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

Abstract

To provide a positive electrode active material capable of enhancing the efficiency of movement of lithium ions and / or electric charges by locally forming a region with a different concentration of an arbitrary transition metal in primary particles.MEANS FOR SOLVING THE PROBLEM: Provided is a positive electrode active material for lithium secondary batteries that includes a primary particle and a secondary particle agglomerated from the primary particles that enable reversible intercalation / deintercalation of a lithium ion. The primary particle is a lithium composite oxide that contains as a transition metal at least one selected from Ni, Co, Mn, and Al. When an average atom ratio of the arbitrary transition metal existing in the primary particle is defined as 'a', the secondary particle includes in the primary particles a primary particle in which a first region where the average atom ratio of the arbitrary transition metal is greater than 'a' and a second region where the average atom ratio of the arbitrary transition metal is equal to or less than 'a' coexist.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode including the positive electrode active material. More specifically, the present invention relates to a positive electrode active material, a positive electrode slurry composition, and a lithium secondary battery using a positive electrode including the positive electrode active material, which locally form regions with different concentrations of any transition metal within primary particles, thereby improving the efficiency of lithium ion and / or charge transfer and structural stability. [Background technology]

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

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

[0004] Lithium composite oxides are used as the positive electrode active material for lithium secondary batteries, and composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are examples of the oxides that have been researched.

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

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

[0007] Furthermore, as the degree of cation mixing deepens, a large amount of Li by-products is generated, and most of these Li by-products consist of compounds of LiOH and Li2CO3, which cause gelation during the manufacture of the positive electrode paste and gas generation during charge and discharge after electrode manufacture. The remaining Li2CO3 not only increases the swelling phenomenon of the cell, reducing cycle life, but also causes the battery to swell.

[0008] Recently, lithium-based composite oxides containing Ni, Co, Mn, and / or Al have been developed as positive electrode active materials. Generally, as with LiNiO2-based positive electrode active materials, these lithium-based composite oxides have the advantage of increasing energy density and improving output characteristics as the Ni content increases. However, they also suffer from the drawback of increased resistance. Therefore, there is a demand for the development of a positive electrode active material containing Ni, Co, Mn, and / or Al that can prevent a decline in resistance and lifespan characteristics while maintaining the excellent reversible capacity of LiNiO2. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2015-0069334 Summary of the Invention [Problem to be solved by the invention]

[0010] In the lithium secondary battery market, the growth of lithium secondary batteries for electric vehicles is driving the market, while the demand for cathode materials used in lithium secondary batteries is also continuously changing.

[0011] For example, lithium secondary batteries using LFP have traditionally been used primarily for reasons such as ensuring safety, but recently there has been a trend toward the widespread use of nickel-based lithium composite oxides, which have a higher energy capacity per weight than LFP.

[0012] In line with these trends in cathode materials, the present invention aims to provide a high-Ni type lithium composite oxide and / or a cathode active material containing the lithium composite oxide for realizing high-capacity automotive cells. However, in the case of known high-Ni type lithium composite oxides, the resistance increases as the Ni content increases, which results in a problem of reduced lifespan.

[0013] One of the reasons for the phenomenon in which the resistance increases as the Ni content in the lithium composite oxide increases is thought to be insufficient movement of lithium ions and / or charges within the lithium composite oxide, particularly on the surface of the lithium composite oxide.

[0014] Furthermore, as the Ni content increases, the structural instability of the lithium composite oxide increases, which increases the possibility that the crystalline structure of the lithium composite oxide will change or collapse during charging and discharging of the lithium secondary battery. Furthermore, the structural instability of the lithium composite oxide can cause side reactions, which can lead to irreversible capacity loss of the positive electrode active material.

[0015] Therefore, the present invention aims to provide a positive electrode active material that improves the efficiency of lithium ion and / or charge transfer by locally forming regions with different concentrations of any transition metal within primary particles.

[0016] Another object of the present invention is to provide a positive electrode active material having improved structural stability by locally forming regions in primary particles where the concentration of an arbitrary transition metal differs.

[0017] Another object of the present invention is to provide a positive electrode slurry composition containing the positive electrode active material defined herein.

[0018] It is yet another object of the present invention to provide a lithium secondary battery including a positive electrode formed by coating a current collector with the positive electrode slurry composition defined herein.

[0019] The objects of the present invention are not limited to the objects mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, it can be easily seen that the objects and advantages of the present invention can be realized by the means and combinations thereof as set forth in the claims. [Means for solving the problem]

[0020] According to one aspect of the present invention, there is provided a positive electrode active material for a lithium secondary battery, comprising primary particles capable of reversible intercalation / deintercalation of lithium ions and secondary particles formed by aggregation of the primary particles.

[0021] Here, the primary particles are a lithium composite oxide containing at least one transition metal selected from Ni, Co, Mn, and Al.

[0022] Specifically, the lithium composite oxide may contain Ni and Co, Ni and Mn, Ni and Al, Ni, Co and Mn, Ni, Co and Al, or Ni, Co, Mn and Al. The lithium composite oxide may further contain a doping metal other than the transition metal.

[0023] The secondary particles are aggregates formed by aggregation of a plurality of the primary particles, and are also called bulk particles. The secondary particles may be divided into a central portion corresponding to a region relatively close to the center of the secondary particle and a surface portion corresponding to a region relatively close to the outer periphery of the secondary particle.

[0024] Simply put, based on the average radius of the secondary particles, a region defined as a distance within half the average radius from the center of the secondary particles can be referred to as the central portion, and a region defined as a distance within half the average radius from the outer peripheral surface of the secondary particles can be referred to as the surface portion.

[0025] In one embodiment, when the average atomic ratio of any transition metal present in the primary particle is referred to as a, the secondary particle may include a primary particle in which a first region in which the average atomic ratio of the any transition metal in the primary particle is greater than a and a second region in which the average atomic ratio of the any transition metal is equal to or less than a coexist. The secondary particle including a primary particle in which the first region and the second region coexist means that the secondary particle may include a primary particle in which there is no concentration change region that is divided into the first region and the second region.

