Positive electrode active material and lithium secondary battery using it

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 positive electrode active material and a lithium secondary battery using the same, wherein the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material are formed to point towards specific crystal planes, and the growth of the crystal planes pointed towards by the lithium ion diffusion pathways is improved. [Background technology]

[0002] A battery stores electricity by using electrochemically reactive materials at its positive and negative electrodes. A typical example of such a battery is the lithium-ion secondary battery, which stores electrical energy through the difference in chemical potential that occurs when lithium ions are intercalated / deintercalated at the positive and negative electrodes.

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

[0004] Lithium composite oxides are used as positive electrode active materials in lithium secondary batteries, and examples of composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are being studied.

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

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

[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 production of the cathode paste and gas generation during charge and discharge after electrode manufacturing. Residual Li2CO3 not only increases the swelling phenomenon of the cell and reduces the cycle, but also causes the battery to bulge.

[0008] To compensate 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 there is a problem that an increase in the Ni content in the cathode active material brings structural instability due to 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, not only cathode active materials containing lithium composite oxides with a polycrystalline structure but also cathode active materials containing lithium composite oxides with a single crystal structure 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 the stability of O₂) is partially improved for 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 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 the presence of an excessive amount of a lithium composite oxide having a phase other than the layered structure may cause deterioration of the positive electrode active material which is an aggregate of these. Such deterioration of the positive electrode active material acts as a cause of reduction in capacity and shortening of life.

[0013] Therefore, there is an apparent 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 the stability. Therefore, when the capacity characteristics of the positive electrode active material are excessively improved, conversely, there is a risk that stable charge-discharge performance cannot be exhibited due to a decrease in the structural stability of the particles constituting the positive electrode active material.

[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] Furthermore, an object of the present invention is to provide a positive electrode active material in which the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material are formed to point toward a specific crystal plane, and the growth of the crystal plane pointed toward by the lithium ion diffusion pathways is improved, thereby improving the electrochemical properties and stability of the positive electrode active material.

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

[0018] The objects of the present invention are not limited to those 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. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be embodied by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0019] According to one aspect of the present invention, a positive electrode active material is provided which includes a lithium composite oxide with a layered structure capable of lithium intercalation / deintercalation, wherein the ratio of peak intensities attributed to the (003) plane and the (012) plane obtained by 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] Furthermore, the lithium composite oxide may have a shape with long and short axes, in which case the lithium ion diffusion pathway formed within the lithium composite oxide may be formed parallel to the long 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 face at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane, thereby improving the lithium ion diffusion ability of the lithium composite oxide and further improving the electrochemical characteristics of the positive electrode active material containing the lithium composite oxide.

[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 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 grain boundaries = (number of interfacial 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 multiple lithium composite oxides, each consisting of at least one primary particle, and the proportion of lithium composite oxides in the aggregate where the density of grain boundaries calculated by the following formula 5 is 0.50 or less, relative to primary particles that lie on a hypothetical straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide, may be 30% or more. (Formula 5) The density of grain boundaries = (number of interface surfaces between primary particles on the imaginary straight line / number of primary particles on the imaginary straight line)

[0025] Furthermore, according to another aspect of the present invention, as a positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation / deintercalation, the lithium composite oxide comprises at least one primary particle, and the density of the grain boundaries calculated by the following formula 5 for a primary particle that lies on a virtual straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide is 0.50 or less. (Formula 5) The density of grain boundaries = (number of interface surfaces between primary particles on the imaginary straight line / number of primary particles on the imaginary straight line) A positive electrode active material is provided in which the lithium ion diffusion pathway formed within the lithium composite oxide is directed toward at least one crystal plane selected from the (012), (101), and (104) planes.

[0026] Furthermore, according to yet another aspect of the present invention, as a positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation / deintercalation, the positive electrode active material is an aggregate of a plurality of lithium composite oxides, each consisting of at least one primary particle, and of the aggregate, the proportion of lithium composite oxides whose grain boundary density, calculated by the following formula 5, is 0.50 or less for primary particles lying on a virtual straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide is 30% or more. (Formula 5) The density of grain boundaries = (number of interface surfaces between primary particles on the imaginary straight line / number of primary particles on the imaginary straight line) A positive electrode active material is provided in which the lithium ion diffusion pathway formed within the lithium composite oxide is directed toward at least one crystal plane selected from the (012), (101), and (104) planes.

[0027] Furthermore, according to yet another aspect of the present invention, a lithium secondary battery is provided that uses a positive electrode active material as defined in this application. [Effects of the Invention]

[0028] According to the present invention, the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material for lithium secondary batteries are formed to direct lithium ion diffusion to crystal planes where lithium ion diffusion is relatively free, rather than to crystal planes where lithium ion diffusion is blocked. This is expected to improve the electrochemical properties of the positive electrode active material containing the lithium composite oxide.

