WO2016175597A1 - Cathode active material for secondary battery, preparation method therefor, and secondary battery comprising same - Google Patents

Abstract

The present invention provides a cathode active material for a secondary battery, and a secondary battery comprising the same, the cathode active material comprising: a core of secondary particles formed by the aggregation of primary particles of a nickel manganese cobalt-based lithium composite metal oxide; an intermediate layer positioned on the core and comprising rod-shaped nickel manganese cobalt-based lithium composite metal oxide particles radially aligned from the center of active material particles toward the surface thereof; and a shell positioned on the intermediate layer and comprising a nickel manganese cobalt-based lithium composite metal oxide. According to the present invention, the cathode active material for a secondary battery can exhibit high capacity, long lifetime and excellent stability when applied to a battery and, particularly, can minimize performance deterioration during a high voltage since each layer of a core, an intermediate layer and a shell has an optimized structure and composition, in consideration of the electrochemical mechanism according to the position in cathode active material particles. Therefore, the cathode active material is useful as a cathode active material of a high voltage battery.

Description

Cathode active material for secondary battery, manufacturing method thereof and secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 2015-0061836 dated April 30, 2015 and Korean Patent Application No. 2016-0052634 dated April 29, 2016. The contents are included as part of this specification.

Technical Field

The present invention relates to a cathode active material for a secondary battery, a manufacturing method thereof, and a secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate have been commercialized and widely used.

Lithium transition metal composite oxide is used as a cathode active material of a lithium secondary battery, and lithium cobalt composite metal oxide of LiCoO ₂ having a high operating voltage and excellent capacity characteristics is mainly used. However, since LiCoO ₂ is very poor in thermal properties due to destabilization of crystal structure due to de-lithium and is expensive, there is a limit to using LiCoO ₂ as a power source in fields such as electric vehicles.

As a material for replacing LiCoO ₂ , lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed. Among them, research and development of lithium nickel composite metal oxides having a high reversible capacity of about 200mAh / g, which is easy to implement a large-capacity battery, are being actively studied. However, LiNiO ₂ has a poor thermal stability compared to LiCoO _2, and when an internal short circuit occurs due to pressure from the outside in a charged state, the positive electrode active material itself is decomposed to cause the battery to rupture and ignite.

Accordingly, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a method of replacing a portion of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi _{1 - x} Co _x O ₂ (x = 0.1 ~ 0.3) in which a part of nickel is substituted with cobalt shows excellent charge and discharge characteristics and life characteristics, but has a problem of low thermal stability. In the case of a nickel manganese lithium composite metal oxide in which a part of Ni is substituted with Mn having excellent thermal stability, and a nickel manganese cobalt lithium composite metal oxide substituted with Mn and Co (hereinafter simply referred to as 'NMC lithium oxide') The output characteristics are low, and there is a fear of dissolution of metal elements and consequent deterioration of battery characteristics.

In order to solve this problem, a lithium transition metal oxide having a concentration gradient of the metal composition has been proposed. This method is carried out by synthesizing the core material, coating a material having a different composition to the outside to prepare a double layer, and then mixing with a lithium salt to heat treatment. In this method, the metal composition of the core and the outer layer can be synthesized differently in synthesis. However, the continuous improvement of the concentration composition of the metal composition is not sufficient in the resulting positive electrode active material. have.

As another method, researches are being made to increase the Ni content in NMC-based lithium oxide for high energy density in small automotive and power storage batteries. In general, in the positive electrode active material, capacity, life, or stability have a trade-off in which the life and stability of a battery decrease rapidly as the capacity increases. Accordingly, a method of using only within a limited composition and voltage range, a method of stabilizing a structure by restricting a partial composition of NMC-based lithium oxide with heterogeneous elements, and a method of reducing surface side reactions through coating have been proposed. However, in all these methods, there is a limit to fundamentally improve the electrochemical and thermal stability of the active material, and the high energy density of the battery is also difficult because the deterioration of performance is accelerated at high voltage.

The first technical problem to be solved by the present invention is to provide a cathode active material for a secondary battery that can be made high in capacity, has excellent lifespan characteristics and stability, and does not cause performance deterioration even at high voltages.

The second technical problem to be solved of the present invention is to provide a manufacturing method for producing the positive electrode active material.

The third technical problem to be solved of the present invention is to provide a positive electrode including the positive electrode active material.

The fourth technical problem to be solved of the present invention is to provide a lithium secondary battery including the positive electrode.

In order to solve the above problems, according to an embodiment of the present invention, a secondary particle core formed by agglomeration of primary particles of a nickel manganese cobalt-based first lithium composite metal oxide; An intermediate layer disposed on the core and including rod-shaped nickel manganese cobalt-based second lithium composite metal oxide particles oriented in a radial direction from a center of an active material particle to a surface thereof; And it is located on the intermediate layer, to provide a cathode active material for a secondary battery comprising a shell containing a nickel manganese cobalt-based third lithium composite metal oxide.

In addition, according to another embodiment of the present invention, a metal salt solution for forming a core containing nickel, cobalt and manganese, and a shell forming agent containing nickel, cobalt and manganese at different concentrations from the core salt metal salt solution Preparing a metal salt solution; The shell-forming metal salt solution in the core-forming metal salt solution so that the mixing ratio of the core-forming metal salt solution and the shell-forming metal salt solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. Simultaneously adding a chelating agent and a basic aqueous solution to prepare a cathode active material precursor; And a step of mixing the cathode active material precursor and the lithium salt, followed by heat treatment, wherein the rate of the shell forming metal salt solution added to the core forming metal salt solution is different for each core, intermediate layer, and shell forming section in the active material particles. It provides a method for producing a cathode active material for a secondary battery.

According to another embodiment of the present invention, a cathode including the cathode active material is provided.

Furthermore, according to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

The positive electrode active material for a secondary battery according to the present invention has an optimized structure and composition in consideration of the electrochemical action mechanism according to the position of the positive electrode active material particles for each layer of the core, the intermediate layer, and the shell, thereby providing high capacity, long life, and excellent performance. Stability can be exhibited and performance degradation can be minimized, especially at high voltages. As a result, it is useful as a positive electrode active material of a high voltage battery.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a schematic cross-sectional view showing a cathode active material for a secondary battery according to an embodiment of the present invention.

2 is a scanning electron microscope (SEM) observation picture of the cross section of the positive electrode active material prepared in Example 1.

