KR20170063418A - 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 relates to a lithium composite metal oxide particle comprising a core in a region corresponding to 1 to 70% by volume of the total volume of particles from the center of the particle; And a core-shell structure of a shell located on an outer surface of the core, wherein the core comprises a doping element present in a concentration gradient decreasing from the center of the particle to the interface between the core and the shell, At least one selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, The present invention relates to a cathode active material for a secondary battery, which comprises a doping element in an inner region of the particle, and the doping element has a concentration gradient in a region inside the cathode active material particle, It is possible to continuously exhibit the effect of the doping element without any fear of degradation of the doping element, so that it exhibits high capacity, long life and thermal stability when applied to a secondary battery, minimizes deterioration in performance at high voltage, The effect can be expressed.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a secondary battery, a method for producing the same, and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a cathode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

Lithium transition metal complex oxides are used as the cathode active material of lithium secondary batteries, and lithium cobalt composite metal oxides of LiCoO ₂ having high action voltage and excellent capacity characteristics are mainly used. However, since LiCoO ₂ has a poor thermal characteristic due to destabilization of crystal structure due to depolythium, and is expensive, it can not be used as a power source in fields such as electric vehicles and the like.

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 as materials for replacing LiCoO ₂ . Research and development of a lithium nickel composite metal oxide having a high reversible capacity of about 200 mAh / g, which is easy to realize a large capacity battery, has been actively studied. However, LiNiO ₂ has poor thermal stability as compared with LiCoO _2, and if an internal short circuit occurs due to external pressure or the like in a charged state, there is a problem that the cathode active material itself is decomposed to cause rupture and ignition of the battery.

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

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 performed by synthesizing a core material and then coating a material having a different composition to the outside to prepare a double layer, and then mixing with a lithium salt and performing a heat treatment. In this method, the metal composition of the core and the outer layer can be differently synthesized at the time of synthesis, but a continuous concentration gradient of the metal composition is not sufficiently formed in the produced cathode active material, so that the effect of improving the output characteristic is not satisfactory, have.

Another method is to increase the content of Ni in NMC-based lithium oxide for high energy density in small automobiles and power storage cells. Generally, capacity, lifetime, or stability of a cathode active material has a trade-off relationship in which, when the capacity is increased, the lifetime and stability of the battery are drastically reduced. Accordingly, there has been proposed a method of using only within a limited composition and voltage range, a method of partially stabilizing the structure by replacing a part of the composition of NCM oxide with a different element, and a method of reducing surface side reaction through coating. However, all of these methods have limitations to fundamentally improve the electrochemical and thermal stability of the active material, and the deterioration of the performance is accelerated at the time of high voltage, so that the high energy density of the battery is also difficult.

KR 2005-0083869 A

A problem to be solved by the present invention is to provide a lithium secondary battery which exhibits a high capacity, a long life and thermal stability when applied to a lithium secondary battery, minimizes deterioration in performance at high voltage, And to provide a positive electrode active material for a battery.

Another object of the present invention is to provide a method for producing the cathode active material.

A further object of the present invention is to provide a method for producing the cathode active material for a secondary battery.

In order to solve the above problems,

Lithium composite metal oxide particles,

Said particles having a core in a region corresponding to 1 to 70% by volume of the total volume of particles from the center of the particle; And a core-shell structure of the shell located on the outer surface of the core,

Wherein the core comprises a doping element present in a concentration gradient from the center of the particle to the interface between the core and the shell,

The doping element is selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, Wherein the positive electrode active material is at least one selected from the group consisting of a lithium salt and a lithium salt.

Further, in order to solve the above-mentioned other problems,

(1) preparing a first metal salt solution containing nickel, cobalt, manganese and a doping element, and a second metal salt solution containing nickel, cobalt and manganese and not containing a doping element;

(2) adding the second metal salt solution 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 vol%: 0 vol% to 0 vol%: 100 vol% Adding a chelating agent and a basic aqueous solution at the same time to prepare a cathode active material precursor; And

(3) a step of mixing the cathode active material precursor and the lithium salt followed by heat treatment

The present invention also provides a method for producing a cathode active material for a secondary battery.

