to the Fd-3m space group, a molybdenum-containing coating layer may be present on at least a portion of the surface of the shell portion.

[0107] Furthermore, when the core portion is a secondary particle formed by agglomeration of a plurality of primary particles, molybdenum may be present at a higher concentration on the surface of the secondary particle than in the interior of the secondary particle, and the molybdenum may form a concentration gradient that decreases from the surface of the secondary particle toward the interior of the secondary particle along the interface between the primary particles.

[0108] The surface-modified positive electrode active material as defined herein may exhibit the following characteristics when subjected to X-ray diffraction analysis using Cu-Kα radiation.

[0109] In one embodiment, in an X-ray diffraction analysis using Cu-Kα radiation on the positive electrode active material, the ratio of the intensities of the diffraction peaks attributable to the (003) plane and the (104) plane satisfies the following formula 1.

[0110] [Formula 1] 1.59≦I(003) / I(104)≦2.6 I(003) / I(104) according to the formula 1 may be 1.59 or more and 2.6 or less, 1.59 or more and 2.5 or less, 1.59 or more and 2.3 or less, 1.591 or more and 2.1 or less, or 1.591 or more and 2.012 or less.

[0111] As defined in the present application, by forming a spinel phase belonging to the Fd-3m space group in the surface-modified positive electrode active material, the intensity of the diffraction peak belonging to the (104) plane that appears in the 2θ=43.5° to 45.0° region may be weakened.

[0112] When the I(003) / I(104) ratio according to Equation 1 is greater than 2.6, it means that an excessive amount of a spinel phase is formed in the lithium manganese-based oxide. In this case, the irreversible capacity and resistance of the positive electrode active material increase, and the charge / discharge capacity and discharge capacity retention of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material may decrease.

[0113] On the other hand, when the I(003) / I(104) ratio according to Equation 1 is less than 1.59, it means that the spinel phase is hardly formed in the lithium manganese-based oxide. In this case, the anionic redox suppression effect of the spinel phase is insufficient, making it difficult to stabilize the unstable surface of the lithium manganese-based oxide, and making it difficult to improve the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0114] In addition, in an X-ray diffraction analysis using Cu-Kα rays on the positive electrode active material, the full width at half maximum (FWHM) of the diffraction peak attributable to the (104) plane may be 0.27 to 0.50, 0.27 to 0.40, or 0.27 to 0.382.

[0115] As defined in the present application, by forming a spinel phase belonging to the Fd-3m space group in the surface-modified positive electrode active material, the half-width of the diffraction peak belonging to the (104) plane that appears in the 2θ=43.5° to 45.0° region may become larger.

[0116] The FWHM of the diffraction peak attributable to the (104) plane being greater than 0.50 means that an excessive amount of a spinel phase is formed in the lithium manganese-based oxide, which may increase the irreversible capacity and resistance of the positive electrode active material, thereby decreasing the charge / discharge capacity and discharge capacity retention of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0117] On the other hand, the fact that the half-width of the diffraction peak attributable to the (104) plane is 0.27 smaller means that the spinel phase is hardly formed in the lithium manganese oxide, and in this case, the anionic redox suppression effect of the spinel phase is insufficient, making it difficult to stabilize the unstable surface of the lithium manganese oxide.

[0118] In addition, in an X-ray diffraction analysis using Cu-Kα radiation on the positive electrode active material, the ratio of the intensities of the diffraction peaks attributable to the (018) plane and the (110) plane satisfies the following formula 2.

[0119] [Formula 2] 1.15≦I(018) / I(110)≦1.55 I(018) / I(110) according to the formula 2 may be 1.15 or more and 1.55 or less, 1.15 or more and 1.50 or less, or 1.157 or more and 1.545 or less.

[0120] As defined in the present application, by forming a spinel phase belonging to the Fd-3m space group in the surface-modified positive electrode active material, the intensity of the diffraction peak belonging to the (110) plane that appears in the 2θ=64.7° to 65.5° region may be weakened.

[0121] When the I(018) / I(110) ratio according to Equation 2 is greater than 1.55, it means that an excessive amount of a spinel phase is formed in the lithium manganese-based oxide. In this case, the irreversible capacity and resistance of the positive electrode active material increase, and the charge / discharge capacity and discharge capacity retention of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material may decrease.

