KR101875674B1 - Positive active material, method for prepare the same and sodium rechargeable battery including the same - Google Patents

Abstract

According to an embodiment of the present invention, there is provided a cathode active material comprising a compound represented by the following general formula (1).
[Chemical Formula 1]
Na ₄ Mn _x Fe _{3 -x} (PO ₄ ) ₂ (P ₂ O ₇ )
Here, x is 0 < x < 3.

Description

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

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

While the development of new and renewable energy and the reduction of carbon dioxide are essential, it is essential to develop a secondary battery capable of storing electric power in order to efficiently use the produced energy.

In recent years, the development of a technology capable of being applied to a large-capacity and power storage device has been actively carried out. Among them, a sodium secondary battery capable of storing more power at a low cost has been developed.

SUMMARY OF THE INVENTION The present invention provides a cathode active material having high voltage, high capacity and high efficiency characteristics and excellent price competitiveness, a method for producing the same, and a secondary battery including the same.

One embodiment of the present invention provides a cathode active material comprising a compound represented by the following general formula (1).

[Chemical Formula 1]

Na ₄ Mn _x Fe _{3 -x} (PO ₄ ) ₂ (P ₂ O ₇ )

Here, x is 0 < x < 3.

X may be 0 < x &lt; = 2.

Formula 1 _{Na 4 Mn 0 .3 Fe 2 .7} (PO 4) 2 (P 2 O 7), Na 4 Mn 0 .75 Fe 2 .25 (PO 4) 2 (P 2 O 7), Na 4 _{MnFe 2 (PO 4) 2 (} P 2 O 7), Na 4 Mn 1 .5 Fe 1 .5 (PO 4) 2 (P 2 O 7) and _{Na 4 Mn 2 Fe (PO 4} ) 2 (P 2 O ₇ ).

In another embodiment of the present invention, there is provided a method for preparing a first mixture, comprising mixing and drying a sodium precursor, an iron precursor, a manganese precursor, and a phosphate precursor to produce a first mixture; And sintering the first mixture in three steps to obtain a compound represented by the following formula (1).

[Chemical Formula 1]

Na ₄ Mn _x Fe _{3 -x} (PO ₄ ) ₂ (P ₂ O ₇ )

Here, x is 0 < x < 3.

The sintering step may include a first sintering step in an argon atmosphere at 250 to 350 ° C and a second sintering step in an argon atmosphere at 550 to 650 ° C.

Mixing the second sintered first mixture with a carbon source to prepare a second mixture, and subjecting the second mixture to a third sintering at 550 to 650 ° C under an argon atmosphere.

The first sintering and the second sintering may be performed in a state where the flow of the inert gas is present.

The third sintering may be performed for 5 to 7 hours, the second sintering may be performed for 11 to 13 hours, and the third sintering may be performed for 1 to 3 hours.

The second mixture may include the first mixture: the carbon source in a weight ratio of 92: 98: 8-2.

The carbon source may be at least one selected from polyvinyl alcohol, polyolefin, polyacrylonitrile, cellulose, starch, granule, acrylonitrile, divinylbenzene, vinyl acetate, glucose, cellulose acetate, pyromellitic acid, acetone and ethanol have.

The sodium precursor is Na ₄ P ₂ O ₇ , and the phosphate precursor is (NH ₄ ) ₂ HPO ₄ And (NH ₄ ) H ₂ PO ₄ , the iron precursor is FeC ₂ O ₄ .2H ₂ O, and the manganese precursor may be MnC ₂ O ₄ .2H ₂ O.

Yet another embodiment of the present invention provides a sodium secondary battery comprising a cathode comprising a cathode active material comprising a compound represented by the following formula (1), a cathode, and an electrolyte disposed between the anode and the cathode .

[Chemical Formula 1]

Na ₄ Mn _x Fe _{3 -x} (PO ₄ ) ₂ (P ₂ O ₇ )

Here, x is 0 < x < 3.

The negative electrode may comprise at least one of a sodium metal, an alloy based on a sodium metal, and a sodium intercalation compound.