Further, in order to solve the above-described problems,

And a cathode active material for the secondary battery.

The cathode active material for a secondary battery according to the present invention includes a doping element in a region inside a particle and the doping element is distributed with a concentration gradient in a region inside the cathode active material particle so that the effect of the doping element is continuously maintained without concern about elution of the doping element. And thus exhibits a high capacity, a high durability and thermal stability when applied to a secondary battery, minimizes deterioration in performance at a high voltage, and can prevent the dissolution of the doping element, thereby continuously exhibiting the effect of the doping element.

FIG. 1 is a graph showing the concentration gradient structures of doping elements contained in the cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The cathode active material for a secondary battery according to the present invention comprises particles of a lithium composite metal oxide, the particles having a core in a region corresponding to 1 to 70% by volume of the total volume of particles from the center of the particle; And a core-shell structure of a shell located on an outer surface of the core, wherein the core comprises a doping element present in a concentration gradient decreasing from the center of the particle to the interface between the core and the shell, At least one selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, to be.

The lithium composite metal oxide particles contained in the cathode active material for a secondary battery of the present invention have a core located at the center of grains and a core-shell structure in which the shell is located on the outer surface of the core. It can be classified according to whether doping element is included or not.

The core may be a region corresponding to 1 to 70% by volume, specifically 1 to 60% by volume, of the total volume of the particles from the center of the particle, and may be a region of Fe, Na, Mg, Ca, Ti, At least one doping element selected from the group consisting of Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, Ta and B, And Ta. The doping element may include one or more doping elements selected from the group consisting of Ta and Ta.

In the cathode active material for a secondary battery of the present invention, the doping element is contained in the core located at the center of the particle, and the elution of the doping element is suppressed, and the effect of the doping element can be continuously exhibited.

The doping element is present in a concentration gradient decreasing from the center of the particle toward the interface between the core and the shell, and when the core contains two or more doping elements, the two or more doping elements may independently have one concentration Gradient slope value. At this time, the concentration gradient slope of the doping element may be constant.

Specifically, the doping element contained in the cathode active material is included in the core of the particle and can be decreased from the center of the particle to the interface of the core and the shell with a continuous concentration gradient, wherein the concentration of the doping element The gradient slope can be constant from the center of the cathode active material particle to the interface of the core and the shell. In addition, the shell may contain no or small amount of doping element, and most of the doping element may be contained in the core, thereby suppressing dissolution of the doping element, so that the effect of the doping element can be continuously exhibited.

The doping element contained in the shell may be 0 to 10 atomic%, specifically 0 to 5 atomic%, of the total doping elements included in the cathode active material for the secondary battery.

On the other hand, in the cathode active material according to an embodiment of the present invention, the doping element may be formed in an amount of 10 vol% or less, based on the total atomic weight of the doping element contained in the cathode active material, in the region in (hereinafter referred to as "Rs ₁₀ region") (hereinafter referred to as "Rc ₁₀ area" referred to), and the positive electrode active material area of less than 10% by volume, based on the total volume of the core toward the center from the interface between the core and the shell of the particles May be 10 to 70 atomic%. In addition, the average concentration ratio of the doping elements in the cathode active material particle core may be 0.4 to 0.7.

In the present invention, "continuously exhibiting a concentration gradient" or "having a gradient of concentration gradient" means that the concentration of a doping element or the like exists in a concentration distribution that gradually changes over the entire particle. Specifically, the concentration distribution is such that the change of the doping element per 0.1 mu m from the center toward the surface in the particle is 0.1 to 30 atomic%, more specifically, 0.1 to 30 atomic% based on the total atomic weight of the doping element contained in the cathode active material 0.1 to 20 atomic%, and more particularly 1 to 10 atomic%.

In the present invention, the concentration gradient structure and concentration of the doping element in the cathode active material particle can be measured by an electron probe micro analyzer (EPMA), an inductively coupled plasma-atomic emission spectrometer (EPA), or a method of analyzing the surface of a cathode active material by using an EPMA, such as ICP-AES or Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) The atomic ratio of each doping element can be measured.

