KR102214514B1 - Electrode Active Material and Method for Preparing the Same - Google Patents

Abstract

The present invention provides an electrode active material and a method of manufacturing the same. The method of preparing the electrode active material includes performing a desodiumization reaction of an olivine-based sodium phosphate, coating a conductive polymer on the desodium-based sodium phosphate, and a desodiumated olivine coated with the polymer. Comprising the step of forming a conductive polymer-olivine-based sodium phosphate complex by performing a sodium intercalation reaction on the empty sodium phosphate, and the secondary battery including the electrode active material according to the present invention has excellent high rate characteristics and high capacity characteristics. It may exhibit an effect of improving chemical properties.

Description

Electrode Active Material and Secondary Battery Containing the Same {Electrode Active Material and Method for Preparing the Same}

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

A secondary battery refers to a battery that can be used repeatedly because it can be charged as well as discharged. In a typical lithium secondary battery among secondary batteries, lithium ions contained in the positive electrode active material are transferred to the negative electrode through the electrolyte and then inserted into the layered structure of the negative electrode active material (charging), and then the lithium ions inserted into the layered structure of the negative electrode active material are again It works through the principle of returning to the anode (discharge). These lithium secondary batteries are currently commercialized and used as small power sources such as mobile phones and notebook computers, and are predicted to be usable as large power sources such as hybrid vehicles, and their demand is expected to increase.

However, the composite metal oxide, which is mainly used as a cathode active material in lithium secondary batteries, contains rare metal elements such as lithium, and thus there is a fear that it cannot meet the increasing demand. Accordingly, studies on sodium secondary batteries in which supply is abundant and cheap sodium is used as a cathode active material are being conducted.

Republic of Korea Patent Publication No. 2012-0133300

Accordingly, a problem to be solved by the present invention is to provide a sodium-based electrode active material and a method of manufacturing the same. In addition, it is to provide a secondary battery having excellent high rate characteristics and high capacity characteristics using this.

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

In order to achieve the above object, a method of manufacturing an electrode active material according to an embodiment of the present invention is provided. The method of preparing the electrode active material includes performing a desodiumization reaction of an olivine-based sodium phosphate, coating a conductive polymer on the desodium-based sodium phosphate, and a desodiumated olivine coated with the polymer. It may include the step of forming a conductive polymer-olivine-based sodium phosphate complex by performing a sodium intercalation reaction on the empty sodium phosphate.

The desodiumization reaction is performed by adding and stirring the olivine-based sodium phosphate in a solution of an oxidizing agent/organic solvent, and the oxidizing agent may be used in an amount of 0.1 to 0.5 times the number of moles of the olivine-based sodium phosphate.

The oxidizing agent may be one using NO ₂ BF ₄ .

The desodiumization reaction may be performed under a temperature condition of 40°C to 60°C.

The conductive polymer is poly(3,4-ethylenedioxythiophene), polyaniline, polythiophene, polyphenylene, poly(p-phenylene sulfide), polypara Phenylene sulfide, polypyrrole, polyacethylene, poly(3-alkyl thiophene), poly(phenylenevinylene), polyparaphenylene vinyl Poly(pphenylenevinylene), poly(thienylenevinylene), poly(pphenylene), polyazulene, polyfuran, polyselenophenes, Polytellurophene (polytellurophene) It may be one containing a mixture or copolymer of two or more of these.

The conductive polymer coating may be performed by immersing the desodiumated olivine-based sodium phosphate in a monomer solution of the conductive polymer.

It may be to add a dopant material to the conductive polymer monomer solution.

The dopant material may include persulfate.

In order to achieve the above object, an electrode active material according to another embodiment of the present invention is provided. The electrode active material may be an olivine-based sodium phosphate and the olivine-based sodium phosphate coated with a conductive polymer.

The olivine-based sodium phosphate may be represented by Formula 1 below.

The electrode active material represented by Formula 1 may be Formula 2 or Formula 3.