[0026] In one embodiment, when the primary particles are lithium composite oxides mainly containing Ni and Co, and the average atomic ratio of Co present in the entire primary particles is referred to as a2, the secondary particles may include primary particles in which a first region in which the average atomic ratio of Co within the primary particles is greater than a2 and a second region in which the average atomic ratio of Co is a2 or less coexist. In one embodiment, when the primary particles are lithium composite oxides mainly containing Ni and Mn, and the average atomic ratio of Mn present in the entire primary particles is referred to as a3, the secondary particles may include primary particles in which a first region in which the average atomic ratio of Mn within the primary particles is greater than a3 and a second region in which the average atomic ratio of Mn is a3 or less coexist.

[0027] The presence or absence of the first and second regions in the primary particles can be confirmed through a cross-sectional TEM image, or by any known means capable of observing a concentration change of any transition metal in the primary particles, other than the cross-sectional TEM image.

[0028] As described above, when the first region and the second region coexist within the primary particle, at least one region selected from the first region and the second region is locally present within the primary particle, thereby realizing a difference in lithium ion and / or charge transfer between the first region and the second region. Such a difference in lithium ion and / or charge transfer can contribute to the formation of lithium ion and / or charge transfer pathways.

[0029] In one embodiment, the primary particles may be a lithium composite oxide containing at least Ni and Co. Here, when the average atomic ratio of Ni present in the primary particles in which the first region and the second region coexist is referred to as a1 and the average atomic ratio of Co present in the primary particles is referred to as a2, the average atomic ratio b1 of Ni in the first region may be equal to or less than a1, and the average atomic ratio b2 of Co in the first region may be greater than a2.

[0030] In another embodiment, the primary particles may be a lithium composite oxide containing at least Ni and Mn. Here, when the average atomic ratio of Ni present in the primary particles in which the first region and the second region coexist is referred to as a1 and the average atomic ratio of Mn present in the primary particles is referred to as a3, the average atomic ratio b1 of Ni in the first region may be equal to or less than a1, and the average atomic ratio b3 of Mn in the first region may be greater than a3.

[0031] According to another aspect of the present invention, there is provided a positive electrode slurry composition comprising a positive electrode active material as defined herein, a conductive material, and a binder.

[0032] According to yet another aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode formed by coating a current collector with the positive electrode slurry composition defined herein. [Effects of the Invention]

[0033] According to the present invention, by locally forming regions with different concentrations of a transition metal within primary particles constituting a positive electrode active material, the efficiency of lithium ion and / or charge transfer can be improved. Such improved efficiency of lithium ion and / or charge transfer can contribute to improved electrochemical properties of a lithium secondary battery using the positive electrode active material.

[0034] This prevents or alleviates the phenomenon in which the resistance of the positive electrode active material increases as the Ni content in the main transition metals constituting the positive electrode active material increases, thereby delaying the deterioration of the positive electrode active material due to repeated charge and discharge.

[0035] Furthermore, as the Ni content increases, the structural instability of the lithium composite oxide increases, which increases the possibility that the crystalline structure of the lithium composite oxide will change or collapse during charging and discharging of the lithium secondary battery. Moreover, the structural instability of the lithium composite oxide can cause side reactions, which can lead to irreversible capacity loss of the positive electrode active material.

[0036] However, according to the present invention, by locally forming regions with different concentrations of any transition metal within the primary particles constituting the positive electrode active material, it is possible to provide a buffering effect against changes in the crystal structure during charge and discharge of the high-Ni type lithium composite oxide, thereby improving the structural stability of the lithium composite oxide.

[0037] The specific effects of the present invention, together with the above-mentioned effects, will be described below together with specific matters for carrying out the invention. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a schematic diagram illustrating a first region and a second region present in a primary particle constituting a positive electrode active material according to an embodiment of the present invention. [Figure 2] FIG. 3 is another schematic diagram illustrating the first and second regions present in a primary particle constituting a positive electrode active material according to an embodiment of the present invention. [Figure 3] FIG. 2 shows a cross-sectional TEM image and EDX mapping results of the positive electrode active material (secondary particles) according to Example 1 of the present invention. [Figure 4] FIG. 4 is a diagram showing the positions where the Co concentration in primary particles was measured in the EDX mapping image for Co shown in FIG. 3. [Figure 5] FIG. 10 is a diagram showing a cross-sectional TEM image and EDX mapping results of a positive electrode active material (secondary particles) according to Example 3 of the present invention. [Figure 6] FIG. 6 is a diagram showing the positions where the Mn concentration in the primary particles was measured in the cross-sectional TEM image shown in FIG. 5. [Figure 7] 1 shows a cross-sectional TEM image and EDX mapping results of the positive electrode active material (secondary particles) according to Comparative Example 1. FIG. [Figure 8] 10 shows a cross-sectional TEM image and EDX mapping results of the positive electrode active material (secondary particles) according to Comparative Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0039] For convenience, certain terms are defined herein to make the present invention more readily understandable. Unless otherwise defined herein, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Furthermore, unless otherwise indicated by context, singular terms shall be understood to include their plural forms, and plural terms shall be understood to include their singular forms.

[0040] Hereinafter, the cathode active material according to the present invention and a lithium secondary battery using a cathode including the cathode active material will be described in more detail.

[0041] positive electrode active material According to one aspect of the present invention, there is provided a positive electrode active material including primary particles capable of reversible intercalation / deintercalation of lithium ions and secondary particles formed by aggregation of the primary particles.

[0042] Here, the primary particle refers to a single particle. Alternatively, the primary particle may refer to one grain or crystallite. The primary particle may have a single crystal structure.

[0043] The secondary particles refer to aggregates formed by aggregation of a plurality of primary particles, and may also be referred to as bulk or bulk particles.

[0044] The average particle size of the primary particles is within a range of 0.05 μm to 5 μm, preferably 0.1 μm to 3 μm, thereby enabling the optimal density of a cathode manufactured using the cathode active material according to various embodiments of the present invention. In addition, the average particle size of the secondary particles may vary depending on the number of agglomerated primary particles, but may generally be 3 μm to 20 μm.

