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 contain a lithium-excess lithium manganese-based 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 proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group are different exist in the lithium manganese-based oxide, whereby a decrease in stability caused by lithium and manganese present in excess in the lithium manganese-based oxide is alleviated and / or prevented.

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 electrical 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 LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiMnO 2 In addition, composite oxides in which Ni, Co, Mn, or Al is compounded, such as Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015), are being studied.

[0005] Among the above-mentioned positive electrode active materials, LiCoO 2 is excellent in life characteristics and charge-discharge efficiency and is the most widely used. However, due to the limited resources of cobalt used as a raw material, it is expensive, so it has the disadvantage of limited price competitiveness.

[0006] LiMnO 2 、LiMn 2 O 4 Lithium manganese oxides such as etc. have the advantages of excellent thermal safety and low price, but have problems such as small capacity and poor high-temperature characteristics. In addition, LiNiO 2 -based positive electrode active materials exhibit battery characteristics with high discharge capacity. However, due to the cation mixing problem between Li and transition metals, synthesis is difficult, and as a result, there are major problems with rate characteristics.

[0007] In addition, depending on the degree of deepening of such cation mixing, a large amount of Li by-products are generated. Most of these Li by-products consist of compounds of LiOH and Li 2 CO 3 . Therefore, it causes problems of gelation during the production of the positive electrode paste and gas generation due to the progress of charge and discharge after the production of the electrode. Residual Li 2 CO 3 not only increases the swelling phenomenon of the cell and reduces the cycle, but also causes the battery to swell.

[0008] Various candidate materials have been discussed to complement the disadvantages of such conventional positive electrode active materials.

[0009] As an example, research is being conducted to use a lithium-excess lithium manganese-based oxide in which Mn among transition metals is contained in excess and at the same time the lithium content is higher than the total content of transition metals as a positive electrode active material for a lithium secondary battery. Such a lithium-excess lithium manganese-based oxide is also referred to as an overlithiated layered oxide (OLO).

[0010] The above-mentioned OLO has the advantage that it can theoretically exhibit high capacity in a high-voltage operating environment. However, in reality, due to the relatively high amount of Mn contained in the oxide, the electrical conductivity is low, resulting in the disadvantage that the capability rate of lithium secondary batteries using OLO is low. Thus, when the capability rate is low, problems such as a decrease in charge-discharge capacity and life efficiency (capacity retention) during the charge-discharge cycle of lithium secondary batteries appear.

[0011] In addition, the decrease in charge-discharge capacity or voltage decay during the charge-discharge cycle of lithium secondary batteries using OLO can also be induced by phase transitions caused by the movement of transition metals in lithium manganese oxides. For example, in lithium manganese oxides with a layered crystal structure, when the transition metals move in an unintended direction and induce a phase transition, a spinel or a crystal structure similar to it may occur entirely and / or partially within the lithium manganese oxide.

[0012] In order to solve the above problems, there have been attempts to improve the problems of OLO through structural improvement and surface modification of particles, such as adjusting the size of OLO particles or coating the surface of OLO, but it has not reached the commercialization level.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0015] For example, conventionally, lithium secondary batteries using LFP have been mainly used from the viewpoints of ensuring safety and the like. However, recently, the use of nickel-based lithium composite oxides, which have a larger energy capacity per unit weight compared to LFP, has been on the rise.

[0016] In addition, recently, many nickel-based lithium composite oxides used as cathode active materials for high-capacity lithium secondary batteries essentially use ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. Among them, 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 a new composition of cathode active material that can reduce the cobalt content or eliminate cobalt.

[0017] From such a viewpoint, lithium-excess lithium manganese-based oxides can meet the expectations of the aforementioned market. However, it can be said that the electrochemical properties and stability of lithium manganese-based oxides are still insufficient as a substitute for commercialized NCM or NCA type cathode active materials.

[0018] However, when compared with other types of commercialized cathode active materials, even if the conventional lithium-excess lithium manganese-based oxides have disadvantages from the viewpoints of electrochemical properties and / or stability, if it is possible to control the concentration of transition metals in different regions in the lithium manganese-based oxides, it has been confirmed by the present inventors that the lithium-excess lithium manganese-based oxides can also exhibit electrochemical properties and stability at a commercially viable level.

[0019] Accordingly, an object of the present invention is to provide a positive electrode active material containing a lithium-excess 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 in the lithium manganese oxide, 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 exist, whereby a decrease in stability caused by excess lithium and manganese present in the lithium manganese oxide is alleviated and / or prevented.

