Positive electrode active material and lithium secondary battery containing 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 containing the same, and more specifically, to a bimodal type positive electrode active material and a lithium secondary battery containing the same, which improves the low energy density per unit volume and stability of lithium-rich lithium manganese oxides. [Background technology]

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

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

[0004] Typical materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. These lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides formed by the combination of Ni, Co, Mn, or Al.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency. However, it has the disadvantage of being expensive due to the resource limitations of cobalt used as a raw material, thus limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages such as excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature performance. On the other hand, LiNiO2-based cathode active materials exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to cation mixing problems between Li and transition metals, which results in significant problems with their rate characteristics.

[0007] Furthermore, a large amount of Li by-products is generated depending on the degree of deepening of such cation mixing. These Li by-products mostly consist of LiOH and Li2CO3, which may cause gelation during the production of the positive electrode paste or generate gas due to repeated charging and discharging after electrode production. In addition, residual Li2CO3 among the Li by-products increases the swelling phenomenon of the cell, which reduces its lifespan characteristics.

[0008] Various candidate materials have been proposed to compensate for the shortcomings of these conventional cathode active materials.

[0009] As an example, research is being conducted to use lithium-rich lithium-manganese oxides, which contain an excess amount of manganese (Mn) among the transition metals, and whose lithium content exceeds the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such lithium-rich lithium-manganese oxides are also called lithium-overlithiated layered oxides (OLOs).

[0010] While the aforementioned OLO has the advantage of theoretically exhibiting high capacity under high-voltage operating conditions, in reality, it has a disadvantage in that its electrical conductivity is relatively low due to the excess amount of Mn contained in the oxide, resulting in poor rate characteristics for lithium secondary batteries using OLO. When rate characteristics are low in this way, problems arise in which the charge / discharge capacity and life efficiency (cycle capacity retention rate) of lithium secondary batteries decrease during cycling.

[0011] Furthermore, due to the material's properties, OLO has a high porosity within its particles, which results in a disadvantage of low energy density per unit volume.

[0012] Research has been ongoing to modify the composition of OLO in order to solve the aforementioned problems, but so far, such attempts have not reached a commercial level. [Overview of the project] [Problems that the invention aims to solve]

[0013] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is driving the market, and this is leading to a sustained increase in the demand for positive electrode active materials used in lithium-ion batteries.

[0014] For example, conventionally, lithium-ion batteries using lithium iron phosphate (LFP) have been primarily used, mainly for safety reasons. However, recently, there has been a growing trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFP.

[0015] Furthermore, nickel-based lithium composite oxides, which are now primarily used as positive electrode active materials in high-capacity lithium secondary batteries, require the essential use of ternary metallic elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only subject to unstable supply and demand but is also excessively expensive compared to other raw materials, thus necessitating new compositions of positive electrode active materials that can reduce or eliminate cobalt content.

[0016] Considering these circumstances, lithium-rich lithium manganese oxides can meet the aforementioned market expectations, but they still have limitations in terms of electrochemical properties and stability, making them suitable as a substitute for commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0017] For example, as mentioned earlier, OLO has the disadvantage of having a low energy density per unit volume due to its material composition (containing excess lithium) and structural properties (high porosity within particles).

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

[0019] Thus, the present invention aims to provide a bimodal type cathode active material for improving the low energy density per unit volume of lithium-rich lithium manganese oxides.

[0020] Furthermore, even though conventional lithium-rich lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability when compared with other commercially available types of cathode active materials, the inventors have confirmed that lithium-rich lithium manganese oxides can also exhibit electrochemical properties and stability at a level suitable for commercialization when they induce the selective growth of primary particles constituting small particles in the cathode active material having the bimodal particle size distribution.

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

[0022] Furthermore, the inventors have confirmed that lithium manganese oxides are more likely to leach transition metals from the particle surface when repeatedly charged and discharged than ternary lithium composite oxides. In particular, there is a high possibility that excess Mn contained in lithium manganese oxides will leach from the particle surface.

[0023] When a transition metal is leached from the lithium manganese oxide, the leached transition metal can react with the electrolyte on the surface of the lithium manganese oxide to form impurities. These impurities not only increase the surface resistance of the lithium manganese oxide but also act as a cause of reduced intercalation / deintercalation efficiency of lithium ions passing through the lithium manganese oxide.

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

[0025] For example, a side reaction may occur with the electrolyte on the surface of the lithium manganese oxide, or an excess of Mn may be present in the lithium manganese oxide due to structural changes in the lithium manganese oxide (such as changes in crystal structure). 2+ Mn can be dissolved into the electrolyte. 2+ During chemical conversion or charging / discharging, Mn can move to the surface of the negative electrode using the electrolyte as a medium and react with various substances present in the battery (electrons, electrolyte, electrodes, or by-products, etc.), resulting in Mn forming on the surface of the negative electrode. 2+It exists as an impurity containing Mn metal or Mn-containing compounds (e.g., MnCO3, MnO, MnF2, etc.).

[0026] The deposition of transition metals or impurities on the surface of the negative electrode can cause a sharp increase in negative electrode resistance, and this abnormal resistance phenomenon is a typical cause of accelerated degradation of the lifespan of lithium secondary batteries.