[0045] The secondary particle may be divided into a central portion corresponding to a region relatively close to the center of the secondary particle and a surface portion corresponding to a region relatively close to the outer periphery of the secondary particle.

[0046] Unless otherwise defined in the present application, based on the average radius of the secondary particles, a region defined as a distance from the center of the secondary particles within half the average radius can be referred to as a central portion, and a region defined as a distance from the outer peripheral surface of the secondary particles within half the average radius can be referred to as a surface portion.

[0047] Voids and / or grain boundaries may exist between the primary particles that make up the secondary particles.

[0048] For example, the primary particles may be separated from adjacent primary particles within the secondary particles to form internal voids, which may be closed pores and / or open pores.

[0049] Furthermore, the primary particles can be defined as grain boundaries, which are boundaries formed by contact between adjacent primary particles. That is, the grain boundaries are boundaries formed by contact between adjacent primary particles, and the grain boundaries cannot be interpreted as being included in the primary particles. Therefore, even if a metal oxide different from the primary particles is present along the grain boundaries and the transition metal concentration in the metal oxide is different from that in the primary particles, this cannot be interpreted as the presence of multiple regions in which the concentration of a given transition metal in the primary particles varies.

[0050] The surfaces of the primary particles present on the surface portions of the secondary particles that are exposed to the outside form the surfaces (outer peripheral surfaces) of the secondary particles.

[0051] Here, the primary particles are a lithium composite oxide containing at least one transition metal selected from Ni, Co, Mn, and Al.

[0052] Specifically, the lithium composite oxide may contain Ni and Co, or may contain Ni and Mn, or may contain Ni and Al, or may contain Ni, Co and Mn, or may contain Ni, Co and Al, or may contain Ni, Co, Mn and Al.

[0053] In one embodiment, the primary particles may be defined as a lithium composite oxide represented by the following Chemical Formula 1. The average composition of the secondary particles, which are aggregates of the lithium composite oxide represented by the following Chemical Formula 1, may also be represented by the following Chemical Formula 1.

[0054] [Chemical formula 1] Li w Ni 1-(x+y+z) Co x M1y M2 z O2 (where, M1 is at least one selected from Mn and Al; M2 is at least one selected from Na, K, Mg, Ca, Ba, Mn, B, Ce, Hf, Ta, Cr, F, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu; M1 and M2 are different from each other, 0.5≦w≦1.5, 0≦x≦0.40, 0≦y≦0.40, 0.001≦z≦0.30.)

[0055] The lithium composite oxide may further include a doping metal other than the transition metal, which is represented by M2 in Chemical Formula 1 and may be an alkali metal, an alkaline earth metal, and / or a metal element other than M1.

[0056] The lithium composite oxide contained in the positive electrode active material defined in the present application may be a high-Ni type lithium composite oxide in which the Ni content in the transition metals is relatively high. In this case, the mole fraction of Ni in the lithium composite oxide represented by Chemical Formula 1 may be 60%, preferably 70%, more preferably 80% or more.

[0057] The cathode active material defined herein includes primary particles having multiple regions with different concentrations of a given transition metal locally formed therein, thereby improving the efficiency of lithium ion and / or charge transfer, thereby preventing or mitigating the phenomenon in which the resistance of the cathode active material increases as the Ni content in the lithium composite oxide increases.

[0058] 1 and 2 are schematic diagrams illustrating a first region and a second region present in a primary particle constituting a positive electrode active material according to one embodiment of the present invention.

[0059] When the average atomic ratio of any transition metal present in the primary particle 100 is referred to as a, the secondary particle may include a primary particle 100 in which a first region 110 in which the average atomic ratio of the any transition metal is greater than a and a second region 120 in which the average atomic ratio of the any transition metal is a or less coexist within the primary particle 100.

[0060] The secondary particles including primary particles 100 in which the first region 110 and the second region 120 coexist means that the secondary particles may also include primary particles 100 in which there is no concentration change region that is divided into the first region 110 and the second region 120.

[0061] The presence of the first region 110 and the second region 120 in the primary particle 100 can be confirmed through a cross-sectional TEM image. In addition to the cross-sectional TEM image, it can also be confirmed by various known means (e.g., EDX mapping, line scanning, EP-EDS (Energy Profiling-Energy Dispersive X-Ray Spectroscopy) analysis, etc.) that can observe the concentration change of any transition metal in the primary particle.

[0062] For example, when EDX mapping is performed on an arbitrary transition metal based on a cross-sectional TEM image of the secondary particle, the first region 110, where the concentration of the transition metal is relatively high, may be detected with a strong detection intensity, making it possible to distinguish it from the second region 120, where the concentration of the transition metal is relatively low.

[0063] As described above, based on a cross-sectional TEM image of the secondary particle, at least one region selected from the first region 110 and the second region 120 is locally present in the primary particle 100 where the first region 110 and the second region 120 coexist, thereby realizing a difference in lithium ion and / or charge mobility between the first region 110 and the second region 120. Such a difference in lithium ion and / or charge mobility can contribute to the formation of lithium ion and / or charge mobility paths.

[0064] In addition, the local presence of at least one region selected from the first region 110 and the second region 120 within the primary particle 100 can provide a buffering effect against changes in the crystal structure during charging and discharging.

[0065] Assuming that the first region 110 exists in a region close to the surface of the primary particle 100, the bright spots of the first region 110 as shown by EDX mapping, etc., are present at least on the surface of the primary particle 100 or inside the surface of the primary particle 100, and the bright spots of the first region 110 are not present in the grain boundaries formed by adjacent primary particles 100 contacting each other.

[0066] The first region 110 and / or the second region 120 being present locally within the primary particle 100 means that any transition metal does not exhibit a gradient throughout the primary particle 100 .

[0067] For example, if a gradient (slope gradient) is formed in which the concentration of a given transition metal continuously decreases from the surface portion 12 of the secondary particle toward the center portion 11 of the secondary particle, then within the surface portion 12 and center portion 11 of the secondary particle, particularly within the primary particle 100 present in the surface portion 12 of the secondary particle, only a gradient in which the concentration of the transition metal continuously decreases along the direction from the surface portion 12 of the secondary particle toward the center portion 11 of the secondary particle exists, and the first region 110 and / or the second region 120 are not observed to be present locally within the primary particle 100.

