KR102345323B1 - Method for preparing cathode active material for high voltage sodium secondary battery - Google Patents

Abstract

The present invention comprises the steps of (a) Na ₂ CO ₃ , (Co _3-xy M ¹ _x M ² _y )O ₄ , and NH ₄ H ₂ PO ₄ Preparing a precursor mixture by mixing with an organic solvent; (b) evaporating the organic solvent from the precursor mixture to prepare a dry mixture; (c) first heat-treating the dry mixture at 400 to 600°C; and (d) subjecting the resultant primary heat treatment to a secondary heat treatment at 700 to 800° C. to prepare a _{cathode active material, Na 4} (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _{7 ;} includes Thereby, the electrochemical characteristics and lifespan characteristics of the sodium secondary battery can be improved.

Description

Method for manufacturing a cathode active material for a high voltage sodium secondary battery

The present invention relates to a method for manufacturing a positive electrode active material for a secondary battery, and more particularly, to a method for manufacturing a positive electrode active material for a sodium secondary battery capable of significantly improving electrochemical performance by using a wet method instead of a conventional dry method.

A secondary battery refers to a battery that can be used repeatedly because it can be charged as well as discharged. In a typical lithium secondary battery among secondary batteries, lithium ions contained in the positive electrode active material move to the negative electrode through the electrolyte, and then are inserted into the layered structure of the negative electrode active material, that is, charged. It works through the principle of return to discharge. These lithium secondary batteries are currently commercialized and used as small power sources for mobile phones and notebook computers, and are expected to be usable as large power sources for hybrid vehicles, and the demand is expected to increase. However, since the composite metal oxide mainly used as a positive electrode active material in a lithium secondary battery contains a rare metal element such as lithium, there is a concern that it may not be able to meet the increase in demand. Accordingly, research on a sodium secondary battery using abundant supply and cheap sodium as a cathode active material is being conducted.

However, the sodium positive electrode materials developed so far still do not have excellent structural stability, and the battery using the same is in need of improvement in discharge capacity retention rate and stability.

Among the positive electrode active materials of sodium secondary batteries, phosphate-based Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ , Na ₄ Co _2.4 Mn _0.3 Ni _0.3 (PO ₄ ) ₂ P ₂ O ₇ etc. A technology for manufacturing by the gel method has been developed. When the cathode active material is manufactured by the sol-gel method, the content of impurities other than the target material can be reduced, and non-uniformity of constituent elements generated during the synthesis process can be suppressed. Therefore, it is necessary to develop a method for manufacturing a cathode active material that can improve electrochemical performance by maximizing the purity of a sodium secondary battery cathode active material that has an expression capacity of 90 mAh/g or more and can exhibit 4.5V class performance.

Korean Patent Registration No. 10-1677535

An object of the present invention is to prepare a cathode active material for a sodium secondary battery such as _{Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O ₇ , Na ₄ Co _2.4 Mn _0.3 Ni _0.3 (PO ₄ ) ₂ P ₂ O _{7 In the conventional method} By introducing the wet solid-state method rather than the sol-gel method, the content of impurities other than the target material is significantly reduced to increase the purity, thereby improving both the electrochemical performance and lifespan characteristics. An object of the present invention is to provide a method for manufacturing a positive active material for a battery.

According to one aspect of the invention,

(a) preparing a precursor mixture by mixing _{Na 2} CO ₃ , (Co _3-xy M ¹ _x M ² _y )O ₄ , and NH ₄ H ₂ PO _{4 with an organic solvent;}

(b) evaporating the organic solvent from the mixture to prepare a dry mixture;

(c) first heat-treating the dry mixture at 400 to 600°C; and

(d) preparing a _{cathode active material, Na 4} (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _{7 ,} by subjecting the first heat-treated product to a second heat treatment at 700 to 800° C.; including,

M ¹ And M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe, and Cu,

0.1≤x≤1.0, 0.1≤y≤1.0, a method for producing a cathode active material for a sodium secondary battery is provided.

