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 lithium secondary battery using a positive electrode active material and a positive electrode containing 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 containing the positive electrode active material, in which regions having different concentrations of any transition metal in primary particles are locally formed to enhance the efficiency and structural stability of lithium ion and / or charge transfer.

Background Art

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

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

[0004] As the positive electrode active material of the lithium secondary battery, lithium composite oxides are used. Examples thereof include composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2, which are being studied.

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

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal safety and low cost, but they have problems such as small capacity and poor high-temperature characteristics. In addition, although LiNiO2-based cathode active materials exhibit battery characteristics with high discharge capacity, synthesis is difficult due to the cation mixing problem between Li and transition metals, and as a result, there are significant problems with rate characteristics.

[0007] In addition, depending on the degree of deepening of such cation mixing, a large amount of Li by-products are generated. Most of these Li by-products consist of compounds of LiOH and Li2CO3, so there are problems of gelation during the manufacture of the cathode paste and the cause of gas generation due to charge and discharge during the manufacture of the electrode. The remaining Li2CO3 not only increases the swelling phenomenon of the cell and reduces the cycle, but also causes the battery to swell.

[0008] Recently, lithium-based composite oxides in which Ni, Co, Mn, and / or Al are combined as cathode active materials have been developed. Generally, such lithium-based composite oxides, like LiNiO2-based cathode active materials, have the advantage that the energy density increases and the output characteristics improve as the Ni content increases. However, on the other hand, they are accompanied by the problem of increasing resistance characteristics. Therefore, in lithium-based composite oxides in which Ni, Co, Mn, and / or Al are combined, there is a demand for the development of a cathode active material that can prevent a decrease in resistance characteristics and life characteristics while maintaining the excellent reversible capacity of LiNiO2.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0011] For example, conventionally, lithium secondary batteries using LFP have been mainly used from the viewpoint of ensuring safety, etc., but recently, the use of nickel-based lithium composite oxides, which have a larger energy capacity per unit weight than LFP, has been on the increase.

[0012] In line with such trends in cathode materials, an object of the present invention is to provide a high-Ni type lithium composite oxide and / or a cathode active material containing the lithium composite oxide for realizing a higher capacity of cells for automobiles. However, in the case of known high-Ni type lithium composite oxides, there is a problem that the resistance increases as the Ni content increases, and thereby the life deteriorates.

[0013] Thus, one of the causes of the phenomenon that the resistance increases as the Ni content in the lithium composite oxide increases is considered to be due to insufficient movement of lithium ions and / or charges in the lithium composite oxide, particularly on the surface of the lithium composite oxide.

[0014] In addition, as the Ni content increases, the structural instability of the lithium composite oxide increases, and thus the possibility that the crystal structure of the lithium composite oxide changes or collapses during charge and discharge of the lithium secondary battery increases. Moreover, the structural instability of the lithium composite oxide can cause side reactions, thereby resulting in irreversible capacity loss of the cathode active material.

[0015] Accordingly, an object of the present invention is to provide a cathode active material in which regions having different concentrations of any transition metal within primary particles are locally formed to enhance the efficiency of lithium ion and / or charge transfer.

[0016] Further, an object of the present invention is to provide a cathode active material with improved structural stability by locally forming regions with different concentrations of any transition metal within the primary particles.

[0017] Another object of the present invention is to provide a cathode slurry composition containing the cathode active material defined in the present application.

[0018] Still another object of the present invention is to provide a lithium secondary battery including a cathode formed by coating the cathode slurry composition defined in the present application on a current collector.

[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 can be understood from the following description and can be further clearly understood from the embodiments of the present invention. Also, it can be easily known that the objects and advantages of the present invention can be realized by the means and combinations thereof shown in the claims.

Means for Solving the Problems

[0020] According to one aspect of the present invention, there is provided a cathode active material for a lithium secondary battery including 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 lithium composite oxides containing at least one selected from Ni, Co, Mn, and Al as transition metals.

[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. Further, the lithium composite oxide may further contain a doping metal other than the transition metal.

[0023] The secondary particles are aggregates formed by the aggregation of a plurality of the primary particles, and are also referred to as bulk or bulk particles. The secondary particles can be divided into a central part corresponding to a region relatively close to the center of the secondary particles and a surface part corresponding to a region close to the outer peripheral surface of the secondary particles.

[0024] Briefly speaking, with reference to the average radius of the secondary particles, a region defined as a distance within half of the average radius from the center of the secondary particles is referred to as the central part, and a region defined as a distance within half of the average radius from the outer peripheral surface of the secondary particles can be referred to as the surface part.