[0027] In particular, lithium secondary batteries using the aforementioned lithium manganese oxide as the positive electrode active material have a higher operating voltage than other commercially available lithium secondary batteries using ternary lithium composite oxides as the positive electrode active material, making them vulnerable to the aforementioned problems.

[0028] However, currently there are no technologies to resolve the issues caused by the leaching of transition metals from lithium-rich lithium-manganese oxides.

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

[0030] Another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined in this application.

[0031] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned can be understood from the following description and will be further made clear from the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations set forth in the claims. [Means for solving the problem]

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

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

[0034] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a single phase belonging to the R-3m space group, whereas the lithium-rich lithium manganese oxides defined in this application are characterized by the solid solution or composite formation 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. 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 oxide is replaced 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 (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, 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 surfaces of the first lithium manganese oxide and the second lithium manganese oxide. 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] Furthermore, according to another aspect of the present invention, a positive electrode containing the positive electrode active material described above is provided.

[0043] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided in which the positive electrode described above is used. [Effects of the Invention]

[0044] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese oxides, which have various disadvantages in terms of electrochemical properties and / or stability compared to commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0045] Specifically, according to the present invention, by preparing the lithium manganese oxide separately as small particles and large particles, and then providing a bimodal type positive electrode active material as a mixture of the small and large particles, the low energy density per unit volume of lithium-rich lithium manganese oxide can be improved.

[0046] Furthermore, according to the present invention, by covering the surfaces of the small and 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 and large particles.

[0047] By suppressing or mitigating the elution of transition metals from the small and large particles, it is possible to prevent the formation of impurities by the reaction of the eluted transition metals with the electrolyte on the surfaces of the small and large particles.

[0048] Transition metals leached from the small and large particles, and / or impurities formed by the reaction of the leached transition metals with the electrolyte, can move to the negative electrode using the electrolyte as a medium, and these impurities can deposit on the surface of the negative electrode, causing a rapid increase in the negative electrode resistance. As a result, it is necessary to restrict the unintended movement of transition metals within the lithium secondary battery, as described in the present invention.

[0049] In other words, according to the present invention, by forming a barrier layer on the surfaces of small and large particles, it is possible to prevent the acceleration of the life degradation of lithium secondary batteries caused by the deposition of impurities on the positive and / or negative electrodes by transition metals dissolved from the lithium manganese oxide.

[0050] Furthermore, the barrier layer can act as a physical barrier between the small and large particles and the electrolyte. In particular, while OLOs such as lithium manganese oxides have the advantage of exhibiting high capacity under high-voltage operating conditions, the possibility of side reactions between the lithium manganese oxide and the electrolyte can be accelerated as the operating voltage increases. Therefore, it is important to reduce side reactions between the lithium manganese oxide and the electrolyte.

[0051] Therefore, by forming a barrier layer on at least a portion of the surfaces of the small and large particles, the side reactions between the lithium manganese oxide and the electrolyte are reduced, thereby improving the stability and lifespan of the lithium secondary battery used as a bimodal type positive electrode active material as defined in this application. In particular, a positive electrode active material in which side reactions with the electrolyte are suppressed can drive the lithium secondary battery at a higher voltage.

[0052] Furthermore, according to the present invention, by inducing the 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 caused by the high specific surface area of ​​the small particles compared to the large particles.

[0053] The specific effects of the present invention, along with the effects mentioned above, will be described together with the embodiments for carrying out the invention described below. [Modes for carrying out the invention]

[0054] For the sake of easier understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0055] Below, we will describe in more detail some embodiments of the present invention, including a positive electrode active material containing a lithium-rich lithium manganese oxide and a lithium secondary battery containing the said positive electrode active material.

[0056] positive electrode active material According to one aspect of the present invention, a positive electrode active material is provided which contains a lithium manganese 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.

[0057] The phases belonging to the C2 / m space group and the phases belonging to the R-3m space group can be distinguished not only by the composition of each phase, but also by specific peaks for each phase during XRD analysis. For example, a specific peak for the phase belonging to the C2 / m space group may appear in the 2θ = 20.8 ± 1° region, and a specific peak for the phase belonging to the R-3m space group may appear in the 2θ = 18.6 ± 1° region.

[0058] The lithium manganese 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 solid-solved, and the phases belonging to the C2 / m space group and the phases belonging to the R-3m space group coexist within the lithium manganese oxide. Furthermore, the lithium manganese oxide is different from composite oxides having a spinel crystal structure belonging to the Fd-3m space group (for example, LiMn2O4 or oxides having a similar composition).

[0059] The lithium manganese oxides can be classified into small-particle first lithium manganese oxides and large-particle second lithium manganese oxides based on their average particle size. In this application, the terms small particles and large particles are relative concepts. Small particles can be defined as a collection of particles with an average particle size smaller than that of the second lithium manganese oxide, and large particles can be defined as a collection of particles with an average particle size larger than that of the first lithium manganese oxide. Furthermore, as will be described later, the terms small particles and large particles can be defined as ranges of average particle size, respectively.

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

[0061] Bimodal particle size distribution refers to a distribution in which two peaks exist for different particle sizes when laser diffraction particle size analysis is performed on the positive electrode active material. As a result, lithium manganese oxides that show a peak at a relatively small particle size in the volume cumulative particle size distribution graph are small particles (first lithium manganese oxide), and lithium manganese oxides that show a peak at a relatively large particle size are large particles (second lithium manganese oxide).

