Positive electrode active material, positive electrode, and lithium secondary battery

Abstract

To provide a positive electrode active material which is able to improve the low discharge capacity and rate capability of conventional lithium-rich lithium manganese-based oxides.SOLUTION: A positive electrode active material includes a lithium-rich lithium manganese-based oxide containing at least lithium, nickel, and manganese. In the lithium manganese-based oxide, a phase belonging to a C2 / m space group and a phase belonging to an R3-m space group coexist. The lithium manganese-based oxide includes regions with different proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a positive electrode, and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode active material, a positive electrode, and a lithium secondary battery including the same, which include a lithium-excess lithium manganese oxide that is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and in which regions where the ratios of the phases belonging to the C2 / m space group and the R3-m space group are different exist in the lithium manganese oxide, thereby alleviating and / or preventing a decrease in stability caused by lithium and manganese present in excess in the lithium manganese oxide.

Background Art

[0002] A battery stores electric power by using substances capable of electrochemical reactions for a positive electrode and a negative electrode. As a typical example of such a battery, there is a lithium secondary battery that stores electric energy due to a difference in chemical potential when lithium ions are intercalated / deintercalated in a positive electrode and a negative electrode.

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

[0004] As the positive electrode active material of the lithium secondary battery, a lithium composite oxide is used. Examples thereof include composite oxides in which Ni, Co, Mn, or Al is combined, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015).

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

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

[0007] Furthermore, depending on the degree of cation mixing, a large amount of Li byproducts are generated. Since the majority of these Li byproducts consist of LiOH and Li2CO3 compounds, they cause gelling problems during the production of the positive electrode paste and gas generation as charging and discharging progresses after the electrode is manufactured. Residual Li2CO3 not only increases the swelling phenomenon of the cell and reduces the number of cycles, but also causes the battery to swell.

[0008] Various candidate materials are being discussed to compensate for the shortcomings of these conventional cathode active materials.

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

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

[0011] Furthermore, the decrease in charge / discharge capacity or voltage decay during charge / discharge cycles of lithium secondary batteries using OLO can also be induced by phase transitions due to the migration of transition metals in lithium manganese oxides. For example, if a phase transition is induced by the unintended migration of a transition metal in a layered crystalline lithium manganese oxide, a spinel or similar crystalline structure may develop entirely and / or partially within the lithium manganese oxide.

[0012] To address the aforementioned problems, there have been attempts to improve the OLO's issues through structural improvements and surface modifications, such as adjusting the particle size or coating the surface of the OLO, but these have not yet reached a commercialization level. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Korean Published Patent Publication No. 10-2015-0069334 (Published June 23, 2015) [Overview of the project] [Problems that the invention aims to solve]

[0014] In the lithium-ion battery market, the growth of lithium-ion batteries for electric vehicles is playing a leading role, and the demand for cathode active materials used in lithium-ion batteries is also continuously changing.

[0015] For example, conventionally, lithium secondary batteries using LFPs have been primarily used from the perspective of ensuring safety, but recently there has been a growing trend towards the use of nickel-based lithium composite oxides, which have a higher energy capacity per unit weight compared to LFPs.

[0016] Furthermore, many nickel-based lithium composite oxides used as positive electrode active materials in high-capacity lithium secondary batteries recently require ternary metallic elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, in the case of cobalt, not only is the supply and demand unstable, but it is also excessively expensive compared to other raw materials. Therefore, there is a need for new compositions of positive electrode active materials that can reduce or eliminate the cobalt content.

[0017] From this perspective, lithium-rich lithium manganese oxides can meet the aforementioned market expectations, but their electrochemical properties and stability are still insufficient to replace commercially available NCM or NCA type cathode active materials.

[0018] However, even though conventional lithium-rich lithium manganese oxides have disadvantages in terms of electrochemical properties and / or stability when compared to other commercially available types of cathode active materials, the inventors have confirmed that lithium-rich lithium manganese oxides can also exhibit electrochemical properties and stability at a level suitable for commercialization if the concentration of transition metals in the lithium manganese oxide can be controlled in different regions.

[0019] Accordingly, the present invention aims to provide a positive electrode active material comprising a lithium-rich lithium manganese oxide which is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, wherein the decrease in stability caused by excess lithium and manganese in the lithium manganese oxide is mitigated and / or prevented by the presence of regions in the lithium manganese oxide where the proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different.

[0020] Furthermore, the present invention aims to provide a positive electrode active material that includes a lithium-rich lithium manganese oxide, which is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and that can improve the low discharge capacity and rate characteristics of conventional lithium-rich lithium manganese oxides by ensuring that the concentration of Ni in the region where the phase belonging to the R3-m space group exists is within a predetermined range.

