Positive electrode active material and lithium secondary battery including the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode including the same: as secondary particles formed by aggregation of a plurality of primary particles, the secondary particles are provided as aggregates of the plurality of primary particles, thereby improving electrochemical characteristics and stability, wherein the plurality of primary particles form a concentration gradient of a doped metal in a direction from a grain boundary between the primary particles toward a central portion of the primary particles.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode containing the same. As secondary particles formed by aggregation of a plurality of primary particles, the secondary particles are provided as aggregates of the plurality of primary particles, thereby improving electrochemical characteristics and stability. Among them, the plurality of primary particles form a concentration gradient of a doped metal in a direction from a grain boundary between the primary particles toward a central portion of the primary particles. Background Art

[0002] A battery stores electrical energy by using substances capable of undergoing an electrochemical reaction at a positive electrode and a negative electrode. As a representative example of such a battery, there is a lithium secondary battery that stores electrical energy through a chemical potential difference when lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode.

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

[0004] A lithium composite oxide is used as a positive electrode active material of a lithium secondary battery. As an example thereof, LiCoO 2 、LiMn 2 O 4 、LiNiO 2 、LiMnO 2 and other composite oxides are being studied.

[0005] Among the above positive electrode active materials, LiCoO 2 is commonly used because of its excellent life characteristics and charge / discharge efficiency. However, the resource of cobalt used as a raw material is limited and the price is expensive, so it has the disadvantage of limited price competitiveness.

[0006] LiMnO 2 、LiMn 2 O 4 and other lithium manganese oxides have the advantages of excellent thermal stability and low price, but have problems of small capacity and poor high-temperature characteristics. And, the LiNiO 2 positive electrode active material shows battery characteristics of high discharge capacity, but due to the cation mixing problem between Li and transition metals, it is difficult to synthesize, and thus has a big problem in terms of rate characteristics.

[0007] Moreover, according to the severity of such cation mixing, a large amount of Li by-products are generated, and most of these Li by-products are composed of LiOH and Li 2 CO 3The composition of the compound causes problems of gelation when preparing the positive electrode paste and the generation of gas during charge and discharge after preparing the electrode. Residual Li 2 CO 3 Reducing the cycle by increasing the swelling phenomenon of the monomer also causes battery swelling.

[0008] To overcome this drawback, as a positive electrode active material for a secondary battery, the demand for a high-Ni type positive electrode active material with a Ni content of 50% or more has started to increase. However, this high-Ni type positive electrode active material exhibits high capacity characteristics. On the contrary, as the Ni content in the positive electrode active material increases, there is a problem of structural instability caused by the mixing of Li / Ni cations. Due to this structural instability of the positive electrode active material, lithium secondary batteries deteriorate rapidly not only under high-temperature conditions but also under normal-temperature conditions.

[0009] In addition, there are existing technologies such as Korean Patent Publication No. 10-2014-0022681 (Patent Document 1) related to positive electrode active materials for lithium secondary batteries.

[0010] The following content is disclosed in the above Patent Document 1: The doping metal represented by Me in the compound represented by the following Chemical Formula 1 forms a concentration gradient that gradually decreases from the surface of the positive electrode active material particles toward the center side, thereby improving the electrochemical characteristics of the positive electrode active material.

[0011] Chemical Formula 1: Li 1+x M 1-k Me k O 2

[0012] However, simply using the concentration gradient of the doping metal that exists only on the surface of the positive electrode active material (secondary particles) is not sufficient to simultaneously improve the electrochemical characteristics and structural stability of the positive electrode active material (especially in the case of high-Ni).

[0013] Therefore, it is necessary to develop a positive electrode active material to overcome the problems of this high-Ni type positive electrode active material. Summary of the Invention

[0014] Technical Problem

[0015] As described above, in the positive electrode active material for a lithium secondary battery, a certain trade-off relationship can be established between some indexes showing the electrochemical characteristics of the positive electrode active material and some indexes showing stability. Therefore, when the capacity characteristics of the positive electrode active material are excessively improved, as the structural stability of the particles constituting the positive electrode active material decreases, there is a problem that stable charge and discharge performance cannot be exhibited.

[0016] Accordingly, an object of the present invention is to provide a positive electrode active material as follows: maintaining the high electrochemical characteristics of the positive electrode active material for existing lithium secondary batteries, and in particular, maintaining the high electrochemical characteristics of the high-Ni type positive electrode active material, while solving the low structural stability.

[0017] Specifically, an object of the present invention is to provide a positive electrode active material, wherein, as secondary particles formed by aggregation of a plurality of primary particles, the secondary particles are provided as aggregates of the plurality of primary particles, thereby improving the electrochemical characteristics and stability, wherein the plurality of primary particles form a concentration gradient of a doped metal in a direction from the grain boundary between the primary particles toward the central portion of the primary particles.

[0018] Moreover, another object of the present invention is to provide a lithium secondary battery using a positive electrode including the positive electrode active material defined in the present application.

[0019] Solution to the problem

[0020] According to an aspect of the present invention, there is provided a positive electrode active material including at least nickel, cobalt, and a doped metal, and including a layered lithium composite oxide capable of intercalating / deintercalating lithium.

[0021] Wherein, the lithium composite oxide includes secondary particles, the secondary particles are aggregates in which a plurality of primary particles are aggregated to form grain boundaries between adjacent primary particles, and the secondary particles are aggregates of a plurality of primary particles showing a concentration gradient having a (-) slope of the doped metal from the grain boundary between the primary particles toward the central portion of the primary particles.

[0022] Wherein, the primary particles can be represented by the following Chemical Formula 1.

[0023] Chemical Formula 1: Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f

[0024] (Wherein,

[0025] M1 is at least one selected from Mn and Al,

[0026] M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, V, Sr, Ti, W, Nb, and Zr,

[0027] M1 to M3 are different from each other,

[0028] 0.90 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.10, 0 ≤ d ≤ 0.025, 0 ≤ e ≤ 0.025, 1.0 ≤ f ≤ 2.0.)

[0029] In one embodiment, the secondary particles may be aggregates of a plurality of primary particles that exhibit a concentration gradient of at least one of M2 and M3 decreasing from the grain boundaries between the primary particles toward the central portions of the primary particles.

[0030] Moreover, from the surface portion of the secondary particles toward the central portion of the secondary particles, there may be a first concentration gradient region where the concentration of the doped metal has a (-) slope and a second concentration gradient region where the concentration of the doped metal has a (+) slope.

[0031] Furthermore, according to another aspect of the present invention, there is provided a positive electrode comprising the positive electrode active material defined in the present application.

[0032] Meanwhile, according to another aspect of the present invention, there is provided a lithium secondary battery using the positive electrode defined in the present application.

[0033] Effects of the Invention

[0034] Generally, a high-Ni type positive electrode active material for achieving high capacity of a lithium secondary battery has a problem of low stability. However, in the positive electrode active material of the present invention, the secondary particles constituting the positive electrode active material are formed as aggregates of a plurality of primary particles as follows: a concentration gradient in which the concentration of the doped metal has a (-) slope is shown from the grain boundaries between the primary particles toward the central portions of the primary particles, thereby improving the low stability of the high-Ni type positive electrode active material and contributing to the exhibition of stable electrochemical characteristics at the same time.

[0035] In addition, in the case of a high-Ni type positive electrode active material, compared to a positive electrode active material with a relatively small Ni content, a large amount of Li by-products such as LiOH and Li 2 CO 3 etc. are present on the surface. These Li by-products act as a cause of gelation when preparing a positive electrode slurry using the positive electrode active material, or may act as a cause of gas generation during charge / discharge and / or storage of the lithium secondary battery.

[0036] However, the positive electrode active material of the present invention forms a concentration gradient with respect to the concentration of the doped metal at the grain boundaries between the primary particles constituting the secondary particles including the surface of the secondary particles, thereby reducing the content of Li by-products inside / outside the positive electrode active material.

[0037] Further, the interface in the secondary particles including the surface of the secondary particles (i.e., the grain boundary between the primary particles) of the positive electrode active material is a region where side reactions with the electrolyte may occur during charge / discharge and / or storage of the lithium secondary battery.

[0038] At this time, as the surface area of the positive electrode active material increases, the area of the region where side reactions may occur increases, and thus the possibility of side reactions increases. Such side reactions can induce a phase transformation (e.g., layered structure → rock salt structure) that changes the crystal structure of the lithium composite oxide constituting the positive electrode active material. The phase transformation of the crystal structure in the surface of the positive electrode active material as described above has been pointed out as one of the reasons for reducing electrochemical characteristics such as the life characteristics of the lithium secondary battery.