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

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

[0027] Whether the first region and the second region exist within the primary particle 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 capable of observing changes in the concentration of any transition metal within the primary particle.

[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 enabling a difference in lithium ion and / or charge movement between the first region and the second region. Such a difference in lithium ion and / or charge movement can contribute to the formation of lithium ion and / or charge movement paths.

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

[0030] In another embodiment, the primary particle may be a lithium composite oxide containing at least Ni and Mn. Here, when the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is a1 and the average atomic ratio of Mn is a3, the average atomic ratio b1 of Ni within the first region is equal to or less than a1, and the average atomic ratio b3 of Mn within 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 containing a positive electrode active material, a conductive material, and a binder as defined in the present application.

[0032] According to still another aspect of the present invention, there is provided a lithium secondary battery including a positive electrode formed by coating a current collector with the positive electrode slurry composition as defined in the present application. [Advantages of the Invention]

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

[0034] Thereby, by preventing or alleviating the phenomenon that the resistance of the positive electrode active material increases as the content of Ni in the main transition metal constituting the positive electrode active material increases, the deterioration of the positive electrode active material due to repeated charge and discharge can be delayed.

[0035] In addition, as the Ni content increases, the structural instability of the lithium composite oxide increases, so that the crystal structure of the lithium composite oxide is likely to change or collapse during charge and discharge of the lithium secondary battery. Moreover, the structural instability of the lithium composite oxide can cause side reactions, thereby resulting in irreversible capacity loss of the positive electrode active material.

[0036] However, according to the present invention, by locally forming regions having different concentrations of an arbitrary transition metal within the primary particles constituting the positive electrode active material, a buffering effect against changes in the crystal structure during charge and discharge of the high-Ni type lithium composite oxide can be provided, and through this, the structural stability of the lithium composite oxide can be improved.

[0037] Together with the above-described effects, the specific effects of the present invention will be described together with the specific matters for carrying out the following invention. [Brief Description of the Drawings]

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

BEST MODE FOR CARRYING OUT THE INVENTION

[0039] For easier understanding of the present invention, for convenience, specific terms are defined in this application. Unless otherwise specifically defined in this application, the scientific terms and technical terms used in the present invention have meanings generally understood by those having ordinary knowledge in the technical field. Also, unless otherwise specified in the context, terms in the singular form are to be understood to include their plural forms, and terms in the plural form are to be understood to include their singular forms.

[0040] Hereinafter, the positive electrode active material according to the present invention and the lithium secondary battery using the positive electrode containing the positive electrode 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 means a single particle. Further, the primary particle may mean one grain or crystallite. The primary particle can have a single crystal structure.

[0043] The secondary particle means an aggregate formed by aggregation of a plurality of primary particles. Further, the secondary particle can be referred to as a bulk or bulk particle.

[0044] By the average particle diameter of the primary particles being in the range of 0.05 μm to 5 μm, preferably 0.1 μm to 3 μm, the optimum density of the positive electrode manufactured using the positive electrode active material according to various embodiments of the present invention can be realized. Also, the average particle diameter of the secondary particles can vary depending on the number of aggregated primary particles, but generally may be 3 μm to 20 μm.

[0045] The secondary particle can 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 close to the outer peripheral surface of the secondary particle.

[0046] In the present application, unless otherwise defined, a region defined as a distance within half of the average radius from the center of the secondary particle is referred to as the central portion with reference to the average radius of the secondary particle, and a region defined as a distance within half of the average radius from the outer peripheral surface of the secondary particle can be referred to as the surface portion.

[0047] There may be voids and / or grain boundaries between the primary particles constituting the secondary particle.

[0048] For example, the primary particles can form internal voids by being separated from adjacent primary particles inside the secondary particles. At this time, the internal voids may be closed pores and / or opened pores.

[0049] Further, the primary particles can define a grain boundary which is a boundary formed by contacting with adjacent primary particles. That is, the grain boundary is a boundary formed by the contact of adjacent primary particles, and the grain boundary cannot be interpreted as being included in the primary particles. Therefore, even if a metal oxide different from the primary particles exists along the grain boundary and the concentration of the transition metal in the metal oxide is different from the concentration of the transition metal in the primary particles, it cannot be interpreted that there are a plurality of regions where there is a change in concentration with respect to any transition metal in the primary particles.

[0050] Among the primary particles present on the surface portion of the secondary particles, the surfaces exposed to the outside form the surface (outer peripheral surface) of the secondary particles.

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

[0052] 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.

