Cathode active material and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material and a lithium secondary battery comprising same and, more specifically, to a cathode active material and a lithium secondary battery comprising same, the cathode active material comprising lithium and manganese-excess lithium manganese-based oxides that have an improved energy density per unit volume and thus have improved electrochemical properties.

Description

Cathode active material and lithium secondary battery containing the same

[0001] The present invention relates to a cathode active material and a lithium secondary battery including the same, and more specifically, to a cathode active material including a lithium manganese oxide having an excess of lithium and manganese and having improved energy density per unit volume, thereby having improved electrochemical properties, and a lithium secondary battery including the same.

[0002]

[0003] Batteries store electricity by using materials capable of electrochemical reactions at the anode and cathode. A representative example of such batteries is the lithium secondary battery, which stores electrical energy through the difference in chemical potential when lithium ions intercalate / deintercalate between the anode and cathode.

[0004] The above lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and negative electrode active material, and filling an organic electrolyte or polymer electrolyte between the positive electrode and negative electrode.

[0005] A representative material used as a positive electrode active material for lithium secondary batteries is a lithium composite oxide. The lithium composite oxide includes LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or oxides in which Ni, Co, Mn, or Al are composited.

[0006] Among the above-mentioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency, but it has the disadvantage of limited price competitiveness due to its high price due to the limited resources of cobalt used as a raw material.

[0007] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they have the problems of small capacity and poor high-temperature characteristics. In addition, LiNiO2-based cathode active materials exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to the problem of cation mixing between Li and transition metals, and as a result, there are significant problems with rate characteristics.

[0008] In addition, depending on the degree of intensification of this cation mixing, a large amount of Li byproducts is generated. The Li byproducts mostly include LiOH and Li2CO3, and can cause gelation during the manufacture of the positive electrode paste or cause gas generation through repeated charge / discharge after the electrode manufacture. In addition, the residual Li2CO3 among the Li byproducts increases the swelling phenomenon of the cell, which acts as a cause of deterioration of the life characteristics.

[0009] Various candidate materials are being proposed to complement the shortcomings of these existing positive electrode active materials.

[0010] For example, research is being conducted to use lithium-over-lithiated lithium manganese oxides, which contain an excess of Mn among transition metals and have a lithium molar ratio greater than the sum of the molar ratios of other metal elements, as positive electrode active materials for lithium secondary batteries. Such lithium-over-lithiated lithium manganese oxides are also referred to as lithium-over-lithiated layered oxides (OLO).

[0011] Although the above OLO theoretically has the advantage of being able to exhibit high capacity under a high-voltage operating environment, in reality, due to the excessive amount of Mn contained in the OLO, the electrical conductivity is relatively low, and thus, the rate characteristics of a lithium secondary battery using the OLO are low, which is a disadvantage. In this way, when the rate characteristics are low, the charge / discharge capacity and life efficiency (cycle capacity retention) of the lithium secondary battery decrease during cycling.

[0012] In addition, in general, OLO has a disadvantage of lower energy density per unit volume compared to high-Ni type cathode active materials such as conventional commercialized ternary lithium composite oxides of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0013]

[0014] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, and accordingly, demand for cathode active materials used in lithium secondary batteries is also continuously increasing.

[0015] For example, in the past, lithium secondary batteries using lithium iron phosphate (LFP) were mainly used from the perspective of ensuring safety, but recently, the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP, is expanding.

[0016] Furthermore, nickel-based lithium composite oxides, which are currently primarily used as cathode active materials in high-capacity lithium secondary batteries, essentially require ternary metal elements such as nickel, cobalt, and manganese, or nickel, cobalt, and aluminum. However, cobalt is not only unstable in supply and demand but is also excessively expensive compared to other raw materials. Therefore, a new cathode active material with a reduced or eliminated cobalt content is needed.

[0017] Considering these various circumstances, lithium-excessive lithium manganese oxides can meet the aforementioned market expectations, but they still have limitations in terms of electrochemical properties and stability as replacements for high-Ni type cathode active materials such as commercialized nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary lithium composite oxides.

[0018] For example, as mentioned above, OLO has the disadvantage of low energy density per unit volume due to the composition of the material (containing excess lithium) and structural characteristics (high porosity within the particles).

[0019] Therefore, to increase the limited volumetric energy density of OLO, the use of cathode active materials with a bimodal particle size distribution can be considered. However, since the particles constituting the OLO precursor typically grow into thick, plate-like particles, increasing the size of the secondary particles increases the internal density, but this can also lead to performance degradation due to low conductivity.

[0020] However, the inventors of the present invention have confirmed that the shape of the primary particles constituting the lithium manganese oxide can be controlled according to the synthesis conditions of the precursor of the lithium manganese oxide, thereby improving the capacity characteristics and rate characteristics of a cathode active material including secondary particles of relatively large size (e.g., neutral and / or anti-neutral particles having an average particle diameter of 5 μm or more).

[0021] Accordingly, the present invention aims to provide a cathode active material including secondary particles (e.g., neutral particles and / or antiparticles having an average particle diameter of 5 μm or more) having a controlled shape of primary particles constituting the lithium manganese oxide in order to improve the low energy density per unit volume of the lithium-excessive lithium manganese oxide.

[0022] In addition, another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined herein.

[0023] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0024]

[0025] According to one aspect of the present invention for solving the above-described technical problem, a cathode active material is provided, which includes a lithium manganese oxide in which a phase belonging to a C2 / m space group and a phase belonging to an R-3m space group are employed.

[0026] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions exist as a single phase of a phase belonging to the R-3m space group, whereas the lithium-rich lithium manganese oxide defined herein is characterized by 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.

[0027] 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 arranged in a surface direction from the center of the secondary particles.

[0028] The major axis of the primary particles exhibiting the above-mentioned orientation structure can be formed to have an angle of within ±70°, within ±60°, within ±40°, within ±20°, or within ±10° from a line connecting the center and surface of the secondary particle.

[0029] 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 in which the primary particles exhibit the oriented structure on the outside of the core portion.

[0030] Since the primary particles have an orientation structure in which the long axes of the primary particles are arranged in the direction of the surface from the center of the secondary particles within the shell, the proportion of the primary particles having the orientation structure among all the primary particles present in the shell may be 50% or more, 60%, 70%, 80%, 85%, or 90% or more.

[0031] Since the primary particles within the core portion do not exhibit a predetermined orientation but rather randomly aggregate, the proportion of the primary particles having the orientation structure among all primary particles present in the core portion may be less than 50%.

[0032] Additionally, the shapes of the primary particles present in the shell portion and the primary particles present in the core portion may be different.

[0033] For example, the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the primary particles present in the core portion, as observed from a cross-sectional SEM image of the secondary particles, may be smaller than the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the primary particles present in the shell portion.

[0034] In one embodiment, the primary particles present in the shell portion may have a thin plate shape, a thin rod shape, or a fine needle shape.

[0035] Accordingly, the surface shape of the primary particles exposed on the surface of the secondary particles observed from the surface SEM image of the secondary particles may have a long axis and a short axis.

[0036] The average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) 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.

[0037] The average value of the ratio of the short axis length to the long axis length (short axis length / long axis length) 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.