[0020] Further, an object of the present invention is to provide a positive electrode active material containing a lithium-excess 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 by making the concentration of Ni within a predetermined range in a region where the phase belonging to the R3-m space group exists, it is possible to improve the low discharge capacity and rate characteristics of a conventional lithium-excess lithium manganese oxide.

[0021] Also, an object of the present invention is to provide a lithium secondary battery in which the low rate characteristics of a conventional OLO are improved by using a positive electrode containing the positive electrode active material defined in the present application.

Means for Solving the Problems

[0022] According to one aspect of the present invention for solving the above-described technical problems, as a positive electrode active material containing a lithium-excess lithium manganese oxide containing at least lithium, nickel, and manganese, in the lithium manganese oxide, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist, and a positive electrode active material is provided in which 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 exist in the lithium manganese oxide.

[0023] In one example, 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 is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide, M 2 is the number of moles of nickel based on all metal elements (excluding lithium) in the lithium manganese oxide.

[0025] By satisfying the content of nickel among the metal elements (excluding lithium) in the lithium manganese oxide with the above formula 1, it is possible to improve the discharge capacity and rate characteristics, etc. that are reduced by excessive Mn in the lithium manganese oxide to a commercially available level.

[0026] The lithium manganese oxide may be core-shell particles including a core and a shell covering at least a part of the surface of the core. At this time, the core and the shell are simply divided for the purpose of referring to regions where the ratios of the phases belonging to the C2 / m space group and the R3-m space group are different in the lithium manganese oxide. That is, even when the lithium manganese oxide is core-shell particles, the core and the shell should be understood to form one solid solution.

[0027] When the lithium manganese oxide is core-shell particles, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist in the core, 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 larger 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] At this time, the concentration of the metal element in the shell can satisfy the following formula 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] rLi 2 MnO 3 ·(1 - r)Li 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.

[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] At this time, the single particle may mean "a non-aggregated particle containing a single primary particle", "a particle formed by aggregation of a relatively small number of primary particles", or "a particle formed by aggregation of a plurality (tens to hundreds or more) of primary particles".

[0035] In the solid solution represented by the chemical formula 1, the phase belonging to the C2 / m space group is Li 2 MnO 3 due to, and the phase belonging to the R3-m space group is Li a Ni x Co y Mn z M1 1-(x+y+z) O 2 caused by.

[0036] Also, according to another aspect of the present invention, a positive electrode containing the above-described positive electrode active material is provided.

[0037] Furthermore, according to still another aspect of the present invention, a lithium secondary battery using the above-described positive electrode is provided.

Advantages of the Invention

[0038] According to the present invention, when compared with other types of commercially available positive electrode active materials, it is possible to improve the limitations of conventional lithium-excess lithium manganese-based oxides, which have various disadvantages, from the viewpoints of electrochemical characteristics and / or stability.

[0039] First, the lithium manganese-based oxide contained in the positive electrode active material according to the present invention is a lithium-excess lithium manganese-based 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 described above, lithium manganese oxides containing excessive amounts of lithium and manganese can exhibit high capacity in a high-voltage operating environment. However, such lithium manganese oxides have the disadvantage that the discharge capacity and the capability rate are low due to excessive lithium and manganese in the oxide. However, when the ratio of the phases belonging to the C2 / m space group and the phases belonging to the R3-m space group is made different for each region like the positive electrode active material according to the present invention, the effects of improving the discharge capacity and the rate characteristics are exhibited.

[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 is large in the surface portion (which can be referred to as the core) of the lithium manganese oxide, the charge-transfer and / or diffusion of Li ions on the surface of the particles (which is likely to be mainly caused by the phase belonging to the C2 / m space group) is alleviated, the low electrical conductivity of the lithium manganese oxide is improved, and it is possible to improve the discharge capacity and the rate characteristics to a commercially available level.

Brief Description of the Drawings

[0042]

Figure 1

Figure 2

Best Mode for Carrying Out the Invention

[0043] For easier understanding of the present invention, for convenience, specific terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in the present invention have meanings generally understood by those with ordinary knowledge in the relevant technical field. Also, unless otherwise specified in the context, terms in the singular form are to be understood as including their plural forms, and terms in the plural form are to be understood as including their singular forms.