3 is a transmission electron microscope (TEM) observation picture of the cross section of the positive electrode active material prepared in Example 1.

4 is a scanning electron microscope (SEM) observation picture of the cross section of the positive electrode active material prepared in Comparative Example 1.

5 is a transmission electron microscope (TEM) observation picture of the cross section of the positive electrode active material prepared in Comparative Example 1.

FIG. 6 is a graph illustrating a result of evaluating a capacity retention rate of a lithium secondary battery including a cathode active material in Example 1 and Comparative Example 1. FIG.

7 is a graph showing the results of evaluating the thermal stability of the lithium secondary battery including the positive electrode active material in Example 1 and Comparative Example 1.

[Description of the code]

1: core 2: middle layer

3: shell 10: positive electrode active material

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

1 is a schematic cross-sectional view showing a cathode active material for a secondary battery according to an embodiment of the present invention. 1 is only an example for describing the present invention and the present invention is not limited thereto.

Referring to FIG. 1, a cathode active material 10 for a secondary battery according to an exemplary embodiment of the present invention may include a core 1, an intermediate layer 2 disposed on the core, and a shell disposed on the intermediate layer. It has a three-layer structure including 3), wherein the core (1) is a secondary particle formed by assembling primary particles of nickel manganese cobalt-based first lithium composite metal oxide (hereinafter simply NMC-based first lithium oxide), The intermediate layer includes rod-shaped nickel manganese cobalt-based second lithium composite metal oxide (hereinafter simply NMC-based second lithium oxide) particles oriented from the center of the active material particles to the surface, and the shell is nickel-manganese cobalt-based third lithium A composite metal oxide (hereinafter simply NMC-based third lithium oxide) is included.

In the present invention, the "rod" means a rod shape long in the direction of one axis, and specifically, the aspect ratio, the length of the long axis passing through the particle center, and the short axis length perpendicular to the long axis and passing the particle center. The ratio (= length of the major axis / length of the minor axis) is greater than 1 and less than or equal to 20, and is distinguished from a particulate of aspect ratio 1 and a fiber phase of greater than 20 aspect ratio.

Specifically, the primary particles of the NMC-based first lithium oxide included in the core 1 of the cathode active material may have a shape of at least one of granular and rod shaped. More specifically, the primary particles may be rod-shaped, wherein the core may be secondary particles in which rod-shaped primary particles are randomly assembled without orientation. As the rod-shaped primary particles are assembled and included in such a randomly aggregated form, the structural stability of the cathode active material may be improved, and as a result, battery performance may be improved.

The NMC-based first lithium oxide included in the core 1 may specifically be a compound of Formula 1 below:

[Formula 1]

Li _a1 M1 _x1 M2 _y1 M3 _z1 M4 _w1 O _{2 + δ1}

(In Formula 1, M1, M2 and M3 are each independently, any one or two or more metal elements selected from the group consisting of Ni, Co and Mn, M4 is Fe, Na, Mg, Ca, Ti, It contains any one or two or more elements selected from the group consisting of V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0 <a1≤1.1, 0 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 1, 0 ≤ z1 ≤ 1, 0 ≤ w1 ≤ 0.1, 0.0 ≤ δ1 ≤ 0.02, 0 <x1 + y1 + z1 ≤ 1)

The composition of the first lithium oxide of Formula 1 is an average composition of the entire core.

In particular, the first lithium oxide is more specifically LiNi _{0 . 6} Mn _{0 . 2} Co _{0 . 2} O ₂ or LiNi _{0 . 9} Mn _{0 . 05} Co _{0 . The amount} of nickel contained in the first lithium oxide, such as ₀₅ O ₂ , may be lithium nickel manganese cobalt-based oxide having 50 atomic% or more, more specifically 70 atomic% or more.

In addition, the concentration of at least one metal element of nickel, cobalt and manganese contained in the core 1 is continuously increased or decreased in the core, that is, from the center of the cathode active material particles to the interface between the core and the intermediate layer. The concentration gradient can be indicated. That is, even in the primary particles themselves that form the core, the metal element exhibits a concentration gradient, and even in the secondary particle core formed by assembling the primary particles, the metal element is reduced from the center of the cathode active material to the surface of the core 1. Concentration gradients may be indicated.

Such a core 1 may have a thickness of 0.5 μm to 3 μm when the distance from the center of the cathode active material particles to the interface between the core and the intermediate layer is the thickness of the core. When the thickness is in the above range, the battery performance is greatly improved due to the structure stabilization of the cathode active material.

On the other hand, in the positive electrode active material, the intermediate layer 2 located on the surface of the core 1 includes rod-shaped NMC-based second lithium oxide particles having radial crystal orientation from the particle center to the surface.

Specifically, in the NMC-based second lithium oxide particles, oxide particles neighboring each other from the surface of the core 1 toward the particle surface grow in a predetermined path to form the intermediate layer 2. At this time, one rod-like NMC-based second lithium oxide may be grown continuously by the thickness of the intermediate layer 2, or another NMC-based second lithium oxide particles may be aligned with one rod-like NMC-based second lithium oxide particle. It may be laminated to form a layer structure and grow in a constant path. Since the rod-like NMC-based second lithium oxide particles are continuously arranged toward the particle surface direction, the contact resistance in the particles is significantly reduced, and electrical energy generated inside the particles is efficiently transferred, resulting in high capacity. Can be represented. In addition, the insertion of lithium ions in the spaces formed between the predetermined paths becomes easier, so that the output of the battery can be improved and high capacity characteristics can be exhibited.

In the intermediate layer 2, the NMC-based second lithium oxide particles are specifically rod-shaped having an aspect ratio (ratio of the short axis length passing through the particle center to the length of the long axis passing through the oxide particle center) of more than 1 and 20 or less. May be particles. If the aspect ratio of the particles is 1 or less, there is a concern that the inter-particle contact resistance inside the particles may increase, and if the aspect ratio of the particles exceeds 20, the length of the particles becomes too long and close to the fibrous phase. There is a fear of cracking of the positive electrode active material due to the deterioration of mechanical properties. In addition, when another NMC-based second lithium oxide particle is stacked in a line with respect to one rod-shaped NMC-based second lithium oxide particle to form a layer structure and grows in a constant path, the anode active material particles are gradually moved from the center to the surface. The aspect ratio of the NMC-based second lithium oxide particles may increase.

