Positive electrode active material and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery comprising the same, and more particularly, to a positive electrode active material comprising lithium and a lithium-rich lithium manganese-based oxide having improved low energy density per unit volume and thus improved electrochemical characteristics, and a lithium secondary battery comprising the same.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery including the thereof, and more specifically, the present invention relates to a positive electrode active material comprising lithium with improved low volumetric energy density and lithium-rich lithium manganese-based oxide and thereby improved electrochemical properties, and a lithium secondary battery including the thereof. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. A representative example of such batteries is the lithium-ion secondary battery, which stores electrical energy through the difference in chemical potential during the insertion / extraction of lithium ions at the positive and negative electrodes.

[0003] The lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative active materials, and filling the space between the positive and negative electrodes with an organic electrolyte or a polymer electrolyte.

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. Examples of such lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or composite oxides complexed with nickel, cobalt, manganese, or aluminum.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifetime characteristics and charge / discharge efficiency. However, due to the limited resources of cobalt used as a raw material, its price is expensive, thus limiting its price competitiveness.

[0006] Lithium manganese-based oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they suffer from small capacity and poor high-temperature performance. In addition, LiNiO2-type cathode active materials exhibit high discharge capacity battery characteristics, but they are difficult to synthesize due to the problem of cation mixing between lithium and transition metals, resulting in significant problems in rate performance.

[0007] Furthermore, depending on the severity of this cation mixing, a large amount of lithium byproducts are generated, most of which consist of compounds of LiOH and Li₂CO₃. Therefore, this can lead to gelation during the preparation of the cathode slurry, or become a cause of gas generation due to repeated charge-discharge cycles after electrode fabrication. In addition, residual LiCoO₂ in these lithium byproducts contributes to reduced lifetime characteristics by increasing monomer swelling.

[0008] Various candidate materials are being discussed to overcome the shortcomings of these existing positive electrode active materials.

[0009] For example, research is underway on using lithium-rich manganese-based oxides, which contain excess manganese in transition metals and have a lithium content greater than the sum of the transition metal contents, as positive electrode active materials for lithium secondary batteries. These lithium-rich manganese-based oxides are also known as overlithiated layered oxides (OLO).

[0010] While the OLO (Oxide Lobe) theoretically offers the advantage of high capacity under high-voltage operating conditions, in practice, due to the excessive manganese content in the oxide, its conductivity is relatively low. Therefore, lithium-ion batteries using the OLO suffer from lower rate performance. As mentioned above, when the rate performance is low, the charge / discharge capacity and lifetime efficiency (cycle capacity retention) decrease during the cycling process of the lithium-ion battery.

[0011] In addition, it generally has the disadvantage of low energy density per unit volume compared with high-nickel cathode active materials such as ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) that are commercially available in the prior art. Summary of the Invention

[0012] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles plays a leading role, while the demand for positive electrode active materials used in lithium secondary batteries is constantly changing.

[0013] For example, in the prior art, from the point of view of ensuring safety, lithium secondary batteries using lithium iron phosphate (LFP) are mainly used. However, recently, the use of nickel-based lithium composite oxides, which have a large energy capacity per unit weight compared to LFP, has been expanded.

[0014] Furthermore, in recent years, nickel-based lithium composite oxides, which are mainly used as positive electrode active materials in high-capacity lithium secondary batteries, must use ternary metal elements such as nickel, cobalt, and manganese, or nickel, cobalt, and aluminum. However, due to the unstable supply and demand of cobalt and its excessively high price compared to other raw materials, there is a need for a new composition of positive electrode active material that can reduce or eliminate cobalt content.

[0015] Considering the overall situation, although lithium-rich lithium manganese-based oxides can meet the market's expectations, they still have limitations in terms of lacking electrochemical properties or stability in replacing commercially available high-nickel type cathode active materials such as ternary lithium composite oxides composed of nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA).

[0016] For example, OLO has a low energy density per unit volume due to the composition of the material (containing excess lithium), and the precursor particles that make up OLO generally grow into thick plate-shaped particles, thus having a particularly poor capacity characteristic.

[0017] Therefore, to improve the insufficient volumetric energy density of OLO, the use of positive electrode active materials with bimodal particle size distribution can be considered. However, as mentioned earlier, the particles constituting the OLO precursor mainly grow into thick plate-like particles. Therefore, as the size of the secondary particles increases, the porosity within the secondary particles decreases excessively, which may lead to problems in exhibiting sufficient capacity characteristics.

[0018] However, the inventors have confirmed that the intraparticle porosity of the lithium manganese-based oxide can be adjusted according to the precursor synthesis conditions of the lithium manganese-based oxide. Based on this, when the intraparticle porosity and specific surface area of ​​the lithium manganese-based oxide are within a predetermined range, the low volumetric energy density of the lithium manganese-based oxide can be improved, thereby improving capacity characteristics and rate performance.

[0019] Therefore, the present invention aims to provide a positive electrode active material that regulates the porosity within particles in order to improve the low unit volume energy density of lithium-rich lithium manganese-based oxides.

[0020] Furthermore, the inventors have confirmed that even though existing lithium-rich manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability compared to other commercially available types of positive electrode active materials, by adjusting the porosity of the lithium manganese-based oxide particles according to the synthesis conditions of the precursor of the lithium manganese-based oxide, the insufficient capacity and rate characteristics of the lithium manganese-based oxide can be achieved to a commercially viable level.

[0021] Therefore, the present invention aims to provide a positive electrode active material in which the intraparticle porosity of the lithium manganese-based oxide is adjusted according to a region in order to improve the insufficient capacity and rate characteristics of lithium-rich lithium manganese-based oxides.

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

[0023] The objectives of this invention are not limited to those mentioned above. Other objectives and advantages not mentioned in this invention can be understood through the following description and will become more apparent through embodiments of the invention. Furthermore, it is obvious that the objectives and advantages of this invention can be achieved by the components and combinations thereof shown in the claims.

[0024] According to one aspect of the present invention for solving the above-mentioned technical problems, a positive electrode active material comprising a lithium manganese-based oxide existing as a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group is provided.

[0025] Generally, the commercial ternary lithium composite oxide composed of nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA) exists as a single phase of a phase belonging to the R-3m space group. On the contrary, the lithium-rich lithium manganese-based oxide defined in this article is characterized by being a solid solution in which a phase belonging to the C2 / m space group coexists with a phase belonging to the R-3m space group.

[0026] In one embodiment, it can be that when the radius of the lithium manganese-based oxide measured from the cross-sectional SEM image of the lithium manganese-based oxide is set as r, the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d is less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r.

[0027] By making the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r, the specific surface area of the lithium manganese-based oxide can be optimized, and the reduction of capacity characteristics and rate characteristics can be prevented.

[0028] In addition, it can be that the porosity in the middle portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r.

[0029] By making the porosity in the middle portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r, the internal porosity of the lithium manganese-based oxide can be optimized, and the reduction of capacity characteristics and rate characteristics can be prevented.

[0030] In addition, it can be that the porosity in the middle portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is less than the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d.

[0031] By making the porosity in the middle portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r less than the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, the specific surface area of the lithium manganese-based oxide can be optimized, and the reduction of capacity characteristics and rate characteristics can be prevented.