In step (a), the (Co _3-xy M ¹ _x M ² _y )O ₄ may be Co ₃ O ₄ .

In step (a), the mixing may be performed by ball milling.

In step (a), the ball and the precursor mixture used for the ball milling may use 10 to 30 parts by weight of the starting material based on 100 parts by weight of the ball.

In step (a), the ball milling may be performed at 50 to 150 rpm for 2 to 5 hours.

In step (b), the organic solvent is acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), and may be any one selected from cyclohexane (cyclohexane).

In step (b), the evaporation may be performed at 70 to 90° C. until the organic solvent is completely dried.

In step (c), the first heat treatment may be performed for 4 to 8 hours.

In step (c), the primary heat treatment may be heat-treated by raising the temperature to a temperature of 450 to 550° C. at a temperature increase rate of 0.5 to 1.5° C./min.

In step (c), the first heat treatment may be performed in air.

In step (d), the second heat treatment may be performed for 20 to 30 hours.

The cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇ may be Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ .

After step (d), (e) _{carbon coating the cathode active material, Na 4} (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇ ; may be additionally performed.

Step (e), the cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y ) (PO ₄ ) ₂ P ₂ O ₇ After adding water by mixing with a carbon source, heat treatment at 500 to 700 ℃ can be carbon coated.

The heat treatment may be performed for 4 to 8 hours.

The heat treatment may be performed under an argon atmosphere.

The carbon source may be any one selected from citric acid, vapor grown carbon fiber (VGCF), acetylene black, carbon black, Ketjen black, channel black, furnace black, and super-P.

Most preferably,

In step (a), the organic solvent is acetone, the precursor mixture includes Na ₂ CO ₃ , Co ₃ O ₄ and NH ₄ H ₂ PO ₄ , and mixing of the precursor mixture is performed by ball milling,

Evaporation of the acetone solvent in step (b) is performed at 78 to 82° C. until completely dry,

The primary heat treatment in step (c) is carried out in air for 5.5 to 6.5 hours while maintaining the temperature after reaching 480 to 520 °C at a temperature increase rate of 0.8 to 1.2 °C / min,

The secondary heat treatment in step (d) is performed in air at 740 to 750° C. for 23 to 25 hours,

In step (e), citric acid is used as the carbon source, and carbon coating may be performed by heat treatment at 580 to 620° C. for 5.5 to 6.5 hours in an argon atmosphere.

According to another aspect of the present invention,

There is provided a method for manufacturing a sodium secondary battery, including the method for manufacturing the cathode active material for a sodium secondary battery.

According to another aspect of the present invention,

There is provided a cathode active material for a sodium secondary battery comprising a compound represented by the following formula, and having a discharge capacity of 100 to 120 mAh/g.

[Formula 1]

Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇

M ¹ and M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe, and Cu, and 0.1≤x≤1.0, 0.1≤y≤1.0.

The cathode active material for a sodium secondary battery of the present invention, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇ The method for preparing the conventional sol-gel method is not a wet-gel method. By introducing the wet solid-state method, it is possible to significantly reduce the content of impurities other than the target material to increase the purity, thereby improving both electrochemical performance and lifespan characteristics.

1 is a flowchart sequentially showing a method of manufacturing a cathode active material for a sodium secondary battery of the present invention.
2 schematically shows the process of Examples 1 to 9 of the present invention.
3 schematically shows the process of Comparative Example 1 of the present invention.
4 shows the results of X-ray diffraction analysis for the positive active materials of Examples 1 to 9 of Test Example 1.
5 shows the results of X-ray diffraction analysis of the positive active material of Comparative Example 1 of Test Example 1.
6 shows the results of analysis of the charge/discharge voltage change according to Test Example 2.
7 shows the results of the capacity change analysis according to the cycle according to Test Example 4.
8 and 9 show the expression capacity and lifespan characteristic analysis results for the carbon-coated positive active materials of Examples 5 and 6 of Test Example 5.
10 shows the expression capacity and lifespan characteristic analysis results for the carbon-coated positive electrode active material of Comparative Example 1.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a flowchart sequentially showing a method of manufacturing a cathode active material for a sodium secondary battery of the present invention. Hereinafter, a method of manufacturing a cathode active material for a sodium secondary battery of the present invention will be described with reference to FIG. 1 .