[0044] Hereinafter, a positive electrode active material containing a lithium-excess lithium manganese-based oxide containing at least lithium, nickel, manganese, and a doping metal according to the present invention and a lithium secondary battery containing the positive electrode active material will be described in more detail.

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

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

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

[0048] The primary particle and the secondary particle may each independently have a rod shape, an elliptical shape, and / or an amorphous shape.

[0049] When using the average major axis length as an indicator showing the sizes of the primary particles and the secondary particles, the average major axis length of the primary particles constituting the lithium manganese-based 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 the primary particles constituting the secondary particles, and particles having various average major axis lengths may be included in the positive electrode active material.

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

[0051] Thus, a lithium manganese-based oxide that is "a non-aggregated particle containing a single primary particle" or "a particle formed by aggregation of a relatively small number of primary particles" generally requires stronger heat treatment conditions (higher heat treatment temperature / long-time heat treatment) than when manufacturing "secondary particles formed by aggregation of dozens to hundreds or more primary particles". For example, when heat-treating at a relatively high temperature (800 °C or higher) for a long time, it is known that particle growth (crystal growth) is promoted and the size of a single particle becomes larger, and at the same time, a positive electrode active material with a lower degree of particle aggregation can be obtained.

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

[0053] Further, the primary particles may include at least one crystallite. That is, the primary particles may exist as particles composed of a single crystallite or particles containing a plurality of crystallites.

[0054] The lithium manganese-based oxide defined in the present application is a composite metal oxide containing an excessive amount of lithium and manganese, and in the lithium manganese-based 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-based 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 the present application, the solid solution means that in the lithium manganese-based 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] At this time, the single particle may mean "a non-aggregated particle containing a single primary particle", "a particle formed by aggregation of a relatively small number of primary particles", or "a particle formed by aggregation of a plurality (tens to hundreds or more) of primary particles".

[0057] In the present application, the 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 existing in the lithium manganese-based oxide are physically and / or chemically bonded or attached.

[0058] For example, a metal oxide having a phase belonging to the R3-m space group obtained 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 R3-m space group, and having a surface-coated metal oxide having a phase belonging to the C2 / m space group does not correspond to a solid solution.

[0059] In addition, in the lithium manganese oxide, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group may coexist, and in the lithium manganese oxide, there may be regions 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 proportions of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group in the lithium manganese oxide are made different for each region, the discharge capacity and rate characteristics of the positive electrode active material containing the lithium manganese oxide can exhibit the effect of being improved.

[0061] Further, 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 is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide, and M 2 is the number of moles of nickel based on all metal elements (excluding lithium) in the lithium manganese oxide.

[0063] When M 2 / M 1 in the formula (1) exceeds 0.55, the content of Ni in the lithium manganese oxide becomes excessively large, and cation mixing with Li may occur, and it is difficult for the lithium manganese oxide to exhibit the characteristics as OLO.

[0064] As described above, since the lithium manganese oxide according to the present application contains excess lithium, when the content of Ni in the lithium manganese oxide increases, cation mixing becomes intense, and in the lithium manganese oxide, LiOH and Li 2 CO 3The amount of lithium impurities such as these can be increased. When producing a positive electrode paste using a positive electrode active material, the lithium impurities are the main cause of causing gelation of the paste and causing swelling of the cell during charge and discharge after positive electrode production.

[0065] On the other hand, in Formula 1, M 2 / M 1 When it is less than 0.24, as the content of Ni in the lithium manganese oxide is insufficient, it is difficult to improve the charge-transfer and / or diffusion of Li ions that is reduced by excessive manganese.

[0066] That is, when the nickel content in the lithium manganese oxide satisfies Formula 1, it is possible to improve the discharge capacity, rate characteristics, etc. that are reduced by excessive Mn in the lithium manganese oxide to a commercially available level.

[0067] Also, in the lithium manganese oxide, nickel exists in the phase belonging to the R3-m space group and does not exist in the phase belonging to the C2 / m space group. Therefore, the nickel content in the lithium manganese oxide can be represented by the following Formula 2.

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

[0069] In Formula 2, M 2′ / M 1′When it exceeds 0.70, the content of Ni in the phase belonging to the R3-m space group becomes excessively large, and cation mixing may occur between Li, and M in Formula 2 2′ / M 1′ When it is less than 0.40, the content of Ni in the phase belonging to the R3-m space group is insufficient, and as the manganese is excessively present, charge-transfer and / or diffusion of Li ions may decrease.