[0029] Furthermore, by intentionally improving the growth of crystal planes within the lithium composite oxide where the diffusion of lithium ions is relatively free, the diffusion capacity of lithium ions through the lithium composite oxide can be improved.

[0030] On the other hand, as described in the Journal of The Electrochemical Society, Volume 164, Number 7, A1534-A1544, generally, in order to obtain uniform single crystals of lithium composite oxides that constitute the positive electrode active material for lithium secondary batteries, sintering must be carried out under relatively harsh conditions.

[0031] The lithium composite oxides thus produced, which have a single-crystal structure or a structure close to a single-crystal structure (for example, with a reduced number of primary particles constituting secondary particles), may have improved stability compared to lithium composite oxides with a polycrystalline structure due to a reduction in specific surface area.

[0032] However, under harsh firing conditions, the cation mixing phenomenon may increase, and this cation mixing phenomenon can cause phase transformation of the lithium composite oxide, resulting in the formation of an excess of lithium composite oxide having a quasi-safe phase or a rock-salt phase in addition to the originally intended layered structure. Thus, the coexistence of an excess of lithium composite oxide having phases other than the layered structure with the layered lithium composite oxide can lead to degradation of the positive electrode active material.

[0033] As a result, in the present invention, the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material are formed to point towards a specific crystal plane, and by improving the growth of the crystal plane pointed towards by the lithium ion diffusion pathways, it is possible to impart sufficient electrochemical properties and stability to the lithium composite oxide by single crystallization performed under relatively less stringent firing conditions alone.

[0034] In addition to the effects described above, the specific effects of the present invention will be described below, along with a detailed explanation of the specific matters for carrying out the invention. [Brief explanation of the drawing]

[0035] [Figure 1] Figures 1 and 2 are schematic diagrams illustrating cross-sectional images of lithium composite oxides contained in positive electrode active materials according to various embodiments of the present invention. [Figure 2] Figures 1 and 2 are schematic diagrams illustrating cross-sectional images of lithium composite oxides contained in positive electrode active materials according to various embodiments of the present invention. [Figure 3] Figures 3 to 6 are TEM images of lithium composite oxides contained in the positive electrode active material according to Examples 1, 2, 3, and 5 of the present invention, and the TEM images show the lithium ion diffusion pathways within the lithium composite oxide. [Figure 4]Figures 3 to 6 are TEM images of lithium composite oxides contained in the positive electrode active material according to Examples 1, 2, 3, and 5 of the present invention, and the TEM images show the lithium ion diffusion pathways within the lithium composite oxide. [Figure 5] Figures 3 to 6 are TEM images of lithium composite oxides contained in the positive electrode active material according to Examples 1, 2, 3, and 5 of the present invention, and the TEM images show the lithium ion diffusion pathways within the lithium composite oxide. [Figure 6] Figures 3 to 6 are TEM images of lithium composite oxides contained in the positive electrode active material according to Examples 1, 2, 3, and 5 of the present invention, and the TEM images show the lithium ion diffusion pathways within the lithium composite oxide. [Modes for carrying out the invention]

[0036] For the convenience of making the present invention easier to understand, certain terms are defined in this application. Unless otherwise specifically defined in this application, the scientific and technical terms used in this invention have meanings that are generally understood by those who have ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms.

[0037] Explanation of terms As used in this application, the term "lithium composite oxide" refers to a layered oxide capable of intercalation / deintercalation of lithium (lithium ions), and includes lithium and a metal element. In particular, as used in this application, the lithium composite oxide refers to a lithium-nickel composite oxide containing lithium and nickel. Furthermore, as used in this application, the lithium composite oxide 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 multiple particles are aggregated).

[0038] As used in this application, the term "single crystal" refers to a crystal in which no crystal grains or grain boundaries are contained within the particles. Furthermore, 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 multiple primary particles. "Lithium composite oxide having a single crystal structure" refers to a primary particle made of lithium composite oxide that consists of multiple crystal grains, or a particle in which no crystal grain boundaries are contained within the primary particle.

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

[0040] In this application, the term "grain boundary density" refers to 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 a secondary particle, the higher the grain boundary density; conversely, the fewer primary particles present within a secondary particle, the lower the grain boundary density.

