阅读说明：本技术 制造正极活性材料的方法 (Method for manufacturing positive electrode active material ) 是由 李优榄 金佑玹 金东震 蔡和锡 金铉旭 于 2021-03-23 设计创作，主要内容包括：提供一种制造正极活性材料的方法,所述方法包括如下步骤：(A)准备正极活性材料前体,所述正极活性材料前体含有包含随机聚集的一次粒子的核部和围绕所述核部并由在从粒子中心到外侧的方向上取向的一次粒子形成的壳部,其中形成所述壳部的一次粒子的(100)面中的晶粒尺寸对(001)面中的晶粒尺寸之比为3以上；以及(B)将所述正极活性材料前体与含锂原料混合并将混合物进行烧制,由此制备锂过渡金属氧化物,其中所述锂过渡金属氧化物的平均粒径(D-(50))与所述正极活性材料前体的平均粒径(D-(50))相比减小0.01％～20％,其中在制造所述正极活性材料期间粒度减小,从而改善了粒子强度和能量密度。(There is provided a method of manufacturing a positive electrode active material, the method including the steps of: (A) preparing a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of the primary particles forming the shell portion is 3 or more; and (B) mixing the positive active material precursor with a lithium-containing raw material and firing the mixture, thereby preparing a lithium transition metal oxide, wherein the lithium transition metal oxide has an average particle diameter (D) 50 ) Before the positive electrode active materialAverage particle diameter (D) of the solid 50 ) A reduction of 0.01% to 20% in comparison, wherein the particle size is reduced during the manufacture of the cathode active material, thereby improving particle strength and energy density.)

1. A method of manufacturing a positive electrode active material, comprising the steps of:

(A) preparing a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of the primary particles forming the shell portion is 3 or more; and

(B) mixing the positive active material precursor with a lithium-containing raw material and firing the mixture, thereby preparing a lithium transition metal oxide,

wherein the average particle diameter (D) of the lithium transition metal oxide₅₀) And the average particle diameter (D) of the positive electrode active material precursor₅₀) Compared with the reduction by 0.01 to 20 percent.

2. The method according to claim 1, wherein, in the positive electrode active material precursor, a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of a primary particle forming the shell portion is in a range of 3 to 6.

3. The method according to claim 1, wherein, in the positive electrode active material precursor, a ratio of a length of the shell portion to a diameter of the core portion is 1 or more.

4. The method according to claim 1, wherein the step (a) includes a method of preparing a positive active material precursor, the method including:

a first step of forming positive electrode active material precursor particles by a coprecipitation reaction while continuously supplying a raw material to a reactor having a filtering unit and an extraction unit;

a second step of discharging the reaction solution filtrate from which the solids have been removed through the filtering unit when the reaction solution reaches a certain level in the reactor, thereby maintaining a constant reaction solution level; and

a third step of extracting a part of the reaction solution containing the positive electrode active material precursor by the extraction unit and discharging it to a sump tank, thereby maintaining the solid concentration of the reaction solution below a certain level.

5. The method of claim 1, wherein the step (a) comprises:

performing a coprecipitation reaction at a pH of 12 or more, thereby forming a core portion including randomly aggregated primary particles; and

followed by a coprecipitation reaction at a pH of less than 12, thereby forming a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the center of the particles to the outside.

6. The method according to claim 4, wherein, in the third step, a part of the reaction solution is extracted from a point in time at which the particle diameter of the positive electrode active material precursor in the reaction solution reaches a minimum desired particle diameter of the positive electrode active material precursor.

7. The method according to claim 4, wherein, in the third step, the solid concentration of the reaction solution is maintained at 85% by weight or less.

8. The method of claim 1, wherein in the step (B), the firing is performed at a temperature of 700 to 1000 ℃ for 5 to 35 hours.

9. The method of claim 1, further comprising the steps of:

(C) the lithium transition metal oxide is mixed with a raw material containing a coating element, and the mixture is subjected to a heat treatment, thereby forming a coating layer on the surface of the lithium transition metal oxide.

10. The method according to claim 1, wherein the positive active material precursor is represented by the following chemical formula 1 or chemical formula 2:

[ chemical formula 1]

[Ni_xCo_yM¹ _zM² _w](OH)₂

[ chemical formula 2]

[Ni_xCo_yM¹ _zM² _w]O·OH

Wherein, in chemical formula 1 and chemical formula 2, x is 0.5-1, y is 0-0.5, z is 0-0.5 and w is 0-0.2,

M¹is one or more selected from the following: mn and Al, and the balance of the alloy,

M²is one or more selected from the following: zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y.

11. The method according to claim 1, wherein the positive electrode active material has an average particle diameter (D) of 1 to 25 μm₅₀)。

12. The method according to claim 1, wherein the positive electrode active material has a particle strength of 100MPa to 250 MPa.

Technical Field

Cross Reference to Related Applications

The priority and benefit of korean patent application No. 10-2020-0036937, filed on 26/3/2020, the disclosure of which is hereby incorporated by reference in its entirety.

The present invention relates to a method of manufacturing a positive electrode active material.

Background

Due to the increase in technical development and demand for mobile devices, the demand for secondary batteries has sharply increased as an energy source. Among these secondary batteries, lithium secondary batteries having high energy density and high voltage, long cycle life and low self-discharge rate have been commercialized and widely used.

As a positive electrode active material for a lithium secondary battery, a lithium transition metal composite oxide has been used, and among these materials, a lithium cobalt composite metal oxide having a high operating voltage and excellent capacity characteristics, such as LiCoO, is mainly used₂. However, LiCoO₂Has an unstable crystal structure due to the deintercalation of lithium, and thus has poor thermal properties. In addition, because of LiCoO₂It is expensive, so it has a limitation in being used as a power source in fields such as electric vehicles in large quantities.

As LiCoO₂Instead of (2), lithium manganese complex metal oxides (LiMnO) have been developed₂、LiMn₂O₄Etc.), lithium iron phosphate compounds (LiFePO)₄Etc.) or lithium nickel composite metal oxide (LiNiO)₂Etc.). Among these materials, research efforts have been particularly actively made to develop lithium nickel composite metal oxides capable of easily realizing large-capacity batteries due to having a high reversible capacity of about 200 mAh/g. However, with LiCoO₂In contrast, LiNiO₂There are problems such as low thermal stability, and when an internal short circuit occurs in a charged state due to pressure applied from the outside, etc., the positive electrode active material itself is decomposed, thereby causing rupture and ignition of the battery. Therefore, LiNiO is maintained₂A lithium transition metal oxide in which a part of nickel (Ni) is replaced with cobalt (Co), manganese (Mn) or aluminum (Al) has been developed as a method of improving low thermal stability while having excellent reversible capacity.

