KR20150101181A - Positive active material, lithium secondary battery having the same and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an anode active material, a lithium secondary battery having the same, and a method for manufacturing the same. The present invention is to: prevent the deterioration capacity of an anode active material based on a lithium cobalt oxide in a high temperature environment and a high voltage greater than or equal to 4.4V (vs. Li/Li+); and prevent the deterioration of anode surfaces by HF generated by moisture included in an electrolyte. The present invention provides the positive active material for a lithium secondary battery in which a nano-sized Zr oxide is uniformly coated on the surface of the lithium cobalt oxide represented by chemical formula below. A nano-sized Si oxides can be uniformly coated on the surface of the lithium cobalt oxide, with the nano-sized Zr oxide. [Chemical formula] LiCo_1-xM_xO_2, wherein 0.00<=x<0.10; and M is one or more metals selected from a group consisting of Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti, and Zr.

Description

[0001] The present invention relates to a positive active material, a lithium secondary battery having the positive active material,

The present invention relates to a lithium secondary battery and a manufacturing method thereof, and more particularly, to a lithium secondary battery and a method of manufacturing the same by forming a coating layer of nano-sized oxide on the surface of lithium cobalt oxide (LiCo _1-x M _x O ₂ ) A lithium secondary battery having the lithium secondary battery, and a method of manufacturing the same.

Of the cathode active materials for lithium secondary batteries, lithium cobalt oxides such as LiCoO ₂ having a layered structure are the most commonly used cathode materials. Co is expensive and toxic, and degradation of structural stability due to phase deformation occurring when more than 50% of lithium in the structure is released during charging is a problem.

Due to this problem, the cathode active material such as LiCoO ₂ is used under a charging voltage of 4.3 V compared to lithium metal. The capacity used is limited to 130 mAh / g, which is the theoretical capacity of 50% of 274 mAh / g. Recently, the use of LiCoO ₂ has been increasing due to a decline in the cost of raw materials for Co and an increase in demand for mobile IT devices, and a higher capacity is required.

On the other hand, when LiCoO ₂ is used at a high voltage of 4.3 V (vs Li / Li +) or more, the following problems may occur. First, capacity deterioration due to mechanical stress repetition due to structural change due to charging and discharging in the high voltage range, and second, due to the dissolution of Co and the formation of the solid electrolyte interface (SEI) due to the side reaction of the electrolyte due to the use of high voltage Which is the capacity deterioration.

These problems are to be overcome in high-voltage charging for the high capacity of LiCoO ₂ . Also, LiCoO ₂ in a high-temperature use environment promotes the dissolution of Co, which also causes capacity deterioration.

Another major cause of the deterioration of the anode in the lithium secondary battery is a small amount of moisture in the electrolyte generated in the battery manufacturing process. This residual water reacts with LiPF ₆ , which is a lithium salt, to form HF, and HF degrades the anode surface as a strong acid.

The above-described factors cause a decrease in the capacity of the cathode active material such as LiCoO ₂ and are problems to be solved in order to suppress deterioration of capacity at high voltage and high temperature which are more deteriorating conditions.

Korean Patent No. 10-0857423 (Sep. 2, 2008)

Accordingly, an object of the present invention is to provide a cathode active material capable of inhibiting capacity deterioration in a high-voltage and high-temperature environment of a lithium-cobalt oxide-based cathode active material, a lithium secondary battery having the same, and a method of manufacturing the same.

Another object of the present invention is to provide a cathode active material having improved high temperature battery characteristics and thermal stability of a cathode active material based on lithium cobalt oxide, a lithium secondary battery having the cathode active material, and a method of manufacturing the same.

It is still another object of the present invention to provide a cathode active material capable of suppressing deterioration of the anode surface due to HF generated due to moisture partially contained in an electrolytic solution, a lithium secondary battery having the cathode active material, and a method of manufacturing the same.

In order to achieve the above object, the present invention provides a cathode active material for a lithium secondary battery, wherein a surface of lithium cobalt oxide represented by the following formula is uniformly coated with a nano-sized Zr oxide.