[0041] In this application, the density of grain boundaries may be calculated by the number of primary particles on a hypothetical straight line that crosses the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide, according to the following formula 5. In this case, the direction of the straight line may be the direction that crosses the center of the lithium composite oxide in the short axis direction. (Formula 5) The density of grain boundaries = (number of interface surfaces between primary particles on the imaginary straight line / number of primary particles on the imaginary straight line)

[0042] If there is one primary particle within the secondary particle, the grain boundary density calculated by the formula is 0. If there are three or more primary particles within the secondary particle, the grain boundary density calculated by the formula will exceed 0.5.

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

[0044] The term "positive electrode active material" as used in this application is a broad concept that includes the secondary particles described above. A single secondary particle itself may be the positive electrode active material, but in this application, a collection of multiple secondary particles having the same and / or different grain boundary densities may be defined as the positive electrode active material.

[0045] Therefore, in the definition of the positive electrode active material described later, the explanation of secondary particles having the characteristics of an aggregate of multiple secondary particles and the explanation of the secondary particles constituting the positive electrode active material and the primary particles constituting the secondary particles must be understood separately.

[0046] The following describes in more detail a lithium secondary battery using the positive electrode active material and a positive electrode containing the positive electrode active material according to the present invention.

[0047] positive electrode active material According to one aspect of the present invention, a positive electrode active material is provided which includes a layered lithium composite oxide capable of lithium intercalation / deintercalation.

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

[0049] The primary particle refers to a single crystal grain (grain or crystallite), and the secondary particle refers to an aggregate formed by the aggregation of multiple primary particles. The primary particle may be rod-shaped, elliptical, and / or circular, or irregular in shape.

[0050] Voids and / or grain boundaries may exist between the primary particles that constitute the secondary particles. For example, the primary particles may separate from adjacent primary particles within the secondary particle to form internal voids. Alternatively, the primary particles may form surfaces within the secondary particle by contacting the internal voids without forming grain boundaries by contacting adjacent primary particles.

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

[0052] Here, the average particle size of the primary particles is within the range of 0.1 μm to 10 μm, preferably 1.0 μm to 10 μm, thereby realizing the optimal density of the positive electrode produced using the positive electrode active material according to various embodiments of the present invention. The average particle size of the secondary particles may vary depending on the number of aggregated primary particles, but may be between 3 μm and 20 μm.

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

[0054] The density of the grain boundaries may be calculated based on the number of primary particles P that lie on a hypothetical straight line L that crosses the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide, using the following equation 5. (Formula 5) The density of grain boundaries = (number of interface surfaces (B) between primary particles on the aforementioned hypothetical straight line (L) / number of primary particles (P) on the aforementioned hypothetical straight line (L))

[0055] For example, the density of the grain boundaries of the lithium composite oxide, calculated with reference to Figures 1 and 2, which are schematic diagrams illustrating cross-sectional images of the lithium composite oxide contained in the positive electrode active material according to various embodiments of the present invention, is as shown in Table 1 below. [Table 1]

[0056] By having a grain boundary density of 0.90 or less, as represented by formula 5, the surface area and grain interface of the lithium composite oxide can be reduced, thereby reducing the possibility of side reactions between the positive electrode active material and the electrolyte, and improving not only the high-temperature stability but also the storage stability of the positive electrode active material.

[0057] On the other hand, according to one embodiment of the present invention, among the aggregate of secondary particles, the proportion of lithium composite oxide in which the density of grain boundaries calculated by formula 5 is 0.50 or less, relative to primary particles that lie 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 30% or more.

[0058] The surface area of ​​the lithium composite oxide contained in the positive electrode active material and the grain boundaries defined by the primary particles constituting the lithium composite oxide are regions where side reactions can occur at the interface and surface between the positive electrode active material and the electrolyte. Here, as shown in Figures 1 and 2, the grain boundaries defined by the primary particles present in the lithium composite oxide can be understood, for example, as the interface between two adjacent primary particles.

[0059] In this case, by reducing the surface area of ​​the lithium composite oxide and the particle interface defined by the primary particles within the lithium composite oxide, it is possible to improve the thermal stability of the positive electrode active material and prevent or mitigate problems caused by the instability of the positive electrode active material (for example, reduced storage stability due to gas generation from side reactions with the electrolyte).

[0060] As a result, by ensuring that the proportion of lithium composite oxides in the aggregate of secondary particles where the density of grain boundaries calculated by formula 5 is 0.50 or less is 30% or more, it is possible to provide a positive electrode active material that can stably maintain its electrochemical properties.

[0061] On the other hand, the proportion of lithium composite oxides in the aggregate of secondary particles in which the density of grain boundaries calculated by formula 5 is 0.50 or less can be improved by modifying the process conditions of some stages in the synthesis process of the lithium composite oxide. For example, the proportion of lithium composite oxides with a grain boundary density of 0.50 or less can be improved by adjusting the primary calcination temperature / time for the precursor of the lithium composite oxide and / or the secondary calcination temperature / time for the result of the primary calcination of the precursor.