In the case of a lithium ion battery using such a lithium transition metal oxide, particularly a lithium transition metal oxide having a high Ni content (Ni-rich) as a positive electrode active material, the capacity of the battery, whether to generate high power output, and whether to generate gas at high temperature are affected not only by chemical properties such as the composition of the positive electrode active material, the amount of impurities, and the amount of lithium byproducts present on the surface, but also by physical properties such as the size, surface area, density, and shape of positive electrode active material particles.

On the other hand, in the process of mixing the positive electrode active material precursor with the lithium compound and firing it to synthesize the above lithium transition metal oxide, the physical properties of the positive electrode active material precursor are greatly changed.

Therefore, there is a need for a method of manufacturing a positive electrode active material, which is capable of appropriately controlling physical properties that change during the manufacture of the positive electrode active material, thereby increasing the mechanical strength of the positive electrode active material and improving the capacity characteristics and resistance characteristics of a battery to which the positive electrode active material is applied.

Disclosure of Invention

[ problem ] to

The present invention is directed to providing a method of manufacturing a positive electrode active material, in which particle size is reduced during the manufacture of the positive electrode active material, thereby improving particle strength and energy density.

[ solution ]

One aspect of the present invention provides a method of manufacturing a positive electrode active material, the method including the steps of:

(A) preparing a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of the primary particles forming the shell portion is 3 or more; and

(B) mixing the positive active material precursor with a lithium-containing raw material and firing the mixture, thereby preparing a lithium transition metal oxide, wherein the lithium transition metal oxide has an average particle diameter (D)₅₀) And the average particle diameter (D) of the positive electrode active material precursor₅₀) Compared with the reduction by 0.01 to 20 percent.

Advantageous effects

According to the present invention, a positive electrode active material is produced using a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of the primary particles forming the shell portion is 3 or more. Since the lithium transition metal oxide particles are smaller than the positive electrode active material precursor particles by a specific percentage, the particle density is increased and thus the mechanical strength of the positive electrode active material can be improved, and when such a positive electrode active material is applied to a secondary battery, the capacity characteristics of the battery, etc. can be improved.

Detailed Description

The terms and words used in the present specification and claims should not be construed as limited to commonly used meanings or dictionary meanings, but interpreted as having meanings and concepts consistent with the technical spirit of the present invention on the basis of the principle that the inventor is able to define the concepts of the terms appropriately for the best explanation of their invention.

It will be understood that terms such as "comprising," "including," "having," or "having," when used in this specification, specify the presence of stated features, values, steps, components, or combinations thereof, and do not preclude the presence or addition of one or more other features, values, steps, components, or combinations thereof.

In the present specification, "particles" mean particles having a micron-sized size, "primary particles" mean a primary structure of a single particle, and "secondary particles" mean an aggregate in which primary particles are aggregated by physical or chemical bonding between the primary particles even if the primary particles forming the secondary particles are not subjected to an intentional aggregation or assembly process, that is, a secondary structure.

In the present specification, the ratio of the grain size in the (100) plane to the grain size in the (001) plane of the primary particle forming the shell section is a value obtained by dividing the grain size calculated by Scherrer equation using the full width at half maximum (FWHM) of the (100) peak measured by X-ray diffraction (XRD) by the grain size calculated by Scherrer equation using the FWHM of the (001) peak.

In the present specification, the average particle diameter (D) may be₅₀) Defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter (D) can be measured using, for example, a laser diffraction method₅₀). In general, the laser diffraction method can measure particle diameters ranging from submicron to several millimeters, and can obtain results with high reproducibility and high resolution.

Hereinafter, the present invention will be described in detail.

Method for manufacturing positive electrode active material

The present inventors have found, based on the fact that the physical properties of a positive electrode active material precursor are changed during the process of manufacturing a positive electrode active material, that particles of a positive electrode active material having a high density can be prepared by reducing unnecessary voids in the particles, and thus have completed the present invention.

Production of Positive electrode active Material of the inventionThe method comprises the following steps: (A) preparing a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane to a crystal grain size in a (001) plane of the primary particles forming the shell portion is 3 or more; and (B) mixing the positive active material precursor with a lithium-containing raw material and firing the mixture, thereby preparing a lithium transition metal oxide. Further, the average particle diameter (D) of the lithium transition metal oxide₅₀) And the average particle diameter (D) of the positive electrode active material precursor₅₀) Compared with the reduction by 0.01 to 20 percent.

The method of manufacturing a positive electrode active material of the present invention may further include the steps of: (C) the lithium transition metal oxide is mixed with a raw material containing a coating element, and the mixture is subjected to a heat treatment, thereby forming a coating layer on the surface of the lithium transition metal oxide.

Hereinafter, each step of the method of manufacturing the positive electrode active material will be described in detail.

Step (A)

In the method of manufacturing a positive electrode active material of the present invention, first, a positive electrode active material precursor is prepared, the positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from a particle center to an outer side, wherein a ratio of a crystal grain size in a (100) plane of the primary particles forming the shell portion to a crystal grain size in a (001) plane is 3 or more.

According to the present invention, since a cathode active material is manufactured using a cathode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the center of the particles to the outside, wherein the ratio of the grain size in the (100) plane to the grain size in the (001) plane of the primary particles forming the shell portion is 3 or more, lithium transition metal oxide particles can be smaller than the cathode active material precursor particles by a specific percentage, and since the density of the particles is increased accordingly, the mechanical strength of the cathode active material can be improved, and when the cathode active material is applied to a secondary battery, the capacity characteristics of the battery can be improved.

According to the present invention, the ratio of the grain size in the (100) plane to the grain size in the (001) plane of the primary particles forming the shell portion of the positive electrode active material precursor may be 3 or more, specifically 3 to 6. In this case, since the length over which lithium ions can move without interruption in the primary particles becomes relatively long, the mobility of lithium can be more effectively improved. In addition, the positive electrode active material manufactured using the positive electrode active material precursor may have a high particle density.

According to the present invention, in the positive electrode active material precursor, the ratio of the length of the shell portion to the diameter of the core portion may be 1 or more. The cathode active material manufactured using the cathode active material precursor may have a high particle density, and may have excellent lithium mobility due to a large area occupied by the shell portion.