[0068] Furthermore, even if a gradient (slope gradient) is formed in which the concentration of any transition metal continuously decreases from the surface portion of the primary particle 100 toward the center of the primary particle 100, the first region 110 and / or the second region 120 are not observed to be locally present within the primary particle 100.

[0069] In addition, in order to form a concentration gradient of any transition metal in the direction from the surface to the center of the primary particles and / or secondary particles, it is generally necessary to induce a gradient solid solution of the transition metal through a coating process on the precursor and / or lithium composite oxide.

[0070] However, the graded solid solution does not allow the first region 110 and / or the second region 120 to be locally present within the primary particle 100. For example, the cathode active material according to the present application can allow the first region 110 and / or the second region 120 to be locally present within the primary particle 100 by using a precursor designed in consideration of the difference in diffusion rate of the main transition metals during heat treatment performed during the manufacturing process.

[0071] Therefore, unlike a typical gradient solid solution for primary particles and / or secondary particles, the positive electrode active material defined in the present application may have at least one region selected from the first region 110 and the second region 120, particularly a plurality of the first region 110, within the primary particle 100 in which the first region 110 and the second region 120 coexist, based on a cross-sectional TEM image of the secondary particle.

[0072] The presence of a plurality of the first regions 110 and / or the second regions 120 within the primary particle 100 allows for the formation of lithium ion and / or charge transfer paths in various directions due to the difference in lithium ion and / or charge transfer between the first region 110 and the second region 120.

[0073] In one embodiment, based on a cross-sectional TEM image of the secondary particle, within the primary particle 100 in which the first region 110 and the second region 120 coexist, at least one region selected from the first region 110 and the second region 120, particularly the first region 110, can extend along a direction from the surface 12 of the secondary particle toward the center 11.

[0074] Here, the phrase "extending in a direction from the surface 12 toward the center 11 of the secondary particle" may mean extending in a direction that exactly matches the direction from the surface 12 toward the center 11 of the secondary particle.

[0075] Furthermore, the phrase "extending in a direction from the surface 12 toward the center 11 of the secondary particle" may mean extending in a direction that does not deviate significantly from the direction from the surface 12 toward the center 11 of the secondary particle. In this case, as shown in FIG. 2, the extension direction of the first region 110 and the direction from the surface 12 toward the center 11 of the secondary particle may form a predetermined included angle (e.g., ±40°).

[0076] The extension direction of the long sides of the primary particles 100 shown in Fig. 2 is oriented along a → a' direction from the surface 12 to the center 11 of the secondary particle. In this case, unlike the example shown in Fig. 2, the extension direction of the long sides of the primary particles 100 may be oriented such that the direction from the surface 12 to the center 11 of the secondary particle forms a predetermined included angle (e.g., ±40°).

[0077] FIG. 2 shows an example in which the first region 110 locally present within the primary particle 100 extends along a direction b→b' that forms a predetermined included angle (e.g., ±40°) with respect to a direction a→a' from the surface 12 toward the center 11 of the secondary particle.

[0078] In this case, when a length measured in a direction c→c' perpendicular to the extension direction b→b' of the first region 110 within the primary particle 100 is defined as a width w of the primary particle 100, the width w1 of the first region may be smaller than the width w of the primary particle 100. More specifically, an average value of the width w of the primary particle 100 measured in a direction c→c' perpendicular to the extension direction b→b' of the first region 110 within a section where the first region 110 exists may be larger than the average value of the width w1 of the first region.

[0079] Furthermore, based on a cross-sectional TEM image of the secondary particle, the proportion of the primary particles 100 in which the first region 110 and the second region 120 coexist among all primary particles present in the surface portion 12 of the secondary particle may be greater than the proportion of the primary particles 100 in which the first region 110 and the second region 120 coexist among all primary particles present in the center portion 11 of the secondary particle.

[0080] In another example, based on a cross-sectional TEM image of the secondary particle, the primary particle 100 in which the first region 110 and the second region 120 coexist may be present locally on the surface portion 12 of the secondary particle.

[0081] In this way, by making the primary particles 100 in which the first region 110 and the second region 120 coexist mainly present in the surface region 12 of the secondary particles, it is possible to improve the electrochemical properties of high-Ni type lithium composite oxides, which have insufficient lithium ion and / or charge movement on the surface of the secondary particles. If the primary particles 100 in which the first region 110 and the second region 120 coexist mainly present in the center region 11 of the secondary particles or uniformly present in the center region 11 and the surface region 12 of the secondary particles, it is difficult to achieve a sufficient lithium ion exchange effect inside the secondary particles.

[0082] In one embodiment, the primary particles 100 may be a lithium composite oxide containing at least Ni and Co.

[0083] Here, when the average atomic ratio of Ni present in the primary particle 100 in which the first region 110 and the second region 120 coexist is referred to as a1 and the average atomic ratio of Co is referred to as a2, the average atomic ratio b1 of Ni in the first region 110 may be less than a1, and the average atomic ratio b2 of Co in the first region 110 may be greater than a2.

[0084] Conversely, the average atomic ratio b1 of Ni in the second region 120 may be greater than a1, and the average atomic ratio b2 of Co in the second region 120 may be equal to or less than a2.

[0085] When the primary particles 100 are lithium composite oxides further containing Mn and the average atomic ratio of Mn present in the primary particles is referred to as a3, the average atomic ratio b3 of Mn in the first region 110 and the second region 120 may be substantially similar to a3 or may exhibit a smaller deviation than the concentration deviation of Ni and / or Co in the first region 110 and the second region 120.

[0086] In another embodiment, the primary particles 100 may be a lithium composite oxide containing at least Ni and Mn.

[0087] Here, when the average atomic ratio of Ni present in the primary particle 100 in which the first region 110 and the second region 120 coexist is referred to as a1 and the average atomic ratio of Mn is referred to as a3, the average atomic ratio b1 of Ni in the first region 110 may be less than a1, and the average atomic ratio b3 of Mn in the first region 110 may be greater than a3.

