Positive electrode active material, positive electrode and lithium secondary battery

Abstract

To provide a positive electrode active material capable of reducing side reactions between a lithium manganese-based oxide and a liquid electrolyte by modifying the surface of the lithium manganese-based oxide.MEANS FOR SOLVING THE PROBLEM: The invention provides a positive electrode active material comprising a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved or complexed. The lithium manganese-based oxide comprises a secondary particle formed by aggregating a plurality of primary particles, an average value of the minor axis lengths of the primary particles calculated from 20 primary particles selected in the order of longest-to-shortest minor axis lengths from the primary particles exposed on the surface of the secondary particle from an SEM image of the secondary particle is greater than or equal to 130 nm and less than 850 nm, and a coating layer comprising a first oxide containing at least one selected from metal elements and metalloid elements and a second oxide containing phosphorus (P) is formed on at least a part of the surface of the primary particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cathode active material and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material including a lithium-excess lithium-manganese-based oxide, which prevents deterioration of electrochemical characteristics of a lithium secondary battery, including rate characteristics, due to excess lithium and manganese present in the lithium-manganese-based oxide, and particularly relates to a cathode active material, a cathode, and a lithium secondary battery that can reduce side reactions between the lithium-manganese-based oxide and an electrolyte during high-voltage operation.

[0002] Batteries store electricity by using electrochemically reactive materials at the positive and negative electrodes. A typical example of such batteries is a lithium secondary battery, which stores electrical energy by utilizing the difference in chemical potential between the positive and negative electrodes when lithium ions are intercalated / deintercalated.

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

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and oxides of Ni, Co, Mn, and Al.

[0005] Among the positive electrode active materials, LiCoO2 is the most widely used due to its excellent life characteristics and charge / discharge efficiency. However, it has a drawback in that it is expensive due to the limited availability of cobalt as a raw material, limiting its price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but suffer from low capacity and poor high-temperature characteristics. LiNiO2-based positive electrode active materials exhibit high discharge capacity, but are difficult to synthesize due to the problem of cation mixing between Li and transition metals, resulting in significant problems with rate characteristics.

[0007] Furthermore, depending on the depth of this cation mixing, a large amount of Li by-products are generated. These Li by-products, mostly consisting of LiOH and Li2CO3, can cause gelation during the preparation of the positive electrode paste or can generate gas during repeated charge / discharge cycles after electrode fabrication. Furthermore, the residual Li2CO3 among these Li by-products can increase cell swelling, thereby reducing the lifespan characteristics.

[0008] Various candidate materials have been proposed to overcome the drawbacks of conventional positive electrode active materials.

[0009] For example, research is being conducted to use overlithiated lithium manganese oxides, which contain an excess amount of Mn among transition metals and have a lithium content greater than the total content of the transition metals, as positive electrode active materials for lithium secondary batteries. Such overlithiated lithium manganese oxides are also called overlithiated layered oxides (OLO).

[0010] While OLO theoretically has the advantage of being able to exhibit high capacity under high-voltage operating conditions, it has the disadvantage of relatively low electrical conductivity due to the excessive Mn content in the oxide, resulting in poor rate performance of lithium secondary batteries using OLO. This poor rate performance can lead to problems such as reduced charge / discharge capacity and life efficiency (capacity retention) during charge / discharge cycling of the lithium secondary battery.

[0011] Furthermore, the decrease in charge / discharge capacity or voltage decay during charge / discharge cycles of a lithium secondary battery using OLO can be caused by a phase transition due to the movement of transition metals in the lithium manganese-based oxide. For example, if a phase transition is induced by the unintended movement of transition metals in a layered crystalline lithium manganese-based oxide, a spinel or similar crystalline structure may be formed entirely and / or partially within the lithium manganese-based oxide.

[0012] To solve the above problems, research has been conducted to change the composition of OLO, but these attempts have not yet reached a commercial level. Summary of the Invention [Problem to be solved by the invention]

[0013] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is playing a role as a market driver, and as a result, the demand for positive electrode active materials used in lithium secondary batteries is also continuously increasing.

[0014] For example, lithium secondary batteries using lithium iron phosphate (LFP) have traditionally been used primarily for safety reasons, but recently there has been a trend toward the use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP.

[0015] In addition, nickel-based lithium composite oxides, which are currently mainly used as positive electrode active materials in high-capacity lithium secondary batteries, essentially contain ternary metal elements such as nickel, cobalt, and manganese or nickel, cobalt, and aluminum. However, cobalt is not only unstable in supply and demand but is also excessively expensive compared to other raw materials, so a new positive electrode active material with a reduced or eliminated cobalt content is needed.

[0016] Considering these various circumstances, lithium-excess lithium manganese-based oxides can meet the aforementioned market expectations, but they still have limitations in that their electrochemical properties and stability are insufficient as an alternative to commercially available ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA)-based ternary lithium composite oxides.

[0017] For example, as mentioned above, if a transition metal in a lithium manganese-based oxide moves in an unintended direction, and a spinel or similar crystalline structure is formed entirely and / or partially in the lithium manganese-based oxide, a decrease in charge / discharge capacity or voltage decay may occur during charge / discharge cycling of a lithium secondary battery using OLO.

[0018] However, compared to other commercially available positive electrode active materials, conventional lithium-excess lithium-manganese-based oxides have disadvantages in terms of electrochemical properties and / or stability. However, the present inventors have confirmed that when the surface of the lithium-manganese-based oxide is modified, the lithium-excess lithium-manganese-based oxide can also exhibit electrochemical properties and stability at a level that allows it to be commercially used.

[0019] The inventors have confirmed that the surface modification of the lithium manganese-based oxide forms a physical barrier between the lithium manganese-based oxide and an electrolyte to reduce side reactions between the lithium manganese-based oxide and an electrolyte. In addition, when a spinel phase and / or a spinel-like phase (hereinafter, unless otherwise defined, the term "spinel phase" refers to both the spinel phase and the spinel-like phase) is formed on at least a portion of the surface of the lithium manganese-based oxide through the surface modification, unlike a spinel phase formed by a phase transition due to migration of a transition metal in the lithium manganese-based oxide, the spinel phase formed by the surface modification can serve as a two-dimensional and / or three-dimensional path for lithium ions to diffuse within the lithium manganese-based oxide.

[0020] In addition, when the surface modification described above is applied after reducing the specific surface area through the induction of crystal growth or particle growth of the primary particles constituting the lithium manganese-based oxide, the intended effect of the surface modification (e.g., improvement in lithium ion diffusivity) can be further improved.

[0021] Therefore, an object of the present invention is to provide a cathode active material that includes a lithium-excess lithium-manganese-based oxide, and that can reduce side reactions between the lithium-manganese-based oxide and an electrolyte by modifying the surface of the lithium-manganese-based oxide.

[0022] Another object of the present invention is to provide a positive electrode active material that can mitigate and / or prevent a decrease in charge-transfer and / or diffusibility (i.e., surface kinetics) of lithium ions on the particle surface by modifying the surface of the lithium-manganese oxide.

[0023] Another object of the present invention is to provide a cathode active material that can alleviate and / or prevent a decrease in rate characteristics due to excess lithium and manganese present in the lithium-manganese-based oxide and reduce side reactions between the lithium-manganese-based oxide and an electrolyte during high-voltage operation by inducing crystal growth or particle growth of the primary particles constituting the lithium-manganese-based oxide and simultaneously modifying the surfaces of the primary particles, particularly the surfaces of the primary particles that form secondary particles formed by aggregation of a plurality of primary particles.

[0024] Another object of the present invention is to provide a lithium secondary battery that can achieve high stability by using a positive electrode containing the positive electrode active material defined herein, thereby mitigating and / or preventing a decrease in rate performance due to the excessive amounts of lithium and manganese present in conventional OLO, and reducing side reactions between the positive electrode active material and an electrolyte during high-voltage operation. [Means for solving the problem]

[0025] According to one aspect of the present invention for solving the above-described technical problems, there is provided a positive electrode active material including a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved or composite.

[0026] Generally, commercially available ternary lithium composite oxides with a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition contain a single phase of the R3-m space group, whereas the lithium-rich lithium manganese oxide defined in this application is characterized by a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group.

[0027] In one embodiment, the positive electrode active material may include a lithium manganese-based oxide that exists as secondary particles formed by agglomeration of a plurality of primary particles.

[0028] In this case, it is preferable that crystal growth or particle growth is induced in the primary particles constituting the lithium manganese-based oxide, and thus the average minor axis length of the primary particles may be 130 nm or more and less than 850 nm, preferably 300 nm or more and 500 nm or less, more preferably 289 nm or more and 353 nm or less.

[0029] The average minor axis length of the primary particles can be measured for the primary particles exposed on the surface of the secondary particles from the SEM image of the secondary particles (for example, calculated from 20 primary particles selected in descending order of minor axis length from the primary particles exposed on the surface of the secondary particles from the SEM image of the secondary particles).