According to the present invention, step (a) may include a method of preparing a positive active material precursor, the method including: a first step of forming positive electrode active material precursor particles by a coprecipitation reaction while continuously supplying a raw material to a reactor having a filtering unit and an extraction unit; a second step of discharging the reaction solution filtrate from which the solids have been removed through a filtering unit when the reaction solution reaches a certain level in the reactor, thereby maintaining a constant reaction solution level; and a third step of extracting a part of the reaction solution containing the positive electrode active material precursor by an extraction unit and discharging it to a sump tank, thereby maintaining the solid concentration of the reaction solution below a certain level. That is, the cathode active material precursor may be prepared by the above-described method of preparing the cathode active material precursor. In this case, since the grain growth on the (001) plane is suppressed, the crystal grains formed on the (100) plane may be relatively dominant in size, and the ratio of the crystal grain size in the (100) plane of the primary particle forming the positive electrode active material precursor to the crystal grain size in the (001) plane may be 3 or more, specifically 3 to 6. In addition, since the positive electrode active material precursor has a small core portion and a long shell portion, a positive electrode active material precursor having excellent lithium mobility can be obtained.

In the method of preparing the positive active material precursor, first, a raw material is continuously supplied to a reactor including a filtration unit and an extraction unit. The raw materials may be continuously supplied to the reactor through an input unit provided in the reactor. The raw materials may be mixed in a reactor and thus a reaction solution is formed, and the cathode active material precursor particles may be formed by a coprecipitation reaction of the reaction solution (first step).

Here, the filtering unit is disposed inside the reactor and serves to discharge the reaction solution filtrate from which the solids are removed to the outside of the reactor when the reaction solution reaches a certain level, and the extracting unit serves to maintain the solid content of the reaction solution below a certain level by extracting a portion of the reaction solution and discharging it to the sump tank. In addition, the reactor is configured to receive the reaction solution and perform a co-precipitation reaction to generate a positive active material precursor.

On the other hand, the raw material may comprise a transition metal-containing solution, an ammonium ion-containing solution, and an aqueous alkaline solution.

The transition metal contained in the transition metal-containing solution may be Ni, Co, M¹(Here, M¹Is one or more selected from the following: mn and Al), and the like. Specifically, the transition metal-containing solution may contain an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide of a transition metal, and these are not particularly limited as long as they are soluble in water and can be used.

For example, Ni may be substituted with Ni (OH)₂、NiO、NiOOH、NiCO₃·2Ni(OH)₂·4H₂O、NiC₂O₂·2H₂O、Ni(NO₃)₂·6H₂O、NiSO₄、NiSO₄·6H₂O, fatty acid nickel salt, nickel halide, etc. in the form of a salt, andand one or more of them may be used. On the other hand, the amount of Ni may be adjusted so that the content thereof becomes 60 mol% or more based on the total number of moles of the transition metal.

Furthermore, Co may be Co (OH)₂、CoOOH、Co(OCOCH₃)₂·4H₂O、Co(NO₃)₂·6H₂O、CoSO₄·7H₂Forms of O and the like are contained in the transition metal-containing solution, and one or more of them may be used.

In addition, when M¹In the case of Mn, Mn may be manganese oxide (e.g., Mn)₂O₃、MnO₂And Mn₃O₄) Manganese salts (e.g. MnCO)₃、Mn(NO₃)₂、MnSO₄Manganese acetate, manganese dicarboxylate, manganese citrate, and fatty acid manganese salts), manganese oxyhydroxide, manganese chloride, and the like are contained in the transition metal-containing solution, and one or more thereof may be used.

In addition, when M¹In the case of Al, Al may be contained in the transition metal-containing solution in the form of an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or the like containing Al.

In addition, the transition metal-containing solution may further contain Ni, Co, and M¹Other metal elements (M) than²). Here, the metal element M²May comprise one or more selected from the group consisting of: zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y.

When the transition metal-containing solution further contains a metal element M²In the case of preparing the transition metal-containing solution, a metal-containing element M may be additionally added²The raw materials of (1).

As containing a metal element M²The raw material (b) may use one or more selected from the following: containing a metal element M²Acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide and oxyhydroxide. For example, when the metal element M²In the case of tungsten (W),tungsten oxide or the like can be used.

On the other hand, containing M¹Or containing M²The raw material of (a) may be added in a powder state and may be doped in a step of preparing a lithium transition metal oxide, i.e., a step of mixing a positive electrode active material precursor with a lithium-containing raw material and firing the mixture, rather than in a step of preparing a positive electrode active material precursor.

The ammonium ion-containing solution may comprise one or more selected from the group consisting of: NH (NH)₄OH、(NH₄)₂SO₄、NH₄NO₃、NH₄Cl、CH₃COONH₄And (NH)₄)₂CO₃. In this case, as the solvent, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be uniformly mixed with water can be used.

The basic aqueous solution may comprise one or more selected from the group consisting of: NaOH, KOH and Ca (OH)₂As the solvent, water or a mixture of water and an organic solvent (specifically, alcohol or the like) which can be uniformly mixed with water can be used. In this case, the concentration of the alkaline aqueous solution may be 5 to 35% by weight, preferably 15 to 35% by weight, more preferably 20 to 30% by weight. When the concentration of the alkaline aqueous solution is within the above range, precursor particles having a uniform size can be formed, the precursor particles can be formed rapidly, and the yield can be excellent.

On the other hand, the raw materials are preferably supplied in an amount such that the pH of the reaction solution becomes 12 or more, preferably 12 to 13. In addition, in order to adjust the pH, the pH may be adjusted by first adding predetermined amounts of the ammonium ion-containing solution and the alkaline aqueous solution before adding the transition metal-containing solution.

The mode of reaction to form the precursor may vary with the pH of the reaction solution. Specifically, when the pH is 12 or more, a reaction of forming a seed crystal of particles mainly occurs, and when the pH is less than 12, a particle growth reaction mainly occurs. Therefore, it is preferable to maintain the pH of the reaction solution at 12 or more for at least a certain amount of time in the initial stage of the reaction so that a large number of particle seeds can be formed.

On the other hand, after the seed crystal of the particle is sufficiently formed, the precursor particle can be grown by adjusting the supply flow rate of the raw material so that the pH of the reaction solution becomes less than 12.

