Positive electrode active material and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a positive electrode active material and a lithium secondary battery containing the same, which comprises a lithium and manganese-rich lithium manganese oxide with improved low energy density per unit volume, thereby improving electrochemical properties.

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 positive electrode active material and a lithium secondary battery containing the same, which comprises a lithium and manganese-rich lithium manganese oxide with improved low energy density per unit volume, thereby improving electrochemical properties. [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 the positive electrode active material and the negative electrode active material, 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 are 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 in which the molar ratio of lithium is greater than the sum of the molar ratios of other metal elements, 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 practice, its electrical conductivity is relatively low due to the excessive amount of Mn contained in the OLO, resulting in the disadvantage of low rate characteristics in 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, compared to conventionally commercialized high-Ni type cathode active materials such as ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions, these materials generally have the disadvantage of having a lower energy density per unit volume. [Overview of the project] [Problems that the invention aims to solve]

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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, preventing them from replacing commercially available high-Ni type cathode active materials such as ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0016] 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 the particles).

[0017] Therefore, to increase the insufficient energy density per unit volume of OLO, the use of a cathode active material with a bimodal particle size distribution can be considered. However, since the particles constituting the precursor of OLO generally grow mainly into thick, plate-like particles, while the internal density increases as the size of the secondary particles increases, this can be accompanied by the problem of reduced performance due to low conductivity.

[0018] However, the inventors have confirmed that the shape of the primary particles constituting the lithium manganese oxide can be controlled by the synthesis conditions of the lithium manganese oxide precursor, and through this, the capacity characteristics and rate characteristics of the positive electrode active material containing relatively large secondary particles (for example, medium and / or large particles with an average particle size of 5 μm or more) can be improved.

[0019] Accordingly, the present invention aims to provide a positive electrode active material that includes secondary particles (for example, medium and / or large particles with an average particle size of 5 μm or more) whose shape is controlled, in order to improve the low energy density per unit volume of lithium-rich lithium manganese oxides.

[0020] Another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined in this application.

[0021] 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 may be more clearly understood from embodiments of the present invention. It can also be readily seen that the objects and advantages of the present invention can be achieved by the means and combinations set forth in the claims. [Means for solving the problem]

[0022] According to one aspect of the present invention for solving the aforementioned technical problems, 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.

[0023] 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 oxide defined in this application is characterized by being a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group coexist.

[0024] In one embodiment, the lithium manganese oxide has a secondary particle form in which a plurality of primary particles are aggregated, and at least a portion of the secondary particles may have an oriented structure in which the long axes of the primary particles are aligned from the center of the secondary particles toward the surface.

[0025] The major axis of the primary particle exhibiting the oriented structure may be formed to have an angle of ±70°, ±60°, ±40°, ±20°, or ±10° from the line connecting the center and surface of the secondary particle.

[0026] In one embodiment, the secondary particles may be divided into a core portion in which the primary particles are randomly aggregated, and a shell portion outside the core portion in which the primary particles exhibit the oriented structure.

[0027] Within the shell portion, the primary particles have an oriented structure in which their long axes are aligned from the center of the secondary particles toward the surface. As a result, the proportion of primary particles having this oriented structure among the total primary particles present in the shell portion may be 50% or more, 60%, 70%, 80%, 85%, or 90% or more.

[0028] Within the core portion, the primary particles do not exhibit a predetermined orientation but aggregate randomly, so the proportion of primary particles having the orientation structure among the total primary particles present in the core portion may be less than 50%.

[0029] Furthermore, the primary particles present in the shell portion and the primary particles present in the core portion may have different shapes.

[0030] For example, the ratio of the length of the major axis to the length of the minor axis of the primary particles present in the core portion (length of the major axis / length of the minor axis), as observed from a cross-sectional SEM image of the secondary particles, may be smaller than the ratio of the length of the major axis to the length of the minor axis of the primary particles present in the shell portion (length of the major axis / length of the minor axis).

[0031] In one embodiment, the primary particles present in the shell portion may have the shape of a thin plate, a thin rod, or a fine needle.

[0032] As a result, the surface shape of the primary particles exposed on the surface of the secondary particles, as observed from the surface SEM image of the secondary particles, can have a long axis and a short axis.

[0033] The average value of the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles may be 1.5 or more and 9.0 or less, 1.6 or more and 8.0 or less, 1.7 or more and 7.0 or less, 1.8 or more and 6.0 or less, 1.9 or more and 5.7 or less, 2.0 or more and 5.5 or less, 2.1 or more and 5.3 or less, 2.2 or more and 5.2 or less, 2.3 or more and 5.1 or less, or 2.37 or more and 4.94 or less.

[0034] The average value of the ratio of the length of the short axis to the length of the long axis (length of the short axis / length of the long axis) of the surface shape of the primary particles exposed on the surface of the secondary particles may be 0.2 or more and 0.5 or less, 0.21 or more and 0.49 or less, or 0.22 or more and 0.45 or less.

[0035] The average length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles may be 150 nm to 350 nm, 160 nm to 320 nm, 170 nm to 290 nm, 180 nm to 270 nm, 190 nm to 260 nm, or 192 nm to 250 nm.

[0036] The average length of the short axis of the surface shape of the primary particles exposed on the surface of the secondary particles may be 30 nm to 130 nm, 35 nm to 120 nm, 40 nm to 110 nm, or 47 nm to 105 nm.

[0037] In one embodiment, the lithium manganese oxide is a composite oxide of lithium, nickel, and manganese, and the lithium manganese oxide may further contain one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0038] The lithium manganese oxide as defined in this application may be represented by the following chemical formula 1 or chemical formula 2. [Chemical formula 1] Li(Li a Ni b Co c Mn d M1 e )O 2-f X f [Here, in the above chemical formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X is a halogen capable of substituting some of the oxygen present in the lithium manganese oxide, 0 <a≦0.7、0≦b<0.5、0≦c≦0.2、0.5≦d<0.8、0<e≦0.1、0≦f≦0.1である。] [Chemical Formula 2] rLi2MnO 3-p X p ·(1 - r)Li u Ni w Co x Mn y M2 z O 2-p′ X′ p′ [Wherein, in the Chemical Formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd, X and X′ are halogens capable of substituting a part of the oxygen present in the lithium manganese-based oxide, 0.2 < r ≦ 0.7, 0 < u ≦ 1, 0 ≦ w ≦ 1, 0 ≦ x ≦ 0.2, 0.3 < y < 1, 0 < z ≦ 0.1, 0 ≦ p ≦ 0.1, 0 ≦ p′ ≦ 0.1.]