[0032] It may be that among the porosity of the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, the porosity of the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r, and the porosity of the central part where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r, the porosity of the central part is the largest.

[0033] In one embodiment, it may be that the porosity of the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d is 8% or more and 40% or less.

[0034] When the porosity of the surface part of the lithium manganese-based oxide is greater than 40%, the specific surface area (which can be defined as the BET specific surface area) of the lithium manganese-based oxide increases excessively, and the stability of the positive electrode active material including the lithium manganese-based oxide may be reduced. On the contrary, when the porosity of the surface part of the lithium manganese-based oxide is less than 8%, the specific surface area of the lithium manganese-based oxide decreases excessively, and it may be difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material including the lithium manganese-based oxide.

[0035] In addition, it may be that the porosity of the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is 5% or more and 35% or less, and the porosity of the central part where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r is 9% or more and 60% or less.

[0036] In one embodiment, it may be that the porosity of the lithium manganese-based oxide measured from the cross-sectional SEM image of the lithium manganese-based oxide is 6% or more and 40% or less.

[0037] When the porosity of the lithium manganese-based oxide is greater than 40%, the energy density per unit volume of the positive electrode active material including the lithium manganese-based oxide may be excessively reduced. On the contrary, when the porosity of the lithium manganese-based oxide is less than 6%, it may be difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material including the lithium manganese-based oxide.

[0038] In one embodiment, it may be that the lithium manganese-based oxide is a composite oxide of lithium, nickel, and manganese, and the lithium manganese-based oxide further includes one or more elements selected from transition metals, post-transition metals, and metalloids other than alkali metals, alkaline earth metals, nickel, and manganese.

[0039] The lithium manganese-based oxide defined herein can be represented by the following Chemical Formula 1 or Chemical Formula 2.

[0040] [Chemical Formula 1]

[0041] Li (Li a Ni b Co c Mn d M1 e )O 2-f X f

[0042] In the chemical formula 1,

[0043] 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.

[0044] X is a halogen that can replace a portion of the oxygen present in the aforementioned lithium manganese-based oxides.

[0045] 0 <a≤0.7,0≤b<0.5,0≤c≤0.2,0.5≤d<0.8,0<e≤0.1,0≤f≤0.1。

[0046] [Chemical Formula 2]

[0047] rLi2MnO 3-p X p ·(1-r)Li u Ni w Co x Mn y M2 z O 2-p' X' p'

[0048] In the chemical formula 2,

[0049] 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.

[0050] X and X' are halogens capable of replacing a portion of the oxygen present in the aforementioned lithium manganese-based oxides.

[0051] 0.2 <r≤0.7,0<u≤1,0≤w≤1,0≤x≤0.2,0.3<y<1,0<z≤0.1,0≤p≤0.1,0≤p'≤0.1。

[0052] Furthermore, according to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material is provided.

[0053] Meanwhile, according to another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

[0054] According to the present invention, the limitations of existing lithium-rich lithium manganese-based oxides, which have several disadvantages in terms of electrochemical properties and / or stability compared with commercially available ternary lithium composite oxides composed of nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA), can be improved.

[0055] Specifically, according to the present invention, the intraparticle porosity of the lithium manganese-based oxide can be adjusted according to the precursor synthesis conditions of the lithium manganese-based oxide. Based on this, the intraparticle porosity and specific surface area of ​​the lithium manganese-based oxide can be controlled to improve the low unit volume energy density of the lithium manganese-based oxide, thereby improving its capacity characteristics and rate performance.

[0056] In particular, according to the present invention, it has the advantage that the insufficient capacity and rate characteristics of the lithium manganese-based oxide can be realized to a commercially viable level by adjusting the porosity of the particles of the lithium manganese-based oxide according to the region.

[0057] Furthermore, the lithium manganese-based oxide and other OLOs have the advantage of high capacity under high voltage operating conditions. However, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte may be promoted as the operating voltage increases. Therefore, it is important to reduce the side reactions between the lithium manganese-based oxide and the electrolyte.

[0058] The lithium manganese-based oxide according to the present invention, by increasing the porosity within the particles while preventing an excessive increase in specific surface area, can reduce side reactions between the lithium manganese-based oxide and the electrolyte. Based on this, the stability and lifespan of lithium secondary batteries using lithium manganese-based oxide as defined herein as the positive electrode active material can be improved. In particular, using a positive electrode active material whose side reactions with the electrolyte are suppressed has the advantage of enabling the lithium secondary battery to be driven at higher voltages.

[0059] Along with the effects described above, the specific effects of the present invention will be explained in conjunction with the following description of the specific matters for carrying out the invention. Detailed Implementation

[0060] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific and technical terms used herein should have the meanings commonly understood by those skilled in the art. Furthermore, it should be understood that, as used herein, the singular form is intended to include the plural form, and vice versa, unless the context clearly indicates otherwise.

[0061] The following will describe in more detail the positive electrode active material comprising a lithium-rich lithium manganese-based oxide and the lithium secondary battery comprising said positive electrode active material.

[0062] Positive electrode active material

[0063] According to one aspect of the present invention, a positive electrode active material is provided, the positive electrode active material comprising a lithium manganese-based oxide in solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group.

[0064] Phases belonging to the C2 / m space group and phases belonging to the R-3m space group can be distinguished not only by the composition of each phase, but also by the characteristic peaks of each phase during XRD analysis. For example, the characteristic peaks of the phase belonging to the C2 / m space group may appear in the region of 2θ = 20.8 ± 1°, while the characteristic peaks of the phase belonging to the R-3m space group may appear in the region of 2θ = 18.6 ± 1°.

[0065] The lithium manganese-based oxide is a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group are dissolved in solid solution, and the phases belonging to the C2 / m space group and the phases belonging to the R-3m space group coexist in the lithium manganese-based oxide. Furthermore, the lithium manganese-based oxide differs from composite oxides having a spinel crystal structure belonging to the Fd-3m space group (e.g., LiMn2O4 or oxides having a similar composition).

[0066] The lithium manganese-based oxide can be a composite oxide of lithium, nickel, and manganese. Furthermore, in addition to alkali metals, alkaline earth metals, nickel, and manganese, the lithium manganese-based oxide may also include one or more elements selected from transition metals, post-transition metals, and metalloids.

[0067] The number of moles of lithium present in the lithium manganese-based 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 (lithium / metal molar ratio) in the lithium manganese-based oxide is greater than 1), therefore it is also called lithium-rich layered oxide (OLO).

[0068] Furthermore, since the manganese content in the lithium manganese-based oxide is greater than the content of other transition metals, the lithium manganese-based oxide is also referred to as a layered oxide with excess lithium and manganese.

[0069] Generally, considering that the content of manganese in the whole metal element other than lithium in commercially available nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary lithium composite oxides is less than 20 mol%, the lithium manganese-based oxide has a relatively high proportion of manganese in the whole metal element compared with commercially available ternary lithium composite oxides (e.g., more than 50 mol%, more than 52 mol%, more than 53 mol%, or more than 55 mol%).