[0053] In one embodiment, the primary particles can be defined as a lithium composite oxide represented by the following Chemical Formula 1. Also, the average composition of the secondary particles which are aggregates of the lithium composite oxide represented by the following Chemical Formula 1 can 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 (Here, 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 contain a doping metal other than the transition metal. The doping metal 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] Note that 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 content of Ni in the transition metal is relatively high. In this case, the molar 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 positive electrode active material defined in the present application can improve the efficiency of lithium ion and / or charge transfer by including primary particles in which a plurality of regions having different concentrations of any transition metal are locally formed. Through this, it is possible to prevent or mitigate the phenomenon that the resistance of the positive electrode active material increases as the content of Ni in the lithium composite oxide increases.

[0058] FIG. 1 and FIG. 2 are schematic diagrams for explaining the first region and the second region present in the primary particles constituting the positive electrode active material according to an embodiment of the present invention.

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

[0060] The fact that the secondary particle includes the primary particle 100 in which the first region 110 and the second region 120 coexist means that the secondary particle can also include a primary particle 100 in which there is no concentration change region divided into the first region 110 and the second region 120.

[0061] Whether the first region 110 and the second region 120 exist 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 capable of observing the concentration change of any transition metal in the primary particle (for example, EDX mapping, line scanning, EP-EDS (Energy Profiling-Energy Dispersive X-Ray Spectroscopy) analysis, etc.).

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

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

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

[0065] When 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 shown by EDX mapping or the like exist at least in the surface portion of the primary particle 100 or inside the surface portion of the primary particle 100, and the bright spots of the first region 110 do not exist at the crystal grain boundaries formed by adjacent primary particles 100 contacting each other.

[0066] The fact that the first region 110 and / or the second region 120 locally exist in the primary particle 100 means that no arbitrary transition metal shows an overall gradient in the primary particle 100.

[0067] For example, if a gradient (slope gradient) in which the concentration of an arbitrary transition metal continuously decreases from the surface portion 12 to the central portion 11 of the secondary particle is formed, in the surface portion 12 and the central portion 11 of the secondary particle, particularly in the primary particle 100 existing in the surface portion 12 of the secondary particle, there is only a gradient in which the concentration of the transition metal continuously decreases along the direction from the surface portion 12 to the central portion 11 of the secondary particle, and it is not observed that the first region 110 and / or the second region 120 locally exist in the primary particle 100.

[0068] Further, even if a gradient (inclination gradient) in which the concentration of an arbitrary transition metal continuously decreases from the surface portion to the central portion of the primary particle 100 is formed, it is not observed that the first region 110 and / or the second region 120 locally exist within the primary particle 100.

[0069] In addition, in order to form a gradient in the concentration of an arbitrary transition metal in the direction from the surface portion to the central portion of the aforementioned primary particle and / or secondary particle, generally, an inclined solid solution of an arbitrary transition metal must be induced through a coating process for the precursor and / or the lithium composite oxide.

[0070] However, through the inclined solid solution, it is not possible to make the first region 110 and / or the second region 120 locally exist within the primary particle 100. For example, the positive electrode active material according to the present application uses a precursor designed in consideration of the difference in the diffusion rate of the main transition metal during the heat treatment performed during the manufacturing process, so that the first region 110 and / or the second region 120 can locally exist within the primary particle 100.

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

[0072] The presence of a plurality of the first region 110 and / or the second region 120 within the primary particle 100 can form lithium ion and / or charge transfer paths in various aspects 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 the cross-sectional TEM image of the secondary particle, at least one region selected from the first region 110 and the second region 120 within the primary particle 100 where the first region 110 and the second region 120 coexist, particularly the first region 110, can extend along the direction from the surface 12 to the center 11 of the secondary particle.

[0074] Here, the statement "extends in the direction from the surface 12 to the center 11 of the secondary particle" may mean extending in a direction that exactly coincides with the direction from the surface 12 to the center 11 of the secondary particle.

[0075] Also, the statement "extends in the direction from the surface 12 to 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 to 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 to the center 11 of the secondary particle can form a predetermined included angle (for example, ±40°).

[0076] The extension direction of the long side of the primary particle 100 shown in FIG. 2 is oriented along the direction a→a′ from the surface 12 to the center 11 of the secondary particle. At this time, different from the example shown in FIG. 2, the primary particle 100 can also be oriented such that the extension direction of the long side of the primary particle 100 and the direction from the surface 12 to the center 11 of the secondary particle form a predetermined included angle (for example, ±40°).

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

[0078] At this time, when the length measured along the direction c→c′ that intersects perpendicularly to the extension direction b→b′ of the first region 110 within the primary particle 100 is defined as the 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, the average value of the width w of the primary particle 100 measured along the direction c→c′ that intersects perpendicularly to the extension direction b→b′ of the first region 110 within the section where the first region 110 exists may be larger than the average value of the width w1 of the first region.