[0070] The lithium manganese oxide may be core-shell particles including a core and a shell covering at least a part of the surface of the core.

[0071] At this time, the core and the shell are simply divided in order to refer to 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 in the lithium manganese oxide. That is, even when the lithium manganese oxide is core-shell particles, it should be understood that the core and the shell form one solid solution.

[0072] At this time, the shell (or surface part) and the core (or central part) of the particle can be distinguished by the concentration of any metal element present in the region, or can be distinguished by the ratio of the phase (crystal structure) present in the region as described later.

[0073] The shell may occupy at least a part of the surface of the core. That is, the shell can be partially present on the surface of the core, or can occupy the entire surface of the core. When the radius of the core-shell particle is r, the thickness of the shell may be 0.001r to 0.9r, but is not necessarily limited to this. As described above, the core and the shell are distinguished by the concentration of any metal element, or are distinguished by the ratio of the phase (crystal structure) present in the region as described later.

[0074] In one embodiment, in the lithium manganese oxide, there may be a region where the phase belonging to the R3-m space group is dominantly present. That is, in the lithium manganese oxide, when the ratio of the presence of the phase belonging to the R3-m space group in the region where the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist is larger than the ratio of the presence of the phase belonging to the C2 / m space group in the lithium manganese oxide, the region can be defined as the region where the phase belonging to the R3-m space group is dominantly present.

[0075] For example, when the lithium manganese oxide is core-shell particles, in the core and the shell, the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist, 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 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 different. At this time, in one of the core and the shell regions, the phase belonging to the R3-m space group may be dominantly present.

[0076] Further, when the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist in the core and the shell of the lithium manganese oxide, 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 is preferably larger 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. 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 and the shell can be confirmed through the Ni content in the core and the shell.

[0077] In another embodiment, when the lithium manganese oxide is core-shell particles, in the core, the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group coexist, and in the shell, only the phase belonging to the R3-m space group may be present.

[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 formula 3.

[0079] [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.

[0080] In addition, in the lithium manganese oxide, nickel exists in the phase belonging to the R3-m space group and does not exist in the phase belonging to the C2 / m space group. Therefore, the content of nickel in the shell can be represented by the following formula 4.

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

[0082] When M 4 / M 3 or M 4′ / M 3′ in the above formula 3 or formula 4 exceeds 0.75, the content of Ni in the phase belonging to the R3-m space group becomes excessively large, and cation mixing may occur between Li. When M 4 / M 3 in the above formula 3 is less than 0.24, or M 4′ / M 3′When it is less than 0.40, the content of Ni in the phase belonging to the R3-m space group is insufficient, and as manganese is present in excess, charge-transfer and / or diffusion of Li ions may decrease.

[0083] In the case of the core-shell particles according to the various embodiments described above, in the core of the lithium manganese oxide, due to the coexistence of the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group, the phase belonging to the R3-m space group can cancel out a certain part of the instability of the phase belonging to the C2 / m space group.

[0084] Also, in the shell of the lithium manganese oxide, as the phase belonging to the R3-m space group predominantly exists, different from the conventional lithium manganese oxide, it is possible to mitigate charge-transfer and / or diffusion of Li ions on the surface of the particles, which is likely to be mainly caused by the phase belonging to the C2 / m space group.

[0085] Also, in the case of a lithium-excess type lithium manganese oxide containing an excessive amount of Mn, it is well known that its electrical conductivity is lower than that of LCO or NCM or NCA containing an excessive amount of Ni. Also, in general NCM, there is a problem that the electrical conductivity decreases as the content of Mn increases.

[0086] On the surface of the positive electrode active material, various reactions can occur. However, the higher the content of Mn in the positive electrode active material, the more the charge-transfer and / or diffusion of Li ions on the surface is hindered, and such a phenomenon can be referred to as surface kinetic or surface reaction kinetic decrease.

[0087] Also, 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 to the shell.

[0088] By forming a gradient 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 from the core toward the shell, a sharp change in the crystal structure can be reduced between the core and the shell, and in the lithium manganese oxide, 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.

[0089] If there is a sharp 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, during charge and discharge cycles, transition metals may move in an unintended direction in the lithium manganese oxide and a phase transition (change in crystal structure) may occur.

[0090] As described above, by having the region where the phase belonging to the R3-m space group exists within the core and the concentration of the metal element within the shell satisfy the above formulas 1 to 4, the surface kinetics of the lithium manganese oxide can be improved.