The separation membrane may include at least one of glass fiber, polyester, Teflon, and polytetrafluoroethylene (PTFE).

As described above, the cathode active material according to one embodiment of the present invention, the secondary battery including the same, the method of manufacturing the same, and the secondary battery including the same have high voltage, high capacity and high efficiency characteristics.

1 is a schematic view of a sodium secondary battery according to an embodiment of the present invention.
2 is a graph showing XRD measurement results of the cathode active material prepared in Example 1 of the present invention.
3 is a graph showing XRD measurement results of the cathode active material prepared in Example 2 of the present invention.
4 is a graph showing XRD measurement results of the cathode active material prepared in Example 3 of the present invention.
5 is a graph showing XRD measurement results of the cathode active material manufactured in Example 4 of the present invention.
6 is a graph showing XRD measurement results of the cathode active material prepared in Example 5 of the present invention.
7 is a photograph showing SEM measurement results of the cathode active material prepared in Example 1 of the present invention.
8 is a photograph showing SEM measurement results of the cathode active material prepared in Example 2 of the present invention.
9 is a photograph showing SEM measurement results of the cathode active material prepared in Example 3 of the present invention.
10 is a photograph showing SEM measurement results of the cathode active material manufactured in Example 4 of the present invention.
11 is a photograph showing SEM measurement results of the cathode active material prepared in Example 5 of the present invention.
12 is a graph showing a result of measuring a voltage of a sodium secondary battery manufactured using the cathode active material prepared in Example 1 of the present invention.
13 is a graph showing a result of measuring a voltage of a sodium secondary battery manufactured using the cathode active material manufactured in Example 2 of the present invention.
14 is a graph showing a result of measuring a voltage of a sodium secondary battery manufactured using the cathode active material prepared in Example 3 of the present invention.
15 is a graph showing a result of measuring a voltage of a sodium secondary battery manufactured using the cathode active material manufactured in Example 4 of the present invention.
16 is a graph showing a result of measuring a voltage of a sodium secondary battery manufactured using the cathode active material manufactured in Example 5 of the present invention.
FIGS. 17 to 18 are graphs showing the results of measurement of a change in a capacitor (dQ / dV) according to a voltage of a sodium secondary battery manufactured using the cathode active material prepared in Examples 1 to 5 of the present invention.
19 is a graph showing a life cycle graph of a sodium secondary battery manufactured using the cathode active materials prepared in Examples 1 to 5 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Throughout the specification, when an element is referred to as &quot; comprising &quot;, it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

The cathode active material according to an embodiment of the present invention may include all of iron (Fe), manganese (Mn), and phosphate compounds.

The cathode active material according to one embodiment of the present invention includes a compound represented by the following general formula (1).

[Chemical Formula 1]

Na ₄ Mn _x Fe _{3 -x} (PO ₄ ) ₂ (P ₂ O ₇ )

Here, x is 0 < x < 3.

The formula (1) may be any one selected from the following formulas (2) to (6).

(2)

Na ₄ Mn _{0 .3} Fe _{2 .7} (PO ₄ ) ₂ (P ₂ O ₇ )

(3)

_{Na 4 Mn 0 .75 Fe 2 .25} (PO 4) 2 (P 2 O 7)

[Chemical Formula 4]

Na ₄ MnFe ₂ (PO ₄ ) ₂ (P ₂ O ₇ )

[Chemical Formula 5]

_{Na 4 Mn 1 .5 Fe 1 .5} (PO 4) 2 (P 2 O 7)

[Chemical Formula 6]

Na ₄ Mn ₂ Fe (PO ₄ ) ₂ (P ₂ O ₇ )

The cathode active material according to one embodiment of the present invention is a phosphate compound containing both iron (Fe) and manganese (Mn), and is a phosphate based cathode active material based on iron (Fe) alone or a phosphate based Compared with the cathode active material, it has high energy density and can be used for a high voltage secondary battery and can have a high capacity.

The cathode active material according to one embodiment of the present invention may further include phosphates commonly used conventionally in addition to the compounds represented by Chemical Formulas 1 to 6.