[0039] The positive electrode active material of the present invention forms a concentration gradient with respect to the concentration of the doped metal at the grain boundary between the primary particles constituting the secondary particles including the surface of the secondary particles, thereby reducing the surface area that may undergo side reactions with the electrolyte during charge / discharge and / or storage of the lithium secondary battery. Thus, the stability of charge / discharge and / or storage can be improved by reducing the possibility of side reactions with the electrolyte during charge / discharge and / or storage of the lithium secondary battery.

[0040] Ultimately, the positive electrode active material of the present invention provides secondary particles including aggregates of a plurality of primary particles that form a concentration gradient of the doped metal in the direction from the grain boundary between the primary particles toward the center of the primary particles, thereby not only improving various physical properties including the structural stability of the positive electrode active material, but also improving electrochemical characteristics such as life characteristics and efficiency.

[0041] In addition to the effects described above, the specific effects of the present invention will be described together with the specific embodiments of the following invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A graph briefly showing the concentration gradient of the secondary particles of the positive electrode active material included in an embodiment of the present invention. In Figure 1 the graph shown, an example of the EDX analysis result of line scanning along the direction from the surface portion of the secondary particles toward the center of the secondary particles for the doped metals designated as M2 and / or M3 is briefly shown.

[0043] Figures 2 to 8Curves obtained by line scanning the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM image obtained after cross-section processing using FIB (Ga ion source) after screening the secondary particles with a radius of 7.5 μm included in the positive electrode active materials of Examples 1 to 7.

[0044] Figures 9 to 11 Curves obtained by line scanning the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM image obtained after cross-section processing using FIB (Ga ion source) after screening the secondary particles with a radius of 7.5 μm included in the positive electrode active materials of Comparative Examples 1 to 3.

[0045] Figure 12 And Figure 13 Curves obtained by line scanning the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM image obtained after cross-section processing using FIB (Ga ion source) after screening the secondary particles with a radius of 7.5 μm included in the positive electrode active materials of Reference Examples 1 and 2.

[0046] Among them, Figures 2 to 13 Extract the line scanning results from the surface part to a depth of 3 μm (3000 nm) of the secondary particles included in each positive electrode active material.

[0047] Figures 14 to 16 Show the XRD analysis results for the positive electrode active materials of Examples 1 to 3, respectively. Detailed Description of the Invention

[0048] For easier understanding of the present invention, specific terms are defined in this application for convenience. Unless otherwise defined in this application, scientific terms and technical terms used in the present invention have the meanings commonly understood by those of ordinary skill in the art. And, unless specifically specified in the context, terms in the singular form include their plural forms, and terms in the plural form should be understood to also include their singular forms.

[0049] Hereinafter, the positive electrode active material of the present invention and the lithium secondary battery using the positive electrode including the above positive electrode active material will be described in more detail.

[0050] Positive electrode active material

[0051] According to an embodiment of the present invention, there is provided a positive electrode active material including a layered lithium composite oxide capable of intercalating / deintercalating lithium.

[0052] The above lithium composite oxide includes secondary particles, which are aggregates formed by aggregation of a plurality of primary particles with grain boundaries formed between adjacent primary particles.

[0053] Herein, a primary particle refers to one grain or crystallite, a secondary particle refers to an aggregate formed by aggregation of a plurality of primary particles, and the above secondary particle may also be referred to as a massive particle. And, the above primary particle may be rod-shaped, oval and / or circular, or irregular in shape.

[0054] Pores and / or grain boundaries may exist between the above primary particles constituting the above secondary particles. For example, the above primary particles may be separated from adjacent primary particles inside the above secondary particles to form internal pores. And, the above primary particles do not contact adjacent primary particles to form grain boundaries, but may form a surface existing inside the above secondary particles by contacting internal pores.

[0055] In addition, the surface of the above primary particles existing on the top surface of the above secondary particles exposed to external air may form the surface of the above secondary particles.

[0056] Herein, the average particle diameter of the above primary particles is 0.1 μm to 10 μm, preferably in the range of 0.1 μm to 5 μm, so that the optimal density of the positive electrode prepared by using the positive electrode active material of various embodiments of the present invention can be achieved. And, the average particle diameter of the secondary particles may vary depending on the number of aggregated primary particles and may be 3 μm to 20 μm.

[0057] And, the above lithium composite oxide may include at least nickel, cobalt and a doped metal. When the above lithium composite oxide further includes manganese in addition to nickel, cobalt and the doped metal, the above lithium composite oxide may be an NCM type composite oxide. And, when the above lithium composite oxide further includes aluminum in addition to cobalt and the doped metal, the above lithium composite oxide may be an NCA type composite oxide.

[0058] As described above, the above secondary particles constituting the above lithium composite oxide are aggregates formed by aggregation of a plurality of primary particles. At this time, the interface between adjacent primary particles or the joint surface of adjacent primary particles may be defined as the grain boundary between primary particles. And, the grain boundary between adjacent primary particles may coincide with the surface of the primary particles constituting the above grain boundary.

[0059] Among them, the plurality of initial particles constituting the above-mentioned secondary particles may show a concentration gradient with a (-) slope of the concentration of the above-mentioned doped metal from the grain boundaries between the above-mentioned initial particles toward the central part of the above-mentioned initial particles.

[0060] The change in the concentration of the doped metal in the above-mentioned initial particles formed along the direction from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles can be measured by EDX analysis (line scan) of the cross-section of the above-mentioned secondary particles.

[0061] In the case where the above-mentioned secondary particles are aggregates of a plurality of initial particles showing a concentration gradient with a (-) slope of the concentration of the above-mentioned doped metal from the grain boundaries between the above-mentioned initial particles toward the central part of the above-mentioned initial particles, it is confirmed from the EDX analysis results of the above-mentioned secondary particles that the pattern of the concentration gradient of the above-mentioned doped metal is repeated.

[0062] For example, in the case of performing a line scan along the direction from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles for the above-mentioned initial particles existing on the top surface of the above-mentioned secondary particles, a concentration gradient with a (-) slope of the concentration of the above-mentioned doped metal in the above-mentioned initial particles is shown from the top surface of the above-mentioned secondary particles. In contrast, in the above-mentioned initial particles adjacent to the central part of the above-mentioned secondary particles, a concentration gradient with a (+) slope of the concentration of the above-mentioned doped metal can be shown conversely. In the above-mentioned case, when taking the above-mentioned initial particles as a reference, the concentration of the above-mentioned doped metal in a single initial particle can show a concentration gradient with a (-) slope from the surface part of the above-mentioned initial particles (at this time, the surface part of the above-mentioned initial particles refers to the grain boundaries between the plurality of initial particles) toward the central part of the above-mentioned initial particles.

[0063] In addition, as a concentration gradient with a (-) slope of the concentration of the above-mentioned doped metal is shown from the grain boundaries between the above-mentioned initial particles toward the central part of the above-mentioned initial particles, when taking the above-mentioned secondary particles as a reference, there is a first concentration gradient interval with a (-) slope of the concentration of the above-mentioned doped metal and a second concentration gradient interval with a (+) slope from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles. And from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles, the first concentration gradient interval with a (-) slope of the concentration of the above-mentioned doped metal and the second concentration gradient interval with a (+) slope can exist repeatedly.

[0064] Among them, the ordinal numbers used when representing the concentration gradient intervals with (+) and / or (-) slopes are only used to distinguish the concentration gradient intervals with a (+) slope and the concentration gradient intervals with a (-) slope.

[0065] In addition, a concentration gradient showing a slope of (+) means that the concentration of the doped metal increases significantly between the starting point and the ending point of the line scan. Conversely, a concentration gradient showing a slope of (-) means that the concentration of the doped metal decreases significantly between the starting point and the ending point of the line scan. For example, the significant increase or decrease in the concentration of the doped metal means that the change in the concentration of the doped metal between the starting point and the ending point of the concentration gradient range is 2 at% or more.

[0066] A concentration gradient showing a slope of (+) only needs the slope of the concentration of the doped metal between the starting point and the ending point of the line scan to be (+), and in a part of the interval between the starting point and the ending point of the line scan, the slope change due to the minute difference in the concentration of the doped metal is not considered.