[0038] The average value of the major axis length of the surface shape of the primary particles exposed on the surface of the secondary particles may be 150 nm or more and 350 nm or less, 160 nm or more and 320 nm or less, 170 nm or more and 290 nm or less, 180 nm or more and 270 nm or less, 190 nm or more and 260 nm or less, or 192 nm or more and 250 nm or less.

[0039] The average value of the short axis length of the surface shape of the primary particles exposed on the surface of the secondary particles may be 30 nm or more and 130 nm or less, 35 nm or more and 120 nm or less, 40 nm or more and 110 nm or less, or 47 nm or more and 105 nm or less.

[0040] In one embodiment, the lithium manganese oxide is a composite oxide of lithium, nickel, and manganese, and the lithium manganese oxide may further include one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0041] The lithium manganese oxide defined herein may be represented by the following chemical formula 1 or chemical formula 2.

[0042] [Chemical Formula 1]

[0043] Li(Li a Ni b Co c Mn d M1 e )O 2-f X f

[0044] In the above chemical formula 1,

[0045] 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,

[0046] X is a halogen capable of replacing some of the oxygen present in the lithium manganese oxide,

[0047] 0 <a≤0.7, 0≤b<0.5, 0≤c≤0.2, 0.5≤d<0.8, 0<e≤0.1, 0≤f≤0.1이다.

[0048] [Chemical Formula 2]

[0049] rLi2MnO 3-p X p ·(1-r)Li u Ni w Co x Mn y M2 z O 2-p' X' p'

[0050] In the above chemical formula 2,

[0051] 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,

[0052] X and X' are halogens capable of replacing some of the oxygen present in the lithium manganese oxide,

[0053] 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'≤0.1이다.

[0054] In addition, according to another aspect of the present invention, a positive electrode including the positive electrode active material described above is provided.

[0055] In addition, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

[0056]

[0057] According to the present invention, it is possible to improve the limitations of existing lithium-rich lithium manganese oxides, which have several disadvantages in terms of electrochemical properties and / or stability, compared to commercially available ternary lithium composite oxides of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions.

[0058] Specifically, according to the present invention, the shape of the primary particles constituting the lithium manganese oxide can be controlled according to the synthesis conditions of the precursor of the lithium manganese oxide, thereby improving the capacity characteristics and rate characteristics of the positive electrode active material including secondary particles having a relatively large size (e.g., neutral and / or anti-neutral particles having an average particle diameter of 5 μm or more).

[0059] In particular, the lithium manganese oxide according to the present invention can improve the capacity characteristics and rate characteristics of a lithium secondary battery using the lithium manganese oxide as a positive electrode active material by making the primary particles existing on the surface of the secondary particles have a thin plate shape, a thin rod shape, or a fine needle shape. In addition, when the lithium manganese oxide is used as a neutral and / or anti-neutral and mixed with lithium manganese oxide as a small particle to exhibit a bimodal or trimodal particle size distribution, the low energy density per unit volume of the lithium secondary battery can be further improved.

[0060] In addition, the lithium manganese oxide according to the present invention can improve the surface kinetic characteristics of the lithium manganese oxide since it has an oriented structure in which the long axes of the primary particles present on the surface of the secondary particles are arranged in the direction of the surface from the center of the secondary particles.

[0061] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0062]

[0063] To facilitate a better understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise specified by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0064]

[0065] Hereinafter, a cathode active material including a lithium-excessive lithium manganese oxide according to some embodiments of the present invention and a lithium secondary battery including the cathode active material will be described in more detail.

[0066]

[0067] positive electrode active material

[0068] According to one aspect of the present invention, a cathode active material is provided, which includes a lithium manganese oxide in which a phase belonging to a C2 / m space group and a phase belonging to an R-3m space group are employed.

[0069] The phase belonging to the C2 / m space group and the phase belonging to the R-3m space group can be distinguished not only through the composition constituting each phase, but also through the specific peak for each phase during XRD analysis. For example, the specific peak for the phase belonging to the C2 / m space group can appear in the region of 2θ=20.8±1°, and the specific peak for the phase belonging to the R-3m space group can appear in the region of 2θ=18.6±1°.

[0070] The above 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 dissolved, and a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group coexist within the lithium manganese oxide. In addition, the lithium manganese oxide is different from a composite oxide having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn2O4 or an oxide having a similar composition).

[0071] The lithium manganese oxide may be a composite oxide of lithium, nickel, and manganese. In addition, the lithium manganese oxide may further include one or more elements selected from alkali metals, alkaline earth metals, transition metals other than nickel and manganese, post-transition metals, and metalloids.

[0072] The lithium manganese oxide is also referred to as an overlithiated layered oxide (OLO) because the number of moles of lithium present in the lithium manganese oxide is greater than the sum of the number of moles of other transition metals (generally, when the molar ratio of lithium to all metal elements other than lithium in the lithium manganese oxide (Li / (Metal molar ratio)) is greater than 1).

[0073] In addition, the lithium manganese oxide is also referred to as a lithium and manganese-excessive layered oxide because the manganese content present in the lithium manganese oxide is greater than the content of other transition metals.

[0074] In general, considering that the content of manganese among the total metal elements excluding lithium in the commercialized nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary lithium composite oxides is 20 mol% or less, the lithium manganese oxide has a relatively high proportion of manganese among 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 the commercialized ternary lithium composite oxides.

[0075] In addition, considering that the commercialized nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary lithium composite oxides have a nickel content of 60 mol% or more (80 mol% or more for the high-Ni type) among all metal elements excluding lithium, the lithium manganese oxides have a relatively low nickel content among all metal elements (e.g., less than 50 mol%, 48 mol% or less, 46 mol% or less, 45 mol% or less, 44 mol% or less, 42 mol% or less, or 40 mol% or less) compared to the commercialized ternary lithium composite oxides.

[0076] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese oxide defined herein 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) has a value close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese oxide defined herein is greater than 1, and preferably has a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0077] Therefore, in the present invention, the lithium manganese oxide may be defined as a composite oxide having a manganese content of 50 mol% or more among all metal elements excluding lithium, or may be defined as a composite oxide having a manganese content of 50 mol% or more among all metal elements excluding lithium and a nickel content of less than 50 mol%.

[0078] In addition, the lithium manganese oxide in the present invention may be defined as a composite oxide in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or has a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, and the content of manganese among all metal elements excluding lithium is 50 mol% or more, or a composite oxide in which the molar ratio of lithium to all metal elements excluding lithium is greater than 1, or has a value of 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, and the content of manganese among all metal elements excluding lithium is 50 mol% or more, and the content of nickel is less than 50 mol%.

[0079] Despite the differences in composition described above, the lithium manganese oxide can also function as a composite metal oxide capable of intercalation / deintercalation of lithium ions.

[0080] The lithium manganese oxide included in the cathode active material defined herein may exist as an aggregate of a plurality of primary particles. When the lithium manganese oxide exists as an aggregate of a plurality of primary particles, the lithium manganese oxide may be referred to as a secondary particle.

[0081] The above primary particle refers to a particle unit that has no apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0082] The primary particles constituting the lithium manganese-based oxide defined herein 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. At this time, the average particle size of the primary particles may be an average value of the length in the major axis direction and the length in the minor axis direction of the primary particles ([major axis length + minor axis length] / 2). The average particle size of the primary particles may be calculated as an average value of the particle sizes of all primary particles observed from a surface SEM image and / or a cross-sectional SEM image of the lithium manganese-based oxide.