[0030] The lithium manganese-based oxide may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1:

[0031] [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b (where, M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, and M2 does not overlap with M1; X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である。)

[0032] In one embodiment, at least a portion of the surfaces of the primary particles and the secondary particles may be modified. Specifically, at least a portion of the surfaces of the primary particles and the secondary particles may have a coating layer containing at least one selected from a first oxide containing at least one selected from a metal element and a metalloid element and a second oxide containing phosphorus (P).

[0033] By modifying the surfaces of the primary particles, particularly the surfaces of the primary particles that form the surfaces of the secondary particles, with the first oxide and the second oxide, it is possible to reduce side reactions with the electrolyte that occur on the surfaces of the secondary particles, and at the same time, to mitigate and / or prevent a decrease in charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surfaces of the secondary particles.

[0034] The spinel phase may also be formed through surface modification of the primary particles and / or the secondary particles.

[0035] Unlike the spinel phase formed by a phase transition due to the migration of a transition metal in the lithium manganese-based oxide, the spinel phase formed on the surface of the primary particles and / or the secondary particles may serve as a two-dimensional and / or three-dimensional path for lithium ions to diffuse within the lithium manganese-based oxide.

[0036] According to another aspect of the present invention, there is provided a positive electrode including the above-described positive electrode active material.

[0037] According to yet another aspect of the present invention, there is provided a lithium secondary battery using the above-described positive electrode. [Effects of the Invention]

[0038] According to the present invention, it is possible to improve upon the limitations of conventional lithium-excess lithium manganese-based oxides, which have various disadvantages in terms of electrochemical properties and / or stability, when compared with commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition.

[0039] Specifically, according to the present invention, a physical barrier between the lithium manganese-based oxide and the electrolyte can be formed through surface modification of the lithium manganese-based oxide, thereby reducing side reactions between the lithium manganese-based oxide and the electrolyte. In particular, OLO, such as the lithium manganese-based oxide, has the advantage of exhibiting high capacity under high-voltage operating conditions. However, the possibility of side reactions between the lithium manganese-based oxide and the electrolyte increases as the operating voltage increases. Therefore, it is important to reduce side reactions between the lithium manganese-based oxide and the electrolyte.

[0040] Therefore, the side reaction between the lithium manganese-based oxide and the electrolyte is reduced, thereby improving the stability and lifespan of a lithium secondary battery using the lithium manganese-based oxide as a cathode active material. In particular, a cathode active material with reduced side reaction with the electrolyte can operate a lithium secondary battery at a higher voltage. In this case, a spinel phase can be formed on at least a portion of the surface of the lithium manganese-based oxide during surface modification of the lithium manganese-based oxide.

[0041] In this case, unlike the spinel phase formed by a phase transition due to the migration of transition metals in the lithium manganese-based oxide, the spinel phase formed on the surface of the lithium manganese-based oxide through the surface modification of the lithium manganese-based oxide serves as a two-dimensional and / or three-dimensional path for lithium ions to diffuse within the lithium manganese-based oxide, and as a result, can contribute to improving the overall lithium ion diffusivity (Li+ diffusivity) of the lithium manganese-based oxide.

[0042] In addition, when the above-described surface modification is applied after reducing the specific surface area through the induction of crystal growth or particle growth of the primary particles constituting the lithium manganese-based oxide, the intended effect of the surface modification (e.g., improvement in lithium ion diffusivity) can be further improved.

[0043] The lithium manganese-based oxide can improve the intercalation / deintercalation efficiency of the primary particles and secondary particles formed by agglomeration of the primary particles by inducing crystal growth or particle growth of the primary particles. In this regard, if at least a portion of the surface of the primary particles is surface-modified while the growth of the primary particles is induced, the surface kinetics, such as charge-transfer and / or diffusivity of lithium ions, can be improved, thereby effectively mitigating and / or preventing the deterioration of rate characteristics due to the presence of excessive amounts of lithium and manganese in the lithium manganese-based oxide.

[0044] As described above, when a positive electrode containing the positive electrode active material defined herein is used, it is possible to mitigate and / or prevent the deterioration of rate characteristics due to the excessive amounts of lithium and manganese present in conventional OLO, and to achieve high stability by reducing side reactions between the positive electrode active material and the electrolyte during high voltage operation.

[0045] The specific effects of the present invention, together with the above-mentioned effects, will be described below while explaining specific matters for carrying out the invention. [Brief explanation of the drawings]

[0046] [Figure 1] 1 is a SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Example 1. [Figure 2] 1 is a SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Example 2. [Figure 3]1 is an SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Comparative Example 1. [Figure 4] 1 is an SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Reference Example 1. [Figure 5] 1 is an SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Reference Example 2. [Figure 6] 1 is an SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Reference Example 3. [Figure 7] FIG. 2 is a diagram showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Example 1. [Figure 8] FIG. 10 is a graph showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Example 2. [Figure 9] FIG. 10 is a graph showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Example 3. [Figure 10] FIG. 10 is a graph showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Comparative Example 1. [Figure 11] FIG. 10 is a graph showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Reference Example 3. [Figure 12] FIG. 10 is a graph showing the dQ / dV profile during initial discharge of a lithium secondary battery manufactured using the positive electrode active material according to Reference Example 4. [Figure 13] 1 is a diagram showing the results of EDS mapping of target elements (Ni, Mn, Al, and P) for a cross-sectional SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Example 1. FIG. [Figure 14] 10 is a diagram showing the results of EDS mapping of target elements (Ni, Mn, Al, and P) for a cross-sectional SEM image of a lithium manganese-based oxide contained in a positive electrode active material according to Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0047] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0048] Hereinafter, a cathode active material including a lithium-excess lithium manganese-based oxide and a lithium secondary battery including the cathode active material according to some embodiments of the present invention will be described in more detail.

[0049] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material containing a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are dissolved or combined.

[0050] The lithium manganese-based oxide contains at least lithium, nickel, and manganese. In this case, the lithium manganese-based oxide is also called an overlithiated layered oxide (OLO) when the lithium content in the lithium manganese-based oxide is greater than the total content of other transition metals (generally, when the molar ratio of lithium to all metal elements other than lithium in the lithium manganese-based oxide (Li / Metal molar ratio) is greater than 1).

[0051] Generally, in commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition, the manganese content of all metal elements excluding lithium is 20 mol % or less. Considering this, the lithium-manganese-based oxide has a relatively high manganese content (e.g., 50 mol % or more, preferably 55 mol % to 75 mol %) of all metal elements compared to commercially available ternary lithium composite oxides.

[0052] In addition, considering that commercially available ternary lithium composite oxides having a nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) composition have a nickel content of 60 mol% or more (80 mol% or more in the case of a high-Ni type) of all metal elements excluding lithium, the lithium-manganese-based oxide has a relatively low ratio of nickel to all metal elements (e.g., less than 50 mol%, preferably 25 mol% to 45 mol%) compared to commercially available ternary lithium composite oxides.

[0053] There is also a difference in that the Li / Metal molar ratio measured from the lithium manganese-based oxide defined herein is larger than that of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA). For example, the Li / Metal molar ratio of ternary lithium composite oxides such as nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) is close to 1. On the other hand, the Li / Metal molar ratio of the lithium manganese-based oxide defined herein is larger than 1, preferably 1.1 to 1.7, and more preferably 1.2 to 1.6.

[0054] Despite the difference in composition, the lithium manganese-based oxide can also function as a composite metal oxide capable of intercalating / deintercalating lithium ions.

[0055] The lithium manganese-based oxide included in the positive electrode active material defined herein includes secondary particles formed by agglomeration of a plurality of primary particles.

[0056] The primary particles constituting the lithium manganese-based oxide may have a rod-like, elliptical, and / or irregular shape, and unless otherwise intended in the manufacturing process, primary particles of various shapes exist within the same positive electrode active material.

[0057] Conventional lithium-excess lithium manganese oxides have a secondary particle form in which a plurality of primary particles are aggregated, and generally have a form in which primary particles having an average particle size of several to several tens of nanometers are aggregated.

[0058] Meanwhile, the primary particles constituting the lithium manganese-based oxide defined in the present application can have an average particle size of 0.1 μm to 5 μm, preferably 0.1 μm to 1.0 μm, and more preferably 0.25 μm to 0.75 μm, due to the induction of crystal growth and particle growth.

[0059] The major axis length of the primary particles, the minor axis length of the primary particles, the ratio of the major axis length to the minor axis length of the primary particles (major axis length / minor axis length), and the average particle size of the primary particles ([major axis length+minor axis length] / 2) can be calculated as the average value after measuring the major axis length and minor axis length of the primary particles exposed on the surface of the secondary particles.

