Positive electrode active material and lithium secondary battery using the same

Abstract

The present application relates to a positive electrode active material and a lithium secondary battery using the same, in which lithium ion diffusion paths in a lithium complex oxide constituting the positive electrode active material are formed in a manner of pointing to specific crystal planes, and electrochemical characteristics and stability are improved by increasing growth of the crystal planes to which the lithium ion diffusion paths point.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material in which lithium ion diffusion paths in a lithium complex oxide constituting the positive electrode active material are formed in a manner directed to a specific crystal plane, and a lithium secondary battery using the same, in which electrochemical characteristics and stability are improved by increasing growth of the crystal plane to which the lithium ion diffusion paths are directed. BACKGROUND

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

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

[0004] A lithium complex oxide is used as a positive electrode active material of a lithium secondary battery, and as an example thereof, a complex oxide of LiCoO2, LiMn2O4, LiNiO2, LiMnO2, etc. is being studied.

[0005] Among the positive electrode active materials, LiCoO2 is commonly used because it has excellent life characteristics and charge / discharge efficiency, but cobalt used as a raw material is limited in resources and is expensive, and thus has a disadvantage in that price competitiveness is limited.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but have problems of small capacity and poor high-temperature characteristics. Also, LiNiO2 positive electrode active materials show battery characteristics of high discharge capacity, but are difficult to synthesize due to a cation mixing problem between Li and transition metals, and thus have a large problem in rate characteristics.

[0007] Also, depending on the severity of such cation mixing, a large amount of Li by-products are generated, most of which are composed of LiOH and Li2CO3 compounds, and when a positive electrode slurry is prepared, become a cause of gelation and gas generation due to charge / discharge after the electrode is prepared. Residual Li2CO3 reduces cycles by increasing a swelling phenomenon of a monomer, and also becomes a cause of battery swelling.

[0008] To compensate for this shortcoming, the demand for high-Ni-type cathode active materials having a Ni content of 50% or more as a cathode active material for secondary batteries has begun to increase. However, such high-Ni-type cathode active materials exhibit high capacity characteristics, and, in contrast, as the Ni content in the cathode active material increases, there is a problem of structural instability caused by Li / Ni cation mixing. Due to the structural instability of such cathode active materials, lithium secondary batteries not only deteriorate sharply under high-temperature conditions, but also deteriorate sharply under normal-temperature conditions.

[0009] In addition, recently, not only cathode active materials including lithium composite oxides having a polycrystalline structure, but also cathode active materials including lithium composite oxides having a single-crystal structure have been proposed (Journal of The Electrochemical Society, Volume 164, Number 7, A1534-A1544 (Publication Date: May 23, 2017)).

[0010] It is disclosed in the above document that the stability of lithium composite oxides (LiNi 0.5 Mn 0.3 Co 0.2 O2) having a single-crystal structure with a crystal size of 2 μm to 3 μm is partially improved compared to lithium composite oxides having a polycrystalline structure of the same composition.

[0011] However, in the case where the firing temperature is excessively increased or the firing time is excessively lengthened in order to single-crystallize the lithium composite oxides constituting the cathode active material, the cation mixing phenomenon mentioned above can increase.

[0012] In particular, in the case where the cation mixing phenomenon in the lithium composite oxides having a single-crystal structure increases, in addition to the originally expected layered structure, an excessive amount of lithium composite oxides having a metastable state or a Rock-salt phase are formed, and when the lithium composite oxides having a phase other than the layered structure are excessively present, this can lead to deterioration of the cathode active material as a collection of them. The deterioration of the cathode active material as described above becomes a cause of, for example, capacity reduction and life reduction.

[0013] Therefore, there is a significant limitation in improving the cathode active material having a single-crystal structure by merely increasing the firing temperature of the lithium composite oxides constituting the cathode active material. SUMMARY

[0014] TECHNICAL PROBLEM

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

[0016] Therefore, an object of the present application is to provide a positive electrode active material which maintains the high electrochemical characteristics of the conventional positive electrode active material for a lithium secondary battery, particularly, the high electrochemical characteristics of the high-Ni type positive electrode active material, while solving the low structural stability.

[0017] Further, an object of the present application is to improve a positive electrode active material in which lithium ion diffusion paths in a lithium complex oxide constituting the positive electrode active material are formed in a manner directed to a specific crystal plane, and to improve the electrochemical characteristics and the stability by improving the growth of the crystal plane to which the lithium ion diffusion paths are directed.

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

[0019] The objects of the present application are not limited to the above-mentioned objects, and other objects and advantages of the present application which are not mentioned can be understood from the following description, and can be more clearly understood from the embodiments of the present application. Also, it will be appreciated that the objects and advantages of the present application can be achieved by the means shown in the appended claims and combinations thereof.

[0020] Solution to the problem

[0021] According to an embodiment of the present application, the present application provides a positive electrode active material including a lithium complex oxide of a layered structure capable of intercalating / deintercalating lithium, wherein a ratio of peak intensities attributed to (003) and (012) planes obtained in X-ray diffraction analysis using Cu-Kα rays of the lithium complex oxide satisfies the following Formula 1.

[0022] Formula 1: 0.131 ≤ I(012) / I(003) ≤ 0.143

[0023] Further, the lithium complex oxide can have a shape having a long axis and a short axis, and in this case, lithium ion diffusion paths formed in the lithium complex oxide can be formed in a manner parallel to the long axis direction of the lithium complex oxide.

[0024] Also, the lithium ion diffusion path formed in the lithium complex oxide is formed in a manner parallel to the (003) plane, and the lithium ion diffusion path formed in the lithium complex oxide is formed in a manner directed to at least one of the (012) plane, the (101) plane, and the (104) plane, whereby the lithium ion diffusion capacity through the lithium complex oxide can be improved, and further, the electrochemical characteristics of the positive electrode active material including the lithium complex oxide can be improved.

[0025] wherein the lithium complex oxide can be represented by the following Chemical Formula 1.

[0026] Chemical Formula 1: Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f

[0027] wherein M1 is at least one selected from the group consisting of Mn and Al, M2 and M3 are each independently selected from the group consisting of Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, M1 to M3 are not the same as 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.

[0028] In one embodiment, the lithium complex oxide includes at least one primary particle, and in a cross-sectional scanning electron microscope (SEM) image of the lithium complex oxide, a grain boundary density calculated from the following Formula 5 for primary particles located on a virtual straight line crossing the center of the lithium complex oxide can be 0.50 or less.

[0029] Formula 5: Grain boundary density = (number of interfaces between primary particles located on the virtual straight line / number of primary particles located on the virtual straight line)

[0030] In this case, the lithium complex oxide can have a single crystal structure.

[0031] In another embodiment, the positive electrode active material is an aggregate of a plurality of lithium complex oxides composed of at least one primary particle, and in the aggregate, a proportion of lithium complex oxides in which, in a cross-sectional scanning electron microscope image of the lithium complex oxide, a grain boundary density calculated from the following Formula 5 for primary particles located on a virtual straight line crossing the center of the lithium complex oxide is 0.50 or less can be 30% or more.

[0032] Formula 5: Grain boundary density = (number of interfaces between primary particles located on the above-mentioned virtual straight line / number of primary particles located on the above-mentioned virtual straight line)

[0033] Also, according to still another embodiment of the present application, the present application provides a positive electrode active material including a lithium complex oxide having a layered structure capable of intercalating / deintercalating lithium, the lithium complex oxide including at least one primary particle, in a cross-sectional scanning electron microscope image of the lithium complex oxide, for primary particles located on a virtual straight line crossing the center of the lithium complex oxide, a grain boundary density calculated from the following Formula 5 is 0.50 or less, and lithium ion diffusion paths formed within the lithium complex oxide are formed in a manner of pointing to at least one crystal plane selected from the group consisting of (012) plane, (101) plane, and (104) plane.

