KR101567039B1 - Manufacuring method of cathode active material for lithium rechargeable battery, and cathode active material made by the same - Google Patents

Abstract

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a positive electrode active material for a lithium secondary battery produced thereby. More particularly, the present invention relates to a method for reducing the amount of unreacted lithium in a positive electrode active material by introducing a water- A method of manufacturing a positive electrode active material for a lithium secondary battery having a high capacity and stability while reducing the amount of unreacted lithium ions even in the case of a nickel rich positive electrode active material by improving deterioration characteristics and a positive electrode for a lithium secondary battery Lt; / RTI >

Description

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

The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a positive electrode active material for a lithium secondary battery produced thereby. More particularly, the present invention relates to a method for reducing the amount of unreacted lithium in a positive electrode active material by a washing process and metal doping, The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery and a positive electrode active material for a lithium secondary battery produced by the method, thereby improving deterioration characteristics which are rather problematic when introducing a washing process for improving lithium and securing a high capacity and stability.

As the technology and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life and low self-discharge rate among such secondary batteries, It has been commercialized and widely used.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material of a lithium secondary battery, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, The use of LiNiO ₂ , which is a non-aqueous electrolyte, is also considered.

Of the above cathode active materials, LiCoO ₂ is most widely used because of its excellent lifetime characteristics and charge / discharge efficiency. However, LiCoO ₂ is expensive because of its small capacity and resource limitations of cobalt used as a raw material. Therefore, it is used as a power source for mid- There is a disadvantage in that price competitiveness is limited. Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ are advantageous in that they are rich in manganese resources used as raw materials, are inexpensive, environmentally friendly, and excellent in thermal stability. However, they have small capacity, high temperature characteristics, This is a poor problem.

In order to overcome such disadvantages, demand for a nickel rich system as a cathode active material of a secondary battery has begun to increase. However, the active material of the nickel rich system has an advantage of providing a high capacity, The reaction lithium is high, causing problems such as generation of a swelling phenomenon and generation of gas due to reaction with an electrolyte solution.

A method for producing a lithium composite oxide generally comprises preparing a transition metal precursor, mixing the transition metal precursor and a lithium compound, and then calcining the mixture. At this time, LiOH and / or Li ₂ CO ₃ is used as the lithium compound. In general, when the Ni content of the cathode active material is less than 65%, Li ₂ CO ₃ is used. When the Ni content is more than 65%, LiOH is preferably used because it is a low-temperature reaction. However, since the Ni rich system having a Ni content of 65% or more is a low-temperature reaction, there is a problem that the residual lithium amount existing in the form of LiOH and Li ₂ CO ₃ on the surface of the cathode active material is high. Such residual lithium, that is, unreacted LiOH and Li ₂ CO ₃ react with an electrolyte or the like in the battery to cause gas generation and swelling phenomenon, thereby causing a problem that the high-temperature safety is seriously deteriorated. In addition, the unreacted LiOH may cause gelation due to high viscosity in slurry mixing before preparation of the electrode plate.

In order to remove such unreacted Li, a water washing process is generally employed. However, in this case, surface damage of the cathode active material occurs during water washing, resulting in deterioration of capacity and rate characteristics and increase of resistance at high temperature storage.

Korean Patent Publication No. 10-2012-0117822

Disclosure of Invention Technical Problem [8] In order to solve the problems of the conventional art as described above, the present invention provides a positive electrode active material for a lithium secondary battery, which is capable of reducing the amount of unreacted lithium and improving deterioration characteristics in a washing process, And a cathode active material for a lithium secondary battery produced by the method.

The present invention has been made to solve the above problems

A first step of preparing a precursor of a cathode active material for a lithium secondary battery represented by the following Chemical Formula 1;

???????? Ni _a1 Co _b1 X _c1 (OH) ₂ ?????

(And in Formula 1 X is Mn, Al, or Mn and _{Al, 0.50≤a 1 ≤0.95, 0.02≤b 1} ≤0.25, 0.01≤c 1 ≤0.20, 2.8≤a 1 / b 1 ≤19)

A second step of reacting the cathode active material precursor with a lithium compound and subjecting the precursor to a first heat treatment to produce a cathode active material;

A third step of washing the cathode active material with distilled water or alkaline aqueous solution;

A fourth step of reacting the washed positive electrode active material with a compound containing a metal Y1 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr;

A fifth step of drying the cathode active material particles; And

A sixth step of reacting the dried cathode active material with a compound containing a metal Y2 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr; And

A seventh step of subjecting the dried cathode active material to a second heat treatment to dope Y1 and Y2 into the particles;

And a process for producing a cathode active material for a lithium secondary battery represented by the following chemical formula (2).