[0060] For example, the average value of the results measured from all primary particles exposed on the surface of the secondary particles or the average value of the results measured from a plurality of primary particles selected from the primary particles exposed on the surface of the secondary particles (for example, calculated from a plurality of primary particles (e.g., 10 primary particles, 20 primary particles, etc.) selected in descending order of minor axis length from the primary particles exposed on the surface of the secondary particles from an SEM image of the secondary particles) can be used.

[0061] If the average particle size of the primary particles is less than 0.1 μm, the specific surface area of ​​the lithium manganese-based oxide (secondary particles) composed of the primary particles is relatively large, which increases the possibility of side reactions occurring between the lithium manganese-based oxide and the electrolyte during storage or operation of the lithium secondary battery.

[0062] On the other hand, when the average particle size of the primary particles is larger than 5 μm, excessive growth of the primary particles is induced, and the diffusion path of lithium ions within the primary particles becomes longer. When the diffusion path of lithium ions within the primary particles is too long, the mobility of lithium ions within the primary particles and the diffusion of lithium ions through the primary particles decrease, which causes an increase in the resistance of the lithium manganese-based oxide (secondary particles) composed of the primary particles.

[0063] In order to reduce the specific surface area of ​​the lithium manganese oxide and prevent a decrease in the mobility of lithium ions within the primary particles and the diffusibility of lithium ions through the primary particles, the average particle size of the primary particles is preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 1.0 μm, and even more preferably 0.25 μm to 0.75 μm.

[0064] In this case, the average minor axis length of the primary particles constituting the lithium manganese-based oxide may be 130 nm or more and less than 850 nm, preferably 300 nm or more and 500 nm or less, and more preferably 289 nm or more and 353 nm or less.

[0065] As described above, the average minor axis length of the primary particles may be an average value of the results measured on all primary particles exposed on the surface of the secondary particles or a plurality of primary particles (e.g., 10 primary particles, 20 primary particles, etc.) selected in descending order of minor axis length from among the primary particles exposed on the surface of the secondary particles.

[0066] The average minor axis length of the primary particles being less than 130 nm means that the crystal growth or particle growth of the primary particles is insufficient. When the average minor axis length of the primary particles is less than 130 nm, the lithium ion diffusivity may be high physically, but as the specific surface area of ​​the lithium-manganese-based oxide increases, side reactions may occur during the initial battery reaction under high voltage conditions, resulting in a rapid decrease in battery performance. Furthermore, not only is the growth of the primary particles insufficient, but as the specific surface area of ​​the lithium-manganese-based oxide increases, it becomes difficult to uniformly modify the surfaces of the primary particles and / or secondary particles.

[0067] Meanwhile, an average minor axis length of the primary particles of 850 nm or more indicates excessive growth of the primary particles. Generally, over-sintering during the preparation of the lithium-manganese-based oxide can unnecessarily accelerate the growth of the primary particles. In particular, excessive growth of the primary particles due to over-sintering, etc., can lengthen the diffusion path of lithium ions within the primary particles, reducing the diffusivity of lithium ions through the primary particles, ultimately resulting in increased resistance of the lithium-manganese-based oxide. As the resistance of the lithium-manganese-based oxide increases, battery reactivity decreases, making it difficult to improve battery capacity and rate characteristics.

[0068] When the lithium manganese-based oxide exists as secondary particles formed by aggregation of a plurality of primary particles, the average particle size of the secondary particles ([major axis length + minor axis length] / 2) may be 0.5 μm to 15 μm. The average particle size of the secondary particles may vary depending on the number of the primary particles constituting the secondary particles. Furthermore, as the average particle size of the primary particles increases due to induced crystal growth or particle growth of the primary particles, the number of the primary particles constituting the secondary particles may decrease.

[0069] The lithium manganese-based oxide defined herein may be a lithium-excess lithium manganese-based oxide represented by the following Chemical Formula 1. The composition represented by the following Chemical Formula 1 may represent an average composition reflecting the composition of a coating layer present on at least a portion of the surface of the lithium manganese-based oxide.

[0070] [Chemical formula 1] Li(Li a M1 x M2 y )O 2-b X b where M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, and M2 does not overlap with M1; X is a halogen capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, and 0 <a≦0.7、0≦b≦0.1、0<x≦1、0≦y<1、0<x+y≦1である。

[0071] The type of halogen usable as X can be determined by referring to the periodic table, and can include F, Cl, Br and / or I, preferably F. The coating layer is preferably formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles.

[0072] A gradient may be formed in which the ratio of at least one selected from x and y, preferably y, in Chemical Formula 1 changes from the surface region of the primary particles toward the center region of the primary particles. Also, a gradient may be formed in which the ratio of at least one selected from x and y, preferably y, in Chemical Formula 1 changes from the surface region of the secondary particles toward the center region of the secondary particles. M2 may contain phosphorus (P), and a gradient may be formed in which the concentration of phosphorus (P) decreases from the surface region of the secondary particles toward the center region of the secondary particles.

[0073] In addition, the lithium-excess lithium manganese-based oxide represented by Chemical Formula 1 may further include a spinel phase in addition to the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group.

[0074] In another embodiment, the lithium manganese-based oxide may be represented by the following Formula 1-1: The composition represented by the following Formula 1-1 may represent an average composition reflecting the composition of a coating layer present on at least a portion of the surface of the lithium manganese-based oxide.

[0075] [Chemical formula 1-1] r′Li2MnO3·(1-r′)Li a′ M1 x′ M2 y′ O 2-b′ X b′ where: M1 is at least one selected from Ni and Mn; M2 is at least one selected from Ni, Mn, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, and M2 does not overlap with M1; X is a halogen capable of substituting at least a part of the oxygen present in the lithium manganese-based oxide, and 0 <r≦0.7、0<a′≦1、0≦b′≦0.1、0<x′≦1、0≦y′<1および0<x′+y′≦1である。

[0076] The type of halogen that can be used as X refers to the periodic table, and F, Cl, Br and / or I can be used, with F being preferred.

[0077] In Chemical Formula 1 and Chemical Formula 1-1, when M1 is Ni, M2 may contain Mn, and when M1 is Mn, M2 may contain Ni. Also, when M1 is Ni and Mn, M2 may be absent, or, if present, may be an element other than Ni and Mn.

[0078] That is, when M1 is Ni, M2 may include at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd (preferably, at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, and W, more preferably, at least one selected from Co, Al, P, B, Ti, Zr, Si, and W, more preferably, Al and P), and Mn.

[0079] When M1 is Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd (preferably, at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, and W, more preferably, at least one selected from Co, Al, P, B, Ti, Zr, Si, and W, more preferably, Al and P), and Ni.

[0080] When M1 is Ni and Mn, M2 may include at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd and Nd, preferably at least one selected from Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si and W, more preferably at least one selected from Co, Al, P, B, Ti, Zr, Si and W, more preferably Al and P.

[0081] The lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may optionally contain cobalt. When the lithium manganese-based oxide contains cobalt, the mole fraction of cobalt relative to the moles of all metal elements in the lithium manganese-based oxide may be 20% or less, preferably 15% or less, and more preferably 10% or less. In other cases, the lithium manganese-based oxide represented by Chemical Formula 1 may have a cobalt-free composition.

[0082] The Li / Metal molar ratio measured from the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 may be greater than 1, preferably 1.1 to 1.7, and more preferably 1.2 to 1.6. When the Li / Metal molar ratio measured from the lithium manganese-based oxide is at least greater than 1, it is possible to form a lithium-excess lithium manganese-based oxide. Furthermore, in order for the lithium manganese-based oxide to properly form a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, and to simultaneously exhibit high capacity under high-voltage operating conditions, the Li / Metal molar ratio of the lithium manganese-based oxide is preferably 1.2 to 1.6.

[0083] In addition, to properly form a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, the manganese content of the lithium manganese-based oxide represented by Formula 1 or Formula 1-1 among all metal elements excluding lithium is preferably 50 mol% or more. To enable the lithium manganese-based oxide to have the OLO characteristic of exhibiting high capacity under high-voltage operating conditions, the manganese content of the lithium manganese-based oxide among all metal elements excluding lithium is more preferably 50 mol% or more but less than 80 mol%, and even more preferably 55 mol% to 75 mol%. When the manganese content of the lithium manganese-based oxide exceeds 80 mol%, a phase transition may occur during the formation and / or operation of a lithium secondary battery due to the migration of transition metals (especially manganese) within the lithium manganese-based oxide. This phase transition forms a spinel phase, and the spinel phase, acting as an impurity in the lithium manganese-based oxide, may cause a decrease in charge / discharge capacity or voltage decay during the charge / discharge cycles of the lithium secondary battery.

[0084] In order to properly form a solid solution or composite of a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group, the content of nickel among all metal elements excluding lithium present in the lithium manganese-based oxide represented by Chemical Formula 1 or Chemical Formula 1-1 is preferably less than 50 mol%.