[0088] Conversely, the average atomic ratio b1 of Ni in the second region 120 may be greater than a1, and the average atomic ratio b3 of Mn in the second region 120 may be equal to or less than a3.

[0089] When the primary particles 100 are lithium composite oxides further containing Co, and the average atomic ratio of Co present in the primary particles is referred to as a2, the average atomic ratio b2 of Co in the first region 110 and the second region 120 may be substantially similar to a2 or may exhibit a smaller deviation than the concentration deviation of Ni and / or Mn in the first region 110 and the second region 120. In another example, Co in the primary particles 100 may exhibit a concentration variation pattern similar to that of Ni, whereby the average atomic ratio b2 of Co in the first region 110 may be less than a2, and the average atomic ratio b2 of Co in the second region 120 may be greater than a2.

[0090] Furthermore, the cathode active material defined herein may include a coating layer covering at least a portion of the surface of the primary particles and / or the secondary particles. The surface of the primary particles may refer to a grain boundary defined by the contact between adjacent primary particles.

[0091] For example, the coating layer may be present to cover at least a portion of the exposed surface of the primary particles, particularly, the coating layer may be present to cover at least a portion of the exposed surface of the primary particles present at the outermost portion of the secondary particles.

[0092] Accordingly, the coating layer may exist as a layer that coats the surfaces of the primary particles and / or the secondary particles continuously or discontinuously. When the coating layer exists discontinuously, it may exist in the form of islands.

[0093] The coating layer covering the surfaces of the primary particles and / or secondary particles can contribute to improving the electrochemical properties of high-Ni type lithium composite oxides, which have insufficient lithium ion and / or charge migration on the surface, and can promote the migration of lithium ions and / or charges toward the lithium ion and / or charge migration path formed by the primary particles 100 where the first region 110 and the second region 120, which are present near the surfaces of the secondary particles, coexist.

[0094] The coating layer may also exist in the form of a solid solution that does not form a boundary with the primary particles and / or the secondary particles formed by aggregation of the primary particles.

[0095] The coating layer may include at least one oxide represented by the following Chemical Formula 2. That is, the coating layer can be defined as a region where the oxide represented by the following Chemical Formula 2 is present.

[0096] [Chemical formula 2] Li a A b O c (where, A is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd; 0≦a≦10, 0≦b≦8, 2≦c≦13.

[0097] In addition, the coating layer may be in a form in which different oxides are present simultaneously in one layer, or in which different oxides represented by Chemical Formula 2 are present in separate layers.

[0098] The oxide represented by Chemical Formula 2 may be physically and / or chemically bonded to the primary particles represented by Chemical Formula 1. The oxide may also exist in a state of forming a solid solution with the primary particles represented by Chemical Formula 1.

[0099] The cathode active material according to this embodiment may have enhanced structural stability by including a coating layer covering at least a portion of the primary particles (e.g., the interfaces between the primary particles) and / or the surfaces of secondary particles formed by aggregation of the primary particles. Furthermore, when such a cathode active material is used in a lithium secondary battery, the high-temperature storage stability and lifespan characteristics of the cathode active material may be improved. Furthermore, the oxide may reduce residual lithium in the cathode active material and simultaneously act as a pathway for lithium ions to move, thereby improving the efficiency characteristics of the lithium secondary battery.

[0100] In some cases, the oxide may be present not only on at least a portion of the surface of the primary particles and / or the secondary particles, but also in internal voids formed inside the secondary particles.

[0101] The oxide is a composite oxide of lithium and an element represented by A, or an oxide of A, and the oxide is, for example, Li a Co b O c , Li a W 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 , Co b O c , W b O c , Zr b Oc , Ti b O c or B b O c However, the above-mentioned examples are merely given for the sake of convenience to facilitate understanding, and the oxides defined in the present application are not limited to the above-mentioned examples.

[0102] In another embodiment, the oxide may be an oxide in which lithium and at least two elements represented by A are combined, or may further include an oxide in which lithium and at least two elements represented by A are combined. The oxide in which lithium and at least two elements represented by A are combined may, for example, be Li a (Co / Al) b O c , Li a (Co / Mg) b O c , Li a (Co / Ba) b O c , 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 It may be, but is not necessarily limited to, these.

[0103] Here, the oxide may exhibit a concentration gradient that decreases from the surface portion of the secondary particle toward the center portion of the secondary particle, whereby the concentration of the oxide may decrease from the outermost surface of the secondary particle toward the center portion of the secondary particle.

[0104] In this case, a concentration gradient of the oxide may be formed by the oxide diffusing from the surface portion of the secondary particle toward the center portion of the secondary particle along the grain boundary formed by the primary particles.

[0105] As described above, the oxide exhibits a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles, thereby effectively reducing residual lithium present on the surface of the positive electrode active material and preventing side reactions due to unreacted residual lithium. Furthermore, the oxide prevents a decrease in crystallinity in the inner surface region of the positive electrode active material. Furthermore, the oxide prevents the overall structure of the positive electrode active material from collapsing during an electrochemical reaction.

[0106] Furthermore, the coating layer may include a first oxide layer containing at least one oxide represented by Chemical Formula 2, and a second oxide layer containing at least one oxide represented by Chemical Formula 2, but different from the oxide contained in the first oxide layer.

[0107] For example, the first oxide layer may be present so as to cover at least a portion of the exposed surfaces of the primary particles present at the outermost periphery of the secondary particles, and the second oxide layer may be present so as to cover at least a portion of the exposed surfaces of the primary particles not covered by the first oxide layer and the surface of the first oxide layer.

[0108] Lithium secondary battery According to yet another aspect of the present invention, a positive electrode may be provided, including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include a positive electrode active material according to various embodiments of the present invention. Therefore, since the positive electrode active material is the same as that described above, detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described below.

[0109] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0110] The positive electrode slurry composition preferably contains the positive electrode active material, a conductive material, and optionally a binder, and the positive electrode active material may be prepared by applying the positive electrode slurry composition to the positive electrode current collector.

[0111] In this case, the positive electrode active material may be included in an amount of 80 to 99 wt %, more specifically, 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when the amount is within this range, but the amount is not necessarily limited thereto.