[Chemical Formula 2] LiNi Co _{a2 b2 c2} X Y1 Y2 _{d2 d1} O ₂

Wherein X is Mn, Al or Mn and Al and Y1 and Y2 are metals selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr. _{and, 0.50≤a 2 ≤0.95, 0.02≤b 2 ≤0.25} , 0.01≤c 2 ≤0.20, 0.01≤d1≤0.20, 0.01≤d2≤0.20, 2≤a 2 / b 2 ≤20)

In the present invention, the introduction amounts of metals Y1 and Y2 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Is 1 to 20 mol% based on the total mass of the active material.

In the present invention, the metal Y1 introduced in the fourth step and the metal Y2 introduced in the sixth step may be the same metal.

In the present invention, it is preferable that the Co content in the active material particles is increased by 1 to 20 mol% with respect to the Co content in the second step by introducing Co in the fourth and sixth steps after the water washing step.

In the second step, a material selected from the group consisting of Ca, Mg, Ba, Ti, Zr, B and Sr is further added when the cathode active material precursor is reacted with the lithium compound. When the material selected from the group consisting of Ca, Mg, Ba, Ti, Zr, B, and Sr is further added in the second step, battery characteristics are improved.

In the present invention, the first heat treatment is performed at 700 to 850 ° C for 6 to 20 hours.

In the fifth step, in the step of drying the cathode active material particles, the cathode active material particles are dried at 100 to 250 ° C for 1 to 10 hours.

In the present invention, in the sixth step, the second heat treatment is performed at 300 to 800 ° C for 1 to 10 hours.

The present invention also provides a cathode active material for a lithium secondary battery produced by the production method of the present invention.

The positive electrode active material for a lithium secondary battery of the present invention is characterized in that the unreacted LiOH is contained in an amount of 0.25 wt% or less and the unreacted Li ₂ CO ₃ is contained in an amount of 0.30 wt% or less.

The cathode active material for a lithium secondary battery of the present invention is characterized in that, when Co is selected in the fourth to sixth steps, 2θ of XRD represents a peak corresponding to LiCoO ₂ between 45 ° and 46 °. This means that the Co selected in the fourth to sixth steps is detected on the surface in the form of LiCoO ₂ by heat treatment after surface coating.

The method for producing a cathode active material for a lithium secondary battery according to the present invention comprises reacting a lithium compound with a precursor in the production of a cathode active material, reducing the amount of unreacted lithium through surface washing, further doping the metal, A negative electrode active material for a nickel-rich lithium secondary battery exhibiting a high capacity characteristic while reducing the amount of the negative electrode active material.

1 shows a diagram relating to the method for measuring the unreacted LiOH and Li ₂ CO ₃ according to the present invention.
FIG. 2 shows the results of measurement of EDX on the entire surface and three points of the cathode active material prepared in one embodiment of the present invention.
FIG. 3 shows the results of XRD measurements of the cathode active material prepared in one embodiment and the comparative example of the present invention.
FIG. 4 shows a result of a charge / discharge test on a coin cell including a cathode active material according to an embodiment of the present invention and a comparative example.
FIGS. 5 and 6 show the results of measuring the c-rate for a coin cell comprising the cathode active material prepared in one embodiment of the present invention and the comparative example.
7 shows the result of measuring viscosity after slurry mixing in the production of a coin cell including a cathode active material in one embodiment and a comparative example of the present invention.
8 shows the result of performing an initial charge-discharge test on a coin cell including the cathode active material of the present invention and Comparative Example.
FIG. 9 shows the results of measuring the c-rate for a coin cell including a cathode active material prepared in an embodiment of the present invention and a comparative example.
FIGS. 10 to 12 show the result of measuring the change in impedance before and after the storage of the coin cell including the cathode active material prepared in one embodiment of the present invention and the comparative example, after storage at a high temperature of 60.degree. C. for 7 days.
FIG. 13 shows the results of measurement of pH change according to consumption of HCl in a coin cell comprising the cathode active material prepared in one embodiment and the comparative example of the present invention.
FIG. 14 shows the result of measuring impedance and c-rate after storage for 7 days at a high temperature of 60.degree. C. for a coin cell comprising a cathode active material prepared in one embodiment of the present invention and a comparative example.
15 shows a result of a cycle test on a coin cell including a cathode active material prepared in an embodiment of the present invention and a comparative example.
16 shows the results of DSC measurement of the cathode active material prepared in one example and comparative example of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