[0085] When the nickel content in the lithium manganese-based oxide is 50 mol% or more, the C2 / m phase may not be sufficiently formed, or the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group may not form a sufficient solid solution, which may cause phase separation during the formation and / or operation of the lithium secondary battery.

[0086] Generally, commercially available ternary lithium composite oxides with nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) compositions exist in a single phase belonging to the R3-m space group.

[0087] On the other hand, the lithium-rich lithium manganese oxide represented by the chemical formula 1 or the chemical formula 1-1 is an oxide of a phase belonging to the C2 / m space group represented by rLi2MnO3 (hereinafter referred to as "C2 / m phase") and (1-r)Li a M1 x M2 y O 2-b X b The lithium manganese-based oxide exists as a composite oxide in which an oxide of the C2 / m phase and an oxide of the R3-m phase form a solid solution.

[0088] In this case, a composite oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are simply physically and / or chemically bonded or attached does not fall under the category of a solid solution as defined in this application.

[0089] For example, a composite oxide having a phase belonging to the C2 / m space group, which is formed by mixing a metal oxide having a phase belonging to the C2 / m space group with a metal oxide having a phase belonging to the R3-m space group and whose surface is coated with a metal oxide having a phase belonging to the R3-m space group, does not fall under the category of a solid solution as defined in the present application.

[0090] In the lithium manganese-based oxide represented by Formula 1-1, if r exceeds 0.7, the proportion of the C2 / m phase oxide, Li2MnO3, in the lithium manganese-based oxide becomes excessively high, which may result in an excessively high manganese content in the positive electrode active material, resulting in a decrease in discharge capacity. That is, in order to sufficiently activate the C2 / m phase oxide, which has a relatively high resistance in the lithium manganese-based oxide, and improve surface kinetics, it is preferable that the R3-m phase oxide be present in a certain proportion or more.

[0091] In one embodiment, at least a portion of the surfaces of the primary particles and the secondary particles may be modified. Specifically, at least a portion of the surfaces of the primary particles and the secondary particles may have a coating layer including a first oxide including at least one selected from a metal element and a metalloid element and a second oxide including phosphorus (P).

[0092] Unless otherwise defined, the term "surface of the primary particle" used herein means the outer surface of the primary particle exposed to the outside. Similarly, the term "surface of the secondary particle" used herein means the outer surface of the secondary particle exposed to the outside. In this case, the "surface of the secondary particle" formed by aggregation of multiple primary particles corresponds to the exposed surface of the primary particle present in the surface portion of the secondary particle.

[0093] Unless otherwise defined, the term "surface portion of a particle" used herein means a region relatively close to the "surface" of a particle, and "core portion of a particle" means a region relatively closer to the "center" of a particle than the "surface portion." Accordingly, "surface portion of a primary particle" means a region relatively closer to the "surface" of the primary particle, and "core portion of a primary particle" means a region relatively closer to the "center" of the primary particle than the "surface portion." Similarly, "surface portion of a secondary particle" means a region relatively closer to the "surface" of the secondary particle, and "core portion of a secondary particle" means a region relatively closer to the "center" of the secondary particle than the "surface portion."

[0094] In this case, the region of any particle excluding the "surface portion of the particle" can be defined as the "center portion of the particle."

[0095] For example, when the radius of the primary particle is r, the area at a distance of 0 to 0.5r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the area at a distance of 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle. If the radius of the primary particle is 0.5 μm, the surface portion of the primary particle can be defined as the area at a distance of 0 to 0.25 μm from the surface of the primary particle, and the center portion of the primary particle can be defined as the area at a distance of 0 to 0.25 μm from the center of the primary particle.

[0096] Furthermore, if necessary, when the radius of the primary particle is referred to as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the primary particle can be defined as the surface portion of the primary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the primary particle can be defined as the center portion of the primary particle.

[0097] Similarly, when the radius of the secondary particle is referred to as r, the region at a distance of 0 to 0.5r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle. If the radius of the secondary particle is 2.0 μm, the surface portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the surface of the secondary particle, and the center portion of the secondary particle can be defined as the region at a distance of 0 to 1.0 μm from the center of the primary particle.

[0098] Furthermore, if necessary, when the radius of the secondary particle is referred to as r, the region at a distance of 0 to 0.1r or 0 to 0.2r from the surface of the secondary particle can be defined as the surface portion of the secondary particle, and the region at a distance of 0 to 0.2r or 0 to 0.5r from the center of the secondary particle can be defined as the center portion of the secondary particle.

[0099] By modifying the surfaces of the primary particles, particularly the surfaces of the primary particles that form the surfaces of the secondary particles, with the first oxide and the second oxide, it is possible to reduce side reactions with the electrolyte that occur on the surfaces of the secondary particles, and at the same time, to mitigate and / or prevent a decrease in charge-transfer and / or diffusivity (i.e., surface kinetics) of lithium ions on the surfaces of the secondary particles.

[0100] The surface where adjacent primary particles contact each other within the secondary particle may be referred to as an interface between the primary particles, and the interface between the primary particles may be defined as a grain boundary between the primary particles. In addition, the primary particles may be separated from adjacent primary particles to form voids within the secondary particle.

[0101] The coating layer is defined as a region where the first oxide and / or the second oxide are present on the surface of the primary particles and / or the secondary particles, and the coating layer may be formed entirely or partially on the surface of the primary particles and / or the secondary particles. When the coating layer is partially formed on the surface of the primary particles and / or the secondary particles, the shape of the coating layer may be referred to as an island shape.

[0102] Furthermore, the first oxide and / or the second oxide may be present in a state of being physically and / or chemically bound to the surface of the primary particles and / or the secondary particles, or may be present in a state of being partially solid-dissolved.

[0103] The coating layer present inside the secondary particles may be formed by diffusion of the first oxide and / or the second oxide from the surface portion to the central portion of the secondary particles along the grain boundaries between the primary particles. By the diffusion of the first oxide and / or the second oxide from the surface portion to the central portion of the secondary particles, at least one of the elements contained in the first oxide and / or the second oxide can exhibit a concentration gradient that decreases from the surface portion to the central portion of the secondary particles.

[0104] The first oxide may be represented by the following Chemical Formula 2.

[0105] [Chemical Formula 2] Li c M3 d O e Here, M3 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, 0 ≦ c ≦ 10, 0 ≦ d ≦ 8, 0 < e ≦ 13, and the case where c and d are both 0 is excluded.

[0106] Non-limiting examples of the first oxide represented by Chemical Formula 2 include Li g Zr h O i 、Li g Ti h O i 、Li g Ni h O i 、Li g Nb h O i 、Li g Co h O i 、Li g Si h O i 、Li g Al h O i 、Co h O i 、Mnh O i , Al h O i , Si h O i , Zr h O i , Ti h O i etc.

[0107] The coating layer is preferably formed on at least a portion of the surface of the primary particles present at the surface of the secondary particles. The first oxide may diffuse from the surface of the secondary particles toward the center of the secondary particles along the grain boundaries between the primary particles, thereby forming a gradient in which the concentration of M3 decreases from the surface of the secondary particles toward the center of the secondary particles. The concentration gradient of M3 can be confirmed by SEM / EDS analysis of the lithium manganese-based oxide.

[0108] The second oxide may be represented by the following Chemical Formula 3:

[0109] [Chemical formula 3] Li f M4 g (P h O i ) j Here, M4 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd, and 0≦f≦10, 0≦g≦8, 0 <h≦4、0<i≦10、0<j≦13である。

[0110] Non-limiting examples of the second oxide represented by Formula 3 include Li j (P l O m ) n , Li j Al k (P l O m ) n , Al k (P l Om ) n , (P l O m ) n , Li j Mn k (P l O m ) n , Mn k (P l O m ) n , Li j Ni k (P l O m ) n , Ni k (P l O m ) n etc.

[0111] The coating layer is preferably formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles. Similarly, the second oxide may diffuse from the surface of the secondary particles toward the center of the secondary particles along the grain boundaries between the primary particles, thereby forming a gradient in which the concentrations of M4 and / or P decrease from the surface of the secondary particles toward the center of the secondary particles. The concentration gradient of M4 and P can be confirmed by SEM / EDS analysis of the lithium manganese-based oxide.

[0112] The first oxide may be present mainly in the form of fine particles on the surfaces of the primary particles and / or the secondary particles, while the second oxide may be present not only on the surfaces of the primary particles and / or the secondary particles but also as rod-shaped particles between the primary particles.

[0113] When the coating layer contains the first oxide and the second oxide simultaneously, the molar fractions of M3, M4, and phosphorus (P) calculated by the following Equation 1 from the ICP analysis results of the positive electrode active material are preferably 1.0 to 30.0, and more preferably 1.13 to 26.25.

