Positive electrode active material and lithium secondary battery using the same

Abstract

To provide a positive electrode active material that can maintain the high electrochemical properties of an existing positive electrode active material for a lithium secondary battery, particularly a high-Ni type positive electrode active material, while eliminating the low structural stability.SOLUTION: A positive electrode active material includes a lithium composite oxide having a layered structure capable of lithium intercalation / deintercalation, and the ratio of peak intensities attributable to the (003) plane and the (012) plane obtained by X-ray diffraction analysis of the lithium composite oxide using Cu-Kα radiation satisfies the formula 1 of 0.131≤I(012) / I(003)≤0.143.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a cathode active material in which a lithium ion diffusion path in a lithium composite oxide constituting a cathode active material is formed to be oriented to a specific crystal plane, and a lithium secondary battery using the same, by improving the growth of the crystal plane to which the lithium ion diffusion path is oriented, thereby improving electrochemical characteristics and stability.

Background Art

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

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

[0004] As the cathode 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 above-mentioned cathode active materials, LiCoO2 is the most widely used because of its excellent life characteristics and charge / discharge efficiency. However, due to the resource limitation of cobalt used as a raw material, it is expensive, and thus has a disadvantage in 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, LiNiO2-based cathode active materials exhibit battery characteristics with high discharge capacity, but due to the cation mixing problem between Li and transition metals, synthesis is difficult, and there are significant problems in rate characteristics accordingly.

[0007] In addition, a large amount of Li by-products will be generated according to the degree of deepening of such cation mixing. Most of these Li by-products consist of compounds of LiOH and Li2CO3, which cause problems such as gelation during the manufacture of the cathode paste and gas generation during charge and discharge after electrode manufacture. Residual Li2CO3 not only increases the swelling phenomenon of the cell and reduces the cycle, but also causes the battery to bulge.

[0008] To make up for such disadvantages, the demand for high-Ni type cathode active materials with a Ni content of 50% or more as secondary battery cathode active materials has begun to increase. However, such high-Ni type cathode active materials exhibit high-capacity characteristics, but on the other hand, as the Ni content in the cathode active material increases, there is a problem that structural instability is caused by Li / Ni cation mixing. Due to such structural instability of the cathode active material, lithium secondary batteries may deteriorate rapidly not only at high temperatures but also at room temperature.

[0009] On the other hand, in recent years, cathode active materials containing not only polycrystalline-structured lithium composite oxides but also single-crystalline-structured lithium composite oxides have been proposed (Journal of The Electrochemical Society, Volume 164, Number 7, A1534-A1544 (Publication Date: 2017.05.23)).

[0010] The literature mentions a single-crystal structure lithium composite oxide (LiNi 0.5 Mn 0.3 Co0.2 It is disclosed that O2) has a partially improved stability with respect to a lithium composite oxide having a polycrystalline structure of the same composition.

[0011] However, when the firing temperature is excessively increased or the firing time is excessively lengthened for the single crystallization of the lithium composite oxide constituting the positive electrode active material, the cation mixing phenomenon mentioned above may increase.

[0012] In particular, when the cation mixing phenomenon increases in the lithium composite oxide having a single crystal structure, in addition to the originally intended layered structure, a lithium composite oxide having a quasi-safe phase or a Rock-salt phase is excessively formed, and a lithium composite oxide having a phase other than the layered structure is excessively present. As a result, deterioration of the positive electrode active material, which is an aggregate of these, may occur. Such deterioration of the positive electrode active material acts as a cause of capacity reduction and life shortening.

[0013] Therefore, there is an obvious limit in providing a positive electrode active material having a single crystal structure only by increasing the firing temperature of the lithium composite oxide constituting the positive electrode active material.

Summary of the Invention

Problems to be Solved by the Invention

[0014] In a positive electrode active material for a lithium secondary battery, a predetermined trade-off relationship may hold between some indices indicating the electrochemical characteristics of the positive electrode active material and some indices indicating stability. Therefore, when the capacity characteristics of the positive electrode active material are excessively improved, conversely, the structural stability of the particles constituting the positive electrode active material may decrease, and there is a possibility that stable charge and discharge performance cannot be exhibited.

[0015] Therefore, an object of the present invention is to provide a positive electrode active material capable of maintaining the high electrochemical characteristics of an existing positive electrode active material for a lithium secondary battery, particularly a high-Ni type positive electrode active material, and eliminating low structural stability.

[0016] Another object of the present invention is to form the lithium ion diffusion path in the lithium composite oxide constituting the positive electrode active material so as to be oriented in a specific crystal plane, and to improve the growth of the crystal plane in which the lithium ion diffusion path is oriented, thereby providing a positive electrode active material with improved electrochemical characteristics and stability.

[0017] Still another object of the present invention is to provide a lithium secondary battery using the positive electrode active material defined in the present application.

[0018] 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 will be more clearly understood from the embodiments of the present invention. Also, it will be easily understood 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

[0019] According to one aspect of the present invention, there is provided a positive electrode active material including a layered lithium composite oxide capable of intercalation / deintercalation of lithium, wherein the ratio of the peak intensities attributed to the (003) plane and the (012) plane obtained in the X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide satisfies the following formula (1). (Formula 1) 0.131 ≦ I(012) / I(003) ≦ 0.143

[0020] Further, the lithium composite oxide may have a shape having a major axis and a minor axis, and at this time, the lithium ion diffusion path formed in the lithium composite oxide may be formed to be parallel to the major axis direction of the lithium composite oxide.

[0021] In addition, the lithium ion diffusion path formed within the lithium composite oxide is formed parallel to the (003) plane, but the lithium ion diffusion path formed within the lithium composite oxide is formed so as to be oriented toward at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane, whereby the lithium ion diffusion ability of the lithium composite oxide and further the electrochemical characteristics of the positive electrode active material containing the lithium composite oxide can be improved.