The conductive polymer may be coated in an amount of 1 to 25% by weight based on the total weight of the olivine-based sodium phosphate.

The conductive polymer may be one to form a coating layer with a thickness of 2 to 30 nm on the surface of the olivine-based sodium phosphate.

As described above, the present invention may exhibit an effect of improving electrochemical properties such as excellent high rate characteristics and high capacity characteristics by coating a polymer on olivine sodium phosphate as an electrode active material.

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

1 is a flowchart illustrating a method of manufacturing an electrode active material according to an embodiment of the present invention.
2 is a schematic diagram showing a secondary battery according to an embodiment of the present invention.
3 is a graph showing the results of FT-IR (Fourier Transform Infrared Spectroscopy) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of pristine Na ₂ FePO ₄ F and an electrode active material.
4 is a high resolution transmission electron microscopy (HRTEM) image of a PEDOT-Na ₂ FePO ₄ F composite prepared according to an electrode active material preparation example.
5A and 5B are images showing the results of energy-dispersive X-ray spectroscopy (EDX) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of the electrode active material, respectively.
6 is a graph showing an EIS (electrochemical impedance spectroscopy) result analysis of a pristine Na ₂ FePO ₄ F and PEDOT-Na ₂ FePO ₄ F composite prepared according to Preparation Example of an electrode active material.
7 is an X-ray diffraction (XRD) analysis result of pristine Na ₂ FePO ₄ F, Na _2-x FePO ₄ F obtained in Preparation Example of electrode active material and PEDOT-Na ₂ FePO ₄ F composite prepared according to Preparation Example of electrode active material It is a graph showing.
8 is a graph showing the results of XRD (X-ray diffraction) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of an electrode active material.
9 is a graph showing charge and discharge characteristics according to C-rate of a secondary battery manufactured according to a secondary battery manufacturing example and a secondary battery comparative example. At this time, charging was performed up to 4.2V, discharging was performed up to 2.0V, and 1C was performed at 124mA/g.
10 and 11 are graphs showing charge and discharge capacity and coulomb efficiency according to the number of cycles of a secondary battery manufactured according to a secondary battery comparative example.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate an overall understanding, the same reference numerals are used for the same elements in the drawings, and duplicate descriptions for the same elements are omitted.

Electrode active material

The electrode active material according to an embodiment of the present invention is an olivine-based sodium phosphate coated with a conductive polymer, and the olivine-based sodium phosphate may be represented by Formula 1 below.

[Formula 1]

Na _x M _y (PO ₄ ) _a (P ₂ O ₇ ) _b X _z

In Formula 1, x may be an integer of 1 to 9. As an example, x may be an integer of 2 to 7. Specifically, it may be an integer of 2 to 4. M may be a transition metal or a post-transition metal, for example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, It may be Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, or Bi. Preferably, it may be Fe or V. y may be an integer from 1 to 4. a may be an integer of 1 to 3. b may be an integer from 0 to 4. X may be N, O, F, or S, and z may be an integer from 0 to 4. As an example of an olivine-based sodium phosphate satisfying Formula 1, Na ₉ V ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) ₃ , Na ₇ V ₄ (PO ₄ )(P ₂ O ₇ ) ₄ , Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ), Na ₃ V ₂ (PO ₄ ) ₃ F _3, Na ₃ V ₂ (PO ₄ ) ₃ or Na ₂ Fe(PO ₄ )F, limited to this It does not become.

According to an example, the olivine-based sodium phosphate may be represented by Formula 2 below.

