Positive electrode active material and lithium secondary battery comprising the same

Abstract

To provide a bimodal-type positive electrode active material and a lithium secondary battery including the same, in which low energy density per unit volume and low stability of an overlithiated lithium manganese-based oxide are ameliorated.SOLUTION: A positive electrode active material having bimodal particle size distribution comprises a first lithium manganese-based oxide and a second lithium manganese-based oxide, which have different average particle diameters. The first lithium manganese-based oxide and the second lithium manganese-based oxide are oxides which include at least lithium and manganese and in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group form a solid solution. At least some of oxygen atoms present in the first lithium manganese-based oxide are substituted by halogen atoms. Barrier layers are present on surfaces of the first lithium manganese-based oxide and the second lithium manganese-based oxide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, to a bimodal type positive electrode active material that improves the low energy density per unit volume and stability of lithium-excess lithium manganese-based oxides, 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] Representative materials used as positive electrode active materials for lithium secondary batteries include lithium composite oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and oxides of Ni, Co, Mn, Al, etc.

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

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

[0007] In addition, a large amount of Li by-products are generated depending on the depth of the cation mixing. The Li by-products mostly contain LiOH and Li2CO3, which may cause gelation during the preparation of the positive electrode paste or gas generation due to repeated charging and discharging after the electrode is manufactured. In addition, the remaining Li2CO3 among the Li by-products increases the swelling phenomenon of the cell, thereby reducing 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 addition, due to the characteristics of the material, OLO has a high intra-particle porosity, which means that it has the disadvantage of low energy density per unit volume.

[0012] 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]

[0013] 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.

[0014] For example, in the past, lithium secondary batteries using lithium iron phosphate (LFP) were mainly used from the perspective of ensuring safety, but recently there has been a trend toward expanding use of nickel-based lithium composite oxides, which have a larger energy capacity per weight than LFP.

[0015] In addition, 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.

[0016] 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.

[0017] For example, as mentioned above, OLO has the disadvantage of low energy density per unit volume due to the material's composition (containing excess lithium) and structural characteristics (high intra-particle porosity).

[0018] However, the present inventors have confirmed that the low energy density per unit volume of lithium-excess lithium manganese-based oxide can be improved by preparing the lithium manganese-based oxide into small particles and large particles, and then providing a bimodal type positive electrode active material as a mixture of the small particles and the large particles.

[0019] Accordingly, an object of the present invention is to provide a bimodal type positive electrode active material for improving the low energy density per unit volume of lithium-excess lithium manganese-based oxides.

[0020] In addition, the present inventors have confirmed that although conventional lithium-excess lithium manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability when compared with other types of commercially available positive electrode active materials, when selective growth of primary particles constituting small particles in the positive electrode active material having the bimodal particle size distribution is induced, the lithium-excess lithium manganese-based oxides can also exhibit electrochemical properties and stability at a level that allows commercialization.

[0021] Accordingly, the present invention provides a cathode active material having a bimodal particle size distribution including small particles and large particles in order to improve the low energy density per unit volume of lithium-excess lithium manganese-based oxide, and which can reduce side reactions due to the high specific surface area of ​​the small particles compared to the large particles by inducing selective growth of the primary particles of the small particles.

[0022] The present inventors have also confirmed that lithium manganese oxides are more likely to have transition metals eluted from the particle surface by repeated charge and discharge than ternary lithium composite oxides. In particular, there is a high possibility that Mn contained in excess in lithium manganese oxides will elute from the particle surface.

[0023] When a transition metal is dissolved from the lithium manganese-based oxide, the dissolved transition metal may react with an electrolyte on the surface of the lithium manganese-based oxide to form impurities, which not only increase the surface resistance of the lithium manganese-based oxide but also act as a cause of reducing the intercalation / deintercalation efficiency of lithium ions through the lithium manganese-based oxide.

[0024] In addition, the transition metal dissolved from the lithium manganese-based oxide or impurities formed by the reaction of the dissolved transition metal with the electrolyte can move to the negative electrode using the electrolyte as a medium and can be deposited on the surface of the negative electrode.

[0025] For example, a side reaction occurs between the surface of the lithium manganese oxide and the electrolyte, or the lithium manganese oxide undergoes a structural change (such as a change in crystal structure) to cause excessive Mn contained in the lithium manganese oxide. 2+ The Mn dissolved in the electrolyte can be dissolved in the electrolyte. 2+ During formation or charging / discharging, Mn moves to the surface of the negative electrode through the electrolyte as a medium and reacts with various substances (electrons, electrolyte, electrodes, by-products, etc.) present in the battery. As a result, Mn 2+, Mn metal or Mn-containing compounds (e.g., MnCO3, MnO, MnF2, etc.) are present as impurities.

[0026] Transition metals or impurities deposited on the surface of the negative electrode can rapidly increase the resistance of the negative electrode, and such an abnormal resistance phenomenon is a typical cause of accelerating the deterioration of the life of a lithium secondary battery.

[0027] In particular, lithium secondary batteries using the lithium manganese-based oxide as a positive electrode active material have a higher operating voltage than lithium secondary batteries using other commercially available ternary lithium composite oxides as a positive electrode active material, and are therefore vulnerable to the above-mentioned problems.

[0028] However, currently there is no technology to solve the problem of transition metal elution from lithium-rich lithium manganese oxides and the associated problems.

[0029] Accordingly, the present invention aims to provide a positive electrode active material having a bimodal particle size distribution including small particles and large particles in order to improve the low energy density per unit volume of lithium-excess lithium-manganese-based oxide, and capable of suppressing or mitigating the elution of transition metals from the lithium-manganese-based oxide by covering the surfaces of the small particles and the large particles with a barrier layer.

[0030] It is still another object of the present invention to provide a lithium secondary battery using the positive electrode active material defined herein.

[0031] 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]

[0032] According to one aspect of the present invention for solving the above technical problems, there is provided a positive electrode active material having a bimodal particle size distribution, which includes a first lithium manganese-based oxide and a second lithium manganese-based oxide having different average particle sizes.

[0033] In the present application, the first lithium manganese-based oxide may be referred to as small particles, and the second lithium manganese-based oxide may be referred to as large particles. The first lithium manganese-based oxide and the second lithium manganese-based oxide constituting the positive electrode active material are each independently an oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-dissolved.