[0079] Also, based on the cross-sectional TEM image of the secondary particle, the ratio of the primary particles 100 in which the first region 110 and the second region 120 coexist among all the primary particles existing in the surface portion 12 of the secondary particle may be larger than the ratio of the primary particles 100 in which the first region 110 and the second region 120 coexist among all the primary particles existing in the central portion 11 of the secondary particle.

[0080] In another example, based on the cross-sectional TEM image of the secondary particle, the primary particles 100 in which the first region 110 and the second region 120 coexist may be locally present in 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 exist in the surface portion 12 of the secondary particle, it is possible to improve the electrochemical properties of high-Ni type lithium composite oxides, especially when the movement of lithium ions and / or charges on the surface of the secondary particle is insufficient. If the primary particles 100 in which the first region 110 and the second region 120 coexist mainly exist in the central portion 11 of the secondary particle or are uniformly present in the central portion 11 and the surface portion 12 of the secondary particle, it is difficult to achieve a sufficient lithium ion exchange effect inside the secondary particle.

[0082] In one embodiment, the primary particle 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 a1 and the average atomic ratio of Co is a2, the average atomic ratio b1 of Ni in the first region 110 is a1 or less, 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 a2 or less.

[0085] The primary particle 100 is a lithium composite oxide further containing Mn. When the average atomic ratio of Mn present in the primary particle is a3, the average atomic ratio b3 of Mn in the first region 110 and the second region 120 is approximately similar to a3, or can show a deviation less 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 particle 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 a1 and the average atomic ratio of Mn is a3, the average atomic ratio b1 of Ni in the first region 110 is a1 or less, 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 a3 or less.

[0089] The primary particle 100 is a lithium composite oxide further containing Co. When the average atomic ratio of Co present in the primary particle is denoted as a2, the average atomic ratio b2 of Co in the first region 110 and the second region 120 is approximately similar to a2, or can exhibit a deviation less than the concentration deviation of Ni and / or Mn in the first region 110 and the second region 120. In other examples, Co within the primary particle 100 can exhibit a concentration change pattern similar to that of Ni, whereby the average atomic ratio b2 of Co in the first region 110 is equal to or less than a2, and the average atomic ratio b2 of Co in the second region 120 may be greater than a2.

[0090] Furthermore, the positive electrode active material defined in the present application may include a coating layer covering at least a part of the surface of the primary particle and / or the secondary particle. The surface of the primary particle can be referred to as a grain boundary defined by adjacent primary particles contacting each other.

[0091] For example, the coating layer may be present so as to cover at least a part of the exposed surface of the primary particle. In particular, the coating layer may be present so as to cover at least a part of the exposed surface of the primary particle existing on the outermost contour of the secondary particle.

[0092] Thereby, the coating layer may exist as a layer that continuously or discontinuously coats the surface of the primary particle and / or the secondary particle. When the coating layer exists discontinuously, it may exist in an island form.

[0093] The coating layer covering the surface of the primary particles and / or the secondary particles can contribute to improving the electrochemical properties of the high-Ni type lithium composite oxide with insufficient lithium ion and / or charge movement on the surface. Further, the movement of lithium ions and / or charges can be promoted toward the lithium ion and / or charge movement path formed by the primary particles 100 in which the first region 110 and the second region 120 coexist near the surface of the secondary particles.

[0094] In addition, the coating layer can also exist in a solid solution form 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 contain 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 exists.

[0096] [Chemical Formula 2] Li a A b O c (Here, 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 coexist in one layer, or in a form in which different oxides represented by Chemical Formula 2 are present in separate layers.

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

[0099] The positive electrode active material according to this example can enhance the structural stability by including a coating layer that covers at least a part of the surface of the primary particles (for example, the interfaces between the primary particles) and / or the secondary particles formed by aggregation of the primary particles. 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 oxide can affect the improvement of the efficiency characteristics of the lithium secondary battery by reducing the residual lithium in the positive electrode active material and at the same time acting as a pathway for lithium ion movement.

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

[0101] The oxide is an oxide in which lithium and an element represented by A are complexed, 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 etc. may be used, but the above examples are only described for convenience to aid understanding and the oxide defined in the present application is not limited to the above examples.

[0102] In other embodiments, the oxide may be an oxide in which at least two elements represented by lithium and A are combined, or may further contain an oxide in which at least two elements represented by lithium and A are combined. The oxide in which at least two elements represented by lithium and A are combined is, for example, 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 etc. may be used, but are not necessarily limited thereto.