[0083] When the average particle size of the above primary particles is smaller than 0.05 μm, the specific surface area of ​​the lithium manganese oxide (secondary particle) composed of the above primary particles is relatively large. In this case, the possibility of a side reaction between the lithium manganese oxide and the electrolyte during storage or operation of the lithium secondary battery may increase.

[0084] On the other hand, when the average particle diameter of the primary particles is greater than 5.0 μm, the growth of the primary particles is excessively induced, and thus the diffusion path of lithium ions within the primary particles also becomes longer. When the diffusion path of lithium ions within the primary particles is excessively long, the mobility of lithium ions within the primary particles and the diffusion of lithium ions via the primary particles are reduced, which causes the resistance of the lithium manganese oxide (secondary particle) composed of the primary particles to increase.

[0085] Accordingly, in order to reduce the specific surface area of ​​the lithium manganese oxide and at the same time prevent the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles from deteriorating, the average particle diameter 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.

[0086] The average particle diameter of the above secondary particles (D 50 ) may 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.

[0087] The average particle diameter of the above secondary particles (D 50 ) may vary depending on the number of the primary particles constituting the secondary particles. The average particle diameter of the secondary particles can be measured using a laser diffraction method. For example, after dispersing the secondary particles in a dispersion medium, the secondary particles are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and then a volume cumulative particle size distribution graph is obtained, and then the particle size corresponding to 50% of the volume cumulative amount is measured.

[0088] 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 median volume-based particle size determined by laser diffraction.

[0089] When the lithium manganese oxide defined herein is used as a counterpart of a positive electrode active material exhibiting a bimodal type particle size distribution, the average particle diameter (D) of the secondary particles 50 ) may 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.

[0090] Meanwhile, when the lithium manganese oxide defined herein is used as a neutral particle (particle having an average particle diameter between small and large particles) of a positive electrode active material exhibiting a trimodal type particle size distribution, the average particle diameter (D) of the secondary particles 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 herein is used as a counterpart of a positive electrode active material exhibiting a trimodal type particle size distribution, the average particle diameter (D) of the secondary particles 50 ) may be 8.0 μm to 24.0 μm, 8.0 μm to 20.0 μm, or 10.0 μm to 15.0 μm.

[0091] In addition, when the cathode active material defined herein exhibits a particle size distribution of a bimodal type or trimodal type, the average particle diameter of the lithium manganese oxide provided as small particles may be 1.0 μm to 8.0 μm, 2.0 μm to 6.0 μm, or 3.0 μm to 5.0 μm.

[0092] In general, when having the same composition as the lithium manganese oxide, the primary particles constituting the secondary particles have a rod shape, an oval shape, and / or an irregular shape, and unless specifically intended in the manufacturing process, primary particles of various shapes may exist within the same secondary particle. In addition, although the conventional lithium manganese oxide may also include plate-shaped primary particles, since most of the primary particles have a thick plate shape, the conductivity of lithium ions is low, and thus the positive electrode active material including the lithium manganese oxide has a problem in that the capacity characteristics and rate characteristics are low.

[0093] On the other hand, at least some of the primary particles constituting the lithium manganese oxide defined herein are characterized by having a thin plate shape, a thin rod shape, and / or a fine needle shape.

[0094] 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 observed from the surface SEM image of the secondary particles and the cross-sectional shape of the primary particles observed from the cross-sectional SEM image of the secondary particles.

[0095] In one embodiment, the surface shape of the primary particles exposed on the surface of the secondary particle observed from the surface SEM image of the secondary particle may have a long axis and a short axis. The surface of the secondary particle corresponds to a set of exposed faces of the primary particles located at the outermost edge of the secondary particle.

[0096] The fact that the surface shapes of the primary particles exposed on the surface of the secondary particles have a long axis and a short axis means that at least the primary particles exposed on the surface of the secondary particles are likely to have a thin plate shape, a thin rod shape, and / or a fine needle shape.

[0097] In particular, when the long axes of the primary particles exposed on the surface of the secondary particles have an oriented structure arranged in the direction of the surface from the center of the secondary particles, the surface shape observed from the surface SEM image of the secondary particles is likely to have a thin plate shape, a thin rod shape, and / or a fine needle shape.

[0098] Additionally, the cross-sectional shape of the primary particles observed from the cross-sectional SEM image of the secondary particles may have a long axis and a short axis.

[0099] If the surface shape of the primary particles exposed on the surface of the secondary particles observed from the 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 observed from the cross-sectional SEM image of the secondary particles has a long axis and a short axis, at least the possibility that the primary particles exposed on the surface of the secondary particles have a thin plate shape, a thin rod shape, and / or a fine needle shape may increase.

[0100] However, even if the surface shape of the primary particles exposed on the surface of the secondary particles observed from the surface SEM image of the secondary particles has a long axis and a short axis, if the ratio of the long axis length to the short axis length (long axis length / short axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles is small (for example, close to 1), the primary particles may have a thick plate-like or thick rod-like shape.

[0101] Accordingly, the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) 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.

[0102] When the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 1.5, the primary particles exposed on the surface of the secondary particles are less likely to have a thin plate shape, a thin rod shape, and / or a fine needle shape. In addition, when the primary particles are formed to be excessively thick or have an excessively small size, the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles may be less than 1.5. When the primary particles are formed to be excessively thick, the porosity in the surface of the secondary particles may decrease, and the surface kinetic may decrease, and when the primary particles have an excessively small size, the specific surface area may increase, which may increase the side reaction between the lithium manganese oxide and the electrolyte.

[0103] On the other hand, if the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 9.0, there is a concern that as the number of primary particles having an excessively thin shape increases, the porosity within the secondary particles may increase, thereby decreasing the energy density per unit volume or increasing the specific surface area, thereby increasing the side reaction between the lithium manganese oxide and the electrolyte.

[0104] In addition, so that the primary particles exposed on the surface of the secondary particles can have a thin plate shape, a thin rod shape, and / or a fine needle shape, the average value of the ratio of the short axis length to the long axis length (short axis length / long axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles can 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.

[0105] If the average value of the ratio of the short axis length to the long axis length (short axis length / long axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles is less than 0.2, there is a concern that as the number of primary particles having an excessively thin shape increases, the porosity within the secondary particles may increase, thereby decreasing the energy density per unit volume or increasing the specific surface area, thereby increasing the side reaction between the lithium manganese oxide and the electrolyte.

[0106] On the other hand, when the average value of the ratio of the short axis length to the long axis length (short axis length / long axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 0.5, the primary particles exposed on the surface of the secondary particles are less likely to have a thin plate shape, a thin rod shape, and / or a fine needle shape. In addition, when the primary particles are formed to be excessively thick or have an excessively small size, the average value of the ratio of the short axis length to the long axis length (short axis length / long axis length) of the surface shape of the primary particles exposed on the surface of the secondary particles may be greater than 0.5. When the primary particles are formed to be excessively thick, the porosity in the surface of the secondary particles may decrease, and the surface kinetic may decrease, and when the primary particles have an excessively small size, the specific surface area may increase, which may increase the side reaction between the lithium manganese oxide and the electrolyte.

