Positive electrode active material and lithium secondary battery including the same

Abstract

To provide a positive electrode active material including an overlithiated lithium manganese-based oxide, which can be synthesized at a lower temperature than that in a conventional synthesis process, and can compensate for phase development and lithium ion conductivity which are insufficient even when synthesized at low temperatures, 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, and a coating part on at least a part of the surface of the lithium manganese-based oxide, the coating part containing fluorine. In X-ray diffraction analysis of the positive electrode active material using Cu-Kα rays, the full width at half maximum (FWHMa) of the diffraction peak appearing in the area of 2θ=18°-19°is 0.14 or more and less than 0.221, and the full width at half maximum (FWHMb) of the diffraction peak appearing in the area of 2θ=44°-45° is 0.31 or more and less than 0.641.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material including a lithium-excess lithium manganese-based oxide, which can be synthesized at a lower temperature than in conventional synthesis processes, and at the same time, when synthesized at a low temperature, can supplement the development of insufficient phases and lithium ion conductivity, and a lithium secondary battery including the same. [Background technology]

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

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

[0004] A typical material used as a positive electrode active material for lithium secondary batteries is a lithium composite oxide. The lithium composite oxide is LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiMnO 2 Alternatively, there may be oxides of Ni, Co, Mn, Al, etc. in combination.

[0005] Among the positive electrode active materials, LiCoO 2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency, but has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] LiMnO 2 , LiMn 2 O 4 Lithium manganese oxides such as LiNiO have the advantages of being thermally safe and inexpensive, but they have problems such as small capacity and poor high-temperature properties. 2 Although the positive electrode active material based on this system shows battery characteristics such as high discharge capacity, it is difficult to synthesize it due to the problem of cation mixing between Li and transition metals, and therefore there are serious problems with the rate characteristics.

[0007] In addition, a large amount of Li by-products are generated depending on the extent of the cation mixing. The Li by-products are mostly LiOH and Li 2 CO 3 This may cause gelation during the preparation of the positive electrode paste, or may cause gas generation during repeated charging and discharging after the electrode is manufactured. 2 CO 3 This increases the swelling phenomenon of the cell and reduces the life characteristics.

[0008] To overcome these shortcomings of conventional positive electrode active materials, various candidate materials have been proposed.

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

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

[0011] In order to solve the above problems, research has been conducted into modifying the composition of OLO, but so far these efforts 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 leading role in the market, 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 concerns, 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 are currently mainly 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, since the supply and demand of cobalt is unstable and it is excessively expensive compared to other raw materials, a new positive electrode active material with a reduced cobalt content or an absence of cobalt is required.

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

[0016] In addition, the lithium manganese-based oxide has a different crystal structure from commercially available ternary lithium composite oxides having nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions, and requires a higher sintering temperature than the ternary lithium composite oxide to form a phase specific to the lithium manganese-based oxide. Thus, the increase in the sintering temperature required for the synthesis process acts as a cause of increasing the manufacturing cost of the lithium manganese-based oxide.

[0017] If the sintering temperature is low and the formation of a specific phase of the lithium manganese-based oxide is insufficient, not only the lithium ion conductivity is reduced and the overall electrochemical properties are reduced, but also the specific surface area is increased, which increases side reactions between the lithium manganese-based oxide and the electrolyte, thereby decreasing stability.

[0018] The appropriate calcination temperature for the lithium manganese-based oxide is 850°C, preferably 900°C or higher. Under such harsh calcination conditions, the size of the primary particles constituting the lithium manganese-based oxide becomes excessively large compared to commercially available ternary type lithium composite oxides, and the specific surface area is excessively reduced, which may result in a deterioration in rate characteristics.

[0019] Accordingly, the present invention aims to provide a positive electrode active material in which the development of a specific phase in the lithium manganese-based oxide can be sufficiently induced even at a relatively low temperature, thereby reducing the manufacturing cost of the lithium manganese-based oxide and simultaneously suppressing overgrowth of primary particles.

[0020] In particular, the present invention aims to provide a positive electrode active material that uses LiF when calcining the lithium manganese oxide, promotes phase development even at low temperatures, and reduces the specific surface area to an appropriate level, thereby reducing side reactions between the lithium manganese oxide and an electrolyte without deteriorating rate characteristics.

[0021] Another object of the present invention is to provide a positive electrode active material capable of compensating for insufficient lithium ion conductivity of the lithium manganese oxide by forming a coating layer containing LiF on the surface of the lithium manganese oxide after the low-temperature synthesis.

[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 having improved capacity and rate characteristics by using a positive electrode defined herein, as compared with a conventional lithium secondary battery using OLO as a positive electrode active material.

[0024] The object of the present invention is not limited to the object mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and will be more clearly understood by the embodiments of the present invention. In addition, it will be easily known that the object and advantages of the present invention can be realized by the means and combinations thereof as set forth in the claims. [Means for solving the problem]

[0025] According to one aspect of the present invention for solving the above technical problems, there is provided a positive electrode 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 dissolved.

[0026] Generally, commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a single phase of a phase belonging to 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.

[0027] In one embodiment, a coating portion containing fluorine is present on at least a portion of the surface of the lithium manganese-based oxide. The coating portion may contain LiF.

[0028] In the X-ray diffraction analysis using Cu-Kα radiation for the positive electrode active material, the half-width (FWHM) of the diffraction peak appearing in the 2θ=18° to 19° region was a ) is 0.14 or more and less than 0.221, and the half width (FWHM) of the diffraction peak appearing in the 2θ = 44° to 45° region is b ) is 0.31 or more and less than 0.641, and in an X-ray diffraction analysis of the positive electrode active material using Cu-Kα rays, the ratio of the half-width at half maximum of the diffraction peak appearing in the 2θ=44° to 45° region to the half-width at half maximum of the diffraction peak appearing in the 2θ=18° to 19° region (FWHM b / FWHM a ) is preferably greater than 1.738 and not greater than 2.665.