[0103] Here, the oxide can exhibit a concentration gradient that decreases from the surface portion to the central portion of the secondary particle. As a result, the concentration of the oxide can decrease from the outermost surface to the central portion of the secondary particle.

[0104] At this time, the concentration gradient of the oxide may be formed by the diffusion of the oxide along the grain boundaries formed by the primary particles from the surface portion to the central portion of the secondary particle.

[0105] As described above, by the oxide showing a concentration gradient decreasing from the surface portion to the central portion of the secondary particles, the residual lithium present on the surface of the positive electrode active material can be effectively reduced, and side reactions due to unreacted residual lithium can be prevented in advance. Further, it is possible to prevent the crystallinity in the inner region of the surface of the positive electrode active material from being lowered by the oxide. Further, it is possible to prevent the overall structure of the positive electrode active material from collapsing due to the oxide during the electrochemical reaction.

[0106] Furthermore, the coating layer may include a first oxide layer containing at least one oxide represented by Chemical Formula 2 above, and a second oxide layer containing at least one oxide represented by Chemical Formula 2 above and containing an oxide 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 part of the exposed surface of the primary particles present on the outermost contour of the secondary particles, and the second oxide layer may be present so as to cover at least a part of the exposed surface 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 still another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. Here, the positive electrode active material layer may 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, for the sake of convenience, a specific description is omitted, and hereinafter, only the remaining configurations not described above will be described.

[0109] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

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

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

[0112] The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing chemical changes. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber and other carbon-based substances, metal powders or metal fibers such as copper, nickel, aluminum, silver, etc., conductive whiskers such as zinc oxide, potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used. The conductive material may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0113] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesion force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0114] Except for using the positive electrode active material, the positive electrode may be manufactured by a normal positive electrode manufacturing method. Specifically, after applying a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent onto a positive electrode current collector, it may be manufactured by drying and rolling.

[0115] The solvent may be a solvent generally used in the art, and examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. Among these, one kind alone or a mixture of two or more kinds may be used. The amount of the solvent used is such that, considering the coating thickness of the slurry and the production yield, it can dissolve or disperse the positive electrode active material, the conductive material, and the binder, and then have a viscosity that can exhibit excellent thickness uniformity during coating for positive electrode manufacturing.

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

[0117] According to still another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

[0118] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is as described above, for the sake of convenience, a specific description thereof is omitted, and hereinafter, only the remaining configurations not described above will be specifically described.

[0119] The lithium secondary battery may further selectively include a battery container for housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0120] The negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned 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 a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a surface-treated product of copper or stainless steel with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, or the like may be used. Further, the negative electrode current collector may usually have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0122] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition containing a conductive material and optionally a binder together with the negative electrode active material to the negative electrode current collector.

[0123] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon, metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy, SiO β (0 < β < 2), metal oxides capable of doping and undoping lithium such as SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, etc. Any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, all of low-crystalline carbon and highly crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of highly crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

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

[0126] The conductive material may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives may be used.

[0127] In one embodiment, the negative electrode active material layer is manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the support on the negative electrode current collector.

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

[0129] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a lithium secondary battery can be used without particular limitation, and it is particularly preferable that it has a low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability. Specifically, a porous polymer film, for example, 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, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

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

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

[0132] As the organic solvent, any solvent may be used without particular limitation as long as it serves as a medium in which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge and discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0133] The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3), LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0134] In addition to the above-described 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, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. At this time, the additive may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

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

[0136] The outer shape of the lithium secondary battery according to the present invention is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape using a can. Further, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also preferably as a unit cell in a medium- to large-sized battery module including a plurality of battery cells.

[0137] According to still another aspect of the present invention, there can 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).

Example

[0139] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only 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 in which a Co uneven distribution region exists within primary particles (1) Example 1 (a) A hydroxide precursor in which Co is present at a high concentration on the surface portion 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 was used so that Ni:Co:Mn was present in a molar ratio of 90:2:8. 0.90 Co 0.02 Mn 0.08A core having an average composition of (OH)₂ was formed. The core was formed to have a diameter of 88 - 98% with respect to the average diameter of the finally obtained precursor.

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

[0143] (b) After mixing the hydroxide precursor synthesized in step (a) with LiOH (Li / (Ni + Co + Mn) mol ratio = 1.03), while maintaining an O₂ atmosphere in a firing furnace, the temperature was raised to 700°C at a rate of 2°C per minute, and heat treatment was performed at 700°C for 10 hours to obtain a positive electrode active material.