[0034] Generally, in commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, a phase belonging to the R-3m space group exists as a single phase, whereas the lithium-rich lithium manganese-based oxide defined in the present application is characterized by a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group.

[0035] In one embodiment, the first lithium manganese oxide and the second lithium manganese oxide are each independently a composite oxide containing lithium, manganese, and a transition metal, and the transition metal may include at least one selected from nickel, cobalt, and aluminum.

[0036] Of the first lithium manganese-based oxide and the second lithium manganese-based oxide constituting the positive electrode active material, the first lithium manganese-based oxide may be selectively substituted with a halogen.

[0037] Specifically, at least a portion of the oxygen present in the first lithium manganese-based oxide is substituted with a halogen.

[0038] As a result, the first lithium manganese oxide can be represented by the following Chemical Formula 1 or Chemical Formula 1-1.

[0039] [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 oxide, 0 < a ≤ 0.7, 0 < b ≤ 0.1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < x + y ≤ 1) [Chemical Formula 1-1] rLi2MnO 3-b″ X′ b″ ·(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 halogens capable of substituting at least a part of the oxygen present in the lithium manganese oxide, 0 < r ≤ 0.7, 0 < a′ ≤ 1, 0 ≤ b′ ≤ 0.1, 0 ≤ b″ ≤ 0.1, 0 < x′ ≤ 1, 0 ≤ y′ < 1, 0 < x′ + y′ ≤ 1, and b′ and b″ are not both 0 at the same time) On the other hand, the second lithium manganese oxide can be represented by the following Chemical Formula 2.

[0040] [Chemical formula 2] rLi2MnO3·(1-r)Li a′ M1 x′ M2 y′ O2 (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, and M2 does not overlap with M1 and is 0. <r≦0.7、0<a′≦1、0<x′≦1、0≦y′<1、0<x′+y′≦1である) In one embodiment, a barrier layer is present on the surface of the first lithium manganese oxide and the second lithium manganese oxide, and the barrier layer can suppress or mitigate the elution of transition metals from the first lithium manganese oxide and the second lithium manganese oxide.

[0041] The barrier layer may include an oxide containing at least one element selected from B, Si, P and Ge.

[0042] According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material.

[0043] 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

[0044] 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.

[0045] Specifically, according to the present invention, the lithium manganese oxide is prepared by dividing it into small particles and large particles, and then a bimodal type positive electrode active material is provided as a mixture of the small particles and the large particles, thereby improving the low energy density per unit volume of lithium-excess lithium manganese oxide.

[0046] Furthermore, according to the present invention, by covering the surfaces of the small particles and the large particles constituting the positive electrode active material having a bimodal particle size distribution with a barrier layer, it is possible to suppress or mitigate the elution of transition metals from the small particles and the large particles.

[0047] By suppressing or mitigating the dissolution of transition metals from the small particles and the large particles, it is possible to prevent the transition metals dissolved on the surfaces of the small particles and the large particles from reacting with the electrolyte to form impurities.

[0048] The transition metals dissolved from the small particles and the large particles and / or impurities formed by the reaction of the dissolved transition metals with the electrolyte can migrate to the negative electrode using the electrolyte as a medium, and the impurities can be deposited on the surface of the negative electrode, causing a rapid increase in the negative electrode resistance. Therefore, as described in the present invention, it is necessary to restrict the unintended migration of transition metals in the lithium secondary battery.

[0049] That is, according to the present invention, by forming a barrier layer on the surfaces of the small particles and the large particles, it is possible to prevent the accelerated deterioration of the life span of the lithium secondary battery caused by the deposition of impurities on the positive electrode and / or the negative electrode due to the transition metal eluted from the lithium manganese-based oxide.

[0050] In addition, the barrier layer can act as a physical barrier between the small and large particles and the electrolyte. In particular, the OLO such as the lithium manganese-based oxide has an advantage of exhibiting high capacity under a high voltage operating environment, but the possibility of side reactions between the lithium manganese-based oxide and the electrolyte may increase as the operating voltage increases, so it is important to reduce the side reactions between the lithium manganese-based oxide and the electrolyte.

[0051] Therefore, by forming a barrier layer on at least a portion of the surface of the small particles and the large particles, the side reaction between the lithium manganese oxide and the electrolyte is reduced, and the stability and life of the lithium secondary battery using the bimodal type cathode active material defined in the present application can be improved. In particular, the cathode active material in which the side reaction with the electrolyte is suppressed can operate the lithium secondary battery at a higher voltage.

[0052] In addition, according to the present invention, by inducing selective growth of the small particles in the positive electrode active material having a bimodal particle size distribution, it is possible to reduce side reactions due to the large specific surface area of ​​the small particles compared to that of the large particles.

[0053] The above-mentioned effects and specific effects of the present invention will be described together with the following description of the preferred embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] 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.

[0055] 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.

[0056] positive electrode active material According to one aspect of the present invention, 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 R-3m space group are dissolved.

[0057] The phase belonging to the C2 / m space group and the phase belonging to the R-3m 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 R-3m space group can appear in the 2θ=18.6±1° region.

[0058] 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 R-3m space group are dissolved, and the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group coexist in the lithium manganese-based oxide. Also, the lithium manganese-based oxide is different from composite oxides having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn2O4 or oxides having a similar composition).

[0059] The lithium manganese-based oxide may be classified into a first lithium manganese-based oxide having small particles and a second lithium manganese-based oxide having large particles based on the average particle size. In the present application, the terms small particles and large particles are relative concepts, and a collection of particles having a smaller average particle size than the second lithium manganese-based oxide may be defined as a small particle, and a collection of particles having a larger average particle size than the first lithium manganese-based oxide may be defined as a large particle. In addition, as described below, the terms small particles and large particles may each be defined as a range of average particle size.

[0060] Therefore, the positive electrode active material defined in the present application is a positive electrode active material having a bimodal particle size distribution by simultaneously containing a first lithium manganese-based oxide having small particles and a second lithium manganese-based oxide having large particles.