[0029] In one embodiment, the lithium manganese-based oxide may exist as secondary particles formed by agglomeration of a plurality of primary particles, and LiF may be present at a higher concentration on the surface of the secondary particles than in the center of the secondary particles.

[0030] In addition, the lithium manganese-based oxide may exist as secondary particles formed by agglomeration of a plurality of primary particles, and a gradient in fluorine concentration may exist along grain boundaries between the primary particles, where the fluorine concentration decreases from the surface of the secondary particles toward the center of the secondary particles.

[0031] In one embodiment, the lithium manganese-based oxide may be represented by the following Formula 1 or Formula 1-1.

[0032] [Chemical formula 1] Li (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 is a halogen capable of substituting at least a part of oxygen present in the lithium manganese-based oxide, and 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である) [Chemical formula 1-1] rLi 2 MnO 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 part of oxygen present in the lithium manganese-based oxide, and 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である) According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material.

[0033] According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-mentioned positive electrode. Effect of the Invention

[0034] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese-based oxides, which have various disadvantages in terms of electrochemical properties and / or stability, as compared with commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[0035] Specifically, according to the present invention, by using LiF during calcination of the lithium manganese oxide, the development of a phase specific to the lithium manganese oxide is sufficiently promoted even at a low temperature, and the specific surface area is reduced to an appropriate level, thereby making it possible to reduce side reactions between the lithium manganese oxide and the electrolyte without deteriorating the rate characteristics.

[0036] As described above, according to the present invention, it is possible to induce the development of a specific phase in the lithium manganese-based oxide even at a relatively low temperature, thereby reducing the manufacturing cost of the lithium manganese-based oxide and simultaneously suppressing overgrowth of primary particles.

[0037] In addition, according to the present invention, the LiF used during the calcination is not doped into the lithium manganese-based oxide, but forms a coating layer containing LiF on the surface of the lithium manganese-based oxide, thereby making up for the insufficient lithium ion conductivity of the lithium manganese-based oxide. In particular, according to the present invention, the hydroxide precursor is converted into an oxide precursor through a roasting treatment before calcination, and then mixed with a lithium source material and LiF and calcined, so that it is possible to effectively prevent LiF from being doped into the lithium manganese-based oxide during the calcination process.

[0038] In addition, in the present invention, the LiF used during sintering exists on the surface of the lithium manganese-based oxide in the form of a coating layer, thereby making it possible to compensate for the insufficient lithium ion conductivity of the lithium manganese-based oxide.

[0039] The specific effects of the present invention, together with the above-mentioned effects, will be described below while explaining specific matters for carrying out the invention. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is a graph showing the change in F element content depending on the etching depth by XPS analysis in Experimental Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] In order to make the present invention easier to understand, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used in the present invention shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified by the context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0042] Hereinafter, a positive electrode active material including a lithium-excess lithium manganese-based oxide according to some embodiments of the present invention and a lithium secondary battery including the positive electrode active material will be described in more detail.

[0043] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material comprising 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.

[0044] The phase belonging to the C2 / m space group and the phase belonging to the R3-m space group can be distinguished not only by the composition of each phase but also by the specific peaks for each phase during XRD analysis. For example, the specific peak for the phase belonging to the C2 / m space group can appear in the 2θ=20.8±1° region, and the specific peak for the phase belonging to the R3-m space group can appear in the 2θ=18.6±1° region.

[0045] 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 phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist in the lithium manganese-based oxide. The lithium manganese-based oxide is also a composite oxide having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn 2 O 4 or oxides having a similar composition).

[0046] The lithium manganese-based oxide contains at least lithium, manganese, and a transition metal. The transition metal may contain at least one selected from nickel, cobalt, and aluminum. The lithium manganese-based oxide may contain lithium, nickel, and manganese, and may further contain a transition metal other than nickel.

[0047] 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, 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).

[0048] In addition, 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 greater than the content of other transition metals.

[0049] In general, in a commercially available ternary lithium composite oxide having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, the manganese content in all metal elements excluding lithium is 20 mol% or less. In consideration of this, the lithium manganese-based oxide has a relatively high ratio of manganese in all metal elements (e.g., 50 mol% or more, 52 mol% or more, 53 mol% or more, or 55 mol% or more) compared to a commercially available ternary lithium composite oxide.

[0050] 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 type) in all metal elements excluding lithium, the lithium manganese-based oxide has a relatively low ratio of nickel to 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.

[0051] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined in the present application 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) has a value close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese-based oxide defined in the present application is larger than 1, and preferably has a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0052] Therefore, in the present application, a lithium manganese-based oxide can be defined as a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol % or more, or a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol % or more and the nickel content is less than 50 mol %.

[0053] In addition, in the present application, the lithium manganese-based oxide may 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 in all metal elements excluding lithium is 50 mol% or more; or the lithium manganese content in 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 in all metal elements excluding lithium is 50 mol% or more, and the nickel content is less than 50 mol%.

[0054] Despite the above-mentioned differences in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0055] The lithium manganese-based oxide contained in the positive electrode active material defined herein may be present as particles including at least one primary particle.

[0056] 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.

[0057] The positive electrode active material may include 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 secondary particles formed by aggregation of a plurality of primary particles.

[0058] The primary particles constituting the lithium manganese oxide may have a rod shape, an elliptical shape, and / or an irregular shape. In addition, unless otherwise intended in the manufacturing process, primary particles of various shapes are present in the same positive electrode active material. In addition, the primary particles refer to particle units that do not have grain boundaries in appearance when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0059] The primary particles constituting the lithium manganese oxide defined in the present application may have an average particle size of 0.05 μm to 5 μm, 0.05 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 the average value of the length in the major axis direction and the length in the minor axis direction of the primary particles ([major axis length + minor axis length] / 2).