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

[0063] The lithium manganese oxide comprises at least lithium, manganese, and a transition metal. The transition metal may comprise at least one selected from nickel, cobalt, and aluminum. Alternatively, the lithium manganese oxide may comprise lithium, nickel, and manganese, or it may further comprise a transition metal other than nickel, selectively.

[0064] The aforementioned lithium manganese oxide is also called an overlithiated layered oxide (OLO) because the lithium content present in the lithium manganese oxide is greater than the total content of other transition metals (generally, when the molar ratio of lithium to all other metal elements in the lithium manganese oxide (Li / Metal molar ratio) is greater than 1).

[0065] Furthermore, because the lithium manganese oxide contains a higher amount of manganese than other transition metals, it is also referred to as a lithium and manganese-rich layered oxide.

[0066] Generally, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a manganese content of 20 mol% or less in the total metal elements excluding lithium, the aforementioned lithium manganese oxides have a relatively higher proportion of manganese in the total metal elements (e.g., 50 mol% or more, 52 mol% or more, 53 mol% or more, or 55 mol% or more) compared to commercially available ternary lithium composite oxides.

[0067] Furthermore, considering that commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions have a nickel content of 60 mol% or more (80 mol% or more in the case of high-Ni types) in the total metal elements excluding lithium, the lithium manganese-based oxides have a relatively lower proportion of nickel in the total metal elements (for example, 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] Another difference is that the Li / Metal molar ratio measured from lithium manganese oxides as defined in this application is greater than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of lithium manganese oxides as defined in this application is greater than 1, preferably having values ​​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 this application, lithium manganese oxide can be defined as a composite oxide in which the manganese content in the total metal elements excluding lithium is 50 mol% or more, or as a composite oxide in which the manganese content in the total metal elements excluding lithium is 50 mol% or more and the nickel content is less than 50 mol%.

[0070] Furthermore, in this application, lithium manganese oxides can be defined as composite oxides in which the molar ratio of lithium to the total metal elements excluding lithium is greater than 1, or has a value of 1.1-1.6, 1.1-1.5, 1.2-1.6, or 1.2-1.5, and the manganese content in the total metal elements excluding lithium is 50 mol% or more; or as composite oxides in which the molar ratio of lithium to the total metal elements excluding lithium is greater than 1, or has a value of 1.1-1.6, 1.1-1.5, 1.2-1.6, or 1.2-1.5, the manganese content in the total metal elements excluding lithium is 50 mol% or more, and the nickel content is less than 50 mol%.

[0071] Despite the aforementioned compositional differences, the lithium manganese-based oxide can also function as a composite metal oxide capable of lithium ion intercalation / deintercalation.

[0072] The lithium manganese-based oxide contained in the positive electrode active material as defined in this application may exist as particles containing at least one primary particle.

[0073] When the lithium manganese oxide exists as a single primary particle, it can be referred to as a single particle. On the other hand, when the lithium manganese oxide exists as an aggregate formed by the aggregation of multiple primary particles, it can be referred to as a secondary particle.

[0074] The positive electrode active material may include at least one selected from lithium manganese oxides existing as single particles and lithium manganese oxides existing as secondary particles formed by the aggregation of multiple primary particles.

[0075] The primary particles constituting the lithium manganese oxide may have a rod shape, an elliptical shape, and / or an amorphous shape. Furthermore, unless specifically intended in the manufacturing process, primary particles of various shapes exist within the same positive electrode active material. Moreover, the primary particles refer to particle units that, when observed with a scanning electron microscope at a magnification of 5,000 to 20,000 times, do not appear to have grain boundaries.

[0076] The primary particles constituting the lithium manganese oxide as defined in this 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 the average value of the length in the long axis direction and the length in the short axis direction of the primary particles ([long axis length + short axis length] / 2).

[0077] When the average particle size of the primary particles is smaller than 0.05 μm, the specific surface area of ​​the lithium manganese oxide (secondary particles) composed of the primary particles is relatively large. In this case, there is a higher possibility that the lithium manganese oxide and the electrolyte will undergo a side reaction during storage or operation of the lithium secondary battery.

[0078] On the other hand, if the average particle size of the primary particles is greater than 5 μm, the diffusion pathway of lithium ions within the primary particles becomes longer as the growth of the primary particles is excessively induced. When the diffusion pathway of lithium ions within the primary particles is excessively long, the mobility of lithium ions within the primary particles and the diffusivity of lithium ions mediated by the primary particles decrease, which increases the resistance of the lithium manganese oxide (secondary particles) composed of the primary particles.

[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 cathode active material can be increased.

[0080] The main peak of the volume-based particle size distribution graph (x-axis: particle size (μm), Y-axis: volume %) for the first lithium manganese oxide may be located between 1 μm and 8 μm, preferably between 2 μm and 7 μm. Furthermore, the average particle size calculated as the average of the length in the long axis direction and the length in the short axis direction ([long axis length + short axis length] / 2) of the first lithium manganese oxide may be between 2 μm and 6 μm.

[0081] The main peak of the volume-based particle size distribution graph (x-axis: particle size (μm), Y-axis: volume %) for the second lithium manganese oxide may be located between 6 μm and 24 μm, preferably between 8 μm and 22 μm. Furthermore, the average particle size calculated as the average of the length in the long axis direction and the length in the short axis direction ([long axis length + short axis length] / 2) of the second lithium manganese oxide may be between 7 μm and 14 μm.