For example, the pH of the reaction solution can be adjusted to less than 12, preferably 10 to 11.9, more preferably 10.5 to 11.7 by adjusting the flow rate of the transition metal-containing solution, the ammonium ion-containing solution and/or the alkaline aqueous solution supplied to the reactor. When the transition metal-containing solution is added while the pH of the reaction solution is adjusted to the above range, the seed crystal formation reaction may be terminated, and the particle growth reaction may occur.

According to the present invention, the step (a) may comprise: forming a core portion including primary particles randomly aggregated by performing a coprecipitation reaction at a pH of 12 or more; and then forming a shell section surrounding the core section and formed of primary particles oriented in a direction from the center to the outside of the particles by performing a coprecipitation reaction at a pH of less than 12. For example, step (a) may comprise: carrying out coprecipitation reaction for 0.5-6 hours at a pH value of more than 12; and then carrying out a coprecipitation reaction at a pH of less than 12 for 1 to 96 hours. In this case, since the positive electrode active material precursor has a small core portion and a long shell portion, a positive electrode active material precursor having excellent lithium mobility can be obtained.

On the other hand, in the above process, the liquid level of the reaction solution in the reactor gradually rises due to the supply of the raw materials. When the reaction solution in the reactor reaches a certain level, the reaction solution filtrate from which solids are removed may be discharged through the filtration unit, thereby performing the coprecipitation reaction while maintaining the reaction solution level constant (second step).

Here, the discharge of the filtrate may be performed in a continuous manner from the point of time when the liquid level of the reaction solution reaches 70% to 100%, preferably 80% to 90%, of the total capacity of the reactor. When the discharge of the filtrate is excessively delayed, the filtrate flow rate may be reduced because the precursor may be trapped in the pores of the filter for separating the precursor from the filtrate or clogging may occur, and when the filtrate flow rate is reduced, the height of the reactant may gradually increase and cause the reaction to be terminated. Therefore, it is necessary to take these results into consideration in advance and appropriately adjust the liquid level of the reaction solution to be filtered.

In order to keep the level of the reaction solution in the reactor constant, it is preferable that the flow rate of the filtrate discharged through the filter unit is the same as the total supply flow rate of the raw materials.

On the other hand, as the coprecipitation reaction proceeds, precursor particles are formed, so that the solid content of the reaction solution gradually increases. When the solid content of the reaction solution is excessively high, since the raw materials are not smoothly mixed due to difficulty in stirring, the coprecipitation reaction is not uniform, and thus a defect in the quality of the precursor of the positive electrode active material may occur. This problem can be prevented by terminating the reaction when the solid content is not yet high, but in this case, there is a problem that the effect of improving productivity is reduced.

However, in the present invention, since the coprecipitation reaction is performed while a part of the reaction solution containing the cathode active material precursor is extracted by the extraction unit and discharged to the liquid collection tank to maintain the solid concentration of the reaction solution below a certain level (third step), the problem caused by the increase in the solid content can be solved.

On the other hand, according to the present invention, it is preferable to start the extraction from the point of time when the particle diameter of the positive electrode active material precursor in the reaction solution reaches the minimum desired particle diameter of the positive electrode active material precursor. This is because when the extraction is started at this time point, the particle size characteristics of the finally obtained positive electrode active material precursor are not adversely affected.

In addition, according to the present invention, it is preferable to extract the reaction solution in an amount to maintain the solid concentration of the reaction solution at 85% by weight or less, preferably 60% by weight to 85% by weight. This is because when the solid concentration of the reaction solution is maintained at 85 wt% or less, stirring can be smoothly performed, whereby occurrence of quality defects of the positive electrode active material precursor can be minimized.

On the other hand, when the positive electrode active material precursor particles are grown to a desired size in the reaction solution, the coprecipitation reaction is terminated, and the positive electrode active material precursor particles are separated from the reaction solution, washed, and dried, thereby obtaining a powder of the positive electrode active material precursor. Preferably, the point of time at which the coprecipitation reaction is terminated is the same as, for example, the point of time at which the particle size of the positive electrode active material precursor particles reaches the desired maximum particle size of the positive electrode active material precursor particles.

The positive active material precursor is a precursor having a core-shell structure, and includes: a core portion; and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the center of the particles to the outside. The nucleus portion is formed at the time of particle seed formation and has a form in which primary particles are randomly aggregated without a specific orientation.

The shell portion is formed when the particles grow and has a form in which the primary particles are aligned while having a specific orientation. Specifically, the shell portion has a form in which primary particles are radially arranged in a direction from the center of the precursor particle to the outside.

In the core portion, since the primary particles are randomly aggregated, a moving path of lithium ions cannot be secured during the intercalation or deintercalation of lithium ions, and thus lithium mobility is low. On the other hand, in the shell portion, since the particles are arranged radially, a movement path of lithium is secured, and thus the mobility of lithium is excellent. Therefore, the mobility of lithium is reduced when the area occupied by the core portion in the particle is large, and the mobility of lithium is improved when the area occupied by the shell portion is large.

On the other hand, according to the present invention, the cathode active material precursor may be represented by, for example, the following chemical formula 1 or chemical formula 2.

[ chemical formula 1]

[Ni_xCo_yM¹ _zM² _w](OH)₂

[ chemical formula 2]

[Ni_xCo_yM¹ _zM² _w]O·OH

In chemical formulas 1 and 2, M¹May be one or more selected from the following: mn and Al, and M²May be one or more selected from the following: zr, B, W, Mo, Cr, Nb,Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y.

In the above, x represents the atomic fraction of Ni in the metal elements in the precursor, and may satisfy 0.5. ltoreq. x <1, 0.6. ltoreq. x. ltoreq.0.98 or 0.7. ltoreq. x. ltoreq.0.95.

In the above, y represents the atomic fraction of Co in the metal elements in the precursor, and may satisfy 0< y.ltoreq.0.5, 0.01. ltoreq. y.ltoreq.0.4, or 0.01. ltoreq. y.ltoreq.0.3.

In the above, z represents M in the metal elements in the precursor¹Atomic fraction of element, and can satisfy 0<z is less than or equal to 0.5, z is less than or equal to 0.01 and less than or equal to 0.4, or z is less than or equal to 0.01 and less than or equal to 0.3.

In the above, w represents M in the metal elements in the precursor²The atomic fraction of the elements can satisfy w is more than or equal to 0 and less than or equal to 0.2, w is more than or equal to 0 and less than or equal to 0.1, w is more than or equal to 0 and less than or equal to 0.05 or w is more than or equal to 0 and less than or equal to 0.02.

