KR102130528B1 - Method for producing positive electrode active material, positive electrode prepared therefrom, and sodium ion secondary battery containing the same - Google Patents

Abstract

Provided is a method for manufacturing a positive electrode active material for a sodium ion secondary battery, and a positive electrode prepared by including the same and a sodium ion secondary battery including the same. The method for preparing a cathode active material for a sodium ion secondary battery of the present invention may include the step of mixing a sodium transition metal oxide powder with a molybdenum oxide precursor and heat-treating it to form a coating layer of a metal molybdate salt on the surface of the sodium transition metal oxide powder. have. According to the present invention, by forming a coating layer on the surface of the positive electrode active material, it is possible to improve the electrical properties of the sodium ion secondary battery using the positive electrode containing it.

Description

Method for producing a positive electrode active material for a sodium ion secondary battery, a positive electrode prepared therefrom, and a sodium ion secondary battery containing the same {Method for producing positive electrode active material, positive electrode prepared therefrom, and sodium ion secondary battery containing the same}

The present invention relates to a sodium secondary battery, and more particularly, to a positive electrode active material for a sodium secondary battery.

Recently, interest in energy storage devices is rapidly increasing worldwide. Among them, lithium secondary batteries are high-performance, small-sized lithium secondary batteries used as energy sources for mobile information communication devices such as smartphones, laptops, and computers, and secondary for high-power large-sized transportation devices such as electric vehicles (EV) and hybrid electric vehicles (HEV). It is being used as a battery. The demand for lithium secondary batteries is expected to increase further as the demand for power storage devices increases rapidly.

However, there is a possibility that, due to the price increase due to the limited reserves of lithium, there is a possibility that it will spread due to the mineralization of resources, and that the development of conventional technologies has already reached the limit. Accordingly, the development of a post lithium secondary battery that can replace such a lithium secondary battery is in an urgent situation.

Of the many resources on earth, sodium (Na) is one of the abundant resources. It can be easily accessed and harvested through seawater. Currently, research is being conducted on a sodium secondary battery using sodium to replace a lithium secondary battery. Sodium secondary battery has a considerable possibility as a secondary battery by performing an insertion and desorption reaction similar to that of a lithium secondary battery.

However, since the study of sodium ion batteries is currently at a basic level, systematic studies on the synthesis of electrode materials are insufficient. In addition, in the case of the cathode active material for a general sodium secondary battery, the irreversible reaction increases as the electrochemical reaction is repeated, and the stability due to structural collapse or the like decreases, resulting in capacity reduction. Therefore, in order to improve these problems, there is a need to study a secondary battery, particularly, a cathode active material for a sodium secondary battery.

Republic of Korea Patent Publication No. 10-2014-0148269

The problem to be solved by the present invention is to provide a method for manufacturing a positive electrode active material having a coating layer and excellent electrical properties of a sodium ion secondary battery using a positive electrode comprising the same.

In order to achieve the above object, an aspect of the present invention provides a method for manufacturing a cathode active material for a sodium ion secondary battery. The method for manufacturing a cathode active material for a sodium ion secondary battery may include mixing a sodium transition metal oxide powder with a molybdenum oxide precursor and heat-treating it to form a coating layer of sodium molybdate on the surface of the sodium transition metal oxide powder. .

The sodium transition metal oxide may be sodium manganese oxide. The sodium transition metal oxide may be Na _0.44 MnO ₂ . The mixing may be to mill the sodium transition metal oxide powder and molybdenum oxide precursor. The molybdenum oxide precursor may be ammonium molybdate hydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O).

The heat treatment thermally decomposes the molybdenum oxide precursor to form molybdenum oxide, and the molybdenum oxide reacts with a sodium compound remaining on the surface of the sodium transition metal oxide powder to form the coating layer of sodium molybdate (Na ₂ MoO ₄ ). May be The heat treatment may be performed in a dry atmosphere.