In addition, the NMC-based second lithium oxide included in the intermediate layer 2 may specifically be a compound of Formula 2 below.

[Formula 2]

Li _a2 M1 _x2 M2 _y2 M3 _z2 M4 _w2 O _{2 + δ2}

(In Formula 2, M1, M2 and M3 are each independently, any one or two or more metal elements selected from the group consisting of Ni, Co and Mn, M4 is Fe, Na, Mg, Ca, Ti, It contains any one or two or more elements selected from the group consisting of V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0 <a2≤1.1, 0 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 1, 0 ≤ z2 ≤ 1, 0 ≤ w2 ≤ 0.1, 0.0 ≤ δ2 ≤ 0.02, and 0 <x2 + y2 + z2 ≤ 1)

The composition of the second lithium oxide of Formula 2 is the average composition of the entire shell.

In particular, the second lithium oxide has a lithium nickel manganese cobalt oxide having a content of 50 atomic% or more, more specifically 55 atomic% or more, in the second lithium oxide in that the capacity and stability of the battery may be improved. Can be.

In addition, the concentration of at least one of the metal elements among nickel, cobalt and manganese contained in the intermediate layer 2 is the interface between the intermediate layer 2 and the shell 3 from the interface between the core 1 and the intermediate layer 2. It can show increasing or decreasing concentration gradient. In this case, the above-described concentration of the metal element may be continuously increased or decreased from the center of the positive electrode active material particles to the interface between the intermediate layer 2 and the shell 3, or at the interface between the core 1 and the intermediate layer 2. The concentration step of the metal element, i.e., a discontinuous section or an inflection point may appear.

Such intermediate layer 2 has a thickness of 2 μm to 10 μm when the distance from the interface between the core 1 and the intermediate layer 2 to the interface between the intermediate layer 2 and the shell 3 is the thickness of the intermediate layer. Can have When the thickness is in the above-described range, the contact resistance inside the particles according to the structure peculiar to the intermediate layer 2 is reduced, and the effect of improving the high capacity and output characteristics of the battery is large.

Moreover, in the said positive electrode active material, the shell 3 is formed on the surface of the said intermediate | middle layer 2 above.

The shell 3 may be a thin film of NMC-based third lithium oxide, or particles of NMC-based third lithium oxide may be dispersed in a dot structure on an intermediate layer.

The NMC-based third lithium oxide included in the shell 3 may specifically be a compound of Formula 3 below.

[Formula 3]

Li _a3 M1 _x3 M2 _y3 M3 _z3 M4 _w3 O _{2 + δ3}

(In Formula 3, M1, M2 and M3 are each independently, any one or two or more metal elements selected from the group consisting of Ni, Co and Mn, M4 is Fe, Na, Mg, Ca, Ti, It contains any one or two or more elements selected from the group consisting of V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B, 0 <a3≤1.1, 0 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 1, 0 ≤ z3 ≤ 1, 0 ≤ w3 ≤ 0.1, 0.0 ≤ δ 3 ≤ 0.02, and 0 <x 3 + y 3 + z 3 ≤ 1)

The composition of the third lithium oxide of Formula 3 is the average composition of the entire shell.

Among these, the third lithium oxide has a lithium nickel manganese cobalt oxide having a content of 50 atomic% or more, more specifically 55 atomic% or more, in the third lithium oxide in that the capacity and stability of the battery can be improved. Can be.

In addition, at least one metal element of nickel, cobalt and manganese contained in the shell 3 may have a concentration gradient that increases or decreases from an interface between the intermediate layer 2 and the shell 3 to the surface of the cathode active material particle. Can be represented. In this case, the concentration of the metal element described above may be continuously increased or decreased throughout the positive electrode active material, or the concentration of the metal element is discontinuously changed at the interface between the intermediate layer 2 and the shell 3, or Inflection points may appear.

In addition, the concentration of nickel, cobalt and manganese contained in the shell 3 may be constant. As such, when the concentration of all metal elements in the shell 3 is constant, the stability and electrochemical properties of the structure itself may be improved.

Such a shell 3 may have a thickness of 0.1 μm to 1 μm when the distance from the interface between the intermediate layer 2 and the shell 3 to the surface of the positive electrode active material is the thickness of the shell. When the thickness is in the above range, the battery performance is greatly improved due to the structure stabilization of the cathode active material.

In addition, in the positive electrode active material according to an embodiment of the present invention, the distance from the center of the positive electrode active material particles to the interface between the core and the intermediate layer is called the thickness of the core, and from the interface of the core and the intermediate layer to the interface between the intermediate layer and the shell. When the distance of the intermediate layer is called the thickness of the intermediate layer, and the distance from the interface of the intermediate layer and the shell to the surface of the cathode active material is the thickness of the shell, the core, the intermediate layer and the shell satisfy the thickness range as defined above, Has a thickness of 3% to 30% with respect to the average particle diameter of the positive electrode active material, and the intermediate layer and the shell may have a thickness ratio of the intermediate layer to the shell ratio of 1: 0.01 to 1: 0.5. When meeting the optimum thickness conditions of each of these layers, the effects due to the unique morphology and orientation of the lithium composite metal oxide particles in the respective regions of the core interlayer and the shell can be maximized, resulting in life characteristics and heat in battery applications. Stability can be greatly improved.

In particular, when the thickness of the shell out of the thickness ratio of the intermediate layer and the shell is less than 1: 0.01 thickness ratio, the improvement effect according to the shell formation is insignificant, and when the thickness of the intermediate layer exceeds 1: 0.01 thickness ratio when rolling in the electrode manufacturing process There is a risk of breakage. In addition, when the thickness of the shell exceeds the thickness ratio of 1: 1, the movement distance of lithium ions becomes long, and thus there is a concern that the resistance increases.

As described above, the cathode active material having the above-described structure according to an embodiment of the present invention has a concentration at which the concentration of at least one metal element of nickel, cobalt, and manganese increases or decreases in each of the core, the intermediate layer, and the shell formation period. Gradient, or from the center of the core 1, the intermediate layer 2, the shell 3, the positive electrode active material particles 10 to the interface between the intermediate layer 2 and the shell 3, or the positive electrode active material particles ( It may also show a concentration gradient that increases or decreases continuously from the center to the surface. Moreover, two or more concentration gradient inclinations of the metal which shows a concentration gradient in each said area | region may be sufficient.