Hereinafter, a method for manufacturing a positive electrode active material according to an embodiment of the present invention will be described.

The method for producing a cathode active material of the present invention comprises mixing and drying a sodium precursor, an iron precursor, a manganese precursor, a phosphate precursor, and a carbon source to prepare a first mixture; Sintering the first mixture; Pelletizing the primary sintered mixture; And then the second pellet is sintered to form a compound represented by Na ₄ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ ). And then sintering the pellet, and then sintering the mixture by mixing the secondary sintered pellet with a carbon source.

Hereinafter, each step will be described in detail in order.

First, a sodium precursor, an iron precursor, a manganese precursor, and a phosphate precursor are mixed and dried to prepare a first mixture.

The sodium precursor may be Na ₄ P ₂ O ₇ and the phosphate precursor may be (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) H ₂ PO ₄ , or a combination thereof, and the iron precursor may be FeC ₂ O ₄ .2H ₂ O, and the manganese precursor may be MnC ₂ O ₄ .2H ₂ O. In addition, it may further contain a carbon source. As the carbon source, any one or more selected from among glucose, cellulose acetate, pyromellitic acid, acetone and ethanol may be used, and pyromellitic acid is preferably used.

The first mixture thus prepared is ball milled to obtain a powder.

The ball mill is preferably a dry ball mill, but the present invention is not limited thereto, and a wet ball mill may be used.

The powder thus obtained through the ball mill of the first mixture is first sintered at 250 to 350 DEG C under an inert gas atmosphere.

Here, the inert gas may be any one selected from nitrogen (N), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon Can be used, and the first sintering can be performed for 5 to 7 hours.

Next, the first-sintered powder is secondarily sintered at 550 to 650 ° C under an inert gas atmosphere.

The inert gas usable in the secondary sintering may also be any one selected from nitrogen (N), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon However, argon can be preferably used, and secondary sintering can be performed for 11 to 13 hours.

The above-described primary sintering and secondary sintering can be performed with an inert gas flow in order to prevent the oxidation of iron (Fe) contained in the powder.

Finally, a second mixture obtained by mixing the second sintered powder with a carbon source is thirdly sintered at 550 to 650 ° C under an inert gas atmosphere to prepare a cathode active material according to an embodiment of the present invention.

Here, the carbon source may be at least one selected from among polyvinyl alcohol, polyolefin, polyacrylonitrile, cellulose, starch, granule, acrylonitrile, divinylbenzene, vinyl acetate, glucose, cellulose acetate, pyromellitic acid, acetone and ethanol Can be used, and pyromellitic acid is preferably used.

In the second mixture, the powder: carbon source may be mixed in a weight ratio of 92 to 98: 8 to 2.

The inert gas usable in the third sintering may also be any one selected from nitrogen (N), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon However, argon can be preferably used, and the third sintering can be performed for 1 to 3 hours.

Hereinafter, a sodium secondary battery including a cathode active material according to an embodiment of the present invention will be described in detail with reference to FIG.

1 is a schematic view of a sodium secondary battery according to an embodiment of the present invention.

1, a sodium secondary battery 1 according to an embodiment of the present invention includes an anode 3, a cathode 2, and a separator 4.

The anode 3, the cathode 2, and the separator 4 may be wound or folded to be accommodated in the battery case 5. An organic electrolytic solution can be injected into the battery case 5 and is sealed with a cap assembly 6. The battery case 5 may have a cylindrical shape, a rectangular shape, a thin film shape, or the like, but is not limited thereto and may be a large thin film type.

A separator (4) is disposed between the anode (3) and the cathode (2) to form a battery structure. After the cell structure is laminated in the bi-cell structure, the cell structure is impregnated with the organic electrolyte solution, and the resultant product is received in the pouch and sealed, thereby completing the sodium secondary battery.

Hereinafter, each configuration will be described in detail.

