WO2017179917A1 - Sodium-based electrode active material and secondary battery comprising same - Google Patents

Abstract

Provided are a sodium-based electrode active material and a secondary battery comiprising the same. The electrode active material is represented by Formula 1 below, and has an orthorhombic structure with a space group of Cmcm. [Formula 1] Na_x[Mn_1-y-zM¹ _yM² _z]O_2-αA_α, where x is 0.5 to 0.8; M¹ and M² are, independently from each other, 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, or Bi; y is 0 to 0.25; z is 0 to 0.25; A is N, O, F, or S; and α is 0 to 0.1.

Description

Sodium-based electrode active material and a secondary battery comprising the same

The present invention relates to a secondary battery, and more particularly, to a secondary battery including a sodium-based electrode active material.

The secondary battery refers to a battery that can be repeatedly used because it can be charged as well as discharged. The representative lithium secondary battery of the secondary battery is lithium ions contained in the positive electrode active material is transferred to the negative electrode through the electrolyte and then inserted into the layered structure of the negative electrode active material (charging), after which the lithium ion inserted into the layered structure of the negative electrode active material is again It works on the principle of returning to the anode (discharge). Such lithium secondary batteries are currently commercialized and used as small power sources for mobile phones, notebook computers, and the like, and are expected to be used as large power sources for hybrid cars, and the demand is expected to increase.

However, a composite metal oxide mainly used as a cathode active material in a lithium secondary battery contains rare metal elements such as lithium, and thus may not meet demand growth. Accordingly, research is being conducted on sodium secondary batteries using abundant and cheap sodium as a cathode active material. As an example, Korean Patent Laid-Open Publication No. 2012-0133300 discloses A _x MnPO ₄ F (A = Li or Na, 0 <x ≦ 2) as a cathode active material.

However, sodium cathode materials developed to date are still not excellent in structural stability, and batteries using the same are known to require improvement in discharge capacity retention rate and stability.

Accordingly, an object of the present invention is to provide an active material for a secondary battery having improved discharge capacity maintenance characteristics and stability, and a secondary battery including the same.

One aspect of the present invention to achieve the above object provides an electrode active material. The electrode active material is represented by the following formula (1), has a tetragonal structure and the space group is a material of Cmcm.

[Formula 1]

Na _x [Mn _1-yz M ¹ _y M ² _z ] O _2-α A _α

In Formula 1, x may be 0.5 to 0.8. M ¹ and M ² are independently selected Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, It may be Cd, Al, Ga, In, Sn, or Bi. y may be 0 to 0.25. z may be 0 to 0.25. A may be N, O, F, or S, and α may be 0 to 0.1.

The active material represented by Chemical Formula 1 may be represented by Chemical Formula 2.

[Formula 2]

Na _x [Mn _1-y M _y ] O _2-α A _α

In Formula 2, x is 0.5 to 0.8, M 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, or Bi, y may be 0 to 0.25, A is N, O, F, or S, and α may be 0 to 0.1.

The active material represented by Chemical Formula 1 may be represented by Chemical Formula 3.

[Formula 3]

Na _x MnO ₂ (x is 0.5 to 0.8)

The active material represented by Chemical Formula 1 may be represented by Chemical Formula 4.

[Formula 4]

Na _x [Mn _1-y M _y ] O ₂

In Formula 4, x is 0.5 to 0.8, M 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, or Bi, and y may be 0.02 to 0.25.

The active material represented by Chemical Formula 1 may be Na _0.7 MnO ₂ .

In the above formulas, x may be 0.65 to 0.75, and y may be 0.025 to 0.1. In addition, M may be Al, Co, Cd, Nd, Rh, Sc, Zn, Fe, or Ni, further M may be Fe or Ni.

In the electrode active material having the tetragonal crystal structure and the space group is Cmcm, the intensity of the first peak representing the (002) plane may represent 5 to 8 times the intensity of the second peak representing the (004) plane. In addition, the half width of the first peak representing the (002) plane may be 0.2 to 0.3.

Another aspect of the present invention to achieve the above object provides a method for producing an electrode active material. First, a metal salt solution containing sodium salt and manganese salt is prepared. Ultrasonic spray pyrolysis of the metal salt solution yields a solid powder. The solid powder is heat-treated to obtain an electrode active material represented by Chemical Formula 1, having a tetragonal structure and having a space group of Cmcm.

The heat treatment may be carried out at 1100 ℃ to 1300 ℃. The heat treatment may be performed in the oxygen and the remaining inert gas atmosphere of 15 vol.% To 100 vol.%.

Another aspect of the present invention to achieve the above object provides a secondary battery. The secondary battery includes a positive electrode including a positive electrode active material represented by Formula 1, a negative electrode containing a negative electrode active material, and an electrolyte disposed between the positive electrode and the negative electrode.

The positive electrode may further include a sodium salt. The sodium salt may be NaNO ₂ . The NaNO ₂ may be contained in 3 to 12 parts by weight based on 100 parts by weight of the positive electrode active material. The positive electrode may further include a conductive material, and the conductive material may be contained in an amount of 2 to 9 parts by weight based on 100 parts by weight of the positive electrode active material. In addition, the positive electrode further comprises a binder, the binder may be contained in 2 to 9 parts by weight based on 100 parts by weight of the positive electrode active material.

According to the present invention, as the sodium-based active material having a tetragonal structure and having a space group of Cmcm has a stable crystal structure, the discharge capacity retention characteristics of a secondary battery containing the cathode active material may be improved. .

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

2 is Na ₀ according to the active material preparation examples 1 to 4 and Comparative Example 1 active material _{. 7} is a graph showing the XRD analysis of MnO ₂ .

3 is Na ₀ according to the active material preparation example 1 _{. 7} is a graph showing an enlarged XRD analysis of MnO ₂ .

4 is Na ₀ according to active material preparation examples 5 to 8 _{. 7} is a graph showing the XRD analysis of MnO ₂ .

5 is a schematic diagram predicting the crystal structure of Na _0.7 MnO ₂ according to the active material Preparation Example 1.

Figure 6 is a graph showing the XRD analysis of the solid powders according to the active material Preparation Example 1 and Comparative Example 2.

7 to 25 are graphs showing the XRD analysis results of Na _x [Mn _1-y M _y ] O ₂ according to Active Material Preparation Examples 9 to 27, respectively.

26A, 26B, 26C, and 26D are graphs illustrating charge and discharge characteristics of half cells according to Battery Preparation Example 1 and Comparative Examples 1 to 3, respectively.