[Formula 2]

Na _x M _y (PO ₄ ) _a X _z

In Formula 2, x may be an integer of 2 to 7. Specifically, it may be an integer of 2 to 4. M may be a transition metal or a post-transition metal, for example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, It may be Nd, Mo, Tc, Ru, Rh, Pd, Pb, Ag, Cd, Al, Ga, In, Sn, or Bi. Preferably, it may be Fe or V. y may be an integer from 1 to 4. As an example, y may be 2 or 3. a may be an integer of 1 to 3. X may be N, O, F, or S, and z may be an integer from 0 to 4. As an example of an olivine-based sodium phosphate that satisfies Formula 2, it may be Na ₃ V ₂ (PO ₄ ) ₃ F _3, Na ₃ V ₂ (PO ₄ ) ₃ or Na ₂ Fe(PO ₄ )F, and thus It is not limited.

According to another example, the olivine-based sodium phosphate may be represented by Formula 3 below.

[Formula 3]

Na ₂ Fe(PO ₄ )F

The olivine-based sodium phosphate may be coated with a conductive polymer. Examples of conductive polymers include poly(3,4-ethylenedioxythiophene), polyaniline, polythiophene, polyphenylene, polyphenylene sulfide, polyphenylene sulfide, and polythiophene. Paraphenylenesulfide, polypyrrole, polyacethylene, poly(3-alkyl thiophene), poly(phenylenevinylene), polyparaphenyl Poly(pphenylenevinylene), poly(thienylenevinylene), poly(pphenylene), polyazulene, polyfuran, polyselenophenes ), polytellurophene, a mixture or copolymer of two or more of these may be included, but is not limited thereto.

By doping the conductive polymer using a dopant, electrical conductivity may be improved. A dopant is a material that acts as a charge transporter by providing or removing a charge to a part of a phi orbital function of a polymer, and may be a counter ion capable of maintaining a charge balance. In the case of providing electric charge to the conductive polymer, it may be n-type doping, and in the case of removing the electric charge from the conductive polymer, it may be p-type doping. As an example, when the conductive polymer is p-doped, persulfate, tosylate, chloride, or polystyrene sulfonate may be used as an opposite charge, but is not limited thereto. .

The conductive polymer may be coated in an amount of 1 to 25% by weight based on the total weight of the olivine-based sodium phosphate. As an example, it may be coated with 5 to 20% by weight, and more specifically, may be coated with 10 to 15% by weight. When the coating amount is within the above numerical range, the electrical conductivity of the olivine-based sodium phosphate may be improved, and the amount of the electrode active material may be reduced, so that the capacity of the secondary battery including the same may not be reduced.

The conductive polymer may be one that forms an amorphous coating layer with a thickness of 2 to 30 nm on the surface of olivine-based sodium phosphate. Specifically, it may be 2 to 8 nm. When the upper limit of the numerical range for the coating thickness is exceeded, movement of sodium ions may be hindered. In addition, if it is less than the lower limit, it may be difficult to sufficiently secure electrical conductivity because uniform coating is difficult.

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

Referring to FIG. 1, a step of performing a desodiumization reaction of olivine-based sodium phosphate (S100) may be included. The desodiumization reaction may be accomplished by adding an olivine-based sodium phosphate in a solution of an oxidizing agent/organic solvent, followed by stirring. The olivine-based sodium phosphate may be represented by Chemical Formula 1, Chemical Formula 2, or Chemical Formula 3.

The oxidizing agent used in the desodiumization reaction may be NO ₂ BF ₄ . The oxidizing agent may be used in an amount of 0.1 to 0.5 times the number of moles of olivine sodium phosphate. As an example, it may be 0.2 to 0.4 times, preferably 0.3 times. When the above value is satisfied, the olivine-based sodium phosphate can sufficiently proceed with the desodiumization reaction. The organic solvent may be acetonitrile, hexanol, ethanol, methanol, or a combination thereof. Preferably, acetonitrile can be used as the organic solvent.

In this case, the desodiumization reaction may be performed under a temperature condition of 40°C to 60°C. In addition, it may be performed under a non-reactive gas atmosphere. As an example of a non-reactive gas atmosphere, it may refer to a nitrogen (N ₂ ) or argon (Ar) atmosphere.

The desodiumization reaction according to an embodiment of the present invention may be represented by Reaction Scheme 1 below.