[0082] Furthermore, in order to optimize the energy density per unit volume of the bimodal cathode active material, it is preferable that the first lithium manganese-based oxide and the second lithium manganese-based oxide are included in the cathode 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 oxide may exist in a form that fills the gaps between the second lithium manganese oxides, or it may exist in a form in which the first lithium manganese oxides aggregate together.

[0084] If the ratio of the first lithium manganese oxide to the second lithium manganese oxide in the positive electrode active material is excessively low, the first lithium manganese oxide may not adequately fill the voids formed by the second lithium manganese oxide.

[0085] On the other hand, if the ratio of the first lithium manganese oxide to the second lithium manganese oxide in the positive electrode active material is excessively 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 can vary depending on the number of primary particles constituting the secondary particles. The average particle size (D50) of the first lithium manganese oxide and the second lithium manganese oxide can be measured using the laser diffraction method. For example, the first lithium manganese oxide and the second lithium manganese oxide can be dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the volume cumulative amount can be determined.

[0087] Furthermore, the first lithium manganese oxide is 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 It has a BET specific surface area of ​​1.5m / g. The second lithium manganese oxide has a BET specific surface area of ​​1.5m 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 It has a BET specific surface area of ​​ / g. The range of the BET specific surface area of ​​the first lithium manganese oxide and the range of the BET specific surface area of ​​the second lithium manganese oxide can be determined as any combination of the numerical ranges described above.

[0088] Furthermore, 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 It may be less than / g.

[0089] The small-particle first lithium manganese oxide has more intra-particle and / or inter-particle voids than the large-particle second lithium manganese oxide, and has a higher specific surface area relative to its particle size, thus increasing the likelihood of side reactions with the electrolyte. Therefore, when selective growth of primary particles constituting the first lithium manganese oxide is induced by substituting at least a portion of the oxygen present in the first lithium manganese oxide with a halogen (e.g., fluorine), it is possible to reduce the specific surface area of ​​the first lithium manganese oxide. Furthermore, as explained above, since the small-particle first lithium manganese oxide has more intra-particle and / or inter-particle voids than the large-particle second lithium manganese oxide, the primary particle growth effect (decrease in intra-particle porosity as primary particles grow) from substituting at least a portion of the oxygen present in the first lithium manganese oxide with a halogen (e.g., fluorine) can be significant.

[0090] Unless otherwise defined, the term "surface of the primary particle" as used in this application means the outer surface of the primary particle that is exposed to the outside. Similarly, the term "surface of the secondary particle" as used in this application means the outer surface of the secondary particle that is exposed to the outside. In this case, the "surface of the secondary particle" formed by the aggregation of multiple primary particles corresponds to the exposed surface of the primary particle present on the surface portion of the secondary particle.

[0091] Furthermore, unless otherwise defined, the terms "particle surface" as used in this application mean the region relatively close to the "outermost surface" of the particle, and "particle center" means the region relatively closer to the "middle" of the particle than the "surface." Thus, "primary particle surface" means the region relatively close to the "outermost surface" of the primary particle, and "primary particle center" means the region relatively closer to the "middle" of the primary particle than the "surface." Similarly, "secondary particle surface" means the region relatively close to the "outermost surface" of the secondary particle, and "secondary particle center" means the region relatively closer to the "middle" of the secondary particle than the "surface."

[0092] In this case, the region within any particle excluding the "particle surface" can be defined as the "particle's central region."

[0093] For example, when the half diameter of the primary particle is denoted as r, the region 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 region at a distance of 0 to 0.5r from the center of the primary particle can be defined as the central portion of the primary particle. If the half diameter of the primary particle is 0.5 μm, the surface portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the surface of the primary particle, and the central portion of the primary particle can be defined as the region at a distance of 0 to 0.25 μm from the center of the primary particle.

[0094] Furthermore, if necessary, when the half-diameter of the primary particle is denoted as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the primary particle can be defined as the central part of the primary particle.

[0095] Similarly, when the half-diameter of the secondary particle is denoted as 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 central portion of the secondary particle. If the half-diameter 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 central 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 half-diameter of the secondary particle is denoted as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the secondary particle can be defined as the central part of the secondary particle.

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

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

[0099] As a result, the first lithium manganese oxide can be represented by the following chemical formula 1 or chemical formula 1-1. Furthermore, the composition represented by the following chemical formula 1 or chemical formula 1-1 can represent the average composition that reflects the composition of the barrier layer present on the surface of the first lithium manganese 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, and 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 both 0 at the same time.

[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 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 and 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 treatment 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] Furthermore, in the case of the over-calcination method, the growth of the primary particles is non-directional, whereas when halogen is doped during the growth of the primary particles, the growth of the primary particles exhibits some directionality, thereby mitigating the decrease in lithium ion diffusivity due to the growth of the primary particles. In particular, using fluorine as an anion dopant for the growth of the primary particles is preferable from the viewpoint of inducing selective crystal growth or particle growth of the primary particles within a range that mitigates the decrease in lithium ion diffusivity mediated by the primary particles.

