KR102227305B1 - Positive electrode active material for lithium secondary battery, method for preparing the same, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention includes particles of a lithium nickel cobalt manganese-based composite metal oxide, the particles having a core in an area corresponding to 1 to 70% by volume of the total volume of the particles from the center of the particle, and located on the outer surface of the core. It has a core-shell structure of a shell, and the core includes at least one first doping element selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and the first doping element is from the center of the particle. It exists in a concentration gradient that gradually decreases toward the interface between the core and the shell, and the shell contains at least one second doping element selected from the group consisting of Al, B, Ga, In, and Mg, and the second doping The element relates to a positive electrode active material for a secondary battery, which exists in a concentration gradient gradually increasing from the interface between the core and the shell toward the surface of the particle, and the positive electrode active material for a secondary battery according to the present invention is doped differently in the inner region of the particle and the outer region of the particle Including an element, and the doping element is distributed with a concentration gradient in the inner region of the particle and the outer region of the particle, respectively, so that side reactions with the electrolyte and elution of the doped element are minimized while having high output and structural stability, When applied, it exhibits high capacity, high lifespan, and thermal stability, and performance degradation can be minimized at high voltage, so it can be usefully used in manufacturing a secondary battery.

Description

A cathode active material for secondary batteries, a method for manufacturing the same, and a lithium secondary battery including the same TECHNICAL FIELD [POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY, METHOD FOR PREPARING THE SAME, AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these 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.

A lithium transition metal composite oxide is used as a positive electrode active material of a lithium secondary battery, and among them, a lithium cobalt composite metal oxide of _{LiCoO 2 having a high working voltage and excellent capacity characteristics is mainly used.} However, LiCoO ₂ has very poor thermal properties due to destabilization of the crystal structure due to delithiation, and is expensive, so it is limited in mass use 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, which have a high reversible capacity of about 200 mAh/g and are 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 external pressure in a charged state, the positive electrode active material itself is decomposed, causing 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 substituting part of nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. _{However, in the case of LiNi 1 - x} Co _x O ₂ (x=0.1~0.3) in which a part of nickel is substituted with cobalt, excellent charge/discharge characteristics and lifespan characteristics are shown, but thermal stability is low. In addition, in the case of a nickel manganese-based lithium composite metal oxide in which a part of Ni is replaced with Mn with excellent thermal stability, and a nickel cobalt manganese-based lithium composite metal oxide (hereinafter simply referred to as'NCM-based lithium oxide') substituted with Mn and Co. The output characteristics are low, and there is a concern of elution of metal elements and a decrease in battery characteristics accordingly.

In order to solve this problem, a lithium transition metal oxide having a concentration gradient of a metal composition has been proposed. This method is carried out by synthesizing a core material and then coating a material having a different composition on the outside to form a double layer, followed by heat treatment by mixing with a lithium salt. This method can synthesize the metal composition of the core and the outer layer differently during synthesis, but the formation of a continuous concentration gradient of the metal composition in the generated positive electrode active material is not sufficient, so the effect of improving the output characteristics is not satisfactory, and the reproducibility is low. have.

As another method, studies are being made to increase the content of Ni in NMC-based lithium oxide in order to increase energy density in batteries for small vehicles and power storage. In general, in a positive electrode active material, capacity, life, or stability are related to a trade off in which the life and stability of the battery rapidly decrease when the capacity is increased. Accordingly, a method of using only within a limited composition and voltage range, a method of restricting structure stabilization by substituting some composition of NCM oxide with a heterogeneous element, and a method of reducing side reactions on the surface through coating have been proposed. However, both of these methods have limitations in fundamentally improving the electrochemical and thermal stability of an active material, and since the deterioration of performance is accelerated at the time of high voltage, it is also difficult to increase the energy density of the battery.

KR 2005-0083869 A

The problem to be solved of the present invention is that when applied to a lithium secondary battery, it exhibits high capacity, high lifespan, and thermal stability, and while performance degradation is minimized at high voltage, the elution of doping elements is suppressed, and thus the effect of the doping element is continuously exhibited. It is to provide a positive electrode active material for a battery.

Another object to be solved by the present invention is to provide a method of manufacturing the positive electrode active material.

Another object to be solved by the present invention is to provide a lithium secondary battery including the positive electrode active material for a secondary battery.

In order to solve the above problem, the present invention

Including particles of lithium nickel cobalt manganese-based composite metal oxide,

The particles have a core in an area corresponding to 1 to 70% by volume of the total volume of the particles from the center of the particle, and a core-shell structure of a shell located on the outer surface of the core,

The core includes at least one first doping element selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and the first doping element gradually increases from the center of the particle toward the interface between the core and the shell. Exists in a decreasing concentration gradient,

The shell contains at least one second doping element selected from the group consisting of Al, B, Ga, In, and Mg, and the second doping element has a concentration gradually increasing from the interface between the core and the shell toward the particle surface. It provides a positive electrode active material for a secondary battery that exists in a gradient.

In addition, the present invention in order to solve the above other problems,

(1) preparing a first metal salt solution containing nickel, cobalt, manganese and a first doping element, and a second metal salt solution containing nickel, cobalt and manganese and a second doping element;

(2) The second metal salt solution was added to the first metal salt solution so that the mixing ratio of the first metal salt solution and the second metal salt solution gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. At the same time as the addition, adding a chelating agent and a basic aqueous solution to prepare a positive electrode active material precursor; And

(3) heat treatment after mixing the cathode active material precursor and lithium salt

It provides a method of manufacturing a cathode active material for a secondary battery comprising a.