[0034] Formula 5: Grain boundary density = (number of interfaces between primary particles located on the above-mentioned virtual straight line / number of primary particles located on the above-mentioned virtual straight line)

[0035] Also, according to another embodiment of the present application, the present application provides a positive electrode active material including a lithium complex oxide having a layered structure capable of intercalating / deintercalating lithium, the positive electrode active material being a collection of a plurality of lithium complex oxides composed of at least one primary particle, in the collection, a proportion of lithium complex oxides having a grain boundary density calculated from the following Formula 5 for primary particles located on a virtual straight line crossing the center of the lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide is 30% or more, and lithium ion diffusion paths formed within the lithium complex oxide are formed in a manner of pointing to at least one crystal plane selected from the group consisting of (012) plane, (101) plane, and (104) plane.

[0036] Formula 5: Grain boundary density = (number of interfaces between primary particles located on the above-mentioned virtual straight line / number of primary particles located on the above-mentioned virtual straight line)

[0037] Meanwhile, according to still another embodiment of the present application, a lithium secondary battery using the positive electrode active material defined in the present application is provided.

[0038] Effects of the Invention

[0039] According to the present application, lithium ion diffusion paths within a lithium complex oxide constituting a positive electrode active material for a lithium secondary battery are formed in a manner of pointing to a crystal plane in which diffusion of lithium ions is relatively free, rather than in a manner of pointing to a crystal plane in which diffusion of lithium ions is concealed, so that it is expected that electrochemical characteristics of the positive electrode active material including the lithium complex oxide are improved.

[0040] Furthermore, the growth of a crystal plane in which lithium ions in the lithium complex oxide described above are relatively free to diffuse is intentionally promoted, whereby the diffusion ability of lithium ions mediated by the lithium complex oxide described above can be improved.

[0041] In addition, as described in Journal of The Electrochemical Society, Volume 164, Number 7, A1534-A1544, in general, in order to uniformly single-crystallize the lithium complex oxide that constitutes the positive electrode active material of a lithium secondary battery, firing under relatively severe conditions is required.

[0042] The specific surface area of the lithium complex oxide having a single-crystal structure or a structure close to a single-crystal structure (e.g., the number of primary particles that constitute secondary particles is reduced) generated by the above-described method is reduced compared to that of a lithium complex oxide having a polycrystal structure, whereby the stability can be improved.

[0043] However, under severe firing conditions, cation mixing can increase, and the cation mixing described above can cause problems in that phase transformation of the lithium complex oxide is induced, and an excess of lithium complex oxide having a metastable phase or a rock-salt phase is formed in addition to the originally intended layered structure. As described above, with an excess of lithium complex oxide having a phase other than the layered structure coexisting with the lithium complex oxide having the layered structure, the positive electrode active material can be degraded.

[0044] Thus, in the present application, the lithium ion diffusion path in the lithium complex oxide that constitutes the positive electrode active material is formed so as to point to a specific crystal plane, and the growth of the crystal plane to which the lithium ion diffusion path described above points is promoted, whereby the lithium complex oxide described above can be given sufficient electrochemical characteristics and stability only by single-crystallization performed under relatively less severe firing conditions.

[0045] In addition to the effects described above, the specific effects of the present application are described together with the detailed description of the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 and FIG. 2 A schematic diagram showing a cross-sectional image of a lithium complex oxide included in a positive electrode active material of various embodiments of the present application.

[0047] FIGS. 3 to 6 A transmission electron microscope (TEM) image of a lithium complex oxide included in a positive electrode active material of Embodiment 1, Embodiment 2, Embodiment 3, and Embodiment 5 of the present application, in which a lithium ion diffusion path in the lithium complex oxide described above is shown. DETAILED DESCRIPTION

[0048] In order to more easily understand the present application, specific terms are defined in the present application for convenience. Unless otherwise defined in the present application, scientific and technical terms used in the present application have meanings commonly understood by those of ordinary skill in the art. Also, unless otherwise specified in context, the singular form of a term includes its plural form, and the plural form of a term should be understood to include its singular form as well.

[0049] Explanation of terms

[0050] The term "lithium complex oxide" used in the present application is an oxide of a layered structure capable of intercalating / deintercalating lithium (lithium ions), and refers to a complex oxide including lithium and a metal element. Particularly, the lithium complex oxide used in the present application refers to a lithium-nickel-based complex oxide including lithium and nickel. Also, the lithium complex oxide used in the present application is an oxide particle constituting a positive electrode active material, and can be a single crystal particle (i.e., a single particle form) or a polycrystal particle (i.e., a form in which a plurality of particles are aggregated).

[0051] The term "single crystal" used in the present application refers to a crystal in a state in which no grain or grain boundary is included in the interior of a particle. Also, the term "primary particle" used in the present application refers to a particle that does not form an aggregate and exists alone, or a primary particle constituting a secondary particle in which a plurality of primary particles are aggregated. The "lithium complex oxide having a single crystal structure" refers to a particle in a state in which a primary particle composed of a lithium complex oxide is composed of a plurality of grains or no grain boundary is included in the interior of the primary particle.

[0052] The term "secondary particle" used in the present application refers to a particle in which at least two primary particles of the above-described lithium complex oxide are aggregated. In this case, a secondary particle composed of a single primary particle and / or a secondary particle in which at least two primary particles are aggregated can coexist in a positive electrode active material. In the case in which a secondary particle is formed by aggregating at least two primary particles, a grain boundary or an interface of criticality is present in the secondary particle at an interface between the two primary particles.

[0053] The term "grain boundary density" used in the present application refers to the number of grain boundaries or interfaces of criticality formed as at least two primary particles are present in a secondary particle. The grain boundary density increases as the number of primary particles present in a secondary particle increases, and decreases as the number of primary particles present in a secondary particle decreases.

[0054] In the present application, the grain boundary density can be calculated from the number of primary particles located on a virtual straight line crossing the center of the lithium complex oxide in the cross-sectional scanning electron microscope image of the lithium complex oxide according to the following formula 5. In this case, the direction of the straight line can be a direction crossing the center of the lithium complex oxide in the direction of the minor axis.

[0055] Formula 5: Grain boundary density = (number of interfaces between primary particles located on the virtual straight line / number of primary particles located on the virtual straight line)

[0056] In the case where the number of primary particles present within the secondary particle is one, the grain boundary density calculated according to the above formula is 0, and in the case where the number of primary particles present within the secondary particle is three or more, the grain boundary density calculated according to the above formula can be greater than 0.5.

[0057] In addition, in the present application, the secondary particle can be a particle composed of a single primary particle having a single crystal structure, but is not 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 at least two single crystal particles aggregated together. The definition of such a secondary particle can be more clearly explained by the definition of the positive electrode active material described later.

[0058] The term "positive electrode active material" used in the present application is a broad concept including the above-described secondary particle, and a single secondary particle itself can be a positive electrode active material, but in the present application, a collection of a plurality of secondary particles having the same grain boundary density and / or different grain boundary densities can be defined as a positive electrode active material.

[0059] Therefore, in the definition of the positive electrode active material described later, it is necessary to distinguish the explanation of the secondary particle having the collection property of a plurality of secondary particles from the explanation of the secondary particle constituting the positive electrode active material and the primary particle constituting the secondary particle.