[0060] When the average particle size of the primary particles is less than 0.05 μm, the specific surface area of ​​the lithium manganese oxide (secondary particles) composed of the primary particles is relatively large, and in this case, the lithium manganese oxide and the electrolyte are more likely to cause a side reaction during storage or operation of the lithium secondary battery.

[0061] On the other hand, when the average particle size of the primary particles is larger than 5 μm, the growth of the primary particles is excessively induced, and the diffusion path of the lithium ions in the primary particles is also lengthened. When the diffusion path of the lithium ions in the primary particles is excessively long, the mobility of the lithium ions in the primary particles and the diffusibility of the lithium ions through the primary particles are reduced, which causes the resistance of the lithium manganese-based oxide (secondary particles) composed of the primary particles to increase.

[0062] 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, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm.

[0063] When the lithium manganese oxide exists as secondary particles formed by agglomeration 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 the primary particles constituting the secondary particles. The average particle size (D50) of the secondary particles may be measured using a laser diffraction method. For example, the secondary particles are dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. Then, a volume cumulative particle size distribution graph is obtained, and the particle size corresponding to 50% of the volume cumulative amount is obtained.

[0064] Unless otherwise defined, the term "surface of the primary particle" used in this application means the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" used in this application means the outer surface of the secondary particle exposed to the outside. In this case, the "surface of the secondary particle" formed by agglomeration of a plurality of primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0065] In addition, unless otherwise defined, the term "surface portion of a particle" used in this application means a region relatively closer to the "outermost surface" of a particle, and the term "center portion of a particle" means a region relatively closer to the "middle" of a particle than the "surface portion". Thus, the term "surface portion of a primary particle" means a region relatively closer to the "outermost surface" of the primary particle, and the term "center portion of a primary particle" means a region relatively closer to the "middle" of the primary particle than the "surface portion". Similarly, the term "surface portion of a secondary particle" means a region relatively closer to the "outermost surface" of the secondary particle, and the term "center portion of a secondary particle" means a region relatively closer to the "middle" of the secondary particle than the "surface portion".

[0066] In this case, the region within any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0067] For example, when the semidiameter of the primary particle is r, the area at 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 area at 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 area at 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 area at a distance of 0 to 0.25 μm from the center of the primary particle.

[0068] Furthermore, if necessary, when the semidiameter of the primary particle is referred to as r, a region that is 0 to 0.1r or 0 to 0.2r away from the surface of the primary particle can be defined as the surface portion of the primary particle, and a region that is 0 to 0.2r or 0 to 0.5r away from the center of the primary particle can be defined as the center portion of the primary particle.

[0069] Similarly, when the semidiameter of the secondary particle is r, the region at 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 at 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 at 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 at a distance of 0 to 1.0 μm from the center of the secondary particle.

[0070] Furthermore, if necessary, when the semidiameter of the secondary particle is referred to as r, a region that is 0 to 0.1r or 0 to 0.2r away from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and a region that is 0 to 0.2r or 0 to 0.5r away from the center of the secondary particle can be defined as the center portion of the secondary particle.

[0071] The lithium manganese-based oxide defined herein may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1. The composition represented by the following Chemical Formula 1 may represent an average composition reflecting the composition of a coating portion present on at least a portion of the surface of the lithium manganese-based oxide.

[0072] [Chemical formula 1] Li (Li a M1 x M2 y )O 2-b X b 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, M2 does not overlap with M1, X is a halogen capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, and 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である。

[0073] The type of halogen that can be used as X refers to the periodic table, and F, Cl, Br and / or I can be used, and preferably F can be used.

[0074] In another embodiment, the lithium manganese-based oxide may be represented by the following formula 1-1: The composition represented by the following formula 1-1 may represent an average composition reflecting the composition of a coating portion present on at least a portion of the surface of the lithium manganese-based oxide.

[0075] [Chemical formula 1-1] rLi 2 MnO 3-c X′ c (1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ 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, M2 does not overlap with M1, X and X′ are each independently a halogen capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, and 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である。

[0076] The types of halogen usable as X and X' refer to the periodic table, and F, Cl, Br and / or I can be used, with F being preferred.

[0077] In the above Chemical Formula 1 and Chemical Formula 1-1, 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 when present, may be other elements except Ni and Mn.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The lithium manganese-based oxide represented by Formula 1 or Formula 1-1 may selectively contain cobalt. When the lithium manganese-based oxide contains cobalt, the mole fraction of the cobalt relative to the moles of all 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 may have a cobalt-free composition that does not contain cobalt.

[0082] The Li / Metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may be more 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 has a value 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 appropriately 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 solid-dissolved and to exhibit high capacity under a high voltage operating environment, it is preferable that the Li / Metal molar ratio of the lithium manganese-based oxide is 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0083] 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 in all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 is preferably 50 mol % or more.

[0084] In order that the lithium manganese-based oxide may have the characteristic of OLO that exhibits high capacity in a high-voltage operating environment, the content of manganese in all metal elements excluding lithium present in the lithium manganese-based oxide may be 50 mol% or more and less than 80 mol%, 51 mol% or more and less than 80 mol%, 52 mol% or more and less than 80 mol%, 53 mol% or more and less than 80 mol%, 54 mol% or more and less than 80 mol%, 55 mol% or more and less than 80 mol%, 50 mol% or more and less than 75 mol%, 51 mol% or more and less than 75 mol%, 52 mol% or more and less than 75 mol%, 53 mol% or more and less than 75 mol%, 54 mol% or more and less than 75 mol%, or 55 mol% to 75 mol%.

[0085] When the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the movement of transition metals (especially manganese) in the lithium manganese-based oxide during formation and / or operation of the lithium secondary battery. Since such a phase transition occurs at random positions in the lithium manganese-based oxide, it may induce a decrease in charge / discharge capacity or a voltage decay during cycling of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. In addition, as the manganese content in the lithium manganese-based oxide exceeds 80 mol%, the lithium manganese-based oxide may become a composite oxide having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn 2 O 4 The properties of the oxide may be similar to those of the oxide having a similar composition.