In addition, the present invention in order to solve the another problem,

It provides a lithium secondary battery including the positive electrode active material for the secondary battery.

The positive electrode active material for a secondary battery according to the present invention contains different doping elements in the inner and outer regions of the particles, and the doping elements are distributed with concentration gradients in the inner and outer regions of the particles, respectively, so high output and structural stability It has high capacity, high lifespan, and thermal stability when applied to a secondary battery, as side reactions with the electrolyte and elution of doping elements are minimized, and performance degradation at high voltage can be minimized. I can.

1 and 2 are graphs showing the results of confirming the concentration gradient structure of a doping element included in the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3, respectively.

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

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The positive electrode active material for a secondary battery according to the present invention includes particles of lithium nickel cobalt manganese-based composite metal oxide, the particles having a core in a region corresponding to 1 to 70% by volume of the total volume of the particles from the center of the particle, and It has a core-shell structure of a shell located on the outer surface. At this time, the core includes at least one first doping element selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and the first doping element goes from the center of the particle toward the interface between the core and the shell. It exists in a gradually decreasing concentration gradient, and the shell contains at least one second doping element selected from the group consisting of Al, B, Ga, In, and Mg, and the second doping element is an interface between the core and the shell. It exists as a concentration gradient gradually increasing from the to the surface of the particle.

The particles of the lithium composite metal oxide contained in the positive electrode active material for a secondary battery of the present invention have a core located at the center of the particle, and a core-shell structure in which a shell is located on the outer surface of the core, the core and the shell It can be classified according to the type of doping element it contains.

The core may be a region corresponding to 1 to 70% by volume of the total volume of the particle from the center of the particle, specifically, a region corresponding to 1 to 60% by volume, and a group consisting of Zr, W, Ti, Nb, Mo, and Ta It contains at least one first doping element selected from.

Since the first doping element is included in the core positioned at the particle center of the positive electrode active material for a secondary battery of the present invention, the output and structural stability of the positive electrode active material can be improved.

In addition, the shell located outside the particles of the positive electrode active material for a secondary battery of the present invention contains at least one second doping element selected from the group consisting of Al, B, Ga, In, and Mg, so that the second doping element is A side reaction between the electrolyte and the positive electrode active material can be suppressed. The second doping element decreases from the interface between the core and the shell toward the outer surface of the particle, but in another example of the present invention, the concentration gradient increases from the interface between the core and the shell toward the outer surface of the particle. Can exist.

By placing the first doping element in the center of the particles of the positive electrode active material, it is possible to suppress elution of the doping element through a reaction with the electrolyte during charge/discharge or high temperature storage, and the second doping element is added to the first doping element. Compared with the composition of a relatively low elution type, by suppressing the elution of the doping element as a whole of the positive electrode active material particles, the positive electrode active material for a secondary battery of the present invention can continuously exhibit the effect of the inclusion of the doping element.

The first doping element may exist in a concentration gradient that decreases from the center of the particle toward the interface between the core and the shell, and the second doping element decreases from the interface between the core and the shell toward the outer surface of the particle. It can exist as a gradient. In addition, when the first doping element or the second doping element includes two or more types of elements, each of the two or more types of elements may independently have one concentration gradient gradient value.

On the other hand, in the positive electrode active material according to an embodiment of the present invention, the first doping element is specifically based on the total atomic weight of the first doping element included in the core, the total volume of the core in the surface direction from the particle center of the core. An area within 10% by volume (hereinafter _{referred to as'Rc 10} area') and an area within 10% by volume with respect to the total volume of the core from the interface between the core and the shell of the positive electrode active material particle to the center (hereinafter referred to _{as'R i10 area').} The difference in concentration of the first doping element in the region') may be 10 to 70 atomic%. In addition, the average concentration ratio of the first doping element in the positive electrode active material particle core may be 0.4 to 0.7.

In addition, in the positive electrode active material according to an embodiment of the present invention, the second doping element is specifically based on the total atomic weight of the second doping element contained in the shell, from the interface between the core and the shell of the positive electrode active material particle. An area within 10% by volume with respect to the total volume of the shell in the surface direction of the cathode active material particles (hereinafter _{referred to as'R si10} area') and 10% by volume with respect to the total volume of the shell in the center direction from the surface of the cathode active material particles The difference in concentration of the second doping element in the region within the range (hereinafter referred to as “R _s10 region”) may be 10 to 70 atomic%. In addition, the average concentration ratio of the second doping element in the cathode active material particle shell may be 0.4 to 0.7.

In one example of the present invention, the core of the particles of the lithium composite metal oxide may have a composition represented by the following formula (1) on average.

[Formula 1]

Li _a Ni _x Mn _y Co _z M1 _w M2 _{w'O 2 +δ}

In Formula 1, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is one selected from the group consisting of Al, B, Ga, In, and Mg. Including above, 0.9<a≤1.1, 0.4≤x≤0.95, 0<y≤0.5, 0<z≤0.5, 0<w≤0.1, 0≤w'≤0.01, 0≤δ≤0.02, 0< x+y+z≤1.

In addition, in an example of the present invention, the shell of the particles of the lithium composite metal oxide may have a composition represented by the following formula (2) on average.

