KR20200036545A - Active Material for Sodium-based Secondary Battery And Zinc-based Secondary Battery And Secondary Battery Having the Same - Google Patents

Abstract

Provided are an electrode active material for a sodium and zinc secondary battery, and a secondary battery comprising the same. The electrode active material is represented by chemical formula 1, Fe_(3-x)M_x(PO_4)_2. The electrode active material has a monoclinic crystal structure and a space group of P2_1/c. In the chemical formula 1, x is 0 to 2, and M is a metal having an oxidation number of +2. Specifically, the present invention is to provide a new electrode active material usable for sodium or zinc secondary batteries.

Description

Electrode active material for sodium and zinc secondary batteries and secondary batteries comprising the same {Active Material for Sodium-based Secondary Battery And Zinc-based Secondary Battery And Secondary Battery Having the Same}

The present invention relates to a secondary battery, and specifically, to an electrode active material for a sodium and zinc secondary battery and a secondary battery including the same.

Secondary battery refers to a battery that can be used repeatedly because it can be charged as well as discharge. A representative lithium secondary battery among secondary batteries, lithium ions contained in the positive electrode active material are transferred to the negative electrode through the electrolyte and then inserted into the layered structure of the negative electrode active material (charge), and then lithium ions that have been inserted into the layered structure of the negative electrode active material are again It works through the principle of returning to the anode (discharging). The lithium secondary battery is currently commercialized and used as a small power source for mobile phones and notebook computers, and is also expected to be used as a large power source for hybrid vehicles, and the demand is expected to increase.

However, a composite metal oxide mainly used as a positive electrode active material in a lithium secondary battery contains a rare metal element such as lithium, and there is a fear that it cannot meet the increasing demand. Accordingly, research is being conducted on a sodium secondary battery using sodium having a high supply and inexpensive as a positive electrode active material. As an example, Republic of Korea Patent Publication No. 2012-0133300 discloses A _x MnPO ₄ F (A = Li or Na, 0 <x ≤ 2) as a positive electrode active material.

However, the sodium anode materials developed to date still do not have excellent structural stability, and it is known that a battery using the same needs to improve the discharge capacity retention rate and stability.

Therefore, the problem to be solved by the present invention is to provide a new electrode active material usable for a sodium or zinc secondary battery. In addition, by including the electrode active material, the discharge capacity retention characteristics and stability improved sodium secondary battery and the lithium secondary battery showing an abundant amount of resources compared to lithium, environmentally friendly, inexpensive and provides a high stability zinc secondary battery.

In order to achieve the above object, one aspect of the present invention provides an electrode active material. The electrode active material is represented by the following Chemical Formula 1, is an electrode active material having a monoclinic crystal structure and having a space group of P2 ₁ / c.

[Formula 1]

Fe _3-x M _x (PO ₄ ) ₂

In Chemical Formula 1, x may be 0 to 2. M may be a metal having an oxidation number of +2.

In addition, in Chemical Formula 1, M may be Ni, Co, Fe, Mn, Cr, V, Cu, Ti or Sr.

The active material represented by Chemical Formula 1 may be an electrode active material of Fe ₃ (PO ₄ ) ₂ .

In order to achieve the above object, another aspect of the present invention provides an electrode active material manufacturing method. First, a metal salt solution containing an iron compound and a phosphate is prepared. The metal salt solution is burned to prepare a gel precursor. The gel precursor is fired to obtain an electrode active material represented by Chemical Formula 1, having a monoclinic crystal structure, and having a space group of P2 ₁ / c.

The iron compound may be ferric oxide (Fe ₂ O ₃ ).

The phosphate salt may be monoammonium phosphate (NH ₄ H ₂ PO ₄ ).

Combustion of the metal salt solution may be performed at 180 ° C to 250 ° C.

The step of firing the gel precursor may include a first firing step of heat treatment in an air atmosphere and a second firing step of heat treatment in a reducing atmosphere.

In order to achieve the above object, another aspect of the present invention provides a secondary battery.