[0122] On the other hand, when the I(018) / I(110) ratio according to Equation 2 is less than 1.15, it means that the spinel phase is hardly formed in the lithium manganese-based oxide. In this case, the anionic redox suppression effect of the spinel phase is insufficient, making it difficult to stabilize the unstable surface of the lithium manganese-based oxide, and making it difficult to improve the life characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0123] That is, the lithium manganese-based oxide surface-modified as defined in the present application is a lithium manganese-based oxide having Mn 4+ is Mn 2+ Therefore, the anionic redox reaction of the lithium manganese-based oxide can be suppressed, thereby stabilizing the unstable surface of the lithium manganese-based oxide.

[0124] In addition, the molybdenum-containing coating layer and spinel phase formed on the surface of the lithium manganese-based oxide by the surface modification act as a barrier to prevent side reactions between the lithium manganese-based oxide and the electrolyte, thereby contributing to improving the stability and lifespan of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. Furthermore, according to the present invention, the surface modification of the lithium manganese-based oxide reduces the surface resistance of the lithium manganese-based oxide, preventing early deterioration of the lithium manganese-based oxide and thereby improving the lifespan of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0125] Lithium secondary battery According to another aspect of the present invention, there is provided a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include a lithium manganese-based oxide according to any of the various embodiments of the present invention described above as a positive electrode active material.

[0126] Therefore, a detailed description of the lithium-manganese-based oxide will be omitted, and only the remaining components not described above will be described below. For convenience, the lithium-manganese-based oxide will be referred to as the positive electrode active material below.

[0127] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0128] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0129] In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0130] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0131] The binder serves to improve adhesion between positive electrode active material particles and 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, and various copolymers thereof. One or more of these may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt % of the total weight of the positive electrode active material layer.

[0132] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0133] 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 may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0134] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0135] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0136] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0137] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0138] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0139] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0140] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0141] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0142] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0143] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0144] 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 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, 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.

[0145] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0146] In another embodiment, the negative electrode active material layer may be fabricated by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0147] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0148] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0149] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0150] The organic solvent may be any solvent that can act 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, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based 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, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0151] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0152] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-based solid electrolyte may be used, and preferably, a sulfide-based solid electrolyte may be used.

[0153] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, an X element (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S may be used. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (wherein m and n are integers and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0154] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0155] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0156] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Alternatively, the solid electrolyte may be included in a portion of the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or in a portion of the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0157] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0158] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0159] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0160] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0161] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0162] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0163] Production Example 1: Production of positive electrode active material Comparative Example 1 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH, and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was completed, the reactor was washed and dehydrated to obtain Ni particles with an average particle size of approximately 12 μm. 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0164] (b) First heat treatment The precursor obtained in step (a) was heat-treated in an air atmosphere at 550° C. for 5 hours, and then cooled in a furnace to obtain a precursor in an oxide state.

[0165] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with the lithium source material LiOH (Li / (Li-excluded metal) molar ratio=1.28) to prepare a mixture.

[0166] Next, the mixture was heat-treated at 900°C in an O2 atmosphere for 8 hours, and then cooled in a furnace and classified to obtain a lithium manganese-based oxide without surface modification.

[0167] Comparative Example 2 2.0 mol% (NH4)6Mo7O in 100 ml of deionized water 24 The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0168] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0169] Next, the mixture was heat-treated at 750°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing Li2MoO4 formed on its surface.

[0170] Comparative Example 3 The lithium manganese oxide obtained in Comparative Example 1 and 1.0 mol% (NH4)6Mo7O 24 were dry mixed to prepare a mixture.

[0171] Next, the mixture was heat-treated at 600°C in an O2 atmosphere for 8 hours, and then cooled in a furnace and classified to obtain a lithium manganese-based oxide.

[0172] (NH4)6Mo7O dry mixed with the lithium manganese oxide 24 Since most of the Mo remained in the form of large particles even after heat treatment, it was removed during the classification process, and it was confirmed that no coating layer containing Mo was formed on the surface of the lithium manganese oxide.