[0039] Also, according to another aspect of the present invention, a positive electrode including the aforementioned positive electrode active material is provided.

[0040] Also, according to still another aspect of the present invention, a lithium secondary battery using the aforementioned positive electrode is provided. [Advantages of the Invention]

[0041] According to the present invention, compared with a ternary lithium composite oxide having a commercialized nickel - cobalt - manganese (NCM) or nickel - cobalt - aluminum (NCA) composition, it is possible to improve the limitations of a conventional lithium - excess lithium manganese-based oxide that has various disadvantages from the viewpoints of electrochemical characteristics and / or stability.

[0042] Specifically, according to the present invention, the shape of the primary particles constituting the lithium manganese oxide can be controlled by the synthesis conditions of the lithium manganese oxide precursor, thereby improving the capacity characteristics and rate characteristics of a positive electrode active material that includes relatively large secondary particles (for example, medium and / or large particles with an average particle size of 5 μm or more).

[0043] In particular, the lithium manganese oxide according to the present invention has primary particles present on the surface of secondary particles that are thin plate-like, thin rod-like, or fine needle-like, which can improve the capacity characteristics and rate characteristics of a lithium secondary battery using the lithium manganese oxide as a positive electrode active material. Furthermore, when the lithium manganese oxide is made into medium and / or large particles and mixed with small-particle lithium manganese oxide to use a positive electrode active material exhibiting a bimodal or trimodal particle size distribution, the low energy density per unit volume of the lithium secondary battery can be further improved.

[0044] Furthermore, the lithium manganese-based oxide according to the present invention has an oriented structure in which the long axes of primary particles present on the surface of secondary particles are aligned from the center of the secondary particles toward the surface, thereby improving the surface kinetic properties of the lithium manganese-based oxide.

[0045] Along with the effects described above, the specific effects of the present invention will be described below while explaining the specific matters for carrying out the invention. [Modes for carrying out the invention]

[0046] For the sake of easier understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, the 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.

[0047] Below, several embodiments of the present invention will be described in more detail regarding positive electrode active materials containing lithium-rich lithium manganese oxides and lithium secondary batteries containing said positive electrode active materials.

[0048] (Cathode 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.

[0049] 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.

[0050] 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).

[0051] The lithium manganese oxide may be a composite oxide of lithium, nickel, and manganese. Furthermore, the lithium manganese oxide may further contain one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0052] 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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] There is also a difference in 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 a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0057] Therefore, in this application, lithium manganese oxide can be defined as a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol% or more, or as a composite oxide in which the manganese content in all metal elements excluding lithium is 50 mol% or more and the nickel content is less than 50 mol%.

[0058] 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%.

[0059] Despite the aforementioned compositional differences, the lithium manganese-based oxide can also function as a composite metal oxide capable of lithium ion intercalation / deintercalation.

[0060] The lithium manganese-based oxide contained in the positive electrode active material as defined in this application may exist as aggregates formed by the aggregation of multiple primary particles. When the lithium manganese-based oxide exists as aggregates formed by the aggregation of multiple primary particles, the lithium manganese-based oxide can be called a secondary particle.

[0061] The aforementioned primary particles refer to particle units that, when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope, do not appear to have grain boundaries.

[0062] The primary particles constituting the lithium manganese oxide as defined in this application may have an average particle size of 0.05 μm to 5.0 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 may be the average value of the length in the long axis direction and the length in the short axis direction of the primary particle ([length in the long axis direction + length in the short axis direction] / 2). The average particle size of the primary particles can be calculated as the average value of the particle sizes of all primary particles observed from surface SEM images and / or cross-sectional SEM images of the lithium manganese oxide.

[0063] 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.

[0064] On the other hand, if the average particle size of the primary particles is greater than 5.0 μm, the growth of the primary particles is excessively induced, which lengthens the diffusion pathway of lithium ions within the primary particles. 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.

[0065] To reduce the specific surface area of ​​the lithium manganese oxide while simultaneously preventing a decrease in the mobility of lithium ions within the primary particles and the diffusivity of lithium ions mediated by the primary particles, the average particle size of the primary particles may be 0.05 μm to 5.0 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm.

[0066] The average particle size (D) of the secondary particles 50 The particle size can be 5.0 μm to 24.0 μm, 6.0 μm to 20.0 μm, 6.0 μm to 18.0 μm, 6.0 μm to 16.0 μm, or 6.0 μm to 15.0 μm.

[0067] The average particle size (D) of the secondary particles 50 The particle size can vary depending on the number of primary particles that make up the secondary particles. The average particle size of the secondary particles can be measured using the laser diffraction method. For example, after dispersing the secondary particles in a dispersion medium, they can be 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 then measured by obtaining a volume cumulative particle size distribution graph and determining the particle size corresponding to 50% of the volume cumulative amount.

[0068] In this application, "particle size" is used interchangeably with "particle diameter" or "particle size," and unless otherwise defined, all "average particle size" refers to the intermediate volume-based particle size determined by laser diffraction.

[0069] When the lithium manganese oxide defined in this application is used as the large particle of the positive electrode active material exhibiting a bimodal particle size distribution, the average particle size (D) of the secondary particles 50 The particle size can be 5.0 μm to 24.0 μm, 6.0 μm to 20.0 μm, 6.0 μm to 18.0 μm, 6.0 μm to 16.0 μm, or 6.0 μm to 15.0 μm.

[0070] Furthermore, when the lithium manganese oxide defined in this application is used as a medium particle (a particle having an average particle size between small and large particles) in a positive electrode active material exhibiting a trimodal particle size distribution, the average particle size (D 50 ) may be 5.0 μm to 15.0 μm, 5.0 μm to 10.0 μm, or 5.0 μm to 8.0 μm. On the other hand, when the lithium manganese oxide defined in this application is used as the large particle of the positive electrode active material exhibiting a trimodal type particle size distribution, the average particle size (D) of the secondary particles 50 The particle size can be 8.0 μm to 24.0 μm, 8.0 μm to 20.0 μm, or 10.0 μm to 15.0 μm.