[0070] Furthermore, considering that the nickel content in the total metal elements other than lithium in commercially available ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is 60 mol% or more (80 mol% or more in the case of high-nickel type lithium composite oxides), the nickel content in the lithium manganese-based oxide is relatively low compared to commercially available ternary lithium composite oxides (e.g., less than 50 mol%, less than 48 mol%, less than 46 mol%, less than 45 mol%, less than 44 mol%, less than 42 mol%, or less than 40 mol%).

[0071] There are also differences in the lithium / metal molar ratios measured from lithium manganese-based oxides as defined herein, which are greater than those of ternary lithium composite oxides such as nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA). For example, the lithium / metal molar ratios of ternary lithium composite oxides such as nickel cobalt manganese (NCM) or nickel cobalt aluminum (NCA) appear to be close to 1. In contrast, the lithium / metal molar ratios of lithium manganese-based oxides as defined herein are greater than 1, preferably 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0072] Therefore, in this paper, lithium manganese-based oxides can be defined as composite oxides in which the content of manganese in the whole metal elements other than lithium is more than 50 mol%, or they can be defined as composite oxides in which the content of manganese in the whole metal elements other than lithium is more than 50 mol% and the content of nickel is less than 50 mol%.

[0073] Furthermore, the lithium manganese-based oxides in this paper have a molar ratio of lithium to the whole metal element other than lithium greater than 1, or 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, and are defined as composite oxides in which the manganese content in the whole metal element other than lithium is 50 mol% or more, or composite oxides in which the molar ratio of lithium to the whole metal element other than lithium is greater than 1, or 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5, the manganese content in the whole metal element other than lithium is 50 mol% or more, and the nickel content is less than 50 mol%.

[0074] Despite the aforementioned differences in composition, the lithium manganese-based oxide can also be used as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0075] The lithium manganese-based oxide contained in the positive electrode active material as defined herein can exist as an aggregate of multiple primary particles. When the lithium manganese-based oxide exists as an aggregate of multiple primary particles, the lithium manganese-based oxide can be referred to as a secondary particle.

[0076] The primary particles constituting the secondary particles have rod-shaped, elliptical, and / or irregular shapes. Unless specifically designed in the preparation process, the same secondary particle can contain primary particles of various shapes. However, generally, when having the same composition as the lithium manganese-based oxide, the primary particles have rod-shaped or plate-shaped forms.

[0077] The primary particle refers to a particle unit that does not exhibit grain boundaries when observed with a scanning electron microscope at a magnification of 5,000 to 20,000 times.

[0078] The average particle size of the primary particles constituting the lithium manganese-based oxide as defined herein can be 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm. In this case, the average particle size can be calculated as the average of the length of the primary particle along its major axis and its length along its minor axis ([major axis length + minor axis length] / 2). The average particle size can be calculated as the average of the particle sizes of all primary particles observed from surface SEM images and / or cross-sectional SEM images of the lithium manganese metal oxide.

[0079] When the average particle size of the primary particles is less than 0.05 μm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of these primary particles is relatively large. In this case, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte during the storage or operation of the lithium secondary battery increases.

[0080] Conversely, when the average particle size of the primary particles is greater than 5 μm, excessive growth of the primary particles is induced, thus lengthening the diffusion path of lithium ions within them. When the diffusion path of lithium ions within the primary particles is too long, the mobility and diffusivity of lithium ions within and through the primary particles decrease, which increases the electrical resistance of the lithium manganese-based oxide (secondary particles) composed of these primary particles.

[0081] Therefore, in order to reduce the specific surface area of ​​the lithium manganese-based oxide while preventing a decrease in the mobility of lithium ions in the primary particles and the diffusion of lithium ions through the primary particles, the average particle size of the primary particles can be 0.05 μm to 5 μm, 0.05 μm to 1.0 μm, 0.1 μm to 1.0 μm, or 0.25 μm to 0.75 μm.

[0082] The average particle size (D50) of the secondary particles can be 5.0 μm to 24.0 μm, 6.0 μm to 20.0 μm, 6.0 μm to 18.0 μm, 6.0 μm to 16.0 μm, or 6.0 μm to 15.0 μm.

[0083] The average particle size (D) of the secondary particles 50 The average particle size (D) of the secondary particles can vary depending on the number of primary particles constituting the secondary particles. 50 The particle size distribution can be determined using laser diffraction. For example, secondary particles are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000). The particles are then irradiated with ultrasound at approximately 28 kHz at a power of 60 W. After obtaining a volumetric cumulative particle size distribution chart, the particle size corresponding to 50% of the volumetric cumulative amount is determined to achieve the measurement.

[0084] In this article, “particle size” is used with “particle diameter” or “particle size” for the same meaning, unless otherwise defined, and all “average particle size” refers to the volume median particle size determined by laser diffraction.

[0085] When lithium manganese-based oxides as defined herein are used as large particles of a positive electrode active material exhibiting a bimodal particle size distribution, the average particle size (D50) of the secondary particles 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.

[0086] On the other hand, when lithium manganese-based oxides as defined herein are used as medium particles (particles with an average particle size between small and large particles) of positive electrode active materials exhibiting a trimodal particle size distribution, the average particle size (D) of the secondary particles... 50 The particle size can be 5.0 μm to 15.0 μm, 5.0 μm to 10.0 μm, or 5.0 μm to 8.0 μm. Conversely, when lithium manganese-based oxides as defined herein are used as large particles of a positive electrode active material exhibiting a trimodal particle size distribution, the average particle size (D) of the secondary particles is...50 The size can be 8.0 μm to 24.0 μm, 8.0 μm to 20.0 μm, or 10.0 μm to 15.0 μm.

[0087] Furthermore, when the positive electrode active material as defined herein exhibits a bimodal or trimodal particle size distribution, the average particle size of the lithium manganese-based oxide provided as small particles can be 1 μm to 8 μm, 2 μm to 6 μm, or 3 μm to 5 μm.

[0088] In one embodiment, the porosity of the lithium manganese-based oxide, as measured from a cross-sectional SEM image of the lithium manganese-based oxide, can be 6% or more and 40% or less, 6% or more and 35% or less, 8% or more and 30% or less, 10% or more and 28% or less, 11% or more and 27% or less, or 11.9% or more and 25.3% or less.

[0089] When the porosity of the lithium manganese-based oxide is greater than 40%, the volumetric energy density of the positive electrode active material comprising the lithium manganese-based oxide may be excessively reduced. Conversely, when the porosity of the lithium manganese-based oxide is less than 6%, the capacity and rate characteristics of the positive electrode active material comprising the lithium manganese-based oxide may be difficult to improve.

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

[0091] Furthermore, unless otherwise defined, the term "surface portion of a particle" as used herein refers to the region relatively close to the "outermost surface" of the particle, and "center portion of a particle" refers to the region relatively close to the "center" of the particle than the "surface portion." Thus, "surface portion of a primary particle" refers to the region relatively close to the "outermost surface" of the primary particle, and "center portion of a primary particle" refers to the region relatively close to the "center" of the primary particle than the "surface portion." Similarly, "surface portion of a secondary particle" refers to the region relatively close to the "outermost surface" of the secondary particle, and "center portion of a secondary particle" refers to the region relatively close to the "center" of the secondary particle than the "surface portion."