[0173] Example 1 0.5 mol% (NH4)6Mo7O in 100 ml of deionized water 24 The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0174] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0175] Next, the mixture was heat-treated at 600°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing MoO3 formed on its surface.

[0176] Example 2 1.0 mol% (NH4)6Mo7O in 100 ml of deionized water 24 The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0177] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0178] Next, the mixture was heat-treated at 600°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing MoO3 formed on its surface.

[0179] Example 3 1.5 mol% (NH4)6Mo7O in 100 ml of deionized water 24The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0180] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0181] Next, the mixture was heat-treated at 600°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing MoO3 formed on its surface.

[0182] Example 4 0.5 mol% (NH4)6Mo7O in 100 ml of deionized water 24 The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0183] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0184] Next, the mixture was heat-treated at 750°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing Li2MoO4 formed on its surface.

[0185] Example 5 1.0 mol% (NH4)6Mo7O in 100 ml of deionized water 24 The coating solution was prepared by adding the above ingredients and stirring at 300 rpm, and adjusting the pH to 9-10 using NH3·H2O.

[0186] The lithium manganese oxide obtained in Comparative Example 1 was added to the coating solution and stirred at 300 rpm for 30 minutes, then further stirred at 300 rpm at 80°C for about 12 hours until the water evaporated, and then further dried at 150°C for 12 hours to prepare a mixture.

[0187] Next, the mixture was heat-treated at 750°C in an O2 atmosphere for 8 hours, and then furnace-cooled and classified to obtain a lithium manganese-based oxide having a coating layer containing Li2MoO4 formed on its surface.

[0188] Comparative Example 4 The lithium manganese-based oxide with a coating layer containing Li2MoO4 formed on its surface obtained in Example 5 was added to 100 ml of deionized water and stirred at 300 rpm for 10 minutes. After filtering, the lithium manganese-based oxide remaining on the filter was dried at 150°C for 12 hours to obtain a final product. By rinsing the lithium manganese-based oxide with deionized water, it was confirmed that no coating layer containing Mo was formed on the surface of the lithium manganese-based oxide in the final product.

[0189] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 1, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0190] A half-cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0191] Manufacturing example 3. Manufacturing of lithium secondary batteries (full cells) 90 wt % of the positive electrode active material prepared in Preparation Example 1, 4.5 wt % of carbon black, and 5.5 wt % of PVDF binder were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry.

[0192] The positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and dried at 135° C. in vacuum to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0193] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution containing 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0194] Experimental Example 1: SEM / EDS analysis of positive electrode active material The lithium manganese-based oxides selected from the positive electrode active materials according to Examples 3 and 4 were subjected to SEM / EDS analysis to confirm the surface modification of the lithium manganese-based oxides.

[0195] Referring to Figure 1, which shows a surface SEM image and surface EDS analysis results (target element: Mo) of the lithium manganese-based oxide (secondary particles) according to Example 3, and Figure 3, which shows a surface SEM image and surface EDS analysis results (target element: Mo) of the lithium manganese-based oxide (secondary particles) according to Example 4, it was confirmed that the lithium manganese-based oxide existed as secondary particles formed by agglomeration of multiple primary particles, and that the target element Mo was present on the surface of the lithium manganese-based oxide. Furthermore, the EDS mapping results confirmed that Mo was present in higher concentration on the surface of the secondary particles than inside the secondary particles.

[0196] In addition, as shown in Figure 2, a cross-sectional SEM image of the lithium manganese-based oxide separated from the cathode active material of Example 3 was obtained, and then EDS mapping of the target elements Ni, Mn, and Mo was performed. The concentrations (at%) of Ni, Mn, and Mo were determined at designated points (circles 1, 2, and 3) in the lithium manganese-based oxide through line scanning. The measurement results are shown in Table 1 below.

[0197] [Table 1]

[0198] Referring to the results in Table 1, it can be seen that molybdenum is present at a higher concentration on the surface of the secondary particles than inside the secondary particles.