[0067] Similarly, a concentration gradient showing a slope of (-) should be understood as long as the slope of the concentration of the doped metal between the starting point and the ending point of the line scan is (-). Thus, in a part of the interval between the starting point and the ending point of the line scan, the slope change due to the minute difference in the concentration of the doped metal is not considered.

[0068] The above-mentioned primary particles constituting the secondary particles defined in the present application can be represented by the following Chemical Formula 1.

[0069] Chemical Formula 1: Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f

[0070] (wherein,

[0071] M1 is at least one selected from Mn and Al,

[0072] M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, V, Sr, Ti, W, Nb, and Zr,

[0073] M1 to M3 are different from each other,

[0074] 0.90 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.15, 0 ≤ c ≤ 0.10, 0 ≤ d ≤ 0.025, 0 ≤ e ≤ 0.025, 1.0 ≤ f ≤ 2.0.)

[0075] The above-mentioned primary particles can be the following high-Ni type lithium composite oxide: in the above Chemical Formula 1, the concentrations (mole percentages) of Ni, Co, M1, M2, and M3 satisfy the following Formula 1.

[0076] Formula 1: Ni / (Ni + Co + M1 + M2 + M3) ≥ 80.0

[0077] Moreover, the above initial particles can be a high-Ni / low-Co type lithium composite oxide as follows: In the above Chemical Formula 1, the concentrations (mole percentages) of Ni, Co, M1, M2, and M3 satisfy the above Formula 1. At the same time, the content of Co is 10 mole percent or less, preferably 5 mole percent or less.

[0078] That is, in the above initial particles, the concentrations (mole percentages) of Ni, Co, M1, M2, and M3 in the above Chemical Formula 1 can satisfy the following Formula 2.

[0079] Formula 2: Co / (Ni + Co + M1 + M2 + M3) ≤ 5.0

[0080] Generally, it is well known that in a lithium composite oxide containing at least Ni and Co, as the content of Ni increases, it causes structural instability of the lithium composite oxide due to Li / Ni cation mixing. And it is reported that in a lithium composite oxide containing at least Ni and Co, as the content of Co decreases, the initial overvoltage (resistance) increases, thereby inevitably reducing the efficiency characteristics.

[0081] However, as the concentration gradient of the doping metal shows a (-) slope from the grain boundary between the initial particles constituting the secondary particles towards the center of the above initial particles in the lithium composite oxide included in the positive electrode active material of an embodiment of the present invention, the structural instability and efficiency characteristics of the high-Ni type or high-Ni / low-Co type lithium composite oxide can be alleviated and / or prevented.

[0082] In addition, M2 and / or M3 in the above Chemical Formula 1 can correspond to the aforementioned doping metal. Thus, the above secondary particles can be an aggregate of a plurality of initial particles in which the concentration gradient of at least one selected from M2 and M3 decreases from the grain boundary between the above initial particles towards the center of the above initial particles.

[0083] Figure 1 A graph briefly showing the concentration gradient of the secondary particles included in the positive electrode active material of an embodiment of the present invention. Figure 1 An example showing the EDX analysis results of a line scan along the direction from the surface portion of the above secondary particles towards the center of the above secondary particles for the doping metal designated as M2 and / or M3 is briefly shown in the graph shown.

[0084] Refer to Figure 1, when based on the above-mentioned secondary particles, the concentration of the above-mentioned doped metal may have a (-) slope along the direction from the top surface of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles. At this time, the interval showing the concentration gradient with the above-mentioned (-) slope is called the first concentration gradient interval s1.

[0085] As described above, as the concentration of the above-mentioned doped metal has a (-) slope along the direction from the top surface of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles, a first peak p0 of the concentration of the above-mentioned doped metal can be shown at the position corresponding to the top surface of the above-mentioned secondary particles in the above-mentioned curve graph.

[0086] When the average particle size of the above-mentioned initial particles is r, a concentration gradient in the above-mentioned initial particles may exist within a depth of 0.2r from the grain boundary between the above-mentioned initial particles. When the concentration gradient in the above-mentioned initial particles exists up to a depth exceeding 0.2r from the grain boundary between the above-mentioned initial particles, it may cause instability of the crystal structure in the above-mentioned initial particles or there may be a concern of reducing the electrochemical characteristics.

[0087] In addition, at a specified depth after the above-mentioned first concentration gradient interval s1, a concentration holding interval s3 for maintaining the concentration of the above-mentioned doped metal may exist.

[0088] The above-mentioned concentration holding interval refers to an interval in which the concentration of the above-mentioned doped metal does not change significantly and is almost uniform, and may refer to all intervals in which the absolute value of the change amount of the concentration of the above-mentioned doped metal is 3 at%, preferably 2 at% or less. The absolute value of the change amount of the concentration of the above-mentioned doped metal in the above-mentioned concentration holding interval may vary depending on the type of the above-mentioned doped metal and the content of the above-mentioned doped metal in the above-mentioned initial particles, etc., but compared with the above-mentioned first concentration gradient interval s1 and the above-mentioned second concentration gradient interval s2, the change in the concentration of the above-mentioned doped metal in the above-mentioned concentration holding interval is a negligible change.

[0089] Inside the above-mentioned concentration holding interval, toward the central part of the above-mentioned secondary particles, the concentration of the above-mentioned doped metal may have a (+) slope. At this time, the interval showing the concentration gradient with the above-mentioned (+) slope is called the second concentration gradient interval s2.

[0090] As Figure 1 shown, when described based on the above-mentioned secondary particles, it can be confirmed that the above-mentioned first concentration gradient interval s1, the above-mentioned concentration holding interval s3, and the above-mentioned second concentration gradient interval s2 repeatedly exist from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles. However, in the above-mentioned case, it can be understood that a concentration gradient with a (-) slope is shown from the grain boundary between the above-mentioned initial particles toward the central part of the above-mentioned initial particles through the above-mentioned second concentration gradient interval s2.

[0091] That is, only when the secondary particles are aggregates of a plurality of primary particles in which the concentration gradient of the doped metal shows a (-) slope from the grain boundary between the primary particles toward the center of the primary particles, a first concentration gradient region in which the concentration of the doped metal shows a (-) slope and a second concentration gradient region in which the concentration shows a (+) slope can repeatedly exist from the surface portion of the secondary particles toward the center of the secondary particles.

[0092] In addition, as the first concentration gradient region in which the concentration of the doped metal shows a (-) slope and the second concentration gradient region in which the concentration shows a (+) slope repeatedly exist from the surface portion of the secondary particles toward the center of the secondary particles, at least one peak p1, p2 after the first peak p0 for the concentration of the doped metal can be shown at a position corresponding to the top surface of the secondary particles.

[0093] The second peak p1 first shown after the first peak p0 can be shown as the first concentration gradient region s1 exists after the second concentration gradient region s2. At this time, the second peak p1 can be formed by the second concentration gradient region s2 existing in the primary particle (present on the top surface of the secondary particle) and the first concentration gradient region s1 existing in the primary particle adjacent to the primary particle. At this time, the second concentration gradient region s2 existing in the primary particle (present on the top surface of the secondary particle) and the first concentration gradient region s1 existing in the primary particle adjacent to the primary particle can be collectively referred to as a peak region a1, and the peak existing in the peak region a1 can be defined as the second peak p1. At this time, the position showing the second peak p1 can become the grain boundary formed between two adjacent primary particles.

[0094] The stability of the surface of the secondary particles can be improved by the first concentration gradient region s1 existing after the first peak p0 shown on the surface portion of the secondary particles. For example, as the first concentration gradient region s1 for the doped metal exists on the surface portion of the secondary particles, the content of Li by-products on the surface of the secondary particles can be reduced, or the possibility of side reactions with the electrolyte can be reduced by reducing the specific surface area of the secondary particles.

[0095] In addition, as the concentration of the doped metal shows a concentration gradient with a (-) slope from the grain boundaries between the above-mentioned initial particles toward the central part of the above-mentioned initial particles, the first concentration gradient region s1, the concentration holding region s3, and the second concentration gradient region s2 sequentially exist in the above-mentioned initial particles from the central part of the above-mentioned secondary particles toward the surface part of the above-mentioned secondary particles. As described above, the first concentration gradient region s1, the concentration holding region s3, and the second concentration gradient region s2 sequentially exist in the above-mentioned initial particles from the central part of the above-mentioned secondary particles toward the surface part of the above-mentioned secondary particles, thereby improving the structural stability of the above-mentioned initial particles.