[0060] Hereinafter, the positive electrode active material of the present application and a lithium secondary battery using a positive electrode including the above-described positive electrode active material will be described in more detail.

[0061] Positive electrode active material

[0062] According to an embodiment of the present application, a positive electrode active material including a lithium complex oxide having a layered structure capable of intercalating / deintercalating lithium is provided.

[0063] The lithium complex oxide can include at least one primary particle, and in the case where the lithium complex oxide includes a plurality of primary particles, the plurality of primary particles can exist as secondary particles of aggregates of the primary particles. In contrast, in the case where the lithium complex oxide includes a single primary particle, the lithium complex oxide refers to a lithium complex oxide of a single-crystal structure.

[0064] The primary particle refers to one grain or crystallite, and the secondary particle refers to an aggregate of a plurality of primary particles. Also, the primary particle can be rod-shaped, elliptical, and / or circular, or irregularly shaped.

[0065] A gap and / or a grain boundary can exist between the primary particles constituting the secondary particle. For example, the primary particles can be spaced apart from adjacent primary particles in the interior of the secondary particle to form an internal gap. Also, the primary particles can not be in contact with adjacent primary particles to form a grain boundary, but can form a surface existing in the interior of the secondary particle by being in contact with the internal gap.

[0066] In addition, a face of the primary particle existing on the top surface of the secondary particle, which is exposed to the outside air, can form a surface of the secondary particle.

[0067] The average particle diameter of the primary particle is 0.1 μm to 10 μm, and preferably, is present in the range of 1.0 μm to 10 μm, so that the optimal density of the positive electrode prepared by using the positive electrode active material according to various embodiments of the present application can be achieved. Also, the average particle diameter of the secondary particle can be 3 μm to 20 μm according to the number of aggregated primary particles.

[0068] In addition, the positive electrode active material according to the present application can be defined as an assembly of a plurality of secondary particles having the same grain boundary density and / or different grain boundary densities.

[0069] The grain boundary density can be calculated based on the number of primary particles P located on a virtual straight line L crossing the center of the lithium complex oxide, in a cross-sectional scanning electron microscope image of the lithium complex oxide, according to Equation 5 below.

[0070] Equation 5: Grain boundary density = (number of interfaces B between primary particles located on the virtual straight line L / number of primary particles P located on the virtual straight line L)

[0071] For example, referring to FIG. 1 as a schematic diagram briefly showing a cross-sectional image of a lithium complex oxide included in a positive electrode active material according to various embodiments of the present application, FIG. 1 and FIG. 2 The grain boundary density of the lithium complex oxide calculated as above is shown in Table 1 below.

[0072] Table 1

[0073]

[0074] With the grain boundary density represented by the above-described formula 5 having a value of 0.90 or less, the surface area and the critical interface of the lithium complex oxide can be reduced, whereby the high-temperature stability and the storage stability of the positive electrode active material can be improved by reducing the possibility of side reactions between the positive electrode active material and the electrolyte.

[0075] In addition, according to an embodiment of the present application, in the aggregate of the secondary particles, the proportion of the lithium complex oxide having a grain boundary density calculated according to the above-described formula 5 of 0.50 or less for the primary particles located on a virtual straight line crossing the center of the lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide can be 30% or more.

[0076] The surface area of the lithium complex oxide included in the positive electrode active material and the grain boundary defined by the primary particles constituting the lithium complex oxide can be a region in which side reactions occur between the positive electrode active material and the electrolyte at the interface and the surface. Among them, as shown in the above-described formula 5, for example, the grain boundary defined by the primary particles present in the lithium complex oxide can be understood as the interface between two adjacent primary particles. FIG. 1 and FIG. 2 As shown in the above-described formula 5, for example, the grain boundary defined by the primary particles present in the lithium complex oxide can be understood as the interface between two adjacent primary particles.

[0077] In this case, the surface area of the lithium complex oxide and the critical interface defined by the primary particles in the lithium complex oxide are reduced, whereby the thermal stability of the positive electrode active material is improved, and at the same time, problems caused by the instability of the positive electrode active material (for example, a decrease in storage stability such as gas generation caused by side reactions with the electrolyte) can be prevented or alleviated.

[0078] Thus, the proportion of the lithium complex oxide having a grain boundary density calculated according to the above-described formula 5 of 0.50 or less in the aggregate of the secondary particles is made 30% or more, thereby providing a positive electrode active material that can stably maintain electrochemical properties.

[0079] In addition, the proportion of the lithium complex oxide having a grain boundary density calculated according to the above-described formula 5 of 0.50 or less in the aggregate of the secondary particles can be increased by changing the process conditions of some of the steps in the synthesis process of the lithium complex oxide. For example, the proportion of the lithium complex oxide having a grain boundary density of 0.50 or less can be increased by adjusting the first firing temperature / time of the precursor of the lithium complex oxide and / or the second firing temperature / time of the first firing product of the precursor, and the like.

[0080] However, if the firing conditions of the above-mentioned precursor and / or the above-mentioned lithium complex oxide are relatively severe, the cation mixing phenomenon can increase, and the cation mixing phenomenon can induce phase transition of the lithium complex oxide.

[0081] Therefore, the proportion of the lithium complex oxide having a grain boundary density of 0.50 or less in the collection of the above-mentioned secondary particles calculated by the above-mentioned formula 5 is made to be 95% or less, preferably, 90% or less, and more preferably, 80% or less, and thus, the balance between the lithium complex oxide having a grain boundary density of 0.50 or less and the lithium complex oxide having a grain boundary density of more than 0.50 in the collection of the above-mentioned secondary particles can be achieved.

[0082] The lithium complex oxide according to an embodiment of the present application can include at least Ni and Co. In addition to Ni and Co, the above-mentioned lithium complex oxide can include Mn and / or Al, and can further include a dopant other than the above-mentioned metal elements.

[0083] Specifically, the above-mentioned lithium complex oxide can be represented by the following chemical formula 1.

[0084] Chemical formula 1: Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e O f

[0085] 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 not the same as 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.

[0086] In addition, the above-mentioned lithium complex oxide can be a high-Ni type lithium complex oxide in which the molar ratio of nickel calculated by the following formula 4 is 0.6 or more, preferably, 0.7, and more preferably, 0.8 or more, in the above-mentioned lithium complex oxide represented by the above-mentioned chemical formula 1.

[0087] Formula 4: Ni (molar ratio) = Ni (molar ratio) / (Ni (molar ratio) + Co (molar ratio) + M1 (molar ratio) + M2 (molar ratio) + M3 (molar ratio))

[0088] As described above, the lithium complex oxide of the high-Ni type has the advantage of relatively high electrochemical characteristics compared to the lithium complex oxide having a small amount of Ni, but as the amount of Ni in the lithium complex oxide increases, there is a problem of structural instability caused by Li / Ni cation mixing. Due to the structural instability of the positive electrode active material, the lithium secondary battery is not only rapidly deteriorated under high temperature conditions, but also rapidly deteriorated under normal temperature conditions.

[0089] However, the lithium complex oxide of the present application, even if having a composition of the high-Ni type, can improve the electrochemical characteristics of the above-described lithium complex oxide by controlling the characteristics of the crystal plane or exposed surface described later, while preventing a decrease in stability.

[0090] Specifically, the lithium ion diffusion path formed within the above-described lithium complex oxide is formed in a manner parallel to the long axis direction of the above-described lithium complex oxide, whereby the diffusion ability of the above-described lithium ion mediated by the above-described lithium complex oxide can be improved.