[0112] The conductive material is used to impart conductivity to the electrode and can be any material that provides electronic conductivity without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon-based materials (e.g., carbon fiber); metal powder or metal fiber (e.g., copper, nickel, aluminum, or silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0113] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0114] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent to prepare a positive electrode slurry composition, coating the composition on a positive electrode current collector, and then drying and rolling the composition.

[0115] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is applied to produce a positive electrode, taking into consideration the coating thickness of the slurry and the production yield.

[0116] In another embodiment, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0117] According to yet another aspect of the present invention, there may be provided an electrochemical device including the above-described positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0118] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, a detailed description thereof will be omitted for convenience, and only the remaining components not described above will be described in detail below.

[0119] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0121] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0122] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition containing the negative electrode active material, a conductive material, and optionally a binder, on the negative electrode current collector.

[0123] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon may also be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0124] The negative electrode active material may be contained in an amount of 80 to 99 wt % based on the total weight of the negative electrode active material layer.

[0125] The binder, which aids in bonding between the conductive material, active material, and current collector, may typically be added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0126] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of such a conductive material include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives.

[0127] In one embodiment, the negative electrode active material layer may be prepared by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and then laminating the resulting film on the negative electrode current collector.

[0128] In another embodiment, the negative electrode active material layer may be fabricated by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector and drying the coating; or by casting the negative electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0129] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator has low resistance to ion migration of the electrolyte and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0130] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0131] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0132] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to produce excellent electrolyte performance.

[0133] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0134] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0135] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0136] The external shape of the lithium secondary battery according to the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit battery for a medium- to large-sized battery module including a plurality of battery cells.

[0137] According to yet another aspect of the present invention, there may be provided a battery module including the lithium secondary battery as a unit cell and / or a battery pack including the same.

[0138] The battery module or the battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system. [Example]

[0139] The present invention will be described in more detail below with reference to examples. However, these examples are for the purpose of illustrating the present invention and are not to be construed as limiting the scope of the present invention.

[0140] Production Example 1: Production of a positive electrode active material with Co unevenly distributed regions within the primary particles (1) Example 1 (a) A hydroxide precursor with a high concentration of Co on the surface was synthesized using a known co-precipitation method.

[0141] Specifically, a first precursor aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed so that Ni:Co:Mn was present in a molar ratio of 90:2:8 was used to prepare Ni. 0.90 Co 0.02 Mn 0.08A core having an average composition of (OH)2 was formed, and the core was formed to have a diameter that was 88 to 98% of the average diameter of the final precursor.

[0142] After the core formation is complete, Ni is deposited on the surface of the core using a second precursor aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate are mixed so that Ni:Co:Mn is present in a molar ratio of 55:43.5:1.5. 0.55 Co 0.435 Mn 0.015 A shell was formed with an average composition of (OH)2.

[0143] (b) The hydroxide precursor synthesized in step (a) was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03), and the mixture was heated to 700°C at a rate of 2°C per minute in a calcination furnace while maintaining an O2 atmosphere. The mixture was then heat-treated at 700°C for 10 hours to obtain a cathode active material.

[0144] The lithium composite oxide contained in the positive electrode active material obtained in the step (b) had primary particles in which regions with different Co concentrations were locally formed.

[0145] (2) Example 2 After step (b), the lithium composite oxide was mixed with 0.3 mol% AlO, 0.3 mol% TiO, and 0.3 mol% ZrO. The mixture was then heated to 700°C at a rate of 2°C per minute while maintaining an O atmosphere in a firing furnace, and heat-treated for 10 hours. A positive electrode active material was prepared in the same manner as in Example 1, except that the surface of the lithium composite oxide was coated with Al, Ti, and Zr.

[0146] (3) Comparative Example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that a shell was not formed on the surface of the core using the second precursor aqueous solution.

[0147] Production Example 2: Production of a positive electrode active material in which Mn unevenly distributed regions exist within the primary particles (1) Example 3 (a) A hydroxide precursor with a high concentration of Mn on the surface was synthesized using a known co-precipitation method.

[0148] Specifically, a first precursor aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed so that Ni:Co:Mn was present in a molar ratio of 90:8:2 was used to prepare Ni. 0.90 Co 0.08 Mn 0.02 A core having an average composition of (OH)2 was formed, and the core was formed to have a diameter that was 85 to 98% of the average diameter of the precursor that was finally obtained.

[0149] After the core formation is complete, Ni is deposited on the surface of the core using a second precursor aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate are mixed so that Ni:Co:Mn is present in a molar ratio of 55:1.5:43.5. 0.55 Co 0.015 Mn 0.435 A shell was formed with an average composition of (OH)2.

[0150] (b) The hydroxide precursor synthesized in step (a) was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03), and the mixture was heated to 700°C at a rate of 2°C per minute in a calcination furnace while maintaining an O2 atmosphere. The mixture was then heat-treated at 700°C for 10 hours to obtain a cathode active material.

[0151] The lithium composite oxide contained in the positive electrode active material obtained in the step (b) had primary particles in which regions with different Mn concentrations were locally formed.

[0152] (2) Example 4 After step (b), the lithium composite oxide was mixed with 0.3 mol% AlO, 0.3 mol% TiO, and 0.3 mol% ZrO, and the mixture was heated to 700°C at a rate of 2°C per minute while maintaining an O atmosphere in a sintering furnace. Then, heat treatment was performed for 10 hours to coat the surface of the lithium composite oxide with Al, Ti, and Zr. A cathode active material was prepared in the same manner as in Example 3.

[0153] (3) Comparative Example 2 A positive electrode active material was prepared in the same manner as in Example 3, except that the second aqueous precursor solution was used and a shell was not formed on the surface of the core.