[0199] Experimental Example 2: XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed on each of the cathode active materials prepared in Preparation Example 1 to identify the space group and coating material of the phase present in the lithium manganese-based oxide contained in the cathode active material, and peaks attributed to the (003), (018), (104), and (110) crystal planes of the lithium manganese-based oxide were detected. The XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu-Kα radiation (1.540598 Å).

[0200] Specifically, in the diffraction pattern obtained from XRD analysis, peaks specific to the phase belonging to the C2 / m space group can appear in the 2θ = 20.8 ± 1° region, and peaks specific to the phase belonging to the R3-m space group can appear in the 2θ = 18.6 ± 1° region. The presence or absence of a spinel phase belonging to the Fd-3m space group can be confirmed by changes in the peaks specific to the (104) plane, which appear in the 2θ = 43.5° to 45.0° region, and the peaks specific to the (110) plane, which appear in the 2θ = 64.7° to 65.5° region.

[0201] Furthermore, in the diffraction pattern obtained from the XRD analysis, peaks specific to the Mo-containing coating layer can be observed around 2θ = 30°. For example, a peak specific to Li2MoO4 can appear in the 2θ = 29.8 ± 0.3° region, and a peak specific to MoO3 can appear in the 2θ = 30.7 ± 0.3° region.

[0202] The XRD analysis results are shown in Tables 2 and 3 below.

[0203] [Table 2]

[0204] [Table 3]

[0205] When a spinel phase belonging to the Fd-3m space group is formed in the lithium manganese-based oxide, the peak specific to the (104) plane and the peak specific to the (110) plane collapse. Therefore, the results for the peak specific to the (104) plane were calculated based on the highest intensity of the pattern appearing in the 2θ = 43.5° to 45.0° range, and the results for the peak specific to the (110) plane were calculated based on the highest intensity of the pattern appearing in the 2θ = 64.7° to 65.5° range.

[0206] Experimental Example 3: Evaluation of the electrochemical properties of a lithium secondary battery (half cell) The lithium secondary battery (half cell) prepared in Preparation Example 2 was subjected to a charge-discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and discharge rates of 0.1 C and 2.0 C to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and rate capability (C-rate). For reference, in Comparative Example 3, most of the Li2MoO4 dry-mixed with the lithium manganese-based oxide remained in the form of coarse powder even after heat treatment, and was removed by the classification process. Since no coating layer containing Li2MoO4 was formed on the surface of the lithium manganese-based oxide, the battery was expected to be substantially the same as Comparative Example 1. Therefore, the half cell was excluded from the evaluation of its electrochemical properties.

[0207] The measurement results are shown in Table 4 below.

[0208] [Table 4]

[0209] Referring to the evaluation results of the half cells in Table 4, it was confirmed that in the case of the lithium secondary battery using the cathode active material of Comparative Example 2, the spinel phase was excessively formed in the cathode active material, resulting in deterioration of the electrochemical characteristics compared to Comparative Example 1. In addition, in the case of the lithium secondary battery using the cathode active material of Comparative Example 4, although the spinel phase was present in the cathode active material, not only was the Mo-containing coating layer removed through the subsequent washing process, but defects were also generated on the surface of the cathode active material through the washing process, resulting in a rapid deterioration of the electrochemical characteristics.

[0210] Experimental Example 4: Evaluation of the electrochemical characteristics of a lithium secondary battery (full cell) The lithium secondary battery (full cell) manufactured in Manufacturing Example 3 was subjected to a 6-cycle formation process at 25°C, voltage range of 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then 500 charge-discharge cycles were carried out at 25°C, voltage range of 2.0V to 4.6V, and 1C / 1C. st 500 cycles) discharge capacity, relative to initial discharge capacity th The percentage of discharge capacity after each cycle (cycle capacity retention) was measured.

[0211] The measurement results are shown in Table 5 below.

[0212] [Table 5]

[0213] Referring to the results in Table 5, it was confirmed that Comparative Example 1, which showed similar electrochemical characteristics to the Examples in the half-cell evaluation results, had excessively poor long-term life characteristics compared to the Examples. This confirmed that the cathode active material defined in the present application is more suitable for ensuring stable long-term life characteristics of lithium secondary batteries than the cathode active material according to Comparative Example 1.

[0214] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention.