27A and 27B are graphs showing charge and discharge characteristics and discharge capacities according to the number of cycles of a half cell according to Battery Preparation Example 1, respectively.

28 to 46 are graphs showing charge and discharge characteristics of half-cells according to battery preparation examples 2 to 20, respectively.

47 is a graph showing discharge capacity according to the number of cycles of a half cell according to Battery Preparation Example 1 and a half cell according to Battery Preparation Example 14. FIG.

48 illustrates an in situ synchrotron XRD graph of positive electrode active materials during an initial cycle of a half cell according to Preparation Example 1 and a half cell according to Preparation Example 14;

FIG. 49 illustrates an in-situ high temperature XRD graph of positive electrode active materials when the half cell according to Battery Preparation Example 1 and the half cell according to Battery Preparation Example 14 are in a charged state.

50A is a graph showing the charge / discharge characteristics of the half cells according to the half cell manufacturing example 25, and FIG. 50B is a graph showing the discharge capacity according to the number of cycles of the half cell according to the half cell manufacturing example 25. FIG.

51A is a graph showing charge / discharge characteristics of the half cell according to the half cell manufacturing example 26, and FIG. 51B is a graph showing the discharge capacity according to the number of cycles of the half cell according to the half cell manufacturing example 26. FIG.

52A is a graph showing charge and discharge characteristics of a half cell according to a full-cell manufacturing example, and FIG. 52B is a graph showing discharge capacity according to the number of cycles of a half cell according to a full-cell manufacturing example.

Hereinafter, exemplary embodiments of the present invention will be described in 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 but may be embodied in other forms. Like numbers refer to like elements throughout.

In this specification, the presence of a layer “on” another layer means that not only are these layers directly in contact, but also another layer (s) between these layers.

Positive electrode active material

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

[Formula 1]

Na _x [Mn _1-yz M ¹ _y M ² _z ] O _{2 - α} A _α

In Formula 1, x may be 0.5 to 0.8. As an example, x may be 0.6 to 0.8, specifically 0.65 to 0.75. M ¹ and M ² are independent of each other as transition metal or post-transition metal, for example 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, or Bi. M ¹ and M ² may be the same or different. y may be 0 to 0.25. z may be 0 to 0.25. A may be N, O, F, or S, and α may be 0 to 0.1.

In one example, the cathode active material may be represented by the following formula (2).

[Formula 2]

Na _x [Mn _1-y M _y ] O _{2 - α} A _α

In Formula 2, x may be 0.5 to 0.8. As an example, x may be 0.6 to 0.8, specifically 0.65 to 0.75. M 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, or Bi. y may be 0 to 0.25. As an example, y may be 0 to 0.2, specifically y may be 0 to 0.1. In addition, y may be 0.02 to 0.25, or 0.025 to 0.1. A may be N, O, F, or S, and α may be 0 to 0.1.

The cathode active material represented by Chemical Formula 1 or 2 may have an orthorhombic crystal system. Specifically, it is a layered compound having a tetragonal structure, in which a sodium layer and a transition metal oxide layer are alternately stacked, and a space group is Cmcm. Such an active material may exhibit an intensity of the first peak representing the (002) plane in the XRD graph 5 to 8 times the intensity of the second peak representing the (004) plane. In addition, the half width of the first peak showing the (002) plane in the XRD graph of the active material may be about 0.2 to about 0.3, specifically, about 0.21 to about 0.24.

Furthermore, the cathode active material may be represented by the following Chemical Formula 3 or 4.

[Formula 3]

Na _x MnO ₂

In Formula 3, x may be 0.5 to 0.8. As an example, x may be 0.6 to 0.8, specifically 0.65 to 0.75.

[Formula 4]

Na _x [Mn _1-y M _y ] O ₂

In Formula 4, x may be 0.5 to 0.8. As an example, x may be 0.6 to 0.8, specifically 0.65 to 0.75. M 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, or Bi. y may be 0.02 to 0.25. As an example, y may be 0.02 to 0.2, specifically y may be 0.025 to 0.1.

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

Referring to FIG. 1, a metal salt solution containing sodium salt and manganese salt may be prepared (S10). The metal salt solution may further mix metal salt (s) other than sodium salt and manganese salt. Sodium, manganese, and other first metal in the metal salt solution (in the above formula 1, M ^1), and other second metal molar ratio of (In Formula 1, M ²⁾ is x: 1-yz: y: z (x, y, and z may be as defined in Formula 1). The metal salt may be a metal carbonate, metal nitrate, or metal oxalate. The sodium salt may be NaNO ₃ , Na ₂ CO ₃ , or NaHCO ₃ , and the manganese salt may be Mn (NO ₃ ) ₂ . These metal salts, specifically, sodium salts, manganese salts, and salts of non-manganese metals may take the form of hydrates. The metal salt solution may contain distilled water as a solvent.

A chelating agent may be further added to the metal salt solution. The chelating agent may be selected from the group consisting of tartaric acid, urea, citric acid, formic acid, glycolic acid, polyacrylic acid, adipic acid, and glycine. The chelating agent may be contained in 10wt% to 30wt% relative to the weight of the metal salt. On the other hand, the metal salt solution may further include a crystal growth inhibitor (crystal growth inhibitor). The crystal growth inhibitor may be, for example, glucose, sucrose, or a derivative thereof as a saccharide or a derivative thereof. Such crystal growth inhibitor may be contained in 1wt% to 10wt% relative to the weight of the metal salt.

The metal salt solution may be sufficiently mixed by stirring.

Thereafter, the metal salt solution may be subjected to ultrasonic spray pyrolysis to obtain a solid powder (S20). The ultrasonic spray pyrolysis is a method of obtaining a metal oxide having a pure composition for a low temperature and a short time compared to a solid phase method. The ultrasonic spray pyrolysis sprays the metal salt solution to make droplets, and then thermally decomposes the droplets. That's how. In the pyrolysis process, the metal salt may be converted into a metal oxide.

Thereafter, the solid powder may be heat-treated in a dry air atmosphere to obtain a cathode active material (S30). The dry air atmosphere may be a dry atmosphere containing 15 vol.% To 100 vol.% Of a dried oxygen atmosphere, specifically 20 vol.% To 100 vol.% Of oxygen and the rest of the inert gas. In this case, the inert gas may be nitrogen. In the present specification, the dry atmosphere may mean an atmosphere that does not contain moisture. Heat treatment in such an atmosphere has the advantage of preventing the volatilization of sodium. In addition, the heat treatment may be carried out at 1100 ℃ to 1300 ℃.