[0114] [Formula 1] P (mol%) / (M3 (mol%) + M4 (mol%))

[0115] A molar fraction of M3, M4, and phosphorus (P) calculated by Equation 1 less than 1.0 means that the contents of M3 and M4 are excessively high or the content of phosphorus (P) is insufficient. If the contents of M3 and M4 in the lithium manganese-based oxide are excessively high, problems such as a decrease in the discharge capacity of a positive electrode active material using the lithium manganese-based oxide may occur. On the other hand, if the content of phosphorus (P) in the lithium manganese-based oxide is excessively low, the effect of suppressing side reactions with the electrolyte on the surfaces of the primary particles and / or secondary particles may be insufficient, or two-dimensional and / or three-dimensional paths for lithium ion diffusion within the lithium manganese-based oxide may be difficult to form. Furthermore, it may be difficult to form a spinel phase on the surface of the lithium manganese-based oxide.

[0116] A molar fraction of M3, M4, and phosphorus (P) calculated by Equation 1 greater than 30.0 means that the contents of M3 and M4 are insufficient or the content of phosphorus (P) is excessively high. If the content of phosphorus (P) in the lithium manganese-based oxide is excessively high, the specific surface area of ​​the lithium manganese-based oxide may become excessively large, which may result in an increase in side reactions with the electrolyte, resulting in a rapid decrease in surface stability. On the other hand, if the contents of M3 and M4 in the lithium manganese-based oxide are excessively low, it may be difficult to sufficiently mitigate the decrease in surface kinetics of primary particles and / or secondary particles.

[0117] Furthermore, when the coating layer contains the first oxide and the second oxide simultaneously, the first oxide and / or the second oxide may diffuse from the surface portion of the secondary particle toward the center portion of the secondary particle along the crystal grain boundaries between the primary particles, thereby forming a gradient in which the concentration of at least one selected from M3, M4, and P decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0118] Such a concentration gradient serves as a path for lithium ions to move within and between the primary particles, thereby improving the transport / diffusion efficiency of lithium ions via the primary particles.

[0119] The lithium manganese-based oxide defined herein may further include a spinel phase and / or a spinel-like phase other than the phase belonging to the C2 / m space group and the phase belonging to the R3-m space group (hereinafter, unless otherwise defined, the spinel phase refers to both the spinel phase and the spinel-like phase). In this case, the spinel phase may be a phase formed by the first oxide and / or the second oxide, preferably the second oxide, but is not necessarily limited thereto.

[0120] Although OLO, such as the lithium manganese-based oxide defined herein, theoretically has the advantage of being able to exhibit high capacity under high-voltage operating conditions, it has the disadvantage of having relatively low electrical conductivity due to the excessive Mn contained in the oxide, resulting in low capacity rate of lithium secondary batteries using OLO. This low capacity rate leads to problems such as reduced charge / discharge capacity and life efficiency (capacity retention) during charge / discharge cycling of the lithium secondary battery.

[0121] It is known that the decrease in charge / discharge capacity or voltage decay during charge / discharge cycles of lithium secondary batteries using OLO is caused by a phase transition due to the movement of transition metals in lithium manganese oxide. For example, if a phase transition is induced by the unintended movement of transition metals in a layered crystalline lithium manganese oxide, a spinel or similar crystalline structure may occur entirely and / or partially within the lithium manganese oxide.

[0122] However, when a spinel phase is formed on the surface of the primary particles and / or the secondary particles, unlike the spinel phase formed by a phase transition due to the migration of a transition metal in the lithium manganese-based oxide, such a spinel phase not only contributes to surface stabilization of the lithium manganese-based oxide but also serves as a two-dimensional and / or three-dimensional path for the diffusion of lithium ions within the lithium manganese-based oxide.

[0123] The formation of a lithium ion diffusion path within the lithium manganese-based oxide reduces the resistance to lithium ion migration via the lithium manganese-based oxide, which can further contribute to improving the rate characteristics of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0124] The spinel phase may be present in a state of being physically and / or chemically bonded to the primary particles and / or the coating layer, or may be present in a state of being partially solid-dissolved. Preferably, the spinel phase or the spinel-like phase is solid-dissolved or composited with at least one selected from the primary particles and the coating layer.

[0125] The spinel phase may be present in at least a portion of the interface between the primary particles and the coating layer. The spinel phase or the spinel-like phase is preferably present in at least a portion of the interface between the primary particles and the coating layer.

[0126] The first oxide and / or the second oxide may diffuse from the surface portions of the secondary particles toward the center portions of the secondary particles along the crystal grain boundaries between the primary particles, so that the proportion of the spinel phase and the spinel-like phase in the entire crystal structure present in the surface portions of the secondary particles may be greater than the proportion of the spinel phase and the spinel-like phase in the entire crystal structure present in the center portions of the secondary particles.

[0127] In addition, a gradient may be formed in which the proportion of the spinel phase or spinel-like phase in the entire crystal structure decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

[0128] In this way, by making the spinel phase and the spinel-like phase exist mainly in the surface portion of the secondary particles, it is possible to prevent unintended voltage drops and the like.

[0129] The presence or absence of the spinel phase in the lithium manganese-based oxide can be confirmed from the dQ / dV profile during initial discharge of a lithium secondary battery using the lithium manganese-based oxide as a positive electrode active material.

[0130] For example, when a lithium secondary battery having a positive electrode active material containing the lithium manganese oxide defined in the present application as a positive electrode and a lithium foil as a negative electrode is charged and discharged under the following charge and discharge conditions:

[0131] [Charge / discharge conditions] -Cut-off voltage: 2.0V~4.6V -Charge: 1.0C (CC) / Discharge: 1.0C (CC)

[0132] In a graph having a voltage V and a battery capacity Q during initial discharge, with the X axis representing the voltage V and the Y axis representing the battery capacity Q, and the value dQ / dV obtained by differentiating the battery capacity Q with respect to the voltage V, a peak may exist in at least one region selected from a first voltage region (3.0 V or more and less than 3.3 V) and a second voltage region (2.7 V or more and less than 3.0 V), preferably in the first voltage region.

[0133] In this case, the peak appearing in the first voltage region (3.0 V or more and less than 3.3 V) indicates the presence of a spinel-like phase in the lithium manganese-based oxide, and the peak appearing in the second voltage region (2.7 V or more and less than 3.0 V) indicates the additional presence of a spinel phase in the lithium manganese-based oxide.

[0134] Here, the spinel phase and the spinel-like phase are not phases formed through a phase transition of a phase belonging to the C2 / m space group and / or a phase belonging to the R3-m space group constituting the lithium manganese-based oxide caused by deterioration in the life of the positive electrode active material, but are phases formed by the first oxide and / or the second oxide, preferably the second oxide.

[0135] Lithium secondary battery According to another aspect of the present invention, there is provided a positive electrode including a positive electrode current collector and the above-described positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include the lithium manganese-based oxide according to the various embodiments of the present invention as a positive electrode active material.

[0136] Therefore, a detailed description of the lithium manganese-based oxide will be omitted, and only the remaining components not described above will be described below. For convenience, the lithium manganese-based oxide will be referred to as the positive electrode active material hereinafter.

[0137] 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, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically 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 strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0138] The positive electrode active material layer may be prepared by coating a positive electrode slurry composition containing the positive electrode active material, a conductive material, and optionally a binder, on the positive electrode current collector.

[0139] In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0140] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0141] The binder serves to improve adhesion between positive electrode active material particles and 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, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

[0142] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0143] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0144] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0145] According to yet another aspect of the present invention, there may be provided a lithium secondary battery using the above-described positive electrode, or an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0146] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing 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, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0147] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0148] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0149] 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, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0150] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0151] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0152] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0153] The binder is a component that aids in bonding between the conductive material, active material, and current collector, and may typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0154] The conductive material may be added as a component for further improving the conductivity of the negative electrode active material in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, 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.

[0155] In one embodiment, the negative electrode active material layer may be prepared by coating 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 and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0156] In another embodiment, the negative electrode active material layer may be fabricated by coating 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 and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0157] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration of the electrolyte and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0158] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in producing lithium secondary batteries, but are not limited to these.

[0159] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0160] The organic solvent may be any solvent that can act 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, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based 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, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0161] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. 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. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0162] When the electrolyte used in the present application is a solid electrolyte, for example, a solid inorganic electrolyte such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a nitride-based solid electrolyte, or a halide-based solid electrolyte may be used, and preferably, a sulfide-based solid electrolyte may be used.

[0163] The sulfide-based solid electrolyte material may be a solid electrolyte containing Li, an X element (wherein X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Examples of the sulfide-based solid electrolyte material include Li2S-P2S5, Li2S-P2S-LiX (wherein X is a halogen element such as I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(wherein p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0164] The solid electrolyte, preferably the sulfide-based solid electrolyte, may be amorphous or crystalline, or may be in a mixed state of amorphous and crystalline.