[0091] Here, the above-described lithium ion diffusion path refers to a one-dimensional path and / or a two-dimensional path that primarily transports / diffuses the lithium ion within the above-described lithium complex oxide according to a vacancy hopping mechanism.

[0092] Further, preferably, the above-described lithium ion diffusion path is formed in a manner parallel to the (003) plane confirmed by X-ray diffraction analysis using Cu-Kα rays on the above-described lithium complex oxide. In the case where the above-described lithium ion diffusion path within the above-described lithium complex oxide is formed in a manner directed to the (003) plane, the diffusion of the above-described lithium ion can be masked by the (003) plane, thereby having a problem of a decrease in the diffusion ability of the above-described lithium ion mediated by the above-described lithium complex oxide.

[0093] In addition, the above-described lithium ion diffusion path is formed in a manner directed to at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane, which are relatively free in the diffusion of the above-described lithium ion compared to the (003) plane, whereby the diffusion ability of the above-described lithium ion mediated by the above-described lithium complex oxide can be improved.

[0094] That is, according to the present application, the lithium ion diffusion path within the lithium complex oxide constituting the positive electrode active material of the lithium secondary battery is formed in a manner directed to a crystal plane relatively free in the diffusion of the lithium ion, rather than in a manner directed to a crystal plane in which the diffusion of the lithium ion is masked, whereby it is expected that the electrochemical characteristics of the positive electrode active material containing the above-described lithium complex oxide can be improved.

[0095] In this case, the lithium ion diffusion path directed to a specific crystal plane means that the angle formed by the direction perpendicular to the above-described specific crystal plane and the direction of the above-described lithium ion diffusion path is 90 degrees or less, preferably 60 degrees or less, and more preferably 45 degrees or less.

[0096] Additionally, according to the present application, before primary firing of the lithium complex oxide by heat-treating a hydroxide precursor of the lithium complex oxide, a flux is added to a mixture of the hydroxide precursor and a lithium raw material (e.g., LiOH or the like) and then heat-treated, thereby improving growth of a crystal plane to which the lithium ion diffusion path points. Particularly, before primary firing, a flux is added to a mixture of the hydroxide precursor and a lithium raw material (e.g., LiOH or the like) and then heat-treated, thereby further improving growth of a crystal plane in which diffusion of lithium ions is relatively free compared to a crystal plane in which diffusion of lithium ions is masked.

[0097] As the flux used to improve growth of a crystal plane in which diffusion of lithium ions is relatively free, for example, an alkali metal compound (hydroxide, chloride, nitride, carbonate, sulfate, or the like) such as NaOH, KCl, NaNO3, or a chloride such as NH4Cl can be used.

[0098] Further, in X-ray diffraction analysis using Cu-Ka rays for the lithium complex oxide, a ratio of peak intensities attributed to (003) and (012) planes can satisfy the following Formula 1.

[0099] Formula 1: 0.131 ≤ I(012) / I(003) ≤ 0.143

[0100] In a case where I(012) / I(003) calculated by Formula 1 is less than 0.131, growth of a (012) plane in which diffusion of lithium ions is relatively free compared to a (003) plane in which diffusion of lithium ions is masked is insufficient, and thus an effect of improving electrochemical characteristics of the lithium complex oxide according to growth of a crystal plane to which the lithium ion diffusion path points is minimal.

[0101] On the contrary, in a case where I(012) / I(003) calculated by Formula 1 is greater than 0.143, as growth of a (012) plane formed in a length direction of the lithium ion diffusion path becomes excessive, the diffusion ability of the lithium ions mediated by the lithium complex oxide or the stability of the crystal structure of the lithium complex oxide is rather reduced.

[0102] Further, in X-ray diffraction analysis using Cu-Ka rays for the lithium complex oxide, a ratio of peak intensities attributed to (003) and (104) planes can satisfy the following Formula 2.

[0103] Formula 2: 0.630 ≤ I(104) / I(003) ≤ 0.698

[0104] Similarly, in a case where I(104) / I(003) calculated by the above-described formula 2 is less than 0.630, the growth of the (104) plane, which is relatively free from the diffusion of lithium ions, is insufficient compared to the (003) plane, which is masked by the diffusion of lithium ions, so that the effect of improving the electrochemical characteristics of the lithium complex oxide by the growth of the crystal plane directed according to the lithium ion diffusion path is minimal.

[0105] On the contrary, in a case where I(104) / I(003) calculated by the above-described formula 2 is greater than 0.698, the growth of the (104) plane formed in the length direction along the lithium ion diffusion path becomes too large, which in turn reduces the diffusion ability of the lithium ions mediated by the lithium complex oxide or reduces the stability of the crystal structure of the lithium complex oxide.

[0106] Also, the ratio of the peak intensities attributed to the (003) plane and the (101) plane obtained in the X-ray diffraction analysis using Cu-Ka rays for the lithium complex oxide can satisfy the following formula 3.

[0107] Formula 3: 0.379 ≤ I(101) / I(003) ≤ 0.421

[0108] Similarly, in a case where I(101) / I(003) calculated by the above-described formula 3 is less than 0.379, the growth of the (101) plane, which is relatively free from the diffusion of lithium ions, is insufficient compared to the (003) plane, which is masked by the diffusion of lithium ions, so that the effect of improving the electrochemical characteristics of the lithium complex oxide by the growth of the crystal plane directed according to the lithium ion diffusion path is minimal.

[0109] On the contrary, in a case where I(101) / I(003) calculated by the above-described formula 3 is greater than 0.421, the growth of the (101) plane formed in the length direction along the lithium ion diffusion path becomes too large, which in turn reduces the diffusion ability of the lithium ions mediated by the lithium complex oxide or reduces the stability of the crystal structure of the lithium complex oxide.

[0110] Additionally, the lithium complex oxide included in the positive electrode active material of some embodiments of the present application can include a coating layer covering at least a portion of the surface of the primary particles (e.g., the grain boundaries between the primary particles) and / or the secondary particles formed by the aggregation of the primary particles.

[0111] For example, the coating layer can be present in a manner of covering at least a portion of the exposed surface of the primary particles. In particular, the coating layer can be present in a manner of covering at least a portion of the exposed surface of the primary particles present in the outermost periphery of the secondary particles.

[0112] Thus, the coating layer can exist as a layer coating the surface of the primary particles and / or the secondary particles formed by aggregation of the primary particles. In the case where the coating layer is discontinuous, it can exist in the form of islands.

[0113] The coating layer existing in the above-described manner maintains the high electrochemical properties of the lithium complex oxide, and in particular, the high electrochemical properties of the high-Ni type lithium complex oxide, while contributing to the solution of the low structural stability.

[0114] Further, the coating layer can exist as a solid solution form not forming a boundary with the secondary particles formed by aggregation of the primary particles and / or the primary particles.

[0115] The coating layer can include at least one oxide represented by the following Chemical Formula 2. That is, the coating layer can be defined as a region having an oxide represented by the following Chemical Formula 2.

[0116] Chemical Formula 2: Li a A b O c

[0117] wherein A is at least one selected from the group consisting of 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.

[0118] Further, the coating layer can be in a form in which different kinds of oxides exist in one layer, or different kinds of oxides represented by the above Chemical Formula 2 can exist in different layers, respectively.

[0119] The oxide represented by the above Chemical Formula 2 can be in a state of being physically and / or chemically bonded to the primary particles represented by the above Chemical Formula 1. Further, the oxide can exist in a state of forming a solid solution with the primary particles represented by the above Chemical Formula 1.