First, Na ₂ CO ₃ , (Co _3-x-y M ^One _x M ² _y )O ₄ , and NH ₄ H ₂ PO ₄ is mixed with an organic solvent to prepare a precursor mixture (step a).

The (Co _3-xy M ¹ _x M ² _y )O ₄ to M ¹ and M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe, and Cu, preferably 0.1≤x≤1.0, 0.1≤y≤1.0, more preferably (Co _3-xy M ¹ _x M ² _y )O ₄ may be Co ₃ O ₄ .

The mixing is preferably performed by ball milling.

The ball and the precursor mixture used for the ball milling preferably use 10 to 30 parts by weight of the starting material based on 100 parts by weight of the ball, more preferably 15 to 25 parts by weight, even more preferably 18 to 30 parts by weight. 22 parts by weight can be used.

The ball milling is preferably performed at 50 to 150 rpm for 2 to 5 hours.

Next, an organic solvent is evaporated from the precursor mixture to prepare a dry mixture (step b).

The organic solvent is acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N-methyl-2) -pyrrolidone, NMP), cyclohexane (cyclohexane) and the like may be used, but the scope of the present invention is not limited thereto.

The evaporation is preferably performed at 70 to 90° C. until the organic solvent is completely dried, more preferably at 75 to 85° C., even more preferably at 78 to 82° C.

Thereafter, the dry mixture is subjected to a primary heat treatment at 400 to 600° C. (step c).

More preferably, the first heat treatment may be performed at 450 to 550 °C, even more preferably 480 to 520 °C.

The first heat treatment is preferably performed for 4 to 8 hours, more preferably 5 to 7 hours, and still more preferably 5.5 to 6.5 hours.

The primary heat treatment is preferably performed by raising the temperature to 400 to 600 °C at a temperature increase rate of 0.5 to 1.5 °C/min, more preferably reaching 480 to 520 °C at a temperature increase rate of 0.8 to 1.2 °C/min. After that, heat treatment may be performed for 5.5 to 6.5 hours.

The primary heat treatment is preferably performed in air.

Next, the resultant of the primary heat treatment is subjected to secondary heat treatment at 700 to 800 ° C. to prepare a cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _{7 (step} d).

M ¹ and M ² may each independently be any one selected from Co, Mn, Ni, Cr, Fe, and Cu.

Also, 0.1≤x≤1.0 and 0.1≤y≤1.0 may be present.

Preferably, the cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇ may be Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ .

More preferably, the secondary heat treatment may be performed at 730 to 760 °C, and even more preferably at 740 to 750 °C. In the case of heat treatment at a temperature lower than 740°C or higher than 750°C, impurities may be generated to deteriorate the electrochemical performance.

The secondary heat treatment is preferably performed for 20 to 30 hours, more preferably for 22 to 27 hours, even more preferably for 23 to 25 hours.

Then, the cathode active material, Na ₄ (Co _3-x-y M ^One _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇ It is preferable to additionally perform the step of carbon coating (step e).

This is because the electrochemical performance can be significantly improved by the carbon coating.

Specifically, in this step, the cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _{7 ,} is mixed with a carbon source, water is added, and then heat-treated at 500 to 700° C. and carbon coating, more preferably at 550 to 650 °C, even more preferably at 580 to 620 °C.

The carbon source may be citric acid, vapor grown carbon fiber (VGCF), acetylene black, carbon black, Ketjen black, channel black, furnace black, super-P, etc., but it is preferable to use citric acid .