[Formula 2]

_B Mn _s Ni _t Co _u Li M1 _v M2 _{v 'O 2 + δ}

In Formula 2, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is one selected from the group consisting of Al, B, Ga, In, and Mg. Including above, 0.9<b≤1.1, 0.4≤s≤0.95, 0<t≤0.5, 0<u≤0.5, 0≤v≤0.01, 0<v'≤0.1, 0≤δ≤0.02, 0< t+u+v≤1.

In the present invention, "continuously expressing a concentration gradient" or "having a concentration gradient value" means that the concentration of a metal or the like is present in a concentration distribution that gradually changes throughout the entire particle. Specifically, the concentration distribution is 0.1 to 30 atomic%, more specifically 0.1 to 20 atomic%, respectively, based on the total atomic weight of the metal contained in the positive electrode active material, the change in the metal concentration per 0.1 μm toward the surface within the particle. There may be a difference of atomic%, more specifically 1 to 10 atomic%.

On the other hand, in the present invention, the concentration gradient structure and concentration of the metal in the positive electrode active material particle is an electron probe micro analyzer (EPMA), inductively coupled plasma-atomic emission spectroscopy (Inductively Coupled Plasma-Atomic Emission Spectrometer, ICP). -AES), or Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), etc., and specifically EPMA from the center of the positive electrode active material to the surface. As it moves, it is possible to measure the atomic ratio of each metal.

The positive electrode active material may have an average particle diameter (D50) of 3 to 50 μm in consideration of the specific surface area and the density of the positive electrode mixture, and in consideration of the effect of improving the rate characteristics and initial capacity characteristics due to the specific structure, 5 to 30 μm It may have an average particle diameter (D50). In the present invention, the average particle diameter (D50) of the positive electrode active material may be defined as a particle diameter based on 50% of the particle diameter distribution. The average particle diameter (D50) of the positive electrode active material particles according to an embodiment of the present invention may be measured using, for example, a laser diffraction method. For example, the method of measuring the average particle diameter (D50) of the positive electrode active material is, after dispersing the particles of the positive electrode active material in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000) to about 28 kHz. After irradiating the ultrasonic wave at an output of 60 W, the average particle diameter (D50) based on 50% of the particle diameter distribution in the measuring device can be calculated.

The present invention also provides a method of manufacturing the positive electrode active material for a secondary battery.

The manufacturing method of the positive electrode active material for a secondary battery of the present invention includes (1) a first metal salt solution containing nickel, cobalt, manganese, and a first doping element, and a second metal salt solution containing nickel, cobalt, manganese and a second doping element. Preparing to; (2) The second metal salt solution was added to the first metal salt solution so that the mixing ratio of the first metal salt solution and the second metal salt solution gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. At the same time as the addition, adding a chelating agent and a basic aqueous solution to prepare a positive electrode active material precursor showing a concentration gradient in which the nickel, cobalt, and manganese each independently change continuously from the center of the particle to the surface; And (3) heat-treating after mixing the cathode active material precursor and the lithium salt.

In step (1), a first metal salt solution containing nickel, cobalt, manganese and a first doping element, and a second metal salt solution containing nickel, cobalt and manganese and a second doping element are prepared.

The first metal salt solution includes a first doping element in addition to nickel, cobalt, manganese, and the doping element may be at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta.

Meanwhile, the second metal salt solution includes a second doping element in addition to nickel, cobalt, and manganese, and the second doping element may be at least one selected from the group consisting of Al, B, Ga, In, and Mg.

The method of preparing the first metal salt solution and the second metal salt solution may overlap with each other. Specifically, in the first metal salt solution and the second metal salt solution, a salt of a first doping element or a salt of a second doping element, respectively, together with a nickel salt, a cobalt salt, and a manganese salt, are added to a solvent, specifically water. Can be manufactured.

The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, or oxyhydroxide of each metal, and is not particularly limited as long as it is a salt that can be dissolved in water. For example, in the case of cobalt salt, Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O or Co(SO ₄ ) ₂ ㆍ7H ₂ O, etc. And any one or a mixture of two or more of them may be used.

In step (2), the second metal salt is added to the first metal salt solution so that the mixing ratio of the first metal salt solution and the second metal salt solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. At the same time as the solution is added, a chelating agent and a basic aqueous solution are added to prepare a positive electrode active material precursor in which the first doping element and the second doping element each independently exhibit a concentration gradient.

Since the reaction (particle nucleation and particle growth) is performed in the presence of only the first metal salt solution at the initial stage of the preparation of the positive electrode active material precursor, the first precursor particles have a composition of the first metal salt solution, and then the first metal salt solution. Since the second metal salt solution is gradually mixed with the first metal salt solution, the composition of the precursor particles gradually changes from the center of the precursor particles to the composition of the second metal salt solution in an outer direction.

Accordingly, by adjusting the composition of the first metal salt solution and the second metal salt solution, and adjusting the mixing speed and ratio thereof, the desired position from the center of the precursor particle to the surface direction can be adjusted to have a desired composition.

Specifically, since the reaction is performed in a state in which only the first metal salt solution is present at the initial stage of the preparation of the positive electrode active material precursor, nickel, cobalt, manganese and nickel, cobalt, manganese and Precursor particles containing the first doping element are made, and then the second metal salt solution is gradually mixed, and thereafter, the reaction is carried out in a state in which the first metal salt solution does not exist, so that the outer surface side of the precursor particles, that is, The shell does not contain the first doping element, and precursor particles containing nickel, cobalt, manganese, and the second doping element are made. Accordingly, the first doping element is included in the core of the region corresponding to 1 to 70% by volume of the total volume of the particles, specifically, 1 to 60% by volume, and is located on the outer surface of the core. A cathode active material precursor including the second doping element in the shell may be prepared.