[0022] Here, the lithium composite oxide is represented by Chemical Formula 1 below. (Chemical Formula 1) Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f (Here, M1 is at least one selected from Mn and Al, M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, M1 to M3 are different from each other, 0.90 ≦ a ≦ 1.15, 0 ≦ b ≦ 0.20, 0 ≦ c ≦ 0.10, 0 ≦ d ≦ 0.05, 0 ≦ e ≦ 0.05, and 1.0 ≦ f ≦ 2.0.)

[0023] In one embodiment, the lithium composite oxide includes at least one primary particle, and the density of the crystal grain boundaries calculated by the following Formula 5 for the primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide may be 0.50 or less. (Formula 5) Density of crystal grain boundaries = (number of boundary surfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line) At this time, the lithium composite oxide may have a single crystal structure.

[0024] In other embodiments, the positive electrode active material is an aggregate of a plurality of lithium composite oxides each composed of at least one primary particle. Among the aggregates, for the primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide, the proportion of the lithium composite oxide having a grain boundary density calculated by the following formula (5) of 0.50 or less may be 30% or more. (Formula 5) Density of grain boundary = (number of interfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line)

[0025] Further, according to another aspect of the present invention, as a positive electrode active material containing a lithium composite oxide having a layered structure capable of intercalation / deintercalation of lithium, the lithium composite oxide contains at least one primary particle, and for the primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide, the density of the grain boundary calculated by the following formula (5) is 0.50 or less. (Formula 5) Density of grain boundary = (number of interfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line) There is provided a positive electrode active material in which the lithium ion diffusion path formed in the lithium composite oxide is formed so as to be directed to at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane.

[0026] Further, according to still another aspect of the present invention, as a positive electrode active material containing a lithium composite oxide having a layered structure capable of intercalation / deintercalation of lithium, the positive electrode active material is an aggregate of a plurality of lithium composite oxides each composed of at least one primary particle. Among the aggregates, for the primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide, the proportion of the lithium composite oxide having a grain boundary density calculated by the following formula (5) of 0.50 or less is 30% or more. (Formula 5) Density of crystal grain boundaries = (Number of grain boundaries between primary particles on the virtual straight line / Number of primary particles on the virtual straight line) The lithium ion diffusion path formed in the lithium composite oxide provides a cathode active material formed so as to be oriented to at least one crystal plane selected from the (012) plane, (101 plane), and (104) plane.

[0027] Moreover, according to still another aspect of the present invention, there is provided a lithium secondary battery using the cathode active material defined in the present application.

Advantages of the Invention

[0028] According to the present invention, instead of the lithium ion diffusion path in the lithium composite oxide constituting the cathode active material for a lithium secondary battery being oriented to a crystal plane where lithium ion diffusion is blocked, it is formed so as to be oriented to a crystal plane where lithium ion diffusion is relatively free, whereby an improvement in the electrochemical characteristics of the cathode active material containing the lithium composite oxide can be expected.

[0029] Also, by intentionally improving the growth of the crystal plane where lithium ion diffusion is relatively free among the crystal planes in the lithium composite oxide, the diffusion ability of lithium ions through the lithium composite oxide can be improved.

[0030] On the other hand, as described in Journal of The Electrochemical Society, Volume 164, Number 7, A1534 - A1544, generally, for the uniform single crystallization of the lithium composite oxide constituting the cathode active material for a lithium secondary battery, firing needs to be performed under relatively severe conditions.

[0031] The single crystal structure or the lithium composite oxide close to the single crystal structure (for example, the number of primary particles constituting the secondary particles is reduced) thus produced can have improved stability due to a decrease in the specific surface area compared to the lithium composite oxide having a polycrystalline structure.

[0032] However, the cation mixing phenomenon may increase under severe firing conditions, and the cation mixing phenomenon causes a phase transformation of the lithium composite oxide, so that in addition to the originally intended layered structure, a lithium composite oxide having a quasi-safe phase or a Rock-salt phase is excessively formed. Thus, the coexistence of an excessive amount of lithium composite oxide having a phase other than the layered structure with the lithium composite oxide having the layered structure may cause deterioration of the positive electrode active material.

[0033] Accordingly, in the present invention, the lithium ion diffusion path in the lithium composite oxide constituting the positive electrode active material is formed to be oriented to a specific crystal plane, and by improving the growth of the crystal plane to which the lithium ion diffusion path is oriented, it is possible to endow the lithium composite oxide with sufficient electrochemical characteristics and stability only by single crystallization performed under relatively mild firing conditions.

[0034] In addition to the above-described effects, the specific effects of the present invention will be described while explaining specific matters for carrying out the following invention.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0036] 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, in the context, unless otherwise specified, 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.

[0037] Term Explanation The term "lithium composite oxide" used in this application refers to an oxide having a layered structure capable of intercalation / deintercalation of lithium (lithium ions), and refers to a composite oxide containing lithium and a metal element. In particular, the lithium composite oxide used in this application refers to a lithium-nickel-based composite oxide containing lithium and nickel. Also, the lithium composite oxide used in this application is an oxide particle constituting the positive electrode active material, and may be a single crystal particle (i.e., a single particle form) or a polycrystalline particle (i.e., a form in which a plurality of particles are aggregated).

[0038] As used in this application, the term "single crystal" means a crystal that does not contain crystal grains or grain boundaries within the particles. Also, as used in this application, the term "primary particle" refers to a particle that exists alone without forming an aggregate, or a primary particle that constitutes a secondary particle formed by the aggregation of a plurality of primary particles. "Lithium composite oxide having a single crystal structure" means a particle in which primary particles composed of lithium composite oxide are composed of a plurality of crystal grains or in which there is no grain boundary within the primary particles.

[0039] As used in this application, the term "secondary particle" means the primary particle itself, which is the above-mentioned lithium composite oxide, or a particle formed by the aggregation of at least two primary particles. In this case, within the positive electrode active material, secondary particles composed of a single primary particle and / or secondary particles formed by the aggregation of at least two primary particles may coexist. When at least two primary particles aggregate to form a secondary particle, there will be a grain boundary or grain interface formed at the interface between the two primary particles within the secondary particle.