[0107] The average value of the major axis length of the surface shape of the primary particles exposed on the surface of the secondary particles may be 150 nm or more and 350 nm or less, 160 nm or more and 320 nm or less, 170 nm or more and 290 nm or less, 180 nm or more and 270 nm or less, 190 nm or more and 260 nm or less, or 192 nm or more and 250 nm or less.

[0108] When the average value of the major axis length 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 may be excessively small, making it difficult to reduce side reactions between the lithium manganese oxide and the electrolyte.

[0109] On the other hand, when the average value of the major axis length of the surface shape of the primary particles exposed on the surface of the secondary particles is greater than 350 nm, the surface kinetics such as lithium ion conductivity may be reduced as the size of the primary particles exposed on the surface of the secondary particles becomes excessively large.

[0110] The average value of the short axis length of the surface shape of the primary particles exposed on the surface of the secondary particles may be 30 nm or more and 130 nm or less, 35 nm or more and 120 nm or less, 40 nm or more and 110 nm or less, or 47 nm or more and 105 nm or less.

[0111] When the average value of the short axis length 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.

[0112] On the other hand, when the average value of the short axis length 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 shape, a thin rod shape, and / or a fine needle shape. In addition, as 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 deteriorate.

[0113] Additionally, the average value of the short axis length of the primary particles exposed on the surface of the secondary particles observed from the cross-sectional SEM image of the secondary particles may be 30 nm or more and 200 nm or less. The average value of the short axis length of the primary particles having an oriented structure observed from the cross-sectional SEM image of the secondary particles may be 30 nm or more and 200 nm or less.

[0114] If the average value of the short axis length of the primary particles exposed on the surface of the secondary particles observed from the cross-sectional SEM image of the secondary particles is less than 30 nm, there is a concern that the porosity within the secondary particles may increase or the energy density per unit volume may decrease as the number of primary particles having an excessively thin shape increases.

[0115] On the other hand, if the average value of the short axis length of the primary particles exposed on the surface of the secondary particles observed from the cross-sectional SEM image of the secondary particles is greater than 200 nm, the primary particles exposed on the surface of the secondary particles are unlikely to have a thin plate shape, a thin rod shape, and / or a fine needle shape. Accordingly, as 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 deteriorate.

[0116] In the present invention, (1) the average value of the major axis length of the surface shape of the primary particles exposed to the surface of the secondary particles, (2) the average value of the minor axis length of the surface shape of the primary particles exposed to the surface of the secondary particles, (3) the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles exposed to the surface of the secondary particles, and (4) the average value of the ratio of the minor axis length to the major axis length (minor axis length / major axis length) 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 to the surface of the secondary particles from a surface SEM image of the secondary particles, and then measuring the major axis length and the minor axis length from the surface shape of the selected primary particles.

[0117] In order to improve the accuracy when calculating the average value from some of the primary particles exposed on the surface of the secondary particle from the surface SEM image of the secondary particle, when selecting some of the primary particles among all the primary particles exposed on the surface of the secondary particle from the surface SEM image of the secondary particle, the upper group and the lower group can be excluded.

[0118] For example, when selecting 40% of the primary particles among the total primary particles exposed on the surface of the secondary particles from the surface SEM image for the secondary particles, (1) the remaining 40% excluding the group in which the major axis length of the surface shape of the primary particles exposed on the surface of the secondary particles is within the upper 30% and the group in which the minor axis length of the surface shape of the primary particles exposed on the surface of the secondary particles is within the upper 30% and the group in which the minor axis length of the surface shape of the primary particles exposed on the surface of the secondary particles is within the lower 30%, (3) the remaining 40% excluding the group in which the major axis length and minor axis length of the surface shape of the primary particles exposed on the surface of the secondary particles is within the upper 30% and the group in which the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles is within the upper 30% and the group in which the minor axis length You can choose the remaining 40%, excluding the 30% inner group.

[0119] As another example, (1) the average value of the major axis length of the surface shape of the primary particles exposed to the surface of the secondary particles, (2) the average value of the minor axis length of the surface shape of the primary particles exposed to the surface of the secondary particles, (3) the average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the surface shape of the primary particles exposed to the surface of the secondary particles, and (4) the average value of the ratio of the minor axis length to the major axis length (minor axis length / major axis length) of the surface shape of the primary particles can be calculated from the average value of the major axis length / minor axis length measured from the surface shape of all primary particles exposed to the surface of the secondary particles from the surface SEM image for the secondary particles.

[0120] Unless otherwise defined, the term "surface of the primary particle" as used herein refers to the outer surface of the primary particle that is exposed to the outside. Similarly, the term "surface of the secondary particle" as used herein refers to the outer surface of the secondary particle that is exposed to the outside. As described above, the "surface of the secondary particle" formed by agglomeration of a plurality of primary particles corresponds to the exposed surface of the primary particle that exists on the surface portion of the secondary particle.

[0121] In addition, unless otherwise defined, the term "surface portion of a particle" as used herein means a region relatively close to the "outermost surface" of the particle, and the "center portion of a particle" means a region relatively closer to the "center (exact center)" of the particle than the "surface portion." Accordingly, the "surface portion of a primary particle" means a region relatively close to the "outermost surface" of the primary particle, and the "center portion of the primary particle" means a region relatively closer to the "center (exact center)" of the primary particle than the "surface portion." Similarly, the "surface portion of a secondary particle" means a region relatively close to the "outermost surface" of the secondary particle, and the "center portion of the secondary particle" means a region relatively closer to the "center (exact center)" of the secondary particle than the "surface portion."

[0122] At this time, the area excluding the “surface of the particle” within any particle can be defined as the “center of the particle.”

[0123] In this invention, when the radius of the lithium manganese oxide measured from the cross-sectional SEM image of the lithium manganese oxide is r, the distance (d) from the center of the lithium manganese oxide is (1 / 2)r <d인 영역을 표면부(surface portion), 상기 리튬 망간계 산화물의 중심으로부터의 거리(d)가 0≤d≤(1 / 2)r인 영역을 중심부(center portion)으로 정의할 수 있다. 여기서, 상기 리튬 망간계 산화물은 2차 입자인 것을 전제로 한다.

[0124] Since the secondary particle may not have a perfect spherical shape, the radius (r) of the secondary particle can be calculated from the average value of the major axis length and the minor axis length 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 a value that is half the average value of the major axis length and the minor axis length of the lithium manganese oxide measured from the cross-sectional SEM image of the secondary particle.

[0125] 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 arranged in a surface direction from the center of the secondary particles.

[0126] The major axes of the primary particles exhibiting the above-described orientation structure may be formed to have an angle of within ±70°, within ±60°, within ±40°, within ±20°, or within ±10° from the line connecting the center and the surface of the secondary particle. The line connecting the center and the surface of the secondary particle refers to the shortest line segment connecting the center and the surface of the primary particle, and the major axis of the primary particle refers to the line segment having the longest length among the straight lines connecting two points on the surface of the primary particle.

[0127] Since at least a portion of the secondary particle has an oriented structure in which the long axes of the primary particles are arranged in the surface direction from the center of the secondary particle, the mobility of lithium ions within the secondary particle can increase.

[0128] 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 in which the primary particles exhibit the oriented structure on the outside of the core portion.

[0129] The above core portion is a region where the primary particles are randomly aggregated without any particular orientation, and corresponds to the center of the secondary particles.

[0130] 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 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.