The lithium composite metal oxide may include nickel, cobalt, and manganese, and the concentrations of nickel, cobalt, and manganese contained in the lithium composite metal oxide may be the same throughout the particles, The concentration may vary.

When the concentration of nickel, cobalt, and manganese contained in the cathode active material varies depending on the position in the particle, the nickel, cobalt, and manganese increase or decrease while continuously exhibiting a concentration gradient from the center of the cathode active material particle to the particle surface . Also, the nickel, cobalt, and manganese contained in the cathode active material may independently have one concentration gradient slope value. At this time, the concentration gradient slope of the metal element may be constant.

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

[Chemical Formula 1]

Li _a Ni _x Mn _y Co _z M _w O _{2 +?}

Wherein M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? W? 0.1, 0??? 0.02, 0 <z? 0.5, 0 <z? 0.5, x + y + z? 1.

Further, in one embodiment of the present invention, the shell of the particles of the lithium composite metal oxide may have an average composition represented by the following formula (2).

(2)

Li _b Ni _s Mn _t Co _u M _v O _{2 + δ}

Wherein M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? T? 0.5, 0? U? 0.5, 0? V? 0.01, 0??? 0.02, 0? T? 0.50, t + u + v? 1.

The cathode active material may have an average particle size (D50) of 3 to 50 占 퐉 in consideration of the specific surface area and the density of the cathode mixture. Considering the specific characteristics and the effect of improving the initial capacity characteristics, And may have an average particle diameter (D50). In the present invention, the average particle diameter (D50) of the cathode active material can be defined as a particle diameter at a 50% of the particle diameter distribution. The average particle diameter (D50) of the cathode active material particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. For example, the average particle size (D50) of the cathode active material is measured by dispersing the particles of the cathode active material in a dispersion medium, introducing the particles into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000) (D50) of 50% of the particle diameter distribution in the measuring apparatus can be calculated.

The present invention also provides a method for producing the cathode active material for the secondary battery.

The method for producing a cathode active material for a secondary battery of the present invention comprises the steps of (1) a first metal salt solution containing nickel, cobalt, manganese and a doping element, and a second metal salt solution containing nickel, cobalt and manganese, Preparing; (2) adding the second metal salt solution 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 vol%: 0 vol% to 0 vol%: 100 vol% Adding a chelating agent and a basic aqueous solution to prepare a cathode active material precursor exhibiting 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) mixing the cathode active material precursor and the lithium salt, followed by heat treatment.

In step (1), a first metal salt solution containing nickel, cobalt, manganese and a doping element, and a second metal salt solution containing nickel, cobalt and manganese and not containing a doping element are prepared.

The first metal salt solution includes a doping element in addition to nickel, cobalt, and manganese. The doping element includes Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, , Mo, Al, Ga, W, Ta, and B may be used.

On the other hand, the second metal salt solution includes nickel, cobalt and manganese, but does not include other doping elements.

The first metal salt solution and the second metal salt solution may be prepared by the same / similar method. Specifically, the first metal salt solution and the second metal salt solution may be prepared by dissolving a nickel salt, a cobalt salt, The first metal salt solution may include nickel, cobalt, and manganese as well as a doping element. Thus, the salt of the doping element may be added to a solvent.

The metal salt may be a sulfate, a nitrate, an acetate, a halide, a hydroxide, or an 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 salts, Co (OH) ₂ , CoOOH, Co (OCOCH ₃ ) ₂揃 4H ₂ O, Co (NO ₃ ) ₂揃 6H ₂ O, or Co (SO ₄ ) ₂揃 7H ₂ O And any one or a mixture of two or more thereof may be used.

In step (2), the second metal salt is added to the first metal salt solution such that the mixing ratio of the first metal salt solution and the second metal salt solution gradually changes from 100 vol%: 0 vol% to 0 vol%: 100 vol% A chelating agent and a basic aqueous solution are added to prepare a cathode active material precursor exhibiting a concentration gradient in which the doping element decreases from the center of the particle toward the interface between the core and the shell.