[0062] However, the more severe the calcination conditions for the precursor and / or the lithium composite oxide, the more the cation mixing phenomenon may increase, and this cation mixing phenomenon may induce phase transformation of the lithium composite oxide.

[0063] Therefore, by ensuring that the proportion of lithium composite oxides in the aggregate of secondary particles whose grain boundary density calculated by formula 5 is 0.50 or less is 95% or less, preferably 90% or less, and more preferably 80% or less, a balance can be achieved between lithium composite oxides with a grain boundary density of 0.50 or less and lithium composite oxides with a grain boundary density greater than 0.50 in the aggregate of secondary particles.

[0064] A lithium composite oxide according to one embodiment of the present invention may contain at least Ni and Co. Furthermore, the lithium composite oxide may further contain Mn and / or Al in addition to Ni and Co, and may further contain dopants other than the aforementioned metal elements.

[0065] Specifically, the lithium composite oxide is represented by the following formula 1. (chemical 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, and M2 and M3 are independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, and M1 to M3 are distinct from each other, with 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, and more preferably 0.8 or more, among the lithium composite oxides represented by formula 1 above. (Formula 4) Ni(molar ratio)=Ni(mol%) / (Ni(mol%)+Co(mol%)+M1(mol%)+M2(mol%)+M3(mol%))

[0067] As mentioned above, high-Ni type lithium composite oxides have the advantage of relatively higher electrochemical properties compared to lithium composite oxides with low Ni content. However, an increase in the Ni content of the lithium composite oxide leads to structural instability due to Li / Ni cation mixing. This structural instability of the positive electrode active material can cause rapid degradation of lithium secondary batteries not only at high temperatures but also at room temperature.

[0068] However, even if the lithium composite oxide according to the present invention has a high-Ni type composition, it is possible to 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.

[0069] Specifically, by forming the lithium ion diffusion pathways within the lithium composite oxide parallel to the long axis direction of the lithium composite oxide, the diffusion capacity of lithium ions through the lithium composite oxide can be improved.

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

[0071] Furthermore, it is preferable that the lithium ion diffusion pathway is formed parallel to the (003) plane, which is confirmed by X-ray diffraction analysis using Cu-Kα rays on the lithium composite oxide. If the lithium ion diffusion pathway within the lithium composite oxide is formed to face the (003) plane, the diffusion of lithium ions may be blocked by the (003) plane, which may reduce the diffusion capacity of lithium ions through the lithium composite oxide.

[0072] On the other hand, the lithium ion diffusion pathway can be formed to direct at least one crystal plane selected from the (012), (101), and (104) planes, which allow lithium ions to diffuse relatively freely with respect to the (003) plane, thereby improving the diffusion capacity of lithium ions through the lithium composite oxide.

[0073] In other words, according to the present invention, the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material for lithium secondary batteries are formed to direct lithium ion diffusion to crystal planes where lithium ion diffusion is relatively free, rather than directing to crystal planes where lithium ion diffusion is blocked. This is expected to improve the electrochemical properties of the positive electrode active material containing the lithium composite oxide.

[0074] In this case, the lithium ion diffusion path being directed toward a specific crystal plane means that the angle between 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, and more preferably 45 degrees or less.

[0075] Furthermore, according to the present invention, by adding flux to a mixture of the hydroxide precursor and lithium raw material (e.g., LiOH) before primary calcination to obtain the lithium composite oxide by heat treatment of the hydroxide precursor of the lithium composite oxide, and then performing heat treatment, the growth of crystal planes directed by the lithium ion diffusion pathway can be improved. In particular, by adding flux to a mixture of the hydroxide precursor and lithium raw material (e.g., LiOH) before primary calcination, and then performing heat treatment, the growth of crystal planes in which lithium ions can diffuse relatively freely with respect to crystal planes in which lithium ion diffusion is blocked can be further improved.

[0076] As a flux used to improve the growth of relatively free crystal planes through lithium ion diffusion, for example, alkali metal compounds such as NaOH, KCl, and NaNO3 (hydroxides, chlorides, nitrides, carbonates, sulfates, etc.) or chlorides such as NH4Cl may be used.

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

[0078] If I(012) / I(003) calculated by Equation 1 is less than 0.131, the growth of the (012) plane, where lithium ion diffusion is relatively free compared to the (003) plane, where lithium ion diffusion is blocked, will be insufficient, and the effect of improving the electrochemical properties of the lithium composite oxide due to the growth of the crystal plane directed by the lithium ion diffusion pathway will be minimal.