< Example  1> NCA  Family Cathode active material  Produce

< Example  1-1>

The precursor of NiCoAl (OH) ₂ was prepared by first coprecipitation reaction to prepare NCA series cathode active material. Was added LiOH as a lithium compound to the prepared precursor and a first heat treatment to _{Li 1 .02 Ni 0 .91 Co 0} .08 Al 0 .014 O 2 To prepare a positive electrode active material for a lithium secondary battery.

Distilled water was prepared and kept at a constant temperature. The prepared cathode active material for a lithium secondary battery was put into distilled water and was rinsed while maintaining the temperature. Thereafter, cobalt aqueous solution was added to the aqueous solution of the cathode active material at a constant rate for 1 hour while stirring to coat the surface with cobalt.

The prepared cathode active material was dried in a vacuum at 150 ° C. and then subjected to a second heat treatment at 500 ° C. to dope the coated cobalt to thereby increase the cobalt content of Li _{1 .02} Ni _{0 .88} Co _{0 .11} Al _{0 . 014} O ₂ To prepare a positive electrode active material for a lithium secondary battery.

< Example  1-2>

_{Li 1 .01 Ni 0 .91 Co 0} .08 Al 0 .014 O 2 After washing with water and prepared the positive electrode active material represented by, and is in Example 1-1 In the same manner as _{Li 1 .02 Ni 0 .89 Co 0} .09 , except that the number of changing the concentration of the cobalt solution to be added to the tax Al _{0 .014} O ₂ To prepare a cathode active material for a lithium secondary battery

< Comparative Example  1>

In the same manner as in Example 1-1, Li _{1 .01} Ni _{0 .91} Co _{0 .079} Al _{0 .014} O ₂ The positive electrode active material for a lithium secondary battery was prepared without adding a cobalt aqueous solution after washing with water.

< Comparative Example  2>

_0.12 in Example 1-1 in the same manner as the Co Li _{1 .01} Ni _{0 .86} concentration of 0.1 or more, by co-precipitation reaction of Co ₀ Al _{0 .013} O ₂ The positive electrode active material for a lithium secondary battery was prepared without adding a cobalt aqueous solution after washing with water.

< Example  1-3>

By first co-precipitation reaction to produce a positive electrode active material of the NCA series NiCoAl (OH) preparing a _second precursor, and the addition of LiOH and Ba as dissimilar metal as the lithium compound, and a first heat treatment to Li _{1 .03} Ni _{0 .91} Co _{0 .079} Al _{0 .014} Ba _{0 .002} O ₂ To prepare a positive electrode active material for a lithium secondary battery.

Then, the Examples 1-1 in the same manner as washing with water, an aqueous solution of cobalt coating and a secondary heat treatment to _{Al 0 .014 .11 Li 1 .02 Ni} 0 .88 Co 0 to _{0 .002} O ₂ Ba To prepare a positive electrode active material for a lithium secondary battery.

< Comparative Example  3>

Producing a NiCoAl (OH) ₂ precursor by a coprecipitation reaction, adding only LiOH as the lithium compound, and a first heat treatment performed only by _{Li 1 .02 Ni 0 .88 Co 0} .11 Al 0 .014 O 2 To prepare a positive electrode active material for a lithium secondary battery.

< Comparative Example  4>

NiCoAl by the co-precipitation reaction (OH) After preparing a _precursor, Ba added as LiOH, and different metal as the lithium compound herein, and the first heat treatment by _{Li 1 .03 Ni 0 .90 Co 0} .08 Al 0 .014 Ba 0.002 O &lt; _{2 &} gt ;.

A positive electrode active material for a lithium secondary battery was prepared in the same manner as in Example 1-3, except that the coating was not performed with a cobalt aqueous solution after being rinsed with distilled water.