The heat treatment is preferably performed for 4 to 8 hours, more preferably 5 to 7 hours, even more preferably 5.5 to 6.5 hours.

In particular, although not explicitly described in the following Examples, in the method for producing a cathode active material for a sodium secondary battery according to the present invention, the type of precursor and the type of the organic solvent in step (a), the mixing conditions, and the precursor in step (b) Change the conditions for evaporating the organic solvent from the mixture, the temperature, temperature, and time conditions of the first heat treatment in step (c), the temperature and time conditions of the second heat treatment in step (d), and the carbon source and carbon coating conditions in step (e) while preparing a cathode active material for a sodium secondary battery.

The electrochemical characteristic test was performed on the thus-prepared cathode active material for a sodium secondary battery to confirm its performance. As a result, unlike in other conditions and other numerical ranges, almost no impurities exist only when all of the following conditions are satisfied, and the expression capacity and lifespan characteristics of the secondary battery were significantly high. Such manufacturing conditions are as follows.

In step (a), the organic solvent is acetone, the precursor mixture includes Na ₂ CO ₃ , Co ₃ O ₄ and NH ₄ H ₂ PO ₄ , and the mixing of the precursor mixture is performed by ball milling, step ( In b), the evaporation of the acetone solvent is carried out at 78 to 82° C. until it is completely dried, and the first heat treatment in step (c) is at a temperature increase rate of 0.8 to 1.2° C./min after reaching 480 to 520° C. is maintained and carried out in air for 5.5 to 6.5 hours, the secondary heat treatment in step (d) is carried out in air at 740 to 750° C. for 23 to 25 hours, and the carbon source in step (e) is citric acid, Carbon coating is performed by heat treatment at 580 to 620° C. under argon atmosphere for 5.5 to 6.5 hours.

The present invention provides a cathode active material for a sodium secondary battery comprising a compound represented by the following formula prepared according to the above manufacturing method, and having a discharge capacity of 100 to 120 mAh/g.

[Formula 1]

Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇

M ¹ and M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe, and Cu, and 0.1≤x≤1.0, 0.1≤y≤1.0.

Hereinafter, preferred examples are presented to help the understanding of the present invention. However, these examples are for explaining the present invention in more detail, the scope of the present invention is not limited thereby, and it is common in the art that various changes and modifications are possible within the scope and spirit of the present invention. It will be obvious to those with knowledge.

[Example]

Example 1: Na by Wet Solid-State method ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ synthesis

Na ₂ CO ₃ 4.614 g, Co ₃ O ₄ 5.312 g, and NH ₄ H ₂ PO ₄ 10.072 g were used as starting materials and mixed in 30 ml of acetone by ball milling at 80 RPM for 3 hours. Then, the acetone solvent was evaporated at 80° C. to dry it completely. Next, the temperature was raised to 500° C. at a rate of 1° C./min for 8 hours and 20 minutes, and the primary heat treatment was performed for 6 hours under air conditions at 500° C. _{Thereafter, the cathode active material Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O ₇ was synthesized by secondary heat treatment at 700° C. for 24 hours under air conditions.

For the charge/discharge test, 1 M NaClO ₄ was dissolved in EC : PC : DMC (1 : 1 : 1 v/v) electrolyte and assembled into a 2032 coin cell. A charge/discharge test was performed at 34 mA/g in a voltage range of 3.0 to 4.7 V.

Example 2

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 710°C instead of 700°C.

Example 3

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 720°C instead of 700°C.

Example 4

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 730°C instead of 700°C.

Example 5

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 740 °C instead of 700 °C.

Example 6

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 750°C instead of 700°C.

Example 7

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 760°C instead of 700°C.

Example 8

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 770°C instead of 700°C.

Example 9

A cathode active material was synthesized in the same manner as in Example 1, except that the secondary heat treatment temperature was set to 780°C instead of 700°C.