[0061] The bimodal particle size distribution means a distribution in which there are two peaks corresponding to different particle sizes when the positive active material is subjected to laser diffraction particle size analysis. Thus, in a volume cumulative particle size distribution graph, the lithium manganese-based oxide showing a peak at a relatively small particle size is the small particle (first lithium manganese-based oxide), and the lithium manganese-based oxide showing a peak at a relatively large particle size is the large particle (second lithium manganese-based oxide).

[0062] Hereinafter, unless otherwise defined, the lithium manganese-based oxide can be understood to refer to both the first lithium manganese-based oxide and the second lithium manganese-based oxide.

[0063] 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.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 %.

[0070] 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%.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm. In this case, the average particle size of the primary particles can be calculated by the average value of the length in the major axis direction and the length in the minor axis direction of the primary particles ([major axis length + minor axis length] / 2).

[0077] 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.

[0078] 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.

[0079] By making the difference between the average particle size of the second lithium manganese-based oxide and the average particle size of the first lithium manganese-based oxide 3 μm or more, preferably 4 μm or more, the energy density per unit volume of the bimodal positive electrode active material can be increased.

[0080] The first lithium manganese oxide may have a main peak in a volumetric particle size distribution graph (x-axis: particle size (μm), y-axis: volume %) between 1 μm and 8 μm, preferably between 2 μm and 7 μm. The first lithium manganese oxide may have an average particle size calculated as the average value of the major axis length and minor axis length ([major axis length+minor axis length] / 2) of 2 μm to 6 μm.

[0081] The second lithium manganese oxide may have a main peak in a volumetric particle size distribution graph (x-axis: particle size (μm), y-axis: volume %) between 6 μm and 24 μm, preferably between 8 μm and 22 μm. The second lithium manganese oxide may have an average particle size calculated as the average value of the major axis length and minor axis length ([major axis length+minor axis length] / 2) of 7 μm to 14 μm.

[0082] In order to optimize the energy density per unit volume of the bimodal positive electrode active material, the first lithium manganese-based oxide and the second lithium manganese-based oxide are preferably contained in the positive electrode active material in a weight ratio of 10:90 to 80:20, 20:80 to 70:30, or 30:70 to 60:40.

[0083] The first lithium manganese-based oxide may be present in a form in which it fills gaps between the second lithium manganese-based oxide, or it may be attached to a surface of the second lithium manganese-based oxide, or the first lithium manganese-based oxide may be present in a form in which the first lithium manganese-based oxide aggregates together.

[0084] When the ratio of the first lithium manganese-based oxide to the second lithium manganese-based oxide in the positive electrode active material is too low, the first lithium manganese-based oxide may not be sufficiently filled into voids formed by the second lithium manganese-based oxide.

[0085] Meanwhile, when the ratio of the first lithium manganese-based oxide to the second lithium manganese-based oxide in the positive electrode active material is too high, the energy density per unit volume of the positive electrode active material may decrease.

[0086] The average particle size of the first lithium manganese oxide and the second lithium manganese oxide may vary depending on the number of the primary particles constituting the secondary particles. The average particle size (D50) of the first lithium manganese oxide and the second lithium manganese oxide may be measured using a laser diffraction method. For example, the first lithium manganese oxide and the second lithium manganese oxide are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and a volume cumulative particle size distribution graph is obtained, and the particle size corresponding to 50% of the volume cumulative amount is obtained.

[0087] The first lithium manganese oxide has a thickness of 1.0 m 2 / g~1.8m 2 / g, 1.0m 2 / g~1.7m 2 / g, 1.2m 2 / g~1.7m 2 / g or 1.3m 2 / g~1.6m 2 The second lithium manganese oxide has a BET specific surface area of ​​1.5 m 2 / g~2.3m 2 / g, 1.5m 2 / g~2.1m 2 / g, 1.5m 2 / g~2.0m 2 / g or 1.6m 2 / g~1.9m 2 The range of the BET specific surface area of ​​the first lithium manganese-based oxide and the range of the BET specific surface area of ​​the second lithium manganese-based oxide can be determined as any combination of the above-mentioned numerical ranges.

[0088] The absolute value of the difference (ΔBET) in the BET specific surface area between the first lithium manganese oxide and the second lithium manganese oxide is 0.8 m 2 / g or less, 0.6m 2 / g or less, 0.5m 2 / g or less or 0.4m 2 / g or less.

[0089] The first lithium manganese-based oxide of small particles has more intra- and / or inter-particle voids than the second lithium manganese-based oxide of large particles, and has a high specific surface area compared to the particle size, so that the possibility of side reactions with the electrolyte is high. Therefore, when selective growth of primary particles constituting the first lithium manganese-based oxide is induced by substituting at least a part of oxygen present in the first lithium manganese-based oxide with a halogen (e.g., fluorine), it is possible to reduce the specific surface area of ​​the first lithium manganese-based oxide. In addition, as described above, the first lithium manganese-based oxide of small particles has more intra- and / or inter-particle voids than the second lithium manganese-based oxide of large particles, so the growth effect of the primary particles (reduction in the void ratio within the particles as the primary particles grow) by substituting at least a part of oxygen present in the first lithium manganese-based oxide with a halogen (e.g., fluorine) may be significant.

[0090] 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.

[0091] 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".

[0092] In this case, the region of any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] In one embodiment, the first lithium manganese-based oxide of the first lithium manganese-based oxide and the second lithium manganese-based oxide constituting the positive electrode active material may be selectively substituted with a halogen. Here, the selective substitution of the first lithium manganese-based oxide with a halogen means that the first lithium manganese-based oxide of the positive electrode active material is substituted with a halogen, whereas the second lithium manganese-based oxide is not substituted with a halogen.

[0098] Specifically, at least a portion of the oxygen present in the first lithium manganese-based oxide is substituted with a halogen.

[0099] Accordingly, the first lithium manganese-based oxide may be represented by the following Formula 1 or Formula 1-1. Also, the composition represented by the following Formula 1 or Formula 1-1 may represent an average composition reflecting the composition of the barrier layer present on the surface of the first lithium manganese-based oxide.

[0100] [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。

[0101] [Chemical formula 1-1] rLi2MnO 3-b″ X′ b″ (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 halogens capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, 0 < r ≦ 0.7, 0 < a′ ≦ 1, 0 ≦ b′ ≦ 0.1, 0 ≦ b″ ≦ 0.1, 0 < x′ ≦ 1, 0 ≦ y′ < 1, 0 < x′ + y′ ≦ 1, and b′ and b″ are not simultaneously 0.