Since the reaction (particle nucleation and grain growth) is performed in the state where only the first metal salt solution is present at the initial stage of the production process of the cathode active material precursor, the precursor particles initially prepared have a composition of 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 also gradually changes from the center of the precursor particle to the composition of the second metal salt solution. Therefore, by adjusting the composition of the first metal salt solution and the second metal salt solution, and controlling the mixing rate and the ratio thereof, the desired position in the direction from the center to the surface of the precursor particles can be controlled to have a desired composition.

Specifically, since the reaction is performed in the state where only the first metal salt solution is present at the beginning of the cathode active material precursor production step, the center of the precursor particles, that is, the core, contains nickel, cobalt, The precursor particles including the doping element are formed. Thereafter, the second metal salt solution not containing the doping element is gradually mixed, and finally, only the second metal salt solution is present, so that the precursor particles The surface side, i.e., the shell, contains no doping element. Accordingly, the cathode active material precursor including the doping element can be produced in the core in the region corresponding to 1 to 70% by volume of the total volume of the particles, specifically in the region corresponding to 1 to 60% by volume.

In one embodiment of the present invention, when the contents of nickel, cobalt and manganese in the first metal salt solution and the second metal salt solution are the same and only the inclusion of the doping element is present, The reaction is carried out in the presence of only the first metal salt solution, and precursor particles including nickel, cobalt, manganese and the doping element are formed according to the composition of the first metal salt solution, and then the second metal salt solution not containing the doping element The content of the doping element is gradually decreased as it is progressively mixed and is directed toward the outer surface of the precursor particle of the cathode active material and finally the reaction is performed in the state where only the second metal salt solution is present so that the outer surface side of the precursor particles, The doping element is not included. Since the doping element is contained only in the first metal salt solution, the content of the doping element is gradually reduced according to the mixing of the second metal salt solution, and the doping element is decreased from the center of the particle toward the interface between the core and the shell Concentration gradient.

Accordingly, the core of the prepared positive electrode active material precursor may have an average composition represented by the following formula (3).

 (3)

Ni _x Mn _y Co _z M _w O _{2 +}

Wherein M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? Y? 0.5, 0? W? 0.1, 0??? 0.02, 0 <x + y + z? 1.

In addition, the shell of the cathode active material precursor may have an average composition represented by the following formula (4).

[Chemical Formula 4]

Ni _s Mn _t Co _u M _v O _{2 + δ}

Wherein M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? T? 0.5, 0? U? 0.5, 0? V? 0.01, 0??? 0.02, 0 <t + u + v? 1.

The addition of the second metal salt solution to the first metal salt solution is continuously performed, and by continuously supplying the second metal salt solution, the concentration of the metal increases from the center of the particle to the surface in one coprecipitation reaction step The concentration gradient of the metal in the active precursor and the slope thereof can be easily controlled by the composition and mixing ratio of the first metal salt solution and the second metal salt solution have.

Further, the concentration gradient of the metal element in the particle can be formed by controlling the reaction rate or the reaction time. In order to obtain a high-density state in which a specific metal concentration is high, it is preferable to lengthen the reaction time and decrease the reaction rate. In order to obtain a low-density state in which the specific metal concentration is low, it is preferable to shorten the reaction time and increase the reaction rate .

Also, the size of the cathode active material particles can be controlled by controlling the amount of the second metal salt solution supplied to the first metal salt solution and the reaction time. Specifically, it may be preferable to appropriately adjust the supply amount of the second metal salt solution and the reaction time so as to have the particle size of the cathode active material as described above.

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

In addition, in the production of the cathode active material precursor, the rate of the second metal salt solution added to the first metal salt solution may be the same as the rate of the basic aqueous solution, and the rate of addition of the chelating agent may be controlled by the rate of the second metal salt solution Gt; 5 to 7 times &lt; / RTI &gt; For example, the addition rate of the chelating agent in the section for forming a core is 1 g / min to 5 g / min, and the addition rate of the basic aqueous solution may be 10 g / min to 20 g / min.