[0154] Manufacturing Example 3: Manufacturing of lithium secondary batteries A positive electrode slurry was prepared by dispersing 92 wt% of each of the positive electrode active materials prepared in Preparation Examples 1 and 2, 4 wt% of artificial graphite, and 4 wt% of a PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0155] A coin battery was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte solution of 1.15 M LiPF in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0156] Experimental Example 1: EDX mapping analysis of positive electrode active material The cathode active materials (secondary particles) according to Example 1, Example 3, Comparative Example 1, and Comparative Example 2 were each cross-sectionally processed using an FIB (Ga-ion source) to obtain cross-sectional TEM images. Next, the distributions of Ni, Co, and Mn within the primary particles were confirmed by EDX mapping of Ni, Co, and Mn in the cross-sectional TEM images.

[0157] 3 and 4 for the positive electrode active material according to Example 1, it can be seen that there are regions where the concentrations of Ni and Co change within the primary particles.

[0158] For example, referring to Figure 4, there is a relatively bright region within the primary particle, and this region corresponds to a region where the density of Co is higher than other regions. In the region where the density of Co is higher, the average atomic ratio b2 of Co is larger than the average atomic ratio a2 of Co within the primary particle.

[0159] Here, a region having a higher Co density than other regions is defined as a first region, and a region other than the first region is defined as a second region. When the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is defined as a1 and the average atomic ratio of Co present in the primary particle in which the first region and the second region coexist is defined as a2, the average atomic ratio b1 of Ni in the first region is equal to or less than a1, and the average atomic ratio b2 of Co in the first region is greater than a2. Meanwhile, it can be confirmed that the uneven distribution of Mn in the primary particle in which the first region and the second region coexist is slight compared to Ni and Co.

[0160] 3, it can be seen from the cross-sectional TEM image that, in the primary particles in which the first region and the second region coexist, at least one region selected from the first region and the second region is locally present within the primary particle, and that in some primary particles, at least one region selected from the first region and the second region is present in a plurality of regions within the primary particle.

[0161] In particular, based on a cross-sectional TEM image of the secondary particles, it can be seen that the primary particles in which the first region and the second region coexist are locally present on the surface of the secondary particles. The local presence of the primary particles in which the first region and the second region coexist on the surface of the secondary particles can improve the stability of the surface of the secondary particles, where most side reactions occur.

[0162] Referring to FIG. 4 for the EDX mapping image of Co shown in FIG. 3, it can be seen that in the primary particle in which the first region and the second region coexist, at least one region selected from the first region and the second region extends in a direction from the surface to the center of the secondary particle, and when the length measured in a direction perpendicular to the extension direction of the first region in the primary particle is referred to as the width of the primary particle, the width of the first region is smaller than the width of the primary particle.

[0163] The formation of the concentration change region of the above-mentioned form within the primary particles can improve the electrochemical properties of the high-Ni type lithium composite oxide, which has insufficient lithium ion and / or charge movement on the surfaces of the secondary particles, while also improving the stability of the crystal structure of the primary particles.

[0164] Table 1 below shows the average atomic ratio of Ni and Co in the primary particles and the results of measuring the atomic ratio of Ni and Co at the positions indicated in FIG.

[0165] [Table 1]

[0166] That is, from the results of FIGS. 3 and 4 and Table 1, it can be seen that there are localized concentration change regions in which the Co concentration is relatively high within the primary particles.

[0167] Similarly, referring to FIGS. 5 and 6 for the positive electrode active material according to Example 3, it can be seen that there are concentration change regions for Ni and Mn within the primary particles.

[0168] For example, in Figure 5, based on the EDX mapping result for Mn, there are relatively bright areas within the primary particles, which correspond to areas where Mn is more densely packed than other areas. In the areas with high Mn density, the average atomic ratio b3 of Mn is greater than the average atomic ratio a3 of Mn within the primary particles.

[0169] Here, a region having a higher Mn density than other regions is referred to as a first region, and a region other than the first region is defined as a second region. When the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is referred to as a1 and the average atomic ratio of Mn is referred to as a3, the average atomic ratio b1 of Ni in the first region is less than or equal to a1, and the average atomic ratio b3 of Mn in the first region is greater than a3.

[0170] It can be seen that the uneven distribution of Co in the primary particles where the first and second regions coexist is expressed in a form similar to that of Ni.

[0171] 5, it can be seen that the first region and / or the second region are locally present within the primary particles, and that a plurality of the first region and / or the second region are present within some primary particles, similar to Example 1. In addition, it can be seen that the shape of the concentration change region is formed similarly to Example 1.

[0172] Table 2 below shows the average atomic ratio of Ni and Mn in the primary particles and the results of measuring the atomic ratio of Ni and Mn at the positions indicated in FIG.

[0173] [Table 2]

[0174] 7 and 8 for the positive electrode active materials according to Comparative Examples 1 and 2, it can be seen that there is no uneven distribution phenomenon of any transition metal element within the primary particles, i.e., no concentration change region exists within the primary particles.

[0175] Furthermore, although not separately attached, it was confirmed that the cathode active materials of Examples 2 and 4, which were subjected to a surface coating treatment on the cathode active materials of Examples 1 and 3, also had a concentration change region formed within the primary particles in a similar form to Examples 1 and 3, apart from the presence of a surface coating and the resulting gradient of coating elements.

[0176] Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries A charge-discharge experiment was carried out on the lithium secondary battery (coin cell) manufactured in Manufacturing Example 2 using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.4V, and a discharge rate of 0.1C, to measure the charge and discharge capacities.

[0177] In addition, the same lithium secondary battery was charged and discharged 50 times at 45°C and 1C / 1C within a driving voltage range of 3.0V to 4.4V, and then the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0178] The measurement results are shown in Table 3 below.

[0179] [Table 3]

[0180] Referring to the results in Table 3, Ni 0.90 Co 0.02 Mn 0.08 Ni on the surface of the core with an average composition of (OH) 0.55 Co 0.435 Mn 0.015 With reference to Examples 1, 2, and Comparative Example 1, which used precursors forming shells with an average composition of (OH), it can be seen that Examples 1 and 3 have superior capacity, charge / discharge efficiency, and lifespan retention rate to Comparative Example 1, which does not have a Co uneven distribution phenomenon within the primary particles, i.e., does not have a Co concentration change region within the primary particles.