[0071] Furthermore, if the positive electrode active material as defined in this application exhibits a bimodal or trimodal particle size distribution, the average particle size of the lithium manganese-based oxide provided as small particles may be 1 μm to 8 μm, 2 μm to 6 μm, or 3 μm to 5 μm.

[0072] Generally, in the case of a lithium manganese oxide having a composition like the one described above, the primary particles constituting the secondary particles may have rod-shaped, elliptical, and / or amorphous shapes, and unless specifically intended in the manufacturing process, primary particles of various shapes may exist within the same secondary particle. Furthermore, conventional lithium manganese oxides may also contain plate-shaped primary particles, but since these primary particles are mostly thick plates, the conductivity of lithium ions is low, and positive electrode active materials containing lithium manganese oxides have the problem of poor capacity characteristics and rate characteristics.

[0073] On the other hand, at least a portion of the primary particles constituting the lithium manganese-based oxide as defined in this application are characterized by having a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape.

[0074] The shape of such primary particles can be inferred from the surface shape of the primary particles exposed on the surface of the secondary particles as observed from surface SEM images of the secondary particles and the cross-sectional shape of the primary particles as observed from cross-sectional SEM images of the secondary particles.

[0075] In one embodiment, the surface shape of the primary particle exposed on the surface of the secondary particle, as observed from a surface SEM image of the secondary particle, may have a major axis and a minor axis. The surface of the secondary particle corresponds to the set of exposed surfaces of the primary particle located at the outermost edge of the secondary particle.

[0076] The fact that the surface shape of the primary particles exposed on the surface of the secondary particles has a long axis and a short axis means that it is highly likely that at least the primary particles exposed on the surface of the secondary particles have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape.

[0077] In particular, if the primary particles exposed on the surface of the secondary particles have an oriented structure in which their long axes are aligned from the center of the secondary particles toward the surface, the surface shape observed from the surface SEM image of the secondary particles is likely to show that the primary particles, which have long and short axes, have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape.

[0078] Furthermore, the cross-sectional shape of the primary particle observed from the cross-sectional SEM image of the secondary particle may have a major axis and a minor axis.

[0079] If the surface shape of the primary particles exposed on the surface of the secondary particles, as observed from a surface SEM image of the secondary particles, has a long axis and a short axis, and the cross-sectional shape of the primary particles exposed on the surface of the secondary particles, as observed from a cross-sectional SEM image of the secondary particles, also has a long axis and a short axis, then it is highly likely that at least the primary particles exposed on the surface of the secondary particles have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape.

[0080] However, even if the surface shape of the primary particle exposed on the surface of the secondary particle, as observed from a surface SEM image of the secondary particle, has a major axis and a minor axis, if the ratio of the length of the major axis to the length of the minor axis of the surface shape of the primary particle exposed on the surface of the secondary particle (length of the major axis / length of the minor axis) is small (for example, close to 1), the primary particle may have a thick plate-like or thick rod-like shape.

[0081] As a result, the primary particles exposed on the surface of the secondary particles can have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape. The average value of the ratio of the length of the major axis to the length of the minor axis of the surface shape of the primary particles exposed on the surface of the secondary particles (length of major axis / length of minor axis) may be 1.5 or more and 9.0 or less, 1.6 or more and 8.0 or less, 1.7 or more and 7.0 or less, 1.8 or more and 6.0 or less, 1.9 or more and 5.7 or less, 2.0 or more and 5.5 or less, 2.1 or more and 5.3 or less, 2.2 or more and 5.2 or less, 2.3 or more and 5.1 or less, or 2.37 or more and 4.94 or less.

[0082] If the average ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 1.5, then the primary particles exposed on the surface of the secondary particles are unlikely to have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape. Also, if the primary particles are formed to be excessively thick or have an excessively small size, then the average ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles may be less than 1.5. If the primary particles are formed to be excessively thick, the porosity within the surface of the secondary particles may decrease, and surface kinetics may decrease. If the primary particles have an excessively small size, the specific surface area may increase, and side reactions between the lithium manganese oxide and the electrolyte may increase.

[0083] On the other hand, if the average value of the ratio of the length of the major axis to the length of the minor axis (length of the major axis / length of the minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 9.0, the number of primary particles with an excessively thin shape will increase, which may conversely increase the porosity within the secondary particles, decrease the energy density per unit volume, or increase the specific surface area, potentially increasing the side reactions between the lithium manganese oxide and the electrolyte.

[0084] Furthermore, so that the primary particles exposed on the surface of the secondary particles can have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape, the average value of the ratio of the length of the short axis to the length of the long axis of the surface shape of the primary particles exposed on the surface of the secondary particles (length of the short axis / length of the long axis) may be 0.2 or more and 0.5 or less, 0.21 or more and 0.49 or less, or 0.22 or more and 0.45 or less.

[0085] If the average ratio of the length of the short axis to the length of the long axis (length of the short axis / length of the long axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 0.2, the number of primary particles with an excessively thin shape will increase, which may conversely increase the porosity within the secondary particles, decrease the energy density per unit volume, or increase the specific surface area, potentially increasing the side reactions between the lithium manganese oxide and the electrolyte.

[0086] On the other hand, if the average ratio of the length of the short axis to the length of the long axis (length of the short axis / length of the long axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 0.5, then the primary particles exposed on the surface of the secondary particles are less likely to have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape. Also, if the primary particles are formed to be excessively thick, or if the primary particles are excessively small in size, then the average ratio of the length of the short axis to the length of the long axis (length of the short axis / length of the long axis) of the surface shape of the primary particles exposed on the surface of the secondary particles may be greater than 0.5. If the primary particles are formed to be excessively thick, the porosity within the surface of the secondary particles may decrease, and surface kinetics may decrease. If the primary particles are excessively small in size, the specific surface area may increase, and side reactions between the lithium manganese oxide and the electrolyte may increase.

[0087] The average length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles may be 150 nm to 350 nm, 160 nm to 320 nm, 170 nm to 290 nm, 180 nm to 270 nm, 190 nm to 260 nm, or 192 nm to 250 nm.

[0088] If the average length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 150 nm, the size of the primary particles exposed on the surface of the secondary particles is excessively small, which may make it difficult to reduce the side reaction between the lithium manganese oxide and the electrolyte.