[0091] The lithium manganese oxide defined in the present application may be represented by the following Chemical Formula 1.

[0092] [Chemical Formula 1] rLi 2 MnO 3 ·(1-r)Li 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.

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

[0094] The lithium manganese-based oxide represented by the chemical formula 1 is Li 2 MnO 3 The oxide of the C2 / m phase represented by and Li a Ni x Co y Mn z M1 1-(x+y+z) O 2 It is a composite oxide in which the oxide of the R3-m phase represented by coexists. At this time, the oxide of the C2 / m phase and the oxide of the R3-m phase exist in a state of forming a solid solution.

[0095] Further, in the lithium manganese-based oxide represented by the chemical formula 1, when r exceeds 0.8, in the lithium manganese-based oxide, the proportion of Li which is an oxide of the C2 / m phase 2 MnO 3 becomes excessively large, and there is a risk that the discharge capacity of the positive electrode active material will decrease.

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

[0097] Therefore, a specific description of the lithium manganese-based oxide is omitted, and hereinafter, only the remaining configurations not described above will be described. Further, hereinafter, for convenience, the lithium manganese-based oxide described above will be referred to as a positive electrode active material.

[0098] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0099] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition containing a conductive material and optionally a binder together with the positive electrode active material to the positive electrode current collector.

[0100] At this time, the positive electrode active material may be contained in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, based on the total weight of the positive electrode active material layer. When contained within this content range, excellent capacity characteristics can be exhibited, but it is not necessarily limited thereto.

[0101] The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing chemical changes. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber and other carbon-based substances, metal powders or metal fibers such as copper, nickel, aluminum, silver, etc., conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used. The conductive material may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

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

[0103] Except for using the positive electrode active material, the positive electrode may be manufactured by a normal positive electrode manufacturing method. Specifically, after applying a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent onto a positive electrode current collector, it may be manufactured by drying and rolling.

[0104] The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N - methylpyrrolidone (NMP), acetone, or water, etc. Among these, one kind alone or a mixture of two or more kinds may be used. The amount of the solvent used is sufficient if it can dissolve or disperse the positive electrode active material, the conductive material, and the binder, and then has a viscosity that can show excellent thickness uniformity during coating for positive electrode manufacturing, considering the coating thickness of the slurry and the manufacturing yield.

[0105] In another embodiment, the positive electrode may be manufactured by laminating, on a positive current collector, a film obtained by casting the positive electrode slurry composition on a separate support and then peeling the film from the support.

[0106] According to still another aspect of the present invention, an electrochemical element including the above-described positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

[0107] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, for the sake of convenience, a specific description thereof is omitted, and hereinafter, only the remaining configurations not described above will be specifically described.

[0108] The lithium secondary battery may further selectively include a battery container for housing an electrode assembly of 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 current collector and a negative electrode active material layer positioned on the negative current collector.

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

[0111] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition containing a conductive material and, optionally, a binder together with the negative electrode active material 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 alloy, Sn alloy, or Al alloy, SiO β (0 < β < 2), SnO 2 , metal oxides capable of doping and undoping lithium such as vanadium oxide and lithium vanadium oxide, or composites containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, etc. Any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, low-crystalline carbon and highly crystalline carbon, etc. may all be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of highly crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite 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 negative electrode active material may be contained in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0114] The binder may usually 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 binding the conductive material, the active material, and the current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, 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 is produced by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the support on the negative electrode current collector.

[0117] In another embodiment, the negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating a film obtained by peeling the film from the support on 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 migration path for lithium ions. Usually, any separator that can be used in a lithium secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to ion migration of the electrolyte and excellent in electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multilayer structure.

[0119] Examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel 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 contain an organic solvent and a lithium salt.

[0121] As the organic solvent, any solvent may be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. 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, which can enhance the charge-discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred. In this case, when the cyclic carbonate and the chain carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0122] The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ), LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can move effectively.

[0123] In addition to the electrolyte constituent components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. At this time, the additive may be contained in an amount of 0.1 to 5% by weight based on 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 stably exhibits excellent discharge capacity, output characteristics and life characteristics, and thus is useful in portable devices such as mobile phones, notebook personal computers, digital cameras, and the field of electric vehicles such as hybrid electric vehicles (HEV).