Comparative Example 1: Na by sol-gel method ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ synthesis

Co(CH ₃ COO) ₂ , Na ₄ P ₂ O ₇ and NH ₄ H ₂ PO ₄ were used as starting materials, and these materials were mixed in a diluted nitric acid solution and then Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ Glycolic acid was added to prevent grain growth of the precursor. The mixed solution was heated while stirring at 80 °C for 12 hours. The resulting gel was heat-treated in air at 700° C. for 50 hours to synthesize _{Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O _{7 .}

Thereafter, the active material Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ and Vapor-Grown Carbon Fiber (VGCF) were mixed in a weight ratio of 5:1, and reheat treatment was performed at 700° C. for 5 hours under argon purging. was coated. Next, an NMP-based slurry was prepared.

The slurry is a _{mixture of Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O ₇ as a cathode active material, 90 wt% of a mixture of VGCF, 5 wt% of acetylene black, and 5 wt% of PVDF as a binder. The whole was cast to prepare a positive electrode.

The CR2032-type coin cell was prepared by using ethylene carbonate (EC)/diethylene carbonate (DEC) in which _{NaPF 6} was dissolved at a concentration of 1.0 mol cm ^-3 as an electrolyte, using the positive electrode prepared as above, and metallic sodium as the negative electrode.

[Experimental example]

Test Example 1: X-ray diffraction analysis

4 shows the results of X-ray diffraction analysis of the positive electrode active material of the present invention prepared according to Examples 1 to 9, and FIG. 5 shows the X-ray diffraction analysis result of the positive electrode active material prepared according to Comparative Example 1.

According to this, the structure of the cathode active material of Example 5 synthesized by secondary heat treatment at 740 ° C. and the cathode active material of Example 6 synthesized by secondary heat treatment at 750 ° C. Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ was confirmed to exist most predominantly, _{and the material having the Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O ₇ structure is the material that best expresses the battery performance. _{On the other hand, Na 2} CoP ₂ O ₇ was present as an impurity in the temperature region lower than 740 ° C. In the temperature region higher than 750 ° C, alpha-NaCoPO ₄ , Na ₄ Co ₇ (PO ₄ ) ₅ , beta-NaCoPO _{4 ,} etc. It appears that impurities are present, and when this is used as a cathode active material, the performance of the sodium ion secondary battery may be deteriorated.

In addition, since the positive active material prepared according to Comparative Example 1 also contains impurities, the performance of the sodium ion secondary battery may be deteriorated.

Test Example 2: Analysis of charge/discharge voltage change (expressed capacity)

6 shows a charge/discharge voltage change curve in the first cycle at a charge/discharge rate of 34 mAh/g and a voltage range of 3.0 to 4.7V of the positive active materials prepared according to Examples 1 to 7, respectively.

According to this, it was measured that the performance of the sodium secondary battery including the cathode active material of Example 5 synthesized by secondary heat treatment at 740 ° C. and the cathode active material of Example 6 synthesized by secondary heat treatment at 750 ° C. was the best, 740 ℃ and 750 ℃ Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ It can be seen that this is because the temperature is the most predominantly present.

Test Example 4: Analysis of capacity change according to cycle (lifetime characteristics)

7 shows the capacity change according to cycles measured in a charge/discharge rate of 34 mAh/g and a voltage range of 3.0 to 5.0V for the positive active materials prepared according to Examples 1 to 7, respectively.

According to this, the performance of the sodium secondary battery including the cathode active material of Example 5 synthesized by secondary heat treatment at 740 ° C. and the cathode active material of Example 6 synthesized by secondary heat treatment at 750 ° C. It can be seen that this is also 740 ℃ and 750 ℃ Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ It can be seen that this is because the temperature is the predominantly present.