[0089] On the other hand, if the average length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 350 nm, the size of the primary particles exposed on the surface of the secondary particles may become excessively large, which can lead to a decrease in surface kinetics such as lithium ion conductivity.

[0090] The average length of the short axis of the surface shape of the primary particles exposed on the surface of the secondary particles may be 30 nm to 130 nm, 35 nm to 120 nm, 40 nm to 110 nm, or 47 nm to 105 nm.

[0091] If the average length of the short axis of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 30 nm, the size of the primary particles exposed on the surface of the secondary particles may be excessively small or excessively thin, making it difficult to reduce the side reaction between the lithium manganese oxide and the electrolyte.

[0092] On the other hand, if the average length of the short axis of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 130 nm, the primary particles exposed on the surface of the secondary particles are less likely to have a thin plate-like shape, a thin rod-like shape, and / or a fine needle-like shape. Furthermore, if the size of the primary particles exposed on the surface of the secondary particles becomes excessively large, surface kinetics such as lithium-ion conductivity may decrease.

[0093] Furthermore, the average length of the short axis of the primary particles exposed on the surface of the secondary particles, as observed from the cross-sectional SEM image of the secondary particles, may be between 30 nm and 200 nm. The average length of the short axis of the primary particles having an oriented structure, as observed from the cross-sectional SEM image of the secondary particles, may be between 30 nm and 200 nm.

[0094] If the average length of the short axis of the primary particles exposed on the surface of the secondary particles, as observed from a cross-sectional SEM image of the secondary particles, is less than 30 nm, there is a risk that the number of primary particles with an excessively thin shape will increase, which may actually increase the porosity within the secondary particles or decrease the energy density per unit volume.

[0095] On the other hand, if the average length of the short axis of the primary particles exposed on the surface of the secondary particles, as observed from a cross-sectional SEM image of the secondary particles, is greater than 200 nm, then the primary particles exposed on the surface of the secondary particles are unlikely to have a thin plate-like, thin rod-like, and / or fine needle-like shape. This can lead to a decrease in surface kinetics, such as lithium-ion conductivity, due to an excessively large size of the primary particles exposed on the surface of the secondary particles.

[0096] In this application, (1) the average value of the length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles, (2) the average value of the length of the minor axis of the surface shape of the primary particles exposed on the surface of the secondary particles, (3) the average value of the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles, and (4) the average value of the ratio of the length of the minor axis to the length of the major axis (length of minor axis / length of major axis) of the surface shape of the primary particles can be calculated by randomly selecting 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more of the total primary particles exposed on the surface of the secondary particles from a surface SEM image of the secondary particles, and then measuring the length of the major axis and the length of the minor axis from the surface shape of the selected primary particles.

[0097] When calculating the average value from a portion of primary particles exposed on the surface of the secondary particles using a surface SEM image of the secondary particles, in order to improve accuracy, when selecting a portion of the primary particles from the total number of primary particles exposed on the surface of the secondary particles using a surface SEM image of the secondary particles, upper and lower groups can be excluded.

[0098] For example, when selecting 40% of the total primary particles exposed on the surface of the secondary particles from a surface SEM image of the secondary particles, the following can be selected: (1) the remaining 40% excluding the top 30% and bottom 30% groups based on the length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles; (2) the remaining 40% excluding the top 30% and bottom 30% groups based on the length of the minor axis of the surface shape of the primary particles exposed on the surface of the secondary particles; (3) the remaining 40% excluding the top 30% and bottom 30% groups based on the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles; and (4) the remaining 40% excluding the top 30% and bottom 30% groups based on the ratio of the length of the minor axis to the length of the major axis (length of minor axis / length of major axis) of the surface shape of the primary particles.

[0099] As another example, (1) the average value of the length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles, (2) the average value of the length of the minor axis of the surface shape of the primary particles exposed on the surface of the secondary particles, (3) the average value of the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles, and (4) the average value of the ratio of the length of the minor axis to the length of the major axis (length of minor axis / length of major axis) of the surface shape of the primary particles can be calculated from the surface SEM image of the secondary particles, using the average value of the length of the major axis / length of minor axis measured from the surface shape of the entire primary particle exposed on the surface of the secondary particles.

[0100] 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. As described above, the "surface of the secondary particle" formed by the aggregation of a plurality of primary particles corresponds to the exposed surface of the primary particle present on the surface portion of the secondary particle.

[0101] Also, unless otherwise defined, the term "surface portion of the particle" used in this application means a region relatively close to the "outermost surface" of the particle, and the "central portion of the particle" means a region relatively closer to the "center" of the particle than the said "surface portion". Accordingly, the "surface portion of the primary particle" means a region relatively close to the "outermost surface" of the said primary particle, and the "central portion of the primary particle" means a region relatively closer to the "center" of the said primary particle than the said "surface portion". Similarly, the "surface portion of the secondary particle" means a region relatively close to the "outermost surface" of the said secondary particle, and the "central portion of the secondary particle" means a region relatively closer to the "center" of the said secondary particle than the said "surface portion".

[0102] At this time, a region excluding the "surface portion of the particle" within any particle can be defined as the "central portion of the particle".

[0103] When the radius of the lithium manganese oxide measured from the cross-sectional SEM image of the lithium manganese oxide in this application is r, a region where the distance (d) from the center of the lithium manganese oxide is (1 / 2)r < d is defined as the surface portion, and a region where the distance (d) from the center of the lithium manganese oxide is 0 ≦ d ≦ (1 / 2)r can be defined as the center portion. Here, it is assumed that the lithium manganese oxide is a secondary particle.

[0104] Since the secondary particle does not have to have a perfect spherical shape, the radius (r) of the secondary particle can be calculated from the average value of the length of the major axis and the length of the minor axis of the lithium manganese oxide measured from the cross-sectional SEM image of the secondary particle. That is, the radius (r) of the secondary particle can be considered as half of the average value of the length of the major axis and the length of the minor axis of the lithium manganese oxide measured from the cross-sectional SEM image of the secondary particle.

[0105] In one embodiment, the lithium manganese oxide has a secondary particle form in which a plurality of primary particles are aggregated, and at least a portion of the secondary particles may have an oriented structure in which the long axes of the primary particles are aligned from the center of the secondary particles toward the surface.