[0096] Moreover, through the concentration gradient pattern of the above-mentioned doped metal, the content of Li by-products in the grain boundaries between the above-mentioned initial particles including the surface of the above-mentioned secondary particles can be reduced, and the possibility of side reactions with the electrolyte can be reduced by reducing the exposed area inside the above-mentioned secondary particles.

[0097] In addition, from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles, there exist a first concentration gradient region s1 with a (-) slope in the concentration of the doped metal and a second concentration gradient region s2 with a (+) slope. Preferably, the first concentration gradient region s1 and the second concentration gradient region s2 exist with at least 2 repetitions. At this time, the concentration holding region s3 may exist between the first concentration gradient region s1 and the second concentration gradient region s2 that exist in at least the same initial particle.

[0098] As the first concentration gradient region s1 and the second concentration gradient region s2 are repeated from the surface part of the above-mentioned secondary particles toward the central part of the above-mentioned secondary particles, peak regions are repeatedly formed along the depth direction from the surface part of the above-mentioned secondary particles.

[0099] Moreover, the above-mentioned peak regions exist not only at positions adjacent to the surface part of the above-mentioned secondary particles but also at positions adjacent to the central part of the above-mentioned secondary particles or the central part of the above-mentioned secondary particles. However, in order for the above-mentioned peak regions to exist up to the central part of the above-mentioned secondary particles according to the type of the above-mentioned doped metal, there may be a case where the content of the raw material substance containing the above-mentioned doped metal added in the process of synthesizing the above-mentioned positive electrode active material is excessively increased. When the content of the raw material substance containing the above-mentioned doped metal added in the process of synthesizing the above-mentioned positive electrode active material is excessively increased, the content of the above-mentioned doped metal in the above-mentioned initial particles becomes unnecessarily large, or the content of the compound derived from the above-mentioned doped metal existing in at least a part of the grain boundaries between the above-mentioned initial particles and the surface of the above-mentioned secondary particles is excessively increased, which instead has a concern of reducing the electrochemical characteristics and stability of the above-mentioned positive electrode active material.

[0100] Therefore, preferably, from the surface portion of the secondary particles toward the central portion of the secondary particles, the first concentration gradient region s1 and the second concentration gradient region s2 exist with at least 2 repetitions or more, and the upper limit value of the number of repetitions of the first concentration gradient region s1 and the second concentration gradient region s2 can be appropriately adjusted in consideration of the composition of the positive electrode active material and the type of the doped metal, etc.

[0101] For example, when the radius of the secondary particles is R, when the first concentration gradient region s1 and the second concentration gradient region s2 exist within a depth limited to 0 to 0.2R from the surface portion of the secondary particles, it can be advantageous in terms of the electrochemical characteristics and stability of the positive electrode active material.

[0102] Preferably, when the first concentration gradient region s1 and the second concentration gradient region s2 exist as a whole from the surface portion of the secondary particles toward the central portion, the number of repetitions of the first concentration gradient region s1 and the second concentration gradient region s2 existing within a depth of 0 to 0.2R from the surface portion of the secondary particles (or, the number of times the peaks (p1, p2,...) exist, the number of times the peak regions (a1,...) exist) is more than the number of repetitions of the first concentration gradient region s1 and the second concentration gradient region s2 existing within a depth of 0.2R to R from the surface portion of the secondary particles (or, the number of times the peaks (p1, p2,...) exist, the number of times the peak regions (a1,...) exist).

[0103] Moreover, the positive electrode active material of some embodiments of the present invention may include a coating covering at least a part of the surface of the above-mentioned initial particles (for example, the grain boundaries between the above-mentioned initial particles) and / or the secondary particles aggregated from the above-mentioned initial particles.

[0104] For example, the above-mentioned coating can exist in such a way as to cover at least a part of the exposed surface of the above-mentioned initial particles. In particular, the above-mentioned coating can exist in such a way as to cover at least a part of the exposed surface of the above-mentioned initial particles existing in the outermost periphery of the above-mentioned secondary particles.

[0105] Thus, the above-mentioned coating can exist as a layer continuously or discontinuously coating the surface of the above-mentioned initial particles and / or the above-mentioned secondary particles aggregated from the above-mentioned initial particles. When the above-mentioned coating is discontinuous, it can exist in an island form.

[0106] The coating existing in the above-described manner maintains the high electrochemical characteristics of the positive electrode active material, and in particular, maintains the high electrochemical characteristics of the high-Ni type positive electrode active material, and at the same time, helps to solve the low structural stability.

[0107] Further, the above coating may also exist in the form of a solid solution that does not form a boundary with the above initial particles and / or the above secondary particles aggregated from the above initial particles.

[0108] The above coating may contain at least one compound represented by Chemical Formula 2 below. That is, the above coating may be defined as a region having a compound represented by Chemical Formula 2 below.

[0109] Chemical Formula 2: Li g M4 h O i

[0110] (wherein,

[0111] M4 is at least one selected from Mn, Al, Co, Ti, Zr, Sr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, and W,

[0112] 0 ≤ g ≤ 10, 0 < h ≤ 8, 0 < i ≤ 15).

[0113] Further, the above coating may be in the following form, that is, different types of compounds coexist in one layer, or different types of compounds represented by the above Chemical Formula 2 may exist in different layers respectively.

[0114] The compound represented by the above Chemical Formula 2 may be in a state of physical bonding and / or chemical bonding with the initial particles represented by the above Chemical Formula 1. Further, the above compound can also exist in a state of forming a solid solution with the initial particles represented by the above Chemical Formula 1.

[0115] The positive electrode active material of this embodiment includes a coating that covers at least a part of the surface of the above initial particles (for example, the interface between the above initial particles) and / or the secondary particles aggregated from the above initial particles, thereby improving the structural stability. Further, when such a positive electrode active material is used in a lithium secondary battery, the high-temperature storage stability and life characteristics of the positive electrode active material can be improved. Further, the above compound can reduce the residual lithium in the above positive electrode active material and at the same time act as a pathway for lithium ions, thereby affecting the improvement of the efficiency characteristics of the lithium secondary battery.

[0116] Further, depending on the situation, the above compound may exist not only in at least a part of the interface between the above initial particles and the surface of the above secondary particles, but also in the internal pores formed inside the above secondary particles.

[0117] The above compound is a compound formed by the complexation of lithium and the element represented by M4, or as a compound of M4, the above compound can also be expressed as Li aW b O c , Li a Zr b O c , Li a Ti b O c , Li a Ni b O c , Li a B b O c , W b O c 、Zr b O c 、Ti b O c or B b O c And, as non-limiting examples of the above compounds, there are Li 2 B 4 O 7 , Li 3 BO 3 , Li 2 B 2 O 7 , Li 2 B 8 O 13 , Li 2 VO 3 , Li 3 VO 4 , Li 6 Zr 3 O 9 , Li 2 ZrO 3 , Li 5.5 Zr 2.6 2O 8 , Li 44 Ba 19 , Li 4 Ba, Li 2 TiO 3 、LiTi 7 O 4 and LiTi 2 O 4 The above examples are merely provided for ease of understanding, and the above compounds defined in the present application are not limited to the above examples.

[0118] In another embodiment, the above compound is a compound formed by complexing lithium with at least two elements represented by M4, or may further contain a compound formed by complexing lithium with at least two elements represented by M4. For example, the compound formed by complexing lithium with at least two elements represented by M4 can be Li a (W / Ti) b O c 、Li a (W / Zr) b O c 、Li a (W / Ti / Zr) b O c 、Li a (W / Ti / B) b O c etc., but not limited thereto.

[0119] Among them, the above compound may show a concentration gradient that decreases from the surface portion of the above secondary particles toward the central portion of the above secondary particles. Thus, the concentration of the above compound can decrease from the surface portion of the above secondary particles toward the central portion of the above secondary particles.

[0120] As described above, showing a concentration gradient of the above compound decreasing from the surface portion of the above secondary particles toward the central portion of the above secondary particles, thus effectively reducing the residual lithium present on the surface of the above positive electrode active material, thereby preventing side reactions caused by unreacted residual lithium in advance. Specifically, as the residual lithium present in the surface portion of the above secondary particles reacts with the raw material substances of the compound represented by the above Chemical Formula 2 to form the compound represented by the above Chemical Formula 2, the residual lithium present in the surface portion of the above secondary particles can be reduced. And the reduction of crystallinity in the inner region of the surface of the above positive electrode active material can be prevented by the above compound. And the overall structure of the positive electrode active material can be prevented from being damaged by the above compound in the electrochemical reaction.