[0079] On the other hand, if I(012) / I(003) calculated by formula 1 is greater than 0.143, the growth of the (012) plane formed along the length of the lithium ion diffusion path may become excessively large, which could lead to a decrease in the diffusion capacity of lithium ions through the lithium composite oxide or a decrease in the stability of the crystal structure of the lithium composite oxide.

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

[0081] Similarly, if I(104) / I(003) calculated by Equation 2 is less than 0.630, the growth of the (104) plane, where lithium ion diffusion is relatively free compared to the (003) plane, will be insufficient, and the effect of improving the electrochemical properties of the lithium composite oxide due to the growth of the crystal plane directed by the lithium ion diffusion pathway will be minimal.

[0082] On the other hand, if I(104) / I(003) calculated by formula 2 is greater than 0.698, the growth of the (104) plane formed along the length of the lithium ion diffusion path may become excessively large, which could lead to a decrease in the diffusion capacity of lithium ions through the lithium composite oxide or a decrease in the stability of the crystal structure of the lithium composite oxide.

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

[0084] Similarly, if I(101) / I(003) calculated by Equation 3 is less than 0.379, the growth of the (101) plane, where lithium ion diffusion is relatively free compared to the (003) plane, where lithium ion diffusion is blocked, will be insufficient, and the effect of improving the electrochemical properties of the lithium composite oxide due to the growth of the crystal plane directed by the lithium ion diffusion pathway will be minimal.

[0085] On the other hand, if I(101) / I(003) calculated by formula 3 is greater than 0.421, the growth of the (101) plane formed along the length of the lithium ion diffusion path may become excessively large, which could lead to a decrease in the diffusion capacity of lithium ions through the lithium composite oxide or a decrease in the stability of the crystal structure of the lithium composite oxide.

[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 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.

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

[0088] As a result, 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 the aggregation of the primary particles. If the coating layer exists discontinuously, it may exist in an island-like manner.

[0089] The coating layer present in this manner can help maintain the high electrochemical properties of lithium composite oxides, particularly high-Ni type lithium composite oxides, while also contributing to the elimination of their low structural stability.

[0090] Furthermore, 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 the aggregation of the primary particles.

[0091] The coating layer may contain at least one oxide represented by the following chemical formula 2. That is, the coating layer can be defined as a region where the oxide represented by the following chemical formula 2 exists. (chemical 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, where 0 ≤ a ≤ 10, 0 ≤ b ≤ 8, and 2 ≤ c ≤ 15.)

[0092] Furthermore, the coating layer may be in a form in which different types of oxides exist simultaneously within a single layer, or in a form in which the different types of oxides represented by the formula 2 exist in separate layers.

[0093] The oxide represented by Formula 2 may be physically and / or chemically bonded to the primary particles represented by Formula 1. Alternatively, the oxide may exist in a state where it forms a solid solution with the primary particles represented by Formula 1.

[0094] The lithium composite oxide according to this embodiment can enhance structural stability by including a coating layer that covers at least a portion of the surface of the primary particles (e.g., the interfaces between the primary particles) and / or the secondary particles formed by the aggregation of the primary particles. Furthermore, when such a lithium composite 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. In addition, the oxide can reduce residual lithium within the lithium composite oxide and act as a lithium ion transport pathway.

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

[0096] The said oxide is an oxide in which lithium and an element represented by A are composited, or an oxide of A, wherein the said 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 also be expressed as such. Furthermore, non-restrictive 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 Examples include Li4Ba, Li2TiO3, LiTi7O4, and LiTi2O4. The aforementioned examples are merely for convenience to enhance understanding, and the oxides defined in this application are not limited to the aforementioned examples.

[0097] In other embodiments, the oxide may be an oxide in which lithium and at least two elements represented by A are combined, or it may further include an oxide in which lithium and at least two elements represented by A are combined. An oxide in which lithium and at least two elements represented by A are combined is, 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 Other options are also acceptable, but the term is not necessarily limited to these.

[0098] Here, the oxide can exhibit a concentration gradient that decreases from the surface of the secondary particle toward the center of the secondary particle. As a result, the concentration of the oxide can decrease from the surface of the secondary particle toward the center of the secondary particle.

[0099] As described above, the oxide exhibits a concentration gradient that decreases from the surface of the secondary particles toward the center of the secondary particles, thereby effectively reducing the residual lithium present on the surface of the lithium composite oxide and preventing side reactions caused by unreacted residual lithium. Furthermore, the oxide can prevent a decrease in crystallinity in the inner region of the surface of the lithium composite oxide. In addition, the oxide can prevent the overall structure of the lithium composite oxide from collapsing during the electrochemical reaction.