[0106] The major axis of the primary particle exhibiting the oriented structure is formed to have an angle of ±70°, ±60°, ±40°, ±20°, or ±10° from the line connecting the center and surface of the secondary particle. The line connecting the center and surface of the secondary particle means the shortest line segment connecting the center and surface of the secondary particle, and the major axis of the primary particle means the line segment with the longest length among the straight lines connecting two points on the surface of the primary particle.

[0107] By having an oriented structure in which the long axes of the primary particles are aligned from the center of the secondary particles toward the surface in at least a portion of the secondary particles, the mobility of lithium ions within the secondary particles can be increased.

[0108] In one embodiment, the secondary particles may be divided into a core portion in which the primary particles are randomly aggregated, and a shell portion outside the core portion in which the primary particles exhibit the oriented structure.

[0109] The core portion is a region in which the primary particles are aggregated in a disordered manner without having any particular orientation, and corresponds to the central part of the secondary particles.

[0110] When the radius of the lithium manganese oxide (secondary particle) measured from the cross-sectional SEM image of the lithium manganese oxide (secondary particle) is denoted as r, the core portion can be defined as a region where the distance (d) from the center of the secondary particle is 0 ≤ d ≤ (1 / 2)r or 0 ≤ d ≤ (1 / 3)r.

[0111] Within the core portion, the primary particles do not exhibit a predetermined orientation and aggregate randomly. Thus, the ratio of the primary particles having the orientation structure among all the primary particles present in the core portion can be less than 50%, less than 40%, less than 30%, less than 20%, or less than 10%.

[0112] The shell portion is present outside the core portion and is a region where the primary particles are arranged in an orientation structure, corresponding to the surface portion of the secondary particles.

[0113] When the radius of the lithium manganese oxide (secondary particles) measured from the cross-sectional SEM image of the lithium manganese oxide (secondary particles) is r, the shell portion can be defined as a region where the distance (d) from the center of the secondary particles is (1 / 2)r < d or (2 / 3)r < d.

[0114] Within the shell portion, due to the primary particles having an orientation structure in which the long axes of the primary particles are arranged in the direction from the center to the surface of the secondary particles, the ratio of the primary particles having the orientation structure among all the primary particles present in the shell portion can be 50% or more, 60%, 70%, 80%, 85%, or 90% or more. The average value of the angle between the long axis of the primary particles present in the shell portion and the line connecting the center and the surface of the secondary particles can be within ±70°, within ±60°, within ±40°, within ±20°, or within ±10°.

[0115] In the present application, the ratio of the primary particles having the orientation structure among all the primary particles present in the core portion or the shell portion means the ratio based on the number of primary particles.

[0116] Also, the shapes of the primary particles present in the shell portion and the primary particles present in the core portion may be different.

[0117] For example, the ratio of the length of the major axis to the length of the minor axis of the primary particles present in the core portion (length of the major axis / length of the minor axis), as observed from a cross-sectional SEM image of the secondary particles, may be smaller than the ratio of the length of the major axis to the length of the minor axis of the primary particles present in the shell portion (length of the major axis / length of the minor axis).

[0118] The primary particles present in the shell portion may have the shape of a thin plate, a thin rod, or a fine needle.

[0119] The BET specific surface area of ​​a positive electrode active material containing lithium manganese oxide, which is an aggregate of primary particles exhibiting the shape and orientation described above, measured by nitrogen adsorption, is 1.0 m². 2 / g~3.5m 2 / g, 1.2m 2 / g~3.4m 2 / g, 1.4m 2 / g~3.3m 2 / g, or 1.7m 2 / g~3.2m 2 It could be / g

[0120] The BET specific surface area of ​​the aforementioned lithium manganese oxide is 3.5 m². 2 If the value is greater than / g, the possibility of side reactions between the lithium manganese oxide and the electrolyte increases, which may reduce the stability of the positive electrode active material containing the lithium manganese oxide. On the other hand, if the BET specific surface area of ​​the lithium manganese oxide is 1.0 m² 2 If the value is less than / g, the specific surface area of ​​the lithium manganese oxide may become excessively small, making it difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material containing the lithium manganese oxide.

[0121] The lithium manganese oxide as defined in this application may be represented by the following chemical formula 1 or chemical formula 2. [Chemical formula 1] Li(Li a Ni b Co c Mn d M1 e )O2-f X f [Here, in the above chemical formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X is a halogen capable of substituting some of the oxygen present in the lithium manganese oxide, 0 <a≦0.7、0≦b<0.5、0≦c≦0.2、0.5≦d<0.8、0<e≦0.1、0≦f≦0.1である。] [Chemical formula 2] rLi2MnO 3-p X p (1-r)Li u Ni w Co x Mn y M2 z O 2-p′ X' p′ [Here, in the chemical formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X and X' are halogens capable of substituting some of the oxygen present in the lithium manganese oxide, 0.2 <r≦0.7、0<u≦1、0≦w≦1、0≦x≦0.2、0.3<y<1、0<z≦0.1、0≦p≦0.1、0≦p′≦0.1である。]

[0122] In chemical formulas 1 and 2, X and X' are halogen elements that can independently substitute for some of the oxygen present in the lithium manganese oxide. The types of halogens that can be used for X and X' refer to the periodic table, but F, Cl, Br and / or I, etc., can be used, and preferably F can be used.

[0123] In the aforementioned chemical formulas 1 and 2, M1 and M2 are each independently at least one selected from 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 can be at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Ca, Mg, W, Ce, V, Ta, and Y, and at least one selected from Al, P, B, Si, Ti, Zr, and W.

[0124] The Li / Metal molar ratio measured from the lithium manganese oxide represented by the aforementioned chemical formula 1 or 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. When the Li / Metal molar ratio measured from the lithium manganese oxide has a value greater than 1, it is possible to form a lithium-rich lithium manganese oxide. 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 solid-dissolved, and at the same time to exhibit high capacity under high-voltage operating conditions, the Li / Metal molar ratio of the lithium manganese oxide is preferably 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0125] Furthermore, 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, it is preferable that the manganese content in the total metal elements excluding lithium present in the lithium manganese oxide represented by chemical formula 1 or chemical formula 2 is 50 mol% or more.