[0021] Furthermore, the present invention aims to provide a lithium secondary battery in which the conventionally low OLO rate characteristics are improved by using a positive electrode containing the positive electrode active material defined in this application. [Means for solving the problem]

[0022] According to one aspect of the present invention for solving the aforementioned technical problems, a positive electrode active material is provided which includes a lithium-rich lithium-manganese oxide containing at least lithium, nickel, and manganese, wherein a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist in the lithium-manganese oxide, and regions exist in the lithium-manganese oxide where the proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different.

[0023] In one embodiment, the concentration of the metal element in the lithium manganese oxide can satisfy the following formula 1.

[0024] [Formula 1] 0.24≦M 2 / M 1 ≤0.55 Here, M 1 This is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide, M 2 This is the number of moles of nickel in the lithium manganese oxide, based on the total number of metal elements (excluding lithium).

[0025] In the lithium manganese oxide, if the nickel content among the metal elements (excluding lithium) satisfies the above formula 1, it is possible to improve the discharge capacity and rate characteristics, which are reduced by excess Mn in the lithium manganese oxide, to a commercially viable level.

[0026] The lithium manganese oxide may be a core-shell particle comprising a core and a shell covering at least a portion of the surface of the core. In this case, the core and the shell are simply distinguished to refer to regions in the lithium manganese oxide where the proportion of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group differs. That is, even when the lithium manganese oxide is a core-shell particle, the core and the shell should be understood to form a single solid solution.

[0027] When the lithium manganese oxide is a core-shell particle, the core contains both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the shell may be greater than the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the core.

[0028] In this case, the concentration of the metal element in the shell can satisfy the following equation 3.

[0029] [Formula 3] 0.24≦M 4 / M 3≦0.75 Here, M 3 is the number of moles of all metal elements (excluding lithium) in the shell, M 4 is the number of moles of nickel based on all metal elements (excluding lithium) in the shell.

[0030] At this time, the ratio of the phase belonging to the R3 - m space group to the phase belonging to the C2 / m space group in the lithium manganese oxide increases in a gradient from the core to the shell, thereby reducing the abrupt change in the crystal structure within the lithium manganese oxide and preventing damage applied to the particles during charge and discharge.

[0031] The lithium manganese oxide can be represented by the following Chemical Formula 1.

[0032] [Chemical Formula 1] rLi2MnO3·(1 - r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2 Here, M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi, 0 < r ≦ 0.8, 0 < a ≦ 1, 0 < x ≦ 1, 0 ≦ y < 1, 0 < z < 1, and 0 < x + y + z ≦ 1.

[0033] As shown in Chemical Formula 1, the lithium manganese oxide defined in the present application is a solid solution in which a phase belonging to the C2 / m space group and a phase belonging to the R3 - m space group coexist within a single particle.

[0034] In this context, a single particle can mean "a non-aggregated particle containing a single primary particle," "a particle formed by the aggregation of a relatively small number of primary particles," or "a particle formed by the aggregation of multiple (tens to hundreds or more) primary particles."

[0035] In the solid solution represented by the chemical formula 1, the phase belonging to the C2 / m space group is due to Li2MnO3, and the phase belonging to the R3-m space group is Li a Ni x Co y Mn z M1 1-(x+y+z) This is due to O2.

[0036] Furthermore, according to another aspect of the present invention, a positive electrode containing the aforementioned positive electrode active material is provided.

[0037] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided in which the aforementioned positive electrode is used. [Effects of the Invention]

[0038] According to the present invention, it is possible to improve upon the limitations of conventional lithium-rich lithium manganese oxides, which have various disadvantages in terms of electrochemical properties and / or stability when compared with other commercially available types of cathode active materials.

[0039] First, the lithium manganese oxide contained in the positive electrode active material according to the present invention is a lithium-rich lithium manganese oxide that is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0040] As mentioned above, lithium-manganese oxides containing excess amounts of lithium and manganese can exhibit high capacity under high-voltage operating conditions. However, such lithium-manganese oxides have the disadvantage of low discharge capacity and rate characteristics due to the excess lithium and manganese in the oxide. However, as in the positive electrode active material of the present invention, when the ratio of phases belonging to the C2 / m space group and phases belonging to the R3-m space group is made different in different regions, the discharge capacity and rate characteristics are improved.