The cathode active material having a tetragonal structure described in the above formulas and having a space group of Cmcm may improve capacity and lifespan characteristics of the sodium secondary battery.

In addition, the secondary battery having high capacity may be used as a unit battery of a battery module which is a power source of medium and large devices. The medium-to-large device includes, for example, a power tool that is powered by an electric motor; Electric vehicles (EVs) including hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs); Electric two-wheeled vehicles including E-bikes and E-scooters; Or an electric golf cart, but is not limited thereto.

Hereinafter, the sodium secondary battery among the applicable secondary batteries will be described.

Sodium secondary battery

A sodium secondary battery according to an embodiment of the present invention includes a positive electrode containing the positive electrode active material described above, a negative electrode containing a negative electrode active material into which sodium can be inserted, and an electrolyte positioned therebetween.

<Anode>

A cathode material may be obtained by mixing the cathode active material, the conductive material, and the binder described in Chemical Formula 1.

The positive electrode active material described in Chemical Formula 1 may have a stable crystal structure, and thus may have a low degree of deterioration due to moisture and a low operating voltage. However, since the molar ratio of sodium to the transition metal (Mn, M ¹ , and M ² in Formula 1) is less than 1, that is, x represents less than 1 in Formula 1, The content of sodium may be lower than that of other positive electrode active materials having x of 1 or more. To compensate for this, sodium salt may be added to the cathode material. Na ions contained in the sodium salt may be reduced during the initial charging of the battery to serve as an additional Na source. In this case, the initial charge capacity of the sodium secondary battery can be improved to improve battery performance. The sodium salt may be NaNO ₂ , the addition amount of the sodium salt is 1 to 20 parts by weight, specifically 3 to 20 parts by weight or 3 to 15 parts by weight based on 100 parts by weight of the positive electrode active material As an example, it may be contained in 5 to 7 parts by weight.

The conductive material may be a carbon material such as natural graphite, artificial graphite, cokes, carbon black, carbon nanotubes, or graphene. The binder may be a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymer, fluorine resin such as hexafluoropropylene, and / or polyolefin resin such as polyethylene or polypropylene. It may include.

When the sodium salt is added, the conductive material may be contained in 2 to 9 parts by weight, specifically 4 to 7 parts by weight and more specifically 5 to 6 parts by weight, based on 100 parts by weight of the positive electrode active material. 2 to 9 parts by weight, specifically 4 to 7 parts by weight, and more specifically 5 to 6 parts by weight, based on 100 parts by weight of the positive electrode active material.

A positive electrode material may be applied onto a positive electrode current collector to form a positive electrode. The positive electrode current collector may be a conductor such as Al, Ni, stainless steel, or the like. The application of the positive electrode material onto the positive electrode current collector may be made by pressure molding or by using an organic solvent or the like to make a paste, and then applying the paste onto the current collector and pressing to fix the paste. The organic solvent is amine type, such as N, N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketones such as methyl ethyl ketone; Esters such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Application of the paste onto the positive electrode current collector can be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, a spray coating method.

<Cathode>

Cathode active materials include metals, metal alloys, metal oxides, metal fluorides, metal sulfides, and natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, and graphene that can deintercalate Na ions or cause conversion reactions. It can also form using carbon materials, such as a fin.

The negative electrode material can be obtained by mixing the negative electrode active material, the conductive material, and the binder. In this case, the conductive material may be a carbon material such as natural graphite, artificial graphite, cokes, carbon black, carbon nanotubes, graphene, or the like. The binder may be a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, vinylidene fluoride copolymer, fluorine resin such as hexafluoropropylene, and / or polyolefin resin such as polyethylene or polypropylene. It may include.

The negative electrode material may be applied onto the positive electrode current collector to form a positive electrode. The positive electrode current collector may be a conductor such as Al, Ni, stainless steel, or the like. The application of the negative electrode material on the positive electrode current collector may be made by pressure molding or a method of making a paste using an organic solvent or the like, and then applying the paste onto the current collector and pressing to fix the paste. The organic solvent is amine type, such as N, N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketones such as methyl ethyl ketone; Esters such as methyl acetate; Aprotic polar solvents such as dimethylacetamide and N-methyl-2-pyrrolidone. Application of the paste onto the negative electrode current collector can be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, a spray coating method.

<Electrolyte>

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 carboxylate, NaAlCl ₄ , and the like. Mixtures can also be used. Among these, it is preferable to use an electrolyte containing fluorine. The electrolyte can also be dissolved in an organic solvent and used as a nonaqueous 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, pentafluoropropylmethylether, 2,2,3,3-tetrafluoropropyldifluoromethylether, 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-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propanesultone; Or what introduce | transduced the fluorine substituent further to the said organic solvent can 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 polymer compound, a polyorganosiloxane chain or a polyoxyalkylene chain. In addition, a so-called gel type electrolyte in which a nonaqueous electrolyte is supported on a high molecular 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 ), Fe ₂ (MoO ₄ ) ₃ Inorganic solid electrolytes, such as these, can also be used. Using these solid electrolytes, the safety of the sodium secondary battery may be further improved. In addition, a solid electrolyte may play the role of the separator mentioned later, and a separator may not be needed in that case.

<Separator>

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

<Method for Manufacturing Sodium Secondary Battery>

After forming the electrode group by laminating the positive electrode, the separator, and the negative electrode in order, the electrode group can be rolled up and stored in a battery can if necessary, and the sodium secondary battery can be manufactured by impregnating the electrode group with a nonaqueous electrolyte. Alternatively, a sodium secondary battery may be manufactured by stacking a positive electrode, a solid electrolyte, and a negative electrode to form an electrode group, and then rolling the electrode group in a battery can if necessary.

Hereinafter, preferred examples are provided to aid the understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

[Experimental Examples; Examples]

Active material preparation examples

<Active Material Preparation Example 1: Na _{0 . 7} MnO ₂ Manufacturing>

Magnetic bars are used to dissolve 0.056 moles of sodium nitrate, 0.08 moles of manganese nitrate tetrahydrate (Manganese (II) nitrate tetrahydrate), citric acid, and sucrose in distilled water and mix well. It stirred for more than 12 hours. The citric acid was used 0.2 times the weight of the nitrates, the sucrose was used at a rate of 0.05 times the weight of the nitrates. The stirred solution was sprayed through a nozzle of ultrasonic spray into a quartz tube maintained at 400 ° C. at a constant rate to obtain a solid powder. After pelletizing the solid powder at a constant pressure, the solid powder was placed in an alumina crucible and the alumina crucible was fed at a rate of 5 ° C./min in a dry air atmosphere containing 21 vol.% O ₂ and 79 vol.% N ₂ . After the temperature was raised, the temperature was maintained at 1200 ° C. for 10 hours, and then gradually cooled to 30 ° C. at a rate of 3 ° C./min to Na _{0 . 7} MnO ₂ was prepared.