[0165] The oxide-based solid electrolyte material is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x Examples include GeO4 (LISICON).

[0166] The solid electrolyte may be disposed as a separate layer (solid electrolyte layer) between the positive electrode and the negative electrode. Alternatively, the solid electrolyte may be partially contained in the positive electrode active material layer of the positive electrode, independent of the solid electrolyte layer, or partially contained in the negative electrode active material layer of the negative electrode, independent of the solid electrolyte layer.

[0167] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0168] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0169] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0170] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0171] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0172] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0173] Production Example 1. Production of positive electrode active material Example 1 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 25:75, NaOH, and NH4OH were added to the reactor while stirring. The temperature inside the reactor 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 completed, the reactor was washed and dehydrated, and the Ni 0.25 Mn 0.75 A hydroxide precursor with the composition (OH)2 was obtained.

[0174] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0175] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (metal other than Li) molar ratio=1.55) as a lithium source material to prepare a mixture.

[0176] Next, the temperature of a firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated at 1,000°C for 8 hours, followed by furnace cooling to obtain a lithium-excess lithium-manganese oxide.

[0177] (d) Wet Coating (Surface Modification #1) A mixture was prepared by dissolving Al(NO3)3·9H2O weighed so that the aluminum (Al) content based on metal elements excluding lithium in the lithium manganese-based oxide obtained in step (c) was 0.3 mol % and NH4H2PO4 weighed so that the phosphorus (P) content was 0.3 mol % in distilled water.

[0178] Next, the lithium manganese oxide obtained in step (c) was added to the mixture, and the mixture was kept at 60°C and stirred at a stirring speed of 350 rpm to evaporate the distilled water, thereby obtaining a lithium manganese oxide having an Al-containing compound and a P-containing compound distributed on the surface.

[0179] (e) Third Heat Treatment (Surface Modification #2) The temperature in the sintering furnace in an O atmosphere was raised to 400°C at a rate of 4.4°C per minute, and the lithium manganese oxide obtained in step (d) was then heat-treated for 5 hours, after which it was classified and crushed to obtain a surface-modified lithium manganese oxide (final product).

[0180] Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that Al(NO3)3·9H2O weighed out to be 0.3 mol% and NH4H2PO4 weighed out to be 3.0 mol% were used in step (d).

[0181] Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that Al(NO3)3·9H2O weighed out to be 0.1 mol% and NH4H2PO4 weighed out to be 3.0 mol% were used in step (d).

[0182] Comparative Example 1 A positive electrode active material was produced in the same manner as in Example 1, except that the steps (d) and (e) were not performed.

[0183] Comparative Example 2 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 25:75, NaOH, and NH4OH were added to the reactor while stirring. The temperature inside the reactor 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 completed, the reactor was washed and dehydrated, and the Ni 0.25 Mn 0.75 A hydroxide precursor with the composition (OH)2 was obtained.

[0184] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 550°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0185] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (metal other than Li) molar ratio=1.55) as a lithium source material to prepare a mixture.

[0186] Next, the temperature of a calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated at 800°C for 8 hours, followed by furnace cooling to obtain a lithium-excess lithium-manganese oxide.

[0187] (d) Wet Coating (Surface Modification #1) A mixture was prepared by dissolving Al(NO3)3·9H2O weighed so that the aluminum (Al) content based on metal elements excluding lithium in the lithium manganese-based oxide obtained in step (c) was 0.3 mol % and NH4H2PO4 weighed so that the phosphorus (P) content was 0.3 mol % in distilled water.

[0188] Next, the lithium manganese oxide obtained in step (c) was added to the mixture, and the mixture was stirred at a stirring speed of 350 rpm while maintaining the temperature at 60°C to evaporate the distilled water, thereby obtaining a lithium manganese oxide having an Al-containing compound and a P-containing compound distributed on the surface.

[0189] (e) Third Heat Treatment (Surface Modification #2) The temperature in the sintering furnace in an O atmosphere was raised to 400°C at a rate of 4.4°C per minute, and the lithium manganese oxide obtained in step (d) was then heat-treated for 5 hours, after which it was classified and crushed to obtain a surface-modified lithium manganese oxide (final product).

[0190] Comparative Example 3 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 25:75, NaOH, and NH4OH were added to the reactor while stirring. The temperature inside the reactor 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 completed, the reactor was washed and dehydrated, and the Ni 0.25 Mn 0.75 A hydroxide precursor with the composition (OH)2 was obtained.

[0191] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the temperature was kept at 900°C. The hydroxide precursor obtained in step (a) was heat-treated for 5 hours, and then the furnace was cooled to obtain a precursor in an oxide state.

[0192] (c) Second heat treatment The oxide precursor obtained in step (b) was mixed with LiOH (Li / (metal other than Li) molar ratio=1.55) as a lithium source material to prepare a mixture.

[0193] Next, the temperature of a firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated at 1,000°C for 8 hours, followed by furnace cooling to obtain a lithium-excess lithium-manganese oxide.

[0194] (d) Wet Coating (Surface Modification #1) A mixture was prepared by dissolving Al(NO3)3·9H2O weighed so that the aluminum (Al) content based on metal elements excluding lithium in the lithium manganese-based oxide obtained in step (c) was 0.3 mol % and NH4H2PO4 weighed so that the phosphorus (P) content was 0.3 mol % in distilled water.

[0195] Next, the lithium manganese oxide obtained in step (c) was added to the mixture, and the mixture was stirred at a stirring speed of 350 rpm while maintaining the temperature at 60°C to evaporate the distilled water, thereby obtaining a lithium manganese oxide having an Al-containing compound and a P-containing compound distributed on the surface.

[0196] (e) Third Heat Treatment (Surface Modification #2) The temperature in the sintering furnace in an O atmosphere was raised to 400°C at a rate of 4.4°C per minute, and the lithium manganese oxide obtained in step (d) was then heat-treated for 5 hours, after which it was classified and crushed to obtain a surface-modified lithium manganese oxide (final product).

[0197] Reference example 1 A positive electrode active material was produced in the same manner as in Example 1, except that Al(NO3)3·9H2O weighed out to be 1.5 mol% and NH4H2PO4 weighed out to be 1.0 mol% were used in step (d).

[0198] Reference example 2 A positive electrode active material was produced in the same manner as in Example 1, except that Al(NO3)3·9H2O weighed out to be 0.01 mol% and NH4H2PO4 weighed out to be 3.0 mol% were used in step (d).

[0199] Reference example 3 A positive electrode active material was prepared in the same manner as in Example 1, except that in step (d), 0.01 mol% of Al(NO3)3·9H2O and 0.01 mol% of NH4H2PO4 were used.

[0200] Reference example 4 (a) Preparation of precursor An aqueous solution of NiSO4·6H2O and MnSO4·H2O mixed in a molar ratio of 25:75, NaOH, and NH4OH were added to the reactor while stirring. The temperature inside the reactor 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 completed, the reactor was washed and dehydrated, and the Ni 0.25 Mn 0.75 A hydroxide precursor with the composition (OH)2 was obtained.

[0201] (b) First heat treatment The temperature of the calcination furnace in an O2 atmosphere was increased at a rate of 2°C / min, and the hydroxide precursor obtained in step (a) was heat-treated at 550°C for 5 hours, followed by furnace cooling to obtain an oxide precursor.

[0202] (c) Second heat treatment The oxide precursor obtained in the step (b) was mixed with LiOH (Li / (metal other than Li) molar ratio=1.55) as a lithium source material to prepare a mixture.

[0203] Next, the temperature of a firing furnace in an O2 atmosphere was increased at a rate of 2°C / min, and then the mixture was heat-treated at 1,000°C for 8 hours, followed by furnace cooling to obtain a lithium-excess lithium-manganese oxide.

[0204] (d) Wet Coating (Surface Modification #1) A mixture was prepared by dissolving Al(NO3)3·9H2O weighed so that the aluminum (Al) content based on metal elements excluding lithium in the lithium manganese-based oxide obtained in step (c) was 0.3 mol% and NH4H2PO4 weighed so that the phosphorus (P) content was 3.0 mol% in distilled water.

[0205] Next, the lithium manganese oxide obtained in step (c) was added to the mixture, and the mixture was kept at 60°C and stirred at a stirring speed of 350 rpm to evaporate the distilled water, thereby obtaining a lithium manganese oxide having an Al-containing compound and a P-containing compound distributed on the surface.

[0206] (e) Third Heat Treatment (Surface Modification #2) The temperature in the sintering furnace in an O atmosphere was raised to 600°C at a rate of 4.4°C per minute, and the lithium manganese oxide obtained in step (d) was then heat-treated for 5 hours, after which it was classified and crushed to obtain a surface-modified lithium manganese oxide (final product).