The secondary battery is represented by the formula (1), has a monoclinic crystal structure and a first electrode comprising an electrode active material having a space group of P2 ₁ / c, a second electrode comprising an active material containing an active metal, and the first It may be a secondary battery comprising an electrolyte disposed between the electrode and the second electrode.

The first electrode may be a cathode.

The second electrode may be an anode.

The active metal is sodium, and the secondary battery may be a sodium secondary battery.

The active metal is zinc, and the secondary battery may be a zinc secondary battery.

According to the present invention, it is possible to obtain an electrode active material having a monoclinic crystal structure and having a space group of P2 ₁ / c and represented by Chemical Formula 1. By including the active material according to an embodiment of the present invention, it is possible to provide an environmentally friendly, inexpensive, and highly stable zinc secondary battery that exhibits a rich amount of resources compared to lithium and a sodium secondary battery having improved discharge capacity retention characteristics and stability.

1 is a flowchart showing a method of manufacturing an electrode active material according to an embodiment of the present invention.
2 is a schematic diagram showing a secondary battery according to an embodiment of the present invention.
Figure 3 is a graph showing the XRD (X-ray diffraction) analysis results for Fe ₃ (PO ₄ ) ₂ according to the active material preparation example of the present invention.
Figure 4 is a graph showing the initial charge and discharge characteristics of the sodium ion reverse cell according to Battery Manufacturing Example 1 of the present invention.
5 is a graph showing the initial charge and discharge characteristics of the sodium ion reverse cell according to the battery comparative example of the present invention.
6 is a graph showing the initial charge and discharge characteristics of the zinc ion reverse cell according to the battery manufacturing example 2 of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in more detail to describe the present invention in more detail. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Throughout the specification, the same reference numbers indicate the same components.

In the present specification, the fact that one layer is located "on" another layer means that not only these layers are directly in contact, but another layer (s) is located between these layers. In addition, the numerical range of “n to n + x” can be interpreted to include n, n + x, and all values existing between n and n + x.

Electrode active material

Electrode active material according to an embodiment of the present invention is represented by the following formula (1).

[Formula 1]

Fe _3-x M _x (PO ₄ ) ₂

In Chemical Formula 1, x may be 0 to 2. M may be a metal having an oxidation number of +2. As an example, M may be a transition metal having an oxidation number of +2. In detail, M may be Ni, Co, Fe, Mn, Cr, V, Cu, Ti or Sr.

1 is a flowchart showing a method of manufacturing an electrode active material according to an embodiment of the present invention.

Referring to FIG. 1, an electrode active material may be obtained using a Sol-Gel Combustion Hybrid Method. First, a metal salt solution containing an iron compound and a phosphate may be prepared (S10). The iron compound and phosphate are dissolved in distilled water in an amount suitable for the stoichiometric formula. At this time, as a preferred example, the iron compound is ferric oxide (Fe ₂ O ₃ ), ferric chloride (FeCl ₃ ), ferric nitrate (Fe (NO ₃ ) ₃ ), iron hydroxide (Fe (OH) ₃ ), and the phosphate may be ammonium monophosphate (NH ₄ H ₂ PO ₄ ), ammonium diphosphate ((NH ₄ ) ₂ HPO ₄ ), or the like.

The metal salt solution may further include a chelating agent. The chelating agent is selected from the group consisting of tartaric acid, urea, citric acid, formic acid, glycolic acid, polyacrylic acid, adipic acid, and glycine. Can be. The chelating agent may be contained in 10wt% to 30wt% by weight of the metal salt. Meanwhile, a crystal growth inhibitor may be further included in the metal salt solution. The crystal growth inhibitor may be a saccharide or a derivative thereof, for example, glucose, sucrose, or a derivative thereof. The crystal growth inhibitor may be contained in 1wt% to 10wt% by weight of the metal salt.