< Experimental Example  1> Measurement of unreacted lithium

The measurement of unreacted lithium is determined by the amount of 0.1 M HCl used until pH 4 by pH titration. First, 5 g of the cathode active material was added to 100 ml of DIW, stirred for 15 minutes, and filtered. 50 ml of the filtered solution was taken, and 0.1 M HCl was added thereto to measure the consumption of HCl according to the pH change. . In Figure 1 Q1, Q2, and determines, according to the following formula unreacted LiOH and Li ₂ CO ₃ Respectively.

M1 = 23.94 (LiOH Molecular weight)

_{M2 = 73.89 (Li 2 CO 3} Molecular weight)

SPL Size = (Sample weight × Solution Weight) / Water Weight

LiOH (wt%) = [(Q1-Q2) x C x M1 x 100] / (SPL Size x 1000)

Li ₂ CO ₃ (wt%) = [2 x Q 2 x C x M2 / 2 x 100] / (SPL Size x 1000)

The results of measurement of the concentrations of unreacted LiOH and Li ₂ CO ₃ in the NCA-based lithium composite oxide prepared in the above Examples and Comparative Examples are shown in Table 1 below.

The prepared cathode active material Measurement of unreacted Li LiOH (ppm) Li ₂ CO ₃ (ppm) total Li (%) Example 1-1 _{.11 Li 1 .02 Ni 0 .88 Co} 0 Al 0 .014 O 2 1630 1455 0.0107 Examples 1-2 _{Li 1 .01 Ni 0 .89 Co 0} .09 Al 0 .014 O 2 1668 1361 0.0106 Example 1-3 _{Li 1 .02 Ni 0 .88 Co 0} .11 Al 0 .014 Ba 0 .002 O 2 2230 1495 0.0134 Comparative Example 1 _{Li 1 .01 Ni 0 .91 Co 0} .079 Al 0 .014 O 2 1860 1350 0.0114 Comparative Example 2 _{Co 0 .12 Li 1 .01 Ni 0} .86 Al 0 .013 O 2 1595 1010 0.0094 Comparative Example 3 _{.11 Li 1 .02 Ni 0 .88 Co} 0 Al 0 .014 O 2 4250 6000 0.0340 Comparative Example 4 _{Li 1 .02 Ni 0 .90 Co 0} .08 Al 0 .014 Ba 0 .002 O 2 2400 2330 0.0163

In the case of Comparative Example 3 in which both the water washing treatment with the distilled water and the Co-doping treatment were not performed in Table 1, unreacted LiOH and Li ₂ CO ₃ were the highest measured. According to the embodiment of the present invention, It can be seen that unreacted LiOH and Li ₂ CO ₃ decrease.

< Experimental Example  2> SEM  Photo measurement and EDX  Measure

SEM photographs and EDX measurements of the entire surface and three points of the cathode active material prepared in Example 1-1 are shown in FIG. 2 and Table 2.

point Whole surface point 1 point 2 point 3 Ni 86.4 76.4 76.4 79.4 Co 11.2 20.9 20.9 10.5 Al 2.5 2.7 2.7 2.1

2 and Table 2, it can be seen that a point where the mole fraction of cobalt is locally high on the surface appears when coating with a cobalt aqueous solution.

< Experimental Example  3> XRD  Measure

XRD was measured for the cathode active material prepared in Example 1-1 and Comparative Example 1, and the results are shown in FIG.

In FIG. 3, in Example 1-1 in which the coating was performed with the aqueous solution of cobalt, LiCoO ₂ peaks were observed at 45 ° to 46 ° at 2θ on the surface.

< Experimental Example  4> Charging and discharging  Character rating

Coin cells were prepared by using the cathode active materials prepared in Examples 1-1, 1-2 and Comparative Examples 1 and 2 as positive electrodes and lithium metal as negative electrodes, 4 and 5 and Table 3 show the results of charging / discharging experiments at a discharge rate of C / 10 (1 C = 150 mA / g) between 3 and 4.3 V. FIG.

division Example 1-1 Examples 1-2 Comparative Example 1 Comparative Example 2
4.3 V to 3.0 V
charge mAh / g 239.8 240.7 243.3 233.5 Discharge 214.5 214.8 211.8 206.1 efficiency % 89.4% 89.2% 87.0% 88.3%

4, 5 and Table 3 show that the charging / discharging efficiency is improved as compared with Comparative Example 1 and Comparative Example 2 in Example 1-1 and Example 1-2, which were coated with a water washing process and a cobalt aqueous solution after the preparation of the cathode active material Able to know.