[0121] Additionally, the above coating may include: a first coating containing at least one compound represented by the above Chemical Formula 2; and a second coating containing at least one compound represented by the above Chemical Formula 2 and containing a compound different from the compound contained in the above first coating.

[0122] For example, the above first coating can exist in such a way as to cover at least a part of the exposed surface of the above initial particles existing in the outermost periphery of the above secondary particles, and the above second coating can exist in such a way as to cover at least a part of the exposed surface of the above initial particles not covered by the above first coating and the surface of the above first coating.

[0123] Lithium secondary battery

[0124] According to another embodiment of the present invention, the present invention can provide a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Among them, the positive electrode active material layer may include the positive electrode active materials of various embodiments of the present invention. Therefore, the positive electrode active material is the same as the previous description, so for the sake of convenience, its specific description is omitted. Hereinafter, only the remaining components not previously described will be described.

[0125] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. And the positive electrode current collector generally may have a thickness of 3 μm to 500 μm, and fine irregularities may also be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, non-woven bodies, etc.

[0126] The positive electrode active material layer can be prepared by coating a positive electrode paste composition containing the positive electrode active material, a conductive material, and optionally a binder on the positive electrode current collector.

[0127] In this case, the content of the positive electrode active material can be 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt% with respect to the total weight of the positive electrode active material layer. When the positive electrode active material is included in the above content range, excellent capacity characteristics can be shown, but it is not limited thereto.

[0128] The conductive material is used to impart conductivity to the electrode, and in the formed battery, it can be used without limitation as long as it does not cause chemical changes and has electronic conductivity. As specific examples, graphite such as natural graphite or artificial graphite can be cited; carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, etc.; metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; or conductive polymers such as polyphenylene derivatives, etc., and one or a mixture of two or more of them can be used. The above conductive material can be included in an amount of 0.1 wt% to 15 wt% with respect to the total weight of the positive electrode active material layer.

[0129] The above-mentioned binder serves to improve the adhesion between multiple positive electrode active material particles and the adhesion force between the positive electrode active material and the current collector. As a specific example, 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 monomer (EPDM), sulfonated ethylene propylene diene monomer, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. can be cited, and one or a mixture of two or more of them can be used. Relative to the total weight of the positive electrode active material layer, 0.1 to 15 weight percent of the above-mentioned binder can be included.

[0130] In addition to using the above-mentioned positive electrode active material, the above-mentioned positive electrode can be prepared according to a general positive electrode preparation method. Specifically, it can be prepared by coating a positive electrode slurry composition on a positive electrode current collector and then drying and calendering. The above-mentioned positive electrode slurry composition is prepared by dissolving or dispersing the above-mentioned positive electrode active material in a solvent and selectively dissolving or dispersing a binder and a conductive material in the solvent.

[0131] The above-mentioned solvent can be a solvent commonly used in this technical field. Examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, etc., and a mixture of one or two or more of them can be used. Considering the coating thickness of the slurry and the preparation yield, the amount of the above-mentioned solvent used only needs to be able to dissolve or disperse the above-mentioned positive electrode active material, conductive material, and binder and have a viscosity that can show excellent thickness uniformity when coating for the preparation of the positive electrode.

[0132] Moreover, in another embodiment, the above-mentioned positive electrode can also be prepared by the following method, that is, pouring the above-mentioned positive electrode slurry composition on a separate support and then laminating the film obtained by peeling from this support on the positive electrode current collector.

[0133] Meanwhile, according to another embodiment of the present invention, an electrochemical device including the above-mentioned positive electrode can be provided. The above-mentioned electrochemical device is specifically a battery, a capacitor, etc., and more specifically a lithium secondary battery.

[0134] Specifically, the above-mentioned lithium secondary battery can include a positive electrode, a negative electrode arranged opposite to the above-mentioned positive electrode, and a separator and an electrolyte arranged between the above-mentioned positive electrode and the above-mentioned negative electrode. Among them, the above-mentioned positive electrode is the same as the previous description, so for convenience, the specific description is omitted. Hereinafter, only the remaining components not described above will be described.

[0135] The above lithium secondary battery may selectively further include: a battery container for accommodating the electrode assembly including the above positive electrode, the above negative electrode, and the above separator; and a sealing member for sealing the above battery container.

[0136] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the above negative electrode current collector.

[0137] The above negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, carbon, nickel, titanium, silver, etc. can be used for surface treatment of the surface of copper or stainless steel, aluminum-cadmium alloy, etc. And, the above negative electrode current collector usually may have a thickness of 3 μm to 500 μm. Similarly to the positive electrode current collector, the binding force of the negative electrode active material can also be strengthened by forming fine irregularities on the surface of the above current collector. For example, it can be used in various forms such as a thin film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, etc.

[0138] The above negative electrode active material layer can be prepared by coating a negative electrode paste composition containing the above negative electrode active material, a conductive material, and optionally a binder according to requirements on the above negative electrode current collector.

[0139] As the above negative electrode active material, a compound capable of reversible insertion and extraction of lithium can be used. As a specific example, carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc. can be cited; metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; such as SiO β (0 < β < 2), SnO 2, metal oxides such as vanadium oxides and lithium vanadium oxides that can be doped and de-doped with lithium; or composites containing the above metal compounds and carbon materials such as Si-C composites or Sn-C composites, etc., and one or a mixture of two or more of them can be used. Also, as the negative electrode active material, a thin film of metallic lithium can also be used. Moreover, low-crystalline carbon and high-crystalline carbon, etc. can all be used as carbon materials. Representative low-crystalline carbon is soft carbon and hard carbon, and representative high-crystalline carbon is amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined cokes derived from petroleum or coal tar pitches, etc.

[0140] Based on the total weight of the negative electrode active material layer, 80 to 99 weight percent of the above negative electrode active material can be included.

[0141] The above binder is a component that helps the binding between the conductive material, the active material, and the current collector. Generally, based on the total weight of the negative electrode active material layer, 0.1 to 10 weight percent of the above binder can be added. As examples of such binders, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber, sulfonated ethylene propylene diene monomer rubber, styrene butadiene rubber, nitrile rubber, fluororubber, various copolymers thereof, etc. can be cited.

[0142] The above conductive material is a component for further improving the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, 10 weight percent or less of the above conductive material can be added. Preferably, 5 weight percent or less of the above conductive material can be added. As long as this conductive material does not induce chemical changes in the corresponding battery and has conductivity, there is no particular limitation. For example, graphite such as natural graphite or artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0143] In one embodiment, the negative electrode active material layer can be prepared by coating a negative electrode paste composition on a negative electrode current collector and drying it. The negative electrode paste composition is prepared by dissolving or dispersing a negative electrode active material in a solvent and optionally dissolving or dispersing a binder and a conductive material in the solvent. Alternatively, after pouring the negative electrode paste composition onto a separate support, the obtained film peeled off from the support is laminated on the negative electrode current collector to prepare it.

[0144] Also, in another embodiment, the negative electrode active material layer can also be prepared by coating a negative electrode paste composition on a negative electrode current collector and drying it. The negative electrode paste composition is prepared by dissolving or dispersing a negative electrode active material in a solvent and optionally dissolving or dispersing a binder and a conductive material in the solvent. Alternatively, after pouring the negative electrode paste composition onto a separate support, the obtained film peeled off from the support is laminated on the negative electrode current collector to prepare it.

[0145] In addition, in the above lithium secondary battery, the separator is used to separate the negative electrode and the positive electrode and provide a movement path for lithium ions. Any separator commonly used in lithium secondary batteries can be used without limitation. In particular, preferably, it has a low impedance and excellent electrolyte moisture retention ability for the ion movement of the electrolyte. Specifically, a porous polymer film can be used. For example, a porous polymer film prepared from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. Also, a common porous non-woven fabric can be used. For example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. can be used. Also, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component and a polymer substance can be used, and it can optionally be used in a single-layer or multi-layer structure.

[0146] And, as the electrolyte used in the present invention, examples include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the preparation of lithium secondary batteries, but it is not limited thereto.

[0147] Specifically, the above electrolyte can contain an organic solvent and a lithium salt.