In order to achieve the above object, another aspect of the present invention provides a positive electrode for a sodium ion secondary battery. The positive electrode for a sodium ion secondary battery includes a current collector and a positive electrode active material layer located on the current collector, and the positive electrode active material layer is formed on the surface of sodium transition metal oxide particles and the sodium transition metal oxide particles, molybdic acid It may be provided with a coating layer that is sodium. The sodium transition metal oxide may be a tunnel structure. The coating layer may be sodium molybdate (Na ₂ MoO ₄ ).

In order to achieve the above object, another aspect of the present invention provides a sodium ion secondary battery. The sodium ion secondary battery includes a current collector and a positive electrode active material layer located on the current collector, and the positive electrode active material layer is sodium molybdate formed on the surface of the sodium transition metal oxide particles and the sodium transition metal oxide particles. It may include a coating layer, a positive electrode for a sodium ion secondary battery, a negative electrode having a negative electrode active material, and an electrolyte disposed between the positive electrode and the negative electrode.

The coating layer may be sodium molybdate (Na ₂ MoO ₄ ). The electrolyte may be a liquid electrolyte containing a sodium salt and a solvent dissolving it.

According to the present invention, by forming a coating layer on the surface of the positive electrode active material, it is possible to improve the electrical properties of the sodium ion secondary battery using the positive electrode containing it.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a schematic view showing a positive electrode for a sodium ion secondary battery according to an embodiment of the present invention.
2 is a flow chart sequentially showing a method of forming a coating layer of the positive electrode active material of the present invention.
3 is an X-ray diffraction analysis result of the positive electrode active material powder of Preparation Example 1 and Comparative Example 1 of the present invention.
4 is a scanning electron microscope (SEM) photograph of the positive electrode active material powder of Preparation Example 1 and Comparative Example 1 of the present invention.
5 is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the positive electrode active material of Preparation Example 1 and Comparative Example 1 of the present invention.
Figure 6 shows the results of the flight time type secondary ion mass spectrometry (TOF-SIMS) of the positive electrode active material of Preparation Example 2 and Comparative Example 2 of the present invention.
7 is a graph showing cycle characteristics of Preparation Example 3 and Comparative Example 3 of the present invention.

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

While the invention allows for various modifications and variations, specific embodiments thereof are illustrated and illustrated by the drawings, which will be described in detail below. However, it is not intended to limit the invention to the specific forms disclosed, but rather the invention includes all modifications, equivalents, and substitutes consistent with the spirit of the invention as defined by the claims.

When an element, such as a layer, region, or substrate, is referred to as being "on" another component, it will be understood that it may be present directly on the other element, or an intermediate element between them. .

A sodium ion secondary battery according to an embodiment of the present invention includes an anode, a cathode, and an electrolyte positioned between them. Such a secondary battery is capable of performing a charging process in which sodium ions come out of the positive electrode and moves through the electrolyte to the negative electrode and a discharge process in which sodium ions come out of the negative electrode and moves through the electrolyte to the positive electrode, wherein the sodium ion is an active metal ion. You can name it.

1 is a schematic diagram showing a positive electrode for a sodium ion secondary battery according to an embodiment of the present invention, Figure 2 is a flow chart showing a method of forming a positive electrode active material having a coating layer of the present invention in order.

1 and 2, the positive electrode 300 for a sodium ion secondary battery of the present invention includes a positive electrode active material layer 200 formed on the current collector 100, wherein the positive electrode active material layer 200 is a positive electrode active material ( Particle) 201 and the positive electrode active material (particle) 201 may include a coating layer 210 formed on the surface. The positive electrode active material 201 is capable of reversible insertion and desorption of active metal ions, that is, sodium ions, and may be, for example, sodium transition metal oxide. For example, the positive electrode active material 201 may be in the form of a powder.