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

The chelating agent may be added in an amount such that the molar ratio is 0.5 to 1 based on 1 mol of the mixed solution of the core and the shell-forming metal salt. Generally, the chelating agent reacts with the metal at a molar ratio of 1: 1 to form a complex. However, since the basic aqueous solution in the complex formed and the unreacted complex that has not reacted can be converted into an intermediate product and recovered as a chelating agent, The chelating use amount can be lowered compared with the conventional method. As a result, the crystallinity of the cathode active material can be enhanced and stabilized.

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

The concentration of the basic aqueous solution may be 2M to 10M. If the concentration of the basic aqueous solution is less than 2 M, the particle formation time becomes longer, the tap density decreases, and the yield of the co-precipitation reaction may be lowered. On the other hand, when the concentration of the basic aqueous solution exceeds 10 M, since the particles grow rapidly due to the abrupt reaction, it is difficult to form uniform particles, and the tap density may also decrease.

The reaction for preparing the cathode active material precursor may be performed within a pH range of 10 to 12. If the pH is out of the above range, there is a possibility that the size of the cathode active material precursor to be produced is changed or the particle cleavage is caused. In addition, metal ions may be eluted on the surface of the precursor of the cathode active material to form various oxides by side reaction. Such pH control can be controlled through the addition of a basic aqueous solution.

The reaction for preparing the cathode active material precursor may be carried out in an inert atmosphere such as nitrogen at a temperature range of 30 ° C to 80 ° C. In order to increase the reaction rate during the reaction, a stirring process may be selectively performed, wherein the stirring speed may be 100 to 2000 rpm.

As a result of the reaction in the above step (2), the precursor of the cathode active material having the structure as described above is precipitated. The precursor of the precipitated cathode active material may be selectively separated and dried according to a conventional method, 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 heat-treated.

As the lithium salt, a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and it is not particularly limited as long as it can be dissolved in water. Specifically, the lithium salt is _{Li 2 CO 3, LiNO 3,} LiNO 2, LiOH, LiOH and _{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 any one or a mixture of two or more of them may be used.

When the cathode active material precursor and lithium salt are mixed, a sintering agent may be optionally added. The sintering agent specifically includes a compound containing an ammonium ion 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 metal halides such as NiCl ₂ or CaCl _2, and any one or a mixture of two or more of them may be used. The sintering may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor. If the content of the sintering agent is less than 0.01 mol, the effect of improving the sintering property of the cathode active material precursor may be insignificant. If the content of the sintering agent is excessively high, the excessive sintering agent may deteriorate the performance of the cathode active material And there is a possibility that the initial capacity of the battery is lowered during the charge / discharge process.

When the lithium salt is mixed with the cathode active material precursor, a moisture removing agent may be optionally added. Specifically, examples of the moisture removing agent include citric acid, tartaric acid, glycolic acid, and maleic acid, and any one or a mixture of two or more thereof may be used. The moisture removing agent may be used in an amount of 0.01 to 0.2 mol based on 1 mol of the positive electrode active material precursor.

The heat treatment process may be performed at 800 ° C to 1100 ° C. If the temperature is less than 800 ° C., there is a fear that the discharge capacity per unit weight, the cycle characteristics, and the operating voltage may be lowered due to the residual unreacted raw material. If the temperature exceeds 1100 ° C., There is a fear of lowering the discharge capacity per weight, lowering the cycle characteristics, and lowering the operating voltage.

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

Meanwhile, the prebaking may be selectively performed by holding the substrate at 250 to 650 ° C for 5 to 20 hours before the heat treatment. After the heat treatment, the annealing may be performed at 600 ° C to 750 ° C for 10 to 20 hours.

By controlling the distribution of transition metal throughout the active material particles, the cathode active material produced by the above-described production method exhibits high capacity, long life and thermal stability at the time of battery application, and can minimize performance deterioration at high voltage.

According to another embodiment of the present invention, there is provided a positive electrode comprising the above-mentioned positive electrode active material.

Specifically, the anode includes a cathode current collector, and a cathode active material layer formed on the cathode current collector and including the cathode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine unevenness may be formed on the surface of the current collector to increase the adhesive force of the cathode 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, and a nonwoven fabric.