[0041] In particular, when the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the surface portion (which can be called the core) of the lithium manganese oxide is large, it is possible to improve the low electrical conductivity of the lithium manganese oxide and raise the discharge capacity and rate characteristics to a commercially viable level by mitigating the charge-transfer and / or diffusion of Li ions on the particle surface (which is likely to be mainly caused by the phase belonging to the C2 / m space group). [Brief explanation of the drawing]

[0042] [Figure 1] Figure 1 shows the TEM analysis results for the lithium manganese oxide contained in the cathode active material according to Example 4. Figure 1 shows a 50 nm scale TEM image, a 5 nm scale TEM image which is an enlarged version of the region shown in the 50 nm scale TEM image, and the crystal structure confirmed by FFT conversion of regions A and B of the 5 nm scale TEM image. [Figure 2] Figure 2 shows the line sum spectrum obtained by line scanning the EDX mapping results of a cross-sectional TEM image of the lithium manganese oxide contained in the cathode active material of Example 4, confirming the change in nickel concentration (at%) from the core to the shell of the lithium manganese oxide. Region A shown in the line sum spectrum of Figure 2 corresponds to region A in Figure 1. [Modes for carrying out the invention]

[0043] For the convenience of making the present invention easier to understand, certain terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in this invention have meanings that are generally understood by those of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0044] The following describes in more detail a positive electrode active material containing a lithium-rich lithium-manganese oxide, which includes at least lithium, nickel, manganese, and a doping metal, and a lithium secondary battery containing the said positive electrode active material, according to the present invention.

[0045] positive electrode active material According to one aspect of the present invention, a positive electrode active material is provided which comprises a lithium-rich lithium-manganese oxide containing at least lithium, nickel, manganese, and a doping metal. The lithium-manganese oxide is a composite metal oxide capable of intercalation and deintercalation of lithium ions.

[0046] The lithium manganese oxide contained in the positive electrode active material as defined in this application may be a secondary particle containing at least one primary particle.

[0047] Here, "secondary particles containing at least one primary particle" should be interpreted as including all "particles formed by the aggregation of multiple primary particles" or "non-aggregated particles containing a single primary particle."

[0048] The primary particles and secondary particles may each independently have a rod-shaped, elliptical, and / or amorphous shape.

[0049] When the average major axis length is used as an indicator of the size of the primary and secondary particles, the average major axis length of the primary particles constituting the lithium manganese oxide may be 0.1 μm to 5 μm, and the average major axis length of the secondary particles may be 1 μm to 30 μm. The average major axis length of the secondary particles can vary depending on the number of primary particles constituting the secondary particles, and the positive electrode active material may contain particles with various average major axis lengths.

[0050] If the lithium manganese oxide is either a "non-aggregated particle containing a single primary particle" or a "particle formed by the aggregation of a relatively small number of primary particles," the size (average particle size) of the primary particles contained within the "non-aggregated particle containing a single primary particle" or the "particle formed by the aggregation of a relatively small number of primary particles" may be larger than the size (average particle size) of the primary particles contained within the "secondary particle formed by the aggregation of tens to hundreds or more primary particles."

[0051] Thus, lithium manganese oxides, which are either "non-aggregated particles containing a single primary particle" or "particles formed by the aggregation of a relatively small number of primary particles," generally require stronger heat treatment conditions (higher heat treatment temperatures / longer heat treatment times) compared to the production of "secondary particles formed by the aggregation of tens to hundreds or more primary particles." For example, it is known that when heat treatment is performed at a relatively high temperature (800°C or higher) for a long time, particle growth (crystal growth) is promoted, resulting in larger individual particle sizes, while at the same time, a positive electrode active material with a lower degree of particle aggregation is obtained.

[0052] For example, if the lithium manganese oxide is a "non-aggregated particle containing a single primary particle" or a "particle formed by the aggregation of a relatively small number of primary particles," the average major axis length of the primary particle may be in the range of 0.5 μm to 20 μm. On the other hand, if the lithium manganese oxide is a "particle formed by the aggregation of multiple (tens to hundreds or more) primary particles," the average major axis length of the primary particle may be in the range of 0.1 μm to 5 μm.

[0053] Furthermore, the primary particle may contain at least one crystallite. That is, the primary particle may consist of a single crystallite or exist as a particle containing multiple crystallites.

[0054] The lithium manganese oxide as defined in this application is a composite metal oxide containing an excess of lithium and manganese, and within the lithium manganese oxide, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist. That is, the lithium manganese oxide is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0055] In this application, "solid solution" means that within the lithium manganese oxide, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group exist as a single particle.

[0056] In this context, a single particle can mean "a non-aggregated particle containing a single primary particle," "a particle formed by the aggregation of a relatively small number of primary particles," or "a particle formed by the aggregation of multiple (tens to hundreds or more) primary particles."

[0057] In this application, "solid solution" does not mean a state in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group present in the lithium manganese oxide are physically and / or chemically bonded or attached.

[0058] For example, a metal oxide having a phase belonging to the C2 / m space group and a metal oxide having a phase belonging to the R3-m space group are mixed to form a metal oxide having a phase belonging to the R3-m space group, and the surface of the metal oxide having a phase belonging to the C2 / m space group is coated, and this resulting metal oxide does not qualify as a solid solution.

[0059] Furthermore, the lithium manganese oxide may contain both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and there may be regions in the lithium manganese oxide where the proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different.

[0060] Thus, when the proportion of phases belonging to the C2 / m space group and phases belonging to the R3-m space group are made to differ in different regions within the lithium manganese oxide, the discharge capacity and rate characteristics of the positive electrode active material containing the lithium manganese oxide can be improved.