On the other hand, the cathode active material precursor prepared by the above method of preparing a cathode active material precursor has excellent tap density and rolling density characteristics. When the cathode active material is manufactured using the cathode active material precursor having high tap density and roll density, the cathode active material having high tap density and roll density can be manufactured, and when the tap density and roll density of the cathode active material are high, the effect of improving the energy density of the battery can be obtained.

Step (B)

When the above-described positive electrode active material precursor, which contains a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the particle center to the outside, in which the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particles forming the shell portion is 3 or more, is mixed with a lithium-containing raw material and fired, an average particle diameter (D) can be obtained₅₀) And the average particle diameter (D) of the positive electrode active material precursor₅₀) A lithium transition metal oxide reduced by 0.01 to 20% compared to the above, and the lithium transition metal oxide can be used to manufacture a positive active material.

In this case, the gap between the primary particles having a ratio of the grain size in the (100) plane to the grain size in the (001) plane of 3 or more, that is, the primary particles forming the shell portion, is reduced by the high-temperature firing step. In the conventional positive electrode active material precursor, the orientation of the primary particles is unclear, and since the above-described void-reducing effect is usually cancelled out by random orientation, a change in the size of the secondary particles before and after firing cannot be directly observed. However, in the cathode active material precursor used in the present invention, since the primary particles of the shell portion are oriented in a specific direction, there may be a combined effect in which the voids between the primary particles are removed in the crystal grain direction, thereby enabling the size of the secondary particles to be reduced. Since unnecessary voids existing in the secondary particles are thus effectively reduced, more dense particles can be formed.

The lithium-containing starting material may be, for example, one or more selected from the group consisting of: lithium carbonate (Li)₂CO₃) Lithium hydroxide (LiOH), LiNO₃、CH₃COOLi and Li₂(COO)₂Preferably Li₂CO₃LiOH, or a combination thereof.

In the preparation of the positive electrode active material, the positive electrode active material precursor and the lithium-containing raw material may be mixed in a molar ratio of 1:1 to 1:1.625 or 1:1 to 1: 1.15. When the mixing amount of the lithium-containing raw material is less than the above range, the capacity of the prepared cathode active material may be reduced, and when the mixing amount of the lithium-containing raw material exceeds the range, unreacted lithium may remain as a by-product, the capacity may be reduced, and the cathode active material particles may be separated after firing (may cause agglomeration of the cathode active material).

On the other hand, as described above, since the M-containing compound in the form of powder may be added during the process of mixing the positive electrode active material precursor with the lithium-containing raw material and firing the mixture¹(Here, M¹Is one or more selected from the following: mn and Al) or M²(one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y), and thereby M-doped therewith¹Or M²The positive electrode active material of (1).

According to the invention, firing can be carried out at temperatures of 700 ℃ to 1000 ℃. When the firing temperature is less than 700 ℃, raw materials may remain in the particles due to insufficient reaction, thereby possibly lowering high-temperature stability of the battery, and structural stability may be lowered because the bulk density and crystallinity are lowered. On the other hand, when the firing temperature exceeds 1000 ℃, the particles may grow unevenly, and the capacity or the like may decrease because the particles are difficult to be crushed. On the other hand, the firing temperature is more preferably in the range of 700 to 980 ℃ in view of particle size control, capacity and stability of the manufactured cathode active material and reduction of lithium-containing by-products.

Firing may be performed for 5 hours to 35 hours. When the firing time is less than 5 hours, it may be difficult to obtain a highly crystalline positive electrode active material because the reaction time is too short, and when the firing time exceeds 35 hours, the particle size may become too large and the manufacturing efficiency may be reduced.

When a positive electrode active material is produced under specific conditions using a positive electrode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the particle center to the outside, wherein the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particles forming the shell portion is 3 or more, as in the present invention, the lithium transition metal oxide prepared in step (B) may have a smaller average particle diameter (D) than the positive electrode active material precursor because the positive electrode active material particles become denser₅₀). Specifically, the average particle diameter (D) of the positive electrode active material precursor₅₀) In contrast, the average particle diameter (D) of the lithium transition metal oxide₅₀) Can be reduced by 0.01-20%, preferably by 0.1-10%.

Step (C)

When the lithium transition metal oxide is mixed with a raw material containing a coating element and subjected to heat treatment, a positive electrode active material in which a coating layer is formed on the surface of the lithium transition metal oxide is obtained.

Comprising in the coatingThe coating element in the raw material of the element may be Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, Y, or the like. The coating element-containing raw material may be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or the like containing the coating element. The raw material containing the coating element may be in a powder state. For example, when the coating element is boron (B), boric acid (B (OH))₃) And the like.

The heat treatment may be carried out at a temperature of 200 to 400 ℃. When the heat treatment temperature is within the above range, the coating layer can be formed while maintaining the structural stability of the transition metal oxide. The heat treatment may be performed for 1 hour to 10 hours. When the heat treatment time is within the above range, the coating layer can be appropriately formed, and the manufacturing efficiency can be improved.

According to the present invention, the cathode active material manufactured by the above-described method of manufacturing a cathode active material may have an average particle diameter (D) of 1 μm to 25 μm₅₀). Preferably, the average particle diameter (D)₅₀) 5 to 15 μm, or 9 to less than 15 μm. When the average particle diameter of the cathode active material is within the above range, a high energy density can be secured because the tap density and the roll density are excellent.

According to the present invention, the positive electrode active material manufactured by the above-described method of manufacturing a positive electrode active material may have improved mechanical strength. Specifically, the positive electrode active material may have a particle strength of 100MPa to 250 MPa. Preferably, the particle strength is 150MPa to 200MPa, 160MPa to 200MPa, or 160MPa to 180 MPa. Therefore, when the cathode active material is applied to a battery, the capacity characteristics, resistance characteristics, and the like of the battery can be improved.

The positive electrode active material may refer to a positive electrode active material having a form of secondary particles formed by aggregation of primary particles and containing a shell portion including primary particles oriented in a specific direction, i.e., oriented in a direction from the center to the outside of the particles.

Since the lithium transition metal oxide particles have a reduced average particle diameter as compared with the above-described positive electrode active material precursor particles, the positive electrode active material particles can be formed more densely than the positive electrode active material precursor particles. Therefore, when the positive electrode active material particles are applied to a battery, energy volume density can be improved, and since mechanical strength is improved, life characteristics can be further improved.

Positive electrode

Another aspect of the present invention provides a positive electrode for a lithium secondary battery including the positive electrode active material manufactured by the above method.