[0207] Composition of lithium manganese oxide The composition (molar ratio of each element) of the lithium manganese-based oxide contained in each of the positive electrode active materials prepared in Preparation Example 1 was measured by ICP analysis.

[0208] The measurement results are shown in Table 1 below.

[0209] [Table 1] *Li / Metal Molar ratio indicates the molar ratio of lithium to all elements other than lithium in the lithium manganese-based oxide. *The element content (mol%) is calculated based on the total amount of elements other than lithium in the lithium manganese-based oxide.

[0210] Manufacturing example 2. Manufacturing of lithium secondary battery (half cell) A positive electrode slurry was prepared by dispersing 90 wt% of the positive electrode active material prepared in Preparation Example 1, 5.5 wt% of carbon black, and 4.5 wt% of PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0211] A half cell was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4.

[0212] Experimental Example 1: Image analysis of positive electrode active material Secondary particle-type lithium manganese-based oxide was separated from each of the positive electrode active materials prepared in Preparation Example 1 and photographed using a scanning electron microscope to obtain SEM images.

[0213] 1 and 2 are SEM images of the lithium manganese-based oxide contained in the positive electrode active materials of Examples 1 and 2, respectively. FIG. 3 is an SEM image of the lithium manganese-based oxide contained in the positive electrode active material of Comparative Example 1. FIGS. 4 to 6 are SEM images of the lithium manganese-based oxide contained in the positive electrode active materials of Reference Examples 1 to 3, respectively.

[0214] Next, using the Image Analyzer program, one secondary particle was selected from the SEM image, and 20 primary particles exposed on the surface of the secondary particle were selected in descending order of minor axis length, and the major and minor axis lengths of each were measured. From the measurement results, the average minor axis length of the primary particles and the average particle size of the primary particles ([major axis length + minor axis length] / 2) were calculated.

[0215] The measurement results are shown in Table 2 below.

[0216] [Table 2]

[0217] Referring to the results in Table 2, it can be seen that the primary particles of the lithium manganese-based oxides contained in the positive electrode active materials according to Examples 1 to 3 grew within an appropriate range.

[0218] Meanwhile, it can be seen that the lithium manganese-based oxide contained in the cathode active material according to Comparative Example 2 does not sufficiently induce crystal growth or particle growth of the primary particles, so that the average minor axis length of the primary particles is less than 130 nm and the average particle size of the primary particles is also relatively small.

[0219] In addition, it can be seen that the lithium manganese-based oxide contained in the cathode active material according to Comparative Example 3 has an average minor axis length of the primary particles greater than 850 nm and a relatively large average particle size due to excessive crystal growth and particle growth of the primary particles.

[0220] Experimental Example 2: Analysis of the crystal structure of the positive electrode active material The lithium manganese-based oxides contained in each of the positive electrode active materials prepared in Preparation Example 1 were separated and then cross-sectioned using a cross-section polisher (accelerating voltage 5.0 kV, milling for 4 hours). Then, cross-sectional TEM images were obtained using a transmission electron microscope.

[0221] Next, the cross-sectional TEM images were subjected to FFT (Fast Fourier Transform) to create diffraction patterns, which were then indexed to confirm the crystalline structure within the lithium manganese-based oxide. As a result, it was confirmed that the lithium manganese-based oxides contained in each of the cathode active materials prepared according to Preparation Example 1 were solid solutions having a crystalline structure 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, i.e., so-called lithium-excess lithium manganese-based oxides.

[0222] In addition, the lithium secondary batteries manufactured in Manufacturing Example 2 using the positive electrode active materials of Examples 1 to 3, Comparative Example 1, Reference Example 3, and Reference Example 4 were subjected to two cycles of formation process at 25°C, voltage range of 2.0V to 4.6V, and 0.1C / 0.1C using an electrochemical analyzer (Toyo, Toscat-3100), and then charged and discharged at 25°C, voltage range of 2.0V to 4.6V, and 1C / 1C.

[0223] In this case, the voltage V and battery capacity Q measured during initial discharge under the charge and discharge conditions were used, the X axis was the voltage V, the Y axis was the battery capacity Q, and the battery capacity Q was differentiated by the voltage V to obtain a dQ / dV profile.

[0224] Figures 7 to 9 are graphs showing the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 3, respectively. Figure 10 is a graph showing the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active material of Comparative Example 1. Figures 11 and 12 are graphs showing the dQ / dV profiles during initial discharge of lithium secondary batteries manufactured using the positive electrode active materials of Reference Examples 3 and 4, respectively.

[0225] Referring to FIG. 10, it can be seen that the dQ / dV profile during initial discharge of the lithium secondary battery using the cathode active material according to Comparative Example 1, in which the surface modification of the lithium manganese-based oxide was not performed, does not show any distinctive peaks in the first voltage region (3.0 V or more and less than 3.3 V) and the second voltage region (2.7 V or more and less than 3.0 V).

[0226] 7 and 8, the dQ / dV profiles during initial discharge of the lithium secondary battery fabricated using the cathode active material according to Example 1 and the lithium secondary battery fabricated using the cathode active material according to Example 2 show a peak in a first voltage region (3.0 V or more and less than 3.3 V). The peak appearing in the first voltage region (3.0 V or more and less than 3.3 V) indicates the presence of a spinel-like phase in the lithium manganese-based oxide.

[0227] 8 and 9, the dQ / dV profiles during initial discharge of the lithium secondary battery prepared using the cathode active material according to Example 2 and the lithium secondary battery prepared using the cathode active material according to Example 3 show an additional peak in the second voltage region (2.7 V or more and less than 3.0 V). The peak appearing in the second voltage region (2.7 V or more and less than 3.0 V) indicates the presence of a spinel phase in the lithium manganese-based oxide. That is, the lithium manganese-based oxide contained in the cathode active material according to Example 2 and the lithium manganese-based oxide contained in the cathode active material according to Example 3 contain a spinel phase and a spinel-like phase.

[0228] 11 and 12, it can be seen that the dQ / dV profiles during initial discharge of the lithium secondary battery using the positive electrode active material according to Reference Example 3 and the lithium secondary battery using the positive electrode active material according to Reference Example 4 do not show any distinctive peaks in the first voltage region (3.0 V or more and less than 3.3 V) and the second voltage region (2.7 V or more and less than 3.0 V).

[0229] In Reference Example 3, the amounts of the Al-containing compound and the P-containing compound used in step (d) are too small, which is likely to result in an insufficient modification effect on the surface of the lithium manganese-based oxide. In particular, it is likely that a sufficient amount of a phosphorus (P)-containing second oxide is not formed in the coating layer on the surface of the lithium manganese-based oxide, which is likely to result in the failure to form a spinel phase and / or a spinel-like phase.

[0230] Similarly, in the case of Reference Example 4, the third heat treatment temperature is too high, and it is expected that the surface modification intended in the present application will not be achieved.

[0231] Experimental Example 3: Analysis of surface modification elements of positive electrode active material The lithium manganese-based oxides contained in the positive electrode active materials according to Examples 1 and 2 were separated, and then each was processed to prepare a cross section using a cross-section polisher (accelerating voltage 5.0 kV, milling for 4 hours), and then photographed using a scanning electron microscope to obtain a cross-sectional SEM image.

[0232] Next, the target elements Ni, Mn, Al, and P were subjected to EDS mapping on the cross-sectional SEM image, and the contents (mol%) of the target elements were measured in the center and surface of the secondary particles through line sum spectrum.

[0233] The EDS mapping results are shown in FIG. 13, FIG. 14 and Table 3.

[0234] [Table 3] *The content (mol%) of the target elements is calculated based on the total amount of elements in the lithium manganese-based oxide, excluding lithium. *Bulk (ICP) indicates the content (mol%) of each target element when the total content of Ni, Mn, Al and P in the lithium manganese-based oxide is 100 mol%. *P1 refers to a point relatively close to the center of a secondary particle among the points indicated on each line (Line 1, Line 2) in Figures 13 and 14, and P2 refers to a point relatively close to the surface of a secondary particle.

[0235] The EDS mapping results show that Al and P in the lithium manganese-based oxide are present not only in the surface regions of the secondary particles but also in some of the centers of the secondary particles, and that the Al and P in the lithium manganese-based oxide have a concentration gradient that decreases from the surface regions of the secondary particles toward the centers of the secondary particles.

[0236] From the above results, it can be expected that the first oxide containing Al and the second oxide containing phosphorus (P) also have a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles. Therefore, when a spinel phase and / or a spinel-like phase is formed on the surface of the secondary particles through surface modification of the lithium manganese-based oxide, the spinel phase and / or the spinel-like phase may also have a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles.