[0102] 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. The types of halogens that can be used as X and X′ can refer to the periodic table, and F, Cl, Br, and / or I, etc. can be used, and preferably, F can be used.

[0103] As described above, when inducing the particle growth of the primary particles constituting the first lithium manganese-based oxide, when doping with a halogen, preferably, at least a part of the oxygen present in the first lithium manganese-based oxide may be substituted with a halogen.

[0104] When using an over-firing method of heat-treating at a relatively high temperature without doping with a halogen to induce the particle growth of the primary particles constituting the first lithium manganese-based oxide, the particle growth of the primary particles is possible, but damage occurs to the crystal structure of the primary particles, and early deterioration of the first lithium manganese-based oxide may occur.

[0105] In addition, in the case of the over-firing method, the primary particles grow in a non-directional manner, whereas when halogen is doped during the growth of the primary particles, the primary particles grow in a partially directional manner, thereby mitigating the decrease in the diffusibility of lithium ions due to the growth of the primary particles. In particular, it is preferable to use fluorine as an anion dopant for the growth of the primary particles, from the viewpoint of inducing crystal growth or particle growth of the primary particles in a selective direction within a range that mitigates the decrease in the diffusibility of lithium ions mediated by the primary particles.

[0106] For fluorine doping of the primary particles, at least one anion dopant selected from LiF, MgF2, HF, F2, XeF2, TbF4, CeF4, CoF3, AgF2, MoF3, AgF, CuF2, FeF3, CuF, VF3, CrF3, ZrF4, BaF2, CaF2, AlF3, NH4F, CeF3 and CsF, preferably at least one anion dopant selected from LiF and MgF2, can be used.

[0107] In the above Chemical Formula 1, when M1 is Ni, M2 may include Mn, and when M1 is Mn, M2 may include Ni. Also, when M1 is Ni and Mn, M2 may be absent, or if present, may be other elements except Ni and Mn.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] Meanwhile, the second lithium manganese-based oxide may be represented by the following Formula 2:

[0112] [Chemical formula 2] rLi2MnO3·(1-r)Li a′ M1 x′ M2 y′ O2 Here, M1 is at least one selected from Ni and Mn, M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, and M2 does not overlap with M1 and is 0. <r≦0.7、0<a′≦1、0<x′≦1、0≦y′<1、0<x′+y′≦1である。

[0113] The second lithium manganese-based oxide having large particles has fewer voids within and / or between particles than the first lithium manganese-based oxide having small particles, and therefore it may be difficult to induce the growth of primary particles by substituting at least a portion of the oxygen present in the second lithium manganese-based oxide with a halogen (e.g., fluorine).

[0114] In addition, when the second lithium manganese-based oxide is doped with a halogen (e.g., fluorine) unlike the first lithium manganese-based oxide, the electrochemical characteristics (e.g., capacity and efficiency reduction) of the positive electrode active material having a bimodal particle size distribution defined herein may be decreased.

[0115] Similarly, in the above Chemical Formula 2, when M1 is Ni, M2 may include Mn, and when M1 is Mn, M2 may include Ni. Also, when M1 is Ni and Mn, M2 may be absent, or, if present, may be another element other than Ni and Mn.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] The lithium manganese-based oxide represented by Chemical Formula 1, Chemical Formula 1-1, and Chemical Formula 2 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 represented by Chemical Formula 1 may have a cobalt-free composition that does not contain cobalt.

[0120] The Li / Metal molar ratio measured from the lithium manganese-based oxides represented by Formula 1, Formula 1-1, and Formula 2 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 is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide.

[0121] In addition, in order for the lithium manganese-based oxide to appropriately form a solid solution or a composite of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group and to exhibit high capacity in a high voltage operating environment, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0122] 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 R-3m space group are dissolved, the content of manganese in all metal elements excluding lithium present in the lithium manganese-based oxide is preferably 50 mol % or more.

[0123] In order for the lithium manganese-based oxide to have the OLO characteristic of exhibiting 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% to less than 80 mol%, 51 mol% to less than 80 mol%, 52 mol% to less than 80 mol%, 53 mol% to less than 80 mol%, 54 mol% to less than 80 mol%, 55 mol% to less than 80 mol%, 50 mol% to 75 mol%, 51 mol% to 75 mol%, 52 mol% to less than 75 mol%, 53 mol% to 75 mol%, 54 mol% to 75 mol%, or 55 mol% to 75 mol%.

[0124] When the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur due to the migration of transition metals (especially manganese) in the lithium manganese-based oxide during formation and / or operation of the lithium secondary battery. Such a phase transition forms a spinel phase, and the spinel phase acting as an impurity in the lithium manganese-based oxide may induce a decrease in charge / discharge capacity or a voltage drop (voltage decay) during cycling of the lithium secondary battery. In addition, when the manganese content in the lithium manganese-based oxide exceeds 80 mol%, the lithium manganese-based oxide may exhibit characteristics similar to those of a composite oxide having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn2O4 or an oxide having a similar composition).

[0125] 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 R-3m space group are dissolved, the content of nickel in all metal elements excluding lithium present in the lithium manganese-based oxide 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.

[0126] When the nickel content in the lithium manganese-based oxide is 50 mol % or more, the C2 / m phase is not sufficiently formed, or the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group do not form a sufficient solid solution, which may cause phase separation during formation and / or operation of the lithium secondary battery.

[0127] Generally, commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition exist in a single phase belonging to the R-3m space group.

[0128] Meanwhile, the lithium-rich lithium manganese oxide represented by the formula 1, the formula 1-1, and the formula 2 is rLi2MnO 3-b″ X′b″ or rLi2MnO3, an oxide belonging to the C2 / m space group (hereinafter referred to as the "C2 / m phase") and (1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ or (1-r)Li a′ M1 x′ M2 y′ The lithium manganese-based oxide exists as a composite oxide in which an oxide of a phase belonging to the R-3m space group represented by O2 (hereinafter referred to as "R-3m phase") is dissolved or combined. For example, the lithium manganese-based oxide may exist in a state in which an oxide of a C2 / m phase and an oxide of an R-3m phase form a solid solution.