In the present invention, "the concentration of the metal element continuously shows the concentration gradient" means that the concentration of the metal element is from the center of the core 1, the intermediate layer 2, the shell 3, and the positive electrode active material particle 10. It means that it exists in the concentration distribution which changes gradually from the center of the particle | grains 10 to the surface, or to the interface of (2) and the shell 3, or to the surface. Specifically, the concentration distribution is from the center of the core 1, the intermediate layer 2, the shell 3, the positive electrode active material particles 10 to the interface between the intermediate layer 2 and the shell 3, or the particles 10 The change in metal concentration per 0.1 μm from the center to the surface is 0.1 atomic% to 30 atomic%, more specifically 0.1 atomic% to 20 atomic%, and more specifically, based on the total atomic weight of the metal included in the positive electrode active material. As may be the difference of 1 atomic% to 10 atomic%.

As such, when the concentration of the metal is continuously changed according to the position in the cathode active material particle, a sudden phase boundary region does not exist, so that the crystal structure is stabilized and thermal stability is increased. At this time, when the concentration gradient value of the metal element is constant from the center of the cathode active material particles to the surface, the effect of improving the structural stability may be further improved.

In addition, by varying the concentration at the center and the surface of the positive electrode active material particles through the concentration gradient, it is possible to easily utilize the characteristics of the metal to further improve the battery performance improvement effect of the positive electrode active material.

Specifically, in the positive electrode active material according to an embodiment of the present invention, the concentration of nickel contained in the positive electrode active material may decrease while having a continuous concentration gradient from the center of the positive electrode active material particles to the interface between the intermediate layer and the shell. . In this case, the gradient of the concentration gradient of nickel may be constant from the center of the cathode active material particle to the interface between the intermediate layer and the shell. When the concentration of nickel in the core maintains a high concentration and decreases toward the shell, the reduction in capacity can be prevented while showing thermal stability.

In addition, in the positive electrode active material 10 according to an embodiment of the present invention, the concentration of cobalt contained in the positive electrode active material is continuous from the center of the positive electrode active material particle 10 to the interface between the intermediate layer 2 and the shell 3. The concentration gradient of the cobalt may be constant from the center of the cathode active material particle 10 to the interface between the intermediate layer 2 and the shell 3. When the concentration of cobalt in the core 1 maintains a high concentration and the concentration decreases toward the shell 3, the reduction in capacity can be prevented while reducing the amount of cobalt used.

In addition, in the positive electrode active material 10 according to an embodiment of the present invention, the concentration of manganese contained in the positive electrode active material is from the center of the positive electrode active material particles 10 to the interface between the intermediate layer 2 and the shell 3. Can be increased with a continuous concentration gradient. In this case, the concentration gradient of manganese may be constant from the center of the cathode active material particle 10 to the surface. When the concentration of manganese in the core 1 maintains a low concentration and the concentration increases toward the shell 3, excellent thermal stability can be obtained without reducing the capacity.

In addition, in the positive electrode active material 10 according to an embodiment of the present invention, the concentration of nickel contained in the positive electrode active material is independently from the center of the positive electrode active material particles 10, the intermediate layer (2) and the shell (3) Cobalt and manganese concentrations decrease with a continuous concentration gradient from the center of the positive electrode active material particles 10 to the interface between the intermediate layer 2 and the shell 3 with a continuous concentration gradient up to the interface of. can do. As such, the concentration of nickel decreases toward the surface of the cathode active material particle 10 and the concentration of cobalt and manganese increases, thereby exhibiting thermal stability while maintaining capacity characteristics.

In addition, in the cathode active material 10 according to an embodiment of the present invention, the concentration of nickel contained in the cathode active material is from the center of the cathode active material particle 10 to the interface between the intermediate layer 2 and the shell 3. Decrease with a continuous concentration gradient, the concentration of any one of the manganese and cobalt metal contained in the positive electrode active material is constant from the center of the positive electrode active material particles 10 to the interface between the intermediate layer (2) and the shell (3). can do.

In addition, the concentration of nickel contained in the positive electrode active material is decreased while having a continuous concentration gradient from the center of the positive electrode active material particles 10 to the surface, each independently, and the concentration of cobalt and manganese is reduced in the positive electrode active material particles 10 It can increase with a continuous concentration gradient from center to surface.

In addition, the concentration of nickel contained in the positive electrode active material decreases while having a continuous concentration gradient from the center of the positive electrode active material particles 10 to the surface, and the concentration of any one of manganese and cobalt contained in the positive electrode active material. May be constant from the center of the cathode active material particle 10 to the surface.

In addition, in the positive electrode active material 10 according to an embodiment of the present invention, the concentration of nickel contained in the positive electrode active material is from the center of the positive electrode active material particles 10 to the interface between the intermediate layer 2 and the shell 3, or When decreasing with a continuous concentration gradient to the surface of the positive electrode active material particles, the difference in the average concentration of nickel in the core (1) and shell (3) is 10 atoms based on the total atomic weight of nickel contained in the positive electrode active material % To 70 atomic%, more specifically 10 atomic% to 45 atomic%, even more specifically 20 atomic% to 40 atomic%.

On the other hand, in the present invention, the concentration gradient structure and concentration of the metal in the positive electrode active material particles are characterized by an Electron Probe Micro Analyzer (EPMA), Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP). -AES) or Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and more specifically, using EPMA from the center of the cathode active material to the surface. While moving, the atomic ratio of each metal can be measured.

In addition, the positive electrode active material according to an embodiment of the present invention is between the primary particles forming the core, the rod-shaped particles forming the intermediate layer, or the rod-shaped particles forming the primary particles and the intermediate layer forming the core It may further include a gap located between the primary particles constituting the positive electrode active material, such as. These pores serve to increase the reaction area of the active material with the electrolyte by buffering during rolling for electrode production and allowing the electrolyte to easily penetrate into the active material and react with the core. Specifically, the positive electrode active material including the pores may have a porosity of 20% to 30% by volume with respect to the total volume of the positive electrode active material. When having a porosity within the above range, it can exhibit an excellent buffering effect and an increase in reaction area with the electrolyte solution without lowering the mechanical strength of the active material itself. In particular, if the porosity in the positive electrode active material exceeds 30% by volume, there is a fear of lowering the structural stability of the positive electrode active material. In consideration of the remarkable improvement of the pore-forming effect, more specifically, the porosity of 20% by volume to 25% by volume may be exhibited. The porosity of the positive electrode active material can be calculated from the difference between the apparent density and the true density.