[0061] Furthermore, the concentration of the metal element in the lithium manganese oxide can satisfy the following formula 1.

[0062] [Formula 1] 0.24≦M 2 / M 1 ≤0.55 Here, M 1 This is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide, M 2 This is the number of moles of nickel in the lithium manganese oxide, based on the total number of metal elements (excluding lithium).

[0063] In the above formula 1, M 2 / M 1 If the value exceeds 0.55, the Ni content in the lithium manganese oxide becomes excessively high, which can lead to cation mixing with Li, making it difficult for the lithium manganese oxide to exhibit its properties as an OLO (Oxygen-Liquid Oxide).

[0064] As mentioned above, the lithium manganese oxide according to this application contains excess lithium. Therefore, when the Ni content in the lithium manganese oxide increases, cation mixing becomes more vigorous, and the amount of lithium impurities such as LiOH and Li2CO3 in the lithium manganese oxide can increase. These lithium impurities are the main cause of gelation of the paste when manufacturing a positive electrode paste using the positive electrode active material, and of the swelling phenomenon of the cell during charging and discharging after positive electrode manufacturing.

[0065] On the other hand, in formula 1, M 2 / M 1 If the value is less than 0.24, it is difficult to improve the charge-transfer and / or diffusion of Li ions in the lithium manganese oxide, which decreases due to excess manganese as the Ni content decreases.

[0066] In other words, by ensuring that the nickel content in the lithium manganese oxide satisfies formula 1, it is possible to improve the discharge capacity and rate characteristics of the lithium manganese oxide, which are reduced by excess Mn, to a commercially viable level.

[0067] Furthermore, in the lithium manganese oxide, nickel is present in the phase belonging to the R3-m space group and not in the phase belonging to the C2 / m space group. Therefore, the nickel content in the lithium manganese oxide can be expressed by the following formula 2.

[0068] [Formula 2] 0.40≦M 2′ / M 1′ ≤0.70 Here, M 1′ This is the number of moles of all metallic elements (excluding lithium) in the phase belonging to the R3-m space group, M 2′ This is the number of moles of nickel relative to all metallic elements (excluding lithium) in the phase belonging to the R3-m space group.

[0069] In the above equation 2, M 2′ / M 1′ If the value exceeds 0.70, the Ni content in the phase belonging to the R3-m space group becomes excessively high, which can cause cation mixing with Li, and in formula 2, M 2′ / M 1′ If the value is less than 0.40, the Ni content in the phase belonging to the R3-m space group may be insufficient, and as manganese is present in excess, the charge-transfer and / or diffusion of Li ions may decrease.

[0070] The lithium manganese-based oxide may be a core-shell particle comprising a core and a shell that covers at least a portion of the surface of the core.

[0071] In this context, the core and the shell are simply distinguished to refer to regions in the lithium manganese oxide where the proportion of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group differs. That is, even when the lithium manganese oxide is a core-shell particle, the core and the shell should be understood to form a single solid solution.

[0072] In this case, the shell (or surface) and core (or central part) of a particle can be distinguished by the concentration of any metal element present in that region, or by the proportion of the phase (crystal structure) present in that region, as will be described later.

[0073] The shell may occupy at least a portion of the surface of the core. That is, the shell may be partially present on the surface of the core, or it may occupy the entire surface of the core. When the radius of the core-shell particle is denoted as r, the thickness of the shell may be between 0.001r and 0.9r, but is not necessarily limited to this range. As mentioned above, the core and the shell may be distinguished by the concentration of any metal element, or by the proportion of phases (crystal structures) present in the region, as will be described later.

[0074] In one embodiment, there may be a region in the lithium manganese oxide where a phase belonging to the R3-m space group is predominantly present. That is, if the proportion of the phase belonging to the R3-m space group in a region where a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist in the lithium manganese oxide is greater than the proportion of the phase belonging to the C2 / m space group in the lithium manganese oxide, then the region can be defined as a region where a phase belonging to the R3-m space group is predominantly present.

[0075] For example, if the lithium manganese oxide is a core-shell particle, then the core and shell may contain both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the core may differ from the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the shell. In this case, the phase belonging to the R3-m space group may be predominantly present in either the core or the shell.

[0076] Furthermore, when the phases belonging to the C2 / m space group and the phases belonging to the R3-m space group coexist in the core and shell of the lithium manganese oxide, it is preferable that the ratio of the phases belonging to the R3-m space group to the phases belonging to the C2 / m space group in the shell is greater than the ratio of the phases belonging to the R3-m space group to the phases belonging to the C2 / m space group in the core. The ratio of the phases belonging to the R3-m space group to the phases belonging to the C2 / m space group in the core and shell can be confirmed by the Ni content in the core and shell.