[0148] As the above-mentioned organic solvent, an organic solvent that can serve as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the above-mentioned organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc. can be used; ether solvents such as dibutyl ether or tetrahydrofuran, etc.; ketone solvents such as cyclohexanone, etc.; aromatic hydrocarbon solvents such as benzene, fluorobenzene, etc.; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; alcohol solvents such as ethanol, isopropanol, etc.; nitriles such as R-CN (R is a linear, branched or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane, etc. Among them, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate having a high ionic conductivity and a high dielectric constant (e.g., ethylene carbonate or propylene carbonate, etc.) and a low-viscosity linear carbonate compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) that can improve the charge-discharge performance of the battery. In this case, when the cyclic carbonate and the chain carbonate are used in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be shown.

[0149] The above-mentioned lithium salt can be used without limitation a compound that can provide lithium ions for use in a lithium secondary battery. Specifically, the above-mentioned lithium salt can use LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3, LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI or LiB(C 2 O 4 ) 2 , etc. Preferably, the concentration of the above lithium salt needs to be used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is included in the above range, the electrolyte has appropriate conductivity and viscosity. Therefore, excellent electrolyte performance can be shown, and lithium ions can move effectively.

[0150] In addition to the above electrolyte components, for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and increasing the discharge capacity of the battery, etc., the above electrolyte may further contain one or more additives such as halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. In this case, 0.1 wt% to 5 wt% of the above additives may be contained relative to the total weight of the electrolyte.

[0151] As described above, the lithium secondary battery containing the positive electrode active material of the present invention stably shows excellent discharge capacity, output characteristics and life characteristics. Therefore, it can be used in portable devices such as mobile phones, laptop computers, digital cameras, etc. and electric vehicle fields such as hybrid electric vehicles (HEV).

[0152] The shape of the lithium secondary battery of the present invention is not particularly limited and can be cylindrical, prismatic, pouch-shaped or coin-type using a can, etc. And preferably, the lithium secondary battery can be used not only as a battery cell for powering small devices but also as a unit cell of a medium or large battery module including a plurality of battery cells.

[0153] According to still another embodiment of the present invention, a battery module including the above lithium secondary battery as a unit cell and / or a battery pack including the same can be provided.

[0154] The above battery module or the above battery pack can be used as a power source for a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or one or more medium or large-sized devices in a power storage system.

[0155] Hereinafter, the present invention will be described in more detail by way of examples. However, these examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention to these examples.

[0156] Preparation Example 1. Preparation of positive electrode active material

[0157] Example 1

[0158] A spherical Ni 0.92 Co 0.06 Mn 0.02 (OH) 2 hydroxide precursor was synthesized by the co-precipitation method.

[0159] Specifically, in a 90L-level reactor, 25 wt% of NaOH and 30 wt% of NH 4 OH were added to a 1.5M composite transition metal sulfuric acid aqueous solution obtained by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 92:6:2. The pH in the reactor was maintained at 11.5, and the temperature of the reactor was maintained at 60°C. Also, N 2 which is an inert gas, was added to the reactor to prevent the prepared precursor from being oxidized.

[0160] After completing the synthesis of the hydroxide precursor, washing and dehydration were performed using a filter press (F / P) device to obtain Ni 0.92 Co 0.06 Mn 0.02 (OH) 2 hydroxide precursor.

[0161] After mixing the obtained above hydroxide precursor with LiOH (Li / (Ni + Co + Mn) molar ratio = 1.05), it was maintained in an O 2 atmosphere in a firing furnace, heated to 700°C at a heating rate of 2°C per minute, and then heat-treated (first heat treatment) at 700°C for 10 hours to obtain a lithium composite oxide.

[0162] Next, without washing the obtained lithium composite oxide, TiO weighed in a manner to be 0.05 mol% is mixed with the above lithium composite oxide. 2 After that, O is maintained. 2 Under an atmosphere, it is heated at a heating rate of 2 °C per minute to 700 °C, and then post-heat treatment (second heat treatment) is carried out at 700 °C for 10 hours, and finally a positive electrode active material is obtained.

[0163] Example 2

[0164] When performing the second heat treatment on the above lithium composite oxide, instead of TiO, 2 ZrO at 0.05 mol% is mixed. 2 After that, O is maintained. 2 Under an atmosphere, it is heated at a heating rate of 2 °C per minute to 710 °C, and then post-heat treatment (second heat treatment) is carried out at 710 °C for 10 hours. In addition, a positive electrode active material is prepared in the same manner as in Example 1.

[0165] Example 3

[0166] When performing the second heat treatment on the above lithium composite oxide, instead of TiO, 2 V at 0.1 mol% is mixed. 2 O 3 After that, O is maintained. 2 Under an atmosphere, it is heated at a heating rate of 2 °C per minute to 720 °C, and then post-heat treatment (second heat treatment) is carried out at 720 °C for 10 hours. In addition, a positive electrode active material is prepared in the same manner as in Example 1.

[0167] Example 4

[0168] When performing the second heat treatment on the above lithium composite oxide, instead of TiO, 2 H at 0.2 mol% is mixed. 3 BO 3 After that, O is maintained. 2 Under an atmosphere, it is heated at a heating rate of 2 °C per minute to 720 °C, and then post-heat treatment (second heat treatment) is carried out at 720 °C for 10 hours. In addition, a positive electrode active material is prepared in the same manner as in Example 1.

[0169] Example 5

[0170] When performing the second heat treatment on the above lithium composite oxide, instead of TiO, 2 WO at 0.2 mol% is mixed. 3 After that, O is maintained. 2The atmosphere was heated to 700°C at a heating rate of 2°C per minute, and then post-heat treatment (second heat treatment) was performed at 700°C for 10 hours. Except for this, the positive electrode active material was prepared in the same manner as in Example 1.

[0171] Example 6

[0172] When performing the second heat treatment on the above lithium composite oxide, instead of TiO 2 0.2 mol% of Sr(OH) was mixed 2 After that, while maintaining an O 2 atmosphere, it was heated to 680°C at a heating rate of 2°C per minute, and then post-heat treatment (second heat treatment) was performed at 680°C for 10 hours. Except for this, the positive electrode active material was prepared in the same manner as in Example 1.

[0173] Example 7

[0174] When performing the second heat treatment on the above lithium composite oxide, instead of TiO 2 0.2 mol% of Al was mixed 2 O 3 After that, while maintaining an O 2 atmosphere, it was heated to 700°C at a heating rate of 2°C per minute, and then post-heat treatment (second heat treatment) was performed at 700°C for 10 hours. Except for this, the positive electrode active material was prepared in the same manner as in Example 1.

[0175] Example 8

[0176] Spherical Ni was synthesized by the coprecipitation method 0.95 Co 0.04 Mn 0.01 (OH) 2 hydroxide precursor.

[0177] Specifically, in a 90L-level reactor, 25 wt% of NaOH and 30 wt% of NH 4 OH were added to a 1.5M composite transition metal sulfuric acid aqueous solution obtained by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 95:4:1. The pH in the reactor was maintained at 11.5, and the temperature of the reactor was maintained at 60°C. Also, N 2 which is an inert gas, was added to the reactor to prevent the prepared precursor from being oxidized.

[0178] After the synthesis of the hydroxide precursor was completed, washing and dehydration were performed using a filter press (F / P) device to obtain Ni 0.95 Co 0.04 Mn 0.01 (OH)2 Hydroxide precursor.

[0179] After mixing the obtained hydroxide precursor with LiOH (Li / (Ni + Co + Mn) molar ratio = 1.05), while maintaining an O 2 atmosphere in a firing furnace, the temperature is raised to 700°C at a rate of 2°C per minute, and then heat-treated (first heat treatment) at 700°C for 10 hours to obtain a lithium composite oxide.

[0180] Next, without washing the obtained lithium composite oxide with water, TiO weighed in such a way as to be 0.05 mol% is mixed into the lithium composite oxide 2 and then, while maintaining an O 2 atmosphere, the temperature is raised to 700°C at a rate of 2°C per minute, and then additional heat treatment (second heat treatment) is carried out at 700°C for 10 hours to finally obtain a positive electrode active material.

[0181] Comparative Example 1

[0182] When performing the second heat treatment on the above lithium composite oxide, TiO is not mixed 2 and, except for this, a positive electrode active material is prepared in the same manner as in Example 1.

[0183] Comparative Example 2

[0184] When performing the second heat treatment on the above lithium composite oxide, instead of TiO 2 0.05 mol% of ZrO is mixed 2 and then, while maintaining an O 2 atmosphere, the temperature is raised to 850°C at a rate of 2°C per minute, and then additional heat treatment (second heat treatment) is carried out at 850°C for 24 hours. Except for this, a positive electrode active material is prepared in the same manner as in Example 1.