The sodium transition metal oxide is Na _x [M ¹ _1-yz M ² _y M ³ _z ]O _2-α A _α (0<x≤1, 0≤y<1, 0≤z<1, 0≤α≤ 0.1, M ¹ , M ² , and M ³ are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, and Bi are different metals selected from the group consisting of, A may be N, O, F, or S). The sodium transition metal oxide is Na _x [M ¹ _1-yz M ² _y M ³ _z ]O ₂ (0.5<x≤0.9, 0≤y<1, 0≤z<1, M ¹ =Mn, M ² , Each of M ³ may be Ni, Co, or Fe, regardless of each other As an example, the sodium transition metal oxide may be NaFeO ₂ , NaMnO ₂ , NaNiO ₂ , NaCoO ₂ , NaCrO ₂ , NaNi _0.5 Mn _0.5 O ₂ have.

The sodium transition metal oxide is Na _0.7 [Me _x Mn _1-x ]O ₂ (0.1<x≤0.9, Me=Ni, Co, or Fe), specifically, Na _0.7 [Ni _x Mn _1-x ]O ₂ (0.1<x≤0.9), for example, Na _2/3 [Ni _1/3 Mn _2/3 ]O ₂ .

More specifically, the positive electrode active material 201, that is, the sodium transition metal oxide is manganese oxide Na _x MnO ₂ (0≤ _X ≤1), and more specifically, the sodium transition metal oxide is manganese having a tunnel-type crystal structure. Based oxide Na _x MnO ₂ (0.4≤ _X ≤1), for example, Na _0.44 MnO ₂ . Thus, the positive electrode active material 201 having a tunnel structure can secure an excellent ion diffusion path of the sodium ion, which is the active metal ion.

The coating layer 210 is formed on the surface of the positive electrode active material 201, a compound formed by reacting with the surface sodium residue of the positive electrode active material 201, for example, sodium salt, for example, 100 nm or less It may be formed in the form of a layer having an average thickness of. The coating layer 210 is formed by reacting mainly with the sodium residue on the surface of the positive electrode active material 201, and may be a surface modification film of the positive electrode active material 201. The coating layer 210 may increase the diffusion effect of sodium ions of the positive electrode active material 201, that is, the positive electrode active material 201 having a tunnel structure, without affecting the structure of the positive electrode active material 201. Can.

The coating layer 210 is reacted with a sodium compound and a metal oxide, for example, molybdenum oxide, for example, molybdenum trioxide (MoO ₃ ) derived from the process of forming the positive electrode active material 201 powder and remaining on the surface. It may be formed by. For example, the coating layer 210 may be sodium molybdate (Na ₂ MoO ₄ ).

In other words, the coating layer 210, for example, sodium molybdate (Na ₂ MoO ₄ ) by inhibiting the formation of byproducts that interfere with the movement of the sodium ion, which is the active metal ion of the positive electrode active material 201, , Accordingly, the diffusion of sodium ions in the positive electrode active material 201 powder having a tunnel structure can be further increased. Thus, the electrochemical properties of the sodium ion secondary battery device including the positive electrode can be further improved. For example, the coating layer 210 may have a thickness range of 5nm to 30nm, specifically, 10nm to 20nm.

A method of manufacturing the positive electrode active material 201 having the coating layer 210 according to an embodiment of the present invention may be as follows. First, the positive electrode active material 201 powder may be formed. Specifically, the positive electrode active material 201 may be in the form of dried powder. As an example, the positive electrode active material 201, that is, the sodium transition metal oxide may be Na _0.44 MnO ₂ , which is a manganese oxide having a tunnel-type crystal structure.

In order to form the positive electrode active material 201 powder, a sodium precursor and a transition metal oxide may be prepared (S10). The sodium precursor is not particularly limited as long as it is capable of providing sodium ions. For example, the sodium precursor is a compound in which sodium and anions form a salt, for example, sodium carbonate (Na ₂ CO ₃ ).

The transition metal oxide may supply a transition metal that is a central metal capable of forming a tunnel structure with the sodium ion in the positive electrode active material, for example, the transition metal is Sc, Ti, V, Cr, Mn, Fe , Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, and Bi Can. As an example, the transition metal may be Mn, and the transition metal oxide may be manganese oxide, specifically, manganese dioxide (MnO ₂ ).