In this case, a small amount of the second doping element may be included in the core, and a small amount of the first doping element may be included in the shell.

The second doping element included in the core may be in an amount of 0 to 10 atom%, and specifically, in an amount of 0 to 5 atom%, based on 100 atom% of the first doping element included in the core. In addition, the first doping element included in the shell may be in an amount of 0 to 10 atom%, and specifically, in an amount of 0 to 5 atom%, based on 100 atom% of the second doping element included in the shell.

In addition, in an example of the present invention, the first metal salt solution contains a first doping element, and the second metal salt solution does not contain the first doping element and contains the second doping element. 2 As the metal salt solution is mixed, the content of the first doping element decreases, so that the first doping element exists in a concentration gradient decreasing from the center of the active material particle toward the interface between the core and the shell. It gradually increases in the direction of the interface between the core and the shell from the center and has a high concentration in the shell.

Therefore, in another example of the present invention, the first metal salt solution includes at least one doping element selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and the second metal salt solution is Al, Since it contains at least one doping element selected from the group consisting of B, Ga, In, and Mg, the types of doping elements present in the core and the shell are different from the first doping element and the second doping element, and the first The doping element and the second doping element may prepare positive electrode active material precursor particles each having a concentration gradient decreasing in the surface direction of the particles.

Further, in another example of the present invention, in the positive electrode active material precursor prepared in step (2). The first doping element may exist in a concentration gradient gradually decreasing from the center of the particle to the interface between the core and the shell, and the second doping element is a concentration gradient gradually increasing from the interface between the core and the shell toward the particle surface. Can exist as

Accordingly, the core of the prepared positive active material precursor may have a composition represented by the following Formula 3 on average.

[Formula 3]

Ni _x Mn _y Co _z M1 _w M2 _{w'O 2 +δ}

In Formula 3, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is one selected from the group consisting of Al, B, Ga, In, and Mg. Including above, 0.4≤x≤0.95, 0<y≤0.5, 0<z≤0.5, 0<w≤0.1, 0≤w'≤0.01, 0≤δ≤0.02, 0<x+y+z≤ It is 1.

In addition, the shell of the positive electrode active material precursor may have a composition represented by the following formula (4) on average.

[Formula 4]

_{Ni s Mn t Co u M1 v} M2 v 'O 2 + δ

In Formula 4, M1 includes one or more selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is one selected from the group consisting of Al, B, Ga, In, and Mg. Including above, 0.4≤s≤0.95, 0<t≤0.5, 0<u≤0.5, 0≤v≤0.01, 0<v'≤0.1, 0≤δ≤0.02, 0<t+u+v≤ It is 1.

The addition of the second metal salt solution to the first metal salt solution is continuously performed, and by continuously supplying and reacting the second metal salt solution, the concentration of the metal increases from the center of the particle to the surface in one coprecipitation reaction process. A precipitate having a continuous concentration gradient can be obtained, and the concentration gradient and the slope of the metal in the active material precursor generated at this time can be easily adjusted by the composition and mixing supply ratio of the first metal salt solution and the second metal salt solution. I can.

In addition, the concentration gradient of the metal element in the particles can be formed by controlling the reaction rate or reaction time. In order to create a high-density state with a high concentration of a specific metal, it is desirable to increase the reaction time and decrease the reaction rate, and to create a low-density state with a low concentration of a specific metal, it is desirable to shorten the reaction time and increase the reaction rate. .

The size of the positive electrode active material particles and the thickness of the shell may be controlled by adjusting the supply amount and reaction time of the second metal salt solution to the first metal salt solution. Specifically, it may be desirable to appropriately adjust the supply amount and reaction time of the second metal salt solution so as to have the positive electrode active material particle size as described above.

The rate of the second metal salt solution added to the first metal salt solution may be 10 to 20 g/min, and the reaction temperature may be 50 to 80°C.

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

Meanwhile, in Step 2, an aqueous ammonia solution, an aqueous ammonium sulfate solution, or a mixture thereof may be used as the chelating agent.

The chelating agent may be added in an amount such that the molar ratio of 0.5 to 1 per 1 mole of the mixed solution of the core and the shell-forming metal salt is obtained. In general, the chelating agent reacts with the metal in a molar ratio of 1:1 or more to form a complex, but the unreacted complex that has not reacted with the basic aqueous solution among the formed complexes is converted into an intermediate product and can be recovered and reused. In compared to usual, the chelating amount can be lowered. As a result, the crystallinity of the positive electrode active material can be improved and stabilized.

The basic aqueous solution may be prepared by dissolving a base such as sodium hydroxide or potassium hydroxide in water.

The concentration of the basic aqueous solution may be 2 M to 10 M. When the concentration of the basic aqueous solution is less than 2 M, there is a concern that the particle formation time increases, the tap density decreases, and the yield of the coprecipitation reactant decreases. On the other hand, when the concentration of the basic aqueous solution exceeds 10 M, it is difficult to form uniform particles because the particles grow rapidly due to a rapid reaction, and there is a fear that the tap density is also lowered.

The reaction for preparing the positive electrode active material precursor may be performed within a pH range of 10 to 12. When the pH is out of the above range, there is a concern that the size of the positive active material precursor to be prepared may be changed or particles may be split. In addition, there is a concern that metal ions are eluted on the surface of the positive electrode active material precursor to form various oxides through side reactions. The pH adjustment as described above can be controlled through the addition of a basic aqueous solution.