The positive electrode active material 10 having the above-described structure may have an average particle diameter (D ₅₀ ) of 3 μm to 50 μm in consideration of the specific surface area and the positive electrode mixture density, and may improve the rate characteristics and initial capacity characteristics due to the specific structure. Considering it may be one having an average particle diameter (D ₅₀ ) of 5㎛ to 30㎛. In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material may be defined as the particle size at 50% of the particle size distribution. The average particle diameter (D ₅₀ ) of the cathode active material particles according to an embodiment of the present invention may be measured using, for example, a laser diffraction method. For example, in the method for measuring the average particle diameter (D ₅₀ ) of the positive electrode active material, the particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) to about 28 after examining the kHz ultrasound of 60 W in output, it can be used to calculate the average particle diameter (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

The cathode active material 10 of the structure according to the embodiment of the present invention, the metal salt solution for forming a core containing nickel, cobalt and manganese, and nickel, cobalt and manganese at different concentrations from the core salt metal salt solution. Preparing a metal salt solution for shell formation comprising a (step 1); The shell-forming metal salt solution in the core-forming metal salt solution such that the mixing ratio of the core-forming metal salt solution and the shell-forming metal salt solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. Preparing a cathode active material precursor by adding a chelating agent and a basic aqueous solution at the same time, varying the speed of the shell forming metal salt solution added to the core forming metal salt solution for each core, intermediate layer and shell forming section ( Step 2); And it may be prepared by a manufacturing method comprising the step (step 3) to heat treatment after mixing the positive electrode active material precursor and a lithium salt. Hereinafter, each step will be described in detail.

In the manufacturing method for producing the positive electrode active material, step 1 is a step of preparing a metal salt solution for forming a core and a metal salt solution for forming a shell containing nickel, cobalt and manganese.

The metal salt solution for shell formation may be prepared in the same manner as the metal salt solution for core formation, except that nickel, cobalt, and manganese are contained at different concentrations from the metal salt solution for core formation. Specifically, the core salt metal salt solution and shell salt metal salt solution may be prepared by adding a salt containing nickel salt, cobalt salt, manganese salt, and other metals (M4) to a solvent, specifically, water. Alternatively, a solution containing each of nickel salts, cobalt salts, manganese salts, and M4 salts, specifically, an aqueous solution may be prepared and then mixed.

As the metal salt, sulfates, nitrates, acetates, halides, hydroxides or oxyhydroxides can be used, and the like, and are not particularly limited as long as they can be dissolved in water. For example, Co (OH) ₂ , CoOOH, Co (OCOCH ₃ ) ₂ 4H ₂ O, Co (NO ₃ ) ₂ 6H ₂ O or Co (SO ₄ ) ₂ ㆍ 7H ₂ O, etc. Any one or a mixture of two or more of these may be used.

Next, in the manufacturing method for producing the positive electrode active material, step 2 is a step of preparing a positive electrode active material precursor by mixing and reacting the metal salt solution for core formation and the metal salt solution for shell formation prepared in step 1.

Specifically, the positive electrode active material precursor can be prepared by mixing the core salt metal salt solution and the shell salt metal salt solution while simultaneously mixing and reacting the chelating agent and the basic aqueous solution.

The addition of the shell forming metal salt solution to the core forming metal salt solution is carried out continuously. By continuously supplying and reacting the metal salt solution for shell formation as described above, a precipitate having a concentration gradient in which metal concentration is continuous from the center of the particles to the surface in one coprecipitation reaction process can be obtained. At this time, the concentration gradient and the slope of the metal in the active material precursor can be easily controlled by the composition and the mixing feed ratio of the metal salt solution for core formation and the metal salt solution for shell formation.

In addition, by controlling the reaction rate of the metal salt solution for forming the core and the metal salt solution for forming the shell, it is possible to form a three-layer structure of a core, an intermediate layer, and a shell having the respective characteristic structures as described above. In detail, the density of the metal complex oxide formed may vary according to the position in the precursor particles prepared by controlling the reaction rate of the metal salt solution for core formation and the metal salt solution for shell formation. It has a unique shape and orientation.

The reaction rate may be controlled by controlling the input rate of the shell-forming metal salt solution to the core-forming metal salt solution, and additionally pH and reaction temperature may be further controlled. Specifically, the input rate of the metal salt solution for shell formation may be 10g / min to 20g / min, the shell formation to be added to the core salt metal salt solution for each core, intermediate layer and shell forming section within the above-mentioned input speed range It can be carried out by increasing or decreasing the speed of the metal salt solution. More specifically, the input rate of the metal salt solution for shell formation may increase within the above range from the core forming section to the shell forming section, and more specifically, in the core forming section, from 10 g / min to 15 g. / Min, 12g / min to 18g / min in the middle layer forming section, at an increased rate than in the core forming section, and 15g / min to 20g / min in the shell forming section, at an increased rate than in the middle layer forming section Can be. At this time, the reaction temperature may be 50 ℃ to 80 ℃.

In addition, the pH in the reaction system may be 10 to 12. If the pH is out of the above range, there is a risk of changing the size of the cathode active material precursor to be prepared or causing particle splitting. In addition, metal ions may be eluted on the surface of the positive electrode active material precursor to form various oxides by side reactions. Such pH adjustment can be controlled through the addition of a basic aqueous solution. In consideration of the formation of the structure peculiar to the positive electrode active material according to the present invention, the reaction may be performed while gradually reducing the pH within the above range.

In addition, in step 2, the chelating agent may be used an aqueous ammonia solution, an ammonium sulfate solution or a mixture thereof.

The chelating agent may be added in an amount such that the molar ratio of 0.5 to 1 per mole of the mixed solution of the metal salt for forming the core and shell. In general, the chelating agent reacts with the metal in a molar ratio of at least 1: 1 to form a complex, but the unreacted complex which does not react with the basic aqueous solution may be converted into an intermediate product, recovered as a chelating agent, and reused. In addition, the chelating usage can be lowered than usual. As a result, the crystallinity of the positive electrode active material can be increased and stabilized.

In addition, the basic aqueous solution may be prepared by dissolving a base such as sodium hydroxide, potassium hydroxide and the like in water.