The metal salt solution can be sufficiently mixed by stirring. When the metal salt solution is stirred, a sol mixture can be obtained by heat treatment. The heat treatment may be performed at 130 ° C to 170 ° C. As an example, it may be 140 ℃ to 160 ℃. The mixture in the sol state may be burned in a heated oven to prepare a gel precursor (S20). The combustion can be carried out in an oven heated to 180 ℃ to 250 ℃. As an example, it may be carried out at 190 ℃ to 230 ℃. By firing the gel precursor, a powder that can be used as an electrode active material can be prepared (S30). At this time, the step of firing the gel precursor may include a first firing step of heat treatment in an air atmosphere and a second firing step of heat treatment in a reducing atmosphere. The air atmosphere may be an atmosphere containing 15 vol.% To 100 vol.% Of oxygen, specifically 70 vol.% To 90 vol.% Of oxygen and the rest of the inert gas. At this time, the inert gas may be nitrogen. In addition, the first firing step may be performed to remove organic and other residues, and heat treatment may be performed at 300 ° C to 600 ° C. The second firing step may be performed for crystal growth, and heat treatment may be performed at 700 ° C to 1200 ° C.

The active material according to an embodiment of the present invention may be used for manufacturing a sodium secondary battery having excellent discharge capacity, and may also be used for the production of a zinc secondary battery. In addition, only the compound according to an embodiment of the present invention may be used as an electrode active material, and may further include other compounds other than the compounds according to the above to be used as an electrode active material. The characteristics of the battery according to this will be described below.

Hereinafter, a secondary battery to which an active material according to an embodiment of the present invention can be applied will be described.

Metal secondary battery

<Structure of metal secondary battery>

2 is a schematic diagram showing a secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, the secondary battery 100 includes a second electrode active material layer 120 containing an electrode active material through which metal can be de-inserted, a first electrode active material layer 140 containing the electrode active material described above, and these And a separator 130 interposed therebetween. The electrolyte 160 may be disposed or charged between the second electrode active material layer 120 and the separator 130 and between the first electrode active material layer 140 and the separator 130. The second electrode active material layer 120 may be disposed on the second electrode current collector 110, and the first electrode active material layer 140 may be disposed on the first electrode current collector 150. The active material according to the exemplary embodiment of the present invention may be included in the electrode active material and used as the first electrode. Accordingly, the second electrode may contain an active metal.

Metal secondary battery

The metal secondary battery according to an embodiment of the present invention includes a first electrode containing the electrode active material described above, a second electrode containing an active material to which the active metal can be de-inserted, and an electrolyte positioned between them.

<First electrode>

A first electrode material can be obtained by mixing the electrode active material, a conductive material, and a binder described in Chemical Formula 1 above.

Since the electrode active material described in Chemical Formula 1 may have a stable crystal structure, the degree of deterioration due to moisture is low and there is an advantage of lowering the operating voltage.

The conductive material may be natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, graphene, or other carbon materials. Binders include thermoplastic resins such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymers, fluorine resins such as propylene hexafluoride, and / or polyolefin resins such as polyethylene and polypropylene. It can contain.

The first electrode material may be applied on the current collector to form the first electrode. The first electrode current collector may be a conductor such as Al, Ni, and stainless steel. Applying the first electrode material on the first electrode current collector may be a method of forming a paste using pressure molding or an organic solvent, and then applying the paste onto the first current collector and pressing to fix it. Organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; Ether systems such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Ester systems such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste on the first electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Second electrode>

The electrode active material of the second electrode is a metal, metal alloy, metal oxide, metal fluoride, metal sulfide, and natural graphite, artificial graphite, coke, carbon black, which can deintercalate or convert an active metal ion or cause a conversion reaction. It can also be formed using carbon materials such as carbon nanotubes and graphene.

A second electrode material can be obtained by mixing an electrode active material, a conductive material, and a binder. At this time, the conductive material may be natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, carbon materials such as graphene. Binders include thermoplastic resins such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymers, fluorine resins such as propylene hexafluoride, and / or polyolefin resins such as polyethylene and polypropylene. It can contain.