[0077] In other embodiments, when the lithium manganese oxide is a core-shell particle, the core may contain both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, while the shell may contain only a phase belonging to the R3-m space group.

[0078] In the core-shell particles according to the various embodiments described above, the concentration of the metal element in the shell can satisfy the following equation 3.

[0079] [Formula 3] 0.24≦M 4 / M 3 ≤0.75 Here, M 3 This is the number of moles of all metallic elements (excluding lithium) in the shell, M 4 This is the number of moles of nickel relative to all metallic elements (excluding lithium) in the aforementioned shell.

[0080] Furthermore, in the lithium manganese oxide, nickel is present in the phase belonging to the R3-m space group and not in the phase belonging to the C2 / m space group. Therefore, the nickel content in the shell can be expressed by the following equation 4.

[0081] [Formula 4] 0.40≦M 4′ / M 3′ ≤0.75 Here, M 3′ This is the number of moles of all metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the shell, M 4′ This is the number of moles of nickel relative to all metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the aforementioned shell.

[0082] In formula 3 or formula 4, M 4 / M 3 or M 4′ / M 3′ If the value exceeds 0.75, the Ni content in the phase belonging to the R3-m space group becomes excessively high, which can cause cation mixing with Li, and in formula 3, M 4 / M 3 If it is less than 0.24, or if M in equation 4 above 4′ / M 3′If the value is less than 0.40, the Ni content in the phase belonging to the R3-m space group may be insufficient, and as manganese is present in excess, the charge-transfer and / or diffusion of Li ions may decrease.

[0083] In the case of core-shell particles according to the various embodiments described above, the lithium manganese oxide core contains both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group. This allows the R3-m space group to partially counteract the instability of the phase belonging to the C2 / m space group.

[0084] Furthermore, as the shell of the lithium manganese oxide predominantly contains a phase belonging to the R3-m space group, it is possible to mitigate the charge-transfer and / or diffusion of Li ions on the particle surface, which is likely to be caused mainly by a phase belonging to the C2 / m space group, unlike conventional lithium manganese oxides.

[0085] Furthermore, it is well known that lithium-rich lithium manganese oxides containing an excess of Mn have lower electrical conductivity than LCO or NCM or NCA containing an excess of Ni. In addition, in typical NCM, there is a problem that electrical conductivity decreases as the Mn content increases.

[0086] Various reactions can occur on the surface of the positive electrode active material. However, as the Mn content of the positive electrode active material increases, the charge-transfer and / or diffusion of Li ions on the surface is hindered. This phenomenon can be referred to as surface kinetic or surface reaction kinetic reduction.

[0087] Furthermore, the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the lithium manganese oxide may have a gradient that increases from the core toward the shell.

[0088] By forming a gradient from the core toward the shell in which the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group increases, abrupt changes in the crystal structure between the core and the shell can be reduced, and the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group can stably form a solid solution in the lithium manganese oxide.

[0089] If there is a rapid change between the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group in the lithium manganese oxide, a phase transition (change in crystal structure) may occur during charge-discharge cycles when the transition metal moves in an unintended direction within the lithium manganese oxide.

[0090] As described above, the surface kinetics of lithium manganese oxides can be improved by ensuring that the regions within the core where the phases belonging to the R3-m space group exist and the concentrations of metal elements within the shell satisfy the aforementioned equations 1 to 4.

[0091] The lithium manganese oxide as defined in this application can be represented by the following chemical formula 1.

[0092] [Chemical formula 1] rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z )O2 Here, M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. 0 <r≦0.8、0<a≦1、0<x≦1、0≦y<1、0<z<1および0<x+y+z≦1である。

[0093] The lithium manganese oxide represented by chemical formula 1 may selectively contain cobalt. Furthermore, if the lithium manganese oxide contains cobalt, the ratio of the number of moles of cobalt to the total number of moles of metal elements in the lithium manganese oxide may be 10% or less.

[0094] The lithium manganese oxide represented by the above chemical formula 1 consists of a C2 / m phase oxide represented as Li2MnO3 and Li a Ni x Co y Mn z M1 1-(x+y+z) This is a composite oxide in which the R3-m phase oxide, represented by O2, coexists. In this case, the C2 / m phase oxide and the R3-m phase oxide exist in a solid solution state.

[0095] Furthermore, in the lithium manganese oxide represented by chemical formula 1, if r exceeds 0.8, the proportion of Li2MnO3, which is the C2 / m phase oxide, in the lithium manganese oxide may become excessively high, potentially reducing the discharge capacity of the positive electrode active material.

[0096] Lithium-ion battery According to another aspect of the present invention, a positive electrode can be provided that includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may contain a lithium manganese-based oxide as the positive electrode active material according to the various embodiments of the present invention described above.

[0097] Therefore, a detailed explanation of lithium manganese oxides will be omitted, and only the remaining components not mentioned above will be described below. Also, for convenience, the aforementioned lithium manganese oxides will be referred to as the positive electrode active material below.