[0086] 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 or Chemical Formula 1-1 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.

[0087] 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 formation and / or operation of the lithium secondary battery.

[0088] Generally, commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition exist as a single phase belonging to the R3-m space group.

[0089] Meanwhile, the lithium-rich lithium manganese oxide represented by the formula 1 or the formula 1-1 is represented by rLi 2 MnO 3-c X′ c The oxides belonging to the C2 / m space group (hereafter referred to as the "C2 / m phase") and (1-r)Li a M1 x M2 y O 2-b X b In the present application, the term "a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group being 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.

[0090] In this case, a complex 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.

[0091] 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 having a surface 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.

[0092] In the lithium manganese-based oxide represented by the chemical formula 1-1, when r is greater than 0.7, the lithium manganese-based oxide is an oxide of C2 / m phase, rLi 2 MnO 3-c X′ c The proportion of R3-m phase oxide is preferably present at a certain ratio or more in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance in the lithium manganese-based oxide, and improve the surface kinetics.

[0093] In one embodiment, a coating portion containing fluorine may be formed on at least a portion of the surface of the lithium manganese-based oxide. When the lithium manganese-based oxide is a secondary particle formed by agglomeration of a plurality of primary particles, the coating portion may cover at least a portion of the surface of the primary particles and / or the secondary particles. By forming a coating portion containing fluorine on the surface of the lithium manganese-based oxide, it is possible to reduce side reactions with the electrolyte occurring on the surface of the lithium manganese-based oxide, and at the same time, to mitigate and / or prevent a decrease in charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surface of the lithium manganese-based oxide.

[0094] A surface where adjacent primary particles in the secondary particle are in contact with each other may be referred to as an interface between the primary particles, and the interface between the primary particles may be defined as a grain boundary between the primary particles. Also, the primary particles may be separated from adjacent primary particles to form voids within the secondary particles.

[0095] The coating portion is defined as a region where fluorine is present on the surface of the primary particle and / or the secondary particle, and the coating portion may be formed entirely or partially on the surface of the primary particle and / or the secondary particle. When the coating layer is partially formed on the surface of the primary particle and / or the secondary particle, the shape of the coating layer may be referred to as an island shape.

[0096] In addition, fluorine may be present on the surfaces of the primary particles and / or the secondary particles in the form of a compound that is physically and / or chemically bonded thereto, or may be present in a partially solid-dissolved state.

[0097] The coating portion present inside the secondary particle may be formed by fluorine diffusing from a surface portion of the secondary particle toward a center portion of the secondary particle along a crystal grain boundary between the primary particles.

[0098] Specifically, the main compound (e.g., a fluorine-containing compound) constituting the coating portion may be present in a state of being diffused from the surface portion of the secondary particle toward the center portion of the secondary particle. Also, as the coating portion diffuses from the surface portion of the secondary particle toward the center portion of the secondary particle, the element (e.g., fluorine) mainly contained in the coating portion may show a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0099] In one embodiment, the coating portion may include a fluorine-containing compound. A representative example of the fluorine-containing compound is LiF. After low-temperature heat treatment of a mixture of the oxide-state precursor of the lithium manganese-based oxide, the lithium source material, and LiF, LiF may be present in a state of forming a coating layer on the surface of the lithium manganese-based oxide.

[0100] For example, the lithium manganese-based oxide may be mixed with a fluorine-containing polymer (e.g., PVDF, PTFE, etc.) and then heat-treated to form LiF on the surface of the lithium manganese-based oxide. However, since the fluorine coating using the fluorine-containing polymer is performed after calcining a hydroxide precursor or an oxide precursor with the lithium manganese-based oxide, it cannot contribute to lowering the calcination temperature of the conventional synthesis process and is not related to the phase development of the lithium manganese-based oxide.

[0101] The positive electrode active material may contain LiF in an amount of 0.5 mol% to 1.5 mol%. The positive electrode active material may contain LiF in an amount of less than 0.5 mol%, which means that the amount of LiF used in the calcination process of the oxide-state precursor of the lithium manganese-based oxide is too small. In this case, the lithium manganese-based oxide phase cannot be sufficiently developed during the calcination process. Meanwhile, the positive electrode active material may contain LiF in an amount of more than 1.5 mol%, which means that the amount of LiF used in the calcination process of the oxide-state precursor of the lithium manganese-based oxide is too large. In this case, the amount of LiF present on the surface of the lithium manganese-based oxide is too large, which may change the surface resistance of the lithium manganese-based oxide, thereby deteriorating the overall electrochemical characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. The amount of LiF present in the positive electrode active material may be calculated based on the amount of LiF mixed with the oxide precursor of the lithium manganese-based oxide.

[0102] In addition, the average thickness of the coating portion present on the surface of the lithium manganese-based oxide is 5 nm to 100 nm, 5 nm to 50 nm, or 5 nm to 30 nm. The thickness of the coating portion present on the surface of the lithium manganese-based oxide can be measured through an XPS analysis of fluorine, which is a target element in the lithium manganese-based oxide (for example, see the F depth profile shown in FIG. 1). When the average etching rate of the XPS analyzer measuring the F depth profile is 0.3 nm / 1 second, if fluorine is significantly detected at an etching time of 0 seconds to 30 seconds, the thickness of the coating portion containing fluorine can be calculated to be 9 nm. Similarly, if fluorine is significantly detected at an etching time of 0 seconds to 100 seconds, the thickness of the coating portion containing fluorine can be calculated to be 30 nm.