< Experimental Example  5> Charging and discharging  Character rating

Charge-discharge experiments were carried out on the coin cells using lithium metal as the anode and the cathode active materials of Examples 1-3 and Comparative Example 4 doped with Ba as the dissimilar metals as the anode and the cathode Are shown in Table 4 and FIG.

division Example 1-3 Comparative Example 4
4.3 V to 3.0 V
charge mAh / g
234.1 239.2 Discharge 213.9 211.1 efficiency % 91.4% 83.3%

In Table 4, it can be seen that the charge-discharge efficiency is greatly improved in Examples 1-3 in which different metal Ba is doped and coated with Co and heat-treated.

< Experimental Example  6> C- rate  Measurement result

The c-rate of the coin cell including the cathode active material of Example 1-1, Comparative Example 1, and Comparative Example 2 prepared in Experimental Example 4 was measured, and the results are shown in Table 5.

Item Example 1-1 Comparative Example 1 Comparative Example 2 DCH, mAh / g 0.1 C 214.5 211.8 206.1 0.2 C 208.0 203.8 199.1 0.5 C 199.5 195.1 189.8 1.0 C 192.7 188.7 182.4 1.5 C 188.3 183.2 177.4 2.0 C 184.8 178.6 173.2 Retention,% 0.1 C 100% 100% 100% 0.2 C 97.0% 96.2% 96.6% 0.5 C 93.0% 92.1% 92.1% 1.0 C 89.8% 89.1% 88.5% 1.5 C 87.8% 86.5% 86.1% 2.0 C 86.2% 84.3% 84.0%

< Experimental Example  7> Storage stability - Slurry  Viscosity measurement

The cathode active materials of Example 1-1 and Comparative Example 3 were mixed with a conductive material and a binder in a ratio of 93: 3: 3, and the viscosity of the slurry was measured while changing the viscosity at room temperature for 3 days. 7.

7, the viscosity of Comparative Example 3 increased sharply, indicating that the slurry viscosity of Example 1-1 was improved compared with Comparative Example 3.

< Example  2> NCM  Family Cathode active material  Produce

To prepare NCM series cathode active material, NiCoMn (OH) ₂ precursor was first prepared by coprecipitation reaction. Was added LiOH as a lithium compound to prepare a first heat treatment to a lithium secondary battery positive electrode active material represented by _{Li 1 .0 Ni 0 .85 Co 0} .10 Mn 0 .05 O 2. After the distilled water was maintained at a constant temperature, the prepared cathode active material for a lithium secondary battery was charged into distilled water, and the mixture was washed with water while being maintained at a temperature. Again, the cobalt aqueous solution was stirred at a constant rate for 1 hour while stirring, The surface was coated. Thereafter, the cathode active material was washed with distilled water, dried at 150 ° C. in a vacuum, and then subjected to a second heat treatment at 500 ° C. to produce Li _1.0 Ni _0.83 Co _0.12 Mn _0.049 O ₂ cathode active material for a lithium secondary battery having an increased cobalt content.

< Comparative Example  5>

Example 2 after the same manner as to prepare a lithium secondary battery positive electrode active material represented by _{Li 1 .0 Ni 0 .85 Co 0} .10 Mn 0 .05 O 2, does not have a cobalt coating was determined as Comparative Example 5.

< Experimental Example  8> Initial Charging and discharging  Character rating

Coin cells were prepared using the cathode active materials prepared in Example 2 and Comparative Example 5 as positive electrodes and lithium metal as negative electrodes, respectively, and C / 10 charging and C / 10 discharge rates (1 C = 150 mA / ) And 3.0 to 4.3 V, respectively. The results are shown in FIG. 8 and Table 6.

division Example 2 Comparative Example 5
4.3 V to 3.0 V
charge mAh / g
231.1 235.4 Discharge 210.3 204.2 efficiency % 91.0% 86.7%

8 and Table 6 show that the initial charge and discharge efficiency was improved as compared with Comparative Example 5 in which the residual lithium was reduced through the flushing process after the preparation of the cathode active material and the surface was coated with the cobalt aqueous solution, .