The reaction for preparing the positive electrode active material precursor may be performed in a temperature range of 30 to 80° C. in an inert atmosphere such as nitrogen. In order to increase the reaction speed during the reaction, a stirring process may be selectively performed, and in this case, the stirring speed may be 100 to 2000 rpm.

As a result of the reaction in step (2), a cathode active material precursor having the structure as described above is precipitated. After separating the precipitated positive electrode active material precursor according to a conventional method, a drying process may be selectively performed, and the drying process may be performed at 110 to 400°C for 15 to 30 hours.

In step (3), the cathode active material precursor and the lithium salt are mixed and then subjected to heat treatment.

As the lithium salt, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides or oxyhydroxides may be used, and as long as they can be dissolved in water, they are not particularly limited. 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 or the like, any one or a mixture of two or more of them may be used.

When mixing the cathode active material precursor and the lithium salt, a sintering agent may be optionally further added. Specifically, the sintering agent is 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 of them may be used. The sintering agent may be used in an amount of 0.01 to 0.2 moles per 1 mole of the positive electrode active material precursor. If the content of the sintering agent is too low, such as less than 0.01 moles, the effect of improving the sintering characteristics of the positive electrode active material precursor may be insignificant, and if the content of the sintering agent exceeds 0.2 moles and being too high, the performance as a positive electrode active material is degraded And there is a concern that the initial capacity of the battery may decrease during charging and discharging.

When mixing the cathode active material precursor and the lithium salt, a moisture remover may be optionally further added. Specifically, the moisture removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more of them may be used. The moisture remover may be used in an amount of 0.01 to 0.2 moles per 1 mole of the positive electrode active material precursor.

The heat treatment process may be performed at 800°C to 1100°C. If the temperature during the heat treatment is less than 800°C, there is a risk of a decrease in discharge capacity per unit weight, a decrease in cycle characteristics, and a decrease in operating voltage due to the remaining unreacted raw materials. There is a risk of a decrease in discharge capacity per weight, a decrease in cycle characteristics, and a decrease in operating voltage.

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 including nitrogen or hydrogen. Through the heat treatment process under such conditions, the diffusion reaction between particles can be sufficiently achieved, and diffusion of metal occurs even in a portion where the internal metal concentration is constant, resulting in a metal oxide having a continuous metal concentration distribution from the center to the surface. Can be manufactured.

Meanwhile, preliminary firing in which the heat treatment process is maintained at 250° C. to 650° C. for 5 to 20 hours may be selectively performed. Further, an annealing process for 10 to 20 hours at 600° C. to 750° C. may be selectively performed after the heat treatment process.

The positive electrode active material prepared by the above-described manufacturing method can exhibit high capacity, high lifespan, and thermal stability when applied to a battery by controlling the distribution of the transition metal throughout the active material particles, and at the same time minimize performance degradation at high voltage.

According to another embodiment of the present invention, a positive electrode including the positive electrode 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 changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , Silver, or the like may be used. In addition, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive electrode active material layer may include a conductive material and a binder in addition to the positive electrode active material described above.

At this time, the conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it may be used without particular limitation as long as it does not cause chemical changes and has electronic conductivity. Specific examples 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, thermal black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, a conductive polymer such as a polyphenylene derivative may be used, and one of them alone or a mixture of two or more 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.

The binder serves to improve 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, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 1 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 active material layer prepared by mixing or dispersing a binder and a conductive material in a solvent may be coated on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or Water, and the like, and one of them alone or a mixture of two or more 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 and production yield of the slurry, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for the production of the positive electrode afterwards. Do.

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

According to another example of the present invention, an electrochemical device including the anode is provided. The electrochemical device may specifically be 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 opposite 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. In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed 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 changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, and the like may be used. In addition, the negative electrode current collector may generally have a thickness of 3 to 500 μm, and, like the positive electrode current collector, microscopic irregularities may be formed on the surface of the current collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The negative active material layer optionally includes a binder and a conductive material together with the negative active material.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; Metal oxides capable of doping and undoping lithium such as SiO _x (0 <x <2), SnO _{2, vanadium oxide, and lithium vanadium oxide;} Or a composite including the metal compound and a carbonaceous material, such as a Si-C composite or an Sn-C composite, and any one or a mixture of two or more of them may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. Further, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are typical, and high crystalline carbon is amorphous, plate, scale, 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 for the positive electrode.

The negative electrode active material layer is, for example, coated with a negative electrode forming composition prepared by dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent on a negative electrode current collector, and then drying, or the negative electrode forming composition on a separate support. It can also be produced by casting a film on the negative electrode current collector and then laminating the film obtained by peeling it from the support.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions, and can be used without particular limitation as long as it is used as a separator in a general lithium secondary battery. On the other hand, it is preferable to have low resistance and excellent electrolyte-moisturizing ability. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A stacked structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and optionally, a single layer or a multilayer structure may be used.

In addition, electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of lithium secondary batteries, and are limited to these. It does not become.

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 a battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate-based 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, and may contain a double bonded aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes or the like may be used. Among them, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (e.g., ethylene carbonate or propylene carbonate, etc.), which can increase the charging/discharging performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

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 or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the electrolyte constituents, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trivalent for the purpose of improving battery life characteristics, suppressing reduction in battery capacity, and improving battery discharge capacity. 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 further included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the positive electrode 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 in 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 battery pack may include a power tool; Electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it may be used as a power source for any one or more medium and large-sized devices among systems for power storage.