[Chemical Formula]

_{LiCo 1-x M x O 2} (0.00≤x <0.10, M is Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti And Zr)

In the cathode active material according to the present invention, the raw material of the Zr oxide may include ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less.

In the cathode active material according to the present invention, the Zr oxide may include 0.01 to 1.0 wt% of the lithium cobalt oxide.

In the cathode active material according to the present invention, the surface of the lithium cobalt oxide may be further coated with nano-sized Si oxide.

In the cathode active material according to the present invention, the raw material of the Si oxide is SiO _x (0 <x? 2), Si (OR) ₄ (R is alkyl, alkenyl or alkynyl) or SiX ₄ X may be halogen, F, Cl, Br, I).

The present invention also provides a lithium secondary battery comprising a cathode active material having a surface of a lithium cobalt oxide represented by the above formula and coated uniformly with a nano-sized Zr oxide.

In the lithium secondary battery according to the present invention, the surface of the lithium cobalt oxide of the cathode active material is further coated with a nano-sized Si oxide uniformly.

The present invention also relates to a process for preparing a lithium cobalt oxide, which comprises the steps of charging a lithium cobalt oxide represented by the above formula into a Zr compound solution, stirring and drying the lithium cobalt oxide to adsorb the Zr compound on the surface of the lithium cobalt oxide, And coating the surface of the lithium cobalt oxide with a nano-sized Zr oxide uniformly on the surface of the lithium cobalt oxide.

In the method for producing a cathode active material according to the present invention, the Zr compound may include ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less. Zr oxide particles of 30 nm or less can be coated on the surface of the lithium cobalt oxide.

In the method for producing a cathode active material according to the present invention, the Zr compound raw material may include a solution containing ZrO ₂ powder having a particle diameter of 100 nm or less or a Zr isoporoxide solution.

In the method for producing a cathode active material according to the present invention, the Zr oxide may be contained in an amount of 0.01 to 1.0 wt% with respect to the lithium cobalt oxide.

The method for producing a cathode active material according to the present invention is characterized in that lithium cobalt oxide is introduced into a Si compound solution before stirring the Zr compound and after coating the Zr oxide, The step of adsorbing the Si compound on the surface of the lithium cobalt oxide and the step of heat treating the lithium cobalt oxide adsorbed on the Si compound to uniformly coat the surface of the lithium cobalt oxide with the nano-sized Si oxide .

In the method for producing a cathode active material according to the present invention, the raw material of the Si oxide is SiO _x (0 <x? 2), Si (OR) ₄ (R is alkyl, alkenyl or alkynyl) SiX ₄ (X is halogen, F, Cl, Br, I). Si oxide particles of several hundreds nm or less can be coated on the surface of the lithium cobalt oxide.

In the production method of the positive electrode active material according to the present invention, the Si compound material comprises a SiO ₂ powder having a particle diameter of 100 nm or less _{solution, Si (OC 2 H 5)} O 4 (Tetraethyl orthosilicate) solution or SiF ₄ solution Lt; / RTI &gt;

In the method of manufacturing a cathode active material according to the present invention, in the step of coating the Zr oxide and the step of coating the Si oxide, the heat treatment may be performed at 200 to 700 ° C for 1 to 24 hours.

According to the present invention, by uniformly coating the surface of the lithium cobalt oxide with the nano-sized Zr oxide, it is possible to suppress deterioration of the lifetime at high voltage and to obtain excellent lifetime characteristics. That is, when the cathode active material coated with the nano-sized Zr oxide uniformly on the surface of the lithium cobalt oxide according to the present invention is used as the anode for the lithium secondary battery, the coating layer of the oxide of Zr in the high- It is possible to suppress the elution of metal elements such as Co from the anode and the deterioration phenomenon.

Further, by using a lithium cobalt oxide coated with Zr oxide as a cathode active material, the output characteristics of the lithium secondary battery can be improved and the overvoltage during high rate discharge can be improved.