[0100] Furthermore, the coating layer may include a first coating layer containing at least one oxide represented by formula 2, and a second coating layer containing at least one oxide represented by 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 portion of the exposed surface of the primary particles that are 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 that is not covered by the first coating layer and at least a portion of the surface of the first coating layer.

[0102] Lithium-ion battery In yet another aspect of the present invention, a positive electrode can be provided that includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. Here, the positive electrode active material layer may include positive electrode active materials according to various embodiments of the present invention. Therefore, since the positive electrode active material is as described above, a detailed explanation will be omitted for convenience, and only the remaining undescribed components will be described below.

[0103] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0104] The positive electrode active material layer may be manufactured by applying a positive electrode slurry composition, which includes a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

[0105] In this case, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98.5 wt%, relative to the total weight of the positive electrode active material layer. When included in this content range, excellent capacity characteristics can be observed, but the material is not necessarily limited to this range.

[0106] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite, carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber, metal powders or metal fibers such as copper, nickel, aluminum, and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or conductive polymers such as polyphenylene derivatives. One of these may be used alone or a mixture of two or more. The conductive material may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0107] The binder plays a role in improving adhesion between positive electrode active material particles and 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used. The binder may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0108] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode may be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0109] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the cathode active material, conductive material, and binder, and then provides a viscosity that allows for excellent thickness uniformity during coating for cathode manufacturing, taking into consideration the coating thickness and production yield of the slurry.

[0110] In other embodiments, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0111] Furthermore, according to yet another aspect of the present invention, an electrochemical element including the aforementioned positive electrode may be provided. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0112] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive and negative electrodes. Here, since the positive electrode is as described above, for convenience, a detailed explanation will be omitted, and only the remaining components not mentioned above will be described in detail below.

[0113] The lithium secondary battery may further selectively include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, 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 located 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 chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0116] The negative electrode active material layer may be manufactured by applying a negative electrode slurry composition, which includes the negative electrode active material together with a conductive material and optionally a binder, 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 alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide, or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystalline carbon and high-crystalline carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural 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 aforementioned negative electrode active material may be present in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

[0119] The binder may 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 bonding between the conductive material, active material, and current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, 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 as a component to further improve the conductivity of the negative electrode active material, in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, 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, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, and nickel powder, conductive whiskey 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 may be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0122] In other embodiments, the negative electrode active material layer may be manufactured by coating a negative electrode slurry composition, prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0123] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0124] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type 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 include an organic solvent and a lithium salt.

[0126] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as 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 include a double-bonded aromatic ring or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, or sulfolanes may be used. 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 that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the electrolyte performance can be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0127] The lithium salt may be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. 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 within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0128] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to 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 exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0130] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-shaped, or coin-shaped using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell used as a power source for small devices, but may also be preferably used as a unit battery in medium-to-large battery modules containing multiple battery cells.

[0131] According to yet another aspect of the present invention, a battery module and / or a battery pack including the lithium secondary battery as a unit cell can be provided.

[0132] The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0133] The present invention will be described in more detail below 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] Manufacturing Example 1. Manufacturing 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 lithium composite oxide hydroxide precursor was 3.0 μm.

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

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

[0137] Finally, the cathode active material containing lithium composite oxide was obtained by heat treatment (secondary calcination) in a calcination furnace while maintaining an O2 atmosphere and increasing the temperature by 2°C per minute to 700°C for 12 hours.

[0138] Example 2 The cathode active material was prepared in the same manner as in Example 1, except that 3.0 mol% NH4Cl was used instead of 2.0 mol% NaNO3.

[0139] Example 3 The cathode 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.

[0140] Example 4 The cathode 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.

[0141] Example 5 The cathode 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.

[0142] Example 6 The cathode 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.

[0143] Example 7 The cathode 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.

[0144] Comparative Example 1 The cathode active material was manufactured in the same manner as in Example 1, except that NaNO3 was not added before the primary calcination.

[0145] Comparative Example 2 The cathode 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.

[0146] Comparative Example 3 The cathode 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.

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

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

[0149] Comparative Example 6 The cathode active material was manufactured in the same manner as in Example 1, except that the NaNO3 content added before the primary calcination was set to 3.0 mol%.

[0150] Comparative Example 7 The cathode active material was manufactured in the same manner as in Example 1, except that the amount of NaNO3 added before the primary calcination was set to 5.0 mol%.

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

[0152] Manufacturing Example 2: Manufacturing of Lithium-ion Rechargeable Batteries A cathode slurry was prepared by dispersing 94 wt% of each cathode active material, 3 wt% of artificial graphite, and 3 wt% of PVDF binder, as prepared according to Production Example 1, in 3.5 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was applied to a 20 μm thick aluminum (Al) thin film, which served as the cathode current collector, and dried. The cathode was then manufactured by roll pressing. The loading level of the cathode was 7 mg / cm². 2 The electrode density is 3.2 g / cm³. 3 That was the case.