[Scheme 1]

Na _x M _y (PO ₄ ) _a (P ₂ O ₇ ) _b X _z + rNO ₂ BF ₄ → Na _xr M _y (PO ₄ ) _a (P ₂ O ₇ ) _b X _z + rNaBF ₄ + rNO ₂

In Reaction Scheme 1, x, M, y, a, b, X and z are as shown in Formula 1. Also, r represents a value equal to or smaller than x.

It may further include washing the desodium olivine-based sodium phosphate with a solution such as acetonitrile.

It may include a step (S200) of coating a conductive polymer on the desodium olivine-based sodium phosphate. The conductive polymer coating may be polymerized by immersing desodium olivine-based sodium phosphate in a monomer solution of a conductive polymer. Chemical polymerization, electrochemical polymerization, thermal polymerization, etc. may be used as a polymerization method. Herein, the chemical polymerization may be oxidation polymerization, in which an oxidizing agent is added to a conductive polymer monomer solution to oxidize the monomer to facilitate polymerization, and then polymerize into a conductive polymer.

In addition, a dopant material may be added to the conductive polymer monomer solution. As an example, for p-doping of the conductive polymer, an oxidizing agent may be used as a dopant material. As an example of the oxidizing agent, sodium persulfate, potassium persulfate (K ₂ S ₂ O ₈ ), or ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) may be used, but is not limited thereto. The oxidizing agent as a dopant may serve to improve electrical conductivity, and further, may serve to initiate oxidation polymerization of the monomer. Accordingly, the cation and the counter ion of the conductive polymer monomer are polymerized in a long chain form by electrical attraction to form a conductive polymer, and the monomer is p-doped to improve electrical properties.

In addition, the transition metal (M) contained in the olivine-based sodium phosphate may increase the number of oxidation as the olivine-based sodium phosphate is desodiumated, and as a result, the oxidized transition metal is an ionic oxidizing agent and polymerization of conductive polymer monomers. Can play a role in promoting

Accordingly, the monomer of the conductive polymer may be polymerized on the surface of the desodium olivine-based sodium phosphate, thereby being coated on the desodium olivine-based sodium phosphate to form a film.

As an example, EDOT (3,4-ethylenedioxythiophene), which is a monomer of a conductive polymer, may be polymerized on the surface of desodium olivine-based sodium phosphate to be coated. The conductive polymer coated on the surface is PEDOT, which can be p-doped using persulfate (S ₂ O ₈ ^2- , persulfate) with a counter ion, and as a result, the electrical conductivity of the PEDOT polymer is improved. I can.

It may include the step (S300) of performing a sodium insertion reaction in the desodium olivine-based sodium phosphate coated with the conductive polymer. As a result, a conductive polymer-olivine-based sodium phosphate complex may be formed. The sodium intercalation reaction can be carried out using a solution of NaI/organic solvent. That is, the sodium intercalation reaction may be achieved by adding desodium olivine-based sodium phosphate in a solution of an oxidizing agent/organic solvent, followed by stirring. The organic solvent may be acetonitrile, hexanol, ethanol, methanol, or a combination thereof. Preferably, acetonitrile can be used as the organic solvent. At this time, the stirring may be performed under a non-reactive gas atmosphere.

When the polymer is coated according to the present invention, it may be performed through a low-temperature process method. Therefore, unlike the case of coating carbon in order to improve electrical conductivity, volatile substances (VOCs, CO, CO _2, etc.) that cause environmental pollution may not be generated. Therefore, when the electrode active material is manufactured by using the manufacturing method according to an exemplary embodiment of the present invention, the risk of contamination may be suppressed.

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

Sodium secondary battery

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

Referring to FIG. 2, the secondary battery 100 includes a negative active material layer 120 containing a negative active material into which an alkali metal can be removed, a positive active material layer 140 containing the positive active material described above, and interposed therebetween. It includes the separated separator 130. The electrolyte 160 may be disposed or charged between the negative active material layer 120 and the separator 130 and between the positive active material layer 140 and the separator 130. The negative active material layer 120 may be disposed on the negative current collector 110, and the positive active material layer 140 may be disposed on the positive current collector 150.