[0040] As used in this application, the term "density of grain boundaries" means the number of grain boundaries or grain interfaces formed by the presence of at least two primary particles within a secondary particle. The greater the number of primary particles present within the secondary particle, the greater the density of grain boundaries, and the smaller the number of primary particles present within the secondary particle, the smaller the density of grain boundaries.

[0041] In this application, the density of grain boundaries may be calculated by the number of primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide according to the following formula (5). At this time, the direction of the straight line may be a direction crossing the center of the lithium composite oxide in the minor axis direction. (Formula 5) Density of grain boundaries = (Number of interfacial boundaries between primary particles on the virtual straight line / Number of primary particles on the virtual straight line)

[0042] If the number of primary particles present in the secondary particle is one, the density of the grain boundaries calculated by the formula is 0. If the number of primary particles present in the secondary particle is three or more, the density of the grain boundaries calculated by the formula will exceed 0.5.

[0043] On the other hand, in the present application, the secondary particle may be a particle composed of a single primary particle having a single crystal structure, but is not necessarily limited thereto. That is, in the present application, the secondary particle can be understood as a particle composed of a single single crystal particle or a particle formed by aggregation of at least two single crystal particles. Such a definition of the secondary particle will be more clearly explained by the definition of the positive electrode active material described later.

[0044] The term "positive electrode active material" used in the present application is a broad concept including the above-described secondary particles. A single secondary particle itself may be the positive electrode active material, but in the present application, an aggregate of a plurality of secondary particles having the same and / or different grain boundary densities from each other can be defined as the positive electrode active material.

[0045] Therefore, in the definition of the positive electrode active material described later, the description of the secondary particle having the aggregate character of a plurality of secondary particles and the description of the secondary particle constituting the positive electrode active material and the primary particle constituting the secondary particle need to be understood separately.

[0046] 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.

[0047] Positive Electrode Active Material According to one aspect of the present invention, there is provided a positive electrode active material containing a layered lithium composite oxide capable of intercalation / deintercalation of lithium.

[0048] The lithium composite oxide may contain at least one primary particle. If the lithium composite oxide contains a plurality of primary particles, the plurality of primary particles may exist as secondary particles that are aggregates aggregated with each other. On the other hand, when the lithium composite oxide contains a single primary particle, the lithium composite oxide is referred to as a lithium composite oxide having a single-crystal structure.

[0049] The primary particle means one grain or crystallite, and the secondary particle means an aggregate formed by aggregation of a plurality of primary particles. Further, the primary particle may be rod-shaped, elliptical and / or circular, or may be amorphous.

[0050] There may be voids and / or grain boundaries between the primary particles constituting the secondary particles. For example, the primary particles may form internal voids by being separated from adjacent primary particles inside the secondary particles. Further, the primary particles may form a surface existing in the secondary particles by contacting an internal void without forming a grain boundary by contacting adjacent primary particles with each other.

[0051] On the other hand, the surface of the primary particle existing on the outermost surface of the secondary particle exposed to the outside air forms the surface of the secondary particle.

[0052] Here, the average particle size of the primary particles is in the range of 0.1 μm to 10 μm, preferably 1.0 μm to 10 μm, so that 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. Further, the average particle size of the secondary particles may vary depending on the number of aggregated primary particles, but may be 3 μm to 20 μm.

[0053] On the other hand, the positive electrode active material according to the present invention may be defined as an aggregate of a plurality of secondary particles having the same and / or different grain boundary densities from each other.

[0054] The density of the crystal grain boundaries may be calculated based on the number of primary particles P on a virtual straight line L that crosses the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide according to the following formula 5. (Formula 5) Density of crystal grain boundaries = (Number of interfacial surfaces B between primary particles on the virtual straight line (L) / Number of primary particles (P) on the virtual straight line (L))

[0055] For example, referring to FIGS. 1 and 2 which are schematic diagrams schematically showing cross-sectional images of the lithium composite oxide included in the cathode active material according to various examples of the present invention, the density of the crystal grain boundaries of the lithium composite oxide calculated is as shown in Table 1 below.

Table 1

[0056] When the density of the crystal grain boundaries represented by the formula 5 has a value of 0.90 or less, the surface area and grain boundaries of the lithium composite oxide can be reduced, thereby reducing the possibility of side reactions between the cathode active material and the electrolytic solution, and improving not only the high-temperature stability but also the storage stability of the cathode active material.

[0057] On the other hand, according to an embodiment of the present invention, among the aggregates of the secondary particles, for the primary particles on a virtual straight line that crosses the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide, the ratio of the lithium composite oxide having a density of crystal grain boundaries calculated by the formula 5 of 0.50 or less may be 30% or more.

[0058] The surface area of the lithium composite oxide included in the cathode active material and the crystal grain boundaries defined by the primary particles constituting the lithium composite oxide are regions where side reactions can occur between the interface and the surface of the cathode active material and the electrolytic solution. Here, as shown in FIGS. 1 and 2, the crystal grain boundaries defined by the primary particles present in the lithium composite oxide can be understood, for example, as the interfaces between two adjacent primary particles.

[0059] At this time, by reducing the surface area of the lithium composite oxide and the grain boundaries defined by the primary particles in the lithium composite oxide, the thermal stability of the positive electrode active material is improved, and problems caused by the instability of the positive electrode active material (for example, deterioration of storage stability such as gas generation due to side reactions with the electrolyte) can be prevented or alleviated.

[0060] Thereby, by making the proportion of the lithium composite oxide having a grain boundary density calculated by the formula 5 of 0.50 or less among the aggregates of the secondary particles 30% or more, it is possible to provide a positive electrode active material capable of stably maintaining electrochemical characteristics.

[0061] On the other hand, the proportion of the lithium composite oxide having a grain boundary density calculated by the formula 5 of 0.50 or less among the aggregates of the secondary particles can be improved by modifying the process conditions of some stages in the synthesis process of the lithium composite oxide. For example, by adjusting the primary firing temperature / time for the precursor of the lithium composite oxide and / or the secondary firing temperature / time for the primary firing product of the precursor, the proportion of the lithium composite oxide having a grain boundary density of 0.50 or less can be improved.