[0181] Similarly, Ni 0.90 Co 0.08 Mn 0.02 Ni on the surface of the core with an average composition of (OH) 0.55 Co 0.015 Mn 0.435 Referring to Examples 3, 4, and Comparative Example 2, which used precursors forming shells with an average composition of (OH), it can be seen that Examples 2 and 4 have superior capacity, charge / discharge efficiency, and lifespan retention rate to Comparative Example 2, which does not have uneven distribution of Mn within primary particles.

[0182] From the above results, it can be seen that when regions with different concentrations of any transition metal are locally formed within primary particles, it is possible to improve the capacity and charge / discharge efficiency of a lithium secondary battery using the positive electrode active material.

[0183] In addition, the increase in the lifespan of lithium secondary batteries using the positive electrode active material is expected to be due to the local formation of regions with different concentrations of any transition metal within the primary particles, which alleviates the deterioration in the stability of the crystalline structure of the lithium composite oxide due to repeated charging and discharging.

[0184] Experimental Example 3: Evaluation of Impedance (EIS; Electrochemical Impedance Spectroscopy) Characteristics of Lithium Secondary Batteries The lithium secondary battery (coin cell) manufactured in Manufacturing Example 2 was charged at 1 C using electrochemical impedance spectroscopy (EIS), and the resistance was measured within a frequency range (10 kHz to 0.01 Hz).

[0185] The Nyquist plot obtained from the resistance measurement by the impedance spectroscopy is R ct The (charge transfer resistance) values ​​are shown in Table 4 below.

[0186] [Table 4]

[0187] Referring to the results in Table 4, Ni 0.90 Co 0.02 Mn 0.08 Ni on the surface of the core with an average composition of (OH) 0.55 Co 0.435 Mn 0.015 With reference to Examples 1, 2, and Comparative Example 1, which used precursors that formed shells with an average composition of (OH), it can be seen that the impedance characteristics of Examples 1 and 2 are superior to those of Comparative Example 1, which does not have a phenomenon of uneven distribution of Co within the primary particles, i.e., does not have a region of Co concentration change within the primary particles.

[0188] Similarly, Ni 0.90 Co 0.08 Mn 0.02 Ni on the surface of the core with an average composition of (OH) 0.55 Co 0.015 Mn 0.435 Referring to Examples 3 and 4 and Comparative Example 2, which used precursors forming shells with an average composition of (OH), it can be seen that Examples 3 and 4 have better impedance characteristics than Comparative Example 2, which does not have uneven distribution of Mn within the primary particles.

[0189] From the above results, it can be seen that when regions with different concentrations of any transition metal are locally formed within primary particles, it is possible to prevent or mitigate the phenomenon in which resistance increases as the content of Ni among the main transition metals constituting the lithium composite oxide increases.

[0190] Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art may modify and change the present invention in various ways by adding, changing, deleting or adding components within the scope of the concept of the present invention as set forth in the claims, and this also falls within the scope of the present invention. [Explanation of symbols]

[0191] 11...center 12...Surface part 100···primary particles 110···1st Area 120···Second Domain

Claims

1. A positive electrode active material for a lithium secondary battery, comprising primary particles capable of reversible intercalation / deintercalation of lithium ions and secondary particles formed by aggregation of the primary particles, the primary particles are a lithium composite oxide containing at least one transition metal selected from Ni, Co, Mn, and Al, When the average atomic ratio of any transition metal present in the primary particles is referred to as a, The secondary particles are a positive electrode active material comprising primary particles in which a first region in which the average atomic ratio of the arbitrary transition metal is greater than a and a second region in which the average atomic ratio of the arbitrary transition metal is a or less coexist within the primary particles.

2. 2. The positive electrode active material according to claim 1, wherein, based on a cross-sectional TEM image of the secondary particle, at least one region selected from the first region and the second region is present locally within the primary particle in which the first region and the second region coexist.

3. 2. The positive electrode active material according to claim 1, wherein, based on a cross-sectional TEM image of the secondary particle, within the primary particle in which the first region and the second region coexist, at least one region selected from the first region and the second region is present in plurality within the primary particle.

4. 2. The positive electrode active material according to claim 1, wherein, based on a cross-sectional TEM image of the secondary particle, within the primary particle in which the first region and the second region coexist, at least one region selected from the first region and the second region extends along a direction from a surface toward a center of the secondary particle.

5. 5. The cathode active material of claim 4, wherein the width of the primary particle is defined as a length measured in a direction perpendicular to an extension direction of the first region within the primary particle, and the width of the first region is smaller than the width of the primary particle.

6. 2 . The positive electrode active material according to claim 1 , wherein, based on a cross-sectional TEM image of the secondary particle, the primary particle in which the first region and the second region coexist is present locally on a surface portion of the secondary particle.

7. the primary particles are a lithium composite oxide containing at least Ni and Co, When the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is referred to as a1 and the average atomic ratio of Co present in the primary particle in which the first region and the second region coexist is referred to as a2, the average atomic ratio b1 of Ni in the first region is equal to or less than a1, The positive electrode active material according to claim 1 , wherein an average atomic ratio b2 of Co in the first region is greater than an average atomic ratio a2.

8. the primary particles are a lithium composite oxide containing at least Ni and Mn, When the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is referred to as a1 and the average atomic ratio of Mn present in the primary particle in which the first region and the second region coexist is referred to as a3, the average atomic ratio b1 of Ni in the first region is equal to or less than a1, The positive electrode active material according to claim 1 , wherein an average atomic ratio b3 of Mn in the first region is greater than an average atomic ratio a3 of Mn.

9. The positive electrode active material of claim 1 , wherein the primary particles further comprise a doping metal.

10. a coating layer covering at least a portion of the surfaces of the primary particles and the secondary particles, The positive electrode active material according to claim 1 , wherein the coating layer comprises at least one oxide represented by the following chemical formula: [Chemical formula 2] Li ａ A ｂ O ｃ (where, A is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd; 0≦a≦10, 0≦b≦8, 2≦c≦13.

11. A positive electrode slurry composition comprising the positive electrode active material according to claim 1 , a conductive material, and a binder.

12. A lithium secondary battery comprising a positive electrode formed by coating a current collector with the positive electrode slurry composition according to claim 11.

Images