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

At this time, the conductive material is used for imparting conductivity to the electrode. The conductive material can be used without particular limitation as long as it has electron 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 whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be typically contained in an amount of 1 to 30% by weight based on the total weight of the cathode active material layer.

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

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the cathode active material and optionally a binder and a conductive material may be mixed or dispersed in a solvent to prepare a composition for forming a cathode active material layer, which is then applied to a cathode current collector, followed by drying and rolling. At this time, the types and contents of the cathode active material, the binder, and the conductive material are as described above.

Examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like. Water and the like, and one kind or a mixture of two or more kinds can be used. The amount of the solvent to be used is sufficient to dissolve or disperse the cathode active material, the conductive material and the binder in consideration of the coating thickness of the slurry and the yield of the slurry, and then to have a viscosity capable of exhibiting excellent thickness uniformity Do.

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

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

Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, as described above. The lithium secondary battery may further include a battery container for storing the positive electrode, the negative electrode and the electrode assembly of 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 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 in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 μm, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to strengthen 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, and a nonwoven fabric.

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

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloys, Sn alloys or Al alloys; Metal oxides capable of doping and dedoping lithium such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Or a composite containing the metallic compound and the carbonaceous material such as Si-C composite or Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. The carbon material may be both low-crystalline carbon and high-crystallinity carbon. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitches. derived cokes).

In addition, the binder and the conductive material may be the same as those described above for the anode.

The negative electrode active material layer may be formed by applying and drying a negative electrode composition prepared by dispersing a negative electrode active material on a negative electrode current collector and optionally a binder and a conductive material in a solvent or by drying the negative electrode composition on a separate support , And then peeling the film from the support to laminate the film on an anode current collector.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a moving path of lithium ions. The separator can be used without limitation, as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable to have a low resistance and an excellent ability to impregnate the electrolyte. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and may be optionally used as a single layer or a multilayer structure.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the production of a lithium secondary battery. It is not.

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

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -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), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a straight, branched or cyclic hydrocarbon group of C2 to C20, which may contain a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, 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 performance of the electrolytic solution may be excellent.

The lithium salt can 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, 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 may be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

In addition to the electrolyte components, the electrolyte may contain, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate or the like, pyridine, triethanolamine, or the like for the purpose of improving lifetime characteristics of the battery, Ethyl phosphite, triethanol amine, cyclic ether, ethylenediamine, glyme, hexametriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, At least one additive such as benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, benzyl alcohol, 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 cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it can be used in portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles hybrid electric vehicle (HEV)).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

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

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

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  One

Manganese sulfate: 0.1 mol / m &lt; ³ &gt; aqueous solution of zirconium sulfate, nickel sulfate: manganese sulfate: cobalt sulfate in a molar ratio of 60:20:20, 20 molar ratio of a second metal salt solution having a concentration of 2.4 M was prepared.

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

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

The reaction was continued while the second metal salt solution was added to the first metal salt solution at 15 g / min. The average residence time of the metal salt solution in the reactor was about 2 hours. After reaching the steady state, the reactants were given a steady state duration to obtain a more dense coprecipitated compound.

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

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

Example  2

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

Comparative Example  One

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

To the reactor was added a 0.1 mol / m ³ aqueous solution of zirconium sulfate and a metal salt solution of 2.4 M in concentration of nickel sulfate: manganese sulfate: cobalt sulfate in a molar ratio of 50:30:20 at a rate of 15 g / min. The pH was adjusted while the ammonia solution of 3.6 M was continuously fed into the reactor at 3 g / min. The pH was maintained at 11 while 2 M sodium hydroxide solution was fed at a rate of 15 g / min.