<Preparation Examples 2 and 3: Na _{0 . 7} MnO ₂ Manufacturing>

Except that the pelletized solid powder was heat treated at 1150 ° C. for 10 hours (active material preparation example 2) or heat treated at 1100 ° C. for 10 hours (active material preparation example 3) Na _0.7 MnO ₂ was prepared.

<Preparation Example 4: Na _{0 . 7} MnO ₂ Manufacturing>

Na _0.7 MnO ₂ was prepared in the same manner as in Preparation Example 1, except that the pelletized solid powder was heat-treated at 1300 ° C. for 10 hours.

<Active Material Preparation Examples 5 to 8: Na _{0 . 7} MnO ₂ Manufacturing>

Except that the pelletized solid powder was heat-treated in the dry atmosphere shown in Table 1 below, the same method as in Preparation Example 1 was carried out to provide Na _{0 . 7} MnO ₂ was prepared.

<Preparation Example 9 to 27: Preparation of Na _x [Mn _1-y M _y ] O ₂ >

Except that sodium nitrate, manganese (II) nitrate tetrahydrate, and other salts of metal (M) were dissolved in distilled water together with citric acid and sucrose in the equivalent amounts shown in Table 1 below. Na _x [Mn _1-y M _y ] O ₂ was prepared by the same method as in Preparation Example 1 of the active material. As the salt of the metal (M), silver nitrate in active material preparation 9, aluminum nitrate nonahydrate in active materials preparation 10 and 11, bismuth nitrate pentahydrate in active material preparation 12, and Bismuth ( III) nitrate pentahydrate, active material preparation examples 13 and 14 cobalt (II) nitrate hexahydrate, active material preparation example 15, cadmium nitrate tetrahydrate, active material preparation examples 16 and 17 nitric acid Copper (II) nitrate trihydrate (Iron (III) nitrate nonahydrate) in active material preparation example 18, Indium (III) nitrate hydrate in active material preparation example 19, active material preparation example 20 (Neodymium (III) nitrate hydrate) in, active material preparation examples 21 and 22 nickel nitrate hexahydrate (Nickel (II) nitrate hexahydrate), in the active material preparation example 23 Lead (iii) nitr ate), Rhodium (III) nitrate hydrate in active material preparation examples 24, Scandium (III) nitrate hydrate in active material preparation examples 25, and zinc nitrate hydrate in active material preparation examples 26 and 27 Zinc nitrate hydrate) was used.

<Active Material Comparative Example 1: Na _{0 . 7} MnO ₂ Manufacturing>

Na _0.7 MnO ₂ was prepared in the same manner as in Preparation Example 1, except that the pelletized solid powder was heat-treated at 1000 ° C. for 10 hours.

<Active Material Comparative Example 2>

Except that the pelletized solid powder was heat-treated in a general atmospheric atmosphere instead of dry air, the same method as in Preparation Example 1 of Active Material was performed to obtain a heat-treated solid powder.

<Active material in Comparative Example 3: Na _{0. 7} (Mn _0.75 Fe _0.25 ) O ₂ Preparation>

0.056 moles of sodium nitrate, 0.06 moles of manganese nitrate tetrahydrate, and 0.02 moles of iron nitrate nitrate (Iron (III) nitrate nonahydrate, citric acid, and Using a solution containing sucrose, the stirred solution was sprayed through a nozzle of ultrasonic spray into a quartz tube maintained at 600 ° C. at a constant rate to obtain a solid powder, and the pelletized solid powder to 900 ° C. Na _0.7 (Mn _0.75 Fe _0.25 ) O ₂ was prepared by the same method as in Preparation Example 1 except that the heat treatment was performed for 10 hours.

<Active material in Comparative Example 4: Na _{0. 7} (Mn _0.5 Fe _0.5 ) O ₂ Preparation>

0.056 moles of sodium nitrate, 0.04 moles of manganese (II) nitrate tetrahydrate, 0.04 moles of iron nitrate nitrate (Iron (III) nitrate nonahydrate), citric acid, and sucrose Using a solution containing (Sucrose) and spraying the stirred solution through a nozzle of ultrasonic spray into a quartz tube maintained at 600 ° C. at a constant rate to obtain a solid powder, and pelletized solid powder to 1000 ° C. except that the heat treatment for a time and performs the same way as active material Preparation example 1 Na _{0. 7} (Mn _0.5 Fe _0.5 ) O ₂ was prepared.

	Furtherance	Heat treatment atmosphere		Heat treatment temperature [℃]
		O 2 [vol.%]	N 2 [vol.%]
Active Material Preparation Example 1	Na 0 . 7 MnO 2	21	79	1200
Active Material Preparation Example 2				1150
Active Material Preparation Example 3				1100
Active Material Preparation Example 4				1300
Active Material Preparation Example 5		100	-	1200
Active Material Preparation Example 6		30	70
Active Material Preparation Example 7		50	50
Active Material Preparation Example 8		70	30
Active Material Preparation Example 9	Na 0.7 (Mn 0.975 Ag 0.025 ) O 2	21	79	1200
Active Material Preparation Example 10	Na 0.7 (Mn 0.95 Al 0.05 ) O 2
Active Material Preparation Example 11	Na 0 . 7 (Mn 0.9 Al 0.1) O 2
Active Material Preparation Example 12	Na 0.7 (Mn 0.975 Bi 0.025 ) O 2
Active Material Preparation Example 13	Na 0.7 (Mn 0.95 Co 0.05 ) O 2
Active Material Preparation Example 14	Na 0 . 7 (Mn 0.9 Co 0.1 ) O 2
Active Material Preparation Example 15	Na 0.7 (Mn 0.975 Cd 0.025 ) O 2
Active Material Preparation Example 16	Na 0.7 (Mn 0.95 Cu 0.05 ) O 2
Active Material Preparation Example 17	Na 0 . 7 (Mn 0.9 Cu 0.1 ) O 2
Active Material Preparation Example 18	Na 0.7 (Mn 0.95 Fe 0.05 ) O 2
Active Material Preparation Example 19	Na 0.7 (Mn 0.975 In 0.025 ) O 2
Active Material Preparation Example 20	Na 0.7 (Mn 0.975 Nd 0.025 ) O 2
Active Material Preparation Example 21	Na 0.7 (Mn 0.95 Ni 0.05 ) O 2
Active Material Preparation Example 22	Na 0 . 7 (Mn 0.9 Ni 0.1 ) O 2
Active Material Preparation Example 23	Na 0.7 (Mn 0.95 Pb 0.05 ) O 2
Active Material Preparation Example 24	Na 0.7 (Mn 0.975 Rh 0.025 ) O 2
Active Material Preparation Example 25	Na 0.7 (Mn 0.975 Sc 0.025 ) O 2
Active Material Preparation Example 26	Na 0.7 (Mn 0.95 Zn 0.05 ) O 2
Active Material Preparation Example 27	Na 0 . 7 (Mn 0.9 Zn 0.1 ) O 2
Active material comparative example 1	Na 0 . 7 MnO 2	21	79	1000
Active material comparative example 2	Mn 3 O 4	General atmosphere		1200
Active material comparative example 3	Na 0.7 (Mn 0.75 Fe 0.25 ) O 2	21	79	900
Active material comparative example 4	Na 0 . 7 (Mn 0.5 Fe 0.5 ) O 2	21	79	1000