The concentration of the basic aqueous solution may be 2M to 10M. When the concentration of the basic aqueous solution is less than 2M there is a fear that the particle formation time is long, the tap density is lowered and the yield of the coprecipitation reactant is lowered. In addition, when the concentration of the basic aqueous solution exceeds 10M, the particles grow rapidly due to the rapid reaction, so that it is difficult to form uniform particles, and the tap density may also decrease.

In addition, in the preparation of the positive electrode active material precursor, the speed of the metal salt solution for forming the shell and the basic aqueous solution may be the same, and the rate of the chelating agent is the metal salt solution for forming the shell It may be 5 to 7 times slower than the speed of. For example, the rate of the chelating agent in the core forming section may be 1g / min to 5g / min, the rate of the basic aqueous solution may be 10g / min to 20g / min.

In addition, the reaction for the preparation of the positive electrode active material precursor may be carried out in a temperature range of 30 ℃ to 80 ℃ under an inert atmosphere such as nitrogen. In addition, the stirring process may be selectively performed to increase the reaction rate during the reaction, wherein the stirring rate may be 100rpm to 2000rpm.

As a result of the reaction in step 2 as described above, a cathode active material precursor having a three-layer structure of a core, an intermediate layer, and a shell is precipitated. The precipitated cathode active material precursor may be selectively separated after separation according to a conventional method, and the drying process may be performed at 110 ° C. to 400 ° C. for 15 hours to 30 hours.

Next, in the manufacturing method for the production of the positive electrode active material, step 3 is a step of preparing a positive electrode active material by mixing the positive electrode active material precursor prepared in step 2 with a lithium salt and heat treatment.

As the lithium salt, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides may be used. The lithium salts are not particularly limited as long as they can be dissolved in water. Specifically, the lithium salt is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH H ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, or Li ₃ C ₆ H ₅ O _{7 and the} like, any one or a mixture of two or more thereof may be used.

In addition, when the cathode active material precursor and the lithium salt are mixed, a sintering agent may be optionally further added. The sintering agent is specifically a compound containing ammonium ions such as NH ₄ F, NH ₄ NO ₃ , or (NH ₄ ) ₂ SO ₄ ; Metal oxides such as B ₂ O ₃ or Bi ₂ O ₃ ; Or a metal halide such as NiCl ₂ or CaCl _2, and any one or a mixture of two or more thereof may be used. The sintering agent may be used in an amount of 0.01 mol to 0.2 mol with respect to 1 mol of the cathode active material precursor. When the content of the sintering agent is too low, less than 0.01 mole, the effect of improving the sintering characteristics of the positive electrode active material precursor may be insignificant, and when the content of the sintering agent is too high, exceeding 0.2 mole, the performance of the positive electrode active material decreases due to the excessive amount of the sintering agent. And an initial capacity of the battery may decrease during charging and discharging.

In addition, when the positive electrode active material precursor and the lithium salt are mixed, a moisture removing agent may be optionally further added. Specifically, the water removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more thereof may be used. The moisture remover may be used in an amount of 0.01 mol to 0.2 mol with respect to 1 mol of the cathode active material precursor.

In addition, the heat treatment process in step 3 may be performed at 800 ℃ to 1100 ℃. If the temperature during the heat treatment is less than 800 ℃, there is a risk of lowering the discharge capacity per unit weight, cycle characteristics and operating voltage due to the residual of the unreacted raw materials, and if it exceeds 1100 ℃ unit due to the generation of side reactions There is a fear of lowering the discharge capacity per weight, lowering cycle characteristics, and lowering operating voltage.

In addition, the heat treatment process may be performed for 5 to 30 hours in an oxidizing atmosphere such as air or oxygen, or a reducing atmosphere containing nitrogen or hydrogen. Through the heat treatment process under such conditions, the diffusion reaction between the particles can be sufficiently performed, and the metal diffusion occurs even in a portion where the internal metal concentration is constant, and as a result, a metal oxide having a continuous metal concentration distribution from the center to the surface is obtained. Can be prepared.

Meanwhile, preliminary firing may be optionally performed at 250 ° C. to 650 ° C. for 5 hours to 20 hours before the heat treatment process. In addition, the annealing process for 10 hours to 20 hours at 600 ℃ to 750 ℃ after the heat treatment process may be optionally performed.

As described above, the cathode active material manufactured by the above-described manufacturing method has an optimized structure and composition in consideration of the electrochemical action mechanism according to the position of the anode active material particles for each layer of the core, the intermediate layer, and the shell. Accordingly, when the cathode active material is applied to a battery, high capacity, high life and excellent stability may be exhibited, and in particular, performance degradation may be minimized even at high voltage.

According to another embodiment of the present invention, a cathode including the cathode active material is provided.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, carbon, nickel, titanium on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of typically 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In addition, the cathode active material layer may include a conductive material and a binder together with the cathode active material described above.

In this case, the conductive material is used to impart conductivity to the electrode. In the battery constituted, the conductive material may be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and 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 powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives, and the like, or a mixture of two or more kinds thereof may be used. The conductive material may typically be included in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof, and the like, and one or a mixture of two or more thereof may be used. The binder may be included in an amount of 1% by weight to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode active material and optionally, a composition for forming a positive electrode active material layer including a binder and a conductive material may be prepared by applying a positive electrode current collector, followed by drying and rolling. In this case, the type and content of the cathode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode. Do.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

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 fibers, 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; Metal oxides capable of doping and undoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular for ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be included. In this case, the additive may be included in an amount of 0.1% by weight to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicle fields such as hybrid electric vehicle (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Preparation Example 1: Preparation of Cathode Active Material

Nickel sulfate: cobalt sulfate: manganese sulfate was mixed in water at a molar ratio of 90: 5: 5 to prepare a metal salt solution for core formation at a concentration of 2M, and nickel sulfate: cobalt sulfate: manganese sulfate was dissolved in water at 50:20:30. By mixing in a molar ratio of to prepare a metal salt solution for shell formation of 2M concentration.