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

[0145] (2) Example 2 After step (b), the positive electrode active material was produced in the same manner as in Example 1, except that after mixing the lithium composite oxide with 0.3 mol% Al₂O₃, 0.3 mol% TiO₂, and 0.3 mol% ZrO₂, while maintaining an O₂ atmosphere in a firing furnace, the temperature was raised to 700°C at a rate of 2°C per minute and then heat treatment was performed for 10 hours to coat the surface of the lithium composite oxide with Al, Ti, and Zr.

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

[0147] Production Example 2. Production of a positive electrode active material in which a Mn uneven distribution region exists within primary particles (1) Example 3 (a) Using the well-known co-precipitation method, a hydroxide precursor with a high concentration of Mn on the surface was synthesized.

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

[0149] After the formation of the core was completed, using a second precursor aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed so that Ni:Co:Mn existed in a molar ratio of 55:1.5:43.5, Ni 0.55 Co 0.015 Mn 0.435 (OH)2 with an average composition was formed to form a shell.

[0150] (b) After mixing the hydroxide precursor synthesized in the step (a) with LiOH (Li / (Ni + Co + Mn) mol ratio = 1.03), while maintaining an O2 atmosphere in a firing furnace, the temperature was raised to 700°C at a rate of 2°C per minute, and heat treatment was performed at 700°C for 10 hours to obtain a positive electrode active material.

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

[0152] (2) Example 4 After the step (b), the positive electrode active material was produced in the same manner as in Example 3, except that the lithium composite oxide was mixed with 0.3 mol% Al2O3, 0.3 mol% TiO2, and 0.3 mol% ZrO2, and then while maintaining an O2 atmosphere in a firing furnace, the temperature was raised to 700°C at a rate of 2°C per minute, and then heat treatment was performed for 10 hours to coat the surface of the lithium composite oxide with Al, Ti, and Zr.

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

[0154] Production Example 3. Production of a lithium secondary battery 92 wt% of each positive electrode active material produced by Production Example 1 and Production Example 2, 4 wt% of artificial graphite, and 4 wt% of a PVDF binder were dispersed in 30 g of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum thin film with a thickness of 15 μm and vacuum dried at 135° C. to produce a positive electrode for a lithium secondary battery.

[0155] A lithium foil was used as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and a coin cell was produced using an electrolytic solution in which LiPF6 was present at a concentration of 1.15 M in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7.

[0156] Experimental Example 1. EDX mapping analysis of the positive electrode active material After cross-sectionally processing the positive electrode active materials (secondary particles) according to Example 1, Example 3, Comparative Example 1, and Comparative Example 2 using FIB (Ga-ion source), cross-sectional TEM images were obtained. Next, the distributions of Ni, Co, and Mn in the primary particles were confirmed through EDX mapping of Ni, Co, and Mn for the cross-sectional TEM images.

[0157] Referring to FIGS. 3 and 4 for the positive electrode active material according to Example 1, it can be confirmed that there are regions of concentration change for Ni and Co in the primary particles.

[0158] For example, with reference to FIG. 4, there is a relatively bright region within the primary particle, and this region corresponds to a region where the Co density is high compared to other regions. In the region where the Co density is high, the average atomic ratio b2 of Co is greater than the average atomic ratio a2 of Co within the primary particle.

[0159] Here, the region where the Co density is high compared to other regions is referred to as the first region, the region other than the first region is defined as the second region, and when the average atomic ratio of Ni present in the primary particle in which the first region and the second region coexist is a1 and the average atomic ratio of Co is a2, the average atomic ratio b1 of Ni within the first region is a1 or less, and the average atomic ratio b2 of Co within the first region is greater than a2. On the other hand, it can be confirmed that the uneven distribution of Mn within the primary particle in which the first region and the second region coexist is slight compared to Ni and Co.

[0160] Also, referring to FIG. 3, based on the cross-sectional TEM image, it can be confirmed that at least one region selected from the first region and the second region exists locally within the primary particle in which the first region and the second region coexist. Also, in some primary particles, it can be confirmed that a plurality of regions selected from the first region and the second region exist within the primary particle.

[0161] In particular, based on the cross-sectional TEM image of the secondary particle, it can be confirmed that the primary particle in which the first region and the second region coexist exists locally on the surface portion of the secondary particle. By the primary particle in which the first region and the second region coexist existing locally on the surface portion of the secondary particle, the stability of the surface portion of the secondary particle where most side reactions occur can be improved.