2 is Na ₀ according to the active material preparation examples 1 to 4 and Comparative Example 1 active material _{. 7 is a} graph showing the XRD analysis results of MnO ₂ , Figure 3 is Na ₀ according to the active material preparation example 1 _{. 7 is a} graph showing an enlarged XRD analysis result of MnO ₂ , Figure 4 is a graph showing the XRD analysis results of Na _0.7 MnO ₂ according to active material preparation examples 5 to 8.

Referring to Figure 2, Na ₀ different from Comparative Example 1 heat-treated at 1000 ℃ _{. 7} MnO ₂ is P6 ₃ / mmc and Cmcm space while showing an XRD peak of the hexagonal P2 structure oriented (hexagonal) with the group, Na in accordance with an active material Preparation Example 1 through 4 the heat treatment at 1100 to 1300 ℃ _0. It can be seen that ₇ MnO ₂ represents an XRD peak of a tetragonal structure having a space group of Cmcm.

Referring to Figure 3, Na ₀ and other active material preparation example 1 heat-treated at 1200 ℃ _{. 7} MnO ₂ is Na _{0 .} Similar to ₇ MnO ₂ , it can be seen that the XRD peak of the tetragonal structure having a space group of Cmcm is shown. Specifically, Na ₀ having a tetragonal structure having a space group of Cmcm _{. 7} MnO ₂ exhibited a first peak representing the (002) plane at about 15 degrees and a second peak representing the (004) plane at about 32 degrees. However, Na ₀ according to the active material preparation example 1 heat-treated at 1200 ℃ _{. 7} MnO ₂ is Na _{0 .} It can be seen that the XRD peaks of the tetragonal structure having a space group of Cmcm compared to ₇ MnO ₂ are somewhat clear.

Referring to Figure 4, Na ₀ according to the active material Preparation Examples 1 to 4 heat-treated in a dry air atmosphere containing 21 vol.% O ₂ and 79vol.% N _{2 .} Na ₀ according to Preparation Examples 5 to 8 heat-treated in a dry air atmosphere (remaining N ₂ ) containing 30, 50, 70, and 100 vol.% O ₂ in the same manner as ₇ MnO _{2 . 7} MnO ₂ It can also be seen that the XRD peak of the tetragonal structure having a space group of Cmcm is shown.

Meanwhile, referring back to FIGS. 2, 3, and 4, in the active material having a tetragonal structure having a space group of Cmcm, the half width of the first peak representing the (002) plane at about 15 degrees is about 0.2 to about 0.3. , From about 0.21 to about 0.24. In addition, the intensity of the first peak was about 5 times to about 8.5 times the intensity of the second peak, specifically, about 5.47 times to about 8.076 times. However, in the hexagonal-oriented P2 structure active material having a space group of P6 ₃ / mmc and Cmcm according to Comparative Example 1, the intensity of the first peak was about 2 times higher than that of the second peak.

The In this manner, (002) the full width at half maximum of the first peak represents the surface being less than 0.3, In addition, the (002) have a very large intensity of the first peak represents the surface is Na _0.7 MnO ₂ is determined in accordance with the preparation Castle It can mean very good. In addition, the ratio of the intensity of the first peak representing the (002) plane to the ratio of 5 or more relative to the intensity of the second peak representing the (004) plane may mean that the (002) plane is continuously formed in the layered structure.

In addition, it can be seen that the active material having a tetragonal structure having a space group of Cmcm according to the present experimental examples showed almost no impurity peaks appearing at about 25 degrees. In other words, the intensity of the first peak representing the (002) plane with respect to the intensity of the impurity peak appearing near 25 degrees may be about 100 times or more. This may mean that the active material having a tetragonal structure having a space group of Cmcm according to the present experimental examples has a very excellent crystal structure.

5 is Na ₀ according to the active material preparation example 1 _{. 7} MnO ₂ is a schematic diagram for predicting the crystal structure, Na _{0 .} The crystal structure of ₇ MnO ₂ is predicted and shown.

Referring to Figure 5, Na ₀ according to the active material preparation example 1 _. It can be seen that the crystal structure of ₇ MnO ₂ is a layered compound in which a sodium layer and a manganese oxide layer are alternately stacked.

Figure 6 is a graph showing the XRD analysis of the solid powders according to the active material Preparation Example 1 and Comparative Example 2.

Referring to FIG. 6, another solid powder of Preparation Example 1 heat-treated at 1200 ° C. in a dry air atmosphere had Na _{0 . While 7} MnO ₂ is shown, it can be seen that the solid powder according to Comparative Example 2 heat-treated at 1200 ° C. in a general atmosphere has Mn ₃ O ₄ . These results show that the volatilization of sodium can be prevented by heat treatment in a dry air atmosphere rather than a normal atmosphere.

7 to 25 are graphs showing XRD analysis results of Na _x [Mn _1-y M _y ] O ₂ according to active material preparation examples 9 to 27, respectively.

Referring to FIGS. 7 to 25, the first peak representing the (002) plane at about 15 degrees and the second peak representing the (004) plane at about 32 degrees are shown, and as shown in FIG. It can be seen that the characteristic peaks of the tetragonal structure having the appearance of Na _x [Mn _1-y M _y ] O ₂ of the tetragonal structure having a space group of Cmcm.