3 liters of deionized water was added to the coprecipitation reactor (capacity 30L), and nitrogen gas was purged into the reactor at a rate of 0.5 liters / minute to remove dissolved oxygen in water and to form a non-oxidizing atmosphere in the reactor. Moreover, it stirred at 1000 rpm, maintaining the reactor temperature at 50 degreeC. After the core salt metal salt solution was introduced into the reactor, the shell salt metal salt solution was mixed at a rate of 14 g / min. At the same time, a 10 M ammonia solution, a chelating agent, was continuously added to the reactor at a rate of 2 g / min, and a 4 M NaOH aqueous solution was continuously added to the reactor at a rate of 14 g / min to maintain a pH of 11. The coprecipitation reaction was performed while stirring the impeller speed of the reactor at 500 rpm. 10 minutes after the start of the coprecipitation reaction, the feed rate of the aqueous metal salt for shell formation supplied at the time when the particle size of the precipitate became 2 μm was changed to 16 g / min, and the metal salt aqueous solution for shell formation was again added at the shell forming portion. Was added at a rate of 17 g / min. A coprecipitation reaction was carried out over a total of 16 hours to obtain a precipitate. The obtained precipitate was washed sequentially with sodium hydroxide and deionized water, filtered and dried in a warm air dryer at 130 ° C. for 12 hours to obtain a cathode active material precursor having an average particle diameter (D ₅₀ ) of 11 μm.

LiOH was mixed as a lithium salt in the cathode active material precursor prepared above, heated at a temperature rising rate of 2 ° C./min, and then maintained at 280 ° C. for 10 hours, followed by preliminary firing at 850 ° C. for 15 hours. The particles were obtained.

[ Production Example  2 and 3: Of positive electrode active material  Produce]

The same method as in Preparation Example 1, except that nickel sulfate, cobalt carbonate, and manganese sulfate were mixed to prepare a metal salt aqueous solution for forming a core and an aqueous metal salt solution for forming a shell, respectively, in a molar ratio as shown in Table 1 below. It was carried out to prepare a cathode active material.

	Metal salt aqueous solution for core formation (molar ratio)			Metal salt solution (molar ratio) for shell formation
	Nickel Sulfate	Cobalt sulfate	Manganese sulfate	Nickel Sulfate	Cobalt sulfate	Manganese sulfate
Preparation Example 1	90	5	5	50	20	30
Preparation Example 2	85	0	20	55	15	30
Preparation Example 3	80	5	20	55	15	30

[ Example  1-3: Manufacture of Lithium Secondary Battery]

A lithium secondary battery was manufactured using the cathode active materials prepared in Preparation Examples 1 to 3, respectively.

In detail, the positive electrode active material, the carbon black conductive material, and the PVdF binder prepared in Preparation Examples 1 to 3 were mixed in a ratio of 90: 5: 5 by weight in an N-methylpyrrolidone solvent in a composition for forming a positive electrode. (Viscosity: 5000 mPa · s) was prepared, and this was applied to an aluminum current collector, followed by dry rolling to prepare a positive electrode.

In addition, MCMB (mesocarbon microbead), carbon black conductive material and PVdF binder, which are artificial graphite as a negative electrode active material, were mixed in an N-methylpyrrolidone solvent in a weight ratio of 85: 10: 5 to prepare a composition for forming a negative electrode, This was applied to a copper current collector to prepare a negative electrode.

An electrode assembly was manufactured by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed in a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) of 1.15M concentration in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was.

[ Comparative example  1: Manufacturing of Lithium Secondary Battery]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that particles including a lithium composite metal oxide of Li (Ni _0.60 Co _0.15 Mn _0.25 ) O ₂ were used as the cathode active material.

[ Experimental Example  1: active material analysis]

Cross sections of the positive electrode active materials prepared in Example 1 and Comparative Example 1 were observed using a scanning electron microscope and a transmission electron microscope, respectively. The results are shown in Figures 2 to 5 below.

2 and 3 are SEM and TEM photographs of the cross section of the cathode active material prepared in Example 1, Figures 4 and 5 are SEM and TEM photographs of the cross section of the cathode active material prepared in Comparative Example 1.

As a result, the average particle diameter (D ₅₀ ) of the positive electrode active material particles prepared in Example 1 was about 11.5 μm, and the secondary particle core (thickness about 2.5 μm) in which rod-shaped primary particles were randomly assembled was centered on the particle. An intermediate layer (thickness of about 3.15 μm), located on the surface of the core and including rod-shaped particles (average aspect ratio = 13) oriented in the surface direction from the center of the active material particles, and a particulate NMC lithium composite metal on the intermediate layer. The three-layer structure of the shell (about 0.1 micrometer in thickness) where an oxide is located was confirmed.

On the other hand, in Comparative Example 1 it can be seen that the primary particles constituting the positive electrode active material without forming a core / intermediate layer / shell is aggregated without the orientation to form a secondary particle shape.

Further, after measuring the true density and the apparent density with respect to the positive electrode active material prepared in Example 1, the porosity was calculated from the measured value, the porosity of the positive electrode active material was 20% by volume.

In addition, the composition of the lithium composite metal oxide in each layer was confirmed through an electron probe X-ray microanalyzer (EPMA) analysis of the cathode active material particles prepared in Example 1.

Specifically, 10 points are selected from the core to the surface of the cathode active material particles prepared in Example 1, and the concentrations of lithium, nickel, manganese, and cobalt at each point are measured, and the core, intermediate layer, and shell are obtained from the results. The average composition of each lithium composite metal oxide in the mixture was confirmed.

As a result, the average composition of the first lithium composite metal oxide in the core formation region (from the center of the core to the interface between the core and the intermediate layer) was Li [Ni _0.82 Co _0.07 Mn _0.13 ] O ₂ , and the intermediate layer formation region (the interface between the core and the intermediate layer). From the middle layer to the shell interface), the average composition of the second lithium composite metal oxide is Li [Ni _0.67 Co _0.11 Mn _0.23 ] O ₂ The average composition of the third lithium composite metal oxide at the interface between the intermediate layer and the shell and the shell surface was Li [Ni _0.56 Co _0.17 Mn _0.27 ] O ₂ , respectively. From these results, it was confirmed that Ni shows a concentration gradient continuously decreasing from the particle center of the active material to the interface between the intermediate layer and the shell, and Co and Mn showed a continuously increasing concentration gradient.

[ Experimental Example  2: Life characteristic evaluation]

The lithium secondary batteries prepared in Example 1 and Comparative Example 1 were charged / discharged 200 times under conditions of 0.5 C / 0.5 C at a high voltage (45 ° C.) within a driving voltage range of 3.0 V to 4.3 V, Cycle capacity retention, which is the ratio of the discharge capacity at the 200th cycle to the initial capacity, was measured. The results are shown in FIG.