[0120] The lithium complex oxide of the present embodiment includes a coating layer covering at least a portion of the primary particles (e.g., the interface between the primary particles) and / or the surface of the secondary particles formed by aggregation of the primary particles, thereby improving the structural stability. Further, in the case where such a lithium complex oxide is used as a positive electrode active material for a lithium secondary battery, the electrochemical properties and stability of the positive electrode active material can be improved. Further, the oxide can function as a lithium ion migration pathway while reducing the lithium remaining in the lithium complex oxide.

[0121] Also, depending on the case, the above oxide can exist not only in at least a part of the interface between the primary particles and the surface of the secondary particles, but also in an internal void formed in the inside of the secondary particles.

[0122] The above oxide is an oxide in which lithium is complexed with an element represented by A, or as an oxide of A, the above oxide can also be represented as, 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 c , and the like. Also, as non-limiting examples of the above oxide, there are 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, and the like. The above examples are merely for convenience of understanding, and the above oxide defined in the present application is not limited to the above examples.

[0123] In another embodiment, the above oxide is an oxide in which lithium is complexed with at least two elements represented by A, or can further include an oxide in which lithium is complexed with at least two elements represented by A. For example, the oxide in which lithium is complexed with at least two elements represented by A can be Li a (W / Ti) b O c , Li a (W / Zr) b O c , Li a (W / Ti / Zr) b O c , Li a(W / Ti / B) b O c etc., but are not limited thereto.

[0124] wherein the oxide can show a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles. Thus, the concentration of the oxide can decrease from the surface of the secondary particles toward the center of the secondary particles.

[0125] As described above, the oxide can show a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles, thereby effectively reducing residual lithium present in the surface of the lithium complex oxide, so that a side reaction caused by unreacted residual lithium can be prevented in advance. Also, the crystallinity in the inner region of the surface of the lithium complex oxide can be prevented from decreasing by the oxide. Also, the overall structure of the lithium complex oxide can be prevented from being destroyed by the oxide in an electrochemical reaction.

[0126] Additionally, the coating layer can include a first coating layer including at least one oxide represented by Chemical Formula 2, and a second coating layer including at least one oxide represented by Chemical Formula 2, including an oxide different from the oxide included in the first coating layer.

[0127] For example, the first coating layer can be present in a manner to cover at least a portion of the exposed surface of the primary particles present at the outermost periphery of the secondary particles, and the second coating layer can be present in a manner to cover at least a portion of the exposed surface of the primary particles not covered by the first coating layer and the surface of the first coating layer.

[0128] Lithium secondary battery

[0129] According to still another embodiment of the present application, the present application can provide a cathode including a cathode current collector and a cathode active material layer formed on the cathode current collector. The cathode active material layer can include the cathode active material of various embodiments of the present application. Thus, the cathode active material is the same as described previously, and thus a detailed description thereof will be omitted for convenience, and hereinafter, only the remaining components not previously described will be described.

[0130] The cathode current collector is not particularly limited as long as it does not induce a chemical change of the battery and has electrical conductivity, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel subjected to surface treatment with carbon, nickel, titanium, silver, etc. can be used. Also, the cathode current collector can generally have a thickness of 3 μm to 500 μm, and a fine concavo-convex can be formed on the surface of the current collector to improve the adhesion of the cathode active material. For example, it can be used in various forms such as a thin film, a sheet, a foil, a mesh, a porous body, a foamed body, a non-woven body, etc.

[0131] The positive electrode active material layer can be prepared by applying a positive electrode slurry composition containing the positive electrode active material, the conductive material, and a binder, if desired, to the positive electrode current collector.

[0132] In this case, the content of the positive electrode active material can be 80 to 99% by weight, more specifically 85 to 98.5% by weight, relative to the total weight of the positive electrode active material layer. When the positive electrode active material is contained in the above content range, excellent capacity characteristics can be exhibited, but are not limited thereto.

[0133] The conductive material is used to impart conductivity to the electrode, and in the battery thus constructed, can be used without limitation as long as it does not cause chemical changes and has electronic conductivity. As specific examples, graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyaniline derivatives, etc. can be used, either alone or as a mixture of two or more thereof. The conductive material can be contained in an amount of 0.1 to 15% by weight, relative to the total weight of the positive electrode active material layer.

[0134] The binder functions to improve adhesion between the plurality of positive electrode active material particles and the adhesion of the positive electrode active material to the current collector. As specific examples, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated ethylene-propylene-diene rubber, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. can be used, either alone or as a mixture of two or more thereof. The binder can be contained in an amount of 0.1 to 15% by weight, relative to the total weight of the positive electrode active material layer.

[0135] The positive electrode can be prepared according to a general positive electrode preparation method, in addition to using the positive electrode active material described above. Specifically, it can be prepared by applying a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material described above in a solvent and optionally dissolving or dispersing a binder and a conductive material in a solvent to a positive electrode current collector, followed by drying and calendering.

[0136] The solvent can be a solvent generally used in the technical field, and examples thereof include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and the like, and one or a mixture of two or more thereof can be used. The amount of the solvent used is not particularly limited as long as it can dissolve or disperse the positive electrode active material, the conductive material, and the binder and has a viscosity that can exhibit excellent thickness uniformity when coated for the production of the positive electrode.

[0137] Also, in another embodiment, the positive electrode can be produced by pouring the positive electrode slurry composition on a separate support and laminating a thin film obtained by peeling the support on a positive electrode current collector.

[0138] Meanwhile, according to another embodiment of the present application, an electrochemical device including the above-described positive electrode can be provided. The electrochemical device is specifically a battery, a capacitor, or the like, and more specifically a lithium secondary battery.

[0139] Specifically, the lithium secondary battery can include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and an electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as described above, and thus, a detailed description thereof will be omitted for convenience, and hereinafter, only the remaining components not described above will be described.

[0140] The lithium secondary battery can optionally further include a battery container for accommodating an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0141] The negative electrode can include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector.

[0142] The negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, a material in which the surface of copper or stainless steel is surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like can be used. Also, the negative electrode current collector can generally have a thickness of 3 μm to 500 μm, and like the positive electrode current collector, the adhesion of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as a thin film, a sheet, a foil, a mesh, a porous body, a foamed body, a nonwoven body, or the like.

[0143] The negative electrode active material layer can be produced by coating a negative electrode slurry composition including the negative electrode active material, a conductive material, and a binder selected as necessary on the negative electrode current collector.

[0144] As the above-mentioned negative active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. As specific examples, carbon materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy, metal oxides capable of doping and dedoping lithium such as Sn02, vanadium oxide, lithium vanadium oxide, or a composite containing the above-mentioned metal compound and carbon material such as Si-C composite or Sn-C composite can be used, or a mixture of one or more of them can be used. Also, as the above-mentioned negative active material, a thin film of metallic lithium can be used. Also, low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, and representative high-crystalline carbons are high-temperature fired carbon such as 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 petroleum or coal tar pitch derived cokes. β (0 < β < 2), Sn02, vanadium oxide, lithium vanadium oxide, or a composite containing the above-mentioned metal compound and carbon material such as Si-C composite or Sn-C composite can be used, or a mixture of one or more of them can be used. Also, as the above-mentioned negative active material, a thin film of metallic lithium can be used. Also, low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, and representative high-crystalline carbons are high-temperature fired carbon such as 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 petroleum or coal tar pitch derived cokes.

[0145] The above-mentioned negative active material can be contained in a range of 80 to 99% by weight, based on the total weight of the negative active material layer.