[0125] The outer shape of the lithium secondary battery according to the present invention is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a pouch shape or a coin shape using a can. Further, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also preferably used as a unit cell in a medium- or large-sized battery module including a plurality of battery cells.

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

[0127] The battery module or the battery pack can be used as a power source for any one or more medium to large-sized devices, including a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV).

[0128] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and it should not be construed that the scope of the present invention is limited by these examples.

[0129] Production Example 1. Production of positive electrode active material Example 1. (a) Production of precursor NiSO 4 ·6H 2 O and MnSO 4 ·H 2 O were mixed in an aqueous solution in a molar ratio of 25:75, and NaOH and NH 4 OH were added while stirring. The temperature inside the reactor was maintained at 45°C, and N 2 gas was introduced into the reactor to carry out the precursor synthesis reaction. After the reaction was completed, washing and dehydration were performed to obtain Ni 0.25 Mn 0.75 (OH) 2 precursor.

[0130] (b) First heat treatment O 2 The firing furnace in an O

[0131] (c) Second heat treatment The precursor in the oxide state obtained in step (b) was mixed with LiOH (Li / (metal other than Li) mol ratio = 1.55) as a lithium compound to prepare a mixture. Next, O 2After the atmosphere baking furnace was heated up at a rate of 2 °C / min and then maintained at 900 °C, the mixture was heat-treated for 8 hours and then furnace cooled to obtain a cathode active material containing lithium-excess lithium manganese-based oxide. As a result of ICP analysis, the cathode active material according to Example 1 was 0.54Li 2 MnO 3 ·0.46LiNi 0.538 Mn 0.462 O 2 It was confirmed to have the composition.

[0132] Example 2 Ni 0.40 Mn 0.60 (OH) 2 A cathode active material was produced in the same manner as in Example 1, except that the precursor was used and LiOH was mixed at a molar ratio of 1.25 (Li / (metal other than Li) mol ratio = 1.25) before the second heat treatment. As a result of ICP analysis, the cathode active material according to Example 2 was 0.23Li 2 MnO 3 ·0.77LiNi 0.523 Mn 0.477 O 2 It was confirmed to have the composition.

[0133] Example 3 Ni 0.45 Mn 0.55 (OH) 2 A cathode active material was produced in the same manner as in Example 1, except that the precursor was used and LiOH was mixed at a molar ratio of 1.20 (Li / (metal other than Li) mol ratio = 1.20) before the second heat treatment. As a result of ICP analysis, the cathode active material according to Example 3 was 0.19Li 2 MnO 3 ·0.81LiNi 0.557 Mn 0.443 O 2 It was confirmed to have the composition.

[0134] Example 4 (a) Production of precursor An aqueous mixed solution in which NiSO 4 ·6H 2 O and MnSO 4 ·H 2 O are mixed at a molar ratio of 40:60, NaOH and NH 4 OH were added while stirring. The temperature inside the reactor was maintained at 45 °C, and N 2 gas was introduced into the reactor while performing a precursor synthesis reaction. After completion of the reaction, washing and dehydration were performed to obtain a Ni 0.40 Mn 0.60 (OH) 2 precursor.

[0135] (b) Precursor coating CoSO 4 ·7H 2 O aqueous solution, NaOH and NH 4 OH were added to the reactor in which the precursor obtained in step (a) was being stirred. At this time, CoSO 4 ·7H 2 O was weighed to be 10 mol% and then added. After completion of the reaction, washing and dehydration were performed, and then drying was performed at 150 °C for 14 hours to obtain a coated precursor.

[0136] (c) First heat treatment O 2 The temperature of the firing furnace in an O

[0137] (d) Second heat treatment The precursor in the oxide state obtained in step (c) and LiOH (Li / (metal other than Li) mol ratio = 1.25) as a lithium compound were mixed to prepare a mixture. Next, the temperature of the firing furnace in an O 2 atmosphere was raised at a rate of 2 °C / min, then maintained at 850 °C, and the mixture was heat-treated for 8 hours, followed by furnace cooling to obtain a positive electrode active material containing a lithium-excess lithium manganese-based oxide. As a result of ICP analysis, the positive electrode active material according to Example 3 was 0.23Li2 MnO 3 ·0.77LiNi 0.46 7Co 0.127 Mn 0.405 O 2 It was confirmed to have the composition.