[0092] At this point, the region within any particle other than the "surface part of the particle" can be defined as the "center part of the particle".

[0093] More specifically, when the radius of the lithium manganese-based oxide measured from the cross-sectional SEM image of the lithium manganese-based oxide in this text is set as r, the region where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d can be defined as the surface portion, the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r can be defined as the intermediate portion, and the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r can be defined as the center portion. Here, as a premise, the lithium manganese-based oxide is a secondary particle. The outermost periphery of the surface portion corresponds to the outermost surface of the secondary particle. Therefore, the surface portion corresponds to the region from the point where the distance d from the center of the secondary particle is (2 / 3)r < d to the outermost surface of the secondary particle.

[0094] The secondary particle may have a shape such as an elliptical non-perfect spherical shape. Or, there may be irregularities on the surface of the secondary particle. In this case, 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-based oxide measured from the cross-sectional SEM image of the secondary particle. The radius (r) of the secondary particle can be considered as half of the value of the average of the major axis length and the minor axis length of the lithium manganese-based oxide measured from the cross-sectional SEM image of the secondary particle.

[0095] According to the present invention, the intra-particle porosity of the lithium manganese-based oxide can be adjusted according to the precursor synthesis conditions of the lithium manganese-based oxide. In particular, it has the advantage that the insufficient capacity characteristics and rate characteristics of the lithium manganese-based oxide can be realized at a commercially viable level by adjusting the porosity according to regions within the particles of the lithium manganese-based oxide.

[0096] In one embodiment, the intra-particle porosity in the surface portion as the region where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, the intermediate portion as the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r, and the center portion as the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r can all be different.

[0097] In particular, in the lithium manganese-based oxide, when the porosity in the surface portion is controlled to be different from the porosity in the center portion, the insufficient energy density per unit volume of the lithium manganese-based oxide can be improved.

[0098] In this text, the porosity in the central part where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (1 / 3)r can be calculated as the ratio of the sum of the areas of all pores existing in the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r to the total area of the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r in the cross-sectional SEM image of the lithium manganese-based oxide.

[0099] The pore area and porosity of the lithium manganese-based oxide can be obtained by cross-sectioning the lithium manganese-based oxide using an ion milling device to obtain a cross-sectional SEM image, and calculating from the cross-sectional SEM image using an image analysis program (Image-Pro image analysis software for SEM). In addition, the total area and the total pore area of any region of the lithium manganese-based oxide are calculated based on the cross-sectional area.

[0100] The pores observed in the cross-sectional SEM image of the lithium manganese-based oxide may be the pores existing between the primary particles constituting the secondary particles. The pores may be open pores exposed on the surface of the secondary particles or closed pores not exposed on the surface of the secondary particles.

[0101] In this text, the porosity in the middle part where the distance d from the center of the lithium manganese-based oxide satisfies (1 / 3)r < d ≤ (2 / 3)r can be calculated as the ratio of the sum of the areas of all pores existing in the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r to the total area of the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r in the cross-sectional SEM image of the lithium manganese-based oxide.

[0102] The total area of the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is the same as the area obtained by subtracting the total area of the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r from the total area of the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (2 / 3)r.

[0103] The sum of the areas of all pores existing in the region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is the same as the area obtained by subtracting the sum of the areas of all pores existing in the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r from the sum of the areas of all pores existing in the region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (2 / 3)r.

[0104] In this text, the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d can be calculated as the ratio of the total pore area existing in the region where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d to the total area of the region in the cross-sectional SEM image of the lithium manganese-based oxide where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d.

[0105] The total area of the region where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d is the same as the area obtained by subtracting the total area of the region where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (2 / 3)r from the total area of the lithium manganese-based oxide.

[0106] The sum of the total pore areas existing in the region where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d is the same as the area obtained by subtracting the sum of the total pore areas existing in the region where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (2 / 3)r from the sum of the total pore areas observed in the cross-sectional SEM image of the lithium manganese-based oxide.

[0107] In one embodiment, the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d can be less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (1 / 3)r.

[0108] By making the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide satisfies (2 / 3)r < d less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (1 / 3)r, the specific surface area of the lithium manganese-based oxide can be optimized, and the reduction of the capacity characteristics and rate characteristics can be prevented.

[0109] In addition, the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide satisfies (1 / 3)r < d ≤ (2 / 3)r can be less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (1 / 3)r.

[0110] By making the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide satisfies (1 / 3)r < d ≤ (2 / 3)r less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide satisfies 0 ≤ d ≤ (1 / 3)r, the specific surface area of the lithium manganese-based oxide can be optimized, and the reduction of the capacity characteristics and rate characteristics can be prevented.

[0111] In addition, the porosity of the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r can be less than the porosity in the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d.

[0112] The porosity in the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r can be made less than the porosity in the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, so that the specific surface area of the lithium manganese-based oxide can be optimized and the reduction of the capacity characteristics and rate characteristics can be prevented.

[0113] Among the porosity in the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, the porosity in the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r, and the porosity in the central part where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r, the porosity in the central part can be the largest.

[0114] Therefore, based on the cross-sectional SEM image of the lithium manganese-based oxide, the porosity in the lithium manganese-based oxide can show a gradient in the form of decreasing first and then increasing as it goes from the center of the lithium manganese-based oxide to the surface of the lithium manganese-based oxide.

[0115] In one embodiment, the porosity in the surface part where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d can be 8% or more and 40% or less, 8% or more and 35% or less, 8% or more and 30% or less, 8% or more and 25% or less, or 8.8% or more and 22.6% or less.

[0116] When the porosity in the surface part of the lithium manganese-based oxide is greater than 40%, the specific surface area (which can be defined as the BET specific surface area) of the lithium manganese-based oxide increases excessively, and the stability of the positive electrode active material including the lithium manganese-based oxide may decrease. On the contrary, when the porosity in the surface part of the lithium manganese-based oxide is less than 8%, the specific surface area of the lithium manganese-based oxide decreases excessively, and it may be difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material including the lithium manganese-based oxide.

[0117] For the lithium manganese-based oxide having the porosity in the surface part as described above, the BET specific surface area measured by the nitrogen adsorption method can be 1.0 m 2 / g to 3.5 m 2 / g, 1.2 m 2 / g to 3.4 m 2 / g, 1.4 m 2 / g to 3.3 m 2 / g, or 1.7 m2 / g to 3.2 m 2 / g.

[0118] When the BET specific surface area of the lithium manganese-based oxide is greater than 3.5 m 2 / g, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte increases, and the stability of the positive electrode active material including the lithium manganese-based oxide may decrease. On the contrary, when the BET specific surface area of the lithium manganese-based oxide is less than 1.0 m 2 / g, the specific surface area of the lithium manganese-based oxide decreases excessively, and it may be difficult to improve the capacity characteristics and rate characteristics of the positive electrode active material including the lithium manganese-based oxide.

[0119] In addition, the porosity in the middle part where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r can be 5% or more and 35% or less, 5% or more and 30% or less, 6% or more and 25% or less, 6% or more and 23% or less, 7% or more and 22% or less, 8% or more and 22% or less, or 8.9% or more and 21.7% or less.