The appearance of the lithium secondary battery of the present invention is not particularly limited, but it may be a cylindrical shape using a can, a square shape, a pouch type, or a coin type.

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Example One

0.1 mol/m ³ of zirconium sulfate aqueous solution and nickel sulfate: manganese sulfate: cobalt sulfate mixed at a molar ratio of 60:20: 2.4 M concentration of the first metal salt solution and 0.002 M boronic acid and nickel sulfate: manganese sulfate: cobalt sulfate A second metal salt solution having a concentration of 2.4 M mixed at a molar ratio of 60:20:20 was prepared.

After 4 l of distilled water was added to the continuous stirring tank reactor (CSTR), nitrogen gas was bubbled into the reactor at a rate of 1 l/min to remove dissolved oxygen, and stirred at 1000 rpm while maintaining the reactor temperature at 50°C.

The first metal salt solution was added to the continuous stirring tank reactor (CSTR) at 15 g/min. The pH was adjusted while continuously adding a 3.6 M ammonia solution to the reactor at 3 g/min. The pH was maintained at 11 while a 2 M sodium hydroxide solution was fed at a rate of 15 g/min.

After 60 minutes, the reaction was continued while adding the second metal salt solution at 15 g/min to the first metal salt solution. The average residence time of the metal salt solution in the reactor was about 2 hours, and after the reaction reached a steady state, a steady state duration was given to the reactant to obtain a more dense coprecipitated compound.

The prepared coprecipitation compound was filtered, washed with water, and then dried in a warm air dryer of 110 for 15 hours to obtain an active material precursor.

LiOH was mixed at a molar ratio of Li/Metal=1.05 and fired at 900 for 6 hours to prepare a positive electrode active material.

Example 2

A positive electrode active material was prepared in the same manner as in Example 1, except that the amount of the second metal salt solution added to the first metal salt solution in Example 1 was changed to 20 g/min.

Comparative example One

After 4 ℓ of distilled water was added to the continuous stirring tank reactor (CSTR), nitrogen gas was bubbled into the reactor at a rate of 1 ℓ/min to remove dissolved oxygen, and stirred at 1000 rpm while maintaining the reactor temperature at 50°C.

A metal salt solution having a concentration of 2.4 M in which 0.1 mol/m ³ of zirconium sulfate aqueous solution and nickel sulfate: manganese sulfate: cobalt sulfate were mixed at a molar ratio of 60:20:20 was added at 15 g/min. The pH was adjusted while continuously adding a 3.6 M ammonia solution to the reactor at 3 g/min. The pH was maintained at 11 while a 2 M sodium hydroxide solution was fed at a rate of 15 g/min.

The flow rate of the mixed metal aqueous solution was adjusted so that the average residence time in the reactor was 6 hours, and after the reaction reached a steady state, the mixed metal aqueous solution was given a steady state duration to give a high-density first complex metal hydroxide precipitate. Got it.

0.4 M of ammonia while continuously adding a 1 M concentration metal salt solution mixed with nickel sulfate: manganese sulfate: cobalt sulfate at a molar ratio of 60:20:20 to the first composite metal hydroxide precipitate that reached a steady state at 5 g/min. A solution and a 0.2 M sodium hydroxide solution were supplied to maintain a pH of 11 and a coprecipitation reaction was performed to obtain a core-shell structured composite metal hydroxide precipitate.

The obtained core-shell structured composite metal hydroxide precipitate was washed and dried in an on-pong dryer at 110° C. for 12 hours to obtain a core-shell structured composite metal oxide precursor.

Comparative example 2

After 4 ℓ of distilled water was added to the continuous stirring tank reactor (CSTR), nitrogen gas was bubbled into the reactor at a rate of 1 ℓ/min to remove dissolved oxygen, and stirred at 1000 rpm while maintaining the reactor temperature at 50°C.

A metal salt solution having a concentration of 2.4 M in which 0.1 mol/m ³ of zirconium sulfate aqueous solution and nickel sulfate: manganese sulfate: cobalt sulfate were mixed at a molar ratio of 60:20:20 was added at 15 g/min. The pH was adjusted while continuously adding a 3.6 M ammonia solution to the reactor at 3 g/min. The pH was maintained at 11 while a 2 M sodium hydroxide solution was fed at a rate of 15 g/min.

The flow rate of the mixed metal aqueous solution was adjusted so that the average residence time in the reactor was 6 hours, and after the reaction reached a steady state, the mixed metal aqueous solution was given a steady state duration to give a high-density first complex metal hydroxide precipitate. Got it.

In the first composite metal hydroxide precipitate that reached a steady state, ^{a 2.4 M concentration metal salt solution of 0.1 mol/m 3} of zirconium sulfate aqueous solution and nickel sulfate: manganese sulfate: cobalt sulfate mixed in a 60:20:20 molar ratio was added to 5 g/m. While continuously added in minutes, 0.4 M ammonia solution and 0.2 M sodium hydroxide solution were supplied, and the coprecipitation reaction was carried out while maintaining the pH at 11 to obtain a core-shell structured composite metal hydroxide precipitate.

The obtained core-shell structured composite metal hydroxide precipitate was washed and dried in an on-pong dryer at 110° C. for 12 hours to obtain a core-shell structured composite metal oxide precursor.