Further, by coating the surface of the lithium cobalt oxide with nano-sized Si oxide in addition to the nano-sized Zr oxide uniformly, the moisture stability of the lithium secondary battery can be improved. That is, the nano-sized Si oxide coated on the surface of the lithium cobalt oxide has a scavenging effect on the HF generated in the lithium secondary battery, preferably by residual moisture in the electrolyte, and as a result, Can be suppressed. Here, the removal effect on HF means that the coating layer of the Si oxide is formed by the moisture contained in the non-aqueous liquid electrolyte, HF preferentially reacts with the Si oxide to form SiF ₄ , and through this, the cathode active material core, that is, LiCo _1-x M _x O ₂ .

As described above, the cathode active material according to the present invention is formed by forming a coating film of Zr oxide and Si oxide on the surface of a cathode active material based on lithium cobalt oxide to improve the electrochemical cell characteristics at a high voltage of 4.4 V (vs. Li / Li +) or higher And improving the thermal stability and moisture stability of the positive electrode active material for a lithium secondary battery.

1 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention.
2 is an SEM photograph of the positive electrode active material of Example 1. Fig.
3 is a photograph showing the SEM photograph and the EDS mapping result of the cathode active material of Example 2. Fig.
FIG. 4 is a graph showing output characteristics of a lithium secondary battery using a cathode active material according to Example 1 and Comparative Example 1 under a 4.4 V charging condition. FIG.
5 is a graph showing output characteristics of a lithium secondary battery using a cathode active material according to Example 1 and Comparative Example 1 under a 4.5 V charging condition.
6 is a graph showing lifetime characteristics of a lithium secondary battery using a cathode active material according to Example 1 and Comparative Example 1 under a 4.4 V charging condition.
7 is a graph showing lifetime characteristics of a lithium secondary battery using a cathode active material according to Example 1 and Comparative Example 1 under a 4.55 V charging condition.
8 is a schematic diagram showing the HF scavenging effect of the Si oxide coated on the cathode active material of Example 2. FIG.
FIG. 9 is a graph showing output characteristics of a lithium secondary battery using a cathode active material according to Example 2 under a 4.4 V charging condition. FIG.
10 is a graph showing lifetime characteristics of a lithium secondary battery (using an electrolytic solution containing 1000 ppm water) using the cathode active material according to Example 2 and Comparative Example 1 under a 4.4 V charging condition.
11 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to another embodiment of the present invention.

In the following description, only parts necessary for understanding embodiments of the present invention will be described, and descriptions of other parts will be omitted to the extent that they do not disturb the gist of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and the inventor is not limited to the meaning of the terms in order to describe his invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention, so that various equivalents And variations are possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The cathode active material according to the present invention is formed by coating a surface of lithium cobalt oxide represented by the following chemical formula 1 uniformly with a nano-sized Zr oxide.

[Chemical Formula 1]

LiCo _1-x M _x O ₂

M is at least one element selected from the group consisting of Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti and Zr One or more metals)

Here, the lithium cobalt oxide is a layered oxide, LiCoO ₂ , or may be provided in a form in which a small amount of a hetero-element (M) is substituted at the Li or Co position.

As the raw material of the Zr oxide, a ZrO ₂ powder having a particle diameter of 100 nm or less can be used. Or a solution containing Zr element as a raw material of Zr oxide, more preferably Zr (OR) ₄ containing Zr isoporoxide (R is alkyl, alkenyl or alkynyl ).

 The Zr oxide content may be 0.01 to 1.0 wt% based on the total weight of the lithium cobalt oxide. If the content of the Zr oxide is less than 0.01 wt%, the effect of suppressing deterioration of the life at high voltage is insignificant. On the other hand, when the content of the Zr oxide exceeds 1.0 wt%, the capacity may decrease and the output characteristic may decrease.

The cathode active material according to the present invention can be formed by coating a surface of a lithium cobalt oxide with a Zr oxide uniformly with a nano-sized Si oxide.

Here, SiO _x (0 < x? 2) particles or powder containing SiO ₂ having a particle diameter of 100 nm or less may be used as a raw material of the Si oxide.

Si (OR) ₄ (R is alkyl, alkenyl or alkynyl) containing Si (OC ₂ H ₅ ) O ₄ (Tetraethyl orthosilicate) or SiX ₄ containing SiF ₄ F, Cl, Br, I).