[0146] The above-mentioned binder is a component that contributes to the binding between the conductive material, the active material, and the current collector, and generally, the above-mentioned binder can be added in a range of 0.1 to 10% by weight, based on the total weight of the negative active material layer. As examples of such a binder, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber, sulfonated ethylene-propylene-diene rubber, styrene butadiene rubber, nitrile rubber, fluorine rubber, various copolymers thereof, and the like can be exemplified.

[0147] The above-mentioned conductive material is a component for further improving the conductivity of the negative active material, and 10% by weight or less of the above-mentioned conductive material can be added, based on the total weight of the negative active material layer, and preferably, 5% by weight or less of the above-mentioned conductive material can be added. Such a conductive material is not particularly limited as long as it does not induce chemical changes in the corresponding battery and has conductivity, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, nickel powder, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; conductive materials such as polyaniline derivatives, etc. can be used.

[0148] In one embodiment, the above-mentioned negative active material layer can be prepared by coating a negative electrode slurry composition on a negative electrode current collector and drying, the above-mentioned negative electrode slurry composition being prepared by dissolving or dispersing a negative active material in a solvent and, optionally, dissolving or dispersing a binder and a conductive material in the solvent, or being prepared by laminating a thin film obtained by peeling a separate support on which the above-mentioned negative electrode slurry composition is cast.

[0149] Also, in another embodiment, the above-mentioned negative active material layer can be prepared by coating a negative electrode slurry composition on a negative electrode current collector and drying, the above-mentioned negative electrode slurry composition being prepared by dissolving or dispersing a negative active material in a solvent and, optionally, dissolving or dispersing a binder and a conductive material in the solvent, or being prepared by laminating a thin film obtained by peeling a separate support on which the above-mentioned negative electrode slurry composition is cast.

[0150] In addition, in the above-mentioned lithium secondary battery, a separator is used to separate the negative electrode and the positive electrode and to provide a moving path for lithium ions, and any separator commonly used in lithium secondary batteries can be used without limitation, and in particular, it is preferable that the impedance be low and the electrolyte moisture holding capacity be excellent for ion movement of the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film prepared using a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Also, a general porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. Also, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component and a polymeric substance can be used, and can be used in a single layer or a multi-layer structure, optionally.

[0151] Further, as the electrolyte used in the present application, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in the production of a lithium secondary battery, can be exemplified, but are not limited thereto.

[0152] Specifically, the above electrolyte can include an organic solvent and a lithium salt.

[0153] As the above organic solvent, an organic solvent capable of playing a medium role of moving ions participating in an electrochemical reaction of a battery can be used without limitation. Specifically, as the above organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, or the like; an ether-based solvent such as dibutyl ether or tetrahydrofuran, or the like; a ketone-based solvent such as cyclohexanone, or the like; an aromatic hydrocarbon-based solvent such as benzene, fluorobenzene, or the like; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), or the like; an alcohol-based solvent such as ethanol, isopropanol, or the like; a nitrile such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double bond aromatic ring or an ether bond); an amide such as dimethylformamide, or the like; a dioxolane such as 1,3-dioxolane, or the like; or sulfolane, or the like, can be used. Among them, a carbonate solvent is preferred, and more preferably a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate, or the like) capable of improving the charge-discharge performance of a battery, and a low-viscosity linear carbonate compound (for example, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, or the like). In this case, when a cyclic carbonate and a chain carbonate are mixed at a volume ratio of about 1:1 to about 1:9, excellent performance of an electrolyte solution can be shown.

[0154] The above lithium salt can use a compound capable of providing lithium ions used in a lithium secondary battery without limitation. Specifically, the above lithium salt can use LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, or the like. Preferably, the concentration of the above lithium salt needs to be used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is included in the above range, the electrolyte has a proper conductivity and viscosity, and thus, can show excellent electrolyte performance, and can effectively move lithium ions.

[0155] In addition to the above electrolyte composition components, the electrolyte can further include one or more additives such as a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, or aluminum trichloride, or the like, for the purpose of improving the life characteristics of the battery, suppressing the reduction of the capacity of the battery, improving the discharge capacity of the battery, or the like. In this case, the above additives can be included in the range of 0.1 weight percent to 5 weight percent with respect to the total weight of the electrolyte.

[0156] As described above, the lithium secondary battery including the positive electrode active material of the present application stably shows excellent discharge capacity, output characteristics, and life characteristics, and thus, can be used in the fields of portable devices such as portable phones, notebook computers, digital cameras, and the like, and electric vehicles such as hybrid electric vehicles (HEV), or the like.

[0157] The outer shape of the lithium secondary battery of the present application is not particularly limited, and can be a cylindrical shape, a prismatic shape, a pouch shape, a coin type, or the like using a can. Also, preferably, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but also as a unit cell for a medium or large battery module including a plurality of battery cells.

[0158] According to another embodiment of the present application, a battery module including the above lithium secondary battery as a unit cell and / or a battery pack including the same can be provided.

[0159] The battery module or the battery pack described above can be used as a power source for one or more of a power tool, an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV), or a power storage system.

[0160] The present application will be described in more detail by way of examples. However, these examples are given for illustration only, and should not be construed as limiting the scope of the present application to the examples.

[0161] Preparation Example 1. Preparation of positive electrode active material

[0162] Example 1

[0163] A lithium complex oxide NiCoMn(OH)2 hydroxide precursor (Ni:Co:Mn = 91:8:1 (at%)) was synthesized by using a known co-precipitation method of nickel sulfate, cobalt sulfate, and manganese sulfate. The average particle diameter (D50) of the lithium complex oxide hydroxide precursor was 3.0 μm.

[0164] Next, after mixing LiOH (Li / (Ni+Co+Mn) mol ratio = 1.05 ± 0.05) to the first hydroxide precursor, heat treatment (first firing) was performed for 12 hours at a temperature rising rate of 2°C per minute to 770°C in an O2 atmosphere in a firing furnace to obtain a lithium complex oxide. In this case, 2.0 mol% of NaNO3 was added with respect to the sum of the first hydroxide precursor and LiOH before starting the heat treatment.

[0165] After the first firing was completed, the lithium complex oxide was added to distilled water, stirred for 1 hour, and dried at 120°C for 12 hours in a vacuum drier.

[0166] Finally, heat treatment (second firing) was performed for 12 hours at a temperature rising rate of 2°C per minute to 700°C in an O2 atmosphere in a firing furnace to obtain a positive electrode active material containing a lithium complex oxide.

[0167] Example 2

[0168] A positive electrode active material was prepared in the same manner as in Example 1, except that 3.0 mol% of NH4Cl was used instead of 2.0 mol% of NaNO3.

[0169] Example 3

[0170] The positive electrode active material was prepared in the same manner as in Example 1, except that 1.0 mol% KCl was used instead of 2.0 mol% NaNO3.

[0171] Example 4

[0172] The positive electrode active material was prepared in the same manner as in Example 1, except that 3.0 mol% KCl was used instead of 2.0 mol% NaNO3.

[0173] Example 5

[0174] The positive electrode active material was prepared in the same manner as in Example 1, except that 3.0 mol% NaOH was used instead of 2.0 mol% NaNO3.

[0175] Example 6

[0176] The positive electrode active material was prepared in the same manner as in Example 1, except that 5.0 mol% NaOH was used instead of 2.0 mol% NaNO3.

[0177] Example 7

[0178] The positive electrode active material was prepared in the same manner as in Example 1, except that 3.0 mol% NaCl was used instead of 2.0 mol% NaNO3.

[0179] Comparative Example 1

[0180] The positive electrode active material was prepared in the same manner as in Example 1, except that NaNO3 was not added before the first firing.

[0181] Comparative Example 2

[0182] The positive electrode active material was prepared in the same manner as in Example 1, except that 0.5 mol% NH4Cl was used instead of 2.0 mol% NaNO3.