Claims

1. A positive electrode active material comprising a lithium manganese-based oxide in which a phase belonging to a C2 / m space group and a phase belonging to an R3-m space group are solid-dissolved, The lithium manganese-based oxide further includes a spinel phase belonging to the Fd-3m space group, a molybdenum-containing coating layer is present on at least a portion of the surface of the lithium manganese-based oxide; In an X-ray diffraction analysis of the positive electrode active material using Cu-Kα radiation, the ratio of the intensities of the diffraction peaks attributable to the (003) plane and the (104) plane satisfies the following formula 1: A positive electrode active material, in which the ratio of the intensities of the diffraction peaks attributable to the (018) plane and the (110) plane satisfies the following formula 2: [Formula 1] 1.59≦I(003) / I(104)≦2.6 [Formula 2] 1.15≦I(018) / I(110)≦1.55

2. The positive electrode active material according to claim 1, wherein the full width at half maximum (FWHM) of a diffraction peak belonging to a (104) plane in an X-ray diffraction analysis using Cu-Kα radiation is 0.27 to 0.

50.

3. The positive electrode active material of claim 1 , wherein the lithium manganese-based oxide is represented by the following Chemical Formula 1: [Chemical formula 1] rLi ２ MnO ３－ｃ X′ ｃ ・(1-r)Li ａ M1 ｘ M2 ｙ O ２－ｂ X ｂ (where, M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and M2 does not overlap with M1; X and X' are each independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, 0<r≦0.7, 0<a≦1, 0≦b≦0.1, 0≦c≦0.1, 0<x≦1, 0≦y<1, 0<x+y≦1)

4. 2. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide is a solid solution of a phase belonging to a C2 / m space group, a phase belonging to an R3-m space group, and a spinel phase belonging to an Fd-3m space group.

5. The positive electrode active material of claim 4 , wherein the lithium manganese-based oxide is represented by the following Chemical Formula 2: [Chemical formula 2] (1-Z) {rLi ２ MnO ３－ｃ X′ ｃ ・(1-r)Li ａ M11 ｘ M2 ｙ O ２－ｂ X ｂ }・zLi(Li ｄ Mn ２－ｄ -eM3 ｅ )O ４－ｇ X″ ｇ (where, M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and M2 does not overlap with M1; M3 is at least one selected from Ni, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd; X, X', and X'' are each independently a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, 0<r≦0.7, 0<a≦1, 0≦b≦0.1, 0≦c≦0.1, 0<x≦1, 0≦y<1, 0<x+y≦1, 0<z≦0.5, 0≦d≦1, 0<e≦1, 0≦g≦0.1)

6. The spinel phase is LiMn １．５ Ni ０．５ O ４ The positive electrode active material according to claim 5 , wherein the positive electrode active material is represented by the formula:

7. The lithium manganese oxide is a core portion in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved; a shell portion present on at least a portion of the surface of the core portion and including a spinel phase belonging to the Fd-3m space group; 2. The positive electrode active material according to claim 1, wherein the core portion and the shell portion are core-shell particles in which the core portion and the shell portion are solid-solved.

8. the core portion is a secondary particle formed by agglomeration of a plurality of primary particles, The positive electrode active material according to claim 7 , wherein the shell portion is present on at least a portion of the surface of the primary particle.

9. the core portion is a secondary particle formed by agglomeration of a plurality of primary particles, The positive electrode active material according to claim 7 , wherein the shell portion is present on at least a portion of the surface of the secondary particle.

10. The positive electrode active material according to claim 7 , wherein a molybdenum-containing coating layer is present on at least a portion of the surface of the shell portion.

11. The molybdenum-containing coating layer is MoO ３ and Li ２ MoO ４ The positive electrode active material according to claim 10 , comprising at least one selected from:

12. The lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, 2. The positive electrode active material according to claim 1, wherein molybdenum is present at a higher concentration on the surface of the secondary particles than in the interior of the secondary particles.

13. The lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, 2. The cathode active material of claim 1, wherein a gradient of decreasing molybdenum concentration exists along the interface between the primary particles from the surface of the secondary particles toward the interior of the secondary particles.

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

15. A lithium secondary battery comprising the positive electrode according to claim 14.

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