As described above, the present invention is characterized by coating a small amount of Zr oxide in the form of nanoparticles on the surface of the cathode active material of LiCoO ₂ , exhibiting excellent lifetime characteristics under a high voltage charging condition of 4.4 V (vs. Li / Li +), The energy increase due to the improvement can be achieved. Also, the cathode active material of LiCoO ₂ according to the present invention has an effect of improving thermal stability due to the coating layer of Zr oxide.

The cathode active material according to the present invention can be formed by coating a surface of a lithium cobalt oxide with a Zr oxide uniformly with a nano-sized Si oxide. Here, the coating layer of Si oxide has a scavenging effect on HF generated by residual water in the lithium secondary battery, preferably the electrolyte, and as a result, deterioration of the life characteristics of the lithium secondary battery can be suppressed.

As described above, the cathode active material according to the present invention is characterized in that a coating film of Zr oxide and Si oxide is formed on the surface of a cathode active material based on lithium cobalt oxide, thereby improving the electrochemical cell characteristics and improving the thermal stability and moisture stability. A positive electrode active material can be provided.

A method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention will now be described with reference to FIG. 1 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a Zr compound solution containing Zr is prepared in step S10. At this time, ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less may be used as a Zr raw material of the Zr compound solution. A Zr compound solution is prepared in consideration of the coating amount of the Zr oxide of 0.01 to 1.0 wt% with respect to the total weight of the lithium cobalt oxide. For example, Zr isopropoxide may be added to isopropyl alcohol (IPA) and stirred at 25 ° C for about 2 hours to prepare a Zr compound solution.

Next, lithium cobalt oxide is added to the Zr compound solution prepared in step S20, followed by stirring and drying to adsorb the Zr compound on the surface of the lithium cobalt oxide. For example, at a stirring rate of 380 rpm at 80 DEG C for about 8 hours to dry the Zr compound on the surface of the lithium cobalt oxide. That is, in the course of stirring for 8 hours at a stirring rate of 380 rpm at 80 ° C, all the IPA is evaporated and the Zr compound is uniformly adsorbed on the surface of the lithium cobalt oxide.

Next, in step S30, the lithium cobalt oxide to which the Zr compound is adsorbed is heat-treated to uniformly coat the surface of the lithium cobalt oxide with the nano-sized Zr oxide. The heat treatment may be performed at 200 to 700 ° C for 1 to 24 hours in air.

Then, in step S40, a lithium cobalt oxide coated with a nano-sized Zr oxide is added to the Si compound solution, followed by stirring and drying to adsorb the Si compound on the surface of the lithium cobalt oxide.

At this time, the Si raw material for the Si compound solution having a particle size of less than _{100 nm SiO x (0 <x≤2} ), Si (OR) 4 (R is alkyl, alkenyl or alkynyl) or SiX ₄ (X is a halogen, F, Cl, Br, I) may be used. For example, SiO ₂ of nanoparticle size may be added to IPA, and the solution may be stirred by ultrasonic treatment at 25 ° C for 10 minutes to prepare a Si compound solution. Subsequently, the Si compound can be adsorbed on the surface of the lithium cobalt oxide by stirring and drying at 80 DEG C at a stirring rate of 380 rpm for about 8 hours. That is, in the course of stirring for 8 hours at a stirring rate of 380 rpm at 80 ° C, the IPA is completely evaporated and the Si compound is uniformly adsorbed on the surface of the lithium cobalt oxide.

The cathode active material according to the present invention can be manufactured by heat-treating the lithium cobalt oxide adsorbed on the Si compound in step S50 and coating the surface of the lithium cobalt oxide uniformly with the nano-sized Si oxide. The heat treatment may be performed at 200 to 700 ° C for 1 to 24 hours in air.

In order to evaluate the electrochemical performance of the cathode active material according to the present invention, the cathode active materials according to Examples 1 and 2 and Comparative Example 1 were prepared.