[0062] However, as the firing conditions of the precursor and / or the lithium composite oxide become relatively severe, the cation mixing phenomenon may increase, and the cation mixing phenomenon may induce a phase transformation of the lithium composite oxide.

[0063] Therefore, by making the proportion of the lithium composite oxide having a grain boundary density calculated by the formula 5 of 0.50 or less among the aggregates of the secondary particles 95% or less, preferably 90% or less, more preferably 80% or less, a balance can be achieved between the lithium composite oxide having a grain boundary density of 0.50 or less and the lithium composite oxide having a grain boundary density exceeding 0.50 among the aggregates of the secondary particles.

[0064] The lithium composite oxide according to an embodiment of the present invention may contain at least Ni and Co. Further, the lithium composite oxide may further contain Mn and / or Al in addition to Ni and Co, and may further contain a dopant other than the above-described metal elements.

[0065] Specifically, the lithium composite oxide is represented by the following Chemical Formula 1. (Chemical Formula 1) Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f (Here, M1 is at least one selected from Mn and Al, M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, M1 to M3 are different from each other, 0.90 ≦ a ≦ 1.15, 0 ≦ b ≦ 0.20, 0 ≦ c ≦ 0.10, 0 ≦ d ≦ 0.05, 0 ≦ e ≦ 0.05, and 1.0 ≦ f ≦ 2.0.)

[0066] On the other hand, the lithium composite oxide may be a high-Ni type lithium composite oxide in which the molar ratio of nickel calculated by the following Formula 4 is 0.6 or more, preferably 0.7, more preferably 0.8 or more, among the lithium composite oxides represented by Chemical Formula 1. (Formula 4) Ni(molar ratio) = Ni(mol%) / (Ni(mol%) + Co(mol%) + M1(mol%) + M2(mol%) + M3(mol%))

[0067] As described above, the high-Ni type lithium composite oxide has the advantage of relatively high electrochemical properties compared to the lithium composite oxide with a low Ni content. However, as the Ni content of the lithium composite oxide increases, there is a problem that structural instability due to Li / Ni cation mixing is brought about. Due to such structural instability of the positive electrode active material, the lithium secondary battery may deteriorate rapidly not only at high temperature but also at room temperature.

[0068] However, the lithium composite oxide according to the present invention can improve the electrochemical properties of the lithium composite oxide and prevent a decrease in stability by controlling the properties of the crystal plane or exposed surface described later, even if it has a high-Ni type composition.

[0069] Specifically, the lithium ion diffusion path formed in the lithium composite oxide is formed to be parallel to the major axis direction of the lithium composite oxide, whereby the diffusion ability of the lithium ions through the lithium composite oxide can be improved.

[0070] Here, the lithium ion diffusion path refers to the main one-dimensional and / or two-dimensional paths through which lithium ions in the lithium composite oxide are transported / diffused by a vacancy hopping mechanism.

[0071] Further, the lithium ion diffusion path is preferably formed to be parallel to the (003) plane confirmed by X-ray diffraction analysis using Cu-Kα rays with respect to the lithium composite oxide. When the lithium ion diffusion path in the lithium composite oxide is formed to be directed to the (003) plane, the diffusion of the lithium ions may be blocked by the (003) plane, and the diffusion ability of the lithium ions through the lithium composite oxide may decrease.

[0072] On the one hand, the lithium ion diffusion path is formed so as to be oriented to at least one crystal plane selected from the (012) plane, (101) plane, and (104) plane where the diffusion of lithium ions is relatively free with respect to the (003) plane, whereby the diffusion ability of lithium ions through the lithium composite oxide can be improved.

[0073] That is, according to the present invention, the lithium ion diffusion path in the lithium composite oxide constituting the positive electrode active material for a lithium secondary battery is formed so as to be oriented to a crystal plane where the diffusion of lithium ions is relatively free, instead of being oriented to a crystal plane where the diffusion of lithium ions is blocked, whereby improvement in the electrochemical characteristics of the positive electrode active material containing the lithium composite oxide can be expected.

[0074] At this time, the fact that the lithium ion diffusion path is oriented to a specific crystal plane means that the included angle formed by the direction perpendicular to the specific crystal plane and the direction of the lithium ion diffusion path is 90 degrees or less, preferably 60 degrees or less, more preferably 45 degrees or less.

[0075] Furthermore, according to the present invention, after adding a flux to a mixture of the hydroxide precursor of the lithium composite oxide and a lithium raw material substance (for example, LiOH, etc.) before the primary firing for obtaining the lithium composite oxide by heat treatment of the hydroxide precursor of the lithium composite oxide, by performing heat treatment, the growth of the crystal plane oriented by the lithium ion diffusion path can be improved. In particular, after adding a flux to a mixture of the hydroxide precursor of the lithium composite oxide and a lithium raw material substance (for example, LiOH, etc.) before the primary firing, by performing heat treatment, the growth of a crystal plane where the diffusion of lithium ions is relatively free with respect to a crystal plane where the diffusion of lithium ions is blocked can be further improved.

[0076] As the flux used for improving the growth of a crystal plane where the diffusion of lithium ions is relatively free, for example, an alkali metal compound (hydroxide, chloride, nitride, carbonate, sulfate, etc.) such as NaOH, KCl, NaNO3, or a chloride such as NH4Cl may be used.

[0077] On the one hand, the ratio of the peak intensities attributed to the (003) plane and the (012) plane obtained from the X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide can satisfy the following formula (1). (Formula 1) 0.131 ≦ I(012) / I(003) ≦ 0.143

[0078] When I(012) / I(003) calculated by the formula (1) is less than 0.131, the growth of the (012) plane where lithium ion diffusion is relatively free is insufficient with respect to the (003) plane where lithium ion diffusion is blocked, and the improvement effect of the electrochemical characteristics of the lithium composite oxide accompanying the growth of the crystal plane towards which the lithium ion diffusion path is directed becomes negligible.