[0106] For fluorine doping of the primary particles, at least one anionic 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 anionic dopant selected from LiF and MgF2, can be used.

[0107] In the aforementioned chemical formula 1, if M1 is Ni, M2 may include Mn, and if M1 is Mn, M2 may include Ni. Also, if M1 is Ni and Mn, M2 may be absent, or if present, it may be other elements other than Ni and Mn.

[0108] That is, if M1 is Ni, then 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; even more preferably at least one selected from P, B, and Si) and Mn.

[0109] If M1 is Mn, then 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; even more preferably at least one selected from P, B, and Si) and Ni.

[0110] If M1 is Ni and Mn, then 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] On the other hand, the second lithium manganese oxide can be represented by the following chemical 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, 0 <r≦0.7、0<a′≦1、0<x′≦1、0≦y′<1、0<x′+y′≦1である。

[0113] Because the large-particle second lithium manganese oxide has fewer intra-particle and / or inter-particle voids than the small-particle first lithium manganese oxide, 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 oxide with a halogen (e.g., fluorine).

[0114] Furthermore, unlike the first lithium manganese oxide, doping the second lithium manganese oxide with a halogen (e.g., fluorine) can actually reduce the electrochemical properties (e.g., decrease in capacity and efficiency) of the positive electrode active material having the bimodal particle size distribution defined in this application.

[0115] Similarly, in the above chemical formula 2, if M1 is Ni, M2 may include Mn, and if M1 is Mn, M2 may include Ni. Also, if M1 is Ni and Mn, M2 may be absent, or if present, it may be other elements other than Ni and Mn.

[0116] That is, if M1 is Ni, then 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; even more preferably at least one selected from P, B, and Si) and Mn.

[0117] If M1 is Mn, then 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; even more preferably at least one selected from P, B, and Si) and Ni.

[0118] If M1 is Ni and Mn, then 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 oxides represented by chemical formula 1, chemical formula 1-1, and chemical formula 2 may selectively contain cobalt. When the lithium manganese oxide contains cobalt, the mole fraction of cobalt relative to the total number of moles of metal elements in the lithium manganese oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese oxide represented by chemical formula 1 may have a cobalt-free composition.

[0120] The Li / Metal molar ratio measured from the lithium manganese oxide represented by Chemical Formula 1, Chemical Formula 1-1, and Chemical Formula 2 may be greater than 1, 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5. If the Li / Metal molar ratio measured from the lithium manganese oxide is greater than 1, it is possible to form a lithium-rich lithium manganese oxide.

[0121] Furthermore, in order for the lithium manganese oxide to appropriately 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 solidly dissolved or combined, and to exhibit high capacity under high voltage operating conditions, the Li / Metal molar ratio of the lithium manganese 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] Furthermore, in order to properly form a solid solution in which the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group are dissolved, it is preferable that the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide be 50 mol% or more.

[0123] In order for the lithium manganese oxide to have OLO characteristics that exhibit high capacity under high voltage operating conditions, the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide may be 50 mol% or more and less than 80 mol%, 51 mol% or more and less than 80 mol%, 52 mol% or more and less than 80 mol%, 53 mol% or more and less than 80 mol%, 54 mol% or more and less than 80 mol%, 55 mol% or more and less than 80 mol%, 50 mol% or more and 75 mol%, 51 mol% or more and 75 mol%, 52 mol% or more and 75 mol%, 53 mol% or more and 75 mol%, 54 mol% or more and 75 mol%, or 55 mol% to 75 mol%.

[0124] When the manganese content in the lithium manganese oxide exceeds 80 mol%, a phase transition may occur in the lithium secondary battery due to the migration of transition metals (particularly manganese) within the lithium manganese oxide during conversion and / or operation. Such a phase transition forms a spinel phase, and this spinel phase, acting as an impurity in the lithium manganese oxide, can induce a decrease in charge / discharge capacity or voltage decay during the cycling of the lithium secondary battery. Furthermore, when the manganese content in the lithium manganese oxide exceeds 80 mol%, the lithium manganese oxide may exhibit properties 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 with 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 nickel content in the total metal elements excluding lithium present in the lithium manganese 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 oxide is 50 mol% or more, the C2 / m phase may not form sufficiently, or the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group may not form a sufficient solid solution, which can cause phase separation during conversion and / or operation of the lithium secondary battery.

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

[0128] On the other hand, lithium-rich lithium manganese oxides represented by chemical formula 1, chemical formula 1-1, and chemical formula 2 are rLi2MnO 3-b″ X'b″ Alternatively, an oxide of a phase belonging to the C2 / m space group represented as rLi2MnO3 (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 oxides of the phase belonging to the R-3m space group represented by O2 (hereinafter referred to as the "R-3m phase") exist as a solid solution or composite oxide. For example, the lithium manganese-based oxide may exist in a state in which the oxide of the C2 / m phase and the oxide of the R-3m phase form a solid solution.

[0129] In this case, 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 simply physically and / or chemically bonded or attached does not fall under the definition 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, obtained by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R-3m space group, and having the surface coated with a metal oxide having a phase belonging to the R-3m space group, does not fall under the definition of a solid solution as defined in this application.