[Example 1]

Zr isopropoxide was determined by calculating a coating amount of 1 wt% of ZrO ₂ relative to 10 g of LiCoO ₂ , and then 30 mL of IPA was dispersed in a solvent. Then, 10 g of LiCoO ₂ was added thereto and the mixture was stirred at 80 ° C. for 8 hours And stirred at 380 rpm. In this process, all of the solvent was evaporated, and LiCoO ₂ adsorbed on the surface of the Zr raw material was obtained. Heat treatment was performed to form a coating layer of Zr oxide on the surface of LiCoO _{2. The} heat treatment was performed in an air atmosphere at 500 ° C. for 4 hours using an electric furnace. The cathode active material according to Example 1 of LiCoO ₂ coated with Zr oxide was obtained through the above process.

2 is an SEM photograph of the positive electrode active material of Example 1. Fig. Referring to FIG. 2, it can be seen that Zr oxides of about 20 nm are uniformly distributed on the surface of LiCoO ₂ .

[Example 2]

Using the Zr oxide-coated LiCoO ₂ obtained in Example 1 as a starting material, an additional coating of Si oxide was desired. SiO ₂ nanoparticles (particle diameter <10 nm) of 0.5 wt% based on the weight of LiCoO ₂ coated with Zr oxide were put into 30 mL of IPA and ultrasonically treated for 10 minutes to uniformly disperse SiO ₂ powder in IPA. 10 g of LiCoO ₂ obtained in Example 1 was added and stirred at 380 rpm for 8 hours at 80 ° C. During this process, all of the IPA is evaporated and at this stage SiO ₂ is evenly distributed on the surface of LiCoO ₂ . Heat treatment was performed to form a coating layer of Si oxide on the surface of LiCoO ₂ , and the heat treatment was performed in an air atmosphere at 500 ° C. for 4 hours using an electric furnace. The cathode active material according to Example 2 in which Si oxide was further coated was obtained through the above process.

3 is a photograph showing the SEM photograph and the EDS mapping result of the cathode active material of Example 2. Fig. Referring to FIG. 3, it can be seen that, besides the coating layer of Zr oxide, Si oxide having a size of several hundreds of nanometers is additionally coated on the surface of LiCoO ₂ . From the results of EDS mapping, it can be seen that the Si oxide is uniformly distributed on the surface of LiCoO ₂ , and thus the coating is well formed.

[Comparative Example 1]

The pure LiCoO ₂ powder used as the starting material in Example 1 was used as a cathode active material according to Comparative Example 1.

[Test Example]

A lithium secondary battery capable of evaluating the electrochemical performance of the cathode active material was prepared by using the cathode active material according to Example 1, Example 2, and Comparative Example 1, and then battery performance was evaluated.

The lithium secondary battery includes a cathode including a cathode active material, a cathode including a cathode active material capable of intercalating / deintercalating lithium ions, a separator existing between the cathode and the anode, and a non-aqueous electrolyte.

[Production of lithium secondary battery]

Using 95 wt% of the cathode active material, 2.5 wt% of Denka black as a conductive material, and 2.5 wt% of N-methylpyrrolidone (NMP) as a binder, using the cathode active materials of Examples 1 and 2 and Comparative Example 1 Slurry. This slurry was applied to an aluminum foil having a thickness of 20 탆, dried, and then compacted by a press and dried in vacuum at 120 캜 for 16 hours to prepare a disc electrode having a diameter of 16 mm.

Relative pole is as was used for the lithium metal foil by a punch, the separation membrane with a diameter of 16 mm of polypropylene (PP) as was used for the film, the electrolyte is 1M of LiPF ₆ in EC / DMC / DEC 1: 2 : 1 v / v was used. After the electrolyte was impregnated into the separator, the separator was sandwiched between the working electrode and the counter electrode, and then a lithium secondary battery for evaluating electrochemical characteristics was prepared from 2032 coin cells.

[Evaluation of Battery Performance]

The charging and discharging characteristics of the lithium secondary battery were evaluated by using a constant current method. The charging and discharging voltage ranges were 3.0 V for discharge and 4.4V, 4.5V and 4.55V for charging voltage. The initial capacity was evaluated at a current density of 0.1 C and the output characteristics were evaluated at 0.1 C, 1 C and 2 C. The room temperature lifetime characteristics were carried out at 25 ℃ and at 0.5 ℃. Here, the charge / discharge voltage is the voltage (vs. Li / Li +) relative to Li metal.