Specifically, the positive electrode includes: a positive electrode current collector; and a positive electrode active material layer disposed on one or more surfaces of the positive electrode current collector and including the positive electrode active material.

The positive electrode collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and for example: stainless steel; aluminum; nickel; titanium; calcining carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. In addition, the cathode current collector may generally have a thickness of 3 to 500 μm, and the current collector may have fine irregularities formed on the surface thereof to improve adhesion of the cathode active material. The cathode current collector may be used in any of various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, a nonwoven fabric, and the like.

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

In this case, the content of the cathode active material may be 80 to 99 wt%, more preferably 85 to 98 wt%, based on the total weight of the cathode active material layer. When the content of the positive electrode active material is within the above content range, excellent capacity characteristics can be exhibited.

In this case, the conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it does not cause chemical changes in the fabricated battery and has electron conductivity. Specific examples thereof include: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; carbon-based materials such as carbon fibers; metal powder or metal fiber of (2) such as copper, nickel, aluminum or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, which may be used alone or in combination of two or more thereof. The content of the conductive material may be 1 to 30 wt% based on the total weight of the positive electrode active material layer.

The binder is used to improve the adhesion between particles of the positive electrode active material and the adhesion between the positive electrode active material and the current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, Ethylene Propylene Diene Monomer (EPDM), sulfonated EPDM, Styrene Butadiene Rubber (SBR), fluororubber, or various copolymers thereof, which may be used alone or in combination of two or more thereof. The binder may be contained in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional method of manufacturing a positive electrode, except for using the above-described positive electrode active material. For example, the positive electrode can be manufactured as follows: coating a positive electrode mixture prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder and a conductive material in a solvent on a positive electrode current collector, and then drying and roll-pressing the resultant; or by casting the positive electrode mixture on a separate support and laminating a film obtained by peeling from the support on a positive electrode current collector. In this case, the kinds and contents of the positive electrode active material, the binder, and the conductive material are the same as described above.

The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and the like, and the above materials may be used alone or in combination of two or more thereof. The amount of the solvent is sufficient if the solvent can dissolve or disperse the positive electrode active material, the conductive material, and the binder, and at a later point in time, a viscosity capable of exhibiting excellent thickness uniformity can be achieved when the slurry is applied to manufacture a positive electrode, in consideration of the coating thickness of the slurry and the manufacturing yield.

Lithium secondary battery

Further, according to the present invention, an electrochemical device including the above-described positive electrode can be manufactured. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, may be a lithium secondary battery.

Specifically, the lithium secondary battery includes a cathode, an anode disposed facing the cathode, a separator disposed between the cathode and the anode, and an electrolyte, and since the cathode is the same as described above, a detailed description thereof will be omitted, and only the remaining configuration will be described in detail below.

In addition, the lithium secondary battery may further optionally include: a battery case accommodating an electrode assembly including a cathode, an anode, and a separator; and a sealing member sealing the battery case.

In the lithium secondary battery, the anode includes an anode current collector and an anode active material layer disposed on the anode current collector.

The anode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity, and for example: copper; stainless steel; aluminum; nickel; titanium; calcining carbon; copper or stainless steel having a surface treated with carbon, nickel, titanium, silver, or the like; aluminum-cadmium alloys, and the like. Further, the anode current collector may generally have a thickness of 3 to 500 μm, and the current collector may have fine irregularities formed on the surface thereof to improve adhesion of the anode active material, similar to the case of the cathode current collector. The anode current collector may be used in any of various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, a nonwoven fabric, and the like.

The negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium may be used. Specific examples of the anode active material include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; (semi) metallic materials capable of forming an alloy with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; (semi) metal oxides capable of doping and dedoping lithium, such as SiO_β(0<β<2)、SnO₂Vanadium oxide or lithium vanadium oxide; or a composite comprising a (semi) metal-based material and a carbonaceous material, such as a Si — C composite or a Sn — C composite, which may be used alone or in combination of two or more thereof. In addition, as the negative electrode active material, a lithium metal thin film may be used. In addition, any of low-crystalline carbon, high-crystalline carbon, and the like may be used as the carbonaceous material. Representative examples of the low crystalline carbon include soft carbon and hard carbon, and representative examples of the high crystalline carbon may include random, plate-like, flake-like, spherical or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature calcined carbon such as coke derived from petroleum or coal tar pitch, and the like.

The content of the negative active material may be 80 to 99 wt% based on the total weight of the negative active material layer.

The binder is a component that facilitates bonding between the conductive material, the active material, and the current collector, and may be generally included in an amount of 0.1 to 10 wt% based on the total weight of the anode active material layer. Examples of the binder include PVDF, polyvinyl alcohol, CMC, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, EPDM, sulfonated EPDM, SBR, nitrile rubber, fluororubber, various copolymers thereof, and the like.

The conductive material is a component for further improving the conductivity of the anode active material, and may be included in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the anode active material layer. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the fabricated battery and has conductivity, and for example: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers such as carbon fibers or metal fibers; a fluorocarbon compound; metal powders such as aluminum powder or nickel powder; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

The anode may be manufactured by: coating an anode mixture prepared by dissolving or dispersing an anode active material and optionally a binder and a conductive material in a solvent on an anode current collector, and then drying it; or casting the anode mixture on a separate support and laminating a film obtained by peeling off the support on an anode current collector.

On the other hand, in the lithium secondary battery, the separator serves to separate the anode and the cathode and provide a passage for the migration of lithium ions, and any separator commonly used in the lithium secondary battery may be used without particular limitation, and in particular, a separator that exhibits low resistance to the migration of electrolyte ions and has excellent electrolyte impregnation ability is preferable. Specifically, it is possible to use: porous polymer films, for example, porous polymer films formed of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers, or ethylene/methacrylate copolymers; or have a stacked structure of two or more layers of the above porous polymer films. In addition, a general porous nonwoven fabric, such as a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, or the like, may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may be optionally used in a single layer or a multi-layer structure.

In addition, examples of the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, an inorganic solid electrolyte, a melt-type inorganic electrolyte, and the like, which may be used to manufacture a lithium secondary battery, but the present invention is not limited thereto.