The mixed metal aqueous solution was adjusted to have an average residence time in the reactor of 6 hours. After the reaction reached a steady state, the mixed metal aqueous solution was allowed to stand for a steady state to give a first composite metal hydroxide precipitate &Lt; / RTI &gt;

To the precipitate of the first composite metal hydroxide which reached the steady state, a metal salt solution of 1 M concentration in which nickel sulfate: manganese sulfate: cobalt sulfate was mixed at a molar ratio of 50:30:20 was continuously fed at 5 g / Solution and a 0.2 M sodium hydroxide solution were supplied to conduct a coprecipitation reaction while maintaining the pH to 11 to obtain a composite metal hydroxide precipitate having a core-shell structure.

The resulting composite metal hydroxide precipitate of the core-shell structure was washed and dried in an on-fog drier at 110 ° C for 12 hours to obtain a composite metal oxide precursor having a core-shell structure.

Comparative Example  2

Nickel sulfate: manganese sulfate: cobalt sulfate was mixed at a molar ratio of 50:30:20 to prepare a 2.4 M metal salt solution.

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

The metal salt solution was fed into the continuous stirred tank reactor (CSTR) at 15 g / min. The pH was adjusted while the ammonia solution of 3.6 M was continuously fed into the reactor at 3 g / min. The pH was maintained at 11 while 2 M sodium hydroxide solution was fed at a rate of 15 g / min. Then, the coprecipitation reaction was carried out by adjusting the impeller speed of the reactor to 1000 rpm. At this time, the flow rate was adjusted so that the average residence time of the solution in the reactor was about 6 hours. After the reaction reached a steady state, a steady state duration was given to the reactant to obtain a more dense coprecipitated compound.

The zirconium-doped precursor was prepared by mixing 0.1 mol / m &lt; ³ &gt; of an aqueous zirconium sulfate solution and heat treating the obtained precursor.

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

Experimental Example  1: Concentration in the active material particle gradient  Identification of structure

In order to confirm the concentration gradient structure of the metals from the center to the surface of the active material particles prepared in Examples 1 and 2 and Comparative Examples 1 and 2, EPMA (Electron Probe Micro Analyzer) The atomic ratio of each cathode active material particle was measured while moving from the center to the surface, and the results are shown in FIG.

1, in the cathode active material particles prepared in Examples 1 and 2, the content of Zr, which is a doping element, gradually decreases from the center of the particle toward the surface, and it is confirmed that doping elements are not contained . On the other hand, in the cathode active material particles prepared in Comparative Examples 1 and 2, Zr, which is a doping element, exists on the surface and the shell, respectively, and it can be confirmed that the cathode active material particles do not have a constant concentration gradient due to a rapid concentration change.

Experimental Example  2 : Charging and discharging  Character rating

A coin cell (using a Li metal anode) was prepared using the cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, and the battery was charged and discharged under the condition of 0.1 C / 0.1 C at room temperature (25 캜) 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 1 199.1 189.0 94.9 172.0 163.2 Example 2 199.0 186.5 93.7 171.8 163.0 Comparative Example 1 199.1 179.5 90.2 168.1 159.5 Comparative Example 2 199.2 181.1 90.9 166.8 158.4

Referring to Table 1, the lithium secondary batteries manufactured using the cathode active materials prepared in Examples 1 and 2 have superior charge / discharge characteristics compared with the lithium secondary batteries prepared using the cathode active materials prepared in Comparative Examples 1 and 2 As shown in Fig.

Experimental Example  3: Cycle characteristic evaluation experiment

A coin cell (Li metal cathode) was prepared using the cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, and electrochemical evaluation tests were conducted as follows to evaluate the relative efficiency according to the number of cycles Respectively.

Specifically, the lithium secondary battery was charged at 25 ° C. until a constant current (CC) of 4.3 V was reached at 1 ° C., and then charged at a constant voltage (CV) of 4.3 V until the charging current reached 0.05 mAh. . Thereafter, the resultant was allowed to stand for 20 minutes, discharged at a constant current of 2 C until it reached 3.0 V, and then repeatedly subjected to 1 to 50 cycles. The results are shown in Table 2 below.

Capacity retention after 50 cycles (%) Example 1 98.9 Example 2 98.5 Comparative Example 1 94.7 Comparative Example 2 95.8

Referring to Table 2, the lithium secondary batteries manufactured using the cathode active materials prepared in Examples 1 and 2 had a capacity after 50 cycles as compared with the lithium secondary batteries manufactured using the cathode active materials prepared in Comparative Examples 1 and 2 It can be confirmed that the retention ratio is excellent.