[0131] Since the primary particles within the core portion do not exhibit a predetermined orientation but rather randomly aggregate, the proportion of the primary particles having the orientation structure among all primary particles present in the core portion may be less than 50%, less than 40%, less than 30%, less than 20%, or less than 10%.

[0132] The above shell portion exists on the outside of the core portion, is a region where the primary particles are arranged in an oriented structure, and corresponds to the surface portion of the secondary particles.

[0133] 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 r, the shell portion is a distance (d) from the center of the secondary particle of (1 / 2)r <d 또는 (2 / 3)r<d인 영역으로서 정의될 수 있다.

[0134] Since the primary particles have an orientation structure in which the long axes of the primary particles are arranged in the direction of the surface from the center of the secondary particles within the shell, the proportion of the primary particles having the orientation structure among all the primary particles present in the shell may be 50% or more, 60%, 70%, 80%, 85%, or 90% or more. The average value of the angle between the long axes of the primary particles present in the shell and the line connecting the center and surface of the secondary particles may be within ±70°, within ±60°, within ±40°, within ±20°, or within ±10°.

[0135] In the present invention, the ratio of the primary particles having the oriented structure among all primary particles present in the core or shell means the ratio according to the number of primary particles.

[0136] Additionally, the shapes of the primary particles present in the shell portion and the primary particles present in the core portion may be different.

[0137] For example, the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the primary particles present in the core portion, as observed from a cross-sectional SEM image of the secondary particles, may be smaller than the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the primary particles present in the shell portion.

[0138] The primary particles present in the above shell portion may have a thin plate shape, a thin rod shape, or a fine needle shape.

[0139] The BET specific surface area measured by the nitrogen adsorption method for the positive electrode active material comprising lithium manganese oxide, which is an aggregate of primary particles exhibiting the shape and orientation as described above, is 1.0 m 2 / g to 3.5m 2 / g, 1.2m 2 / g to 3.4m 2 / g, 1.4m 2 / g to 3.3m 2 / g, or 1.7m 2 / g to 3.2m 2 / g may be.

[0140] The BET surface area of ​​the above lithium manganese oxide is 3.5 m 2 / g, the possibility of side reactions between the lithium manganese oxide and the electrolyte increases, which may lower the stability of the positive electrode active material including the lithium manganese oxide. On the other hand, if the BET specific surface area of ​​the lithium manganese oxide is 1.0 m 2 / g, the specific surface area of ​​the lithium manganese oxide becomes excessively small, making it difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material including the lithium manganese oxide.

[0141] The lithium manganese oxide defined herein may be represented by the following chemical formula 1 or chemical formula 2.

[0142] [Chemical Formula 1]

[0143] Li(Li a Ni b Co c Mn d M1 e )O 2-f X f

[0144] In the above chemical formula 1,

[0145] 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,

[0146] X is a halogen capable of replacing some of the oxygen present in the lithium manganese oxide,

[0147] 0 <a≤0.7, 0≤b<0.5, 0≤c≤0.2, 0.5≤d<0.8, 0<e≤0.1, 0≤f≤0.1이다.

[0148] [Chemical Formula 2]

[0149] rLi2MnO 3-p X p ·(1-r)Li u Ni w Co x Mn y M2 z O 2-p' X' p'

[0150] In the above chemical formula 2,

[0151] 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,

[0152] X and X' are halogens capable of replacing some of the oxygen present in the lithium manganese oxide,

[0153] 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'≤0.1이다.

[0154] In the above chemical formula 1 and chemical formula 2, X and X' are each independently a halogen element capable of replacing a portion of the oxygen present in the lithium manganese oxide. The types of halogen that can be used as X and X' refer to the periodic table, and F, Cl, Br, and / or I, etc. can be used, and preferably F can be used.

[0155] In the above chemical formula 1 and the above chemical formula 2, M1 and M2 may each independently be 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, 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.

[0156] The Li / Metal molar ratio measured from the lithium manganese oxide represented by the above chemical formula 1 or the above 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. It is possible to form a lithium-excessive lithium manganese oxide when the Li / Metal molar ratio measured from the lithium manganese oxide has a value at least greater than 1. In addition, 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 dissolved and at the same time exhibit a high capacity under a high-voltage operating environment, 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.

[0157] In addition, in order to properly form a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are employed, it is preferable that the content of manganese among all metal elements excluding lithium present in the lithium manganese oxide represented by the chemical formula 1 or the chemical formula 2 is 50 mol% or more.

[0158] In order for the lithium manganese-based oxide to have the characteristics of OLO that exhibits high capacity under a high-voltage operating environment, the content of manganese among all metal elements excluding lithium present in the lithium manganese-based oxide may be 50 mol% 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% or less, 51 mol% or more and 75 mol% or less, 52 mol% or more and 75 mol% or less, 53 mol% or more and 75 mol% or less, 54 mol% or more and 75 mol% or less, or 55 mol% to 75 mol%. When the content of manganese in the lithium manganese oxide exceeds 80 mol%, a phase transition may occur due to the movement of a transition metal (particularly, manganese) in the lithium manganese oxide during the formation and / or operation of a lithium secondary battery. This phase transition forms a spinel phase, and the spinel phase, which acts as an impurity in the lithium manganese oxide, may cause a decrease in charge / discharge capacity or voltage decay during cycling of the lithium secondary battery. In addition, when the content of manganese in the lithium manganese oxide exceeds 80 mol%, it may be difficult to sufficiently form a phase belonging to the R-3m space group.

[0159] 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 employed, the content of nickel among all metal elements excluding lithium present in the lithium manganese oxide represented by the above chemical formula 1 or the above chemical formula 2 may be 0% or more and less than 50 mol%, 5 mol% or more and 48 mol% or less, 10 mol% or more and 46 mol% or less, 15 mol% or more and 45 mol% or less, 20 mol% or more and 44 mol% or less, 20 mol% or more and 42 mol% or less, or 20 mol% or more and 40 mol% or less.

[0160] When the nickel content in the lithium manganese oxide is 50 mol% or more, it is difficult to sufficiently form the C2 / m phase, or the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group cannot form a sufficient solid solution, which may cause phase separation during formation and / or operation of the lithium secondary battery.

[0161] The lithium manganese oxide represented by the above chemical formula 1 or the above chemical formula 2 may optionally include cobalt. When the lithium manganese oxide includes cobalt, the mole fraction of cobalt relative to the mole number of total 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 the above chemical formula 1 or the above chemical formula 2 may have a cobalt-free composition that does not include cobalt.

[0162] Typically, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions exist as a single phase belonging to the R-3m space group.

[0163] On the other hand, the lithium-excessive lithium manganese oxide represented by the above chemical formula 1 or the above chemical formula 2 is an oxide of a phase belonging to the C2 / m space group represented by Li2MnO3 (hereinafter referred to as 'C2 / m phase') and Li u Ni w Co x Mn y M2 z It 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.

[0164] At this time, a complex oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are simply physically and / or chemically combined or attached does not correspond to a solid solution as defined herein.

[0165] For example, a composite oxide having a phase belonging to the C2 / m space group and having a surface coated with a metal oxide having a phase belonging to the R-3m space group by mixing a metal oxide having a phase belonging to the C2 / m space group and a metal oxide having a phase belonging to the R-3m space group does not correspond to a solid solution as defined herein.