[0126] 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%. If the manganese content in the lithium manganese oxide exceeds 80 mol%, a phase transition may occur due to the movement of transition metals (especially manganese) within the lithium manganese oxide during conversion to a lithium secondary battery 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 a lithium secondary battery. Furthermore, if the manganese content in the lithium manganese oxide exceeds 80 mol%, it may be difficult to sufficiently generate a phase belonging to the R-3m space group.

[0127] 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 represented by chemical formula 1 or chemical formula 2 may be 0% or more and less than 50 mol%, 5 mol% or more and 48 mol%, 10 mol% or more and 46 mol%, 15 mol% or more and 45 mol%, 20 mol% or more and 44 molmol%, 20 mol% or more and 42 mol%, or 20 mol% or more and 40 mol%.

[0128] 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.

[0129] The lithium manganese oxide represented by chemical formula 1 or 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, 15% or less, or 10% or less. In other cases, the lithium manganese oxide represented by chemical formula 1 or chemical formula 2 may have a cobalt-free composition.

[0130] 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.

[0131] On the other hand, lithium-rich lithium manganese oxides represented by chemical formula 1 or chemical formula 2 are oxides of a phase belonging to the C2 / m space group represented by Li2MnO3 (hereinafter referred to as the "C2 / m phase") and Li u Ni w Co x Mn y M2 z The lithium manganese oxide exists as a composite oxide in which an oxide of a phase belonging to the R-3m space group represented by O2 (hereinafter referred to as the "R-3m phase") is dissolved. For example, the lithium manganese oxide may exist in a state in which an oxide of the C2 / m phase and an oxide of the R-3m phase form a solid solution.

[0132] 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.

[0133] 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 the 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.

[0134] In the lithium manganese oxide represented by the chemical formula 2, if r exceeds 0.7, the proportion of Li2MnO3, which is an oxide of the phase belonging to the space group in the lithium manganese oxide, becomes excessively large. This can lead to an increase in the irreversible capacity and resistance of the positive electrode active material, potentially reducing the discharge capacity. In other words, in order to sufficiently activate the oxide of the phase belonging to the C2 / m space group, which has relatively high resistance in the lithium manganese oxide, and improve surface kinetics, it is preferable that the oxide of the phase belonging to the R-3m space group be present in a predetermined proportion or higher. The ratio of the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group in the lithium manganese oxide can be calculated through the composition ratio of lithium and transition metal present in the lithium manganese oxide.

[0135] In one embodiment, a coating layer may be present on at least a portion of the surface of the lithium manganese oxide. The coating layer can suppress or mitigate the elution of transition metals from the lithium manganese oxide. Furthermore, when an ion-conductive coating layer is formed on the surface of the lithium manganese oxide, the charge transfer and / or diffusivity (i.e., surface kinetics) of lithium ions can be improved.

[0136] The coating layer may exist as an island on a portion of the surface of the lithium manganese oxide. Alternatively, the coating 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.

[0137] The coating layer may exist on the surface of the lithium manganese oxide as a film having an average thickness of 1 nm to 300 nm. The thickness of the coating layer can be measured by EDX analysis of the coating elements based on a cross-sectional SEM image of the lithium manganese oxide. The existence of the coating layer as a film must be distinguished from the oxide constituting the coating layer being dispersed and attached to the surface of the lithium manganese oxide in the form of individual particles.

[0138] If the average thickness of the coating layer is less than 1 nm, the surface modification effect of the lithium manganese oxide may be insufficient. If the average thickness of the coating layer is thicker than 300 nm, the surface kinetics of the lithium manganese oxide may decrease or its electrical conductivity may become low.

[0139] The coating layer may contain an oxide represented by the following chemical formula 3. [Chemical formula 3] Li g M3hO i In the aforementioned chemical formula 3, M3 is at least one selected from Ni, Mn, Co, Al, B, Nb, Si, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Ce, Gd, and Nd, with 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13, excluding the case where h and i are both 0. In the above chemical formula 3, g, h, and i represent numbers determined from the stoichiometric ratio by the valence (oxidation number) of M3. For example, g, h, and i can be appropriately selected from the ranges 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13, respectively.

[0140] A non-limiting example of the oxide represented by the chemical formula 3 is Li g Zr h O i Li g Ti h O i, Li g Ni h O i , Li g Nb h O i , Li g Co h O i , Li g Si h O i , Li g Al h O i , Li g B h , Co h O i , Mn h O i , Al h O i , Si h O i , Zr h O i , Ti h O i , B h O i and others.

[0141] (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.

[0142] Therefore, a specific description of the lithium manganese-based oxide is omitted, and hereinafter, only the remaining configurations not described above will be described. Also, hereinafter, for convenience, the lithium manganese-based oxide described above is referred to as a positive electrode active material.

[0143] 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, nonwoven fabric, etc.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] In another embodiment, 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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, conductive materials such as 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, conductive 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 and its derivatives may be used.

[0161] 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.

[0162] In another 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 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.

[0163] 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.

[0164] 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.

[0165] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0166] 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. 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.

[0167] 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.

[0168] 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.)

[0169] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0170] 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.

[0171] The above-mentioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Further, the solid electrolyte may be partially included within the positive electrode active material layer independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the negative electrode active material layer independently of the solid electrolyte layer.

[0172] 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.

[0173] 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).

[0174] 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.

[0175] 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.

[0176] 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. [Examples]

[0177] 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.

[0178] (Manufacturing Example 1: Manufacturing of Cathode Active Material) (Comparative Example 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(aq) and NH4OH(aq), was added to the reactor while stirring. The reactor pH was maintained at 10.0 and the temperature at 50°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 precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain an average particle size (D 50 ) is 12.0 μm Ni 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0179] (b) First heat treatment Ni obtained in step (a) above 0.4 Mn 0.6 The (OH)2 precursor was heat-treated in an air-filled furnace at 550°C for 5 hours, followed by furnace cooling to obtain the oxide-state precursor.

[0180] (c) Second heat treatment The oxide precursor obtained in step (b) above was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.25), which is a lithium raw material, to prepare a mixture.

[0181] Next, the mixture was heat-treated in an O2 atmosphere furnace at 850°C for 8 hours, followed by furnace cooling to obtain a positive electrode active material containing lithium manganese oxide.