After mixing the sodium precursor and the transition metal oxide, a first heat treatment may be performed (S20). The mixing may be to mechanically mill the sodium precursor and the transition metal oxide in a molar ratio of 0.5:1.5 to 1.5:0.5, for example, 1:1, for example, using a mortar mixer. have.

delete

In the first heat treatment, the sodium precursor, for example, sodium ions of sodium carbonate (Na ₂ CO ₃ ) may form a compound with the transition metal oxide, for example, manganese dioxide (MnO ₂ ). The compound may be sodium transition metal oxide, for example, Na _0.44 MnO ₂ .

The first heat treatment may be, for example, at least two or more times, for example, a continuous heat treatment that continuously performs heat treatment twice. For example, in the continuous heat treatment, the mixture after the mixing is, for example, 100° C. to 900° C., specifically, 200° C. to 800° C., more specifically, within a temperature range of 250° C. to 800° C., for example 2 It may be to perform heat treatment continuously.

More specifically, the continuous heat treatment may be to continuously perform the second slow cooling after the first heat treatment and the first slow cooling after the first heat treatment of the mixture. In this case, the first heat treatment and the second heat treatment may further include a process of maintaining the temperature for 7 hours to 10 hours before starting each slow cooling after each heat treatment. That is, the continuous heat treatment may be performed by performing the first heat treatment-maintenance-first slow cooling and the second heat treatment-maintenance-second slow cooling.

As an example, the mixture is placed in a metal crucible, for example, an aluminum crucible, and a primary heat treatment is performed to increase the temperature to 300° C. at a rate of 2° C./min to 7° C./min, for example, 5° C./min. , For example, after maintaining for 8 hours, the first slow cooling may be performed at 2°C/min to 7°C/min, for example, slow cooling at a rate of 4°C/min. Subsequently, a second heat treatment is performed at 2° C./min to 7° C./min, up to 750° C., for example, at a rate of 5° C./min, and then, for example, maintained for 9 hours, 2° C./min to 7 °C / min, for example, may perform a secondary slow cooling to slow cooling at a rate of 4 °C / min.

The continuous heat treatment may be performed in a dry atmosphere, specifically, a dry air atmosphere (ex. O _2(g) :N _2(g) =21%:79%).

That is, the positive electrode active material 201 powder of the present invention does not contain a solvent and may be formed by a solid state reaction as an example of performing heat treatment in a dry air atmosphere. Thus, a sodium transition metal oxide having a tunnel structure, for example, Na _0.44 MnO ₂ powder can be obtained.

After mixing (mixing) the sodium transition metal oxide powder with a metal oxide precursor, for example, a molybdenum oxide precursor, a second heat treatment may be performed (S30). The molybdenum oxide precursor is not particularly limited as long as it can provide molybdenum oxide. For example, the molybdenum oxide may be molybdenum trioxide (MoO ₃ ), and the molybdenum oxide precursor is ammonium molybdate, specifically, ammonium molybdate hydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O) Can be

The mixing may be, for example, mechanical milling using a mortar mixer.

In the second heat treatment, the molybdenum oxide precursor, that is, ammonium molybdate hydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O) is thermally decomposed to form molybdenum oxide, for example, molybdenum trioxide (MoO ₃ ). ((1) of Scheme 1), and the molybdenum trioxide (MoO ₃ ) is to form a compound by reacting with the positive electrode active material 201, specifically, sodium transition metal oxide, for example, Na _0.44 MnO ₂ powder Can. The second heat treatment temperature is, for example, 300 ℃ to 400 ℃. For example, it may be 350 ℃.

The compound may be the positive electrode active material 201 powder, specifically, a coating layer 210 formed on the surface of a sodium transition metal oxide powder. Specifically, the coating layer 210, the molybdenum oxide is an example, sodium transition metal oxide powder, for example, Na _0.44 MnO ₂ sodium compound remaining on the surface of the powder, for example, NaCO ₃ , NaOH, Na ₂ O, etc. It may be formed on the surface of the positive electrode active material 201 by reacting (Scheme 1 (2)).