Comparative example 3

After 4 l of distilled water was added to the continuous stirring tank reactor (CSTR), nitrogen gas was bubbled into the reactor at a rate of 1 l/min to remove dissolved oxygen, and stirred at 1000 rpm while maintaining the reactor temperature at 50°C.

Into the continuous stirring tank reactor (CSTR), 0.1 mol/m ³ of zirconium sulfate aqueous solution and nickel sulfate: manganese sulfate: cobalt sulfate were mixed in a 60:20:20 molar ratio of 2.4 M metal salt solution at 15 g/min. I did. The pH was adjusted while continuously adding a 3.6 M ammonia solution to the reactor at 3 g/min. The pH was maintained at 11 while a 2 M sodium hydroxide solution was fed at a rate of 15 g/min. Then, a co-precipitation reaction obtained by adjusting the impeller speed of the reactor to 1000 rpm was performed. At this time, the flow rate was adjusted so that the average residence time of the solution in the reactor was about 6 hours, and after the reaction reached a steady state, a steady state duration was given to the reactant to form a denser first composite metal hydroxide precipitate. Got it.

A 2.4 M concentration metal salt solution of 0.002 M boronic acid and nickel sulfate: manganese sulfate: cobalt sulfate in a 60:20:20 molar ratio was continuously added to the first composite metal hydroxide precipitate that reached the steady state at 5 g/min. By supplying 0.4 M ammonia solution and 0.2 M sodium hydroxide solution, while maintaining the pH to 11, the co-precipitation reaction proceeded to obtain a composite metal hydroxide precipitate having a core-shell structure.

LiOH was mixed at a molar ratio of Li/Metal=1.05 and fired at 900 for 6 hours to prepare a positive electrode active material.

Experimental example 1: concentration in active material particles gradient Confirmation of structure

In order to confirm the concentration gradient structure of each metal from the center to the surface in the active material particles prepared in Examples 1 and 2 and Comparative Examples 1 to 3, EPMA (electron probe micro analyzer) was used. While moving from the center to the surface, the atomic ratio of each precursor particle was measured, and the results are shown in FIGS. 1 and 2.

Referring to FIG. 1, the positive electrode active material particles prepared in Examples 1 and 2 respectively gradually decrease the content of Zr, which is a doping element, toward the surface from the center of the particle, so that the doping element is not included as it approaches the surface, and B Is not included in the center of the particle, and its content increases from approximately 50% from the center of the particle. Meanwhile, the positive electrode active material particles prepared in Comparative Example 1 had Zr in the center of the particles and no Zr contained in the shell, and the positive active material particles prepared in Comparative Example 2 did not have Zr in the center of the particles and contained Zr in the shell. It can be confirmed that there is. In addition, it can be seen that in the positive electrode active material particles prepared in Comparative Example 3, Zr is present in the center of the particle, and Zr is not included in the shell, but B is included.

Experimental example 2 : Charge and discharge Property evaluation

Using the positive electrode active material prepared in Examples 1 and 2 and Comparative Examples 1 to 3, a coin cell (Li metal negative electrode was used) was prepared, and charging and discharging was performed at room temperature (25° C.) at 0.1 C/0.1 C. After carrying out the initial charge and discharge characteristics were evaluated.

The results are shown in Table 1 below.

0.1 C charge
(mAh/g) 0.1 C discharge
(mAh/g) efficiency
(%) 1.0 C discharge
(mAh/g) 2.0 C discharge
(mAh/g) Example 1 199.8 189.7 94.9 173.9 165.1 Example 2 199.7 188.5 94.4 173.6 164.9 Comparative Example 1 199.5 187.8 94.1 172.6 164.5 Comparative Example 2 199.1 183.0 91.9 170.1 162.5 Comparative Example 3 199.2 182.8 91.8 169.8 162.4

Referring to Table 1, the lithium secondary battery manufactured using the positive electrode active material prepared in Examples 1 and 2 has excellent charge/discharge characteristics compared to the lithium secondary battery manufactured using the positive electrode active material prepared in Comparative Examples 1 to 3. It can be confirmed that it has.

Experimental example 3: Cycle characteristic evaluation experiment

To prepare a coin cell (using Li metal negative electrode) using the positive electrode active material prepared in Examples 1 and 2, and Comparative Examples 1 to 3, and to find out the relative efficiency according to the number of cycles, an electrochemical evaluation experiment was conducted as follows. Performed.

Specifically, the lithium secondary battery is charged at 25 °C to a constant current (CC) of 4.3V at 1C, and then charged at a constant voltage (CV) of 4.3V to charge the first time until the charging current reaches 0.05mAh. Was done. After leaving it for 20 minutes, it was discharged at a constant current of 2C until it reached 3.0V, and this was repeated in 1 to 50 cycles. The results are shown in Table 2 below.

Capacity retention rate after 50 cycles (%) Example 1 99.6 Example 2 99.0 Comparative Example 1 92.5 Comparative Example 2 91.8 Comparative Example 3 90.7

Referring to Table 2, the lithium secondary battery manufactured using the positive electrode active material prepared in Examples 1 and 2 has the capacity after 50 cycles compared to the lithium secondary battery manufactured using the positive electrode active material prepared in Comparative Examples 1 to 3. It can be confirmed that the retention rate is excellent.