[0103] When LiF is also present at the grain boundaries between the primary particles, and thus fluorine is also detected inside the secondary particles, the thickness of the coating portion present on the surface of the lithium manganese-based oxide can be defined as the thickness from the outermost surface of the secondary particles to the depth at which the fluorine concentration begins to be maintained constant. In addition, the average thickness of the coating portion present on the surface of the lithium manganese-based oxide can be calculated as the average value of thicknesses measured by repeating the above-mentioned XPS analysis several times (10 or more times).

[0104] The fluorine content in the coating portion calculated through the XPS analysis may be 2 at% to 10 at%. The fluorine content in the coating portion being less than 2 at% means that the LiF content used in the calcination process of the oxide-state precursor of the lithium manganese-based oxide is too low. In this case, the lithium manganese-based oxide phase cannot be sufficiently developed during the calcination process. Meanwhile, the fluorine content in the coating portion being more than 10 at% means that the LiF content used in the calcination process of the oxide-state precursor of the lithium manganese-based oxide is too high. In this case, the LiF content present on the surface of the lithium manganese-based oxide becomes too high, which changes the surface resistance of the lithium manganese-based oxide, and thus may deteriorate the overall electrochemical characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0105] In addition, the LiF present in the coating portion can act as a lithium ion diffusion path, that is, a two-dimensional and / or three-dimensional path through which lithium ions diffuse within the lithium manganese-based oxide.

[0106] The formation of the lithium ion diffusion path in the lithium manganese-based oxide reduces the resistance to lithium ion migration via the lithium manganese-based oxide, which in turn contributes to improving the rate characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0107] The positive electrode active material according to the present invention is 1.6 m 2 / g or more 3.2m 2 / g or less, 1.6m 2 / g or more 3.1m 2 / g or less, 1.7m 2 / g or more 3.1m 2 / g or less, or 1.72m 2 / g or more 3.09m 2 / g or less.

[0108] According to the present invention, by using LiF during the calcination of the lithium manganese oxide, the phase development can be promoted even at low temperatures, and the specific surface area can be reduced, thereby reducing the side reaction between the lithium manganese oxide and the electrolyte.

[0109] In addition, as defined herein, the lithium manganese oxide precursor is calcined at a low temperature using LiF as a positive electrode active material, and the positive electrode active material exhibits the following characteristics when subjected to X-ray diffraction analysis using Cu-Kα radiation.

[0110] In the X-ray diffraction analysis using Cu-Kα radiation for the positive electrode active material, the half-width (FWHM) of the diffraction peak appearing in the 2θ=18° to 19° region was a ) is 0.14 or more and less than 0.221, or 0.14 or more and 0.205 or less, and the half width (FWHM) of the diffraction peak appearing in the 2θ = 44 ° to 45 ° region is b ) may be 0.31 or more and less than 0.641, 0.31 or more and less than 0.614, or 0.31 or more and less than 0.516.

[0111] In addition, the half widths of the diffraction peaks appearing in the 2θ=18°-19° region and the half widths of the diffraction peaks appearing in the 2θ=44°-45° region can all be reduced compared to when LiF is not used during low-temperature sintering. The fact that the half widths of the diffraction peaks appearing in the 2θ=18°-19° region and the half widths of the diffraction peaks appearing in the 2θ=44°-45° region are all reduced compared to when LiF is not used during low-temperature sintering means that the development of a phase specific to the lithium manganese oxide is promoted.

[0112] In addition, in an X-ray diffraction analysis using Cu-Kα radiation for the positive electrode active material, the ratio of the half-width of the diffraction peak appearing in the 2θ=44° to 45° region to the half-width of the diffraction peak appearing in the 2θ=18° to 19° region (FWHM b / FWHM a ) may be greater than 1.738 and less than or equal to 2.665, or greater than or equal to 2.214 and less than or equal to 2.665.

[0113] In addition, when a coating layer containing LiF is present on the surface of the lithium manganese-based oxide, LiF reacts with deionized water during pH titration to generate HF, and HF dissolves in deionized water to form LiF. 2 CO 3 A reversible reaction occurs that decomposes

[0114] <LiFによるLi 2 CO 3 Decomposition reaction of> LiF+H 2 O → LiOH + HF 2HF+Li 2 CO 3 →2LiF+CO 2 +H 2 O In other words, the more LiF is contained on the surface of the positive electrode active material (lithium manganese oxide), the more LiOH is contained in the positive electrode active material during pH titration. 2 CO 3 Therefore, if LiF is decomposed and doped into the lithium manganese oxide during the heat treatment instead of being coated on the surface of the lithium manganese oxide, the LiOH and Li 2 CO 3 No change in the content is observed.

[0115] Due to the reversible reaction with LiF described above, the content of LiOH measured by neutralization titration for the positive electrode active material defined in this application is Li 2 CO 3 The content may be more than that.

[0116] 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. The positive electrode active material layer may include a lithium manganese-based oxide having a coating portion formed on at least a portion of a surface thereof according to any of the above-described embodiments of the present invention as a positive electrode active material.

[0117] Therefore, a specific description of the lithium manganese oxide will be omitted, and only the remaining components not described above will be described below. For convenience, the lithium manganese oxide described above will be referred to as the positive electrode active material.

[0118] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0119] 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.

[0120] At this time, the positive electrode active material may be included in a content 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 content is within this range, but is not necessarily limited thereto.

[0121] The conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials such as carbon fibers, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in combination. The conductive material may be contained in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0122] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and among these, one type alone or a mixture of two or more types may be used. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0123] The positive electrode may be manufactured by a typical method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0124] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when applied to manufacture a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0125] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the positive electrode slurry composition from the support, and laminating the resulting film on a positive electrode current collector.

[0126] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-mentioned positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0127] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0128] 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.

[0129] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0130] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0131] 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.

[0132] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys, and SiO β (0<β<2), SnO 2, a metal oxide capable of doping and dedoping lithium, such as vanadium oxide or lithium vanadium oxide, or a composite containing the metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, may be used. Any one or a mixture of two or more of these may be used. A thin film of metallic lithium may be used as the negative electrode active material. As the carbon material, low-crystalline carbon and high-crystalline carbon may be used. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0133] 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.