More specifically, the coating layer 210 is the second heat treatment, specifically, 300 ℃ to 400 ℃. For example, by performing heat treatment in a temperature range of 350° C., the molybdenum oxide may be a metal molybdate salt, that is, sodium molybdate (Na ₂ MoO ₄ ) formed by reacting with NaOH among the remaining sodium compounds. 1 (2)-(ⅰ)).

<Scheme 1>

(1) (NH ₄ ) ₆ MoO ₄ 4H ₂ 0 → MoO ₃ (350℃)

(2) MoO ₃ + NaOH → Na ₂ MoO ₄ + H ₂ 0(g) ...(ⅰ)

MoO ₃ + Na ₂ CO ₃ → Na ₂ MoO ₄ + CO ₂ (g)

The coating layer 210 of the present invention is a compound formed through reaction with the sodium compound remaining on the surface of the positive electrode active material 201, and removes the residual sodium compound to activate metal ions of the positive electrode active material 201 It can exert an effect of inhibiting the formation of byproducts that interfere with the movement of sodium phosphate. Accordingly, by further increasing the diffusion of sodium ions in the positive electrode active material powder having a tunnel structure, the electrochemical characteristics of the sodium ion secondary battery device including the positive electrode can be further improved.

The second heat treatment is performed for 3 hours to 5 hours, for example, 4 hours, and a dry heat treatment, that is, a dry air atmosphere (ex. O _2(g) :N _2(g) =21%: 79%). The second heat treatment may be performed at a heating rate of 2°C/min to 7°C/min, for example, 5°C/min.

The positive electrode active material layer 200 may further include a conductive material (not shown), a binder (not shown), etc. in addition to the positive electrode active material 201. The conductive material may be natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, graphene, or other carbon materials. The conductive material may be contained in 2 to 20 parts by weight based on 100 parts by weight of the positive electrode active material 201.

The binder is a thermoplastic resin, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, a vinylidene fluoride copolymer, a fluorine resin such as propylene hexafluoride, and/or a polyolefin resin such as polyethylene or polypropylene. It may include. The binder may be contained in 2 to 20 parts by weight based on 100 parts by weight of the positive electrode active material (201).

As a method of forming the positive electrode 300, a positive electrode slurry including the positive electrode active material 201 on which the coating layer 210 is formed, the conductive material, the binder, and a solvent is coated on the current collector 100 to be fixed. It may be to form the positive electrode active material layer 200. The solvent is an organic solvent, for example, amine-based N,N-dimethylaminopropylamine, diethyltriamine, etc.; Ether systems such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Ester systems such as methyl acetate; And aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. The current collector may be a conductor such as Al, Ni, and stainless steel.

The sodium ion secondary battery of the present invention may include the positive electrode 300, a negative electrode (not shown) including the negative electrode active material, and an electrolyte disposed between the positive electrode 300 and the negative electrode (not shown). The negative electrode active material is a metal, metal alloy, metal oxide, metal fluoride, metal sulfide, and natural graphite, artificial graphite, coke, carbon black, carbon nanotube, which can de-insert metal ions or cause a conversion reaction. Carbon materials, such as graphene, can be used.

The electrolyte may be a liquid electrolyte containing a sodium salt and a solvent dissolving it. The sodium salt may be NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN(SO ₂ CF ₃ ) ₂ , NaAlCl ₄ , lower aliphatic carboxylic acid sodium salt, or the like. It is also possible to use a mixture of two or more. The solvent may be an organic solvent. Examples of the organic solvent are 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.

A separator may be disposed between the anode 300 and the cathode. The separator may be a material having a form of a porous film, a nonwoven fabric, or a woven fabric made of a material such as polyolefin resin such as polyethylene or polypropylene, fluorine resin, or aromatic polymer containing nitrogen. The thickness of the separator is preferably as thin as possible, as long as the mechanical strength is maintained, in that the bulk energy density of the battery increases and the internal resistance decreases.