The second electrode material may be applied on the second electrode current collector to form a second electrode. The second electrode current collector may be a conductor such as Al, Ni, and stainless steel. Applying the second electrode material on the second electrode current collector may be a method of forming a paste using pressure molding or an organic solvent, and then applying the paste onto the second current collector and pressing to fix it. Organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; Ether systems such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Ester systems such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste on the second electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Electrolyte>

The electrolyte may be a liquid electrolyte containing a metal salt and a solvent dissolving it. Specifically,

In the case of a sodium secondary battery, the electrolyte may be NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower aliphatic sodium carboxylate, NaAlCl _4, etc. , Mixtures of two or more of these may also be used. Among these, it is preferable to use an electrolyte containing fluorine. Further, the electrolyte can be dissolved in an organic solvent and used as a non-aqueous electrolyte. As an organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4- Carbonates such as trifluoromethyl-1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, 2-methyltetrahydro Ethers such as furan; Esters such as methyl formate, methyl acetate, and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidon; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propanesultone; Alternatively, a fluorine substituent introduced into the above-described organic solvent may be used. Alternatively, a solid electrolyte may be used. The solid electrolyte may be an organic solid electrolyte such as a polymer compound containing at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain, or a polyoxyalkylene chain. Further, a so-called gel type electrolyte in which a nonaqueous electrolyte solution is supported on a polymer compound can also be used. Meanwhile, Na ₂ S-SiS ₂ , Na ₂ S-GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ), And Fe ₂ (MoO ₄ ) ₃ . In some cases, the safety of the secondary battery can be improved by using these solid electrolytes.

In the case of a zinc secondary battery, the zinc salt contained in the electrolyte may be ZnSO ₄ , ZnCl, ZnCF ₃ SO ₃ , ZnC ₄ H ₆ O ₄ , Zn (NO ₃ ) ₂ , or a mixture of two or more of them may be used. have. Further, the solvent may be an aqueous solvent or an organic solvent. However, the electrolyte is not limited thereto, and the liquid electrolyte may be a polymer-type solid electrolyte or a ceramic-type solid electrolyte impregnated into the polymer. The polymer in the polymer-type solid electrolyte may be a polymer compound containing at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain or a polyoxyalkylene chain. The ceramic solid electrolyte may also use inorganic ceramics such as sulfides, oxides, and phosphates of the metal.

In addition, the solid electrolyte may serve as a separator to be described later, and in that case, a separator may not be required.

<Separator>

A separator may be disposed between the first electrode and the second electrode. The separator may be a material having a form of a porous film made of a material such as polyolefin resin such as polyethylene or polypropylene, a fluorine resin, or an aromatic polymer containing nitrogen, a nonwoven fabric or a woven fabric. The thickness of the separator is preferably as thin as possible as long as mechanical strength is maintained, in that the bulk energy density of the battery becomes high and the internal resistance becomes small. The thickness of the separator may generally be on the order of 5 to 200 μm, and more specifically 5 to 40 μm.

<Method of manufacturing a metal secondary battery>

A metal secondary battery can be manufactured by stacking the second electrode, the separator, and the first electrode in order to form an electrode group, then rolling the electrode group, if necessary, and storing it in a battery can, and impregnating the electrode group with an electrolyte solution. Alternatively, a second electrode, a solid electrolyte, and a first electrode may be stacked to form an electrode group, and then, if necessary, the electrode group may be rolled and stored in a battery can to manufacture a metal secondary battery.

Hereinafter, a preferred experimental example (example) is presented to help understanding of the present invention. However, the following experimental examples are only to aid the understanding of the present invention, and the present invention is not limited by the following experimental examples.

[Experimental Examples; Examples]

Active material preparation example: Fe ₃ (PO ₄ ) ₂  Produce

Ferric oxide (Fe ₂ O ₃ ), monoammonium phosphate (NH ₄ H ₂ PO ₄ ), citric acid and sucrose in distilled water according to the amount of stoichiometry and magnetic to ensure sufficient mixing It was sufficiently stirred using a bar. The stirred solution was heated to 150 and stirred again to obtain a sol mixture. The sol state mixture is burned in an oven heated to 200 ° C. to obtain a gel precursor. The gel precursor was heat treated at 400 ° C. in an air atmosphere, and then heat treated at 900 ° C. in a reducing atmosphere. Thus, a Fe ₃ (PO ₄ ) ₂ powder was obtained.