[0129] In this case, a complex oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m 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.

[0130] For example, a composite oxide having a phase belonging to the C2 / m space group, in which a metal oxide having a phase belonging to the C2 / m space group and a metal oxide having a phase belonging to the R-3m space group are mixed and the surface of the composite oxide is coated with a metal oxide having a phase belonging to the R-3m space group, does not fall under the category of a solid solution as defined in the present application.

[0131] In the lithium manganese-based oxide, when r exceeds 0.7, the ratio of the C2 / m phase oxide in the lithium manganese-based oxide becomes excessively large, which may ultimately increase the irreversible capacity and resistance of the positive electrode active material, resulting in a decrease in discharge capacity. That is, in order to improve the surface kinetics by sufficiently activating the C2 / m phase oxide, which has a relatively high resistance in the lithium manganese-based oxide, it is preferable that the R-3m phase oxide is present at a predetermined ratio or more.

[0132] In one embodiment, a barrier layer is present on the surface of the first lithium manganese-based oxide and the second lithium manganese-based oxide. The barrier layer can suppress or mitigate the elution of transition metals from the first lithium manganese-based oxide and the second lithium manganese-based oxide. In addition, the barrier layer covers the surface of the first lithium manganese-based oxide and the second lithium manganese-based oxide, thereby preventing side reactions with the electrolyte and improving the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions.

[0133] The barrier layer may be in the form of islands that cover at least a portion of the surfaces of the first lithium manganese-based oxide and the second lithium manganese-based oxide. Even if the barrier layer is in the form of islands, the barrier layer can suppress or reduce the elution of transition metals through the area covered by the barrier layer.

[0134] In addition, when the first lithium manganese oxide and the second lithium manganese oxide exist as secondary particles, the barrier layer may exist in a state of being diffused from the surface of the secondary particles toward the center of the secondary particles along the crystal grain boundaries between the primary particles. The main element constituting the barrier layer (e.g., at least one selected from boron (B), silicon (Si), phosphorus (P) and germanium (Ge), preferably boron (B)) may form a concentration gradient that decreases from the surface (outermost part) of the secondary particles toward the inside of the secondary particles.

[0135] The barrier layer forms a gradient from the surface portion of the secondary particle toward the center portion of the secondary particle, thereby effectively suppressing or mitigating the elution of transition metal mainly at the surface portion of the secondary particle.

[0136] Thus, when the main elements constituting the barrier layer (e.g., boron (B), silicon (Si), phosphorus (P) and germanium (Ge)) are referred to as barrier elements, the atomic ratio of the barrier elements calculated based on the atomic number of nickel, manganese and barrier elements present inside the secondary particles may be smaller than the atomic ratio of the barrier elements calculated based on the atomic number of nickel, manganese and barrier elements present on the surface of the secondary particles. Also, the atomic ratio of the barrier elements calculated based on the total atomic number of nickel, manganese and barrier elements constituting the secondary particles may be smaller than the atomic ratio of the barrier elements calculated based on the atomic number of nickel, manganese and barrier elements present on the surface (outermost part) of the secondary particles.

[0137] In some embodiments, some of the main elements constituting the barrier layer (e.g., at least one selected from boron (B), silicon (Si), phosphorus (P) and germanium (Ge), preferably boron (B)) may be present in a higher concentration on the surface of the primary particles than in the interior of the primary particles.

[0138] Thus, when the main elements constituting the barrier layer (e.g., boron (B), silicon (Si), phosphorus (P) and germanium (Ge)) are referred to as barrier elements, the atomic ratio of the barrier elements calculated based on the atomic numbers of nickel, manganese and barrier elements present inside the primary particles may be smaller than the atomic ratio of the barrier elements calculated based on the atomic numbers of nickel, manganese and barrier elements present on the surface (outermost shell) of the primary particles. Also, the atomic ratio of the barrier elements calculated based on the total atomic number of nickel, manganese and barrier elements constituting the primary particles may be smaller than the atomic ratio of the barrier elements calculated based on the atomic numbers of nickel, manganese and barrier elements present on the surface (outermost shell) of the primary particles.

[0139] The barrier layer may be present on the surface of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of a coating having a thickness of 1 nm to 300 nm. The barrier layer being present in the form of a coating must be distinguished from the oxide constituting the barrier layer being dispersed and attached to the surface of the lithium manganese-based oxide in the form of individual particles.

[0140] If the average thickness of the barrier layer is less than 1 nm, it may be difficult to sufficiently suppress the elution of transition metals from the first lithium manganese oxide and the second lithium manganese oxide, whereas if the average thickness of the barrier layer is greater than 300 nm, the surface kinetics of the first lithium manganese oxide and the second lithium manganese oxide may decrease, or the electrical conductivity may decrease.

[0141] In addition, as the thickness of the barrier layer present on the surface of the lithium manganese-based oxide increases, the transition metal can be prevented from eluting from the lithium manganese-based oxide, thereby improving the short-term life of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material. However, if the barrier layer is too thick (e.g., exceeds 300 nm), a problem of a rapid increase in the amount of gas generated in the lithium secondary battery may occur.

[0142] The barrier layer may include an oxide containing at least one element selected from B, Si, P and Ge.

[0143] For example, the barrier layer may include an oxide represented by Formula 3 below.

[0144] [Chemical formula 3] zLi2O* (1-z) M3 d O e Here, M3 is at least one element selected from B, Si, P, and Ge, and 0 < z ≦ 0.8, 0 < d ≦ 10, 0 < e ≦ 10. Here, d and e represent numbers determined from the stoichiometric ratio according to the valence of M3.

[0145] Also, preferably, the barrier layer contains B2O3, H α B β O γ (0 < α < 10, 0 < β < 10, 0 < γ < 20) and Li α′ B β′ O γ′ and may contain at least one boron-containing compound selected from (0 < α′ < 10, 0 < β′ < 10, 0 < γ′ < 20). Here, α, β, γ, α′, β′, and γ′ represent numbers determined from the stoichiometric ratio. Non-limiting examples of the boron-containing compound include H3BO3, B2O3, Li2O - B2O3, Li3BO3, Li2B4O7, Li2B2O7, Li2B8O 13 and the like.