[0120] When the porosity in the middle part of the lithium manganese-based oxide is greater than 35%, the specific surface area (which can be defined as the BET specific surface area) of the lithium manganese-based oxide increases excessively, and the stability of the positive electrode active material including the lithium manganese-based oxide may decrease. On the contrary, when the porosity of the middle part of the lithium manganese-based oxide is less than 5%, it may be difficult for the positive electrode active material including the lithium manganese-based oxide to exhibit sufficient capacity characteristics and rate characteristics.

[0121] The porosity in the central part where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r can be 9% or more and 60% or less, 12% or more and 55% or less, 15% or more and 50% or less, 16% or more and 49% or less, 17% or more and 48% or less, 18% or more and 48% or less, or 18.1% or more and 47.8% or less.

[0122] When the porosity in the central part of the lithium manganese-based oxide is greater than 60%, there is a risk that the particle strength of the lithium manganese-based oxide decreases sharply, and the energy density per unit volume may also decrease. On the contrary, when the porosity in the central part of the lithium manganese-based oxide is less than 9%, it may be difficult for the positive electrode active material including the lithium manganese-based oxide to exhibit sufficient capacity characteristics and rate characteristics.

[0123] The lithium manganese-based oxide defined herein can be represented by the following Chemical Formula 1 or Chemical Formula 2.

[0124] [Chemical Formula 1]

[0125] Li(Lia Ni b Co c Mn d M1 e )O 2-f X f

[0126] In the chemical formula 1,

[0127] 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.

[0128] X is a halogen capable of replacing a portion of the oxygen present in the lithium manganese-based oxide.

[0129] 0 <a≤0.7,0≤b<0.5,0≤c≤0.2,0.5≤d<0.8,0<e≤0.1,0≤f≤0.1。

[0130] [Chemical Formula 2]

[0131] rLi2MnO 3-p X p ·(1-r)Li u Ni w Co x Mn y M2 z O 2-p' X' p'

[0132] In the chemical formula 2,

[0133] 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.

[0134] X and X' are halogens capable of replacing a portion of the oxygen present in the lithium manganese-based oxide.

[0135] 0.2 <r≤0.7,0<u≤1,0≤w≤1,0≤x≤0.2,0.3<y<1,0<z≤0.1,0≤p≤0.1,0≤p'≤0.1。

[0136] In both Chemical Formula 1 and Chemical Formula 2, X and X' are each independently a halogen capable of replacing a portion of the oxygen present in the lithium manganese-based oxide. Referring to the periodic table, F, Cl, Br, and / or I, etc., can be used as halogens that can be used as X and X', with F being preferred.

[0137] In both chemical formulas 1 and 2, M1 and M2 can 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; or at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Ca, Mg, W, Ce, V, Ta, and Y; or at least one selected from Al, P, B, Si, Ti, Zr, and W.

[0138] The lithium / metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 2 can be greater than 1, or can be 1.1 to 1.6, 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5. Only when the lithium / metal molar ratio measured from the lithium manganese-based oxide is at least greater than 1 can a lithium-rich lithium manganese-based oxide be formed. Furthermore, in order for the lithium manganese-based oxide to appropriately form a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group, while simultaneously exhibiting high capacity under high-voltage operating conditions, the lithium / metal molar ratio of the lithium manganese-based oxide is preferably 1.1 to 1.5, 1.2 to 1.6, or 1.2 to 1.5.

[0139] Furthermore, in order to properly form a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group, the content of manganese in the entire metal element other than lithium present in the lithium manganese-based oxide represented by the chemical formula 1 or the chemical formula 2 is preferably 50 mol% or more.

[0140] To enable the lithium manganese-based oxide to exhibit high-capacity OLO characteristics under high-voltage operating conditions, the manganese content in the lithium manganese-based oxide, excluding lithium, can be 50 mol% or more and less than 80 mol%, 51 mol% or more and less than 80 mol%, 52 mol% or more and less than 80 mol%, 53 mol% or more and less than 80 mol%, 54 mol% or more and less than 80 mol%, 55 mol% or more and less than 80 mol%, 50 mol% or more and less than 75 mol%, 51 mol% or more and less than 75 mol%, 52 mol% or more and less than 75 mol%, 53 mol% or more and less than 75 mol%, 54 mol% or more and less than 75 mol%, or 55 mol% to 75 mol%. When the manganese content in the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur during the formation and / or operation of the lithium secondary battery due to the movement of transition metals (especially manganese) in the lithium manganese-based oxide. The phase transformation forms a spinel phase, which, acting as an impurity in the lithium manganese-based oxide, can lead to a decrease in charge / discharge capacity or voltage decay during lithium secondary battery cycling. Furthermore, when the manganese content in the lithium manganese-based oxide exceeds 80 mol%, it may be difficult to sufficiently generate a phase belonging to the R-3m space group.

[0141] In order to properly form a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group, the content of nickel in the entire metal element other than lithium present in the lithium manganese-based oxide represented by the chemical formula 1 or the chemical formula 2 may be 0% or more and less than 50 mol%, 5 mol% or more and less than 48 mol%, 10 mol% or more and less than 46 mol%, 15 mol% or more and less than 45 mol%, 20 mol% or more and less than 44 mol%, 20 mol% or more and less than 42 mol%, or 20 mol% or more and less than 40 mol%.

[0142] When the nickel content in the lithium manganese-based oxide is 50 mol% or more, it is difficult to fully 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 may not be able to form a sufficient solid solution, resulting in phase separation of the lithium secondary battery during formation and / or operation.

[0143] The lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 2 may optionally include cobalt. When the lithium manganese-based oxide includes cobalt, the molar amount of cobalt in the lithium manganese-based oxide relative to the total molar amount of the metal element may be less than 20%, less than 15%, or less than 10%. In another case, the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 2 may have a cobalt-free composition.

[0144] Typically, in commercially available ternary lithium composite oxides composed of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA), the phase belonging to the R-3m space group exists as a single phase.

[0145] Conversely, lithium-rich lithium manganese-based oxides represented by chemical formula 1 or chemical formula 2 are oxides of the phase belonging to the C2 / m space group represented by Li2MnO3 (hereinafter referred to as "C2 / m phase") and oxides of Li u Ni w Co x Mn y M2 z O2 represents a composite oxide formed by the solid solution of an oxide belonging to the R-3m space group (hereinafter referred to as the "R-3m phase"). For example, the lithium manganese-based oxide can exist as a solid solution of an oxide of the C2 / m phase and an oxide of the R-3m phase.

[0146] At this point, a composite oxide in which the phase belonging to the C2 / m space group and the phase belonging to the R-3m space group are simply physically and / or chemically bonded or attached does not correspond to a solid solution as defined herein.

[0147] For example, 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, the metal oxide having a phase belonging to the R-3m space group coated on the surface is not equivalent to a solid solution as defined herein.