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

[0163] By forming the concentration change region of the above-described form within the primary particle, it is possible to improve the electrochemical characteristics of the high-Ni type lithium composite oxide in which the movement of lithium ions and / or charges on the surface of the secondary particle is insufficient, and at the same time improve the stability of the crystal structure of the primary particle.

[0164] Table 1 below shows the results of measuring the average atomic ratios of Ni and Co in the primary particle and the atomic ratios of Ni and Co at the positions marked in FIG. 4.

[0165]

Table 1

[0166] That is, through the results of FIGS. 3, 4, and Table 1, it can be confirmed that a region with a relatively high concentration of Co within the primary particle exists locally.

[0167] Similarly, referring to FIGS. 5 and 6 for the positive electrode active material according to Example 3, it can be confirmed that a concentration change region exists for Ni and Mn within the primary particle.

[0168] For example, in FIG. 5, based on the EDX mapping result for Mn, a relatively bright region exists within the primary particle, and the region corresponds to a region where the density of Mn is higher than that of other regions. The average atomic ratio b3 of Mn in the region where the density of Mn is high is larger than the average atomic ratio a3 of Mn in the primary particle.

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

[0170] It can be confirmed that the segregation of Co in the primary particle in which the first region and the second region coexist occurred in a form similar to that of Ni.

[0171] Also, referring to FIG. 5, as in Example 1, it can be confirmed that the first region and / or the second region is locally present in the primary particle, and in some primary particles, a plurality of the first region and / or the second region exist. In addition, it can be confirmed that the form of the concentration change region was formed similarly to that in Example 1.

[0172] Table 2 below shows the results of measuring the average atomic ratios of Ni and Mn in the primary particle and the atomic ratios of Ni and Mn at the positions indicated in FIG. 6.

[0173]

Table 2

[0174] Referring to FIGS. 7 and 8 for the positive electrode active materials according to Comparative Example 1 and Comparative Example 2, it can be confirmed that there is no segregation phenomenon for any transition metal element in the primary particle, that is, there is no concentration change region in the primary particle.

[0175] Also, although not separately attached, the positive electrode active materials according to Examples 2 and 4 with surface coating treatment for the positive electrode active materials according to Example 1 and Example 3 were also confirmed to have a concentration change region formed in the primary particles in a form similar to that of Example 1 and Example 3, apart from the presence of the surface coating and the gradient of the coating elements thereby.

[0176] Experimental Example 2. Evaluation of the electrochemical characteristics of the lithium secondary battery For the lithium secondary battery (coin cell) manufactured in Production Example 2, an electrochemical analyzer (Toyo, Toscat-3100) was used to conduct charge and discharge experiments at 25 °C, with a discharge rate of 0.1C applied in a voltage range of 3.0V to 4.4V, and the charge and discharge capacities were measured.

[0177] Also, for the same lithium secondary battery, after performing 50 charge and discharge cycles under the conditions of 1C / 1C within the driving voltage range of 45 °C and 3.0V to 4.4V, the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention rate) 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 Referring to Example 1, Example 2 and Comparative Example 1 using a precursor in which a shell having an average composition of Ni 0.55 Co 0.435 Mn 0.015 (OH)2 was formed on the surface of the core having an average composition, it can be confirmed that the capacity, charge and discharge efficiency and life retention rate of Example 1 and Example 3 are superior to those of Comparative Example 1 in which there is no uneven distribution phenomenon of Co in the primary particles, that is, no concentration change region of Co in the primary particles.

[0181] Similarly, Ni 0.90 Co 0.08 Mn 0.02 On the surface of the core having an average composition of Ni 0.55 Co 0.015 Mn 0.435 Referring to Example 3, Example 4, and Comparative Example 2 using a precursor in which a shell having an average composition of (OH)2 was formed, it can be confirmed that the capacity, charge-discharge efficiency, and life retention rate of Example 2 and Example 4 are superior to those of Comparative Example 2 in which there is no uneven distribution phenomenon for Mn in the primary particles.

[0182] Through the above results, it can be confirmed that when regions with different concentrations of any transition metal are locally formed within the 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 life retention rate of the lithium secondary battery using the positive electrode active material is presumably because the decrease in the stability of the crystal structure of the lithium composite oxide due to repeated charge and discharge is alleviated by locally forming regions with different concentrations of any transition metal within the primary particles.

[0184] Experimental Example 3. Evaluation of the impedance (EIS; Electrochemical Impedence Spectroscopy) characteristics of the lithium secondary battery After charging the lithium secondary battery (coin cell) manufactured in Production Example 2 under 1C conditions using electrochemical impedance spectroscopy (EIS; Electrochemical Impedance Spectroscopy), the resistance was measured within the range of frequency (10 kHz to 0.01 Hz).