[0131] In the lithium manganese oxide, if r exceeds 0.7, the proportion of C2 / m phase oxide in the lithium manganese oxide becomes excessively high, which may ultimately lead to a decrease in discharge capacity as the irreversible capacity and resistance of the positive electrode active material increase. In other words, in order to sufficiently activate the C2 / m phase oxide, which has relatively high resistance, in the lithium manganese oxide and improve surface kinetics, it is preferable that the R-3m phase oxide be present in a predetermined proportion or higher.

[0132] In one embodiment, a barrier layer is present on the surfaces of the first lithium manganese oxide and the second lithium manganese oxide. The barrier layer can suppress or mitigate the elution of transition metals from the first lithium manganese oxide and the second lithium manganese oxide. Furthermore, by covering the surfaces of the first lithium manganese oxide and the second lithium manganese oxide, the barrier layer can prevent side reactions with the electrolyte and simultaneously improve the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions.

[0133] The barrier layer may exist in an island form, covering at least a portion of the surfaces of the first lithium manganese oxide and the second lithium manganese oxide. Even if the barrier layer exists in an island form, the elution of transition metals can be suppressed or mitigated through the region covered by the barrier layer.

[0134] Furthermore, when the first lithium manganese oxide and the second lithium manganese oxide are present as secondary particles, the barrier layer may exist diffused along the grain boundaries between primary particles, from the surface of the secondary particles toward the center of the secondary particles. The main elements constituting the barrier layer (for example, at least one selected from boron (B), silicon (Si), phosphorus (P), and germanium (Ge), preferably boron (B)) can form a concentration gradient that decreases from the surface (outermost edge) of the secondary particles toward the interior of the secondary particles.

[0135] The barrier layer forms a gradient from the surface of the secondary particles toward the center of the secondary particles, thereby effectively suppressing or mitigating the elution of transition metals, mainly on the surface of the secondary particles.

[0136] As a result, when the main elements constituting the barrier layer (for example, 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 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 number of nickel, manganese, and barrier elements present on the surface of the secondary particles. Furthermore, the atomic ratio of the barrier elements calculated based on the total 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 number of nickel, manganese, and barrier elements present on the surface (outermost layer) of the secondary particles.

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

[0138] As a result, when the main elements constituting the barrier layer (for example, 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 number 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 number of nickel, manganese, and barrier elements present on the surface (outermost layer) of the primary particles. Furthermore, the atomic ratio of the barrier elements calculated based on the total 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 number of nickel, manganese, and barrier elements present on the surface (outermost layer) of the primary particles.

[0139] Furthermore, the barrier layer may exist on the surfaces of the first lithium manganese oxide and the second lithium manganese oxide as a film with a thickness of 1 nm to 300 nm. The existence of the barrier layer as a film must be distinguished from the case where the oxide constituting the barrier layer is dispersed and attached to the surface of the lithium manganese 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. On the other hand, if the average thickness of the barrier layer is thicker than 300 nm, the surface kinetics of the first lithium manganese oxide and the second lithium manganese oxide may decrease, or their electrical conductivity may decrease.

[0141] Furthermore, increasing the thickness of the barrier layer present on the surface of the lithium manganese oxide prevents the elution of transition metals from the lithium manganese oxide, thereby improving the short lifespan of lithium secondary batteries using the lithium manganese oxide as the positive electrode active material. Conversely, if the thickness of the barrier layer becomes excessively thick (for example, exceeding 300 nm), a problem may occur where the amount of gas generated in the lithium secondary battery increases rapidly.

[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 contain an oxide represented by the following chemical formula 3.

[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 depending on the valence of M3.

[0145] Also, preferably, the barrier layer contains at least one boron-containing compound selected from B2O3, H α B β O γ (0 < α < 10, 0 < β < 10, 0 < γ < 20) and Li α′ B β′ O γ′ (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 so on.

[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, a specific description of the lithium manganese-based oxide is 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 is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0149] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0150] In this case, the positive electrode active material may be present in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When present within this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0151] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, 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, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 wt% to 15 wt% relative to the total weight of the positive electrode active material layer.

[0152] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15 wt% relative to the total weight of the positive electrode active material layer.

[0153] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0154] The solvent may be any 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 individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0155] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0156] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0157] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0158] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing 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. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0161] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and, if necessary, a selective binder, to the negative electrode current collector.

[0162] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, 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, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0163] The aforementioned negative electrode active material may be present in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0164] The binder 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, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 to further improve 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 for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0166] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0167] In other embodiments, 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 a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0168] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0169] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0171] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the 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 electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

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

[0173] In the present invention, when the electrolyte used is a solid electrolyte, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, oxide-based solid electrolyte, nitride-based solid electrolyte, or halogen-based solid electrolyte may be used, and preferably a sulfide-based solid electrolyte may be used.

[0174] As the material for the sulfide-based solid electrolyte, a solid electrolyte containing Li, element X (where 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 materials include Li2S-P2S5, Li2S-P2S-LiX (where 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 (where m and n are integers and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li p MO q(Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In), etc.

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

[0176] As materials for oxide-based solid electrolytes, there are Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0177] The solid electrolyte described above may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Also, the solid electrolyte may be partially included within the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0178] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 wt% relative to the total weight of the electrolyte.

[0179] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0180] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0181] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0182] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0183] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0184] Manufacturing Example 1. Manufacturing of positive electrode active material Production of Lithium Manganese Oxide (A-1) (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn 0.6 Hydroxide precursors with an (OH)2 composition (average particle size 3.0 μm) were obtained.