In addition, as shown in FIGS. 2 and 4, Na _x [Mn _1-y M _y ] O ₂ according to Active Material Preparation Examples 9 to 27 Also, the half width of the first peak representing the (002) plane is about 0.2 to about About 0.3 specifically, about 0.21 to about 0.24. In addition, the intensity of the first peak may be about 5 times to about 8.5 times the intensity of the second peak, specifically, about 5.47 times to about 8.076 times. In addition, it can be seen that Na _x [Mn _1-y M _y ] O ₂ according to active material preparation examples 9 to 27 also hardly exhibit an impurity peak appearing at about 25 degrees. In other words, the intensity of the first peak representing the (002) plane with respect to the intensity of the impurity peak appearing near 25 degrees may be about 100 times or more.

Battery Preparation Example 1: Orthotropic Na _{0 . 7} Fabrication of Anode and Half Cell Using MnO ₂ >

The tetragonal Na ₀ prepared in Preparation Example 1 of the active material _{. 7} MnO ₂ powder, conductive material (Super-P, KS-6), and binder (Poly vinylidene fluoride) were mixed in an organic solvent (N-Methyl-2-Pyrrolidone (NMP)) at a weight ratio of 85: 7.5: 7.5 After the coating on the aluminum current collector, it was pressed to form a positive electrode.

Thereafter, was used as the metal sodium as a cathode, using a glass filter as a separator, and an electrolyte NaPF ₆ and fluoro with the organic solvent of propylene carbonate (PC, 98vol.%) Non-aqueous containing ethylene carbonate (FEC, 2vol.%) A half cell was prepared using electrolyte solution.

<Preparation Examples 2 to 20: Preparation of a positive electrode and a _half cell using a tetragonal Na _x [Mn _1-y M _y ] O ₂ >

The tetragonal Na ₀ prepared in Preparation Example 1 of the active material _{. 7} Positive electrode using the same method as in Battery Preparation Example 1, except that one of the tetragonal Na _x [Mn _1-y M _y ] O ₂ prepared in Active Materials Preparation Examples 9 to 27 was used instead of the ₇ MnO ₂ powder. And half cells were prepared.

Comparative Example 1: Hexagonal Na _{0 . 7} Fabrication of Anode and Half Cell Using MnO ₂ >

Na ₀ prepared in Active Material Preparation Example 1 _. Instead of ₇ MnO ₂ powder, hexagonal Na _{0 . A} positive electrode and a half cell were prepared using the same method as in Battery Preparation Example 1, except that ₇ MnO ₂ powder was used.

Comparative Example 2: Hexagonal Na _{0 . 7} Fabrication of Anode and Half Cell Using (Mn _0.75 Fe _0.25 ) O ₂ >

Na ₀ prepared in Active Material Preparation Example 1 _{. 7} compares the active material in place of MnO ₂ powder, the hexagonal system prepared in Example 3 Na _0. Except for using ₇ (Mn _0.75 Fe _0.25 ) O ₂ powder to prepare a positive electrode and a half cell using the same method as in Battery Preparation Example 1.

Comparative Example 3: Hexagonal System Na _{0 .} Fabrication of Anode and Half Cell Using ₇ (Mn _0.5 Fe _0.5 ) O ₂ >

Na ₀ prepared in Active Material Preparation Example 1 _. Hexagonal Na _0. Prepared in Comparative Example 4 instead of the ₇ MnO ₂ powder _. Except for using ₇ (Mn _0.5 Fe _0.5 ) O ₂ powder to prepare a positive electrode and a _half cell using the same method as in Battery Preparation Example 1.

26A, 26B, 26C, and 26D are graphs illustrating charge and discharge characteristics of half cells according to Battery Preparation Example 1 and Comparative Examples 1 to 3, respectively. At this time, the charge was constant current charged at 20 mA / g up to 4.3 V, and the discharge was performed at 1.5 V at the same speed as the above charge rate. Charge and discharge proceeded 2 cycles.

Referring to FIGS. 26A, 26B, 26C, and 26D, Na _0.7 MnO ₂ (battery comparison example 1, FIG. 26B) having a hexagonal crystal structure, Na _{0 . 7} (Mn _0.75 Fe _0.25 ) O ₂ (Comparative Example 2, FIG. 26C), and Na ₀ having a tetragonal crystal structure compared to a _half cell prepared using Na _0.7 (Mn _0.5 Fe _0.5 ) O ₂ (Comparative Example 3, FIG. 26D) _{. 7} by using the MnO ₂ when manufactured if inverted (cells prepared in Example 1, Fig. 26a) the discharge capacity is 200 mAhg ^- it can be seen that indicates the capacity of a superior performance such as greater than ^1.

27A and 27B are graphs showing charge and discharge characteristics and discharge capacities according to the number of cycles of a half cell according to Battery Preparation Example 1, respectively. At this time, the charge was constant current charged at 20 mA / g up to 4.3 V, and the discharge was performed at 1.5 V at the same speed as the above charge rate. Charge and discharge proceeded for 25 cycles.

27A and 27B, Na ₀ having a tetragonal crystal structure _{. When the half} cell was manufactured using ₇ MnO ₂ , even if the charge / discharge cycle was increased, the discharge capacity was not significantly decreased (about 90% at 25 cycles), that is, the capacity retention ratio was excellent and the stability was excellent. As described above, the improvement in discharge capacity retention characteristics is a tetragonal system and a structure used as the positive electrode active material, and the space group is Na _{0 . 7} MnO ₂ is believed to be the result of having a stable crystal structure.

28 to 46 are graphs showing charge and discharge characteristics of half-cells according to battery preparation examples 2 to 20, respectively. At this time, the charge was constant current charged at 20 mA / g up to 4.3 V, and the discharge was performed at 1.5 V at the same speed as the above charge rate. Charge and discharge proceeded 2 cycles.

28 to 46, it can be seen that the operation of the battery is performed when a _half cell is manufactured using Na _x [Mn _1-y M _y ] O ₂ having a tetragonal crystal structure. In particular, in Na _x [Mn _1-y M _y ] O ₂ , when M is Al, Co, Cd, Nd, Rh, Sc, Zn, the discharge capacity is 150 mAhg ^{- 1} or more, and M is Fe and Ni. In this case, it can be seen that the discharge capacity is excellent in high capacity, such as more than 200 mAhg ^-1 .