[0079] On the other hand, when I(012) / I(003) calculated by the formula (1) exceeds 0.143, the growth of the (012) plane formed along the length direction of the lithium ion diffusion path becomes excessively large, and rather, the diffusion ability of the lithium ions through the lithium composite oxide may decrease, or the stability of the crystal structure of the lithium composite oxide may decrease.

[0080] Also, the ratio of the peak intensities attributed to the (003) plane and the (104) plane obtained from the X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide can satisfy the following formula (2). (Formula 2) 0.630 ≦ I(104) / I(003) ≦ 0.698

[0081] Similarly, when I(104) / I(003) calculated by the formula (2) is less than 0.630, the growth of the (104) plane where lithium ion diffusion is relatively free is insufficient with respect to the (003) plane where lithium ion diffusion is blocked, and the improvement effect of the electrochemical characteristics of the lithium composite oxide accompanying the growth of the crystal plane towards which the lithium ion diffusion path is directed becomes negligible.

[0082] On the other hand, when I(104) / I(003) calculated by the formula 2 exceeds 0.698, the growth of the (104) plane formed along the length direction of the lithium ion diffusion path becomes excessively large, rather, the diffusion ability of the lithium ions through the lithium composite oxide may decrease, or the stability of the crystal structure of the lithium composite oxide may decrease.

[0083] Further, the ratio of the peak intensities attributed to the (003) plane and the (101) plane obtained from the X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide can satisfy the following formula 3. (Formula 3) 0.379 ≦ I(101) / I(003) ≦ 0.421

[0084] Similarly, when I(101) / I(003) calculated by the formula 3 is less than 0.379, the growth of the (101) plane where lithium ion diffusion is relatively free with respect to the (003) plane where lithium ion diffusion is blocked is insufficient, and the improvement effect of the electrochemical characteristics of the lithium composite oxide accompanying the growth of the crystal plane toward which the lithium ion diffusion path is directed becomes negligible.

[0085] On the other hand, when I(101) / I(003) calculated by the formula 3 exceeds 0.421, the growth of the (101) plane formed along the length direction of the lithium ion diffusion path becomes excessively large, rather, the diffusion ability of the lithium ions through the lithium composite oxide may decrease, or the stability of the crystal structure of the lithium composite oxide may decrease.

[0086] Furthermore, the lithium composite oxide contained in the positive electrode active material according to some embodiments of the present invention may include a coating layer that covers at least a part of the primary particles (for example, the crystal grain boundaries between the primary particles) and / or the surface of the secondary particles formed by aggregation of the primary particles.

[0087] For example, the coating layer may be present so as to cover at least a part of the exposed surface of the primary particles. In particular, the coating layer may be present so as to cover at least a part of the exposed surface of the primary particles existing on the outermost side of the secondary particles.

[0088] Thereby, the coating layer may exist as a layer that continuously or discontinuously coats the surface of the primary particles and / or the secondary particles formed by aggregation of the primary particles. When the coating layer exists discontinuously, it may exist in an island shape.

[0089] The coating layer existing in this way can contribute to maintaining the high electrochemical properties of the lithium composite oxide, particularly the high-Ni type lithium composite oxide, and eliminating its low structural stability.

[0090] Further, the coating layer may 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.

[0091] The coating layer may contain at least one oxide represented by Chemical Formula 2 below. That is, the coating layer can be defined as a region where the oxide represented by Chemical Formula 2 below exists. (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, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, 0 ≦ a ≦ 10, 0 ≦ b ≦ 8, and 2 ≦ c ≦ 15.)

[0092] Further, different oxides may simultaneously exist in one layer, or different oxides represented by Chemical Formula 2 may exist in separate layers.

[0093] The oxide represented by Chemical Formula 2 may be in a state physically and / or chemically bonded to the primary particles represented by Chemical Formula 1. Further, the oxide may be present in a state of forming a solid solution with the primary particles represented by Chemical Formula 1.

[0094] The lithium composite oxide according to this example includes a coating layer covering at least a part of the surface of the primary particles (for example, the interface between the primary particles) and / or the secondary particles formed by aggregation of the primary particles, thereby enhancing the structural stability. Further, when such a lithium composite oxide is used as a positive electrode active material for a lithium secondary battery, the electrochemical characteristics and stability of the positive electrode active material can be improved. Further, the oxide can reduce the residual lithium in the lithium composite oxide and can act as a pathway for lithium ion movement.

[0095] In some cases, the oxide may be present not only at least a part of the interface between the primary particles and the surface of the secondary particles, but also in the internal voids formed inside the secondary particles.

[0096] The oxide is an oxide in which lithium and an element represented by A are combined, or an oxide of A, and the oxide is, for example, 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 、W b O c 、Zr b O c 、Ti b O c or B b O cIt may be expressed as etc. Also, non-limiting examples of the oxide include Li2B4O7, Li3BO3, Li2B2O7, Li2B8O 13 , Li2VO3, Li3VO4, Li6Zr3O9, Li2ZrO3, Li 5.5 Zr 2.6 2O8, Li 44 Ba 19 , Li4Ba, Li2TiO3, LiTi7O4, and LiTi2O4, etc. The above examples are merely for convenience of understanding and the oxide defined in the present application is not limited to the above examples.

[0097] 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. Examples of the oxide in which at least two elements represented by lithium and A are combined include, for example, 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 and so on, but are not necessarily limited thereto.

[0098] Here, the oxide can exhibit a concentration gradient that decreases from the surface portion to the central portion of the secondary particle. Thereby, the concentration of the oxide can decrease from the surface portion to the central portion of the secondary particle.

[0099] As described above, by the oxide showing a concentration gradient decreasing from the surface portion to the central portion of the secondary particles, residual lithium present on the surface of the lithium composite oxide can be effectively reduced, and side reactions due to unreacted residual lithium can be prevented. Further, by the oxide, it is possible to prevent a decrease in crystallinity in the inner surface region of the lithium composite oxide. Further, it is possible to prevent the overall structure of the lithium composite oxide from collapsing due to the oxide during the electrochemical reaction.