Claims (14)

Lithium composite metal oxide particles,
Said particles having a core in a region corresponding to 1 to 70% by volume of the total volume of particles from the center of the particle; And a core-shell structure of the shell located on the outer surface of the core,
Wherein the core comprises a doping element present in a concentration gradient from the center of the particle to the interface between the core and the shell,
The doping element is selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, Wherein the positive electrode active material is a positive electrode active material for a secondary battery.
The method according to claim 1,
Wherein the doping element is at least one selected from the group consisting of Zr, W, Ti, Nb, Mo and Ta.
The method according to claim 1,
Wherein when the core comprises two or more doping elements, each of the two or more doping elements independently has a gradient slope of one concentration gradient.
The method according to claim 1,
An Rc ₁₀ region corresponding to ₁₀ % by volume based on the total volume of the cathode active material particles from the center of the cathode active material particle to the surface direction,
Wherein the difference in concentration of the doping element in the region of Ri ₁₀ corresponding to ₁₀ % by volume of the total volume of the core in the center direction from the interface between the core and the shell of the cathode active material particle is 10 to 70 atomic%.
The method according to claim 1,
Wherein the core of the lithium composite metal oxide particles has an average composition represented by the following formula (1).
[Chemical Formula 1]
Li _a Ni _x Mn _y Co _z M _w O _{2 +?}
(M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0.9? A? 1.1, 0.4? X? 0.95, 0 <y? 0.5, 0 <z? 0.5, 0 <w? 0.1, 0??? 0.02, 0 < x + y + z < / = 1)
The method according to claim 1,
Wherein the shell of said lithium composite metal oxide particles has an average composition represented by the following formula (2).
(2)
Li _b Ni _s Mn _t Co _u M _v O _{2 + δ}
(M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0.5? 0? T? 0.5, 0? U? 0.5, 0? V? 0.01, 0??? 0.02, 0? <t + u + v? 1)
(1) preparing a first metal salt solution containing nickel, cobalt, manganese and a doping element, and a second metal salt solution containing nickel, cobalt and manganese and not containing a doping element;
(2) adding the second metal salt solution 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 vol%: 0 vol% to 0 vol%: 100 vol% Adding a chelating agent and a basic aqueous solution at the same time to prepare a cathode active material precursor; And
(3) a step of mixing the cathode active material precursor and the lithium salt followed by heat treatment
Wherein the positive electrode active material is a positive electrode active material.
8. The method of claim 7,
The doping element is selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, W, Wherein the positive electrode active material is at least one selected from the group consisting of lithium hydroxide and lithium hydroxide.
8. The method of claim 7,
Wherein the cathode active material precursor has a core in a region corresponding to 1 to 70 volume% of the total volume from the center of the precursor, and a core-shell structure of a shell located on an outer surface of the core. .
10. The method of claim 9,
Wherein the core of the positive electrode active material precursor has an average composition represented by the following formula (3).
(3)
Ni _x Mn _y Co _z M _w O _{2 +}
(M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? Y? 0.5, 0? W? 0.1, 0??? 0.02, 0 <x + y + z, Lt; = 1)
10. The method of claim 9,
Wherein the shell of the positive electrode active material precursor has an average composition represented by the following formula (4).
[Chemical Formula 4]
Ni _s Mn _t Co _u M _v O _{2 + δ}
(M is at least one element selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, 0? T? 0.5, 0? U? 0.5, 0? V? 0.01, 0??? 0.02, 0 <t + u + v Lt; = 1)
8. The method of claim 7,
In the production of the cathode active material precursor, the addition rate of the second metal salt solution to the first metal salt solution is the same as the addition rate of the basic aqueous solution, and the addition rate of the chelating agent is Wherein the cathode active material is 5 to 7 times slower than the cathode active material.
A positive electrode for a lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 6.
14. A lithium secondary battery comprising a positive electrode according to claim 13.

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