[0098] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0099] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0100] In this case, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When included in this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0101] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0102] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0103] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0104] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0105] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0106] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0107] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0108] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0109] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0110] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0111] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and optionally a binder, to the negative electrode current collector.

[0112] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0113] The aforementioned negative electrode active material may be present in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0114] The binder may be added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer, as a component that assists in bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0115] The conductive material may be added as a component to further improve the conductivity of the negative electrode active material, in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0116] In one embodiment, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0117] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0118] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, and it is especially preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0119] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0120] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0121] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC), alcohol solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0122] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0123] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0124] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0125] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0126] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0127] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0128] The present invention will be described in more detail below with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0129] Manufacturing Example 1. Manufacturing of positive electrode active material Example 1. (a) Production of precursors A mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 25:75, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was complete, the mixture was washed and dehydrated, and Ni 0.25 Mn 0.75 (OH)2 precursor was obtained.

[0130] (b) First heat treatment After heating the O2 atmosphere furnace at a rate of 2°C / min, the temperature was maintained at 550°C, and the precursor obtained in step (a) was heat-treated for 5 hours, followed by furnace cooling.

[0131] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (non-Li metal) mol ratio = 1.55) as a lithium compound to prepare a mixture. Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min, maintained at 900°C for 8 hours, and then furnace-cooled to obtain a positive electrode active material containing lithium-rich lithium manganese oxide. ICP analysis results show that the positive electrode active material in Example 1 is 0.54Li2MnO3·0.46LiNi 0.538 Mn 0.462 It was confirmed to have an O2 composition.

[0132] Example 2 Ni 0.40 Mn 0.60 The positive electrode active material was prepared in the same manner as in Example 1, except that a (OH)2 precursor was used and LiOH was mixed in at a molar ratio of 1.25 (Li / (non-Li metal) mol ratio = 1.25) before the second heat treatment. ICP analysis results show that the positive electrode active material in Example 2 is 0.23Li2MnO3·0.77LiNi 0.523 Mn 0.477 It was confirmed to have an O2 composition.

[0133] Example 3 Ni 0.45 Mn 0.55 The positive electrode active material was prepared in the same manner as in Example 1, except that a (OH)2 precursor was used and LiOH was mixed in a molar ratio of 1.20 (Li / (non-Li metal) mol ratio = 1.20) before the second heat treatment. ICP analysis results show that the positive electrode active material in Example 3 is 0.19Li2MnO3·0.81LiNi 0.557 Mn0.443 It was confirmed to have an O2 composition.

[0134] Example 4 (a) Production of precursors A mixed aqueous solution of NiSO4·6H2O and MnSO4·H2O in a molar ratio of 40:60, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45°C, and the precursor synthesis reaction was carried out while N2 gas was introduced into the reactor. After the reaction was complete, the mixture was washed and dehydrated, and Ni 0.40 Mn 0.60 (OH)2 precursor was obtained.

[0135] (b) Precursor coating In the reactor where the precursor obtained in step (a) was being stirred, an aqueous solution of CoSO4·7H2O, NaOH, and NH4OH were added. At this time, the CoSO4·7H2O was weighed to a concentration of 10 mol% before being added. After the reaction was complete, the precursor was washed and dehydrated, and then dried at 150°C for 14 hours to obtain the coated precursor.

[0136] (c) First heat treatment The furnace in an O2 atmosphere was heated at a rate of 2°C / min, then maintained at 550°C, and the precursor obtained in step (b) was heat-treated for 5 hours, followed by furnace cooling.

[0137] (d) Second heat treatment The oxide precursor obtained in step (c) was mixed with LiOH (Li / (non-Li metal) mol ratio = 1.25) as a lithium compound to prepare a mixture. Next, the mixture was heat-treated in an O2 atmosphere furnace at a rate of 2°C / min, maintained at 850°C for 8 hours, and then furnace-cooled to obtain a positive electrode active material containing lithium-rich lithium manganese oxide. ICP analysis results show that the positive electrode active material in Example 3 is 0.23Li2MnO3·0.77LiNi 0.46 7Co 0.127 Mn 0.405It was confirmed to have an O2 composition.

[0138] Comparative Example 1 The positive electrode active material was prepared in the same manner as in Example 1, except that LiOH was mixed in at a molar ratio of 1.35 (Li / (non-Li metal) mol ratio = 1.35) before the second heat treatment. ICP analysis results show that the positive electrode active material in Comparative Example 1 is 0.36Li2MnO3·0.64LiNi 0.389 Mn 0.611 It was confirmed to have an O2 composition.

[0139] Comparative Example 2 The positive electrode active material was prepared in the same manner as in Example 2, except that LiOH was mixed in at a molar ratio of 1.50 (Li / (non-Li metal) mol ratio = 1.50) before the second heat treatment. ICP analysis results show that the positive electrode active material in Comparative Example 2 is 0.49Li2MnO3·0.51LiNi 0.793 Mn 0.207 It was confirmed to have an O2 composition.