[0183] Comparative Example 3

[0184] The positive electrode active material was prepared in the same manner as in Example 1, except that 1.0 mol% NH4Cl was used instead of 2.0 mol% NaNO3.

[0185] Comparative Example 4

[0186] An anode active material was prepared in the same manner as in Example 1, except that 0.5 mole percent of KCl was used instead of 2.0 mole percent of NaNO3.

[0187] Comparative Example 5

[0188] An anode active material was prepared in the same manner as in Example 1, except that 1.0 mole percent of NaOH was used instead of 2.0 mole percent of NaNO3.

[0189] Comparative Example 6

[0190] An anode active material was prepared in the same manner as in Example 1, except that the content of NaNO3to be added before the first firing was set to 3.0 mole percent.

[0191] Comparative Example 7

[0192] An anode active material was prepared in the same manner as in Example 1, except that the content of NaNO3to be added before the first firing was set to 5.0 mole percent.

[0193] Comparative Example 8

[0194] An anode active material was prepared in the same manner as in Example 1, except that 5.0 mole percent of NaCl was used instead of 2.0 mole percent of NaNO3.

[0195] Preparation Example 2. Preparation of lithium secondary battery

[0196] An anode slurry was prepared by dispersing 94 weight percent of each of the anode active materials prepared according to Preparation Example 1, 3 weight percent of artificial graphite, and 3 weight percent of a polyvinylidene fluoride binder in 3.5 g of N-methylpyrrolidone. An anode was prepared by applying the above anode slurry to an aluminum (Al) film having a thickness of 20 μm as an anode current collector and drying, followed by roll pressing. The load level of the anode was 7 mg / cm 2 , and the electrode density was 3.2 g / cm 3 .

[0197] A lithium foil was used as a counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, 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, and a coin cell was prepared according to a generally known preparation procedure.

[0198] Experimental Example 1. Analysis of structure of positive electrode active material

[0199] (1) Cross-sectional scanning electron microscope (SEM) analysis of positive electrode active material

[0200] After cross-sectional scanning electron microscope images of lithium complex oxides contained in the positive electrode active material prepared according to Preparation Example 1 were obtained by using a field emission scanning electron microscope (FE-SEM) (Bruker Corporation), the proportion of lithium complex oxides having a grain boundary density calculated according to the following Formula 5 of 0.50 or less was calculated from the cross sections of 100 lithium complex oxides captured in the above cross-sectional scanning electron microscope images.

[0201] Formula 5: Grain boundary density = (number of interfaces between primary particles located on a virtual straight line crossing the center of a lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide / number of primary particles located on the above virtual straight line)

[0202] The measurement results of the above grain boundary density are shown in Table 2 below.

[0203] Table 2

[0204]

[0205]

[0206] (2) Transmission electron microscope analysis of positive electrode active material

[0207] After transmission electron microscope images of lithium complex oxides contained in the positive electrode active material of Example 1, Example 2, Example 3, and Example 5 in Preparation Example 1 were obtained, the directionality of lithium ion diffusion paths formed within the above lithium complex oxides was confirmed from the above transmission electron microscope images. Also, the crystal plane of the above lithium complex oxide to which the lithium ion diffusion path formed within the above lithium complex oxide was directed was confirmed by indexing the SAD diffraction pattern. In the above FIGS. 3 to 6 The above measurement results are shown.

[0208] Reference FIGS. 3 to 6It was confirmed that the lithium ion diffusion path formed in the lithium complex oxide included in each of the positive electrode active materials of Example 1, Example 2, Example 3, and Example 5 was formed in the same direction as the long axis direction of the above-described lithium complex oxide. In particular, it was confirmed that the lithium ion diffusion path formed in the above-described lithium complex oxide was formed in a direction almost parallel to the (003) plane.

[0209] It was confirmed that the lithium ion diffusion path formed in the above-described lithium complex oxide was formed in a manner directed toward the (012) plane, the (101) plane, and / or the (104) plane.

[0210] That is, in each of the positive electrode active materials of Example 1, Example 2, Example 3, and Example 5, the lithium ion diffusion path formed in the lithium complex oxide included therein was formed in a manner directed toward the (012) plane, the (101) plane, and / or the (104) plane, in which lithium ion diffusion is relatively free, rather than in a manner directed toward the (003) plane, in which lithium ion diffusion is masked, and thus, it is expected that the electrochemical characteristics of the positive electrode active material including the above-described lithium complex oxide are improved.

[0211] (3) X-ray Diffraction (XRD) Analysis of Positive Electrode Active Material

[0212] X-ray diffraction analysis was performed on each of the positive electrode active materials prepared according to Preparation Example 1, and thus, peaks attributed to the crystal planes of the lithium complex oxide included in the above-described positive electrode active material were detected. The X-ray diffraction analysis was performed by using a Bruker D8 Advance diffractometer using Cu-Kα radiation at a tube voltage of 40 kV and a tube current of 40 mA, and the intensity ratio between peaks attributed to specific crystal planes is shown in Table 3 and Table 4 below.

[0213] Table 3

[0214]

[0215] Table 4

[0216]

[0217]

[0218] Experimental Example 2. Evaluation of electrochemical characteristics of lithium secondary battery

[0219] For the lithium secondary battery (button cell) prepared in Preparation Example 2, the C-rate efficiency of 5.0C / 0.1C was measured using an electrochemical analysis device (Toyo, Toscat-3100) by applying a temperature of 25°C, a voltage range of 3.0V to 4.3V, and a charge-discharge experiment of a discharge rate of 0.1C to 5.0C. ​

[0220] And, for the same lithium secondary battery, after 50 times of charging / discharging were performed at a temperature of 25°C, a driving voltage range of 3.0 V to 4.4 V, and a condition of 1C / 1C, the ratio of the discharge capacity of the 50th cycle to the initial capacity (cycle capacity retention) was measured.

[0221] The above measurement results are shown in Table 5 below.

[0222] Table 5

[0223] Classification C-rate efficiency (%) Retention @ 50 cy (%) Example 1 82.60％ 88.10％ Example 2 81.00％ 66.80％ Example 3 80.50％ 61.50％ Example 4 80.20％ 64.50％ Example 5 82.70％ 66.50％ Example 6 81.80％ 70.20％ Example 7 80.7％ 75.3％ Comparative Example 1 79.70％ 56.70％ Comparative Example 2 78.40％ 50.90％ Comparative Example 3 77.80％ 56.50％ Comparative Example 4 79.10％ 58.80％ Comparative Example 5 78.70％ 55.60％ Comparative Example 6 76.50％ 49.90％ Comparative Example 7 77.80％ 46.50％ Comparative Example 8 76.80％ 51.70％

[0224] It can be confirmed from the results of Table 5 that the lithium secondary battery prepared by using the positive electrode active material of Examples 1 to 7 shows excellent effects in terms of C-rate efficiency (output characteristics) and cycle capacity retention, compared to the lithium secondary battery prepared by using the positive electrode active material of Comparative Examples 1 to 8.

[0225] Specifically, in the case of Comparative Example 1, it can be confirmed that, as the intentional growth of the crystal plane pointed by the lithium ion diffusion path is excluded, the electrochemical characteristics are lower than those of Examples 1 to 7.

[0226] In addition, in the case of Comparative Example 7 in which the content of NaNO3 added before the first firing is set to 5.0 mol%, as 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 positive electrode active material is excessively reduced, it can be predicted that the electrochemical characteristics are reduced compared to Examples 1 to 7.