[0185] Comparative Example 3

[0186] When performing the first heat treatment, Ni 0.92 Co 0.06 Mn 0.02 (OH) 2 hydroxide precursor, LiOH (Li / (Ni + Co + Mn) molar ratio = 1.05), and Al 2 O 3 (in the whole mixture, weighed and mixed in such a way as to be 0.5 mol%) are mixed, and then, while maintaining an O 2The atmosphere was heated at a rate of 2 °C per minute to 700 °C and then heat-treated at 700 °C for 10 hours. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1.

[0187] Reference Example 1

[0188] When the above lithium composite oxide was subjected to a second heat treatment, 0.1 mol% of TiO was mixed. 2 After that, O was maintained. 2 The atmosphere was heated at a rate of 2 °C per minute to 350 °C and then post-heat-treated (second heat treatment) at 350 °C for 10 hours. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1.

[0189] Reference Example 2

[0190] When the above lithium composite oxide was subjected to a second heat treatment, 0.8 mol% of TiO was mixed. 2 After that, O was maintained. 2 The atmosphere was heated at a rate of 2 °C per minute to 720 °C and then post-heat-treated (second heat treatment) at 720 °C for 24 hours. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1.

[0191] Preparation Example 2. Preparation of lithium secondary battery

[0192] 94 wt% of each positive electrode active material prepared according to Preparation Example 1, 3 wt% of artificial graphite, and 3 wt% of polyvinylidene fluoride binder were dispersed in 3.5 g of N-methylpyrrolidone to prepare a positive electrode paste. The above positive electrode paste was coated on an aluminum (Al) thin film with a thickness of 20 μm as a positive electrode current collector and dried, and a positive electrode was prepared by performing roll pressing. The load level of the positive electrode was 7 mg / cm 2 , and the electrode density was 3.2 g / cm 3 .

[0193] With respect to the above positive electrode, a lithium foil was used as a counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and a liquid electrolyte in which LiPF 6 was present at a concentration of 1.15 M in a solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 was used to prepare a button cell according to a generally well-known preparation process.

[0194] Experimental Example 1. SEM / EDX analysis of metal composite hydroxide and positive electrode active material

[0195] Figures 2 to 8Graphs showing line scans of the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM images obtained after cross-section processing using FIB (Ga ion source) after screening secondary particles having a radius of 7.5 μm included in the positive electrode active materials of Examples 1 to 7. Figures 9 to 11 Graphs showing line scans of the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM images obtained after cross-section processing using FIB (Ga ion source) after screening secondary particles having a radius of 7.5 μm included in the positive electrode active materials of Comparative Examples 1 to 3.

[0196] And, Figure 12 and Figure 13 Graphs showing line scans of the content of the doped metal in the secondary particles, where the doped metal in the secondary particles was confirmed by performing EDX analysis on the cross-sectional SEM images obtained after cross-section processing using FIB (Ga ion source) after screening secondary particles having a radius of 7.5 μm included in the positive electrode active materials of Reference Examples 1 and 2.

[0197] Wherein, Figures 2 to 13 Extract the line scan results from the surface portion to a depth of 3 μm (3000 nm) of the secondary particles included in each positive electrode active material.

[0198] For reference, Comparative Example 1 does not contain a doped metal, and thus, Figure 9 the line scan graph shows a baseline. Also, the line scan results for the secondary particles included in the positive electrode active material of Example 8 were not separately attached, but it was confirmed that the secondary particles included in the positive electrode active material of Example 8 also showed a concentration gradient pattern similar to that of Figures 2 to 8 the positive electrode active materials of Examples 1 to 7 shown.

[0199] Table 1

[0200] Classification Doped metal Example 1 Ti Example 2 Zr Example 3 V Example 4 B Example 5 W Example 6 Sr Example 7 Al Example 8 Ti Comparative Example 1 - Comparative Example 2 Zr Comparative Example 3 Al Reference Example 1 Ti Reference Example 2 Ti

[0201] Refer to Figures 2 to 8, among the secondary particles included in the positive electrode active materials of Examples 1 to 7, when the radius (7.5 μm) of the above secondary particles is R, it can be confirmed that within a depth range of 0 to 0.2R (1.5 μm) from the surface portion of the above secondary particles towards the central portion of the above secondary particles, there repeatedly exist a first concentration gradient region with a (-) slope and a second concentration gradient region with a (+) slope in the concentration of the above doped metal.

[0202] In addition, referring to Figure 10 it can be confirmed that in the secondary particles included in the positive electrode active material of Comparative Example 2, there is no concentration gradient region with a (+) slope in the concentration of the above doped metal from the surface portion of the above secondary particles towards the central portion of the above secondary particles. That is, in the secondary particles included in the positive electrode active material of Comparative Example 2, from the surface portion of the above secondary particles towards the central portion of the above secondary particles, there is a concentration gradient in the form that the concentration of the above doped metal gradually decreases.

[0203] Referring to Figure 11 it can be confirmed that in the secondary particles included in the positive electrode active material of Comparative Example 3, from the surface portion of the above secondary particles towards the central portion of the above secondary particles, the concentration of the above doped metal does not change significantly and remains almost uniformly.

[0204] Moreover, it can be confirmed that in the secondary particles included in the positive electrode active material of Reference Example 1, similar to the positive electrode active materials of Examples 1 to 7, within a depth range of 0 to 0.2R (1.5 μm) from the surface portion of the above secondary particles towards the central portion of the above secondary particles, there exist a first concentration gradient region with a (-) slope and a second concentration gradient region with a (+) slope in the concentration of the above doped metal. However, in the secondary particles included in the positive electrode active material of Reference Example 1, from the surface portion of the above secondary particles towards the central portion of the above secondary particles, the above first concentration gradient region and the above second concentration gradient region do not repeatedly exist.

[0205] Similar to the positive electrode active materials of Examples 1 to 7, in the secondary particles included in the positive electrode active material of Reference Example 2, from the surface portion of the above secondary particles towards the central portion of the above secondary particles, there also repeatedly exist a first concentration gradient region with a (-) slope and a second concentration gradient region with a (+) slope in the concentration of the above doped metal. However, it can be confirmed that in the secondary particles included in the positive electrode active material of Reference Example 2, within a region with a depth exceeding 0.2R (1.5 μm) from the surface portion of the above secondary particles, the above first concentration gradient region and the above second concentration gradient region repeatedly exist.

[0206] Experimental Example 2. XRD analysis of positive electrode active material

[0207] X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials prepared according to Preparation Example 1 to confirm whether there was a compound other than the lithium composite oxide having the crystal structure represented by Chemical Formula 1 in the above positive electrode active material. The XRD analysis was performed using a Bruker D8 Advance diffractometer, wherein the above Bruker D8 Advance diffractometer used Cu Kα radiation

[0208] Figures 14 to 16 The XRD analysis results for the positive electrode active materials of Examples 1 to 3 are shown respectively.

[0209] Refer to Figures 14 to 16 , peaks corresponding to the crystal structure of the compound represented by Li g Ti h O i / Li g Zr h O i / Li g V h O i (0 ≤ g ≤ 10, 0 < h ≤ 8, 0 < i ≤ 15) were observed from the positive electrode active materials of Examples 1 to 3 respectively.

[0210] That is, it was confirmed that when the above lithium composite oxide obtained by the first heat treatment was not washed with water and the second heat treatment was performed after mixing the raw material containing the dopant with the above lithium composite oxide, the residual lithium in the surface portion of the above lithium composite oxide (secondary particles) obtained by the first heat treatment reacted with the raw material containing the dopant to form a compound represented by the following Chemical Formula 2.

[0211] Chemical Formula 2: Li g M4 h O i

[0212] (wherein

[0213] M4 is at least one selected from Mn, Al, Co, Ti, Zr, Sr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce, and W,

[0214] 0 ≤ g ≤ 10, 0 < h ≤ 8, 0 < i ≤ 15.)

[0215] Experimental Example 3. Measurement of residual lithium and specific surface area of positive electrode active material

[0216] When measuring the residual lithium, it is measured by the amount of 0.1 M HCl used until the pH becomes 4 by pH titration. First, 5 g of each positive electrode active material prepared according to Preparation Example 1 was added to 100 ml of DIW, stirred for 15 minutes, and then filtered. After that, 50 ml of the filtered solution was taken, and 0.1 M HCl was added thereto to measure the HCl consumption according to the pH change, whereby Q1 and Q2 were determined, and the residual LiOH and Li were calculated according to the following calculation formula 2 CO 3 .