[0182] (Comparative Example 2) A cathode active material containing lithium manganese oxide was produced in the same manner as in Comparative Example 1, except that the pH inside the reactor was maintained at 9.5 in step (a) and the second heat treatment temperature was set to 900°C in step (c).

[0183] (Comparative Example 3) A cathode active material containing a lithium manganese oxide was produced in the same manner as in Comparative Example 1, except that the pH inside the reactor was maintained at 9.0 in step (a) and the second heat treatment temperature was set to 900°C in step (c).

[0184] (Comparative Example 4) In step (a) above, the reactor pH was maintained at 8.5 and the temperature at 60°C, and the precursor synthesis reaction was carried out while simultaneously introducing a mixed gas of N2 gas and air (N2 (vol%):air (vol%) = 8:2) into the reactor. Except that the second heat treatment temperature in step (c) above was set to 900°C, a cathode active material containing lithium manganese oxide was produced in the same manner as in Comparative Example 1.

[0185] (Comparative Example 5) In step (a) above, the reactor pH was maintained at 9.0 and the temperature at 60°C, and the precursor synthesis reaction was carried out while simultaneously introducing a mixed gas of N2 gas and air (N2 (vol%):air (vol%) = 9:1) into the reactor. Except that the second heat treatment temperature in step (c) above was set to 650°C, a cathode active material containing lithium manganese oxide was produced in the same manner as in Comparative Example 1.

[0186] (Example 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(aq) and NH4OH(aq), was added to the reactor while stirring. The reactor pH was maintained at 9.0 and the temperature at 60°C, and the precursor synthesis reaction was carried out for 24 hours while simultaneously adding a mixed gas of N2 gas and air (N2(vol%):air(vol%)=9:1) to the reactor. After the reaction was complete, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain an average particle size (D 50 ) is 12.0 μm Ni 0.4 Mn 0.6 (OH)2 precursor was obtained.

[0187] (b) First heat treatment Ni obtained in step (a) above 0.4 Mn 0.6 The (OH)2 precursor was heat-treated in an air-filled furnace at 550°C for 5 hours, followed by furnace cooling to obtain the oxide-state precursor.

[0188] (c) Second heat treatment The oxide precursor obtained in step (b) above was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.25), which is a lithium raw material, to prepare a mixture.

[0189] Next, the mixture was heat-treated in an O2 atmosphere furnace at 900°C for 8 hours, followed by furnace cooling to obtain a positive electrode active material containing lithium manganese oxide.

[0190] (Example 2) (a) Production of precursors An aqueous solution of NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O mixed in a molar ratio of 40:2:58, along with NaOH(aq) and NH4OH(aq), was added to the reactor while stirring. The reactor pH was maintained at 9.0 and the temperature at 60°C, and the precursor synthesis reaction was carried out for 24 hours while simultaneously adding a mixed gas of N2 gas and air (N2(vol%):air(vol%)=9:1) to the reactor. After the reaction was complete, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain an average particle size (D 50 ) is 12.0 μm Ni 0.4 Co 0.02 Mn 0.58 (OH)2 precursor was obtained.

[0191] (b) First heat treatment Ni obtained in step (a) above 0.4 Co 0.02 Mn 0.58 The (OH)2 precursor was heat-treated in an air-filled furnace at 550°C for 5 hours, followed by furnace cooling to obtain the oxide-state precursor.

[0192] (c) Second heat treatment The oxide precursor obtained in step (b) above was mixed with LiOH (Li / (Li-excluded metal) molar ratio = 1.22), which is a lithium raw material, to prepare a mixture.

[0193] Next, the mixture was heat-treated in an O2 atmosphere furnace at 750°C for 8 hours, followed by furnace cooling to obtain a positive electrode active material containing lithium manganese oxide.

[0194] (Example 3) A cathode active material containing lithium manganese oxide was produced in the same manner as in Example 2, except that the second heat treatment temperature in step (c) was set to 850°C.

[0195] (Example 4) A cathode active material containing a lithium manganese oxide was produced in the same manner as in Example 2, except that the second heat treatment temperature in step (c) was set to 900°C.

[0196] (Example 5) In Example 3, the lithium manganese oxide produced in step (c) was mixed with H3BO3 (weighed so that the boron content relative to the total transition metal elements of the lithium manganese oxide was 1.2 mol%), and then heat-treated in an O2 atmosphere furnace at 300°C for 8 hours to obtain a positive electrode active material in which a boron-containing coating layer was formed on the surface of the lithium manganese oxide.

[0197] (Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries (Half-Cells)) A cathode slurry was prepared by dispersing 90 wt% each of the cathode active materials produced according to Production Example 1, 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.

[0198] 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.

[0199] (Experimental Example 1: Particle Structure Analysis of Cathode Active Material) (1) Surface SEM image analysis of lithium manganese oxide (secondary particles) After selecting a total of 20 lithium manganese oxide secondary particle forms from the positive electrode active material produced in Production Example 1, surface SEM images of the secondary particles were obtained by scanning electron microscopy. Using an image analysis program (Image-Pro image analysis software for SEM), 30% (based on the number of primary particles) of the total primary particles exposed on the surface of the secondary particles observed from the surface SEM images were randomly selected. For the selected primary particles, the length of the major axis of the surface shape of the primary particle, the length of the minor axis of the surface shape of the primary particle, the ratio of the length of the major axis to the minor axis (length of major axis / length of minor axis), and the ratio of the length of the minor axis to the major axis (length of minor axis / length of major axis) were measured, and the average values ​​of these were calculated.

[0200] The average values ​​obtained from the above analysis are shown in Table 1.

[0201] (2) Cross-sectional SEM image analysis of lithium manganese oxide (secondary particles) After selecting a total of 20 secondary particle-shaped lithium manganese oxides from the positive electrode active material manufactured in Production Example 1, the lithium manganese oxide was cross-sectioned using an ion-milling device, and then photographed with a scanning electron microscope to obtain a cross-sectional SEM image. The radius (about 6 μm) of the lithium manganese oxide measured from the cross-sectional SEM image of the lithium manganese oxide is referred to as r. In the cross-sectional SEM image, a region where the distance (d) from the center of the lithium manganese oxide to the lithium manganese oxide satisfies (2 / 3)r < d is defined as the shell part. After randomly selecting 20 primary particles from all the primary particles present in the shell part from the cross-sectional SEM image using an image analysis program (Image-Pro image analysis software for SEM), the length of the short axis (thickness) of the selected primary particles and the angle between the long axis of the primary particles and the line connecting the center and surface of the secondary particles were measured, and the average values of these were calculated. For reference, the radius of the lithium manganese oxide was calculated as the arithmetic mean value of the length of the long axis and the length of the short axis of the lithium manganese oxide measured from the cross-sectional SEM image. The average value of the angle between the long axis of the primary particles present in the shell part and the line connecting the center and surface of the secondary particles was calculated as the average value of the absolute values.