In the sodium secondary battery 1 according to the present embodiment, the cathode 2 may include, but is not necessarily limited to, a sodium metal, a sodium metal-based alloy, a sodium intercalating compound, or a carbon- Any material that can be used as an anode active material in the technical field includes sodium or can absorb / release sodium. The sodium metal-based alloy may include, but is not limited to, an alloy of aluminum, tin, indium, calcium, titanium, vanadium, etc. with sodium.

The cathode 2 may be made of metal in a thickness of 3 to 500 μm and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

When a negative electrode active material other than a sodium metal or a sodium alloy is used, a carbon-based material having a graphene structure or the like can be used. A mixed cathode of a material such as graphite and graphitic carbon, a mixed cathode of a carbon-based material and a metal or an alloy, and a composite cathode may be used. As the carbonaceous material, natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor growth carbon fiber, pitch carbonaceous material, needle coke, petroleum coke, A carbonaceous material such as polyacrylonitrile-based carbon fiber or carbon black, or an amorphous carbon material synthesized by thermal decomposition of a cyclic hydrocarbon or a cyclic oxygen-containing organic compound of a 5-membered ring or a 6-membered ring.

The separator 4 may be interposed between the anode 2 and the cathode 3. The separator 4 is not limited as long as it can withstand the use environment of the sodium battery. For example, a nonwoven fabric made of polypropylene or polyphenylene sulfide A nonwoven fabric such as a nonwoven fabric of polyethylene or polypropylene, or a porous film of an olefin resin, or a combination of two or more of them may be used.

The separator 4 may have a low resistance to ion movement of the electrolyte and an excellent ability to impregnate the electrolyte. For example, glass fiber, polyester, Teflon, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric.

The electrolyte is a liquid containing sodium in an ionic state, and the sodium salt as an electrolyte is dissolved in a solvent.

Sodium salt used as an electrolyte is _{NaClO 4, NaPF 6, NaBF 4} , NaCF 3 SO 3, NaN (CF 3 SO 2) 2, NaN (C 2 F 5 SO 2) 2, NaC (CF 3 SO 2) 3 , etc. May be used, but are not necessarily limited thereto and can be used as sodium salts in the art.

As the organic solvent for dissolving the electrolyte, a polar organic solvent may be used.

Examples of the organic solvent include dimethyl ether, diethyl ether, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethylene carbonate, propylenecarbonate, butylene carbonate, but are not limited to, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate,? -butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, Butyl ether, tetraglyme, diglyme, polyethylene glycol dime

Methyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, cyclohexanone, triethylamine, triphenylamine, triethylphosphine oxide, But are not limited to, one or more organic solvents selected from the group consisting of acetonitrile, dimethylformamide, 1,3-dioxolane, and sulfolane, and if they can be used as organic solvents in the art Everything is possible.

In the anode 3, the cathode active material composition in which the cathode active material, the conductive material, and the solvent are mixed according to one embodiment of the present invention may be directly coated on the current collector.

As the conductive material of the positive electrode active material composition, one or more of high specific surface area carbon materials such as carbon black, activated carbon, acetylene black, and graphite fine particles may be included. Further, electroconductive fibers such as fibers produced by carbonizing vapor grown carbon or pitch (byproducts such as petroleum, coal, coal tar, etc.) at high temperature and carbon fibers prepared from acrylic fibers (polyacrylonitrile) have. Carbon fiber and a carbon material having a high specific surface area can be used simultaneously. The use of the carbon fiber and the carbon material having a high specific surface area simultaneously can further improve the electric conductivity. Further, a metal-based conductive material having a lower electrical resistance than that of the cathode active material can be used as a material which does not dissolve in the charge and discharge range of the anode. For example, a corrosion-resistant metal such as titanium or gold, a carbide such as SiC or WC, or a nitride such as Si ₃ N ₄ or BN, but the present invention is not limited thereto, and any material can be used as the conductive material.

As the solvent of the positive electrode active material composition, N-methylpyrrolidone, acetone or water may be used, but the present invention is not limited thereto.