[0140] Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries A cathode slurry was prepared by dispersing 90 wt% of the cathode active material, 5.5 wt% of carbon black, and 4.5 wt% of the PVDF binder produced by Production Example 1 in 30 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was uniformly coated onto a 15 μm thick aluminum thin film and vacuum-dried at 135°C to produce a cathode for a lithium secondary battery.

[0141] A coin cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separator, and an electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.15 M.

[0142] Experimental Example 1. TEM Analysis of Lithium Manganese Oxides After selecting the lithium manganese oxides contained in each cathode active material manufactured in Manufacturing Example 1, each was cross-sectionally treated with a Cross-section Polisher (accelerating voltage 5.0kV, 4-hour milling), and cross-sectional TEM images were obtained using a transmission electron microscope. Next, a Fast Fourier Transform (FFT) was performed on the TEM images to create diffraction patterns, and then indexing was performed to confirm the crystal structure within the core and shell regions of the lithium manganese oxide.

[0143] Figure 1 shows the TEM analysis results for the lithium manganese oxide contained in the cathode active material according to Example 4. Figure 1 shows a 50 nm scale TEM image, a 5 nm scale TEM image which is an enlarged version of the region shown in the 50 nm scale TEM image, and the crystal structure confirmed by FFT conversion of regions A and B of the 5 nm scale TEM image.

[0144] In this process, the crystal structure within the shell region was confirmed in the region at a distance of 0 to 0.03 μm from the outermost edge of the lithium manganese oxide, and the crystal structure within the core region was confirmed in the region at a distance of 0.12 to 0.15 μm from the outermost edge of the lithium manganese oxide.

[0145] The results of the above analysis are shown in Table 1 below.

[0146] [Table 1]

[0147] Furthermore, EDX mapping was performed on cross-sectional TEM images of lithium manganese oxides contained in each cathode active material manufactured according to Manufacturing Example 1, and the change in nickel concentration (at%) from the shell to the core of the lithium manganese oxide was confirmed by line scanning of the EDX mapping results.

[0148] In this case, the nickel concentration within the shell region was expressed as the average nickel concentration (at%) based on the lithium manganese oxide (bulk) measured from a region at a distance of 0 to 0.03 μm from the outermost edge of the lithium manganese oxide, and the average nickel concentration (at%) in the lithium manganese oxide converted based on the R3-m phase.

[0149] Furthermore, the nickel concentration within the core region was expressed as the average nickel concentration (at%) based on the lithium manganese oxide (bulk) measured from a region at a distance of 0.12 to 0.15 μm from the outermost edge of the lithium manganese oxide, and the average nickel concentration (at%) in the lithium manganese oxide converted based on the R3-m phase.

[0150] Furthermore, the nickel concentration in the intermediate region was expressed as the average nickel concentration (at%) based on the lithium manganese oxide (bulk) measured from a distance of 0.075 to 0.1 μm from the outermost layer of the lithium manganese oxide, and the average nickel concentration (at%) in the lithium manganese oxide converted based on the R3-m phase.

[0151] Figure 2 shows the line sum spectrum obtained by line scanning the EDX mapping results of a cross-sectional TEM image of the lithium manganese oxide contained in the cathode active material of Example 4, confirming the change in nickel concentration (at%) from the core to the shell of the lithium manganese oxide. Region A shown in the line sum spectrum of Figure 2 corresponds to region A in Figure 1.

[0152] The results of the above analysis are shown in Table 2 below.

[0153] [Table 2]

[0154] Referring to the results in Table 1 above, it can be confirmed that in each of the lithium manganese oxides contained in the positive electrode active materials produced according to Production Example 1, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist within a single particle. That is, the lithium manganese oxides contained in each of the positive electrode active materials produced according to Production Example 1 are solid solutions represented by the following Chemical Formula 1,

[0155] [Chemical Formula 1] rLi2MnO3·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O2

[0156] The phase belonging to the C2 / m space group in the solid solution is attributed to Li2MnO3, and the phase belonging to the R3-m space group can be predicted to be attributed to Li a Ni x Co y Mn z M1 1-(x+y+z) O2. Also, it can be confirmed that in the lithium manganese oxides contained in the positive electrode active materials according to Examples 1 to 3, there are regions where the ratios of the presence of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different.

[0157] Referring to the results in Table 1 and Table 2 above, it can be confirmed that in the core region and the shell region of the lithium manganese oxides contained in the positive electrode active materials according to Examples 1 to 3, a phase belonging to the R3-m space group and a phase belonging to the C2 / m space group coexist, and in the lithium manganese oxides, there are a plurality of regions where the ratios of the presence of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different.