< Experimental Example  9> C- rate  Measurement result

The c-rate of the coin cell including the cathode active material prepared in Experimental Example 8 was measured, and the results are shown in FIG. 9 and Table 7. FIG.

Item Example 2 Comparative Example 4 DCH, mAh / g 0.1 C 209.7 204.3 0.2 C 204.3 198.7 0.5 C 196.9 190.8 1.0 C 190.8 184.3 1.5 C 186.1 179.0 2.0 C 183.1 173.2 Retention,% 0.1 C 100% 100% 0.2 C 97.4% 97.2% 0.5 C 93.9% 93.4% 1.0 C 91.0% 90.2% 1.5 C 88.8% 87.6% 2.0 C 87.3% 84.8%

< Experimental Example  10> Storage stability - Impedance measurement result

The batteries prepared in Examples 1-1 and 1-3 and Comparative Example 1 were stored at a high temperature of 60 ° C. for 7 days, and the change in impedance before and after storage was measured. The results are shown in FIGS. 10 to 12 Respectively.

10 to 12, it can be seen that the battery including the cathode active material prepared according to the present invention has a smaller measured impedance than that of Comparative Example 1 before storage and an increase in impedance after storage compared to Comparative Example 1 have.

< Example  3> NCA  Family Cathode active material  Produce

A precursor of Ni _x Co _y Al _z (OH) _{2 having the} composition shown in Table 8 below was prepared by coprecipitation reaction. LiOH as a lithium compound and Ba, Mg, Ti, B as a dissimilar metal were added and subjected to a first heat treatment to prepare a cathode active material for a lithium secondary battery.

Distilled water was prepared and maintained at a constant temperature. Then, the prepared cathode active material for a lithium secondary battery was put into distilled water to maintain the temperature and was washed with water. The water-soluble raw materials of Co, P, and F to be coated at the time of washing were stirred for 30 minutes to 1 hour, and the surface of the cathode active material was coated as shown in Table 8 above.

The washed and coated materials were dried in a vacuum of 150 캜 and then subjected to a second heat treatment at 700 to 850 캜 to prepare a cathode active material for a lithium secondary battery.

In Comparative Example 3-1, neither water nor metal was introduced at all. In Comparative Examples 3-2 to 3-5 and Examples 3-11 to 3-13, the water was washed, but no metal was introduced.

< Experimental Example  11> Measurement of unreacted lithium

Experimental Example 1, and measuring the consumption of HCl according to the pH change in the same way, and Q1, Q2, and determines, was calculated unreacted LiOH and Li ₂ CO _3, and are shown in Table 9 below according to the following formula.

The consumption of HCl according to the pH change was measured for Example 3-2, Example 3-4 and Comparative Example 3-1, and the results are shown in FIG. It can be confirmed that the residual lithium was significantly reduced in Examples 3-2 and 3-4, which were subjected to water washing and metal coating, as compared with Comparative Example 3-1 in which no rinsing was performed in Fig.

< Experimental Example  12> Charging and discharging  Character rating

Each of the coin cells was prepared by using the cathode active material prepared in Examples 3-1 to 3-29 as an anode and lithium metal as a cathode, and a C / 10 charge and a C / 10 discharge rate (1 C = 150 mA / g) were subjected to a charge-discharge test at a voltage of 3 to 4.3 V. The results are shown in FIG. 14 and Table 9.

14, it can be confirmed that the C-rate result after storage of Example 3-10 in which Al was introduced in comparison with Comparative Example 3-2 in which there is no post-introduction of the metal is superior. Example 3-18 in which Al, B and Ti were introduced later showed better C-rate characteristics after storage than in Comparative Example 3-2 in which post-introduction was not applied and in Example 3-10 in which Al was introduced Respectively.

< Experimental Example  13> After storage, C- rate  And impedance measurement results

The impedance of the coin cell including the positive electrode active material prepared in each of Examples 3-1 to 3-29 as an anode was measured after storage and the results are shown in Table 9 and FIG. 14, it can be seen that the impedance after storage of Example 3-10 in which Al was introduced is decreased as compared with Comparative Example 3-2 in which Al was not introduced.

In addition, in Example 3-18 in which Al, B, and Ti were introduced after the above-mentioned storage results as in the case of the c-rate characteristic results, in Comparative Example 3-2 in which the dissimilar metals were not introduced afterward and in Example 3 Impedance after storage was measured lower than -10.