As a result, the lithium secondary battery of Example 1 including the cathode active material according to the present invention had a higher capacity retention rate at the 200th cycle compared to Comparative Example 1, and it can be confirmed that the lithium secondary battery had better life characteristics therefrom. .

[ Experimental Example  3: thermal stability evaluation]

Thermal stability of the lithium secondary batteries according to Example 1 and Comparative Example 1 was evaluated.

In detail, after charging the lithium secondary batteries prepared in Example 1 and Comparative Example 1 to 4.3V, using a differential scanning calorimeter (DSC) to increase the temperature at a rate of 10 ℃ / min to confirm the position of the exothermic temperature. The results are shown in FIG.

As a result of the experiment, the lithium secondary battery of Example 1 including the cathode active material according to the present invention moved to a higher position of the exothermic temperature in comparison with Comparative Example 1, which does not include the concentration gradient and the rod-shaped particulate in the intermediate layer. From this, it was confirmed that it has more excellent thermal stability.

Claims (18)

1. A secondary particulate core formed by agglomeration of primary particles of a nickel manganese cobalt-based first lithium composite metal oxide;

   An intermediate layer disposed on the core and including rod-shaped nickel manganese cobalt-based second lithium composite metal oxide particles oriented radially from the center of the active material particles to the surface; And

   A shell disposed on the intermediate layer and containing a nickel manganese cobalt-based third lithium composite metal oxide

   A cathode active material for a secondary battery comprising a.
2. The method of claim 1,

   The primary particles of the nickel manganese cobalt-based first lithium composite metal oxide contained in the core has a shape of at least one of a granular type and a rod type.
3. The method of claim 1,

   The primary particles of the nickel manganese cobalt-based first lithium composite metal oxide contained in the core has a rod-like, it does not exhibit the orientation of the positive electrode active material for secondary batteries.
4. The method of claim 1,

   The nickel manganese cobalt-based second lithium composite metal oxide particles contained in the intermediate layer is a rod-type particle having an aspect ratio of more than 1 and 20 or less.
5. The method of claim 1,

   At least one metal element of nickel, cobalt, and manganese contained in the positive electrode active material is from the center of the positive electrode active material particles to the interface between the intermediate layer and the shell; Or a positive electrode active material for a secondary battery that shows a concentration gradient that increases or decreases from the center of the positive electrode active material particles to the surface of the positive electrode active material particles.
6. The method of claim 1,

   The concentration of nickel contained in the positive electrode active material is a positive electrode active material for a secondary battery that exhibits a concentration gradient continuously decreasing from the center of the positive electrode active material particles to the interface between the intermediate layer and the shell.
7. The method of claim 1,

   The concentration of cobalt contained in the positive electrode active material is a positive electrode active material for a secondary battery that shows a concentration gradient continuously increasing from the center of the positive electrode active material particles to the interface between the intermediate layer and the shell.
8. The method of claim 1,

   The concentration of manganese contained in the cathode active material is a positive electrode active material for a secondary battery that shows a concentration gradient continuously increasing from the center of the cathode active material particles to the interface between the intermediate layer and the shell.
9. The method of claim 1,

   Nickel, cobalt and manganese contained in the shell are each independently a positive electrode active material for a secondary battery having a constant concentration value throughout the shell.
10. The method of claim 1,

    The distance from the center of the anode active material particles to the interface between the core and the intermediate layer is called the thickness of the core, and the distance from the interface of the core and the intermediate layer to the interface between the intermediate layer and the shell is called the thickness of the intermediate layer, and the interface between the intermediate layer and the shell When the distance from the surface of the cathode active material to the surface of the cathode active material is called the thickness of the shell,

    The core has a thickness of 3% to 30% with respect to the average particle diameter of the positive electrode active material,

    The intermediate layer and the shell is a cathode active material for a secondary battery is formed in a thickness ratio of 1: 0.01 to 1: 1.
11. The method of claim 1,

    The first to third lithium composite metal oxides each independently have a content of nickel of 50 atomic% or more with respect to the total atomic weight of nickel, cobalt and manganese elements contained in the oxide,

    The difference in the average concentration of nickel in the core and shell is 10 atomic% to 45 atomic% of the positive electrode active material for secondary batteries.
12. Preparing a metal salt solution for forming a core including nickel, cobalt and manganese, and a metal salt solution for forming a shell including nickel, cobalt and manganese at a different concentration from the core salt metal salt solution;

    The shell-forming metal salt solution in the core-forming metal salt solution such that the mixing ratio of the core-forming metal salt solution and the shell-forming metal salt solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. Simultaneously adding a chelating agent and a basic aqueous solution to prepare a cathode active material precursor; And

    It includes the step of heat treatment after mixing the positive electrode active material precursor and lithium salt,

    The preparation of the cathode active material for a secondary battery according to claim 1, wherein the preparation rate of the shell forming metal salt solution added to the core salt metal salt solution is different for each core, intermediate layer, and shell forming section of the active material precursor. Way.
13. The method of claim 12,

    In the preparation of the positive electrode active material precursor, the injection speed of the metal salt solution for shell formation added to the metal salt solution for core formation is 10 g / min to 20 g / min, and gradually goes to the core, intermediate layer, and shell formation section within the injection speed range. Method of producing a positive electrode active material for a secondary battery that the input rate of the shell-forming metal salt solution added to the core salt-forming metal salt solution is increased.
14. The method of claim 12,

    In the preparation of the cathode active material precursor, the addition rate of the metal salt solution for shell formation added to the metal salt solution for core formation and the addition rate of the basic aqueous solution are the same, and the rate of the chelating agent is the addition of the metal salt solution for shell formation. Method of manufacturing a positive electrode active material for secondary batteries that is 5 to 7 times slower than the speed.
15. The method of claim 12,

    Method for producing a cathode active material for a lithium secondary battery that the step of preparing the cathode active material precursor is carried out at pH 10 to pH 12.
16. The method of claim 12,

    The heat treatment is a method for producing a cathode active material for a lithium secondary battery that is carried out at 800 ℃ to 1100 ℃.
17. A cathode for a lithium secondary battery comprising the cathode active material according to claim 1.
18. A lithium secondary battery comprising the positive electrode according to claim 17.

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