[0100] Furthermore, the coating layer may include a first coating layer containing at least one oxide represented by Chemical Formula 2 and a second coating layer containing at least one oxide represented by Chemical Formula 2 but containing an oxide different from the oxide contained in the first coating layer.

[0101] For example, the first coating layer may be present so as to cover at least a part of the exposed surface of the primary particles existing on the outermost side of the secondary particles, and the second coating layer may be present so as to cover the exposed surface of the primary particles not covered by the first coating layer and at least a part of the surface of the first coating layer.

[0102] 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 as described above, a specific description is omitted for convenience, and hereinafter, only the remaining configurations not described above will be described.

[0103] The positive 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 with surface treatment such as carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive 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.

[0104] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition containing a conductive material and optionally a binder together with the positive electrode active material to the positive current collector.

[0105] At this time, the positive electrode active material may be contained in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, based on the total weight of the positive electrode active material layer. When contained within this content range, excellent capacity characteristics can be exhibited, but it is not necessarily limited thereto.

[0106] The conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it has electron conductivity without causing chemical changes in the configured battery. Specific examples include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, carbon-based substances such as carbon fibers, metal powders or metal fibers such as copper, nickel, aluminum, silver, etc., conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used. The conductive material may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0107] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesion 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.

[0108] 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.

[0109] The solvent may be a solvent generally used in the art, such as 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 sufficient as long as it can dissolve or disperse the positive electrode active material, the conductive material, and the binder and then give a viscosity that can exhibit excellent thickness uniformity during coating for positive electrode manufacturing, considering the coating thickness of the slurry and the manufacturing yield.

[0110] 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.

[0111] According to still another aspect of the present invention, an electrochemical element including the above-described positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

[0112] 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.

[0113] 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.

[0114] The negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0115] 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, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used. Further, the negative 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, a non-woven fabric.

[0116] 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.

[0117] 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 oxides, and lithium vanadium oxides, or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. Any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, low-crystalline carbon and highly crystalline carbon, etc. may all be used. Representative low-crystalline carbon includes soft carbon and hard carbon, and representative highly crystalline carbon includes 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] In one embodiment, the negative electrode active material layer is produced by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating the film obtained by peeling the film from the support onto the negative electrode current collector.

[0122] In another embodiment, the negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support and then laminating a film obtained by peeling the film from the support on the negative electrode current collector.

[0123] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide 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 a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point 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.

[0124] Examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0125] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0126] As the organic solvent, any solvent may be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge-discharge performance of the battery, and a linear carbonate compound having low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred. In this case, when the cyclic carbonate and the 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.

[0127] The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt 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, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0128] In addition to the above-mentioned electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc., such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexalinic acid, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. 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.

[0129] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, so it is useful in portable devices such as mobile phones, notebook computers, digital cameras, and the field of electric vehicles such as hybrid electric vehicles (HEV).

[0130] The external 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 or large-sized battery module including a plurality of battery cells.

[0131] 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.

[0132] The battery module or the battery pack can be used as a power source for any one or more of 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.

[0133] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0134] Production Example 1. Production of Positive Electrode Active Material Example 1 A NiCoMn(OH)2 hydroxide precursor (Ni:Co:Mn = 91:8:1 (at%)) of a lithium composite oxide was synthesized by a known co-precipitation method using nickel sulfate, cobalt sulfate, and manganese sulfate. The average particle size (D50) of the hydroxide precursor of the lithium composite oxide was 3.0 μm.

[0135] Next, LiOH (Li / (Ni+Co+Mn) mol ratio = 1.05±0.05) was mixed with the first hydroxide precursor, and then the atmosphere of O2 was maintained in a firing furnace, and the temperature was raised at a rate of 2°C per minute to 770°C and heat-treated for 12 hours (primary firing) to obtain a lithium composite oxide. At this time, before starting the heat treatment, 2.0 mol% of NaNO3 was added to the total of the first hydroxide precursor and LiOH.

[0136] After the primary firing was completed, the lithium composite oxide was put into distilled water, stirred for 1 hour, and dried in a vacuum dryer at 120°C for 12 hours.

[0137] Finally, the atmosphere of O2 was maintained in a firing furnace, and the temperature was raised at a rate of 2°C per minute to 700°C and heat-treated for 12 hours (secondary firing) to obtain a positive electrode active material containing a lithium composite oxide.

[0138] Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that 3.0 mol% of NH4Cl was used instead of 2.0 mol% of NaNO3.

[0139] Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that 1.0 mol% of KCl was used instead of 2.0 mol% of NaNO3.

[0140] Example 4 A positive electrode active material was produced in the same manner as in Example 1, except that 3.0 mol% of KCl was used instead of 2.0 mol% of NaNO3.

[0141] Example 5 A positive electrode active material was produced in the same manner as in Example 1, except that 3.0 mol% of NaOH was used instead of 2.0 mol% of NaNO3.

[0142] Example 6 The positive electrode active material was produced in the same manner as in Example 1, except that 5.0 mol% of NaOH was used instead of 2.0 mol% of NaNO3.

[0143] Example 7 The positive electrode active material was produced in the same manner as in Example 1, except that 3.0 mol% of NaCl was used instead of 2.0 mol% of NaNO3.

[0144] Comparative Example 1 The positive electrode active material was produced in the same manner as in Example 1, except that NaNO3 was not added before the primary firing.

[0145] Comparative Example 2 The positive electrode active material was produced in the same manner as in Example 1, except that 0.5 mol% of NH4Cl was used instead of 2.0 mol% of NaNO3.

[0146] Comparative Example 3 The positive electrode active material was produced in the same manner as in Example 1, except that 1.0 mol% of NH4Cl was used instead of 2.0 mol% of NaNO3.

[0147] Comparative Example 4 The positive electrode active material was produced in the same manner as in Example 1, except that 0.5 mol% of KCl was used instead of 2.0 mol% of NaNO3.

[0148] Comparative Example 5 The positive electrode active material was produced in the same manner as in Example 1, except that 1.0 mol% of NaOH was used instead of 2.0 mol% of NaNO3.