<Anode>

The positive electrode may be prepared by mixing the electrode active material, a conductive material, and a binder described above to obtain a positive electrode material.

The conductive material is used to improve the conductivity of the electrode, and any material capable of imparting electronic conductivity characteristics without causing chemical changes in the secondary battery constructed according to the present invention can be used. Preferably, it may include one or a mixture of two or more selected from a graphite-based material, a carbon-based material, a metal-based or metal compound-based material, and a conductive polymer. As an example of the graphite-based material, artificial graphite or natural graphite may be used. As an example of the carbon-based material, Super P carbon black, Ketjen black. It may be Denka black, acetylene black, carbon black, or the like. The metal or metal compound-based material may be a tin oxide, tin phosphate, titanium oxide, or perovskite material. In addition, the material of the conductive material is not limited thereto. In this case, the content of the conductive material may be appropriately adjusted and used, and as an example, the conductive material may be contained in an amount of 10 to 30 parts by weight based on 100 parts by weight of the positive electrode active material.

The binder is a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene, vinylidene fluoride copolymer, fluorine resin such as propylene hexafluoride, and/or polyolefin resin such as polyethylene and polypropylene. Can include. The binder 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.

A slurry may be prepared by dissolving the positive electrode active material and the binder obtained according to the above in a solvent. The resulting slurry can be applied on a positive electrode current collector to form a positive electrode. The positive electrode current collector may be a conductor such as aluminum (Al), nickel (Ni), stainless steel (SUS), or molybdenum (Mo). Applying the slurry on the positive electrode current collector may be a method of forming a paste using pressure molding or an organic solvent, and then applying the paste on the current collector and pressing to fix it. Examples of the organic solvent include amines such as N,N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Esters such as methyl acetate; It may be an aprotic polar solvent such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste onto the positive electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<cathode>

The negative electrode active material includes metals, metal alloys, metal oxides, metal fluorides, metal sulfides, and natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, and graphite capable of deintercalating sodium ions or causing a conversion reaction. It can also be formed using carbon materials such as fins.

A negative electrode material can be obtained by mixing a negative electrode active material, a conductive material, and a binder. In this case, the conductive material may be a carbon material such as natural graphite, artificial graphite, coke, carbon black, carbon nanotubes, and graphene. The binder is a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene, vinylidene fluoride copolymer, fluorine resin such as propylene hexafluoride, and/or polyolefin resin such as polyethylene and polypropylene. Can include.

A negative electrode material can be applied on the negative electrode current collector to form a negative electrode. The negative electrode current collector may be a conductor such as aluminum (Al), nickel (Ni), stainless steel (SUS), or molybdenum (Mo). Applying the negative electrode material on the positive electrode current collector may be performed 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 it. Examples of the organic solvent include amines such as N,N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketone systems such as methyl ethyl ketone; Esters such as methyl acetate; It may be an aprotic polar solvent such as dimethylacetamide and N-methyl-2-pyrrolidone. Applying the paste onto the negative electrode current collector may be performed using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Electrolyte>

Electrolyte may be NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN(SO ₂ CF ₃ ) ₂ , lower aliphatic sodium carboxylate, NaAlCl _4, etc., and at least two Mixtures can also be used. Among these, it is preferable to use an electrolyte containing fluorine. Further, the electrolyte can be dissolved in an organic solvent and used as a non-aqueous electrolyte. As an organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4- Carbonates such as trifluoromethyl-1,3-dioxolan-2-one and 1,2-di(methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, 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-propane sultone; Alternatively, a fluorine substituent may be further introduced into the organic solvent described above.