[0237] Furthermore, it can be expected that the first oxide and / or the second oxide, which have a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle, diffuse from the surface portion of the secondary particle toward the center portion of the secondary particle along the crystal grain boundaries between the primary particles that make up the secondary particle.

[0238] Experimental Example 4: Evaluation of the electrochemical properties of lithium secondary batteries The lithium secondary battery (half cell) prepared in Preparation Example 2 was subjected to a charge-discharge experiment using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 2.0 V to 4.6 V, and a discharge rate of 0.1 C to 5.0 C to measure the initial charge capacity, initial discharge capacity, initial reversible efficiency, and rate capability (rate capability (C-rate)).

[0239] In addition, the same lithium secondary battery was charged and discharged 50 times at 25°C and 1C / 1C within a driving voltage range of 2.0V to 4.6V, and then the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity (cycle capacity retention rate; capacity retention) was measured.

[0240] The measurement results are shown in Tables 4 and 5 below.

[0241] [Table 4]

[0242] [Table 5]

[0243] Referring to the results in Table 4, it can be seen that the lithium secondary battery using the cathode active material according to Comparative Example 1, in which the surface of the lithium manganese-based oxide was not modified, had lower initial discharge capacity, initial reversible efficiency, and discharge capacity ratio than the lithium secondary batteries using the cathode active materials containing the lithium manganese-based oxides according to Examples 1 to 3. It can also be seen that the lithium secondary batteries using the cathode active materials containing the lithium manganese-based oxides according to Examples 1 to 3 exhibited higher initial discharge capacity (1 C-rate) and cycle capacity retention rate than those of Comparative Example 1.

[0244] Similarly, it can be seen that the lithium secondary batteries using the positive electrode active materials containing the lithium manganese-based oxides according to Comparative Examples 2 and 3 exhibit excessively lower initial discharge capacities, initial reversible efficiencies, and discharge capacity rates than the lithium secondary batteries using the positive electrode active materials containing the lithium manganese-based oxides according to Examples 1 to 3.

[0245] It can be seen that the lithium secondary batteries using the cathode active materials containing the lithium manganese-based oxides according to Reference Examples 1 to 3 exhibit generally improved electrochemical characteristics compared to the lithium secondary batteries using the cathode active materials containing the lithium manganese-based oxides according to Comparative Examples 1 to 3. However, it can be seen that the lithium manganese-based oxides according to Reference Examples 1 to 3 have slightly lower initial reversible efficiencies or discharge capacity rates than the lithium secondary batteries using the cathode active materials containing the lithium manganese-based oxides according to Examples 1 to 3 because the Al content derived from the first oxide, the P content derived from the second oxide, and / or the ratio of Al to P are designed differently from the lithium manganese-based oxides according to Examples 1 to 3.

[0246] Furthermore, it can be seen that the lithium secondary battery using the positive electrode active material containing the lithium manganese-based oxide according to Reference Example 4 exhibits excessively lower initial discharge capacity, initial reversible efficiency, and discharge capacity rate than the lithium secondary batteries using the positive electrode active materials containing the lithium manganese-based oxide according to Reference Examples 1 to 3 and the lithium secondary batteries using the positive electrode active materials containing the lithium manganese-based oxide according to Examples 1 to 3.

[0247] As confirmed in Experimental Example 2, the above results are presumably due to the fact that the third heat treatment temperature for the lithium manganese-based oxide having the Al-containing compound and the P-containing compound distributed on the surface thereof was too high, which resulted in surface damage to the lithium manganese-based oxide instead of the intended surface modification in the present application.

[0248] Although the embodiments of the present invention have been described above, a person having ordinary skill in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this would also be considered to be within the scope of the present invention.

Claims

1. A positive electrode active material comprising a lithium manganese-based oxide in which a phase belonging to the C2 / m space group and a phase belonging to the R3-m space group are solid-solved, The lithium manganese-based oxide includes secondary particles formed by agglomeration of a plurality of primary particles, an average value of the minor axis length of the primary particles calculated from 20 primary particles selected in descending order of minor axis length from the primary particles exposed on the surfaces of the secondary particles from an SEM image of the secondary particles is 130 nm or more and less than 850 nm; a coating layer including a first oxide including at least one selected from a metal element and a metalloid element and a second oxide including phosphorus (P) formed on at least a portion of the surface of the primary particles.

2. 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] Li(ii ａ 71 ｘ 72 ｙ )9 ２－ｂ 8 ｂ (where, M1 is Mn, M2 is at least one selected from Ni, Co, Al, P, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; X is a halogen capable of substituting at least a portion of the oxygen present in the lithium manganese-based oxide, 0<a≦0.7, 0≦b≦0.1, 0<x≦1, 0≦y<1, 0<x+y≦1.)

3. The positive electrode active material according to claim 1 , wherein the coating layer is formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles.

4. 3. The positive electrode active material according to claim 2, wherein a gradient is formed in which the ratio of at least one selected from x and y in Formula 1 changes from the surface portion of the secondary particle toward the center portion of the secondary particle.

5. M2 contains phosphorus (P), The positive electrode active material according to claim 2 , wherein a gradient is formed in which the concentration of phosphorus (P) decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

6. The positive electrode active material of claim 1 , wherein the first oxide is represented by the following Chemical Formula 2: [Chemical formula 2] Li ｃ M3 ｄ O ｅ (where, M3 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦c≦10, 0≦d≦8, 0<e≦13, excluding the case where c and d are both 0.

7. the coating layer is formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles, The positive electrode active material according to claim 6 , wherein a gradient is formed in which the concentration of M3 decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

8. The positive electrode active material of claim 1 , wherein the second oxide is represented by the following chemical formula 3: [Chemical formula 3] Li ｆ M4 ｇ (P ｈ O ｉ ) ｊ (where, M4 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦f≦10, 0≦g≦8, 0<h≦4, 0<i≦10, 0<j≦13.

9. the coating layer is formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles, The positive electrode active material according to claim 8 , wherein a gradient is formed in which the concentration of at least one selected from M4 and P decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

10. The coating layer includes a first oxide represented by the following Chemical Formula 2 and a second oxide represented by the following Chemical Formula 3: [Chemical formula 2] Li ｃ M3 ｄ O ｅ (where, M3 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦c≦10, 0≦d≦8, 0<e≦13, excluding the case where c and d are both 0. [Chemical formula 3] Li ｆ M4 ｇ (P ｈ O ｉ ) ｊ (where, M4 is at least one selected from Ni, Mn, Co, Al, Nb, B, Ti, Zr, Ba, K, Mo, Si, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, V, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦f≦10, 0≦g≦8, 0<h≦4, 0<i≦10, 0<j≦13.

2. The positive electrode active material according to claim 1, wherein the molar fractions of M3, M4, and P in the positive electrode active material are 1.0 to 30.0, as calculated by the following Equation 1: [Formula 1] P (mol%) / (M3 (mol%) + M4 (mol%))

11. the coating layer is formed on at least a portion of the surface of the primary particles present on the surface portion of the secondary particles, 11. The positive electrode active material according to claim 10, wherein a gradient is formed in which the concentration of at least one selected from M3, M4, and P decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

12. The positive electrode active material of claim 1 , wherein the lithium manganese-based oxide further comprises at least one phase selected from a spinel phase and a spinel-like phase.

13. The positive electrode active material according to claim 12 , wherein the spinel phase or the spinel-like phase is solid-solved or composited with at least one selected from the primary particles and the coating layer.

14. The positive electrode active material according to claim 12 , wherein the spinel phase or the spinel-like phase is present in at least a portion of an interface between the primary particles and the coating layer.

15. When a lithium secondary battery having the positive electrode active material as a positive electrode and lithium foil as a negative electrode was charged and discharged under the following charge and discharge conditions, [Charge / discharge conditions] -Cut off voltage: 2.0V ~ 4.6V -Charge: 1.0C (CC) / Discharge: 1.0C (CC) 2. The positive electrode active material according to claim 1, wherein, in a graph having a voltage V and a battery capacity Q during initial discharge, the X axis being the voltage V, the Y axis being the battery capacity Q, and the value dQ / dV obtained by differentiating the battery capacity Q with respect to the voltage V, a peak exists in at least one region selected from a first voltage region (3.0 V or more and less than 3.3 V) and a second voltage region (2.7 V or more and less than 3.0 V).

16. 2. The positive electrode active material according to claim 1, wherein a ratio of the spinel phase and the spinel-like phase in the entire crystalline structure present in the surface regions of the secondary particles is greater than a ratio of the spinel phase and the spinel-like phase in the entire crystalline structure present in the center regions of the secondary particles.

17. 17. The positive electrode active material according to claim 16, wherein a gradient is formed in which the proportion of the spinel phase or spinel-like phase in the entire crystal structure decreases from the surface portion of the secondary particle toward the center portion of the secondary particle.

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

19. A lithium secondary battery using the positive electrode according to claim 18.

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