The initial capacities for the lithium secondary batteries produced using the cathode active materials according to Examples 1, 2 and Comparative Example 1 are as shown in Table 1. It can be confirmed that the initial capacity is slightly reduced as the coating layer of the metal oxide is formed. This is due to an increase in the weight of the cathode active material as the coating is added.

FIGS. 4 and 5 show measurement graphs of output characteristics of a lithium secondary battery using the cathode active material of Example 1 and Comparative Example 1 according to charging voltage. Here, FIG. 4 shows a result of evaluation under the condition of a charging voltage of 4.4 V and a charging voltage of 4.5 V in FIG. 4.4 V and 4.5 V The detailed capacities and energies according to the C-rate at each charging voltage are shown in Table 2 and Table 3, respectively.

Referring to Table 2, it can be seen that Example 1 is somewhat lower in the case of the capacity for the whole output at 4.4 V, but as seen from FIG. 4, in the case of Example 1, It can be confirmed that the overvoltage is improved in the discharge curve.

Accordingly, as shown in Table 2, the energy at 0.1 C of Example 1 is 704.3 mWh / g, which is 691.9 mWh / g of Comparative Example 1, as shown in Table 2. It is also confirmed that the energy of Example 1 is improved at 2C, which is high power, at 656.5 mWh / g in Example 1 and 623.4 mWh / g in Comparative Example 1. In addition, the output retention ratio against 0.1C was 93.2% in Example 1, which is improved compared with 90.1% in Comparative Example.

The charging / discharging curve of the output characteristic at 4.5 V, which is a higher voltage condition, is shown in FIG. 5, and the discharging capacity and the energy are shown in Table 3. It can be confirmed that Example 1 exhibits higher capacity than Comparative Example 1 in the entire C-rate region, and energy increase due to the overvoltage improvement of the discharge curve can also be confirmed at the same time.

As shown in Table 3, it can be seen that the energy at 0.1 C is 770.1 mWh / g of Example 1, which is 763.1 mWh / g of Comparative Example 1. In Example 2 at high power 2C, 724.6 mWh / 1 was 681.0 mWh / g, indicating that the energy of Example 1 was improved. In addition, the output retention ratio in comparison with 0.1C was 92.7% in Example 1, which is improved compared to 89.2% in Comparative Example.

 Therefore, it has been confirmed that the coating of the Zr oxide provided by the present invention is effective in improving the output characteristics.

FIGS. 6 and 7 show measurement graphs of lifetime characteristics of a lithium secondary battery using the cathode active material of Example 1 and Comparative Example 1 according to the charging voltage. FIG. 6 shows a result of evaluation under the condition of a charging voltage of 4.4 V and a charging voltage of 4.55 V in FIG. Table 4 and Table 5 show the capacity and the retention ratio relative to the initial capacity as the cycle increases.

It can be seen that the initial capacity at the 4.4V charge voltage is 166.5 mAh / g for Comparative Example 1, and 167.7 mAh / g for the Zr oxide coated first Example. In the case of Comparative Example 1, the capacity retention rate after 50 cycles was 73.2%, which is a remarkable decrease in capacity. On the other hand, Example 1 exhibits an excellent life characteristic of 96.3%.

Further, in the case of the lifetime characteristic of a charging voltage of 4.55 V, which is a further deteriorating condition, the initial capacity is 187.7 mAh / g in Comparative Example 1, and 199.6 mAh / g in Example 1 in which the Zr oxide is coated, can confirm. In Comparative Example 1, the capacity after 50 cycles shows a rapid deterioration of capacity to 21.9 mAh / g, whereas in Example 1, the capacity inhibition is controlled to be 163.1 mAh / g after 50 cycles. When expressed as the retention ratio relative to the initial capacity, the capacity retention ratio after 50 cycles is 11.7% for Comparative Example 1 and 81.7% for Example 1, which indicates that the surface coating of Zr oxide is very effective for improving the high voltage lifetime of the LiCoO ₂ cathode active material.

The reaction mechanism for the effect of improving the water stability by the coating of the Si oxide is shown in Fig. The remaining water in the electrolyte reacts with the lithium salt to form HF. The resulting HF reacts on the surface of the anode, resulting in deterioration of the anode. The Si oxide has an HF scavenging effect which selectively and preferentially reacts with HF to form SiF ₄ , and it is possible to effectively control anodic deterioration by effectively protecting the cathode active material core, that is, LiCoO ₂ by HF.