Test Example 5: Expression capacity and lifespan characteristics analysis of carbon-coated positive electrode active material

The cathode active material of Examples 5 and 6 Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ and citric acid as a carbon source were mixed, DI water was added, dried in an oven, and then heated to 600° C. in an argon atmosphere. It was heat-treated for 6 hours and carbon-coated. _{Thereafter, life characteristics were analyzed for the cathode active materials Na 4} Co ₃ (PO ₄ ) ₂ P ₂ O ₇ of Examples 5 and 6 coated with carbon, and the results are shown in FIGS. 8 and 9 . In addition, the results (a) and life characteristics analysis results (b) of the charge/discharge voltage change analysis of the positive active material of Comparative Example 1 are shown in FIG. 10 .

According to this, the carbon-coated positive active material of Examples 5 and 6 showed a high value close to 110 mAh/g in discharge capacity, but the carbon-coated positive active material of Comparative Example 1 had a discharge capacity of 90 mAh/g, which is about 90 mAh/g. showed a lower level than In addition, it was confirmed that the carbon-coated positive active materials of Examples 5 and 6 had very good cycle characteristics.

Claims (17)

(a) preparing a precursor mixture by mixing _{Na 2} CO ₃ , (Co _3-xy M ¹ _x M ² _y )O ₄ , and NH ₄ H ₂ PO _{4 with an organic solvent;}
(b) evaporating the organic solvent from the precursor mixture to prepare a dry mixture;
(c) first heat-treating the dry mixture;
(d) preparing a _{cathode active material, Na 4} (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _{7 ,} by performing a second heat treatment on the resultant of the first heat treatment; and
(e) carbon coating the cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O _7;
In step (a), the organic solvent is acetone, and mixing of the precursor mixture is performed by ball milling,
Evaporation of the organic solvent in step (b) is performed at 78 to 82° C. until it is completely dried,
The primary heat treatment in step (c) is carried out in air for 5.5 to 6.5 hours while maintaining the temperature after reaching 480 to 520 °C at a temperature increase rate of 0.8 to 1.2 °C / min,
The secondary heat treatment in step (d) is performed in air at 740 to 750° C. for 23 to 25 hours,
In the step (e), the carbon source is citric acid, heat-treated at 580 to 620° C. for 5.5 to 6.5 hours under an argon atmosphere to coat carbon,
M ¹ And M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe and Cu,
0.1≤x≤1.0, 0.1≤y≤1.0 A method of manufacturing a cathode active material for a sodium secondary battery, characterized in that. According to claim 1,
In step (a), the (Co _3-xy M ¹ _x M ² _y )O ₄ is a method for producing a cathode active material for a sodium secondary battery, characterized in that _{Co 3} O _{4 .} delete According to claim 1,
In step (a), the ball and the precursor mixture used for the ball milling is a method of manufacturing a cathode active material for a sodium secondary battery, characterized in that using 10 to 30 parts by weight of the precursor mixture based on 100 parts by weight of the ball. delete delete delete delete delete According to claim 1,
The cathode active material, Na ₄ (Co _3-xy M ¹ _x M ² _y ) (PO ₄ ) ₂ P ₂ O ₇ is Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O _{7 A} cathode for a sodium secondary battery, characterized in that A method for producing an active material. delete delete delete delete delete A method of manufacturing a sodium secondary battery comprising the method for manufacturing a cathode active material for a sodium secondary battery of any one of claims 1, 2, 4 and 10. Claims 1, 2, 4 and 10, prepared according to the method for producing a cathode active material for a sodium secondary battery according to any one of claims 1 to 10, comprising a compound represented by the following formula, coated with carbon, and having a discharge capacity A cathode active material for a sodium secondary battery, characterized in that 100 to 120 mAh/g.
[Formula 1]
Na ₄ (Co _3-xy M ¹ _x M ² _y )(PO ₄ ) ₂ P ₂ O ₇
M ¹ and M ² are each independently any one selected from Co, Mn, Ni, Cr, Fe, and Cu, and 0.1≤x≤1.0, 0.1≤y≤1.0.

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