[0202] The average values obtained from the above analysis are shown in Table 2.

[0203] (3) BET specific surface area analysis of the positive electrode active material In addition, the BET specific surface area for each of the positive electrode active materials manufactured in Production Example 1 was calculated through the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.

[0204] The measurement results are shown in Table 3.

[0205]

Table 1

[0206] [Table 2]

[0207] Unlike Examples 1 to 5, the primary particles present in the shell portion of the lithium manganese oxide (secondary particles) in Comparative Examples 1 and 4 did not exhibit the predetermined orientation and aggregated randomly, making it impossible to calculate the average angle between the long axis of the primary particles and the line connecting the center and surface of the secondary particles.

[0208] [Table 3]

[0209] (Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries (half-cells)) For lithium secondary batteries (half-cells) manufactured in Manufacturing Example 2, the charge capacity, discharge capacity, and rate characteristics (discharge capacity ratio; rate capability (C-rate)) were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 2.0V to 4.6V and a discharge rate of 0.1C to 2.0C.

[0210] The measurement results are shown in Table 4 below.

[0211] [Table 4]

[0212] Comparing the results of Examples 1 to 5, Comparative Example 1, and Comparative Example 2, it can be confirmed that when an oriented structure is formed in at least a portion of the lithium manganese oxide (for example, the shell portion of the secondary particles) in which the long axes of the primary particles are aligned from the center of the secondary particles toward the surface, the surface kinetic properties of the lithium manganese oxide are improved, thereby contributing to improvements in charge / discharge capacity and rate characteristics.

[0213] Furthermore, comparing the results of Examples 1 to 5 and Comparative Examples 1 to 5, it can be seen that when the primary particles present on the surface of the lithium manganese oxide have an appropriate level of thin plate-like, thin rod-like, or fine needle-like shape, the porosity within the lithium manganese oxide is adjusted, and an appropriate level of BET specific surface area can be achieved. This improves the surface kinetic properties of the lithium manganese oxide, which in turn contributes to improvements in charge / discharge capacity and rate characteristics.

[0214] Although embodiments of the present invention have been described above, any 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. It 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 exist as a solid solution. The lithium manganese oxide has a secondary particle form in which multiple primary particles are aggregated, A positive electrode active material having an oriented structure in which at least a portion of the secondary particles have the long axes of the primary particles aligned from the center of the secondary particles toward the surface.

2. The positive electrode active material according to claim 1, wherein the surface shape of the primary particles exposed on the surface of the secondary particles, as observed from a surface SEM image of the secondary particles, has a long axis and a short axis.

3. The positive electrode active material according to claim 2, wherein the average value of the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is 1.5 or more and 9.0 or less.

4. The positive electrode active material according to claim 1, wherein the average value of the ratio of the length of the short axis to the length of the long axis (length of the short axis / length of the long axis) of the surface shape of the primary particles exposed on the surface of the secondary particles is 0.2 or more and 0.5 or less.

5. The positive electrode active material according to claim 1, wherein the average length of the major axis of the surface shape of the primary particles exposed on the surface of the secondary particles is 150 nm or more and 350 nm or less.

6. The positive electrode active material according to claim 1, wherein the average value of the length of the short axis of the surface shape of the primary particles exposed on the surface of the secondary particles is 30 nm or more and 130 nm or less.

7. The positive electrode active material according to claim 1, wherein the long axis of the primary particle exhibiting the oriented structure is formed to have an angle of within ±70° from a line connecting the center and surface of the secondary particle.

8. The positive electrode active material according to claim 1, wherein the average length of the short axis of the primary particles having the oriented structure, as observed from a cross-sectional SEM image of the secondary particles, is 30 nm or more and 200 nm or less.

9. The secondary particles consist of a core portion formed by the random aggregation of the primary particles, The positive electrode active material according to claim 1, wherein the core portion is separated from the shell portion in which the primary particles exhibit the orientation structure.

10. The positive electrode active material according to claim 9, wherein the proportion of primary particles having the oriented structure among the total primary particles present in the shell portion is 50% or more.

11. The positive electrode active material according to claim 9, wherein the proportion of primary particles having the oriented structure among the total primary particles present in the core is less than 50%.

12. The BET specific surface area measured by the nitrogen adsorption method is 1.0 m². ２ / g to 3.5m ２ The positive electrode active material according to claim 1, wherein the value is / g.

13. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide is a composite oxide of lithium, nickel, and manganese.

14. The positive electrode active material according to claim 13, wherein the lithium manganese oxide further comprises one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

15. The lithium manganese oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1. [Chemical formula 1] Li(Li ａ Ni ｂ Co ｃ Mn ｄ M1 ｅ )O ２－ｆ X ｆ [Here, in the chemical formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X is a halogen capable of substituting some of the oxygen present in the lithium manganese oxide, 0 < a ≤ 0.7, 0 ≤ b < 0.5, 0 ≤ c ≤ 0.2, 0.5 ≤ d < 0.8, 0 < e ≤ 0.1, 0 ≤ f ≤ 0.

1.

16. The lithium manganese oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 2. [Chemical formula 2] rLi ２ MnO ３－ｐ X ｐ ・(1-r)- ｕ Ni ｗ Co ｘ Mn ｙ M2 ｚ O ２－ｐ′ X′ ｐ′ [Here, in the chemical formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X and X' are halogens capable of substituting some of the oxygen present in the lithium manganese oxide, 0.2 < r ≤ 0.7, 0 < u ≤ 1, 0 ≤ w ≤ 1, 0 ≤ x ≤ 0.2, 0.3 < y < 1, 0 < z ≤ 0.1, 0 ≤ p ≤ 0.1, 0 ≤ p' ≤ 0.

1.

17. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 16.

18. A lithium secondary battery comprising the positive electrode described in claim 17.

Images