The collector of the positive electrode may be made of a metal such as nickel, aluminum, titanium, copper, gold, silver, platinum, aluminum alloy or stainless steel, carbon material, activated carbon fiber, nickel, aluminum, zinc, copper, tin, lead, A conductive film obtained by dispersing a conductive agent in a resin such as a rubber or a styrene-ethylene-butylene-styrene copolymer (SEBS), or the like can be used.

The shape of the current collector is not particularly limited and may be, for example, a thin film, a flat plate, a mesh, a net, a punch or an embossed or a combination thereof (for example, a mesh plate or the like) have. For example, irregularities can be formed on the surface of the current collector by etching.

The sodium secondary battery according to an embodiment of the present invention may be used in all of the devices requiring a battery pack, for example, a notebook computer, a smart phone, an electric vehicle, Devices and the like.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only illustrative of the present invention and are not intended to limit the scope of the present invention.

Example  One: Na ₄ Mn _{0 .3} Fe _{2 .7} ( PO ₄ ) ₂ (P ₂ O ₇ ) &Lt; / RTI &gt; (x = 0.3)

Na ₄ P ₂ O _{7 6.286g, FeC 2 O 4 · 2H} 2 O 11.018g, MnC 2 O 4 · 2H 2 O 1.218g, NH 4 H 2 PO 4 pyromellitic acid and 5.272g of a first mixture of 5% by weight, based on the weight of the total of (Pyromellitic acid ) Was blended by dry ball milling to obtain a powder.

The obtained powder was firstly sintered at 300 DEG C for 6 hours under an argon atmosphere, then pelletized, and secondary sintering was performed at 600 DEG C for 12 hours under an argon atmosphere.

The second mixture was prepared by mixing the powder / pyromellitic acid with the second sintered powder at a ratio of 95: 5 wt%, and the second mixture was sintered at 600 ° C for 2 hours under an argon atmosphere to obtain Na ₄ Mn _{0 . 3} Fe _{2 .7} (PO ₄ ) ₂ (P ₂ O ₇ ) was synthesized.

Example  2: Na ₄ Mn _{0 .75} Fe _{2 .25} ( PO ₄ ) ₂ (P ₂ O ₇ ) &Lt; / RTI &gt; (x = 0.75)

Embodiment _{Na 4 Mn 0 .75 Fe 2 .25} (PO 4) ₂ according to Example 2 (P ₂ O ₇₎ in Example 1 as compared _{to, FeC 2 O 4 · 2H 2} O to 9.182g, MnC ₂ O ₄ · 2H ₂ O with a 3.045g of carrying out experiments in the same manner as in example 1 except that this one, unlike the mixing amount of the first mixture _{Na 4 Mn 0 .75 Fe 2 .25} (PO 4) 2 (P 2 O 7) Were synthesized.

Example  3: Na ₄ MnFe ₂ ( PO ₄ ) ₂ (P ₂ O ₇ ) (X = 1)

The Na ₄ MnFe ₂ (PO ₄ ) ₂ (P ₂ O ₇ ) according to Example 3 has a higher boiling point than the Na ₄ P ₂ O ₇ Same as _{4.490g, FeC 2 O 4 · 2H} 2 O 5.771g, MnC 2 O 4 · 2H 2 O 2.871g, Example 1 is to a different blending amount of the first mixture with NH ₄ H ₂ PO ₄ 3.766g, except Na ₄ MnFe ₂ (PO ₄ ) ₂ (P ₂ O ₇ ) was synthesized.

Example  4: Na ₄ Mn _{One .5} Fe _{One .5} ( PO ₄ ) ₂ (P ₂ O ₇ ) &Lt; / RTI &gt; (x = 1.5)

Example ₄ Na 4 Mn _{1 .5} according to the _{Fe 1 .5 (PO 4) 2} (P 2 O 7) , as compared to Example _{1, FeC 2 O 4 · 2H} 2 O 6.121g, MnC 2 O 4 · in the same manner as in example 1 with the 2H ₂ O 6.091g to a different blending amount of the first mixture, except that the experiment with _{Na 4 Mn 1 .5 Fe 1 .5} (PO 4) 2 (P 2 O 7) synthesis of Respectively.