[0166] In the lithium manganese oxide represented by the above chemical formula 2, when r exceeds 0.7, the ratio of Li2MnO3, which is an oxide of a phase belonging to the C2 / m space group among the lithium manganese oxides, becomes excessively large, and as a result, the irreversible capacity and resistance of the positive electrode active material increase, which may lead to a decrease in discharge capacity. That is, in order to sufficiently activate the oxide of a phase belonging to the C2 / m space group, which has relatively high resistance among the lithium manganese oxides, and improve the surface kinetics, it is preferable that the oxide of a phase belonging to the R-3m space group is present at a predetermined ratio or more. The ratio of the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group among the lithium manganese oxides can be calculated through the composition ratio of lithium and transition metal present in the lithium manganese oxide.

[0167] 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 may suppress or mitigate the leaching of transition metals from the lithium manganese oxide. In addition, when an ion-conductive coating layer is formed on the surface of the lithium manganese oxide, the charge-transfer and / or diffusion (i.e., surface kinetic) of lithium ions may be improved.

[0168] The coating layer may exist in the form of an island on a portion of the surface of the lithium manganese oxide. Additionally, the coating layer may exist in a state of being diffused from the surface of the secondary particle toward the center of the secondary particle along the grain boundaries between the primary particles.

[0169] The coating layer may be present in the form of a film having an average film thickness of 1 nm to 300 nm on the surface of the lithium manganese oxide. The thickness of the coating layer may be measured through EDX analysis of the coating elements based on a cross-sectional SEM image of the lithium manganese oxide. The existence of the coating layer in the form of a film should be distinguished from the case where the oxide constituting the coating layer is dispersed and attached in the form of individual particles on the surface of the lithium manganese oxide.

[0170] If the average film thickness of the coating layer is thinner than 1 nm, the surface modification effect of the lithium manganese oxide may be insufficient. If the average film thickness of the coating layer is thicker than 300 nm, there is a concern that the surface kinetics of the lithium manganese oxide may deteriorate or the electrical conductivity may decrease.

[0171] The above coating layer may include an oxide represented by the following chemical formula 3.

[0172] [Chemical Formula 3]

[0173] Li g M3 h O i

[0174] In the above chemical formula 3,

[0175] 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, and 0≤g≤8, 0≤h≤8, 2≤i≤13, excluding the case where h and i are both 0. In addition, in the above chemical formula 3, g, h and i represent numbers determined from the stoichiometric ratio according to the valence (oxidation number) of M3. For example, g, h and i may be appropriately selected in the ranges of 0≤g≤8, 0≤h≤8, 2≤i≤13, respectively.

[0176] Non-limiting examples of the oxide represented by the above chemical formula 3 include 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 O i , 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 There is a back.

[0177]

[0178] lithium secondary battery

[0179] According to another aspect of the present invention, a positive electrode may be provided, comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include a lithium manganese oxide according to various embodiments of the present invention described above as a positive electrode active material.

[0180] Therefore, a detailed description of the lithium manganese oxide will be omitted, and only the remaining components not previously described will be described below. In addition, for convenience, the lithium manganese oxide described above will be referred to as a positive electrode active material below.

[0181] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0182] The above positive electrode active material layer can be manufactured by applying a positive electrode slurry composition including the positive electrode active material, a conductive material, and optionally a binder as needed, to the positive electrode current collector.

[0183] At this time, the positive electrode active material may be included in a content of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer. When included in the content range described above, excellent capacity characteristics may be exhibited, but the present invention is not necessarily limited thereto.

[0184] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0185] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0186] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material described above and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, followed by drying and rolling.

[0187] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0188] Additionally, in another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, and then laminating the resulting film onto a positive electrode current collector by peeling it off from the support.

[0189] In addition, according to another aspect of the present invention, an electrochemical device including the above-described positive electrode may be provided. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0190] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Here, the positive electrode is the same as described above, so a detailed description thereof is omitted for convenience, and only the remaining components not described above will be described in detail below.

[0191] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0192] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0193] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0194] The above negative electrode active material layer can be manufactured by applying a negative electrode slurry composition including the negative electrode active material, a conductive material, and optionally a binder as needed, to the negative electrode current collector.

[0195] As the negative electrode active material, a compound capable of reversible intercalation / deintercalation of lithium can 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 alloy, Sn alloy, or Al alloy; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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.

[0196] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0197] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0198] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include 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 fiber or metal fiber; conductive powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene and derivatives thereof.

[0199] In one embodiment, the negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the resulting film on a negative electrode current collector by peeling it off from the support.

[0200] In addition, in another embodiment, the negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the resulting film on a negative electrode current collector by peeling it off from the support.

[0201] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0202] In addition, examples of the electrolyte 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.

[0203] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0204] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc., can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0205] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is preferable to use the lithium salt at a concentration within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0206] When the electrolyte used herein is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, a halide-based solid electrolyte, etc. can be used, and preferably, a sulfide-based solid electrolyte can be used.

[0207] As a material of the sulfide-based solid electrolyte, a solid electrolyte containing Li, X element (wherein, X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S can be used. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein, X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where, m, n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0208] The solid electrolyte, preferably a sulfide-based solid electrolyte, may be amorphous, crystalline, or a mixture of amorphous and crystalline.

[0209] Li7La3Zr2O is used as a material for oxide-based solid electrolytes. 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 PO4-x N x (LiPON), Li 2+2x Zn 1-x There are GeO4 (LISICON), etc.

[0210] The aforementioned solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. In addition, the solid electrolyte may be partially included in the positive electrode active material layer of the positive electrode independently of the solid electrolyte layer, or the solid electrolyte may be partially included in the negative electrode active material layer of the negative electrode independently of the solid electrolyte layer.

[0211] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0212] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0213] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. In addition, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0214] According to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same can be provided.

[0215] The above battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0216]

[0217] Hereinafter, the present invention will be described in more detail through examples. However, these examples are intended solely to illustrate the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

[0218]

[0219] Manufacturing Example 1. Manufacturing of positive electrode active material

[0220] Comparative Example 1

[0221] (a) Precursor manufacturing

[0222] An aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, NaOH (aq), and NH4OH (aq) was added to the reactor and stirred. The pH and temperature in the reactor were maintained at 10.0 and 50°C, respectively. The precursor synthesis reaction was carried out for 24 hours while N2 gas was added to the reactor. After completion of the reaction, 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.

[0223]

[0224] (b) First heat treatment

[0225] Ni obtained in the above step (a) 0.4 Mn 0.6 The (OH)2 precursor was heat-treated at 550°C for 5 hours in a furnace in an air atmosphere, and then furnace-cooled to obtain a precursor in an oxide state.

[0226]

[0227] (c) Second heat treatment

[0228] A mixture was prepared by mixing the oxide precursor obtained in the above step (b) and LiOH (Li / (metal excluding Li) molar ratio = 1.25), which is a lithium raw material.

[0229] Next, the mixture was heat-treated at 850°C for 8 hours in a furnace in an O2 atmosphere, and then furnace-cooled to obtain a cathode active material including lithium manganese oxide.

[0230]

[0231] Comparative Example 2

[0232] A positive electrode active material including a lithium manganese oxide was manufactured in the same manner as in Comparative Example 1, except that the pH in the reactor was maintained at 9.5 in the above step (a) and the second heat treatment temperature was set to 900°C in the above step (c).