< Experimental Example  14> Measurement of lifetime characteristics

The life characteristics of the coin cells including the positive electrode active materials prepared in Examples 3-1 to 3-29 as anodes were measured and the results are shown in Table 9 and FIG.

It can be seen that the life characteristics are improved in Examples 15-1 and 15-2 in which the Al-doped introduction is applied in FIG. 15 and in Comparative Example 3-2 in which the dissimilar metal is not introduced after the water washing. Example 3-16, in which Ti doping and post-introduction of Al and B were applied, showed better lifetime characteristics than Comparative Example 3-2 in which post-introduction was not applied, and Example 3-1 and Example 3- 10.

< Experimental Example 15 > Measurement of thermal stability properties

DSC peak temperatures were measured to evaluate the thermal stability of the coin cells comprising the positive electrode active materials prepared in Examples 3-1 to 3-29 as positive electrodes, and the results are shown in Table 9 and FIG.

The peak temperature of Example 3-7 in which Al was introduced after 1 mol% was higher than that in Comparative Example 3-2 in which Al was not introduced in FIG. 16, It was confirmed that Example 3-21, which was introduced at a later stage, exhibited better thermal stability.

Claims (9)

A first step of preparing a precursor of a cathode active material for a lithium secondary battery represented by the following Chemical Formula 1;
???????? Ni _a1 Co _b1 X _c1 (OH) ₂ ?????
(And in Formula 1 X is Mn or _{Al, 0.7≤a 1 ≤0.95, 0.05≤b 1} ≤0.25, 0.01≤c 1 ≤0.05, 2.8≤a 1 / b 1 ≤19)
A second step of reacting the cathode active material precursor with a lithium compound and subjecting the precursor to a first heat treatment to produce a cathode active material;
A third step of washing the cathode active material with distilled water or alkaline aqueous solution;
A fourth step of reacting the washed positive electrode active material with a solution containing a metal Y1 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr;
A fifth step of drying the cathode active material particles;
A sixth step of reacting the dried cathode active material with a compound containing a metal Y2 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr; And
The dried cathode active material is subjected to a second heat treatment to form a seventh conductive film which is doped with a metal Y2 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Comprising:
A method for producing a cathode active material for a lithium secondary battery,
[Chemical Formula 2] LiNi Co _{a2 b2 c2} X Y1 Y2 _{d2 d1} O ₂
(Wherein X is a sum of Mn, Al or two elements and Y1 and Y2 are selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr metal _{and, 0.50≤a 2 ≤0.95, 0.02≤b 2 ≤0.25} , 0.01≤c 2 ≤0.20, 0.01≤d1≤0.20, 0.01≤d2≤0.20, 2≤a 2 / b 2 ≤20)
The method according to claim 1,
The doping amount of the metals Y1 and Y2 selected from the group consisting of Co, Al, B, Ba, Cr, F, Li, Mo, P, Sr, Ti and Zr is 1 to 20 mol% Wherein the positive electrode active material is a lithium secondary battery.
The method according to claim 1,
Wherein when the cathode active material precursor is reacted with the lithium compound in the second step, a material selected from the group consisting of Ca, Mg, Ba, Ti, Zr, B, and Sr is further added to the cathode active material precursor. Gt;
The method according to claim 1,
Wherein the first heat treatment in the second step is performed at 700 to 850 캜 for 6 to 20 hours.
The method according to claim 1,
Wherein the drying is performed at 100 to 250 ° C for 1 to 10 hours in the fifth step.
The method according to claim 1,
And the second heat treatment in the seventh step is a heat treatment at 300 to 800 ° C for 1 hour to 10 hours.
A cathode active material for a lithium secondary battery produced by the method of any one of claims 1 to 6.
8. The method of claim 7,
The positive electrode active material for a lithium secondary battery is characterized in that unreacted LiOH accounts for 0.25 wt% or less, unreacted Li ₂ CO ₃ Is 0.30% by weight or less based on the total weight of the positive electrode active material for lithium secondary battery.
8. The method of claim 7,
Wherein the cathode active material for lithium secondary batteries exhibits a peak corresponding to LiCoO ₂ at 2? Between 45 and 46 when XRD is measured.

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