Example  5: Na ₄ Mn ₂ Fe ( PO ₄ ) ₂ (P ₂ O ₇ ) &Lt; / RTI &gt; (x = 2)

Embodiment _{Na 4 Mn 2 Fe (PO 4} ) according to Example 5 ₂ (P ₂ O _7), as compared to Example _{3, FeC 2 O 4 · 2H} 2 O 2.886g, MnC 2 O 4 · 2H 2 O 5.742g Na ₂ Mn ₂ Fe (PO ₄ ) ₂ (P ₂ O ₇ ) was synthesized in the same manner as in Example 1, except that the amount of the first mixture was varied.

Hereinafter, the evaluation results of the characteristics of the cathode active material prepared in Examples 1 to 5 will be described in detail.

First, referring to FIG. 2 to FIG. 6, the XRD measurement result of the cathode active material according to an embodiment of the present invention will be described.

FIGS. 2 to 6 are graphs showing XRD measurement results of the cathode active materials prepared in Examples 1 to 5 of the present invention, respectively.

As shown in FIGS. 2 to 6, the cathode active materials prepared in Examples 1 to 5 were Na ₄ Mn _{0 .3} Fe _{2 .7} (PO ₄ ) ₂ (P ₂ O ₇ ) without impurities, Na _{4 Mn 0 .75 Fe 2 .25 (PO} 4) 2 (P 2 O 7), Na 4 MnFe 2 (PO 4) 2 (P 2 O 7), Na 4 Mn 1 .5 Fe 1 .5 (PO 4) ₂ (P ₂ O ₇ ), and Na ₄ Mn ₂ Fe (PO ₄ ) ₂ (P ₂ O ₇ ) were synthesized, respectively.

7 to 11, SEM measurement results of the cathode active material according to an embodiment of the present invention will be described.

7 to 11 are photographs showing SEM measurement results of the cathode active materials prepared in Examples 1 to 5 of the present invention, respectively.

As shown in FIGS. 7 to 11, it was confirmed that the cathode active materials prepared in Examples 1 to 5 had a particle size of about 300 to 500 nm.

Next, the evaluation results of the electrochemical characteristics of the cathode active material prepared in Examples 1 to 5 will be described in detail.

In order to evaluate the electrochemical characteristics of the cathode active material according to the embodiment of the present invention, 2032 type coin cells were coated with sodium metal as a negative electrode, glass fiber separator as a separator, A 1: 1 mixture of ethylene carbonate and propylene carbonate containing 1 mole of NaBF ₄ , NaClO ₄ or NaPF ₆ was used, and as a positive electrode, &Lt; tb &gt;&lt; TABLE &gt;

12 to 16, the results of measurement of the voltage of the redox section of the sodium secondary battery including the cathode active material according to an embodiment of the present invention will be described.

FIGS. 12 to 16 are graphs showing the results of measurement of voltage of a sodium secondary battery manufactured using the cathode active materials prepared in Examples 1 to 5 of the present invention. FIG.

As shown in FIGS. 12 to 16, it was confirmed that as the amount of manganese (Mn) increases, the redox reaction of the cathode active material in the vicinity of 3.8 V to 4 V increases and thus has a high energy density.

17 to 18, the results of measurement of a capacitor according to a voltage of a sodium secondary battery including a cathode active material according to an embodiment of the present invention will be described.

FIGS. 17 to 18 are graphs showing the results of measurement of a change in a capacitor (dQ / dV) according to a voltage of a sodium secondary battery manufactured using the cathode active material prepared in Examples 1 to 5 of the present invention.

As shown in FIGS. 17 to 18, the increase and decrease in the iron ions (Fe2 + / Fe3 +) and the manganese ions (Mn2 + / Mn3 +) in the sodium secondary battery according to the present example were confirmed.

Next, the life cycle of the sodium secondary battery including the cathode active material according to one embodiment of the present invention will be described with reference to FIG.

19 is a graph showing a life cycle graph of a sodium secondary battery manufactured using the cathode active materials prepared in Examples 1 to 5 of the present invention.