[0148] In the lithium manganese-based oxide represented by the aforementioned chemical formula 2, when r exceeds 0.7, the proportion of Li2MnO3, which is an oxide belonging to the C2 / m space group, increases excessively. This may lead to an increase in the irreversible capacity and resistance of the positive electrode active material, thereby reducing the discharge capacity. That is, in order to fully activate the oxides belonging to the C2 / m space group in the lithium manganese-based oxide, which have relatively high resistance, to improve surface kinetic properties, the oxides belonging to the R-3m space group are preferably present in a predetermined proportion or higher. The ratio of the phase belonging to the C2 / m space group to the phase belonging to the R-3m space group in the lithium manganese-based oxide can be calculated from the composition ratio of lithium and transition metals present in the lithium manganese-based oxide.

[0149] In one embodiment, a coating may be present in at least a portion of the surface of the lithium manganese-based oxide. The coating can inhibit or mitigate the dissolution of transition metals from the lithium manganese-based oxide. Furthermore, when an ion-conducting coating is formed on the surface of the lithium manganese-based oxide, the charge transfer and / or diffusion of lithium ions (i.e., surface kinetics) can be improved.

[0150] The coating may exist in an island-like form on a portion of the surface of the lithium manganese-based oxide. Furthermore, the coating may exist in a state where it diffuses along the grain boundaries between primary particles from the surface of the secondary particles toward the center of the secondary particles.

[0151] The coating may exist on the surface of the lithium manganese-based oxide as a film with an average thickness of 1 nm to 300 nm. The thickness of the coating may be determined based on a cross-sectional SEM image of the lithium manganese-based oxide by EDX analysis of the coating elements. The coating exists in the form of a film, which should be distinguished from the oxides constituting the coating being dispersed and attached to the surface of the lithium manganese-based oxide as individual particles.

[0152] When the average film thickness of the coating is less than 1 nm, the surface modification effect of the lithium manganese-based oxide may be insufficient. When the average film thickness of the coating is greater than 300 nm, there is a risk of reduced surface dynamic properties or decreased conductivity of the lithium manganese-based oxide.

[0153] The coating may include an oxide represented by the following chemical formula 3.

[0154] [Chemical Formula 3]

[0155] Li g M3 h O i

[0156] In the chemical formula 3,

[0157] 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 is 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13, excluding the case where h and i are both 0. Furthermore, in the aforementioned chemical formula 3, g, h, and i refer to numbers determined from the stoichiometric ratio based on the valence state (oxidation number) of M3. For example, g, h, and i can be appropriately selected within the ranges of 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13, respectively.

[0158] Non-limiting examples of the oxides represented by chemical formula 3 include Li. g Zr h O i Li g Ti h O i Li g Ni h O i Li g Nbh 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 wait.

[0159] Lithium secondary batteries

[0160] According to another aspect of the present invention, a positive electrode can be provided comprising a positive current collector and a positive active material layer formed on the positive current collector. Here, the positive active material layer may comprise lithium manganese-based oxide as the positive active material according to some embodiments of the present invention.

[0161] Therefore, specific details regarding lithium manganese-based oxides will be omitted; the following description will only cover the remaining components not previously mentioned. Furthermore, for convenience, the lithium manganese-based oxides will be referred to as the positive electrode active material.

[0162] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, it can be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector can typically have a thickness of 3μm to 500μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0163] The positive electrode active material layer can be prepared by coating the positive electrode current collector with a positive electrode slurry composition comprising the positive electrode active material, a conductive material, and, if desired, a binder.

[0164] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight. When the positive electrode active material is contained within the above-mentioned content range, excellent capacity characteristics can be exhibited, but it is not limited thereto.

[0165] The conductive material is used to impart conductivity to the electrodes. In the constructed battery, it can be used without restriction as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One or more mixtures of these materials can be used. The conductive material can be included in the total weight of the positive electrode active material layer from 0.1% to 15% by weight.

[0166] The binder enhances the adhesion between the multiple positive electrode active material particles and the bonding force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), ethylene-vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more mixtures thereof may be used. The binder may comprise 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0167] In addition to utilizing the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition onto a positive electrode current collector and then drying and calendering it. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent.

[0168] The solvent can be any solvent commonly used in this art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more of them can be used. Considering the coating thickness and preparation yield of the slurry, the amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that exhibits excellent thickness uniformity when subsequently coated for the preparation of the positive electrode.

[0169] In another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then pressing a film obtained by peeling it off from the support onto the positive electrode current collector.

[0170] Meanwhile, according to another aspect of the present invention, an electrochemical device including the aforementioned positive electrode can be provided. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0171] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as described above; therefore, for convenience, detailed descriptions are omitted, and the following description only covers the remaining components not previously mentioned.

[0172] The lithium secondary battery may optionally include: a battery container for housing an electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane; and a sealing component for sealing the battery container.

[0173] The negative electrode may include a negative current collector and a layer of negative active material located on the negative current collector.

[0174] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, it can be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, materials that have undergone surface treatment of copper or stainless steel using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys. Furthermore, the negative electrode current collector typically has a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0175] The negative electrode active material layer can be prepared by coating the negative electrode current collector with a negative electrode slurry composition comprising the negative electrode active material, a conductive material, and, selectively, a binder as needed.

[0176] As the negative electrode active material, compounds capable of reversible lithium insertion and extraction can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO₂. β Metal oxides capable of being doped and dedoped with lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metal compounds and carbon materials, such as Si-C composites or Sn-C composites, may be used, and mixtures of one or more of these may be used. Furthermore, a thin film of metallic lithium may also be used as the negative electrode active material. In addition, both low-crystalline and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, while representative high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0177] Based on the total weight of the negative electrode active material layer, it may contain 80% to 99% of the negative electrode active material.

[0178] The binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, 0.1% to 10% by weight of the binder can be added 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 monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0179] The conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, up to 10% by weight of the conductive material can be added, preferably up to 5% by weight. There are no particular limitations on this conductive material as long as it does not induce chemical changes in the corresponding battery and has conductivity. For example, graphite such as natural graphite or artificial graphite can be used; 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; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene and its derivatives.

[0180] In one embodiment, the negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing a binder and conductive material in a solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and a film obtained by peeling it off from the support can be pressed onto the negative electrode current collector.

[0181] In another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then pressing the film obtained by peeling it off from the support onto the positive electrode current collector.

[0182] On the other hand, in the lithium secondary battery, the separator membrane is used to separate the negative electrode and the positive electrode and provide a channel for the movement of lithium ions. Any separator membrane commonly used in lithium secondary batteries can be used without limitation. In particular, it is preferable to have low impedance and excellent electrolyte moisture-holding capacity for electrolyte ion movement. Specifically, porous polymer films can be used, for example, porous polymer films prepared using polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separator membranes coated with ceramic components and polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0183] Furthermore, examples of electrolytes used in this invention include 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 preparation of lithium secondary batteries, but are not limited to these.

[0184] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0185] As the organic solvent, any organic solvent capable of mediating the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate can be used. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where r is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxanes such as 1,3-dioxane; or sulfolane. Among these, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge-discharge characteristics of the battery, is more suitable. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte properties can be exhibited.

[0186] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without limitation. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. Preferably, the concentration of the lithium salt is used in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte properties that allow for efficient lithium ion movement.