[0185] The R ct (charge transfer resistance) value at the 50th cycle in the Nyquist plot obtained from the resistance measurement by the impedance spectroscopy is 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 Referring to Example 1, Example 2 and Comparative Example 1 which used a precursor having a shell with an average composition of Ni 0.55 Co 0.435 Mn 0.015 (OH)₂ formed on the surface of a core having an average composition, it can be confirmed that the impedance characteristics of Example 1 and Example 2 are superior to those of Comparative Example 1 in which there is no segregation phenomenon of Co in the primary particles, that is, there is no region of concentration change of Co in the primary particles.

[0188] Similarly, referring to Example 3, Example 4 and Comparative Example 2 which used a precursor having a shell with an average composition of Ni 0.90 Co 0.08 Mn 0.02 (OH)₂ formed on the surface of a core having an average composition, it can be confirmed that the impedance characteristics of Example 3 and Example 4 are superior to those of Comparative Example 2 in which there is no segregation phenomenon of Mn in the primary particles. 0.55 Co 0.015 Mn 0.435 (OH)₂ formed on the surface of a core having an average composition, it can be confirmed that the impedance characteristics of Example 3 and Example 4 are superior to those of Comparative Example 2 in which there is no segregation phenomenon of Mn in the primary particles.

[0189] Through the above results, it can be confirmed that when a region where the concentration of any transition metal is locally formed in the primary particles, it is possible to prevent or mitigate the phenomenon that the resistance increases as the content of Ni in the main transition metals constituting the lithium composite oxide increases.

[0190] As described above, the embodiments of the present invention have been described. However, those having ordinary knowledge in the technical field can make various modifications and changes to the present invention by adding, changing, deleting or adding components without departing from the idea of the present invention described in the claims, and it can be said that this is also included within the scope of the rights of the present invention.

Explanation of Signs

[0191] 11 ··· Central part 12 ··· Surface part 100... Primary particle 110... First region 120... Second region

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, wherein the primary particles are a lithium composite oxide containing at least one metal element selected from Ni, Co, Mn, and Al, when the average atomic ratio of any metal element excluding lithium present in the primary particles is denoted as a, the secondary particles, include primary particles in which a first region where the atomic ratio of any metal element excluding lithium is greater than a and a second region where the atomic ratio of any metal element excluding lithium is a or less coexist within the primary particles, Based on a cross-sectional TEM image of the secondary particles, at least one region selected from the first region and the second region within the primary particles where the first region and the second region coexist extends along the direction from the surface to the center of the secondary particles. A positive electrode active material.

2. Based on a cross-sectional TEM image of the secondary particles, at least one region selected from the first region and the second region within the primary particles where the first region and the second region coexist is locally present within the primary particles. The positive electrode active material according to Claim 1.

3. Based on a cross-sectional TEM image of the secondary particles, at least one region selected from the first region and the second region within the primary particles where the first region and the second region coexist is present in plurality within the primary particles. The positive electrode active material according to Claim 1.

4. When the length measured along a direction perpendicular to the extension direction of the first region within the primary particles is defined as the width of the primary particles, the width of the first region is smaller than the width of the primary particles. The positive electrode active material according to Claim 1.

5. Based on a cross-sectional TEM image of the secondary particles, the primary particles where the first region and the second region coexist are locally present in the surface portion of the secondary particles. The positive electrode active material according to Claim 1.

6. 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 particles where the first region and the second region coexist is denoted as a1 and the average atomic ratio of Co is denoted as a2, the average atomic ratio b1 of Ni within the first region is a1 or less, The positive electrode active material according to claim 1, wherein the average atomic ratio b2 of Co in the first region is larger than a2.

7. 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 particles in which the first region and the second region coexist is a1 and the average atomic ratio of Mn is a3, the average atomic ratio b1 of Ni in the first region is a1 or less, The positive electrode active material according to claim 1, wherein the average atomic ratio b3 of Mn in the first region is larger than a3.

8. The positive electrode active material according to claim 1, wherein the primary particles further contain a doping metal.

9. including a coating layer covering at least a part of the surfaces of the primary particles and the secondary particles, The positive electrode active material according to claim 1, wherein the coating layer contains at least one oxide represented by the following chemical formula. [Chemical formula 2] Li ａ A ｂ O ｃ (Here, 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.)

10. A positive electrode slurry composition comprising the positive electrode active material, a conductive material and a binder according to any one of claims 1 to 9.

11. A lithium secondary battery including a positive electrode formed by coating the positive electrode slurry composition according to claim 10 on a current collector.

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