In order to measure the life cycle of the sodium secondary battery according to the present embodiment, charging and discharging were carried out at 0.2 C rate, and it was confirmed that the capacity of the sodium secondary battery was maintained well up to 100 cycles as shown in FIG. I could.

As described above, the cathode active material according to one embodiment of the present invention, the secondary battery including the same, the method of manufacturing the same, and the secondary battery including the same can have high voltage, high capacity, and high efficiency characteristics.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1: sodium secondary battery 2: negative electrode
3: anode 4: membrane
5: Battery case 6: Cap assembly

Claims (15)

1. A cathode active material comprising a compound represented by the following formula (1).
[Chemical Formula 1]
Na ₄ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ )
Here, x is 0.3? X? 0.75. The method of claim 1,
(1) is at least one selected from the group consisting of Na ₄ Mn _0.3 Fe _2.7 (PO ₄ ) ₂ (P ₂ O ₇ ), and Na ₄ Mn _0.75 Fe _2.25 (PO ₄ ) ₂ (P ₂ O ₇ ). delete Preparing a first mixture by mixing and drying a sodium precursor, an iron precursor, a manganese precursor, a phosphate precursor, and a carbon source;
Sintering the first mixture;
Pelletizing the primary sintered mixture;
Secondary sintering the pellet;
To obtain a compound represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]
Na ₄ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ )
Here, x is 0.3? X? 0.75. delete 5. The method of claim 4,
The first sintering step is performed in an argon atmosphere at 250 to 350 ° C,
Wherein the second sintering step is performed under an argon atmosphere at 550 to 650 ° C.
A method for producing a cathode active material. 5. The method of claim 4,
Second sintering the pellets, and thereafter
Further comprising a third sintering step of mixing the carbon source with the second sintered pellets,
Wherein the third sintering step is performed under an argon atmosphere at 550 to 650 ° C.
A method for producing a cathode active material. 5. The method of claim 4,
Wherein the first sintering and the second sintering are performed in a state in which there is flow of an inert gas. 8. The method of claim 7,
The primary sintering is performed for 5 to 7 hours,
The second sintering is performed for 11 to 13 hours,
Wherein the third sintering is performed for 1 to 3 hours. 8. The method of claim 7,
Mixing and sintering the secondary sintered pellets with a carbon source;
Wherein the pellet is mixed with the carbon source in a weight ratio of 92 to 98: 8 to 2. 8. The method of claim 7,
Wherein the carbon source is at least one selected from polyvinyl alcohol, polyolefin, polyacrylonitrile, cellulose, starch, granule, acrylonitrile, divinylbenzene, vinyl acetate, glucose, cellulose acetate, pyromellitic acid, acetone, A method for manufacturing an active material. 5. The method of claim 4,
The sodium precursor is Na ₄ P ₂ O ₇ ,
The phosphate precursor is at least one of (NH ₄ ) ₂ HPO ₄ and (NH ₄ ) H ₂ PO ₄ ,
The iron precursor is FeC ₂ O ₄ .2H ₂ O,
Wherein the manganese precursor is MnC ₂ O ₄ .2H ₂ O. The method for producing a cathode active material for a sodium secondary battery according to claim 1, A positive electrode comprising a positive electrode active material comprising a compound represented by the following formula (1)
Cathode, and
And an electrolyte disposed between the anode and the cathode, the sodium secondary battery comprising:
[Chemical Formula 1]
Na ₄ Mn _x Fe _3-x (PO ₄ ) ₂ (P ₂ O ₇ )
Here, x is 0.3? X? 0.75. The method of claim 13,
Wherein the formula 1 is at least one selected from Na ₄ Mn _0.3 Fe _2.7 (PO ₄ ) ₂ (P ₂ O ₇ ), and Na ₄ Mn _0.75 Fe _2.25 (PO ₄ ) ₂ (P ₂ O ₇ ). The method of claim 13,
Wherein the negative electrode comprises at least one of a sodium metal, an alloy based on a sodium metal, and a sodium insertion compound.

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