[0149] Comparative Example 6 The positive electrode active material was produced in the same manner as in Example 1, except that the content of NaNO3 added before the primary firing was 3.0 mol%.

[0150] Comparative Example 7 The positive electrode active material was produced in the same manner as in Example 1, except that the content of NaNO3 introduced before the first firing was set to 5.0 mol%.

[0151] Comparative Example 8 The positive electrode active material was produced in the same manner as in Example 1, except that 5.0 mol% of NaCl was used instead of 2.0 mol% of NaNO3.

[0152] Production Example 2. Production of Lithium Secondary Battery 94 wt% of each positive electrode active material produced by Production Example 1, 3 wt% of artificial graphite, and 3 wt% of a PVDF binder were dispersed in 3.5 g of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The positive electrode slurry was applied to and dried on an aluminum (Al) thin film, which is a positive electrode current collector with a thickness of 20 μm, and roll press was performed to produce a positive electrode. The loading level of the positive electrode was 7 mg / cm 2 and the electrode density was 3.2 g / cm 3 .

[0153] A lithium foil was used as a counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as a separator, and a coin cell was produced by a generally known manufacturing process using a liquid electrolyte 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.

[0154] Experimental Example 1. Structure Analysis of Positive Electrode Active Material (1) Cross-sectional SEM analysis of the positive electrode active material After obtaining a cross-sectional SEM image of the lithium composite oxide contained in the positive electrode active material produced by Production Example 1 using FE-SEM (Bruker), from the cross-sections of 100 lithium composite oxides captured in the cross-sectional SEM image, the ratio of the lithium composite oxide having a grain boundary density calculated by the following formula 5 of 0.50 or less was calculated. (Formula 5) Density of crystal grain boundaries = (Number of grain boundaries between primary particles on a virtual straight line crossing the center of the lithium composite oxide in the cross-sectional SEM image of the lithium composite oxide / Number of primary particles on the virtual straight line)

[0155] The measurement results of the crystal grain boundary density are shown in Table 2 below.

Table 2

[0156] (2) TEM analysis of the positive electrode active material After obtaining TEM images of the lithium composite oxide contained in the positive electrode active materials according to Examples 1, 2, 3, and 5 in Production Example 1, the directionality of the lithium ion diffusion paths formed in the lithium composite oxide was confirmed from the TEM images. Also, the SAD diffraction pattern was indexed to confirm the crystal planes of the lithium composite oxide towards which the lithium ion diffusion paths formed in the lithium composite oxide are directed. The measurement results are shown in FIGS. 3 to 6.

[0157] Referring to FIGS. 3 to 6, it can be confirmed that the lithium ion diffusion paths formed in the lithium composite oxide contained in each of the positive electrode active materials according to Examples 1, 2, 3, and 5 are formed in the same direction as the major axis direction of the lithium composite oxide. In particular, it can be confirmed that the lithium ion diffusion paths formed in the lithium composite oxide are formed in a direction substantially parallel to the (003) plane.

[0158] It can be confirmed that the lithium ion diffusion paths formed in the lithium composite oxide are formed so as to direct towards the (012) plane, the (101) plane, and / or the (104) plane.

[0159] That is, the lithium ion diffusion paths formed in the lithium composite oxides included in the respective cathode active materials according to Example 1, Example 2, Example 3, and Example 5 are formed to direct to the (012) plane, (101) plane, and / or (104) plane where lithium ion diffusion is relatively free, instead of directing to the (003) plane where lithium ion diffusion is blocked. As a result, improvement in the electrochemical characteristics of the cathode active material including the lithium composite oxide can be expected.

[0160] (3) XRD Analysis of Cathode Active Material X-ray diffraction (XRD) analysis was performed on each of the cathode active materials manufactured according to Production Example 1, and peaks attributable to the crystal planes of the lithium composite oxides included in the cathode active materials were detected. The XRD analysis was carried out using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å), and the intensity ratios between the peaks attributable to specific crystal planes are shown in Table 3 and Table 4 below.

Table 3

Table 4

[0161] Experimental Example 2. Evaluation of Electrochemical Characteristics of Lithium Secondary Battery For the lithium secondary battery (coin cell) manufactured in Production Example 2, a charge-discharge experiment was conducted at 25 °C with a discharge rate in the voltage range of 3.0 V to 4.3 V and 0.1 C to 5.0 C using an electrochemical analyzer (Toyo, Toscat-3100), and the C-rate efficiency of 5.0 C / 0.1 C was measured.

[0162] Also, for the same lithium secondary battery, after performing 50 charge / discharges under the condition of 1 C / 1 C within the driving voltage range of 25 °C and 3.0 V to 4.4 V, the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0163] The measurement results are shown in Table 5 below.

Table 5

[0164] Referring to the results in Table 5, it can be confirmed that the lithium secondary batteries manufactured using the cathode active materials according to Examples 1 to 7 exhibit excellent effects in terms of C-rate efficiency (output characteristics) and cycle capacity retention rate compared to the lithium secondary batteries manufactured using the cathode active materials according to Comparative Examples 1 to 8.

[0165] Specifically, in the case of Comparative Example 1, it can be confirmed that the electrochemical characteristics are lower compared to Examples 1 to 7 because the intentional growth of the crystal plane toward which the lithium ion diffusion path is directed is eliminated.

[0166] On the other hand, in the case of Comparative Example 7 in which the content of NaNO3 introduced before the first firing is 5.0 mol%, it is expected that the electrochemical characteristics are deteriorated compared to Examples 1 to 7 because the proportion of the lithium composite oxide having a grain boundary density of 0.5 or less among all the lithium composite oxides constituting the cathode active material excessively decreases.

[0167] Also, in the case of Comparative Example 8 in which the content of NaCl introduced before the first firing is 5.0 mol%, it is expected that the electrochemical characteristics are deteriorated rather than Examples 1 to 8 because the proportion of the lithium composite oxide having a grain boundary density of 0.5 or less among all the lithium composite oxides constituting the cathode active material excessively increases.