Figure 3 is a graph showing the XRD (X-ray diffraction) analysis results for Fe ₃ (PO ₄ ) ₂ according to the active material preparation example of the present invention.

Referring to FIG. 3, Fe ₃ (PO ₄ ) ₂ synthesized according to an active material preparation example shows a clear XRD peak. Through this, it can be confirmed that Fe ₃ (PO ₄ ) ₂ synthesized according to the active material preparation example does not contain impurities and has a single phase crystal. In addition, it can be seen that Fe ₃ (PO ₄ ) ₂ synthesized according to the active material preparation example has a monoclinic crystal structure and the space group is P2 ₁ / c.

Battery Preparation Example 1: Preparation of sodium ion reverse paper

After mixing the Fe ₃ (PO ₄ ) ₂ powder synthesized according to the active material preparation example, the conductive material (Super-P: Ketjen black = 1: 1), and the binder (Poly vinylidene fluoride) in a weight ratio of 8: 1: 1 , After coating on an aluminum current collector and pressing, a first electrode was formed.

Thereafter, metal sodium was used as a second electrode as an active metal, and an electrolyte in which 0.5 M NaPF ₆ was dissolved in a solvent in which propylene carbonate (PC) and fluoroethylene carbonate (FEC) was mixed at a volume ratio of 3: 7 was used. Using, a half sheet was prepared.

Figure 4 is a graph showing the initial charge and discharge characteristics of the sodium ion reverse cell according to Battery Manufacturing Example 1 of the present invention.

At this time, the discharge was a constant current discharge at 10 mA / g to 3.0 V, and the charging was performed at a rate equal to the discharge rate to a constant current charge to 0.1 V.

Referring to FIG. 4, when the sodium ion half cell according to Battery Manufacturing Example 1 of the present invention was manufactured, it can be confirmed that the discharge capacity exceeded 1700 mAh / g. In addition, the Fe ₃ (PO ₄ ) ₂ powder synthesized according to the active material preparation example is practical in the sodium ion battery system, and it can be seen that the battery prepared according to the battery production example 1 of the present invention has excellent capacity performance. .

Battery Comparative Example: Preparation of sodium ion reverse paper

A half-cell was prepared in the same manner as in Battery Preparation Example 1, except that FePO ₄ powder was used as the active material instead of Fe ₃ (PO ₄ ) ₂ prepared according to the active material preparation example.

5 is a graph showing the initial charge and discharge characteristics of the sodium ion reverse cell according to the battery comparative example of the present invention.

At this time, the discharge was a constant current discharge at 10 mA / g to 3.0 V, and the charging was performed at a rate equal to the discharge rate to a constant current charge to 0.1 V.

Referring to FIG. 5, when a sodium ion half cell was prepared using FePO ₄ powder as an active material according to a battery comparative example, the discharge capacity does not reach 80 mAh / g. This, compared to the _half- cell prepared by using the Fe ₃ (PO ₄ ) ₂ powder synthesized according to the active material manufacturing example as an active material, the value of the discharge capacity is significantly reduced.

Thus, improvement in the Fe ₃ (PO _{4) 2} powder of active material and one inverted fingers sustain discharge capacity prepared by using a characteristic synthesized according to the active material for example is an Fe ₃ (PO _{4) 2} is monoclinic crystal used as the active material structure It is considered to be the result of the space group having a stable crystal structure of P2 ₁ / c.

Battery Manufacturing Example 2: Preparation of zinc ion reversed paper

After mixing the Fe ₃ (PO ₄ ) ₂ powder synthesized according to the active material preparation example, the conductive material (Super-P: Ketjen black = 1: 1), and the binder (Poly vinylidene fluoride) in a weight ratio of 8: 1: 1 , After coating on the current collector, press to form a first electrode.