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

<Production Example 1: Positive electrode active material powder having a coating layer>

Milling was performed in a mortar mixer to sufficiently mix 0.02 mol of sodium carbonate and 0.02 mol of manganese dioxide (Manganese(II) oxide). Thereafter, the mixture was placed in an alumina crucible, and then heated to 300° C. at a heating rate of 5° C./min in a dry air (Dry Air (O ₂ :N ₂ =21%:79%) atmosphere, maintained for 8 hours, 4° C./min Slowly cooling at a cooling rate of, heating up to 750° C., maintaining for 9 hours, and slow cooling at a cooling rate of 4° C./min were sequentially performed to obtain Na _0.44 MnO ₂ (SGPbam) powder having a tunnel structure. After mixing the ammonium acid in a mortar mixer, dry heat treatment was performed at 350°C for 4 hours at a heating rate of 5°C/min in a dry air (O ₂ :N ₂ =21%:79%) atmosphere. Thereby, Na _0.44 MnO ₂ (SGPbam) powder coated with sodium molybdate (Na ₂ MoO ₄ ) was formed on the surface.

<Comparative Example 1: Positive electrode active material powder (uncoated coating layer)>

Na _0.44 MnO ₂ (SGPbam) powder, a positive electrode active material powder, was synthesized in the same manner as in Preparation Example 1, except that a coating layer was formed using ammonium molybdate.

<Production Example 2: A positive electrode comprising a positive electrode active material having a coating layer>

The positive electrode active material powder prepared in Preparation Example 1, the conductive material (Super-P (Super-P): Denka black (Denka black) = 1:1) and the binder (polyvinylidene fluoride (PVDF)) 8:1:1 To prepare a slurry dispersed in an organic solvent (NMP (N-Methyl-2-Pyrrolidone)) by mixing in a weight ratio of 80. Then, the slurry was applied onto an aluminum foil, and then in a vacuum atmosphere at 80° C., overnight. During drying, an anode was prepared.

<Comparative Example 2: A positive electrode containing an existing positive electrode active material>

A positive electrode was prepared in the same manner as in Preparation Example 2, except that Na _0.44 MnO ₂ (SGPbam) powder, which is a positive electrode active material powder of Comparative Example 1, was used.

<Production Example 3: Preparation of sodium ion reversed paper>

Using a non-aqueous electrolyte solution containing the positive electrode, the negative electrode sodium metal plate prepared in Preparation Example 2, and electrolyte NaPF ₆ , an organic solvent propylene carbonate (PC, 98 vol.%) and fluoroethylene carbonate (FEC, 2 vol.%). Sodium ion half-cells were prepared in an argon atmosphere (Ar-filled glove box).

<Comparative Example 3: Preparation of sodium ion reversed paper>

A sodium ion half cell was prepared in the same manner as in Production Example 3, except that the positive electrode of Comparative Example 2 was used.

<Evaluation Example 1: Evaluation of sodium ion reverse cell cycle characteristics>

The sodium ion half-cell paper obtained in Preparation Example 3 was charged with a constant current up to 4.3 V, and the discharge was performed with a constant current discharge up to 1.5 V at the same rate as the charging speed. When evaluating cycle characteristics, charge and discharge proceeded for a total of 50 cycles.

3 is an X-ray diffraction analysis result of the positive electrode active material powder of Preparation Example 1 and Comparative Example 1 of the present invention.

Referring to FIG. 3, the crystal phase of the tunnel structure of Na _0.44 MnO ₂ powder, which is Comparative Example 1, was confirmed, and Na _0.44 MnO ₂ powder coated with sodium molybdate of Preparation Example 1 (Na ₂ MoO ₄ coated Na _0.44 MnO ₂ powder ) Also, the crystal phase of the same tunnel structure was confirmed. Thus, the method of manufacturing the coating layer of the present invention proves that it did not affect the tunnel structure of pure Na _0.44 MnO ₂ and acted only on the surface of the positive electrode active material.

4 is a scanning electron microscope (SEM) photograph of the positive electrode active material powder of Preparation Example 1 and Comparative Example 1 of the present invention.