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

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

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

[0188] The BET specific surface area of ​​the first lithium manganese oxide (A-1) (calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 1.93 m². 2 It was measured to be / g.

[0189] Production of Lithium Manganese Oxide (A-2) (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn 0.6 Hydroxide precursors with an (OH)2 composition (average particle size 3.0 μm) were obtained.

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

[0191] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b) above, the lithium raw material LiOH (Li / metal (metal excluding Li) molar ratio = 1.28), and LiF weighed out with a metallic element-based fluorine (F) content of 1.0 mol% excluding lithium from the precursor.

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

[0193] The BET specific surface area of ​​the first lithium manganese oxide (A-2) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 1.72 m². 2 It was measured to be / g.

[0194] Production of Lithium Manganese Oxide (A-3) (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn 0.6 Hydroxide precursors with an (OH)2 composition (average particle size 3.0 μm) were obtained.

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

[0196] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b) above, the lithium raw material LiOH (Li / metal (metal excluding Li) molar ratio = 1.28), and LiF weighed out with a metallic element-based fluorine (F) content of 1.0 mol% excluding lithium from the precursor.

[0197] Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 900°C. After furnace cooling, lithium-rich lithium manganese oxide was obtained.

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

[0199] The BET specific surface area of ​​the first lithium manganese oxide (A-3) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 1.43 m². 2 It was measured to be / g.

[0200] Production of Lithium Manganese Oxide (A-4) (a) Production of precursors An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out for 5 hours while N2 gas was introduced into the reactor. After the reaction was complete, the product was washed and dehydrated, and Ni 0.4 Mn 0.6 Hydroxide precursors with an (OH)2 composition (average particle size 3.0 μm) were obtained.

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

[0202] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b) above, the lithium raw material LiOH (Li / metal (Li-excluded metal) molar ratio = 1.28), and LiF weighed out with a metallic element-based fluorine (F) content of 0.75 mol% excluding lithium from the precursor.

[0203] Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 900°C. After furnace cooling, lithium-rich lithium manganese oxide was obtained.

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

[0205] The BET specific surface area of ​​the first lithium manganese oxide (A-4) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 1.50 m². 2 It was measured to be / g.

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

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

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

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

[0210] The BET specific surface area of ​​the second lithium manganese oxide (B-1) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 2.38 m². 2 It was measured to be / g.

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

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

[0213] (c) Second heat treatment A mixture was prepared by mixing the oxide precursor obtained in step (b) above, the lithium raw material LiOH (Li / metal (metal excluding Li) molar ratio = 1.28), and LiF weighed out with a metallic element-based fluorine (F) content of 1.0 mol% excluding lithium from the precursor.

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

[0215] The BET specific surface area of ​​the second lithium manganese oxide (B-2) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 0.86 m². 2 It was measured to be / g.

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

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

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

[0219] Next, the furnace in an O2 atmosphere was heated at a rate of 2°C / min, and the mixture was heat-treated for 8 hours while maintaining a temperature of 900°C. After furnace cooling, lithium-rich lithium manganese oxide was obtained.

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

[0221] The BET specific surface area of ​​the second lithium manganese oxide (B-3) (calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan) is 1.81 m². 2 It was measured to be / g.

[0222] Manufacturing Example 2. Manufacturing of Cathode Active Material The first lithium manganese oxide and the second lithium manganese oxide produced according to Production Example 1 were mixed in the weight ratios shown in Table 1 below to produce a cathode active material having a unimodal or bimodal particle size distribution.

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

[0224] [Table 1]

[0225] Manufacturing Example 3: Manufacturing of Lithium-ion Secondary Batteries (Half-Cells) A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced according to Production Example 2, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

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

[0227] Manufacturing Example 4. Manufacturing of Lithium-ion secondary batteries (full cells) A cathode slurry was prepared by dispersing 90 wt% of each of the cathode active materials produced according to Production Example 2, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0228] A graphite electrode was used as the counter electrode with respect to the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as the separator, and an electrolyte solution in which LiPF6 was present at a concentration of 1.15 M in a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 2:4:4 was used to manufacture a full cell.

[0229] Experimental Example 1. Measurement of Compression Density of Positive Electrode Active Material After pressing 3 g of each positive electrode active material produced according to Production Example 2 at 4.5 tons for 5 seconds using a pelletizer, the compression density was measured.

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

[0231]

Table 2

[0232] Referring to the results in Table 2 above, it was confirmed that the compression density of the positive electrode active material having a bimodal particle size distribution was greater than that of the positive electrode active materials according to Comparative Example 1 and Comparative Example 2 having a unimodal particle size distribution.

[0233] Also, it was confirmed that the positive electrode active materials according to Example 1 and Example 2, which are positive electrode active materials using halogen-doped small particles and having a barrier layer formed on the surfaces of the small particles and large particles, had a greater compression density than other positive electrode active materials having a bimodal particle size distribution.

[0234] Experimental Example 2. Evaluation of Electrochemical Characteristics of Lithium Secondary Battery (Half Cell) For the lithium secondary battery (half cell) manufactured in Production Example 3, an initial discharge capacity, capacity per unit volume, and rate characteristics (discharge capacity ratio; rate capability (C-rate)) were measured through charge-discharge experiments at 25 °C, applying a discharge rate in a voltage range of 2.0 V to 4.6 V and 0.1 C to 5.0 C using an electrochemical analyzer (Toyo, Toscat-3100).