[0138] Comparative Example 1 Before the second heat treatment, a positive electrode active material was produced in the same manner as in Example 1, except that LiOH was mixed at a molar ratio of 1.35 (Li / (metal other than Li) mol ratio = 1.35). As a result of ICP analysis, the positive electrode active material according to Comparative Example 1 was 0.36Li 2 MnO 3 ·0.64LiNi 0.389 Mn 0.611 O 2 It was confirmed to have the composition.

[0139] Comparative Example 2 Before the second heat treatment, a positive electrode active material was produced in the same manner as in Example 2, except that LiOH was mixed at a molar ratio of 1.50 (Li / (metal other than Li) mol ratio = 1.50). As a result of ICP analysis, the positive electrode active material according to Comparative Example 2 was 0.49Li 2 MnO 3 ·0.51LiNi 0.793 Mn 0.207 O 2 It was confirmed to have the composition.

[0140] Production Example 2. Production of lithium secondary battery 90 wt% of the positive electrode active material produced according to Production Example 1, 5.5 wt% of carbon black, and 4.5 wt% of a PVDF binder were each dispersed in 30 g of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The positive electrode slurry was uniformly applied to an aluminum thin film with a thickness of 15 μm and vacuum dried at 135°C to produce a positive electrode for a lithium secondary battery.

[0141] A lithium foil was used as a counter electrode with respect to the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and LiPF 6 was present at a concentration of 1.15 M in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7 to manufacture a coin cell.

[0142] Experimental Example 1. TEM analysis of lithium manganese oxide After selecting the lithium manganese-based oxides contained in each of the positive electrode active materials manufactured in Production Example 1, each was subjected to cross-section treatment with a Cross-section Polisher (acceleration voltage 5.0 kV, milling for 4 hours), and then a cross-section TEM photograph was obtained with a transmission electron microscope. Next, FFT (Fast Fourier Transform) was performed on the TEM image to create a diffraction pattern, and then indexing was performed to confirm the crystal structures in the core region and the shell region of the lithium manganese-based oxide.

[0143] Figure 1 is a diagram showing the results of TEM analysis of the lithium manganese-based oxide contained in the positive electrode active material according to Example 4. Figure 1 shows a TEM image on a 50 nm scale, a TEM image on a 5 nm scale obtained by enlarging the region displayed in the TEM image on the 50 nm scale, and the crystal structures confirmed through FFT conversion for region A and region B of the TEM image on the 5 nm scale.

[0144] At this time, the crystal structure in the shell region was confirmed in the region where the distance from the outermost contour of the lithium manganese-based oxide was 0 to 0.03 μm, and the crystal structure in the core region was confirmed in the region where the distance from the outermost contour of the lithium manganese-based oxide was 0.12 to 0.15 μm.

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

[0146]

Table 1

[0147] In addition, EDX mapping was performed on the cross-sectional TEM image of the lithium manganese oxide contained in each of the positive electrode active materials produced in Production Example 1, and the EDX mapping results were line scanned to confirm the change in the nickel concentration (at%) from the shell to the core of the lithium manganese oxide.

[0148] At this time, the nickel concentration in the shell region was shown by the average nickel concentration (at%) measured from the region where the distance from the outermost contour of the lithium manganese oxide was 0 to 0.03 μm, based on the lithium manganese oxide (bulk), and the average nickel concentration (at%) converted based on the R3-m phase in the lithium manganese oxide.

[0149] In addition, the nickel concentration in the core region was shown by the average nickel concentration (at%) measured from the region where the distance from the outermost contour of the lithium manganese oxide was 0.12 to 0.15 μm, based on the lithium manganese oxide (bulk), and the average nickel concentration (at%) converted based on the R3-m phase in the lithium manganese oxide.

[0150] In addition, the nickel concentration in the intermediate region was shown by the average nickel concentration (at%) measured from the region where the distance from the outermost contour of the lithium manganese oxide was 0.075 to 0.1 μm, based on the lithium manganese oxide (bulk), and the average nickel concentration (at%) converted based on the R3-m phase in the lithium manganese oxide.

[0151] Figure 2 is a line sum spectrum in which the EDX mapping results for the cross-sectional TEM image of the lithium manganese oxide contained in the positive electrode active material according to Example 4 were line scanned to confirm the change in the 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 analysis results were 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 by 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 by Production Example 1 are solid solutions represented by Chemical Formula 1 below,

[0155] [Chemical Formula 1] rLi 2 MnO 3 ·(1-r)Li a Ni x Co y Mn z M1 1-(x+y+z) O 2

[0156] The phase belonging to the C2 / m space group in the solid solution is due to Li 2 MnO 3 and the phase belonging to the R3-m space group can be predicted to be due to Li a Ni x Co y Mn z M1 1-(x+y+z) O 2 It can also 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 shell region of the lithium manganese oxide 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 oxide, there are a plurality of regions 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.