[0146] Lithium secondary battery According to another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. Here, the positive electrode active material layer may contain a lithium manganese-based oxide according to various embodiments of the present invention described above as a positive electrode active material.

[0147] Therefore, specific descriptions of the lithium manganese-based oxide are omitted, and hereinafter, only the remaining configurations not described above will be explained. Also, hereinafter, for convenience, the above-described lithium manganese-based oxide is referred to as a positive electrode active material.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] The binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and among these, one type alone or a mixture of two or more types may be used. The binder may be contained in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0160] 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.

[0161] 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.

[0162] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys, and SiO β (0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, may be used. A metallic lithium thin film may be used as the negative electrode active material. Low-crystalline carbon and high-crystalline carbon may both be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0170] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0171] The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone, an ether solvent such as dibutyl ether or tetrahydrofuran, a ketone solvent such as cyclohexanone, an aromatic hydrocarbon solvent such as benzene or fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that may be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be excellent if the cyclic carbonate and the chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9.

[0172] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

[0173] 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.

[0174] 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 Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (wherein m and n are integers and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(where p, q are integers and M is P, Si, Ge, B, Al, Ga or In).

[0175] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed amorphous and crystalline state.

[0176] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zinc 1-x Examples include GeO4 (LISICON).

[0177] 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.

[0178] 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.

[0179] 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).

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] Production Example 1. Production of positive electrode active material First, preparation of lithium manganese oxide (A-1) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was added to the reactor. After the reaction was completed, the reactor was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 3.0 μm) with (OH)2 composition was obtained.

[0185] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0186] (c) Second heat treatment The oxide precursor obtained in step (b) and a lithium source material LiOH (Li / Metal (excluding Li) molar ratio=1.28) were mixed to prepare a mixture.

[0187] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then cooled in the furnace to obtain a first lithium manganese-based oxide (A-1).

[0188] The BET specific surface area of ​​the first lithium manganese oxide (A-1) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 1.93 m 2 / g.

[0189] First, preparation of lithium manganese oxide (A-2) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was added to the reactor. After the reaction was completed, the reactor was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 3.0 μm) with (OH)2 composition was obtained.

[0190] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0191] (c) Second heat treatment The oxide precursor obtained in step (b), the lithium source material LiOH (Li / metal (excluding Li) molar ratio = 1.28), and LiF weighed out to have a fluorine (F) content of 1.0 mol% based on the metal elements excluding lithium in the precursor were mixed to prepare a mixture.

[0192] Next, the temperature of a sintering furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. The mixture was then cooled in the furnace to obtain a first lithium manganese-based oxide (A-2).

[0193] The BET specific surface area of ​​the first lithium manganese oxide (A-2) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 1.72 m 2 / g.

[0194] First, preparation of lithium manganese oxide (A-3) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was added to the reactor. After the reaction was completed, the reactor was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 3.0 μm) with (OH)2 composition was obtained.

[0195] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0196] (c) Second heat treatment The oxide precursor obtained in step (b), the lithium source material LiOH (Li / metal (excluding Li) molar ratio = 1.28), and LiF weighed out to have a fluorine (F) content of 1.0 mol% based on the metal elements excluding lithium in the precursor were mixed to prepare a mixture.

[0197] Next, the temperature of a sintering furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. The mixture was then cooled in the furnace to obtain a lithium-rich lithium manganese-based oxide.

[0198] (d) Third heat treatment (formation of barrier layer) The lithium manganese-based oxide obtained in step (c) was mixed with H3BO3 (the boron content based on the total metal elements excluding lithium in the lithium manganese-based oxide was measured to be 2 mol%), and then the mixture was heated to 400°C at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a sintering furnace, and heat-treated for 8 hours. The mixture was then classified and crushed to obtain a first lithium manganese-based oxide (A-3) having a barrier layer containing a B-containing compound formed on the surface.

[0199] The BET specific surface area of ​​the first lithium manganese oxide (A-3) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 1.43 m 2 / g.

[0200] First, preparation of lithium manganese oxide (A-4) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was added to the reactor. After the reaction was completed, the reactor was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 3.0 μm) with (OH)2 composition was obtained.

[0201] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0202] (c) Second heat treatment The oxide precursor obtained in step (b), the lithium source material LiOH (Li / metal (excluding Li) molar ratio = 1.28), and LiF weighed out to have a fluorine (F) content of 0.75 mol% based on the metal elements excluding lithium in the precursor were mixed to prepare a mixture.

[0203] Next, the temperature of a sintering furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. The mixture was then cooled in the furnace to obtain a lithium-rich lithium manganese-based oxide.

[0204] (d) Third heat treatment (formation of barrier layer) The lithium manganese-based oxide obtained in step (c) was mixed with H3BO3 (the boron content based on the total metal elements excluding lithium in the lithium manganese-based oxide was measured to be 2 mol%), and then the mixture was heated to 400°C at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a sintering furnace, and heat-treated for 8 hours. The mixture was then classified and crushed to obtain a first lithium manganese-based oxide (A-4) having a barrier layer containing a B-containing compound formed on the surface.

[0205] The BET specific surface area of ​​the first lithium manganese oxide (A-4) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 1.50 m 2 / g.

[0206] Preparation of second lithium manganese oxide (B-1) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 24 hours while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated, and the Ni 0.4 Mn0.6 A hydroxide precursor (average particle size 12.0 μm) with (OH)2 composition was obtained.

[0207] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0208] (c) Second heat treatment The oxide precursor obtained in step (b) and a lithium source material LiOH (Li / Metal (excluding Li) molar ratio=1.28) were mixed to prepare a mixture.

[0209] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then cooled in the furnace to obtain a second lithium manganese-based oxide (B-1).

[0210] The BET specific surface area of ​​the second lithium manganese oxide (B-1) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 2.38 m 2 / g.

[0211] Production of second lithium manganese oxide (B-2) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 24 hours while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 12.0 μm) with (OH)2 composition was obtained.

[0212] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0213] (c) Second heat treatment The oxide precursor obtained in step (b), the lithium source material LiOH (Li / metal (excluding Li) molar ratio = 1.28), and LiF weighed out to have a fluorine (F) content of 1.0 mol% based on the metal elements excluding lithium in the precursor were mixed to prepare a mixture.