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

As the organic solvent, any organic solvent that can be used as a medium through which ions participating in an electrical reaction of the battery can move may be used without particular limitation. Specifically, as the organic solvent, there can be used: ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone or epsilon-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), or Propylene Carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitriles such as R-CN (R is a C2 to C20 hydrocarbon group having a linear, branched or cyclic structure and may contain a double bond, an aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1, 3-dioxolane; sulfolane, and the like. Among these solvents, carbonate-based solvents are preferable, and a combination of cyclic carbonates (e.g., EC, PC, etc.) having high ion conductivity and high dielectric constant, which can improve the charge/discharge performance of the battery, and linear carbonate-based compounds (e.g., EMC, DMC, DEC, etc.) having low viscosity is more preferable. In this case, when the cyclic carbonate and the linear carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

As the lithium salt, any compound capable of providing lithium ions for a lithium secondary battery may be used without particular limitation. Specifically, as the lithium salt, there can be used: LiPF₆、LiClO₄、LiAsF₆、LiBF₄、LiSbF₆、LiAlO₄、LiAlCl₄、LiCF₃SO₃、LiC₄F₉SO₃、LiN(C₂F₅SO₃)₂、LiN(C₂F₅SO₂)₂、LiN(CF₃SO₂)₂、LiCl、LiI、LiB(C₂O₄)₂And the like. The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0M. When the concentration of the lithium salt satisfies this range, the performance of the electrolyte can be excellent and lithium ions can be efficiently moved because the electrolyte has appropriate conductivity and viscosity.

In order to enhance the life characteristics of the battery, suppress the decrease in the capacity of the battery, improve the discharge capacity of the battery, and the like, in the electrolyte, one or more additives such as halogenated alkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (glycidyl) dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted compounds may be contained in addition to the above-mentioned electrolyte componentsOxazolidinones, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like. In this case, the content of the additive may be 0.1 to 5% by weight, based on the total weight of the electrolyte.

The secondary battery including the positive electrode active material of the present invention stably exhibits excellent discharge capacity, excellent output characteristics, and excellent life characteristics, and thus can be usefully used for: portable devices such as mobile phones, laptop computers, and digital cameras; and the field of electric vehicles such as Hybrid Electric Vehicles (HEVs).

Accordingly, still another aspect of the present invention provides a battery module including the above-described lithium secondary battery as a unit cell (unit cell) and a battery pack including the same.

The battery module or the battery pack may be used as a power source for a medium-large-sized device selected from one or more of: an electric tool; electric Vehicles (EVs), including HEVs and plug-in hybrid electric vehicles (PHEVs); and an electrical storage system.

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

The lithium secondary battery of the present invention can be used in a battery cell (battery cell) used as a power source for a small-sized device, and can be preferably used as a unit battery in a middle or large-sized battery module including a plurality of battery cells.

Description of the preferred embodiments

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

Examples and comparative examples

The transition metal-containing solution, the ammonium ion-containing solution and the alkaline aqueous solution used in the following examples and comparative examples are as follows.

(A) Solutions containing transition metals

By mixing NiSO₄、CoSO₄And MnSO₄A 2M transition metal-containing solution was prepared by dissolving Ni: Co: Mn in distilled water in such an amount that the molar ratio of Ni: Co: Mn was 0.88:0.05: 0.07.

(B) Solutions containing ammonium ions

15% (w/w) NH₄Aqueous OH solution

(C) Alkaline aqueous solution

25% (w/w) NaOH solution in water

Example 1

20% of the total volume of the reactor equipped with the filter and the pump was filled with distilled water, and dissolved oxygen in the water was removed by purging the reactor with nitrogen gas at a rate of 10L/min. Subsequently, NH was added in an amount of 5 parts by weight with respect to 100 parts by weight of distilled water₄An aqueous OH solution, an aqueous NaOH solution was added, thereby maintaining the pH at 12.2, the temperature inside the continuous reactor at 50 ℃, and stirring was performed at a stirring speed of 250 rpm.

Subsequently, each transition metal-containing solution, NH₄The OH aqueous solution and the NaOH aqueous solution are respectively at 250 mL/min, 40 mL/min anda rate suitable for maintaining the pH of the reaction solution at 12.2 was continuously supplied into the reactor, and coprecipitated for reaction for 2 hours while stirring to form seed crystals of the positive active material precursor particles.

When the reaction solution reached the full level during the coprecipitation reaction, the filter was operated to discharge the filtrate in a continuous manner, thereby maintaining the level of the reaction solution constant.

Subsequently, further aqueous NaOH solution and NH were added₄The OH aqueous solution was added to adjust the pH of the reaction solution to 11.6, and a coprecipitation reaction was additionally performed for 86 hours to grow positive active material precursor particles.

When the particle diameter of the positive electrode active material precursor particles formed in the reactor during the additional coprecipitation reaction reached 14.5 μm, the pump was operated to draw a portion of the reaction solution containing the positive electrode active material precursor particles and discharge it into the sump at a rate of 1L/hour until the reaction was terminated, whereby the solid concentration of the reaction solution was maintained below 85%.

Subsequently, the positive electrode active material precursor particles formed as described above were separated from the reaction solution, washed, and dried at 130 ℃ for 24 hours in a dryer, thereby obtaining Ni having a stoichiometric formula_0.88Co_0.05Mn_0.07(OH)₂The positive electrode active material precursor of (1).

20kg of the positive electrode active material precursor prepared above was mixed with 9.541kg of LiOH. H₂O and 225g Al (OH)₃Mixing to make LiOH H₂After the amount of O was 1.03 equivalent of the amount of the precursor, the mixture was fired at 765 ℃ for 13.5 hours in an oxygen atmosphere to obtain Li [ Ni ] in a stoichiometric formula_0.86Co_0.05Mn_0.07Al_0.02]O₂The lithium transition metal oxide of (1).

After washing the lithium transition metal oxide prepared above, B (OH) is added to the lithium transition metal oxide₃The powder was heat-treated at 295 deg.c for 5 hours at a concentration of 1000ppm to obtain a positive electrode active material having a coating layer formed on the surface of the lithium transition metal oxide.

Example 2

A cathode active material was manufactured in the same manner as in example 1, except that the coprecipitation reaction time was adjusted to 1 hour during the formation of the seed crystals of the cathode active material precursor particles, and when the particle diameter of the cathode active material precursor particles formed in the reactor during the additional coprecipitation reaction reached 9.5 μm, a pump was operated to draw and discharge a portion of the reaction solution containing the cathode active material precursor particles.

Comparative example 1

Except that the average particle diameter (D) was purchased from Zoomwe Science and Technology₅₀) Is 15 μm and is represented by Ni_0.88Co_0.05Mn_0.07(OH)₂A positive electrode active material was produced in the same manner as in example 1, except that the precursor of (a) was used.