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

[0159] Considering that the phase in which nickel exists among the phase belonging to the R3-m space group and the phase belonging to the C2 / m space group constituting the lithium manganese oxide is the phase belonging to the R3-m space group, the above results mean that the proportion of the phase belonging to the R3-m space group increases from the core to the shell of the lithium manganese oxide. Accordingly, the proportion 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 of increasing from the core to the shell.

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

[0161] That is, it can be confirmed that in the lithium manganese oxide contained in the positive electrode active material according to Comparative Example 1 and Comparative Example 2, there are no a plurality of regions where the ratios of the phases belonging to the C2 / m space group and the phases belonging to the R3-m space group are different. The above results mean that the lithium manganese oxide exists in a state where the phases belonging to the C2 / m space group and the R3-m space group are uniformly solid-solved.

[0162] Experimental Example 2. Evaluation of electrochemical characteristics of lithium secondary battery For the lithium secondary battery (coin cell) manufactured in Production Example 2, an electrochemical analyzer (Toyo, Toscat-3100) was used to conduct charge and discharge experiments at 25 °C, with a voltage range of 2.0 V to 4.6 V and a discharge rate of 0.1 C to 5.0 C, and the initial charge capacity, initial discharge capacity, initial reversible efficiency, and the ratio of discharge capacity were measured.

[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 above, in the lithium manganese oxide, there are regions where the ratios of the phases belonging to the C2 / m space group and the phases belonging to the R3-m space group are different. When the molar number of nickel based on all the metal elements (excluding lithium) in the phases belonging to the R3-m space group within the region where the phases belonging to the R3-m space group predominantly exist is within a predetermined range with respect to all the metal elements (excluding lithium), it can be confirmed that the discharge capacity and rate characteristics are improved by alleviating and / or preventing the decrease in stability caused by the excessive lithium and manganese present in the lithium manganese oxide.

[0167] Although the embodiments of the present invention have been described above, those having ordinary knowledge in the art can make various modifications and changes to the present invention by adding, changing, deleting, or adding components, etc., without departing from the idea of the present invention described in the claims, and it can be said that this is also included within the scope of the rights of the present invention.

Claims

1. A positive electrode active material comprising a lithium-excess lithium-manganese-based oxide containing at least lithium, nickel, and manganese, In the lithium manganese-based oxide, a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group coexist, and The positive electrode active material has regions in which the ratio of a phase belonging to the C2 / m space group to a phase belonging to the R3-m space group is different in the lithium manganese oxide.

2. The positive electrode active material according to claim 1 , wherein the concentration of the metal element in the lithium manganese-based oxide satisfies the following formula 1: [Formula 1] 0.24≦M ２ / M １ ≦0.55 Where: M １ is the number of moles of all metal elements (excluding lithium) in the lithium manganese oxide, M ２ is the number of moles of nickel based on all metal elements (excluding lithium) in the lithium manganese oxide.

3. The positive electrode active material according to claim 1 , wherein the concentration of the metal element in the lithium manganese-based oxide satisfies the following formula 2: [Formula 2] 0.40≦M ２′ / M １′ ≦0.70 Here, M １′ is the number of moles of all metal elements (excluding lithium) in a phase belonging to the R3-m space group, M ２′ is the number of moles of nickel based on all metal elements (excluding lithium) in the phase belonging to the R3-m space group.

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

5. The positive electrode active material according to claim 4 , wherein the concentration of the metal element in the shell satisfies the following formula 3: [Formula 3] 0.24≦M ４ / M ３ ≦0.75 Where: 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.

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

7. 5. The positive electrode active material according to claim 4, 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-based oxide has an increasing gradient from the core to the shell.

8. The positive electrode active material according to claim 4, wherein only a phase belonging to the R3-m space group is present in the shell.

9. The positive electrode active material of claim 1 , wherein the lithium manganese-based oxide is 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 Where: 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.

10. A positive electrode comprising the positive electrode active material according to claim 1 .

11. A lithium secondary battery using the positive electrode according to claim 10.

Images