[0187] When the electrolyte used herein is a solid electrolyte, such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc., solid inorganic electrolytes can be used. Preferably, sulfide solid electrolytes can be used.

[0188] As materials for sulfide-based solid electrolytes, solid electrolytes containing Li, X (where 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 such sulfide-based solid electrolyte materials include Li₂S-P₂S₅, Li₂S-P₂S-LiX (where X is a halogen element such as I or Cl), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (Where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.)

[0189] The solid electrolyte, preferably a sulfide solid electrolyte, can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0190] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 Li 7-x La3Zr1-x Nb x O 12 Li 7- 3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0191] The aforementioned solid electrolyte can be arranged as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Furthermore, the solid electrolyte can be partially contained independently of the solid electrolyte layer within the positive electrode active material layer of the positive electrode, or the solid electrolyte can be partially contained independently of the solid electrolyte layer within the negative electrode active material layer of the negative electrode.

[0192] In addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity, the electrolyte may also contain one or more additives such as halogenated alkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the electrolyte may contain 0.1% to 5% of the additives relative to its total weight.

[0193] As described above, lithium secondary batteries including the positive electrode active material of the present invention stably exhibit excellent discharge capacity, output characteristics and lifespan characteristics, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0194] The shape of the lithium secondary battery according to the present invention is not particularly limited, but it can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc. Furthermore, preferably, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also as a unit battery in medium or large battery modules comprising multiple battery cells.

[0195] According to another aspect of the invention, a battery module comprising the lithium secondary battery as a single unit and / or a battery pack comprising the same can be provided.

[0196] The battery module or battery pack can be used as a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or a power source for one or more medium or large-sized devices in an energy storage system.

[0197] The present invention will be described in more detail below through embodiments. However, these embodiments are merely illustrative and the scope of the invention should not be construed as being limited to these embodiments.

[0198] Preparation Example 1. Preparation of Positive Electrode Active Material

[0199] Comparative Example 1

[0200] (a) Precursor preparation

[0201] An aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, along with NaOH(aq) and NH4OH(aq), were added to the reactor while stirring. The pH and temperature inside the reactor were maintained at 10.0 and 50°C. The precursor synthesis reaction was carried out for 24 hours while N2 gas was introduced into the reactor. After the reaction, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain the average particle size (D). 50 Ni with a thickness of 12 μm 0.4 Co 0.02 Mn 0.58 (OH)2 precursor.

[0202] (b) First heat treatment

[0203] The Ni obtained in step (a) 0.4 Co 0.02 Mn 0.58The (OH)2 precursor was heat-treated at 550°C for 5 hours in an air-atmosphere furnace and then furnace-cooled to obtain the precursor in oxide form.

[0204] (c) Second heat treatment

[0205] The oxide precursor obtained in step (b) is mixed with LiOH (Li / (metal other than lithium) molar ratio = 1.25) as a lithium raw material to prepare a mixture.

[0206] Subsequently, the mixture was heat-treated at 850°C for 8 hours in an O2 atmosphere furnace and then furnace-cooled to obtain a positive electrode active material including lithium manganese-based oxide.

[0207] Comparative Example 2

[0208] Except that the pH in the reactor is maintained at 9.5 in step (a) and the second heat treatment temperature is set at 900°C in step (c), the positive electrode active material comprising lithium manganese-based oxide is prepared in the same manner as in Comparative Example 1.

[0209] Comparative Example 3

[0210] Except that the pH in the reactor is maintained at 9.0 in step (a) and the second heat treatment temperature is set at 900°C in step (c), the positive electrode active material comprising lithium manganese-based oxide is prepared in the same manner as in Comparative Example 1.

[0211] Comparative Example 4

[0212] Except that in step (a) the pH in the reactor is maintained at 8.5 and the temperature is maintained at 60°C, and a mixture of N2 gas and air (N2(vol%):air(vol%) = 9:1) is simultaneously introduced into the reactor to carry out the precursor synthesis reaction, and in step (c) the second heat treatment temperature is set at 900°C, the positive electrode active material including lithium manganese-based oxide is prepared in the same manner as in Comparative Example 1.

[0213] Comparative Example 5

[0214] Except that in step (a) the pH in the reactor is maintained at 9.0 and the temperature is maintained at 60°C, and a mixture of N2 gas and air (N2(vol%):air(vol%) = 9:1) is simultaneously introduced into the reactor to carry out the precursor synthesis reaction, and in step (c) the second heat treatment temperature is set at 650°C, the positive electrode active material including lithium manganese-based oxide is prepared in the same manner as in Comparative Example 1.

[0215] Example 1

[0216] (a) Precursor preparation

[0217] An aqueous solution of NiSO4·6H2O and MnSO4·H2O, along with NaOH(aq) and NH4OH(aq) in a molar ratio of 40:60, was added to the reactor while stirring. The pH and temperature inside the reactor were maintained at 9.0 and 60°C. The precursor synthesis reaction was carried out for 24 hours while a mixture of N2 gas and air (N2(vol%):air(vol%) = 9:1) was simultaneously introduced into the reactor. After the reaction, the precursor was separated, washed with deionized water, and dried at 120°C for 10 hours to obtain the average particle size (D). 50 Ni is 12.0 μm 0.4 Mn 0.6 (OH)2 precursor.

[0218] (b) First heat treatment

[0219] The Ni obtained in step (a) 0.4 Mn 0.6 The (OH)2 precursor was heat-treated at 550°C for 5 hours in an air-atmosphere furnace and then furnace-cooled to obtain the precursor in oxide form.

[0220] (c) Second heat treatment

[0221] The oxide precursor obtained in step (b) is mixed with LiOH (Li / (metal other than lithium) molar ratio = 1.25) as a lithium raw material to prepare a mixture.

[0222] Subsequently, the mixture was heat-treated at 900°C for 8 hours in an O2 atmosphere furnace and then furnace-cooled to obtain a positive electrode active material including lithium manganese-based oxide.

[0223] Example 2

[0224] (a) Precursor preparation

[0225] An aqueous solution of NiSO4·6H2O, CoSO4·6H2O, and MnSO4·H2O in a molar ratio of 40:2:58, along with NaOH(aq) and NH4OH, was added to the reactor while stirring. The pH and temperature inside the reactor were maintained at 9.0 and 60°C. The precursor synthesis reaction was carried out for 24 hours while a mixture of N2 gas and air (N2(vol%):air(vol%) = 9:1) was simultaneously introduced into the reactor. After 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 Ni is 12.0 μm 0.4 Co 0.02 Mn 0.58 (OH)2 precursor.

[0226] (b) First heat treatment

[0227] The Ni obtained in step (a) 0.4 Co 0.02 Mn 0.58 The (OH)2 precursor was heat-treated at 550°C for 5 hours in an air-atmosphere furnace and then furnace-cooled to obtain the precursor in oxide form.

[0228] (c) Second heat treatment

[0229] The oxide precursor obtained in step (b) is mixed with LiOH (Li / (metal other than lithium) molar ratio = 1.22) as a lithium raw material to prepare a mixture.

[0230] Subsequently, the mixture was heat-treated at 750°C for 8 hours in an O2 atmosphere furnace and then furnace-cooled to obtain a positive electrode active material including lithium manganese-based oxide.