[0227] In addition, in the case of Comparative Example 7 in which the content of NaNO3 added before the first firing is set to 5.0 mol%, as 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 positive electrode active material is excessively reduced, it can be predicted that the electrochemical characteristics are reduced compared to Examples 1 to 7.

[0228] Experimental Example 2. Evaluation of stability of positive electrode active material

[0229] In order to measure the weight loss rate of each positive electrode active material prepared according to Preparation Example 1, a thermogravimetric-mass spectrometry (TGA-MS) apparatus was used to measure the weight loss rate under an Ar atmosphere at normal pressure, at a temperature increase rate of 10°C / min until 810°C. In this case, the intensity of the mass spectrometry signal (MS signal) can be changed, and thus the measurement sample amount was set to 65 mg to 66 mg and used.

[0230] The temperature at which the first weight loss peak appeared was also measured by the same method for the positive electrode prepared in Preparation Example 2.

[0231] The above measurement results are shown in Table 6 below.

[0232] Table 6

[0233]

[0234]

[0235] It is confirmed from the results of Table 6 that the thermal stability of the positive electrode active material of Examples 1 to 7 is higher overall than that of the positive electrode active materials of Comparative Examples 1 to 8. It is confirmed that the stability of the positive electrode active material as described above has a complex correlation with the proportion of lithium complex oxides having a grain boundary density of 0.5 or less among all the lithium complex oxides constituting the positive electrode active material and the intentional growth of a specific crystal plane with respect to the lithium complex oxides.

[0236] The above describes the embodiments of the present application, but as long as a person having ordinary skill in the art can make various modifications and changes to the present application by adding, changing, deleting, or adding structural elements, etc. within the scope of the idea of the present application described in the scope of the claimed invention, this is also included in the scope of the claimed invention of the present application.

Claims

1. A positive electrode active material, characterized in that, A lithium complex oxide including a layered structure capable of intercalation / deintercalation of lithium, A ratio of peak intensities attributed to (003) and (012) planes obtained in X-ray diffraction analysis using Cu-Kα rays on the above lithium complex oxide satisfies the following formula 1: Formula 1: 0.131 ≤ I(012) / I(003) ≤ 0.143, The above lithium complex 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 not the same, 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.

2. The positive electrode active material according to claim 1, wherein A ratio of peak intensities attributed to (003) and (104) planes obtained in X-ray diffraction analysis using Cu-Kα rays on the above lithium complex 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 A ratio of peak intensities attributed to (003) and (101) planes obtained in X-ray diffraction analysis using Cu-Kα rays on the above lithium complex 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, characterized by The lithium ion diffusion path formed in the above lithium complex oxide is formed in a manner parallel to a long axis direction of the above lithium complex oxide.

5. The positive electrode active material according to claim 1, characterized by The lithium ion diffusion path formed in the above lithium complex oxide is formed in a manner parallel to the (003) plane.

6. The positive electrode active material according to claim 1, characterized by The lithium ion diffusion path formed in the above lithium complex oxide is formed in a manner pointing to at least one of the (012) plane, the (101) plane, and the (104) plane.

7. The positive electrode active material according to claim 1, wherein The molar ratio of nickel in the above lithium complex oxide represented by the above Chemical Formula 1 calculated by the following formula 4 is 0.6 or more, Formula 4: Ni (molar ratio) = Ni (molar percentage) / (Ni (molar percentage) + Co (molar percentage) + M1 (molar percentage) + M2 (molar percentage) + M3 (molar percentage)).

8. The positive electrode active material according to claim 1, characterized by The average particle diameter of the above lithium complex oxide is 0.1 μm to 20 μm.

9. The positive electrode active material according to claim 1, wherein The above lithium complex oxide includes at least one primary particle, In a cross-sectional scanning electron microscope image of the above lithium complex oxide, for primary particles located on a virtual straight line crossing the center of the above lithium complex oxide, the grain boundary density calculated by the following formula 5 is 0.50 or less, Formula 5: Grain boundary density = (number of interfaces between primary particles located on the above virtual straight line / number of primary particles located on the above virtual straight line).

10. The positive electrode active material according to claim 9, characterized by The above lithium complex oxide has a single crystal structure.

11. The positive electrode active material according to claim 1, characterized in that, the positive electrode active material is a collection of a plurality of lithium complex oxides composed of at least one primary particle, in the collection, the proportion of lithium complex oxides having a grain boundary density of 0.50 or less, calculated from the following Formula 5, for primary particles located on a virtual straight line that passes through the center of the lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide, is 30% or more, Formula 5: Grain boundary density = (number of interfaces between primary particles located on the virtual straight line / number of primary particles located on the virtual straight line).

12. The positive electrode active material according to claim 1, characterized by a coating layer that covers at least a portion of the surface of the lithium complex oxide, the coating layer contains at least one oxide represented by the following Chemical Formula 2, Formula 2: Li a A b O c , wherein A is at least one selected from the group consisting of 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, Gd, and Nd, 0≤a≤10, 0≤b≤8, 2≤c≤15.

13. A positive electrode active material comprising a lithium complex oxide having a layered structure capable of intercalating / deintercalating lithium, characterized in that, the lithium complex oxide contains at least one primary particle, in a cross-sectional scanning electron microscope image of the lithium complex oxide, the proportion of lithium complex oxides having a grain boundary density of 0.50 or less, calculated from the following Formula 5, for primary particles located on a virtual straight line that passes through the center of the lithium complex oxide, is 30% or more, Formula 5: Grain boundary density = (number of interfaces between primary particles located on the virtual straight line / number of primary particles located on the virtual straight line), a lithium ion diffusion path formed within the lithium complex oxide is formed so as to point to at least one crystal plane selected from the group consisting of (012) plane, (101) plane, and (104) plane, the ratio of the peak intensities attributed to (003) plane and (012) plane obtained in X-ray diffraction analysis using Cu-Kα rays of the lithium complex oxide satisfies the following Formula 1: Formula 1: 0.131≤I(012) / I(003)≤0.143, the lithium complex 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 the group consisting of Mn and Al, M2 and M3 are each independently selected from the group consisting of Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, M1 to M3 are not the same, 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.

14. A positive electrode active material comprising a lithium complex oxide having a layered structure capable of intercalating / deintercalating lithium, characterized in that, the positive electrode active material is a collection of a plurality of lithium complex oxides composed of at least one primary particle, in the collection, the proportion of lithium complex oxides having a grain boundary density of 0.50 or less, calculated from the following Formula 5, for primary particles located on a virtual straight line that passes through the center of the lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide, is 30% or more, In the above aggregate, the proportion of the lithium complex oxide in which the grain boundary density calculated from the following Formula 5 for primary particles located on a virtual straight line that passes through the center of the lithium complex oxide in a cross-sectional scanning electron microscope image of the lithium complex oxide is 0.50 or less is 30% or more, Formula 5: Grain boundary density = (number of interfaces between primary particles located on the virtual straight line / number of primary particles located on the virtual straight line), The lithium ion diffusion path formed within the lithium complex oxide is formed in a manner that points to at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane, The ratio of the peak intensities attributed to the (003) plane and the (012) plane obtained in X-ray diffraction analysis using Cu-Kα rays for the lithium complex oxide satisfies the following Formula 1: Formula 1: 0.131 ≤ I(012) / I(003) ≤ 0.143, The lithium complex 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 not the same as 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.

15. A positive electrode, characterized by comprising: A positive electrode active material according to any one of claims 1 to 14.

16. A lithium secondary battery, characterized by comprising: A positive electrode using the positive electrode according to claim 15.

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