FIG. 9 shows the output characteristics of Example 2 in which the Si oxide was additionally coated, and the discharge capacity according to each C-rate is shown in Table 6. It can be confirmed that there is little deterioration in the output characteristics of Example 2 in which the Si oxide was additionally coated as compared with Example 1 in which only the Zr oxide was coated alone.

In order to evaluate water stability, a coin cell was manufactured using an electrolytic solution containing 1000 ppm of distilled water, and the life characteristics at 1C were evaluated. The results are shown in FIG. 10, Respectively.

Compared with Example 2, the initial capacity of Comparative Example 1 is greatly reduced, which is expected to decrease by the reaction with HF in the electrolyte solution. The capacity after 40 cycles was 121.9 mAh / g for Comparative Example 1 and 161.6 mAh / g for Example 2, indicating that Example 2 exhibits high capacity. The capacity retention ratio was 78% for Comparative Example 1 and 97.3% for Example 2, which indicates that the water stability by the coating of the Si oxide is improved.

In the method of manufacturing a cathode active material according to an embodiment of the present invention, the surface of lithium cobalt oxide is coated with Zr oxide and then coated with Si oxide, but the present invention is not limited thereto. For example, as shown in FIG. 11, a cathode active material may be prepared by coating Si oxide on the surface of lithium cobalt oxide, followed by coating Zr oxide.

11 is a flowchart illustrating a method of manufacturing a cathode active material for a lithium secondary battery according to another embodiment of the present invention.

Referring to FIG. 11, a Si compound solution containing Si is prepared in step S110. At this time, the Si raw material for the Si compound solution having a particle size of less than _{100 nm SiO x (0 <x≤2} ), Si (OR) 4 (R is alkyl, alkenyl or alkynyl) or SiX ₄ (X is a halogen, F, Cl, Br, I) may be used. For example, SiO ₂ of nanoparticle size may be added to IPA, and the solution may be stirred by ultrasonic treatment at 25 ° C for 10 minutes to prepare a Si compound solution.

Next, lithium cobalt oxide is added to the Si compound solution prepared in step S120, followed by stirring and drying to adsorb the Si compound on the surface of the lithium cobalt oxide. That is, the Si compound can be adsorbed on the surface of the lithium cobalt oxide by stirring and drying at a stirring rate of 380 rpm at 80 DEG C for about 8 hours. At this time, in the process of stirring for 8 hours at a stirring speed of 380 rpm at 80 ° C, the IPA is completely evaporated and the Si compound is uniformly adsorbed on the surface of the lithium cobalt oxide.

Next, in step S130, the lithium cobalt oxide to which the Si compound is adsorbed is heat-treated to uniformly coat the surface of the lithium cobalt oxide with the nano-sized Si oxide. The heat treatment may be performed at 200 to 700 ° C for 1 to 24 hours in air.

Then, in step S140, the lithium cobalt oxide coated with the nano-sized Si oxide is put into the Zr compound solution, stirred and dried to adsorb the Zr compound to the surface of the lithium cobalt oxide. At this time, ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less may be used as a Zr raw material of the Zr compound solution. A Zr compound solution is prepared in consideration of the coating amount of the Zr oxide of 0.01 to 1.0 wt% with respect to the total weight of the lithium cobalt oxide. For example, Zr isopropoxide is added to IPA and stirred at 25 DEG C for about 2 hours to prepare a Zr compound solution. And then stirred and dried at 80 DEG C at a stirring rate of 380 rpm for about 8 hours to adsorb the Zr compound to the surface of the lithium cobalt oxide. At this time, in the course of stirring for 8 hours at a stirring rate of 380 rpm at 80 ° C, the IPA is completely evaporated and the Zr compound is uniformly adsorbed on the surface of the lithium cobalt oxide.

The cathode active material according to the present invention can be manufactured by heat-treating the lithium cobalt oxide adsorbed on the Zr compound and coating the surface of the lithium cobalt oxide uniformly with the nano-sized Zr oxide in step S150. The heat treatment may be performed at 200 to 700 ° C for 1 to 24 hours in air.