Alternatively, a solid electrolyte may be used. The solid electrolyte may be an organic solid electrolyte such as a polyethylene oxide polymer compound, a polymer compound including at least one of a polyorganosiloxane chain, or a polyoxyalkylene chain. In addition, a so-called gel-type electrolyte in which a non-aqueous electrolyte is supported on a polymer compound can also be used. Meanwhile, Na ₂ S-SiS ₂ , Na ₂ S-GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ), Fe ₂ (MoO ₄ ) _{3 It} is also possible to use an inorganic solid electrolyte. In some cases, the safety of a sodium secondary battery can be further improved by using these solid electrolytes. In addition, the solid electrolyte may serve as a separator to be described later, and in that case, a separator may not be required.

<Separator>

A separator may be disposed between the anode and the cathode. Such a separator may be a material having a form such as a porous film, a nonwoven fabric, or a woven fabric made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluorine resin, or a nitrogen-containing aromatic polymer. The thickness of the separator is preferably thinner as long as the mechanical strength is maintained from the viewpoint that the bulk energy density of the battery is increased and the internal resistance is decreased. The thickness of the separator may be generally 5 to 200 μm, and more specifically 5 to 40 μm.

<Method of manufacturing secondary battery>

After forming an electrode group by sequentially stacking a positive electrode, a separator, and a negative electrode, if necessary, the electrode group is rolled up and stored in a battery can, and a sodium secondary battery can be manufactured by impregnating the electrode group with a non-aqueous electrolyte. In contrast, after forming an electrode group by stacking a positive electrode, a solid electrolyte, and a negative electrode, if necessary, the electrode group may be rolled up and stored in a battery can to manufacture a sodium secondary battery.

A secondary battery having a high capacity characteristic can be used as a unit cell of a battery module, which is a power source for medium and large devices. The medium or large-sized device may include, for example, a power tool that is driven 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; Alternatively, an electric golf cart may be used, but the present invention is not limited thereto.

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

[Experimental examples; Examples]

Example of manufacturing electrode active material

1. Desodiumization

Na ₂ FePO ₄ F and NO ₂ BF ₄ with a molar ratio of about 1:0.3 were added to high-purity acetonitrile (Aldrich, 98%), and sufficiently stirred under a temperature condition of 60°C and an argon atmosphere I gave it.

The mixture after stirring was filtered and washed with acetonitrile, and then sufficiently dried to obtain Na _2-x FePO ₄ F powder.

2. Coating

0.5 g of Na _2-x FePO ₄ F, 1 g of Na ₂ S ₂ O ₈ (sodium persulfate) and 0.4 mL of EDOT (3,4-ethylenedioxythiophene) obtained according to the desodiumization reaction were added to 12 mL of ethanol, It was sufficiently stirred at 35° C. for one day. Accordingly, it was possible to obtain a mixture having a dark blue color. The mixture was filtered and washed with acetonitrile and ethanol, and then sufficiently dried in a vacuum oven at 80° C. to obtain Na _2-x FePO ₄ F powder coated with PEDOT.

3. Sodium insert

PEDOT-coated Na _2-x FePO ₄ F and NaI were put in high-purity acetonitrile (Aldrich, 98%), stirred sufficiently under an argon atmosphere, and PEDOT-coated Na ₂ FePO ₄ F (PEDOT- Na ₂ FePO ₄ F complex) was obtained.

3 is a graph showing the results of FT-IR (Fourier Transform Infrared Spectroscopy) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of pristine Na ₂ FePO ₄ F and an electrode active material.

Referring to FIG. 3, it can be seen that the graph of the PEDOT-Na ₂ FePO ₄ F composite has an additional vibration of the polymer p-doped band at 1320 cm ^-1 compared to the graph of the pristine Na ₂ FePO ₄ F without PEDOT coating. have. Through this, it can be seen that PEDOT is formed in the composite.

4 is a high resolution transmission electron microscopy (HRTEM) image of a PEDOT-Na ₂ FePO ₄ F composite prepared according to an electrode active material preparation example.