[0231] Example 3

[0232] Except that the second heat treatment temperature in step (c) is set to 850°C, the positive electrode active material comprising lithium manganese-based oxide is prepared in the same manner as in Example 2.

[0233] Example 4

[0234] Except that the second heat treatment temperature in step (c) is set to 900°C, the positive electrode active material comprising lithium manganese-based oxide is prepared in the same manner as in Example 2.

[0235] Example 5

[0236] The lithium manganese-based oxide prepared in step (c) of Example 3 was mixed with H3BO3 (weighed such that the boron content of all transition metal elements in the lithium manganese-based oxide was 1.2 mol%), and then heat-treated in a sintering furnace under an O2 atmosphere at 300°C for 8 hours to obtain a positive electrode active material with a boron-containing coating formed on the surface of the lithium manganese-based oxide.

[0237] Preparation Example 2. Preparation of Lithium Secondary Battery (Half-Cell)

[0238] A positive electrode slurry was prepared by dispersing 90% by weight of each of the positive electrode active material prepared according to Preparation Example 1, 4.5% by weight of carbon black, and 5.5% by weight of PVDF binder in N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on an aluminum film with a thickness of 15 μm and vacuum dried at 135 °C to prepare a positive electrode for lithium secondary batteries.

[0239] A half-cell was prepared by using lithium foil as a counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as a separation membrane, and an electrolyte containing LiPF6 at a concentration of 1.15 M, in a solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate mixed in a volume ratio of 2:4:4.

[0240] Experimental Example 1. Determination of Porosity and BET Specific Surface Area of ​​Lithium Manganese-Based Oxides

[0241] For each of the positive electrode active materials prepared in Preparation Example 1, the lithium manganese-based oxide was cross-sectionalized using an ion milling apparatus to obtain a cross-sectional SEM image, and the total porosity of the lithium manganese-based oxide observed was calculated from the cross-sectional SEM image using an image analysis program (Image-Pro image analysis software for SEM).

[0242] In addition, the radius (about 66 μm) of the lithium manganese-based oxide measured from the cross-sectional SEM image of the lithium manganese-based oxide is set as r. In the cross-sectional SEM image, the lithium manganese-based oxide is divided into a surface portion which is a region where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, an intermediate portion which is a region where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r, and a center portion which is a region where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r. Then, the porosity within the surface portion, the intermediate portion, and the center portion is calculated respectively. The porosity of the lithium manganese-based oxide (total porosity, porosity within the surface portion, the intermediate portion, and the center portion) is calculated by taking the average value of the porosity measured from a total of 20 lithium manganese-based oxides included in each of the positive electrode active materials prepared in Preparation Example 1.

[0243] In addition, for the BET specific surface area of each of the positive electrode active materials prepared in Preparation Example 1, it is calculated by the nitrogen adsorption amount at the liquid nitrogen temperature (77K) using BELSORP-miniII of BEL Japan Inc.

[0244] The measurement results are shown in Table 1.

[0245]

Table 1

[0246]

[0247] Example 2. Evaluation of the electrochemical characteristics of lithium secondary batteries (half-cells)

[0248] For the lithium secondary battery (half cell) prepared in Preparation Example 2, using an electrochemical analyzer (Toyo, Toscat-3100), charge capacity, discharge capacity, and rate characteristics (discharge capacity ratio; rate capability (C-rate)) are measured through charge / discharge experiments with a temperature of 25°C, a voltage range of 2.0V to 4.6V, and a discharge rate of 0.1C to 2.0C.

[0249] The measurement results are shown in Table 2 below.

[0250]

Table 2

[0251]

[0252] Referring to the results in Table 2 above, it was confirmed that for the positive electrode active materials according to Examples 1 to 5, as the porosity in the secondary particles is controlled by region, the capacity characteristics and rate characteristics are improved.

[0253] The embodiments of the present invention have been described above. However, those skilled in the art can make various modifications and alterations to the present invention by adding, modifying, deleting, or adding constituent elements without departing from the concept of the present invention as described in the claims. These modifications and alterations should also be included within the scope of the present invention.

Claims

1. A positive electrode active material comprising a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R-3m space group exist as a solid solution. When the radius of the lithium manganese-based oxide measured from a cross-sectional SEM image of the lithium manganese-based oxide is set as r, the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d is less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r.

2. The positive electrode active material according to claim 1, wherein the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is less than the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r.

3. The positive electrode active material according to claim 1, wherein the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is less than the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d.

4. The positive electrode active material according to claim 1, wherein among the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d, the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r, and the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r, the porosity in the central portion is the largest.

5. The positive electrode active material according to claim 1, wherein the porosity in the surface portion where the distance d from the center of the lithium manganese-based oxide is (2 / 3)r < d is 8% or more and 40% or less.

6. The positive electrode active material according to claim 1, wherein the porosity in the intermediate portion where the distance d from the center of the lithium manganese-based oxide is (1 / 3)r < d ≤ (2 / 3)r is 5% or more and 35% or less.

7. The positive electrode active material according to claim 1, wherein the porosity in the central portion where the distance d from the center of the lithium manganese-based oxide is 0 ≤ d ≤ (1 / 3)r is 9% or more and 60% or less.

8. The positive electrode active material according to claim 1, wherein the porosity of the lithium manganese-based oxide measured from a cross-sectional SEM image of the lithium manganese-based oxide is 6% or more and 40% or less.

9. The positive electrode active material according to claim 1, wherein The BET specific surface area, as determined by nitrogen adsorption, is 1.0 m². 2 / g to 3.5m 2 / g.

10. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide has the form of secondary particles aggregated by a plurality of primary particles, and the D50 of the secondary particles is 5.0 μm to 24.0 μm.

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

12. The positive electrode active material according to claim 11, wherein the lithium manganese-based oxide further includes one or more elements selected from transition metals, post-transition metals, and metalloids other than alkali metals, alkaline earth metals, nickel, and manganese.

13. The positive electrode active material according to claim 1, wherein, The lithium manganese-based oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li (Li a Ni b Co c Mr d M1 e )O 2-f X f In the chemical formula 1, M1 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X is a halogen that can replace a portion of the oxygen present in the aforementioned lithium manganese-based oxides. 0 <a≤0.7,0≤b<0.5,0≤c≤0.2,0.5≤d<0.8,0<e≤0.1,0≤f≤0.1。 14. The positive electrode active material according to claim 1, wherein, The lithium manganese-based oxide is represented by the following chemical formula 2. [Chemical Formula 2] rLi2MnO 3-p X p ·(1-r)Li u Nor w Co x Mn y M2 z O 2-p' X' p' In the chemical formula 2, M2 is at least one selected from Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, Y, Ru, Ge, and Nd. X and X' are halogens capable of replacing a portion of the oxygen present in the lithium manganese-based oxide, 0.2 <r≤0.7,0<u≤1,0≤w≤1,0≤x≤0.2,0.3<y<1,0<z≤0.1,0≤p≤0.1,0≤p'≤0.1。 15. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 14.

16. A lithium secondary battery comprising the positive electrode as described in claim 15.

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