[0153] A coin cell was manufactured using a commonly known manufacturing process, with lithium foil as the counter electrode relative to the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and a liquid electrolyte containing ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7, with LiPF6 present at a concentration of 1.15 M.

[0154] Experimental Example 1. Structural Analysis of Cathode Active Material (1) Cross-sectional SEM analysis of the positive electrode active material After obtaining cross-sectional SEM images of the lithium composite oxide contained in the cathode active material manufactured according to Manufacturing Example 1 using FE-SEM (Bruker), the proportion of lithium composite oxides with a grain boundary density of 0.50 or less, calculated by the following equation 5, was calculated from the cross-sections of 100 lithium composite oxides captured in the cross-sectional SEM images. (Formula 5) Grain boundary density = (Number of interfaces between primary particles on a hypothetical straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide / Number of primary particles on the said hypothetical straight line)

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

[0156] (2) TEM analysis of positive electrode active material In Manufacturing Example 1, TEM images of the lithium composite oxide contained in the positive electrode active material according to Examples 1, 2, 3, and 5 were obtained, and the directionality of the lithium ion diffusion pathway formed within the lithium composite oxide was confirmed from the TEM images. Furthermore, the crystal plane of the lithium composite oxide directed by the lithium ion diffusion pathway formed within the lithium composite oxide was confirmed by indexing the SAD diffraction pattern. The measurement results are shown in Figures 3 to 6.

[0157] Referring to Figures 3 to 6, it can be confirmed that the lithium ion diffusion pathways formed within the lithium composite oxide contained in the respective positive electrode active materials of Examples 1, 2, 3, and 5 were formed in the same direction as the long axis of the lithium composite oxide. In particular, it can be confirmed that the lithium ion diffusion pathways formed within the lithium composite oxide were formed in a direction substantially parallel to the (003) plane.

[0158] It can be confirmed that the lithium ion diffusion pathways formed within the lithium composite oxide are directed toward the (012) plane, the (101) plane and / or the (104) plane.

[0159] In other words, the lithium ion diffusion pathways formed within the lithium composite oxide contained in the respective positive electrode active materials according to Examples 1, 2, 3, and 5 are formed to direct lithium ion diffusion to the (012), (101), and / or (104) planes, where lithium ion diffusion is relatively free, rather than to the (003) plane where lithium ion diffusion is blocked. This is expected to improve the electrochemical properties of the positive electrode active material containing the lithium composite oxide.

[0160] (3) XRD analysis of positive electrode active material X-ray diffraction (XRD) analysis was performed on each positive electrode active material manufactured according to Manufacturing Example 1, and peaks attributable to the crystal planes of the lithium composite oxide contained in the positive electrode active material were detected. The XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å), and the intensity ratios between peaks attributable to specific crystal planes are shown in Tables 3 and 4 below. [Table 3] [Table 4]

[0161] Experimental Example 2. Evaluation of the electrochemical properties of lithium secondary batteries. The C-rate efficiency of the lithium secondary battery (coin cell) manufactured in Manufacturing Example 2 was measured at 5.0C / 0.1C through charge-discharge experiments using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, a voltage range of 3.0V to 4.3V, and a discharge rate of 0.1C to 5.0C.

[0162] Furthermore, the same lithium secondary battery was subjected to 50 charge / discharge cycles under 1C / 1C conditions at 25°C and a drive voltage range of 3.0V to 4.4V. The ratio of the discharged capacity at the 50th cycle to the initial capacity (cycle capacity retention) was then 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 lithium secondary batteries manufactured using the positive electrode active materials of Examples 1 to 7 show superior performance in terms of C-rate efficiency (output characteristics) and cycle capacity maintenance rate compared to lithium secondary batteries manufactured using the positive electrode active materials of Comparative Examples 1 to 8.

[0165] Specifically, in the case of Comparative Example 1, intentional growth of the crystal plane directed by the lithium ion diffusion pathway is eliminated, resulting in lower electrochemical properties compared to Examples 1 to 7.

[0166] On the other hand, in Comparative Example 7, where the NaNO3 content added before primary calcination was 5.0 mol%, it is expected that the electrochemical properties were reduced compared to Examples 1 to 7 due to an excessive decrease in the proportion of lithium composite oxides with a grain boundary density of 0.5 or less among the total lithium composite oxides constituting the positive electrode active material.