Claims (16)

Including particles of lithium nickel cobalt manganese-based composite metal oxide,
The particles have a core in a region corresponding to 1 to 70% by volume of the total volume of the particles from the center of the particle, and a core-shell structure of a shell located on the outer surface of the core
The core includes at least one first doping element selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and the first doping element gradually increases from the center of the particle toward the interface between the core and the shell. Exists in a decreasing concentration gradient,
The shell contains at least one second doping element selected from the group consisting of Al, B, Ga, In, and Mg, and the second doping element has a concentration gradually increasing from the interface between the core and the shell toward the particle surface. A positive electrode active material for secondary batteries that exists in a gradient.
The method of claim 1,
When the first doping element or the second doping element includes two or more types of elements, the two or more types of elements each independently have one concentration gradient gradient value.
The method of claim 1,
_{An Rc 10} region within 10% by volume of the total core volume from the center of the positive electrode active material particle to the surface direction, and
A positive electrode active material for a secondary battery in which the difference in concentration of the first doping element in the _{R i10} region, which is within 10% by volume of the total core volume from the interface between the core and the shell of the positive electrode active material particle, is 10 to 70 atomic% .
The method of claim 1,
_{An R Si10} region within 10% by volume of the total volume of the shell from the interface between the core and the shell of the positive electrode active material particle toward the surface of the positive electrode active material particle;
The positive electrode active material for a secondary battery, wherein the difference in concentration of the second doping element in the _{R S10} region, which is within 10% by volume of the total volume of the shell from the surface of the positive electrode active material particle, is 10 to 70 atomic%.
The method of claim 1,
A positive electrode active material for a secondary battery in which the core of the particles of the lithium composite metal oxide has a composition represented by the following formula (1) on average.
[Formula 1]
Li _a Ni _x Mn _y Co _z M1 _w M2 _{w'O 2 +δ}
(In Formula 1, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is 1 selected from the group consisting of Al, B, Ga, In, and Mg. Contains more than species, 0.9<a≤1.1, 0.4≤x≤0.95, 0<y≤0.5, 0<z≤0.5, 0<w≤0.1, 0≤w'≤0.01, 0≤δ≤0.02, 0 <x+y+z≤1)
The method of claim 1,
A cathode active material for a secondary battery having a composition represented by the following formula (2) on average in the shell of the lithium composite metal oxide particles.
[Formula 2]
_B Mn _s Ni _t Co _u Li M1 _v M2 _{v 'O 2 + δ}
(In Formula 2, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is 1 selected from the group consisting of Al, B, Ga, In, and Mg. Contains more than species, 0.9<b≤1.1, 0.4≤s≤0.95, 0<t≤0.5, 0<u≤0.5, 0≤v≤0.01, 0<v'≤0.1, 0≤δ≤0.02, 0 <t+u+v≤1)
(1) preparing a first metal salt solution containing nickel, cobalt, manganese and a first doping element, and a second metal salt solution containing nickel, cobalt and manganese and a second doping element;
(2) The second metal salt solution was added to the first metal salt solution so that the mixing ratio of the first metal salt solution and the second metal salt solution gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. At the same time as the addition, adding a chelating agent and a basic aqueous solution to prepare a positive electrode active material precursor; And
(3) heat treatment after mixing the cathode active material precursor and lithium salt
Including,
The first doping element is at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta,
The second doping element is at least one selected from the group consisting of Al, B, Ga, In and Mg, a method of manufacturing a cathode active material for a secondary battery.
delete delete The method of claim 7,
The cathode active material precursor has a core in a region corresponding to 1 to 70% by volume of the total volume from the center of the precursor, and a core-shell structure of a shell located on the outer surface of the core, a method for producing a cathode active material for a secondary battery .
The method of claim 10,
In the positive electrode active material precursor,
The first doping element exists in a concentration gradient gradually decreasing from the center of the particle toward the interface between the core and the shell,
The second doping element is present in a concentration gradient gradually increasing from the interface between the core and the shell toward the particle surface.
The method of claim 10,
A method of manufacturing a positive electrode active material for a secondary battery in which the core of the positive electrode active material precursor has a composition represented by the following formula (3) on average.
[Formula 3]
Ni _x Mn _y Co _z M1 _w M2 _{w'O 2 +δ}
(In Formula 3, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is 1 selected from the group consisting of Al, B, Ga, In, and Mg. Contains more than species, 0.4≤x≤0.95, 0<y≤0.5, 0<z≤0.5, 0<w≤0.1, 0≤w'≤0.01, 0≤δ≤0.02, 0<x+y+z ≤1)
The method of claim 10,
A method of manufacturing a cathode active material for a secondary battery in which the shell of the cathode active material precursor has a composition represented by the following formula (4) on average.
[Formula 4]
_{Ni s Mn t Co u M1 v} M2 v 'O 2 + δ
(In Formula 4, M1 includes at least one selected from the group consisting of Zr, W, Ti, Nb, Mo, and Ta, and M2 is 1 selected from the group consisting of Al, B, Ga, In, and Mg. Contains more than species, 0.4≤s≤0.95, 0<t≤0.5, 0<u≤0.5, 0≤v≤0.01, 0<v'≤0.1, 0≤δ≤0.02, 0<t+u+v ≤1)
The method of claim 7,
When preparing the positive electrode active material precursor, the addition rate of the second metal salt solution added to the first metal salt solution and the addition rate of the basic aqueous solution are the same, and the addition rate of the chelating agent is the addition rate of the second metal salt solution. The method of manufacturing a cathode active material for a secondary battery that is 5 to 7 times slower than that.
A positive electrode for a lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 6.
A lithium secondary battery comprising the positive electrode according to claim 15.

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