It should be noted that the embodiments disclosed in the present specification and drawings are only illustrative of specific examples for the purpose of understanding, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

Claims (15)

A positive electrode active material for a lithium secondary battery, wherein a surface of a lithium cobalt oxide represented by the following formula is uniformly coated with a nano-sized Zr oxide.
[Chemical Formula]
_{LiCo 1-x M x O 2} (0.00≤x <0.10, M is Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti And Zr) The method according to claim 1,
And ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less. The method according to claim 1,
Wherein the Zr oxide is contained in an amount of 0.01 to 1.0 wt% with respect to the lithium cobalt oxide. The method according to claim 1,
And a surface of the lithium cobalt oxide is further coated with a nano-sized Si oxide uniformly. 5. The method according to claim 4,
SiO _x (0 <x≤2) having a particle diameter of below 100 nm, including the Si (OR) ₄ (R is alkyl, alkenyl or alkynyl) or SiX ₄ (X is a halogen, F, Cl, Br, I) And a positive electrode active material for a lithium secondary battery. A lithium secondary battery comprising a lithium cobalt oxide represented by the following chemical formula, wherein the surface of the lithium cobalt oxide is uniformly coated with a nano-sized Zr oxide.
[Chemical Formula]
_{LiCo 1-x M x O 2} (0.00≤x <0.10, M is Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti And Zr) The method according to claim 6,
Wherein a surface of the lithium cobalt oxide of the cathode active material is further coated with a nano-sized Si oxide uniformly. Introducing a lithium cobalt oxide expressed by the following formula into a Zr compound solution, stirring and drying to adsorb the Zr compound on the surface of the lithium cobalt oxide;
Treating the lithium cobalt oxide adsorbed with the Zr compound to heat uniformly coat the surface of the lithium cobalt oxide with a nano-sized Zr oxide;
Wherein the positive electrode active material is a positive electrode active material.
[Chemical Formula]
_{LiCo 1-x M x O 2} (0.00≤x <0.10, M is Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti And Zr) 9. The method of claim 8,
The Zr compound includes ZrO ₂ or Zr (OR) ₄ (R is alkyl, alkenyl or alkynyl) having a particle diameter of 100 nm or less,
Wherein the surface of the lithium cobalt oxide is coated with Zr oxide particles of 30 nm or less in thickness. 9. The method of claim 8,
Wherein the Zr compound raw material comprises a solution containing ZrO ₂ powder having a particle diameter of 100 nm or less or a solution of Zr isoporoxide. 9. The method of claim 8,
Wherein the Zr oxide is contained in an amount of 0.01 to 1.0 wt% with respect to the lithium cobalt oxide. 9. The method of claim 8, wherein the step of adsorbing the Zr compound is performed prior to the step of adsorbing the Zr compound and the step of coating the Zr oxide.
Introducing a lithium cobalt oxide into a solution of a Si compound, stirring and drying the solution to adsorb the Si compound on the surface of the lithium cobalt oxide;
Coating the surface of the lithium cobalt oxide with uniformly nano-sized Si oxide by heat-treating the lithium cobalt oxide adsorbed on the Si compound;
The method of claim 1, wherein the positive electrode active material is a lithium salt. 13. The method of claim 12,
The raw material of the Si oxide is SiO _x (0 <x? 2), Si (OR) ₄ (R is alkyl, alkenyl or alkynyl) or SiX ₄ (X is halogen, F, Cl, Br , &Lt; / RTI &gt; I)
Wherein the surface of the lithium cobalt oxide is coated with Si oxide particles of several hundreds nm or less. 13. The method of claim 12,
Wherein the Si compound raw material is a solution containing SiO ₂ powder having a particle diameter of 100 nm or less, a solution of Si (OC ₂ H ₅ ) O ₄ (Tetraethyl orthosilicate) or a solution of SiF _4. Way. 13. The method of claim 12, wherein in the coating of the Zr oxide and the coating of the Si oxide,
Wherein the heat treatment is performed at 200 to 700 ° C for 1 to 24 hours.

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