[0214] Next, the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C in a sintering furnace in an O2 atmosphere at a rate of 2°C / min, and then cooled in the furnace to obtain a second lithium manganese-based oxide (B-2).

[0215] The BET specific surface area of ​​the second lithium manganese oxide (B-2) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 0.86 m 2 / g.

[0216] Production of second lithium manganese oxide (B-3) (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, NaOH and NH4OH were added to the reactor while stirring. The temperature inside the reactor was maintained at 45°C, and the precursor synthesis reaction was carried out for 24 hours while N2 gas was added to the reactor. After the reaction was completed, the product was washed and dehydrated, and the Ni 0.4 Mn 0.6 A hydroxide precursor (average particle size 12.0 μm) with (OH)2 composition was obtained.

[0217] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated for 5 hours while maintaining the temperature at 550°C. The hydroxide precursor was then cooled in the furnace to obtain an oxide precursor.

[0218] (c) Second heat treatment The oxide precursor obtained in step (b) and a lithium source material LiOH (Li / metal (except Li) molar ratio=1.28) were mixed to prepare a mixture.

[0219] Next, the temperature of a sintering furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining the temperature at 900°C. The mixture was then cooled in the furnace to obtain a lithium-rich lithium manganese-based oxide.

[0220] (d) Third heat treatment (formation of barrier layer) The lithium manganese-based oxide obtained in step (c) was mixed with H3BO3 (the boron content based on the total metal elements excluding lithium in the lithium manganese-based oxide was measured to be 2 mol%), and then the mixture was heated to 400°C at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a sintering furnace, and heat-treated for 8 hours. The mixture was then classified and crushed to obtain a second lithium manganese-based oxide (B-3) having a barrier layer containing a B-containing compound formed on the surface.

[0221] The BET specific surface area of ​​the second lithium manganese oxide (B-3) (calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using BELSORP-mino II from BEL Japan) is 1.81 m 2 / g.

[0222] Production Example 2: Production of Positive Electrode Active Material The first lithium manganese-based oxide and the second lithium manganese-based oxide prepared in Preparation Example 1 were mixed in a weight ratio shown in Table 1 below to prepare a positive electrode active material having a unimodal particle size distribution or a bimodal particle size distribution.

[0223] In addition, in the case of a positive electrode active material having a bimodal particle size distribution, the absolute value of the difference (ΔBET) in the BET specific surface area between the first lithium composite oxide of small particles and the second lithium composite oxide of large particles was calculated.

[0224] [Table 1]

[0225] Manufacturing Example 3: Manufacturing of lithium secondary batteries (half cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 2, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly applied to an aluminum thin 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.

[0226] A half cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte of LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 2:4:4.

[0227] Manufacturing Example 4. Manufacturing of lithium secondary batteries (full cells) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 2, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly applied to an aluminum thin 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.

[0228] A full cell was fabricated using a graphite electrode as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution containing LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0229] Experimental Example 1: Measurement of the compressed density of positive electrode active material 3 g of each of the positive electrode active materials prepared in Preparation Example 2 was pressed at 4.5 tons for 5 seconds using a pelletizer, and then the compressed density was measured.

[0230] The measurement results are shown in Table 2 below.

[0231] [Table 2]

[0232] Referring to the results in Table 2, it was found that the positive electrode active materials having a bimodal particle size distribution had a higher compressed density than the positive electrode active materials according to Comparative Examples 1 and 2 having a unimodal particle size distribution.

[0233] In addition, it was confirmed that the cathode active materials according to Examples 1 and 2, which are cathode active materials using halogen-doped small particles and in which barrier layers are formed on the surfaces of the small and large particles, have a higher compressed density than other cathode active materials having a bimodal particle size distribution.

[0234] 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 3 was subjected to a charge-discharge experiment at 25° C., voltage range of 2.0 V to 4.6 V, and discharge rate of 0.1 C to 5.0 C using an electrochemical analyzer (Toyo, Toscat-3100) to measure the initial discharge capacity, capacity per volume, and rate capability (C-rate).

[0235] The capacity per volume was calculated by multiplying the initial discharge capacity by the compressed density (compressed density of 4.5 tons in Table 4).

[0236] The measurement results are shown in Table 3 below.

[0237] [Table 3]

[0238] Referring to the results in Table 3, it was found that the capacity per unit volume of the positive electrode active material having a bimodal particle size distribution was larger than that of the positive electrode active materials according to Comparative Examples 1 and 2 having a unimodal particle size distribution.

[0239] In addition, it was confirmed that the cathode active materials according to Examples 1 and 2, which are cathode active materials using halogen-doped small particles and having barrier layers formed on the surfaces of the small and large particles, have a larger capacity per unit volume than other cathode active materials having a bimodal particle size distribution. It was also confirmed that the cathode active materials according to Examples 1 and 2 exhibit improved discharge capacity and rate characteristics compared to other cathode active materials having a bimodal particle size distribution.

[0240] Experimental Example 3: Evaluation of the electrochemical characteristics of a lithium secondary battery (full cell) The lithium secondary batteries (full cells) manufactured in Manufacturing Example 4 using the positive electrode active materials according to Example 1, Comparative Example 5, and Comparative Example 6 were subjected to a 6-cycle formation process at 25°C, voltage range 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then charged and discharged 500 times at 25°C, voltage range 2.0V to 4.6V, and 1C / 1C. st Cycle) Discharge capacity, 100% of initial discharge capacity th Cycles, 300 th Cycle, 500 thThe ratio of discharge capacity per cycle (cycle capacity retention) was measured.

[0241] The measurement results are shown in Table 4 below.

[0242] [Table 4]

[0243] Referring to the results in Table 4, it can be seen that the cycle capacity retention rates of Comparative Examples 5 and 6 are lower than that of Example 1. This result is presumably due to the fact that the transition metal is eluted from the lithium manganese-based oxide, causing a resistance anomaly in the negative electrode, which accelerates the deterioration of the life span of the lithium secondary battery.

[0244] This confirms that the positive electrode active material according to Example 1 is suitable for lithium secondary batteries that require a longer life.