Examples of the experiments

Experimental example 1: evaluation of the ratio of the grain size in the (100) plane to the grain size in the (001) plane of the primary particles forming the shell portion of the positive electrode active material precursor

After the cathode active material precursors of examples 1, 2 and comparative example 1 were analyzed by XRD, the ratio of the grain size in the (100) plane of the primary particle forming the shell section to the grain size in the (001) plane was calculated by dividing the grain size determined using the FWHM of the (100) peak of the XRD data by the grain size determined using the FWHM of the (001) peak, and the results were shown in table 1 and used as a measure of orientation.

In the shell section that surrounds the core section and is formed of primary particles oriented in a direction from the particle center to the outside, when the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particles forming the shell section is 3 or more, it can be determined that the primary particles exhibit a distinct orientation.

[ Table 1]

Experimental example 2: evaluation of Performance of Positive electrode active Material precursor and Positive electrode active Material

(1) Average particle diameter (D)₅₀)

The average particle diameters of the positive electrode active material precursors and the positive electrode active materials of examples 1, 2 and comparative example 1 were measured using a particle size distribution meter (S3500 manufactured by Microtrac Retsch company), and the results are shown in table 2 below.

(2) Strength of particles

Samples of the positive electrode active materials of examples 1, 2 and comparative example 1 were prepared, and while applying pressure to the collected samples and increasing the pressure, the time point at which the positive electrode active material particles started to rupture was measured and converted to pressure units (MPa). The results are shown in table 2 below.

[ Table 2]

Referring to tables 1 and 2, it can be seen that, in the case of examples 1 and 2, since the cathode active material was manufactured from the cathode active material precursor in which the primary particle forming the shell section exhibited a significant orientation in the direction from the center of the particle to the outside and the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particle forming the shell section was 3 or more, the particle strength of the cathode active material was significantly higher than that of the cathode active material of comparative example 1.

On the other hand, in the case of examples 1 and 2, it can be seen that the average particle diameter of the positive electrode active material (lithium transition metal oxide) was respectively 3.3% and 4.0% smaller than the average particle diameter of the positive electrode active material precursor, but in the case of comparative example 1, the average particle diameter of the positive electrode active material was the same as the average particle diameter of the positive electrode active material precursor. That is, it can be seen that when the positive electrode active material is manufactured according to the manufacturing method of the present invention, the particle density is excellent because the particle size is reduced.

Experimental example 3: evaluation of the ratio of the length of the shell portion to the diameter of the core portion of the positive electrode active material precursor

The sections of the positive electrode active material precursors of examples 1, 2 and comparative example 1 were photographed with a scanning electron microscope to measure the diameter of the core portion and the length of the shell portion, and the ratio of the length of the shell portion to the diameter of the core portion is shown in table 3 below.

[ Table 3]

Experimental example 4: evaluation of Battery characteristics

Lithium secondary batteries were manufactured using the positive electrode active materials manufactured in examples 1 and 2 and comparative example 1, and the capacities of the lithium secondary batteries were evaluated.

Specifically, each of the positive electrode active materials manufactured in examples 1, 2 and comparative example 1 was mixed with FX35 conductive material and KF9700/BM730H binder in a weight ratio of 97.5:1:1.35:0.15 in NMP solvent to prepare a positive electrode slurry. The positive electrode slurry was coated on one side of an aluminum current collector, dried at 130 ℃, and rolled to obtain a positive electrode. On the other hand, a Li metal disk is used as the anode active material. After an electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, the electrode assembly was placed in a battery case, and an electrolyte was injected into the case, thereby obtaining a lithium secondary battery. In this case, as the electrolyte, LiPF is injected₆An electrolyte prepared by dissolving in an organic solvent of EC/EMC/DEC (3/3/4 by volume) at a concentration of 1M, thereby manufacturing a lithium secondary battery.

The lithium secondary battery manufactured as described above was charged at a constant current of 0.1C at 25 ℃ until a voltage of 4.25V was reached, and then charged at a constant voltage of 4.25V until 0.05C. Subsequently, the lithium secondary battery was discharged at a constant current of 0.1C until a voltage of 3.0V was reached. The numerical values of the charge capacity and the discharge capacity are shown in table 4.

In addition, the capacity of the lithium secondary battery was measured by repeating charging and discharging the battery at a constant current of 0.33C in the range of 3.0V to 4.25V at 45 ℃ for 30 charge/discharge cycles, and in particular, the capacity retention ratio was measured as a percentage of the capacity at the 30 th cycle with respect to the capacity at the 1 st cycle, and is shown in table 4 below. In addition, in each cycle, the high temperature resistance was measured by measuring the voltage drop 60 seconds after the start of discharge and dividing the voltage drop by the applied current value, and particularly, the increase rate of the resistance value at the 30 th cycle with respect to the resistance value at the 1 st cycle was calculated and shown in table 4.

[ Table 4]

Referring to tables 1 to 4, it can be seen that in the case of secondary batteries including the positive electrode active material of examples 1 and 2 manufactured using the positive electrode active material precursor in which the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particle forming the shell portion is 3 or more, more excellent charge/discharge capacity characteristics and more excellent battery efficiency are exhibited, as compared to the case of secondary batteries including the positive electrode active material of comparative example 1 manufactured using the positive electrode active material precursor in which the ratio of the crystal grain size in the (100) plane to the crystal grain size in the (001) plane of the primary particle forming the shell portion is less than 3.

Further, it can be seen that in the case of the secondary batteries including the cathode active materials of examples 1 and 2, the effect of improving the resistance characteristics was excellent in consideration of the fact that the increase rate of the resistance value at the 30 th cycle relative to the resistance value at the 1 st cycle was significantly lower than that in the case of the secondary battery including the cathode active material of comparative example 1.

Therefore, it can be seen that, when a cathode active material is manufactured using a cathode active material precursor containing a core portion including randomly aggregated primary particles and a shell portion surrounding the core portion and formed of primary particles oriented in a direction from the particle center to the outside, and wherein the ratio of the length of the shell portion to the diameter of the core portion is 1 or more, and the ratio of the grain size in the (100) plane of the primary particles forming the shell portion to the grain size in the (001) plane is 3 or more, since lithium transition metal oxide particles are smaller by a certain percentage than the cathode active material precursor particles, the particle density is increased and thus the mechanical strength of the cathode active material can be improved, and when the cathode active material is applied to a secondary battery, the capacity characteristics of the battery and the like can be improved.