4, it was confirmed that Na, Mn, Mo, and O elements were detected on the surface of Na _0.44 MnO ₂ powder (Na ₂ MoO ₄ coated Na _0.44 MnO ₂ powder) of Preparation Example 1. Thus, it maintains the shape of the existing Na _0.44 MnO ₂ powder, which is Comparative Example 1, and proves that the molybdenum oxide is uniformly coated on the surface of the Na _0.44 MnO ₂ powder (Na ₂ MoO ₄ coated Na _0.44 MnO ₂ powder-Preparation Example 1) do.

5 is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the positive electrode active material of Preparation Example 1 and Comparative Example 1 of the present invention.

Referring to FIG. 5, in Comparative Example 1, there was no signal of Mo, whereas in Preparation Example 1, a signal corresponding to Mo ⁶⁺ was confirmed on the Na _0.44 MnO ₂ powder surface.

Figure 6 shows the flight time type secondary ion mass spectrometry (TOF-SIMS) of the positive electrode of Preparation Example 2 and Comparative Example 2 of the present invention.

Referring to FIG. 6, in the case of the positive electrode of Comparative Example 2, no positive charge fragments of Mo ⁶⁺ were detected, whereas the positive electrode of Preparation Example 2 (including the positive electrode active material powder including the coating layer) was very strong. Positive charge fragments of Mo ⁶⁺ were detected (a). _{^{Also, NaMoO 4 -, MoO 4 2-}} , MoO ₄ ⁺ was confirmed positive / negative charge fragments (negative / positive fragment) that are only detected only Na ₂ MoO _4, a positive electrode coating of Preparation 2 of (d, e, b).

Thus, when referring to FIGS. 3 to 5 together, it was proved that the coating layer of Preparation Example 2 has a composition of Na ₂ MoO ₄ .

In addition, in relation to the formation mechanism of the Na ₂ MoO ₄ coating layer of Reaction Scheme 1, the time-of-flight secondary ion mass spectrometry (TOF-SIMS) fragment (NaCO ₂ ⁺ , NaO ₃ H ₃ ⁻ related to NaOH, Na ₂ Co ₃ ) As a result of checking ), it can be confirmed that a relatively low fragment intensity (intensity) was detected in Production Example 1 compared to Comparative Example 1 (c,f). This proves that residual sodium was consumed while forming the Na ₂ MoO ₄ coating layer.

7 is a graph showing cycle characteristics of Preparation Example 3 and Comparative Example 3 of the present invention.

7A to 7C, as a result of 50 cycles of charging and discharging in Comparative Example 3 and Manufacturing Example 3, the discharge capacity of Manufacturing Example 3 (initial cycle: 120 mAhg ^-1 , 50 cycles: 108 mAhg ^-1 ) It was confirmed that the discharge capacity of the comparative example 3 (initial cycle: 110mAhg ^-1 , 50 cycles: 80 mAhg ^-1 ) compared to the discharge cycle shows an excellent discharge rate. As described above, it can be seen that Preparation Example 3, that is, a semi-conductor having a coating layer on the surface of a positive electrode active material exhibits excellent life characteristics. In addition, as a result of experiments while increasing the C-rate (that is, increasing the discharge rate), it can be seen that the reverse paper of Preparation Example 3 exhibits superior rate-rate characteristics compared to Comparative Example 3.

That is, it is interpreted to improve the electrochemical performance by protecting the surface of the positive electrode active material by suppressing the generation of by-products that interfere with the movement of sodium ions between charge and discharge due to the coating layer on the surface of the positive electrode active material powder of the present invention.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented as specific examples for ease of understanding, and are not intended to limit the scope of the present invention. It is apparent to those skilled in the art to which the present invention pertains that other modifications based on the technical idea of the present invention can be implemented in addition to the embodiments disclosed herein.