47 is a graph showing discharge capacity according to the number of cycles of a half cell according to Battery Preparation Example 1 and a half cell according to Battery Preparation Example 14. FIG. At this time, the charge was constant current charged at 20 mA / g up to 4.3 V, and the discharge was performed at 1.5 V at the same speed as the above charge rate. Charge and discharge proceeded 50 cycles.

Referring to FIG. 47, a half cell according to Battery Preparation Example 1, that is, Na _{0 . The} half cell using ₇ MnO ₂ showed a discharge capacity of 75% of the initial discharge capacity after 50 cycles. However, the reverse paper according to Battery Preparation Example 14, that is, the Na _{0 . The} half cell using ₇ (Mn _0.95 Ni _0.05 ) O ₂ showed a discharge capacity of 92% compared to the initial discharge capacity after 50 cycles.

48 illustrates an in situ synchrotron XRD graph of positive electrode active materials during an initial cycle of a half cell according to Preparation Example 1 and a half cell according to Preparation Example 14; At this time, charging and discharging were performed in a voltage range of 1.5 to 4.3 V and a constant current of 20 mAh.

Referring to FIG. 48, a half cell according to Battery Preparation Example 1, that is, Na _{0 . 7 A half} cell using MnO ₂ and a _half cell according to Preparation Example 14, that is, a Na _{0 . In} both _half cells using ₇ (Mn _0.95 Ni _0.05 ) O ₂ , the positive electrode active materials commonly showed a phase change to the OP 4 structure (space group: P-6 m 2) during the charging process. Phase change was shown. On the other hand, Na _{0 . In the case of 7} (Mn _0.95 Ni _0.05 ) O ₂ , a superlattice structure (Superstructure or Superlattice) was observed in the 2θ region between 15.6 and 16 degrees.

FIG. 49 illustrates an in-situ high temperature XRD graph of positive electrode active materials when the half cell according to Battery Preparation Example 1 and the half cell according to Battery Preparation Example 14 are in a charged state. At this time, the half cell was charged with a constant current of 20 mAh up to a voltage of 4.3 V (sodium was detached from the positive electrode active material), and the XRD data was obtained while the positive electrode active material was raised from room temperature to 600 ° C and again at room temperature.

Referring to FIG. 49, a half cell according to Battery Preparation Example 1, that is, Na _{0 . 7 A half} cell using MnO ₂ and a _half cell according to Preparation Example 14, that is, a Na _{0 . In} both _half- cells using ₇ (Mn _0.95 Ni _0.05 ) O ₂ , positive electrode active materials showed peaks of OP4 structure and tetragonal structure. In addition, in the temperature range of 100 to 150 ℃ all the intensity of the hydrate peak was reduced, which means that the water evaporated to the peak due to water or moisture present in the atmosphere. Thereafter, manganese oxide is observed due to evaporation of sodium and oxygen in the high temperature region. As the manganese oxide is mainly located in MnO _2, it can be inferred that the main oxidation number of Mn is tetravalent.

On the other hand, Na _{0 . In the case of 7} (Mn _0.95 Ni _0.05 ) O ₂ , a superlattice structure (Superstructure or Superlattice) was observed in the 2θ region between 15.6 and 16 degrees.

Half Battery Manufacturing Example 25: Rhombic System Na _{0 . 7} Fabrication of Anode and Half Cell Using (Mn _0.95 Ni _0.05 ) O ₂ and Additives>

Orthotropic Na ₀ prepared in Preparation 21 of the active material _{. 7} (Mn _0.95 Ni _0.05 ) O ₂ Powders, additives NaNO ₂ , conductive materials (Super-P, KS-6), and binders (Poly vinylidene fluoride) in an organic solvent (NMP (N-Methyl-2-Pyrrolidone) (NMP) in a weight ratio of 85: 6: 4.5: 4.5 After mixing in), it was coated on an aluminum current collector and then pressed to form a positive electrode.

Thereafter, metal sodium was used as a cathode, a glass filter was used as a separator, and a nonaqueous solution containing electrolyte NaPF ₆ and an organic solvent propylene carbonate (PC, 98 vol.%) And fluoroethylene carbonate (FEC, 2 vol.%) Was used. A half cell was prepared using electrolyte solution.

Half Battery Manufacturing Example 26 Hexagonal System Na _{0 . 7} Fabrication of Anode and Half Cell Using (Mn _0.7 Fe _0.3 ) O ₂ and Additives>

Orthotropic Na ₀ prepared in Preparation 21 of the active material _{. 7} (Mn _0.95 Ni _0.05 ) O ₂ Hexagonal Na ₀ prepared in Preparation Example 32 instead of powder _{. A} positive electrode and a _half cell were prepared in the same manner as in the preparation of Example 25, except that ₇ (Mn _0.7 Fe _0.3 ) O ₂ powder was used.

<Full-Cell Manufacturing Example>

Instead of using sodium metal as a cathode, a mixture of hard carbon anode material and carbon black as a conductive material and PVdF as a binder in a weight ratio of 70:15:15 is mixed in NMP and the coating is applied to a copper foil used as a current collector. After the drying was completed using the same method as in Preparation Example 25, except that a negative electrode was used to produce an on-cell.

50A is a graph showing the charge / discharge characteristics of the half cells according to the half cell manufacturing example 25, and FIG. 50B is a graph showing the discharge capacity according to the number of cycles of the half cell according to the half cell manufacturing example 25. FIG. 51A is a graph showing charge / discharge characteristics of the half cell according to the half cell manufacturing example 26, and FIG. 51B is a graph showing the discharge capacity according to the number of cycles of the half cell according to the half cell manufacturing example 26. FIG. At this time, the charge was constant current charged at 20 mA / g up to 4.3 V, and the discharge was performed at 1.5 V at the same speed as the above charge rate. Charge and discharge proceeded 2 cycles.

Table 2 below summarizes the initial charge capacity and the initial discharge capacity of the half-cell according to the half-cell manufacturing examples 14, 24, 25, and 26.