[0134] The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and may be added in an amount of 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.

[0135] 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. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and may be, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives.

[0136] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, and then peeled off from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0137] In another embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating, or by casting the negative electrode slurry composition on a separate support and peeling the composition from the support to obtain a film, which may be laminated on the negative electrode current collector.

[0138] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ions to move. Any separator generally used in lithium secondary batteries may be used without any particular limitation. In particular, it is preferable that the separator has low resistance to ion movement of the electrolyte and has excellent electrolyte humidification ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like, may be used. In addition, in order to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0139] In addition, examples of the electrolyte used in the present application 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.

[0140] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0141] The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone, an ether solvent such as dibutyl ether or tetrahydrofuran, a ketone solvent such as cyclohexanone, an aromatic hydrocarbon solvent such as benzene or fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that may be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be excellent if the cyclic carbonate and the chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9.

[0142] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ), LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 The lithium salt may be used at a concentration within the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, and therefore excellent electrolyte performance can be exhibited, and lithium ions can migrate effectively.

[0143] 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.

[0144] As the material of 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 Li 2 SP2 S 5 , Li 2 SP 2 S-LiX (where X is a halogen element such as I or Cl), Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS 2 - LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 - LiI, Li 2 S-SiS 2 -P 2 S5-LiI, Li 2 S.B. 2 S 3 , Li 2 SP 2 S 5 -ZmSn (where m and n are integers and Z is Ge, Zn or Ga), Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li p MO q (where p, q are integers and M is P, Si, Ge, B, Al, Ga or In).

[0145] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed amorphous and crystalline state.

[0146] As a material for oxide-based solid electrolytes, Li7 La 3 Zr 2 O 12 , Li 7-x La 3 Zr 1-x Nb x O 12 , Li 7-3x La 3 Zr 2 Al x O 12 , Li 3x La 2 / 3-x TiO 3 , Li 1+x Al x Ti 2-x (PO 4 ) 3 , Li 1+x Al x Ge 2-x (PO 4 ) 3 , Li 3 PO 4 , Li 3+x PO 4-x N x (LiPON), Li 2+2x Zinc 1-x GeO 4 (LISICON), etc.

[0147] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. 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 the solid electrolyte may be included in a portion of the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0148] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0149] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0150] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0151] 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.

[0152] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (Electric Vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0153] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0154] Production Example 1. Production of positive electrode active material Comparative Example 1 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0155] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0156] (c) Second heat treatment The oxide precursor obtained in step (b) and a lithium source material LiOH (Li / Metal molar ratio=1.22) were mixed to prepare a mixture.

[0157] Next, O 2 The mixture was heat-treated at 750° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0158] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 3.30 m 2 / g.

[0159] Comparative Example 2 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0160] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0161] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 2.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0162] Next, O 2 The mixture was heat-treated at 750° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0163] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 2.24 m 2 / g.

[0164] Comparative Example 3 A positive active material was prepared in the same manner as in Comparative Example 1, except that in step (c), LiF was used in an amount of 3.0 mol % based on the total mixture.

[0165] The BET specific surface area of ​​the final product obtained in Comparative Example 3 (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 1.55 m 2 / g.

[0166] Comparative Example 4 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0167] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0168] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 1.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0169] Next, O 2 After heat treatment at 825° C. for 8 hours in an atmosphere, the mixture was cooled in a furnace to obtain a final positive electrode active material containing lithium manganese oxide.

[0170] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 1.42 m 2 / g.

[0171] Comparative Example 5 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0172] (b) First heat treatment The hydroxide-state precursor obtained in step (a), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 1.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0173] Next, O 2 The mixture was heat-treated at 750° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0174] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 1.57m 2 / g.

[0175] Comparative Example 6 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0176] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0177] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 1.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0178] Next, O 2 The mixture was heat-treated at 705° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0179] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 3.60 m 2 / g.

[0180] Example 1 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2The hydroxide precursor of the composition was obtained.

[0181] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0182] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 0.5 mol% based on the total mixture) were mixed to prepare a mixture.

[0183] Next, O 2 The mixture was heat-treated at 750° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0184] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 3.09 m 2 / g.

[0185] Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (c), LiF was used in an amount of 1.0 mol % based on the total mixture.

[0186] The BET specific surface area of ​​the final product obtained in Example 2 (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) was 2.72 m 2 / g.

[0187] Example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (c), LiF was used in an amount of 1.5 mol % based on the total mixture.

[0188] The BET specific surface area of ​​the final product obtained in Example 3 (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II made by BEL Japan) was 2.57 m 2 / g.

[0189] Example 4 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0190] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0191] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 1.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0192] Next, O 2 The mixture was heat-treated at 775° C. for 8 hours in an atmosphere and then cooled in a furnace to obtain a final cathode active material containing lithium manganese oxide.

[0193] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 2.46 m 2 / g.

[0194] Example 5 (a) Preparation of precursor NiSO in the reactor 4 6H 2 O, CoSO 4 6H 2 O and MnSO 4 H 2 O in a molar ratio of 40:2:58, NaOH and NH 4 The temperature in the reactor was maintained at 50° C., and N 2 and O 2 The precursor synthesis reaction was carried out while feeding in a gas containing Ni. After the reaction was completed, the material was washed and dehydrated. 0.4 Co 0.02 Mn 0.58 (OH) 2 The hydroxide precursor of the composition was obtained.

[0195] (b) First heat treatment The hydroxide precursor obtained in step (a) is O 2 After heat treatment at 550° C. for 5 hours in an atmosphere, the material was cooled in a furnace to obtain a precursor in an oxide state.