[0233]

[0234] Comparative Example 3

[0235] A positive electrode active material including a lithium manganese oxide was manufactured in the same manner as in Comparative Example 1, except that the pH in the reactor was maintained at 9.0 in the above step (a) and the second heat treatment temperature was set to 900°C in the above step (c).

[0236]

[0237] Comparative Example 4

[0238] In the above step (a), the pH in the reactor was maintained at 8.5 and the temperature at 60°C, and a precursor synthesis reaction was performed while simultaneously injecting a mixture of N2 gas and air (N2 (vol%):air (vol%) = 8:2) into the reactor, and a cathode active material including a lithium manganese oxide was manufactured in the same manner as in Comparative Example 1, except that the second heat treatment temperature in the above step (c) was set to 900°C.

[0239]

[0240] Comparative Example 5

[0241] In the above step (a), the pH in the reactor was maintained at 9.0 and the temperature at 60°C, and a precursor synthesis reaction was performed while simultaneously injecting a mixture of N2 gas and air (N2 (vol%):air (vol%) = 9:1) into the reactor, and a cathode active material including a lithium manganese oxide was manufactured in the same manner as in Comparative Example 1, except that the second heat treatment temperature in the above step (c) was set to 650°C.

[0242]

[0243] Example 1

[0244] (a) Precursor manufacturing

[0245] An aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, NaOH (aq) and NH4OH (aq) was introduced into the reactor and stirred. The pH and temperature in the reactor were maintained at 9.0 and 60°C, respectively. A mixture of N2 gas and air (N2 (vol%): air (vol%) = 9:1) was simultaneously introduced into the reactor, and the precursor synthesis reaction was performed for 24 hours. After completion of the reaction, 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.

[0246]

[0247] (b) First heat treatment

[0248] Ni obtained in the above step (a) 0.4 Mn 0.6 The (OH)2 precursor was heat-treated at 550°C for 5 hours in a furnace in an air atmosphere, and then furnace-cooled to obtain a precursor in an oxide state.

[0249]

[0250] (c) Second heat treatment

[0251] A mixture was prepared by mixing the oxide precursor obtained in the above step (b) and LiOH (Li / (metal excluding Li) molar ratio = 1.25), which is a lithium raw material.

[0252] Next, the mixture was heat-treated at 900°C for 8 hours in a furnace in an O2 atmosphere, and then furnace-cooled to obtain a cathode active material including lithium manganese oxide.

[0253]

[0254] Example 2

[0255] (a) Precursor manufacturing

[0256] An aqueous solution of NiSO4·6H2O, CoSO4·6H2O and MnSO4·H2O in a molar ratio of 40:2:58, NaOH (aq) and NH4OH (aq) was introduced into the reactor and stirred. The pH and temperature in the reactor were maintained at 9.0 and 60°C, respectively. A mixture of N2 gas and air (N2(vol%):air(vol%)=9:1) was simultaneously introduced into the reactor, and the precursor synthesis reaction was performed for 24 hours. After completion of the reaction, 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.

[0257]

[0258] (b) First heat treatment

[0259] Ni obtained in the above step (a) 0.4 Co 0.02 Mn 0.58 The (OH)2 precursor was heat-treated at 550°C for 5 hours in a furnace in an air atmosphere, and then furnace-cooled to obtain a precursor in an oxide state.

[0260]

[0261] (c) Second heat treatment

[0262] A mixture was prepared by mixing the oxide precursor obtained in the above step (b) and LiOH (Li / (metal excluding Li) molar ratio = 1.22), which is a lithium raw material.

[0263] Next, the mixture was heat-treated at 750°C for 8 hours in a furnace in an O2 atmosphere, and then furnace-cooled to obtain a cathode active material including lithium manganese oxide.

[0264]

[0265] Example 3

[0266] A positive electrode active material including a lithium manganese oxide was manufactured in the same manner as in Example 2, except that the second heat treatment temperature in step (c) was set to 850°C.

[0267]

[0268] Example 4

[0269] A positive electrode active material including a lithium manganese oxide was manufactured in the same manner as in Example 2, except that the second heat treatment temperature in step (c) was set to 900°C.

[0270]

[0271] Example 5

[0272] The lithium manganese oxide prepared in step (c) of Example 3 and H3BO3 (weighed so that the boron content is 1.2 mol% based on the total transition metal elements of the lithium manganese oxide) were mixed, and then heat-treated at 300°C for 8 hours in a furnace in an O2 atmosphere to obtain a positive electrode active material having a coating layer containing boron formed on the surface of the lithium manganese oxide.

[0273]

[0274] Manufacturing Example 2. Manufacturing of a lithium secondary battery (half-cell)

[0275] A positive electrode slurry was prepared by dispersing 90 wt% of each of the positive electrode active materials manufactured according to Manufacturing Example 1, 4.5 wt% of carbon black, and 5.5 wt% of PVDF binder in N-methyl-2 pyrrolidone (NMP). The positive electrode slurry was uniformly applied to a 15 μm thick aluminum thin film and vacuum-dried at 135°C to prepare a positive electrode for a lithium secondary battery.

[0276] A half-cell was manufactured using a lithium foil as a counter electrode for the above anode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte containing LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 2:4:4.

[0277]

[0278] Experimental Example 1. Analysis of particle structure of positive electrode active material

[0279] (1) Surface SEM image analysis of lithium manganese oxide (secondary particle)

[0280] After selecting a total of 20 secondary particle-shaped lithium manganese oxides from the positive electrode active material manufactured in Manufacturing Example 1, surface SEM images of the secondary particles were obtained by photographing them with a scanning electron microscope. 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 major axis length of the surface shape of the primary particle, the minor axis length of the surface shape of the primary particle, the ratio of the major axis length to the minor axis length of the surface shape of the primary particle (major axis length / minor axis length), and the ratio of the minor axis length to the major axis length of the surface shape of the primary particle (minor axis length / major axis length) were measured, and their average values ​​were calculated.

[0281] The average values ​​according to the above analysis are shown in Table 1.

[0282]

[0283] (2) Analysis of cross-sectional SEM images of lithium manganese oxide (secondary particles)

[0284] After selecting a total of 20 secondary particle-shaped lithium manganese oxides from the positive electrode active material manufactured in Manufacturing Example 1, the lithium manganese oxides were subjected to cross-sectional processing using an ion-milling device and then photographed with a scanning electron microscope to obtain a cross-sectional SEM image. The radius of the lithium manganese oxide (about 6 μm) measured from the cross-sectional SEM image of the lithium manganese oxide is r, and the distance (d) from the center of the lithium manganese oxide in the cross-sectional SEM image is (2 / 3)r. <d인 영역을 쉘부로 정의하고, 이미지 분석 프로그램(Image-Pro image analysis software for SEM)을 사용하여 상기 단면 SEM 이미지로부터 상기 쉘부에 존재하는 전체 1차 입자 중 20개의 1차 입자를 랜덤하게 선택한 후, 선택된 상기 1차 입자들의 단축 길이(두께) 및 상기 1차 입자들의 장축과 상기 2차 입자의 중심과 표면을 연결하는 선 사이의 각도를 측정하고, 이들의 평균값을 계산하였다. 참고로, 상기 리튬 망간계 산화물의 반직경은 상기 단면 SEM 이미지로부터 측정된 상기 리튬 망간계 산화물의 장축 길이와 단축 길이의 산술 평균값으로서 계산되었다. 상기 쉘부에 존재하는 1차 입자들의 장축과 상기 2차 입자의 중심과 표면을 연결하는 선 사이의 각도의 평균값은 절대값의 평균값으로서 계산되었다.