[0217] M1 = 23.94 (molecular weight of LiOH)

[0218] M2 = 73.89 (Li 2 CO 3 molecular weight)

[0219]

[0220]

[0221] Moreover, for the BET specific surface area, it was calculated from the nitrogen adsorption amount at the liquid nitrogen temperature (77 K) using a gas adsorption method specific surface area measurement device (BELSORP-miniⅡ of Microtarac BEL Co., Ltd.).

[0222] The measurement results of the above residual lithium and BET specific surface area are shown in Table 2 below.

[0223] Table 2

[0224]

[0225]

[0226] From the results of Table 2 above, it can be confirmed that, compared with Comparative Example 1, the specific surface area of the positive electrode active material of Example 1 did not increase, and the content of residual lithium decreased.

[0227] Moreover, it can be confirmed that, in the case of the positive electrode active material of Comparative Example 2 having a concentration gradient in which the concentration of the above doping metal gradually decreases from the surface portion to the center portion of the above secondary particles, the content of residual lithium is excessive compared with Examples 1 to 7.

[0228] In addition, it was confirmed that in Reference Example 1 where the first concentration gradient range and the second concentration gradient range of the doped metal did not repeatedly exist from the surface portion to the central portion of the secondary particles, and in Reference Example 2 where the first concentration gradient range and the second concentration gradient range repeatedly existed in the region exceeding a depth of 0.2R (1.5 μm) from the surface portion of the secondary particles, compared with the positive electrode active material of Example 1, the effect of reducing residual lithium was negligible, but the specific surface area increased instead.

[0229] As Figure 12 shown, in the case of the positive electrode active material of Reference Example 1, as going from the surface portion to the central portion of the secondary particles, the first concentration gradient range and the second concentration gradient range did not repeatedly exist, and it was predicted that the effect of reducing residual lithium in the region close to the central portion of the secondary particles was insufficient compared to Example 1. It was predicted that in the case of the positive electrode active material of Reference Example 2, due to the heat treatment maintained for a relatively long time, as going from the surface portion to the central portion of the secondary particles, the number of repetitions of the first concentration gradient range and the second concentration gradient range increased. Therefore, lithium was eluted again in the form of impurities from the lithium composite oxide, increasing the content of residual lithium.

[0230] Experimental Example 4. Evaluation of capacity and life characteristics of lithium secondary battery

[0231] For the lithium secondary battery (button battery) prepared in Preparation Example 2, the charge and discharge capacities were measured using an electrochemical analysis device (Toyo, Toscat-3100) through a charge-discharge experiment with a temperature of 25 °C, a voltage range of 3.0 V to 4.3 V, and a discharge rate of 0.1C.

[0232] Furthermore, for the same lithium secondary battery, after performing charge / discharge 50 times under the condition of 1C / 1C within the driving voltage range of 25 °C and 3.0 V to 4.4 V, the ratio of the discharge capacity of the 50th cycle to the initial capacity (cycle capacity retention; capacity retention) was measured.

[0233] The above measurement results are shown in Table 3 below.

[0234] Table 3

[0235]

[0236] From the results in Table 3 above, it was confirmed that for the absence of a concentration gradient of the doped metal in the secondary particles, compared with Comparative Example 1, the charge-discharge efficiency and cycle capacity retention of the lithium secondary battery using the positive electrode active materials of Examples 1 to 8 were improved.

[0237] Further, it can be confirmed that, compared with Comparative Example 1, in the case of Comparative Example 2 having a concentration gradient in which the concentration of the doped metal gradually decreases from the surface portion to the central portion of the secondary particles, the cycle capacity retention rate slightly increases, but the charge-discharge efficiency decreases instead.

[0238] In addition, as going from the surface portion to the central portion of the secondary particles, the first concentration gradient range and the second concentration gradient range for the doped metal do not repeatedly exist (that is, after the first peak p0 of the concentration of the doped metal shown at the position corresponding to the top surface of the secondary particles, at least two peaks p1 and p2 do not exist), or the first concentration gradient range and the second concentration gradient range are excessively repeated. In the case of Reference Example 1 and Reference Example 2 where peaks of the first concentration gradient range and the second concentration gradient range exist in a region close to the central portion of the secondary particles, it can be confirmed that the improvement effect on the charge-discharge efficiency and / or the cycle capacity retention rate is negligible compared with Comparative Example 1.

[0239] As described above, embodiments of the present invention have been described. However, as long as those skilled in the art can make various modifications and changes to the present invention by adding, changing, deleting, or adding structural elements without exceeding the inventive concept described in the claims of the present invention, these are also included in the claims of the present invention.

Claims

1. A positive electrode active material, comprising at least nickel, cobalt, manganese and a doped metal, and being a lithium composite oxide having a layered structure capable of intercalating / deintercalating lithium, characterized in that, the lithium composite oxide comprises secondary particles, and the secondary particles are aggregates in which a plurality of primary particles are aggregated to form grain boundaries between adjacent primary particles, the secondary particles are aggregates of a plurality of primary particles showing a concentration gradient with a (-) slope in the concentration of the doped metal from the grain boundaries between the primary particles toward the central part of the primary particles, the primary particles are represented by the following Chemical Formula 1: Chemical formula 1: Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f , wherein, M1 is Mn, M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mo, Na, K, P, V, Sr, Ti, W, Nb and Zr, M2 and M3 are different from each other, 0.90 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.15, 0 < c ≤ 0.10, 0 ≤ d ≤ 0.025, 0 ≤ e ≤ 0.025, 1.0 ≤ f ≤ 2.0, d and e are not simultaneously 0, the secondary particles are aggregates of a plurality of primary particles showing a concentration gradient in a form in which the concentration of at least one selected from M2 and M3 decreases from the grain boundaries between the primary particles toward the central part of the primary particles, from the surface part of the secondary particles toward the central part of the secondary particles, there are a first concentration gradient region having a (-) slope in the concentration of the doped metal and a second concentration gradient region having a (+) slope, from the surface part of the secondary particles toward the central part of the secondary particles, the first concentration gradient region and the second concentration gradient region repeatedly exist at least 2 times, between the first concentration gradient region and the second concentration gradient region, there is a concentration holding region in which the absolute value of the change amount of the concentration of the doped metal is 3 at% or less, when the average particle size of the primary particles is r, the concentration gradient in the primary particles exists within a depth of 0 to 0.2r from the grain boundaries between the primary particles.

2. The positive electrode active material according to claim 1, characterized in that, the concentration of Co in the primary particles represented by the Chemical Formula 1 is 5 mol% or less.

3. The positive electrode active material according to claim 1, characterized in that, a compound represented by the following Chemical Formula 2 exists in at least a part of the grain boundaries between the primary particles and the surface of the secondary particles, Chemical formula 2: Li g M4 h O i , wherein, M4 is at least one selected from Mn, Al, Co, Ti, Zr, Sr, Mg, V, B, Mo, Zn, Nb, Ba, Ca, Ta, Fe, Cr, Sn, Hf, Ce and W, 0 ≤ g ≤ 10, 0 < h ≤ 8, 0 < i ≤ 15.

4. The positive electrode active material according to claim 1, characterized in that, At least a part of the grain boundaries between the above-mentioned primary particles and the surfaces of the above-mentioned secondary particles contains at least one compound selected from Li 2 B 4 O 7 、Li 3 BO 3 、Li 2 B 2 O 7 、Li 2 B 8 O 13 、Li 2 VO 3 、Li 3 VO 4 、Li 6 Zr 3 O 9 、Li 2 ZrO 3 、Li 5.5 Zr 2.6 2O 8 、Li 2 TiO 3 、LiTi 7 O 4 and LiTi 2 O 4 among others.

5. The positive electrode active material according to claim 1, characterized in that, the average particle size of the primary particles is 0.1 μm to 10.0 μm.

6. The positive electrode active material according to claim 1, characterized in that, the average particle size of the secondary particles is 3 μm to 20 μm.

7. The positive electrode active material according to claim 6, wherein, when the radius of the secondary particle is R, a first concentration gradient region having a slope of (-) and a second concentration gradient region having a slope of (+) exist within a depth of 0 to 0.2R from the surface portion of the secondary particle in terms of the concentration of the doped metal.

8. A positive electrode, wherein, it contains the positive electrode active material according to any one of claims 1 to 7.

9. A lithium secondary battery, wherein, it uses the positive electrode according to claim 8.

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