[0196] (c) Second heat treatment The oxide precursor obtained in step (b), lithium source material LiOH (Li / Metal molar ratio=1.22) and LiF (weighed out to be 1.0 mol% based on the total mixture) were mixed to prepare a mixture.

[0197] Next, O 2 After heat treatment at 800° C. for 8 hours in an atmosphere, the mixture was cooled in a furnace to obtain a final positive electrode active material containing a lithium manganese oxide.

[0198] The BET specific surface area of ​​the final product (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) was 1.72 m 2 / g.

[0199] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) 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.

[0200] The positive electrode slurry was uniformly applied to a thin aluminum film having a thickness of 15 μm and dried in a vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery having a positive electrode active material layer formed thereon.

[0201] Lithium foil was used as the counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as the separator, and LiPF was dissolved in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4. 6 A half-cell was fabricated using an electrolyte in which Zn was present at a concentration of 1.15M.

[0202] Experimental Example 1. XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials produced in Production Example 1, and diffraction peaks appearing in the 2θ=18° to 19° region and the 2θ=44° to 45° region were detected from the positive electrode active materials, and the full width at half maximum (FWHM) of the diffraction peaks was calculated. The XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu-Kα radiation (1.540598 Å).

[0203] The results of the XRD analysis are shown in Table 1 below.

[0204] [Table 1]

[0205] Referring to the results in Table 1, it was confirmed that the positive electrode active materials according to Examples 1 to 5 had smaller half-widths of the diffraction peaks appearing in the region of 2θ=18° to 19° and the region of 2θ=44° to 45° than the positive electrode active material according to Comparative Example 1. However, the FWHMs calculated from the positive electrode active materials according to Examples 1 to 5 were smaller than those of the positive electrode active material according to Comparative Example 1. b / FWHM a It was confirmed that the results were similar to those of Comparative Example 1.

[0206] On the other hand, it was confirmed that the positive electrode active materials of Comparative Examples 2 and 3 had a smaller half-width of the diffraction peak appearing in the 2θ=18° to 19° region than the positive electrode active material of Comparative Example 1, but on the contrary, the half-width of the diffraction peak appearing in the 2θ=44° to 45° region increased.

[0207] In addition, in the cathode active material according to Comparative Example 4, the second heat treatment temperature is set to a temperature equal to or higher than the eutectic point based on the LiF-LiOH binary phase diagram. As a result, LiF is decomposed and does not form a coating layer containing LiF on the surface of the lithium manganese-based oxide, but is mostly doped into the lithium manganese-based oxide. As a result, it was confirmed that the cathode active material according to Comparative Example 4 exhibits a half width of the diffraction peak similar to that of the cathode active material according to Comparative Example 1.

[0208] In addition, the positive electrode active material of Comparative Example 5 had a decreased half-width of the diffraction peak appearing in the 2θ=44° to 45° region compared to the positive electrode active material of Comparative Example 1, but the half-width of the diffraction peak appearing in the 2θ=18° to 19° region increased. It was also confirmed that the positive electrode active material of Comparative Example 6 had increased half-widths of the diffraction peaks appearing in the 2θ=18° to 19° region and the diffraction peaks appearing in the 2θ=44° to 45° region compared to the positive electrode active material of Comparative Example 1.

[0209] Experimental Example 2: Evaluation of the electrochemical characteristics of a lithium secondary battery (half cell) The lithium secondary battery (half cell) manufactured in Manufacturing Example 2 was subjected to a charge-discharge experiment at 25° C., voltage range of 2.5V to 4.7V, and discharge rate of 2.0C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100) to measure the initial charge capacity and rate capability (discharge capacity retention rate; rate capability (C-rate)).

[0210] In addition, the same half cell was charged and discharged 50 times at 25°C and within a driving voltage range of 2.5V to 4.7V at 2.0C / 0.2C, and then the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity (cycle capacity retention) was measured.

[0211] The measurement results are shown in Table 2 below.

[0212] [Table 2]

[0213] Referring to the evaluation results of the half cells in Table 2, it can be seen that the initial charge capacity, initial discharge capacity, and rate characteristics of the lithium secondary batteries using the positive electrode active materials according to Examples 1 to 5 were generally improved compared to the lithium secondary batteries using the positive electrode active materials according to Comparative Examples 1 to 6.

[0214] In particular, in the case of the positive electrode active material according to Comparative Example 3, as the content of LiF used before the second heat treatment became excessively high, the BET specific surface area of ​​the positive electrode active material became excessively low, which is expected to result in lower rate characteristics than the positive electrode active material according to Comparative Example 1. Also, in the case of the positive electrode active material according to Comparative Example 4, as the second heat treatment temperature became excessively high, the BET specific surface area of ​​the positive electrode active material became excessively low, which is expected to result in lower rate characteristics than the positive electrode active material according to Comparative Example 1.

[0215] In the case of the positive electrode active material of Comparative Example 5, when the same second heat treatment temperature was applied, the BET specific surface area was excessively lower than that in the case of using the oxide precursor, which is expected to result in lower rate characteristics than the positive electrode active material using the oxide precursor.

[0216] Experimental Example 3: Analysis of residual lithium in positive electrode active material The residual lithium (lithium impurity) content in the positive electrode active material prepared according to Preparation Example 1 was analyzed by pH titration. In the pH titration, the residual lithium (lithium impurity) content was measured by the amount of 0.1N HCl used until the pH reached 4 by pH titration of the positive electrode active material. Specifically, 5 g of each positive electrode active material prepared according to Preparation Example 1 was placed in 100 ml of DIW, stirred for 15 minutes, and filtered. 50 ml of the filtered solution was taken, and 0.1 M HCl was added thereto to measure the amount of HCl consumed due to the change in pH. The amounts of LiOH and Li 2 CO 3 The content was calculated.