[0158] Furthermore, referring to the results in Table 2 and Figure 2, it can be confirmed that in the core region of the lithium manganese oxide contained in the positive electrode active material of Example 4, phases belonging to the C2 / m space group and phases belonging to the R3-m space group coexist, but in the shell region, only phases belonging to the R3-m space group are present, and the nickel concentration in the lithium manganese oxide has a gradient that increases from the core to the shell.

[0159] Considering that the phases belonging to the R3-m space group and the C2 / m space group that constitute the lithium manganese oxide, and that the phases containing nickel belong to the R3-m space group, the above result means that the proportion of phases belonging to the R3-m space group increases from the core to the shell of the lithium manganese oxide. As a result, the proportion of phases belonging to the R3-m space group relative to phases belonging to the C2 / m space group in the lithium manganese oxide has a gradient that increases from the core to the shell.

[0160] On the other hand, in both Comparative Example 1 and Comparative Example 2, the core and shell of the lithium manganese oxide contained in the positive electrode active material contained both a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and it can be confirmed that there is no significant difference between the average nickel concentration in the shell and the average nickel concentration in the core.

[0161] In other words, it can be confirmed that the lithium manganese oxide contained in the positive electrode active materials of Comparative Example 1 and Comparative Example 2 does not have multiple regions in which the proportion of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group differs. The above result means that the lithium manganese oxide exists in a state in which the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are uniformly dissolved.

[0162] Experimental Example 2. Evaluation of the electrochemical properties of lithium secondary batteries. For the lithium secondary batteries (coin cells) manufactured in Manufacturing Example 2, the initial charge capacity, initial discharge capacity, initial reversibility efficiency, and discharge capacity ratio were measured through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 2.0V to 4.6V and a discharge rate of 0.1C to 5.0C.

[0163] The measurement results are shown in Tables 3 and 4 below.

[0164] [Table 3]

[0165] [Table 4]

[0166] Referring to the results in Tables 3 and 4, it can be confirmed that in lithium manganese oxides, there are regions where the proportion of phases belonging to the C2 / m space group and phases belonging to the R3-m space group differs. When the number of moles of nickel in the R3-m space group relative to all metal elements (excluding lithium) in the region where the R3-m space group phase is dominant is within a predetermined range, the decrease in stability caused by the excess lithium and manganese present in the lithium manganese oxide is mitigated and / or prevented, thereby improving the discharge capacity and rate characteristics.

[0167] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be within the scope of the rights of the present invention.

Claims

1. A positive electrode active material comprising a lithium-rich lithium-manganese oxide containing at least lithium, nickel, and manganese, The aforementioned lithium manganese oxide is a solid solution of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group. In the solid solution, there exists a region where the proportion of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different. The lithium manganese oxide in the positive electrode active material satisfies the following formula 1, where the concentration of the metal element satisfies the following formula 1. [Formula 1] 0.24≦M ２ / M １ ≦0.55 Here, M １ This is the total number of moles of metal elements (excluding lithium) in the lithium manganese-based oxide, M ２ This is the number of moles of nickel in the lithium manganese oxide, based on the total number of metal elements (excluding lithium).

2. The lithium manganese-based oxide is a core-shell particle comprising a core and a shell covering at least a portion of the surface of the core, Within the core, the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist. The positive electrode active material according to claim 1, wherein the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group within the shell is greater than the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group within the core.

3. The positive electrode active material according to claim 2, wherein the concentration of the metal element inside the shell satisfies the following formula 3. [Formula 3] 0.24≦M ４ / M ３ ≦0.75 Here, M ３ This is the total number of moles of metal elements (excluding lithium) within the shell, M ４ This is the number of moles of nickel based on the total amount of metallic elements (excluding lithium) within the shell.

4. The positive electrode active material according to claim 2, wherein the concentration of the metal element inside the shell satisfies the following formula 4. [Formula 4] 0.40≦M ４′ / M ３′ ≦0.75 Here, M ３′ This is the total number of moles of metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the shell, M ４′ This is the number of moles of nickel relative to the total number of metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the shell.

5. The positive electrode active material according to claim 2, wherein the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2 / m space group in the lithium manganese oxide has a gradient that increases from the core toward the shell.

6. The lithium manganese oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1. [Chemical formula 1] rLi ２ MnO ３ ・(1-r)- ａ Ni ｘ Co ｙ Mn ｚ M1 １－（ｘ＋ｙ＋ｚ） O ２ Here, M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. 0 < r ≤ 0.8, 0 < a ≤ 1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z < 1, and 0 < x + y + z ≤ 1.

7. The positive electrode active material according to claim 1, wherein the lithium manganese oxide comprises at least one selected from non-aggregated particles containing a single primary particle and secondary particles formed by the aggregation of a plurality of primary particles.

8. The positive electrode active material according to claim 7, wherein the average major axis length of the primary particles is 0.1 μm to 20 μm.

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