	Active material	additive	Charge capacity (mAh)	Discharge Capacity (mAh)
Half-cell manufacture example 14	Rhombic system Na 0 . 7 (Mn 0.95 Ni 0.05 ) O 2	-	0.263	0.351
Half-cell manufacture example 25		NaNO 2	0.362	0.361
Half-cell manufacture example 24	Hexagonal Na 0 . 7 (Mn 0.7 Fe 0.3 ) O 2	-	0.166	0.204
Half-cell production example 26		NaNO 2	0.234	0.223

Referring to FIGS. 50A, 50B, 51A, and 51B, and Table 2, when NaNO ₂ as an additive is added to a positive electrode, tetragonal Na _0.7 (Mn _0.95 Ni _0.05 ) O ₂ according to Preparation Example 21 is used as a positive electrode active material. It can be seen that both the use and the use of hexagonal Na _0.7 (Mn _0.7 Fe _0.3 ) O ₂ according to Preparation Example 32 showed a large increase in initial charge capacity and a slight increase in initial discharge capacity. This was presumably because the additive NaNO ₂ served as a source of Na + ions during the charging process. In particular, the positive electrode active material to the orthorhombic Na _{0. When 7} (Mn _0.95 Ni _0.05 ) O ₂ is used and an additive is added, it can be seen that the initial charging capacity is 0.362 mAh, which is significantly improved compared to a sodium secondary battery using a cathode active material having a general P2 structure.

In addition, it can be seen that the life characteristics are further improved when the additive is used compared to the case where the additive is not used.

52A is a graph showing charge and discharge characteristics of a half cell according to a full-cell manufacturing example, and FIG. 52B is a graph showing discharge capacity according to the number of cycles of a half cell according to a full-cell manufacturing example.

52A and 52B, tetragonal Na ₀ according to Preparation Example 21 of the active material as the positive electrode active material _{. When using 7} (Mn _0.95 Ni _0.05 ) O ₂ and adding an additive to form a positive electrode and constructing an on-cell using the same, the initial charging capacity is about 0.362 mAh, which is significantly higher than that of a sodium secondary battery using a cathode active material having a general P2 structure. It can be seen that the life characteristics have been improved.

In the 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 by those skilled in the art within the spirit and scope of the present invention. This is possible.

Claims (22)

1. An electrode active material represented by the following Chemical Formula 1 and having a tetragonal crystal structure and having a space group of Cmcm:

   [Formula 1]

   Na _x [Mn _1-yz M ¹ _y M ² _z ] O _2-α A _α

   In Chemical Formula 1,

   x is 0.5 to 0.8,

   M ¹ and M ² are independently of each other 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, or Bi,

   y is 0 to 0.25,

   z is from 0 to 0.25,

   A is N, O, F, or S,

   α is 0 to 0.1.
2. The method of claim 1,

   The active material represented by Chemical Formula 1 is an electrode active material represented by Chemical Formula 2:

   [Formula 2]

   Na _x [Mn _1-y M _y ] O _2-α A _α

   In Formula 2, x is 0.5 to 0.8,

   M 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, or Bi,

   y is 0 to 0.25,

   A is N, O, F, or S,

   α is 0 to 0.1.
3. The method of claim 1,

   The active material represented by Chemical Formula 1 is an electrode active material represented by Chemical Formula 3:

   [Formula 3]

   Na _x MnO ₂ (x is from 0.5 to 0.8).
4. The method of claim 1,

   The active material represented by Chemical Formula 1 is an electrode active material represented by Chemical Formula 4:

   [Formula 4]

   Na _x [Mn _1-y M _y ] O ₂

   In Chemical Formula 4,

   x is 0.5 to 0.8,

   M 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, or Bi,

   y is 0.02 to 0.25.
5. The method according to any one of claims 1 to 4,

   x is 0.65 to 0.75 electrode active material.
6. The method according to any one of claims 2 and 4,

   y is 0.025 to 0.1 electrode active material.
7. The method of claim 1,

   The active material represented by Chemical Formula 1 is Na _0.7 MnO ₂ electrode active material.
8. The method according to any one of claims 2 and 4,

   M is Al, Co, Cd, Nd, Rh, Sc, Zn, Fe, or Ni electrode active material.
9. The method of claim 8,

   M is Fe or Ni electrode active material.
10. The method of claim 1,

    The electrode active material having the tetragonal crystal structure and the space group is Cmcm, the intensity of the first peak representing the (002) plane is 5 to 8.5 times the intensity of the second peak representing the (004) plane.
11. The method of claim 1,

    The electrode active material having the tetragonal crystal structure and the space active group of Cmcm has a half width of the first peak showing the (002) plane is 0.2 to 0.3.
12. Preparing a metal salt solution containing sodium salt and manganese salt;

    Ultrasonic spray pyrolysis of the metal salt solution to obtain a solid powder; And

    Heat treatment of the solid powder is represented by the following formula (1), and has a tetragonal structure and comprises a step of obtaining an electrode active material having a space group of Cmcm:

    [Formula 1]

    Na _x [Mn _1-yz M ¹ _y M ² _z ] O _2-α A _α

    In Chemical Formula 1,

    x is 0.5 to 0.8,

    M ¹ and M ² are independently selected 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, or Bi,

    y is 0 to 0.25,

    z is from 0 to 0.25,

    A is N, O, F, or S,

    α is 0 to 0.1.
13. The method of claim 12,

    The heat treatment is an electrode active material manufacturing method performed at 1100 ℃ to 1300 ℃.
14. The method of claim 12,

    The heat treatment is a method of manufacturing an electrode active material is carried out in the oxygen and the remaining inert gas atmosphere of 15 vol.% To 100 vol.%.
15. The method of claim 14,

    The atmosphere is a dry atmosphere electrode active material manufacturing method.
16. The method of claim 14,

    The inert gas is nitrogen electrode active material manufacturing method.
17. An anode represented by the following Chemical Formula 1, having a tetragonal crystal structure and having a space group containing a Cmcm anode active material;

    A negative electrode containing a negative electrode active material; And

    A secondary battery comprising an electrolyte disposed between the positive electrode and the negative electrode.

    [Formula 1]

    Na _x [Mn _1-yz M ¹ _y M ² _z ] O _2-α A _α

    In Chemical Formula 1,

    x is 0.5 to 0.8,

    M ¹ and M ² are independently of each other 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, or Bi,

    y is 0 to 0.25,

    z is from 0 to 0.25,

    A is N, O, F, or S,

    α is 0 to 0.1.
18. The method of claim 17,

    The positive electrode further comprises a sodium salt.
19. The method of claim 18,

    The sodium salt is NaNO ₂ secondary battery.
20. The method of claim 19,

    The NaNO ₂ is a secondary battery containing 3 to 20 parts by weight based on 100 parts by weight of the positive electrode active material.
21. The method of claim 18,

    The anode further includes a conductive material,

    The conductive material is a secondary battery containing 2 to 9 parts by weight based on 100 parts by weight of the positive electrode active material.
22. The method of claim 18,

    The anode further comprises a binder,

    The binder is a secondary battery containing 2 to 9 parts by weight based on 100 parts by weight of the positive electrode active material.

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