[0217] In addition, when a coating layer containing LiF is present on the surface of the positive electrode active material (lithium manganese oxide) produced by Production Example 1, LiF reacts with deionized water during pH titration to generate HF, and the HF dissolves in the deionized water to form LiF. 2 CO 3 A reversible reaction occurs that decomposes

[0218] <LiFによるLi 2 CO 3 Decomposition reaction of> LiF+H 2 O → LiOH + HF 2HF+Li 2 CO 3 →2LiF+CO 2 +H 2 O In other words, the more LiF is contained on the surface of the positive electrode active material (lithium manganese oxide), the more LiOH is contained in the positive electrode active material during pH titration. 2 CO 3 Therefore, if LiF is decomposed and doped into the lithium manganese oxide during the heat treatment instead of being coated on the surface of the lithium manganese oxide, the LiOH and Li 2 CO 3 No change in the content is observed.

[0219] The residual lithium analysis results are shown in Table 3 below.

[0220] [Table 3]

[0221] Referring to the results in Table 3, the content of LiOH in the positive electrode active materials according to Examples 1 and 2 is increased compared to the positive electrode active material according to Comparative Example 1, and the content of LiOH in the positive electrode active materials according to Examples 1 and 2 is increased. 2 CO 3It was confirmed that the content of LiOH in the positive electrode active material decreased, whereas the total amount of residual lithium remained almost unchanged. In addition, when comparing the positive electrode active material according to Example 1 with the positive electrode active material according to Example 2, the content of LiOH increased as the LiF content in the positive electrode active material increased, and the Li 2 CO 3 It was confirmed that the content of

[0222] In addition, in the case of the positive electrode active material according to Comparative Example 4, the second heat treatment temperature is set to a temperature equal to or higher than the eutectic point based on the LiF-LiOH binary phase diagram, so that LiF is decomposed and, instead of forming a coating layer containing LiF on the surface of the lithium manganese oxide, is doped into most of the lithium manganese oxide, resulting in Li 2 CO 3 It was confirmed that the change in the content was smaller than that in Examples 1 and 2.

[0223] Experimental Example 4. XPS analysis of positive electrode active material The lithium manganese-based oxides selected from the positive electrode active materials according to Examples 1 and 2 were subjected to XPS analysis to measure the content of the target element (F) contained in the lithium manganese-based oxides.

[0224] Specifically, the change in the content of the target element (F) was measured from the surface of the lithium manganese-based oxide (secondary particles) to the lithium manganese-based oxide (secondary particles) by increasing the etching time of the surface of the lithium manganese-based oxide using an XPS depth profile analysis method (ion energy 2000 eV, spot size 200 μm).

[0225] Referring to FIG. 1 showing the XPS analysis results, it was confirmed that F was present at a high concentration on the surface of the lithium manganese-based oxide contained in the positive electrode active materials according to Examples 1 and 2. The results indicate that a LiF coating layer was formed on the surface of the lithium manganese-based oxide contained in the positive electrode active materials according to Examples 1 and 2. It was also confirmed that the concentration of F decreased as the etching time increased. This is because LiF diffuses from the surface to the center of the lithium manganese-based oxide along the grain boundaries, thereby forming a gradient in which the concentration of F decreases.

[0226] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding elements without departing from the concept of the present invention described in the claims, and this may also be considered to be within the scope of the claims of the present invention.

Claims

1. a 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; A coating portion present on at least a portion of the surface of the lithium manganese-based oxide, the coating portion contains fluorine, The full width at half maximum (FWHM) of the diffraction peak appearing in the 2θ=18° to 19° region in the X-ray diffraction analysis using Cu-Kα radiation for the positive electrode active material ａ ) is 0.14 or more and less than 0.221, and the full width at half maximum (FWHM) of the diffraction peak appearing in the 2θ=44° to 45° region is ｂ ) is 0.31 or more and less than 0.

641.

2. The full width at half maximum (FWHM) of the diffraction peak appearing in the 2θ=18° to 19° region in the X-ray diffraction analysis using Cu-Kα radiation for the positive electrode active material ａ ) for the half-width (FWHM) of the diffraction peak appearing in the 2θ=44° to 45° region ｂ ) (FWHM ｂ / FWHM ａ 2. The positive electrode active material according to claim 1, wherein the positive electrode active material (A) is greater than 1.738 and is equal to or less than 2.

665.

3. 2. The positive electrode active material of claim 1, wherein the lithium manganese-based oxide comprises lithium, manganese, and a transition metal.

4. The positive electrode active material according to claim 1 , wherein the coating portion includes LiF.

5. The positive electrode active material according to claim 1 , wherein LiF is present in the positive electrode active material at 0.5 mol % to 1.5 mol %.

6. The average thickness of the coating is 5 nm to 30 nm; The cathode active material according to claim 1 , wherein the fluorine content in the coating portion is 2 at % to 10 at %.

7. The lithium manganese oxide exists as secondary particles formed by agglomeration of a plurality of primary particles, 2. The positive electrode active material according to claim 1, wherein LiF is present in a higher concentration in a surface portion of the secondary particle than in a center portion of the secondary particle.

8. The lithium manganese oxide exists as secondary particles formed by agglomeration of a plurality of primary particles, 2. The positive electrode active material of claim 1, wherein a gradient exists in which the fluorine concentration decreases from a surface portion of the secondary particle to a center portion of the secondary particle along a grain boundary between the primary particles.

9. 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] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 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 is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese oxide; 0<a≦0.7, 0≦b≦0.1, 0<x≦1, 0≦y<1, 0<x+y≦1)

10. 2. The positive electrode active material of claim 1, wherein the lithium manganese-based oxide is represented by the following formula 1-1: [Chemical formula 1-1] 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 oxide; 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).

11. The positive electrode active material is 1.6 m ２ / g or more 3.2m ２ The positive electrode active material according to claim 1 , having a BET specific surface area of ​​no more than 1 / g.

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

13. A lithium secondary battery using the positive electrode according to claim 12.

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