Thereafter, metal zinc was used as a second electrode, and a half-cell was prepared using 1 M of ZnSO ₄ electrolyte.

6 is a graph showing the initial charge and discharge characteristics of the zinc ion reverse cell according to the battery manufacturing example 2 of the present invention.

At this time, the discharge was a constant current discharge at 10 mA / g up to 1.2 V, and the charging was performed at a rate equal to the discharge rate to a constant current charge up to 0.3 V.

Referring to FIG. 6, when a zinc ion half cell was prepared using Fe ₃ (PO ₄ ) ₂ powder synthesized according to an active material preparation example having a monoclinic crystal structure as an active material, it was confirmed that the discharge capacity exceeded 75 mAh / g. You can. Through this, it can be seen that the Fe ₃ (PO ₄ ) ₂ powder synthesized according to the active material preparation example is practical in a zinc ion battery system.

The electrode active material for sodium secondary batteries and zinc secondary batteries according to the present invention can replace electrode materials used in electronic devices such as portable devices such as mobile phones and small household appliances.

As described above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes are made by those skilled in the art within the technical spirit and scope of the present invention. This is possible.

100: secondary battery
110: second electrode current collector
120: second electrode active material layer
130: separator
140: first electrode active material layer
150: first electrode current collector
160: electrolyte

Claims (14)

An electrode active material represented by the following Chemical Formula 1, having a monoclinic crystal structure and having a space group of P2 ₁ / c:
[Formula 1]
Fe _3-x M _x (PO ₄ ) ₂
In Chemical Formula 1,
x is 0 to 2,
M is a metal having an oxidation number of +2. The method according to claim 1,
M is an electrode active material of Ni, Co, Fe, Mn, Cr, V, Cu, Ti or Sr. The method according to claim 1,
The active material represented by Chemical Formula 1 is an electrode active material of Fe ₃ (PO ₄ ) ₂ . Preparing a metal salt solution containing an iron compound and a phosphate;
Preparing a gel precursor by burning the metal salt solution; And
A method of manufacturing an electrode active material comprising the step of firing the gel precursor, and obtaining an electrode active material represented by the following Chemical Formula 1, having a monoclinic crystal structure and having a space group of P2 ₁ / c:
[Formula 1]
Fe _3-x M _x (PO ₄ ) ₂
In Chemical Formula 1,
x is 0 to 2,
M is a metal having an oxidation number of +2. The method according to claim 5,
The active material represented by Formula 1 is Fe ₃ (PO ₄ ) ₂ electrode active material manufacturing method. The method according to claim 5,
The iron compound is ferric oxide (Fe ₂ O ₃ ) electrode active material manufacturing method. The method according to claim 5,
The phosphate is a method of manufacturing an electrode active material that is ammonium monophosphate (NH ₄ H ₂ PO ₄ ). The method according to claim 5,
Combustion of the metal salt solution is an electrode active material manufacturing method performed at 180 ℃ to 250 ℃. The method according to claim 5,
The step of firing the gel precursor comprises a first firing step of heat treatment in an air atmosphere and a second firing step of heat treatment in a reducing atmosphere. A first electrode including an electrode active material represented by the following Chemical Formula 1, having a monoclinic crystal structure and having a space group of P2 ₁ / c;
A second electrode comprising an active material containing an active metal; And
Secondary battery comprising an electrolyte disposed between the first electrode and the second electrode:
[Formula 1]
Fe _3-x M _x (PO ₄ ) ₂
In Chemical Formula 1,
x is 0 to 2,
M is a metal having an oxidation number of +2. The method according to claim 10,
The first electrode is a secondary battery that is a negative electrode. The method according to claim 10,
The second electrode is a secondary battery that is an anode. The method according to claim 10,
The active metal is sodium, the secondary battery is a secondary battery, characterized in that the sodium secondary battery. The method according to claim 10,
The active metal is zinc, the secondary battery is a secondary battery characterized in that the sodium secondary battery.

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