100: current collector 200: positive electrode active material layer
201: coating layer 210: positive electrode active material (powder)
300: anode

Claims (13)

After mixing the sodium transition metal oxide powder with a molybdenum oxide precursor and heat-treating, forming a sodium molybdate coating layer on the surface of the sodium transition metal oxide powder,
The sodium transition metal oxide is Na _x [M ¹ _1-yz M ² _y M ³ _z ]O _2-α A _α (0<x≤1, 0≤y<1, 0≤z<1, 0≤α≤ 0.1, M ¹ , M ² , and M ³ are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, and Bi are different metals selected from the group consisting of, A is N, O, F, or S), and the sodium molybdate is Na ₂ MoO ₄ sign,
Method for manufacturing a positive electrode active material for a sodium ion secondary battery. According to claim 1,
The sodium transition metal oxide is a sodium manganese oxide, sodium ion secondary battery positive electrode active material manufacturing method. According to claim 2,
The sodium transition metal oxide is Na _0.44 MnO ₂ , sodium ion secondary battery positive electrode active material manufacturing method. According to claim 1,
The mixing is to mill the sodium transition metal oxide powder and molybdenum oxide precursor, a method for preparing a positive electrode active material for a sodium ion secondary battery. According to claim 1,
The molybdenum oxide precursor is a ammonium molybdate hydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O), sodium ion secondary battery positive electrode active material manufacturing method. According to claim 1,
The heat treatment thermally decomposes the molybdenum oxide precursor to form molybdenum oxide, and the molybdenum oxide reacts with a sodium compound remaining on the surface of the sodium transition metal oxide powder to form a sodium molybdate (Na ₂ MoO ₄ ) coating layer. , Sodium ion secondary battery positive electrode active material manufacturing method. According to claim 1,
The heat treatment is performed in a dry atmosphere, a method for producing a positive electrode active material for a sodium ion secondary battery. Current collector; And
It includes a positive electrode active material layer located on the current collector,
The positive electrode active material layer, Na _x [M ¹ _1-yz M ² _y M ³ _z ]O _2-α A _α (0<x≤1, 0≤y<1, 0≤z<1, 0≤α≤ 0.1, M ¹ , M ² , and M ³ are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Sodium transition metal oxide particles having the formula of A, Cd, Al, Ga, In, Sn, and Bi, and different metals selected from the group consisting of A, N, O, F, or S) and the sodium transition A positive electrode for a sodium ion secondary battery comprising a positive electrode active material composed of a sodium molybdate coating layer having a formula of Na ₂ MoO ₄ formed on a metal oxide particle surface. The method of claim 8,
The sodium transition metal oxide is a tunnel structure, sodium ion secondary battery anode. As core Na _x [M ¹ _1-yz M ² _y M ³ _z ]O _2-α A _α (0<x≤1, 0≤y<1, 0≤z<1, 0≤α≤0.1, M ¹ , M ² , and M ³ are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, and different metals selected from the group consisting of Bi, A is N, O, F, or S) transition metal oxide particles having the formula: And
A cathode active material for a sodium ion secondary battery comprising a sodium molybdate coating layer having the formula Na ₂ MoO ₄ formed on the surface of the sodium transition metal oxide particle. It includes a current collector and a positive electrode active material layer located on the current collector,
The positive electrode active material layer, Na _x [M ¹ _1-yz M ² _y M ³ _z ]O _2-α A _α (0<x≤1, 0≤y<1, 0≤z<1, 0≤α≤ 0.1, M ¹ , M ² , and M ³ are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Sodium transition metal oxide particles having the formula of A, Cd, Al, Ga, In, Sn, and Bi, and different metals selected from the group consisting of A, N, O, F, or S) and the sodium transition It comprises a positive electrode active material consisting of a sodium molybdate coating layer having the formula of Na ₂ MoO ₄ formed on the surface of the metal oxide particles, sodium ion secondary battery positive electrode;
A negative electrode having a negative electrode active material; And
A sodium ion secondary battery comprising an electrolyte disposed between the positive electrode and the negative electrode. delete The method of claim 11,
The electrolyte is a liquid electrolyte containing a sodium salt and a solvent for dissolving it, sodium ion secondary battery.

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