[0245] Experimental Example 4. Experiment on transition metal elution The lithium secondary batteries (full cells) manufactured in Manufacturing Example 4 using the positive electrode active materials according to Example 1, Comparative Example 5, and Comparative Example 6 were subjected to a 6-cycle formation process at 25° C., voltage range 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then the full cells were stabilized by 2 cycles of charge / discharge at 25° C., voltage range 2.0V to 4.6V, and 0.05C / 0.05C. Next, the full cells were disassembled, and the negative electrodes were washed with diethyl carbonate solvent, vacuum dried at 60° C., and then collected.

[0246] Only the negative electrode active material was separated from the recovered Cu foil (current collector) of the negative electrode, and the separated negative electrode active material was subjected to ICP analysis to measure the Ni and Mn contents contained in the negative electrode active material.

[0247] In addition, the lithium secondary batteries (full cells) manufactured in Manufacturing Example 4 using the positive electrode active materials according to Example 1, Comparative Example 5, and Comparative Example 6 were subjected to a 6-cycle formation process at 25°C, voltage range 2.0V to 4.6V, and 0.2C / 0.2C using an electrochemical analyzer (Toyo, Toscat-3100), and then charged and discharged 500 times at 25°C, voltage range 2.0V to 4.6V, and 1C / 1C. Next, each full cell was charged and discharged for 2 cycles at 25°C, voltage range 2.0V to 4.6V, and 0.05C / 0.05C to stabilize it. Next, the full cells were disassembled, and the negative electrodes were washed with diethyl carbonate solvent, vacuum dried at 60°C, and then collected.

[0248] Only the negative electrode active material was separated from the recovered Cu foil (current collector) of the negative electrode, and the separated negative electrode active material was subjected to ICP analysis to measure the Ni and Mn contents contained in the negative electrode active material.

[0249] The measurement results are shown in Table 5 below.

[0250] [Table 5]

[0251] Referring to the results of Table 5, as expected from Experimental Example 4, it can be seen that the lower cycle capacity retention rates of Comparative Example 5 and Comparative Example 6 compared to Example 1 are due to the increased content of transition metals deposited on the negative active material after formation and / or after 500 charge / discharge cycles.

[0252] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding elements without departing from the concept of the present invention described in the claims, and this may also be considered to be within the scope of the claims of the present invention.

Claims

1. A positive electrode active material having a bimodal particle size distribution, comprising a first lithium manganese-based oxide and a second lithium manganese-based oxide having different average particle sizes, The first lithium manganese-based oxide and the second lithium manganese-based oxide contain at least lithium and manganese, and are oxides in which a phase belonging to a C2 / m space group and a phase belonging to an R-3m space group are dissolved, At least a portion of the oxygen present in the first lithium manganese-based oxide is replaced with a halogen; a barrier layer is present on a surface of the first lithium manganese-based oxide and the second lithium manganese-based oxide;

2. 2 . The positive electrode active material according to claim 1 , wherein the first lithium-manganese-based oxide and the second lithium-manganese-based oxide are composite oxides containing lithium, manganese, and a transition metal.

3. The positive electrode active material according to claim 2 , wherein the transition metal is at least one selected from nickel, cobalt, and aluminum.

4. The positive electrode active material of claim 1 , wherein the first lithium manganese-based oxide is doped with fluorine.

5. 2. The positive electrode active material of claim 1, wherein the first lithium manganese-based oxide is represented by the following Formula 1 or Formula 1-1: [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) [Chemical formula 1-1] rLi ２ MnO ３－ｂ″ X′ ｂ″ ・(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 halogens capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, 0<r≦0.7, 0<a'≦1, 0≦b'≦0.1, 0≦b''≦0.1, 0<x'≦1, 0≦y'<1, 0<x'+y'≦1, and b' and b'' are not 0 at the same time.

6. 2. The positive electrode active material according to claim 1, wherein the first lithium manganese-based oxide has an average particle size of 2 μm to 6 μm.

7. The first lithium manganese-based oxide has a thickness of 1.0 m ２ / g to 1.8m ２ The positive electrode active material according to claim 1 , having a BET specific surface area of ​​100 / g.

8. The positive electrode active material of claim 1 , wherein the second lithium manganese-based oxide is represented by Formula 2: [Chemical formula 2] <h2 style=";text-align:left;direction:ltr">rLi<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> MnO<h2 style=";text-align:left;direction:ltr"> ３ <h2 style=";text-align:left;direction:ltr"> (1)<h2 style=";text-align:left;direction:ltr"> ａ′ <h2 style=";text-align:left;direction:ltr"> 11<h2 style=";text-align:left;direction:ltr"> ｘ′ <h2 style=";text-align:left;direction:ltr"> 12<h2 style=";text-align:left;direction:ltr"> ｙ′ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ２ (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; 0<r≦0.7, 0<a′≦1, 0<x′≦1, 0≦y′<1, 0<x′+y′≦1)

9. 2. The positive electrode active material according to claim 1, wherein the second lithium manganese-based oxide has an average particle size of 7 μm to 14 μm.

10. The second lithium manganese oxide has a thickness of 1.5 m. ２ / g to 2.3 m ２ The positive electrode active material according to claim 1 , having a BET specific surface area of ​​100 / g.

11. The positive electrode active material according to claim 1 , wherein the barrier layer comprises an oxide containing at least one element selected from the group consisting of B, Si, P, and Ge.

12. The positive electrode active material of claim 11 , wherein the barrier layer comprises an oxide represented by Formula 3: [Chemical formula 3] zLi ２ O*(1-z)M3 ｄ O ｅ (where: M3 is at least one element selected from B, Si, P and Ge; 0<z≦0.8, 0<d≦10, 0<e≦10)

13. The barrier layer is B ２ O ３ , H α B β O γ (0<α<10, 0<β<10, 0<γ<20) and Li α′ B β′ O γ′ 12. The cathode active material of claim 11, comprising at least one boron-containing compound selected from (0<α'<10, 0<β'<10, 0<γ'<20).

14. 2. The positive electrode active material according to claim 1, wherein the barrier layer is present on the surfaces of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of a coating having a thickness of 1 nm to 300 nm.

15. 2. The positive electrode active material according to claim 1, wherein the first lithium manganese-based oxide and the second lithium manganese-based oxide are contained in the positive electrode active material in a weight ratio of 10:90 to 80:

20.

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

17. A lithium secondary battery comprising the positive electrode according to claim 16.

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