[0167] Furthermore, in Comparative Example 8, where the NaCl content added before primary calcination was 5.0 mol%, it is expected that the electrochemical properties were actually reduced compared to Examples 1 to 8 due to an excessive increase in the proportion of lithium composite oxides with a grain boundary density of 0.5 or less among the total lithium composite oxides constituting the positive electrode active material.

[0168] Experimental Example 2. Evaluation of the stability of the positive electrode active material. To measure the weight loss rate of each positive electrode active material produced according to Production Example 1, the weight loss rate was measured using a TGA-MS instrument while heating to 810°C at a heating rate of 10°C / min under atmospheric pressure and an Ar atmosphere. Since the intensity of the MS signal may vary during this process, the sample volume used was 65 mg to 66 mg.

[0169] The weight loss rate of the positive electrode manufactured in manufacturing example 2 was similarly measured, and the temperature at which the weight loss peak first appeared was determined.

[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 from Examples 1 to 7 is generally higher than that of the positive electrode active materials from Comparative Examples 1 to 8. It can be confirmed that this stability of the positive electrode active material is related in combination with the proportion of lithium composite oxides having a grain boundary density of 0.5 or less among the total lithium composite oxides constituting the positive electrode active material, and the intentional growth of the lithium composite oxides on specific crystal planes.

[0172] Although embodiments of the present invention have been described above, a person with ordinary skill in the art can modify and change the present invention in various ways, such as by adding, changing, deleting, or adding components, without departing from the spirit of the invention as described in the claims, and this can also be said to be 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, The molar ratio of Ni to all metal elements other than lithium in the lithium composite oxide is 0.6 or more. The ratio of peak intensities attributed to the (003) plane and the (104) plane obtained from X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide satisfies the following equation 2: The positive electrode active material exhibits a weight loss rate of 0.91% or less when heated to 810°C at a heating rate of 10°C / min under an Ar atmosphere at normal pressure. [Formula 2] 0.630≦I(104) / I(003)≦0.698

2. A positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation / deintercalation, The molar ratio of Ni to all metal elements other than lithium in the lithium composite oxide is 0.6 or more. The ratio of peak intensities attributed to the (003) plane and the (101) plane obtained from X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide satisfies the following equation 3: The positive electrode active material exhibits a weight loss rate of 0.91% or less when heated to 810°C at a heating rate of 10°C / min under an Ar atmosphere at normal pressure. [Formula 3] 0.379≦I(101) / I(003)≦0.421

3. The positive electrode active material according to claim 1 or 2, wherein the lithium ion diffusion pathway formed within the lithium composite oxide is formed parallel to the long axis direction of the lithium composite oxide.

4. The positive electrode active material according to claim 1 or 2, wherein the lithium ion diffusion pathway formed within the lithium composite oxide is formed parallel to the (003) plane.

5. The positive electrode active material according to claim 1 or 2, wherein the lithium ion diffusion pathway formed within the lithium composite oxide is formed to direct at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane.

6. The lithium composite oxide is the positive electrode active material according to claim 1 or 2, represented by the following chemical formula 1. (Chem.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, 1.0 ≤ f ≤ 2.0.)

7. The lithium composite oxide contains at least one primary particle, The positive electrode active material according to claim 1 or 2, wherein, in a cross-sectional SEM image of the lithium composite oxide, the density of grain boundaries calculated by the following formula 5 for primary particles lying on a hypothetical straight line crossing the center of the lithium composite oxide is 0.50 or less. [Formula 5] Grain boundary density = (Number of interface surfaces between primary particles on the imaginary straight line / Number of primary particles on the imaginary straight line)

8. The positive electrode active material is an aggregate of multiple lithium composite oxides, each consisting of at least one primary particle. The positive electrode active material according to claim 1 or 2, wherein, in the aggregate, the proportion of lithium composite oxides in which the density of crystal grain boundaries calculated by the following formula 5 is 0.50 or less for primary particles that lie on a hypothetical straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide is 30% or more. [Formula 5] Grain boundary density = (Number of interface surfaces between primary particles on the imaginary straight line / Number of primary particles on the imaginary straight line)

9. The present invention further includes a coating layer covering at least a portion of the surface of the lithium composite oxide, The positive electrode active material according to claim 1 or 2, wherein the coating layer comprises at least one oxide represented by the following chemical formula 2. (Case 2) Li ａ A ｂ O ｃ (Here, A is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd. 0 ≤ a ≤ 10, 0 ≤ b ≤ 8, 2 ≤ c ≤ 15.

10. The positive electrode active material according to claim 1 or 2, wherein the ratio of peak intensities attributed to the (003) plane and the (110) plane obtained from X-ray diffraction analysis using Cu-Kα rays on the lithium composite oxide (I(110) / I(003)) is 0.149 or more and 0.172 or less.

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