[0285] The average values ​​according to the above analysis are shown in Table 2.

[0286]

[0287] (3) BET surface area analysis of positive electrode active material

[0288] In addition, the BET specific surface area for each positive electrode active material manufactured in Manufacturing Example 1 was calculated through the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mini II of BEL Japan.

[0289] The above measurement results are shown in Table 3.

[0290] Division Major axis lengthShortened lengthMajor axis length / Shortened lengthShortened length / Major axis lengthUnit nm nm--Example 1 250 1052.49 0.44Example 2 222 474.94 0.22Example 3 193 772.55 0.43Example 4 192 802.49 0.44Example 5 210 902.37 0.45Comparative example 1 590 2802.09 0.51Comparative example 2 666 1913.64 0.31Comparative example 3 390 1682.35 0.45Comparative example 4 135 991.48 0.75Comparative example 5 277 299.55 0.11

[0291] Division Shortening length average angle unit nm˚ (degree) Example 1 111232.5 Example 25722.5 Example 38430.2 Example 4 10934.7 Example 5 11735.5 Comparative example 1621 Not measurable Comparative example 4127 Not measurable

[0292] *Unlike Examples 1 to 5, the primary particles present in the shell of the lithium manganese oxide (secondary particles) according to Comparative Examples 1 and 4 did not exhibit a predetermined orientation but rather randomly aggregated, so that the average value of the angle between the long axis of the primary particles and the line connecting the center and surface of the secondary particles could not be calculated.

[0293] BET specific surface area unit m 2 / gExample 11.7Example 23.2Example 32.5Example 41.8Example 52.2Comparative Example 10.4Comparative Example 20.7Comparative Example 30.8Comparative Example 40.6Comparative Example 55.8

[0294]

[0295] Experimental Example 2. Evaluation of the Electrochemical Characteristics of a Lithium Secondary Battery (Half-Cell)

[0296] For the lithium secondary battery (half-cell) manufactured in Manufacturing Example 2, the charge capacity, discharge capacity, and rate capability (C-rate) were measured through a charge / discharge experiment using an electrochemical analysis device (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and a discharge rate of 0.1 C to 2.0 C.

[0297] The above measurement results are shown in Table 4 below.

[0298] Classification Charge capacity Discharge capacity Discharge capacity Ratio (2.0C / 0.1C) Unit mAh / gmAh / cc% Example 1 259.6 230.58 1.0 Example 2 248.4 229.36 2.3 Example 3 255.8 234.68 0.3 Example 4 250.9 226.28 1.3 Example 5 254.2 235.18 1.1 Comparative Example 1 156.5 116.7 15.4 Comparative Example 2 218.3 189.95 6.5 Comparative Example 3 217.4 189.15 3.3 Comparative Example 4 213.2 189.8 49.1 Comparative Example 5 213.0 198.43 9.8

[0299] Comparing the results of Examples 1 to 5 and Comparative Examples 1 and 2, it can be confirmed that when an oriented structure in which the major axes of the primary particles are arranged from the center of the secondary particles toward the surface is formed in at least a portion of the lithium manganese-based oxide (e.g., the shell portion of the secondary particles), the surface kinetic characteristics of the lithium manganese-based oxide are improved, thereby contributing to the improvement of the charge / discharge capacity and rate characteristics. In addition, comparing the results of Examples 1 to 5 and Comparative Examples 1 to 5, it can be confirmed that when the primary particles present on the surface of the lithium manganese-based oxide have an appropriate level of thin plate shape, thin rod shape, or fine needle shape, the porosity within the lithium manganese-based oxide is controlled, thereby providing an appropriate level of BET specific surface area. Accordingly, it can be confirmed that the surface kinetic characteristics of the lithium manganese-based oxide are improved, thereby contributing to the improvement of the charge / discharge capacity and rate characteristics.

[0300]

[0301] Above, the embodiments of the present invention have been described, but those of ordinary skill in the art will be able to modify and change the present invention in various ways by adding, changing, deleting or adding components, etc., within the scope that does not depart from the spirit of the present invention described in the claims, and this will also be considered to be included within the scope of the rights of the present invention.

Claims

1. It includes lithium manganese oxides in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as solid solutions. The above lithium manganese oxide has a secondary particle form in which multiple primary particles are aggregated. At least a portion of the secondary particles has an orientation structure in which the long axes of the primary particles are arranged in a surface direction from the center of the secondary particles. Bipolar active material.

2. In paragraph 1, The surface shape of the primary particles exposed on the surface of the secondary particles observed from the surface SEM image of the secondary particles has a long axis and a short axis. Bipolar active material.

3. In paragraph 2, The average value of the ratio of the major axis length to the minor axis length (major axis length / minor axis length) 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. Bipolar active material.

4. In paragraph 1, The average value of the ratio of the short axis length and the long axis length (short axis length / long axis length) 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. Bipolar active material.

5. In paragraph 1, The average value of the major axis length 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. Bipolar active material.

6. In paragraph 1, The average value of the short axis length 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. Bipolar active material.

7. In paragraph 1, The long axes of the primary particles exhibiting the above orientation structure are formed to have an angle of ±70° or less from the line connecting the center and surface of the secondary particles. Bipolar active material.

8. In paragraph 1, The average value of the short axis length of the primary particles having the orientation structure observed from the cross-sectional SEM image of the secondary particles is 30 nm or more and 200 nm or less. Bipolar active material.

9. In paragraph 1, The above secondary particles have a core portion in which the above primary particles are randomly aggregated, The primary particles are partitioned into a shell portion outside the core portion, which exhibits the orientation structure. Bipolar active material.

10. In paragraph 9, Among all primary particles present in the above shell, the proportion of primary particles having the above orientation structure is 50% or more. Bipolar active material.

11. In paragraph 9, Among all primary particles present in the core portion, the proportion of primary particles having the orientation structure is less than 50%. Bipolar active material.

12. In paragraph 1, The BET surface area measured by the nitrogen adsorption method is 1.0 m 2 / g to 3.5m 2 / g person, Bipolar active material.

13. In paragraph 1, The above lithium manganese oxide is a composite oxide of lithium, nickel and manganese. Bipolar active material.

14. In paragraph 13, The lithium manganese oxide further comprises at least one element selected from transition metals, post-transition metals and metalloids other than alkali metals, alkaline earth metals, nickel and manganese. Bipolar active material.

15. In paragraph 1, The above lithium manganese oxide is represented by the following chemical formula 1: Cathode active material: [Chemical Formula 1] Li (Li a Ni b Co c Mr d M1 e )O 2-f X f 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 replacing 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≤0.1이다.

16. In paragraph 1, The above lithium manganese oxide is represented by the following chemical formula 2: Cathode active material: [Chemical formula 2] rLi 2 MnO 3-p X p ·(1-r) Li u Ni w Co x Mr y M2 z O 2-p' X' p' In the above 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 portion 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'≤0.1이다.

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

18. A lithium secondary battery comprising a positive electrode according to Article 17.