[0168] Experimental Example 2. Evaluation of Stability of Positive Electrode Active Material To measure the weight loss rate of each of the cathode active materials manufactured according to Production Example 1, the weight loss rate was measured while increasing the temperature at a rate of 10 °C / min up to 810 °C in an Ar atmosphere at normal pressure using a TGA-MS apparatus. At this time, since the intensity of the MS signal may be changed, the measurement sample amount was used in an amount of 65 mg to 66 mg.

[0169] The positive electrode manufactured in Production Example 2 was similarly measured for the weight loss rate, and the temperature at which the weight loss peak first appeared was measured.

[0170] The measurement results are shown in Table 6 below.

Table 6

[0171] Referring to the results in Table 6, it can be confirmed that the thermal stability of the positive electrode active materials according to Examples 1 to 7 is generally higher than that of the positive electrode active materials according to Comparative Examples 1 to 8. Such stability of the positive electrode active material is related to the ratio of the lithium composite oxide having a grain boundary density of 0.5 or less among all the lithium composite oxides constituting the positive electrode active material and the intentional growth with respect to a specific crystal plane of the lithium composite oxide in a complex manner.

[0172] As described above, the embodiments of the present invention have been explained. However, those having ordinary knowledge in the technical field can modify and change the present invention in various ways 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.

Claims

1. A positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation / deintercalation, wherein the ratio of the peak intensities attributed to the (003) plane and the (012) plane obtained from X-ray diffraction analysis using Cu-Kα rays with respect to the lithium composite oxide satisfies the following formula 1, the molar ratio of Ni to all metal elements other than lithium in the lithium composite oxide is 0.6 or more, and when the temperature is raised at a rate of 10 °C / min to 810 °C in an Ar atmosphere at normal pressure, the weight loss rate of the positive electrode active material is less than 1.07%. (Formula 1) 0.131 ≦ I(012) / I(003) ≦ 0.143

2. The positive electrode active material according to claim 1, wherein the ratio of the peak intensities attributed to the (003) plane and the (104) plane obtained from X-ray diffraction analysis using Cu-Kα rays with respect to the lithium composite oxide satisfies the following formula 2. (Formula 2) 0.630 ≦ I(104) / I(003) ≦ 0.698

3. The positive electrode active material according to claim 1, wherein the ratio of the peak intensities attributed to the (003) plane and the (101) plane obtained from X-ray diffraction analysis using Cu-Kα rays with respect to the lithium composite oxide satisfies the following formula 3. (Formula 3) 0.379 ≦ I(101) / I(003) ≦ 0.421

4. The positive electrode active material according to claim 1, wherein the lithium ion diffusion path formed in the lithium composite oxide is formed parallel to the major axis direction of the lithium composite oxide.

5. The positive electrode active material according to claim 1, wherein the lithium ion diffusion path formed in the lithium composite oxide is formed parallel to the (003) plane.

6. The positive electrode active material according to claim 1, wherein the lithium ion diffusion path formed in the lithium composite oxide is formed so as to direct at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane.

7. The positive electrode active material according to claim 1, wherein the lithium composite oxide is represented by the following Chemical Formula 1. (Chemical Formula 1) Li ａ Ni １－（ｂ＋ｃ＋ｄ＋ｅ） Co ｂ M1 c M2 ｄ M3 ｅ O ｆ (wherein, M1 is at least one selected from Mn and Al, M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, M1 to M3 are different from each other, 0.90 ≦ a ≦ 1.15, 0 ≦ b ≦ 0.20, 0 ≦ c ≦ 0.10, 0 ≦ d ≦ 0.05, 0 ≦ e ≦ 0.05, 1.0 ≦ f ≦ 2.0.)

8. The cathode active material according to claim 7, wherein, among the lithium composite oxides represented by Chemical Formula 1, the molar ratio of nickel calculated by the following Formula 4 is 0.6 or more. (Formula 4) Ni (molar ratio) = Ni (mol%) / (Ni (mol%) + Co (mol%) + M1 (mol%) + M2 (mol%) + M3 (mol%))

9. The cathode active material according to claim 1, wherein the average particle diameter of the lithium composite oxide is 0.1 μm to 20 μm.

10. The lithium composite oxide contains at least one primary particle, In the cross-sectional SEM image of the lithium composite oxide, for the primary particles on the virtual straight line crossing the center of the lithium composite oxide, the density of grain boundaries calculated by the following Formula 5 is 0.50 or less. The cathode active material according to claim 1. (Formula 5) Density of grain boundaries = (number of interfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line)

11. The cathode active material is an aggregate of a plurality of lithium composite oxides composed of at least one primary particle, Among the aggregates, in the cross-sectional SEM image of the lithium composite oxide, for the primary particles on the virtual straight line crossing the center of the lithium composite oxide, the proportion of the lithium composite oxide having a grain boundary density calculated by the following Formula 5 of 0.50 or less is 30% or more. The cathode active material according to claim 1. (Formula 5) Density of grain boundaries = (number of interfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line)

12. It further includes a coating layer covering at least a part of the surface of the lithium composite oxide, The coating layer contains at least one oxide represented by Chemical Formula 2 below. The cathode active material according to claim 1. (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 ≦ 15.)

13. A cathode active material containing a lithium composite oxide having a layered structure capable of lithium intercalation / deintercalation, In the lithium composite oxide, the molar ratio of Ni to all metal elements other than lithium is 0.6 or more. The lithium composite oxide contains at least one primary particle, in the cross-sectional SEM image of the lithium composite oxide, for the primary particles on the virtual straight line crossing the center of the lithium composite oxide, the density of the grain boundaries calculated by the following formula 5 is 0.50 or less, (Formula 5) Density of grain boundaries = (number of interfaces between primary particles on the virtual straight line / number of primary particles on the virtual straight line) The lithium ion diffusion path formed in the lithium composite oxide is formed to direct at least one crystal plane selected from the (012) plane, (101) plane and (104) plane, A positive electrode active material having a weight loss rate of less than 1.07% when heated at a heating rate of 10 ° C. / min up to 810 ° C. in an Ar atmosphere at normal pressure.

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