[0235] The capacity per unit volume was calculated by multiplying the initial discharge capacity by the compression density (compression 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 confirmed 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 of Comparative Example 1 and Comparative Example 2 having a unimodal particle size distribution.

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

[0240] Experimental Example 3. Evaluation of Electrochemical Characteristics of Lithium Secondary Battery (Full Cell) After completing a 6-cycle formation process at 25 °C, voltage range 2.0 V to 4.6 V, 0.2C / 0.2C conditions using an electrochemical analyzer (Toyo, Toscat-3100) for the lithium secondary battery (full cell) manufactured in Production Example 4 using the positive electrode active materials according to Example 1, Comparative Example 5, and Comparative Example 6, charge and discharge were performed 500 times at 25 °C, voltage range 2.0 V to 4.6 V, 1C / 1C conditions. Initial (1 st cycle) discharge capacity, 100 th cycles, 300 th cycles, 500 thThe cycle capacity retention rate (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 confirmed that the cycle capacity retention rate is lower in Comparative Examples 5 and 6 than in Example 1. This result is presumed to be due to the leaching of transition metals from the lithium manganese oxide, which causes an abnormal resistance phenomenon in the negative electrode, thereby accelerating the degradation of the lithium secondary battery's lifespan.

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

[0245] Experimental Example 4. Experiment on transition metal elution Using the positive electrode active materials from Example 1, Comparative Example 5, and Comparative Example 6, the lithium secondary battery (full cell) manufactured in Manufacturing Example 4 was subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. After that, the full cell was stabilized by 2 cycles of charge and discharge at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. Next, after disassembling the full cell, the negative electrode was washed with diethyl carbonate solvent, vacuum dried at 60°C, and then recovered.

[0246] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the Ni and Mn content of the separated negative electrode active material was measured by ICP analysis.

[0247] Furthermore, lithium secondary batteries (full cells) manufactured in Manufacturing Example 4 using the positive electrode active materials from Example 1, Comparative Example 5, and Comparative Example 6 were subjected to a 6-cycle conversion process using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0V to 4.6V, and 0.2C / 0.2C. Following this, 500 charge-discharge cycles were performed at 25°C, a voltage range of 2.0V to 4.6V, and 1C / 1C. Next, each full cell was stabilized by 2-cycle charge-discharge at 25°C, a voltage range of 2.0V to 4.6V, and 0.05C / 0.05C. After disassembling the full cells, the negative electrode was washed with diethyl carbonate solvent, vacuum-dried at 60°C, and then recovered.

[0248] The negative electrode active material was separated from the recovered negative electrode Cu foil (current collector), and the Ni and Mn content of the separated negative electrode active material was measured by ICP analysis.

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

[0250] [Table 5]

[0251] Referring to the results in Table 5 above, as predicted in Experimental Example 4, it can be confirmed that the lower cycle capacity retention rates of Comparative Examples 5 and 6 compared to Example 1 are due to an increased content of transition metals deposited in the negative electrode active material after chemical conversion and / or after 500 charge-discharge cycles.

[0252] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A positive electrode active material having a bimodal particle size distribution containing a first lithium manganese oxide and a second lithium manganese oxide with different average particle sizes, The first lithium manganese oxide and the second lithium manganese oxide are oxides containing at least lithium and manganese, in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are solid-dissolved. At least a portion of the oxygen present in the first lithium manganese oxide is substituted with a halogen, A barrier layer exists on the surfaces of the first lithium manganese oxide and the second lithium manganese oxide. The average particle size of the second lithium manganese oxide is 3 μm or more larger than the average particle size of the first lithium manganese oxide. The barrier layer is a positive electrode active material comprising at least one boron-containing compound selected from B₂O₃, HαBβOγ (0<α<10, 0<β<10, 0<γ<20) and Liα′Bβ′Oγ′ (0<α′<10, 0<β′<10, 0<γ′<20).

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 and cobalt.

4. The first lithium manganese oxide is a fluorine-doped cathode active material according to claim 1.

5. The positive electrode active material according to claim 1, wherein the first lithium manganese oxide is represented by the following chemical formula 1 or chemical formula 1-1. [Chemical formula 1] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 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, 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′ (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. 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. The positive electrode active material according to claim 1, wherein the average particle size of the first lithium manganese-based oxide is 2 μm to 6 μm.

7. The first lithium manganese oxide is 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 ​​1 / g.

8. The second lithium manganese oxide is represented by the following chemical formula 2, and is the positive electrode active material according to claim 1. [Chemical formula 2] rLi ２ MnO ３ ・(1-r)Li ａ′ M11 ｘ′ M2 ｙ′ O ２ (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. (0 < r ≤ 0.7, 0 < a' ≤ 1, 0 < x' ≤ 1, 0 ≤ y' < 1, 0 < x' + y' ≤ 1)

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

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

11. The positive electrode active material according to claim 1, wherein the barrier layer exists on the surface of the first lithium manganese-based oxide and the second lithium manganese-based oxide in the form of a film with a thickness of 1 nm to 300 nm.

12. 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.

13. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 12.

14. A lithium secondary battery comprising the positive electrode described in claim 13.

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