Looking at the HRTEM image of FIG. 4, it can be seen that 200 nm particles are coated by an amorphous layer having a thickness of 5 nm.

5A and 5B are images showing the results of energy-dispersive X-ray spectroscopy (EDX) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of the electrode active material, respectively.

Referring to FIG. 5A, it can be seen that the amorphous layer is PEDOT containing elemental sulfur. Further, looking at the elemental line scan analysis according to FIG. 5B, it can be seen that the amount of iron and phosphorus at the edge of the particle is lower than the amount of sulfur.

Accordingly, through the analysis of FIGS. 3, 4 and 5, it can be seen that the structure of the composite is that PEDOT is coated on the surface of the particles of Na ₂ FePO ₄ F.

6 is a graph showing an EIS (electrochemical impedance spectroscopy) result analysis of a pristine Na ₂ FePO ₄ F and PEDOT-Na ₂ FePO ₄ F composite prepared according to Preparation Example of an electrode active material.

Referring to FIG. 6, it can be seen that the charge-transfer resistance of the PEDOT-Na ₂ FePO ₄ F complex is significantly lower than that of pristine Na ₂ FePO ₄ F. This may mean that PEDOT in the composite serves to improve the electrical conductivity of Na ₂ FePO ₄ F.

7 is an X-ray diffraction (XRD) analysis result of pristine Na ₂ FePO ₄ F, Na _2-x FePO ₄ F obtained in Preparation Example of electrode active material and PEDOT-Na ₂ FePO ₄ F composite prepared according to Preparation Example of electrode active material It is a graph showing.

In addition, Table 1 below shows result data according to Rietveld refinement of Na _2-x FePO ₄ F obtained in Preparation Example of an electrode active material.

[Table 1]

It can be seen that Figure 7 and reference to table 1 above, Na ₂ FePO ₄ F structure does not cause the contamination, or the phase change by a chemical de-sodium reaction, a sodium ion is removed from the Na ₂ FePO ₄ F structure.

8 is a graph showing the results of XRD (X-ray diffraction) analysis of the PEDOT-Na ₂ FePO ₄ F composite prepared according to the preparation example of an electrode active material.

In addition, Table 2 below summarizes the lattice constants of the pristine Na ₂ FePO ₄ F, Na _2-x FePO ₄ F obtained in the electrode active material Preparation Example, and the PEDOT-Na ₂ FePO ₄ F composite prepared according to the electrode active material preparation example. will be.

[Table 2]

8 and Table 2 above, the structure of the PEDOT-Na ₂ FePO ₄ F complex is after chemical sodium intercalation and polymer coating, but no contamination or phase change of the complex is caused by the reaction, and the final composition of the complex It can be seen that the structure is Na ₂ FePO ₄ F in which sodium ions are inserted.

That is, PEDOT-Na ₂ FePO ₄ F was irreversible reactions did not occur in the coating process according to complexing, the PEDOT-Na ₂ FePO ₄ F complexes can see that indicates a pure phase without impurity.

Secondary battery manufacturing example

PEDOT-coated Na ₂ FePO ₄ F (74% by weight of Na ₂ FePO ₄ F and 6% by weight of PEDOT) as an electrode active material prepared by the same method as the electrode active material Preparation Example, Super-P and bonding as a conductive material Zero PVDF (poly vinylidene fluoride) was mixed in an organic solvent of NMP (N-methyl-2-pyrrolidone) at 8:1:1 wt%, coated on an aluminum current collector, and pressed to form a reference electrode. .

Thereafter, in a glove box filled with argon, sodium metal was used as a counter electrode, a GF/F glass filter was used as a separator, and 1 M NaPF ₆ as an electrolyte and a 1:1 volume ratio of ethyl carbonate as an organic solvent/ Using an electrolytic solution containing propylene carbonate (EC/PC), a CR2032 coin cell was manufactured.

Comparative Example of Secondary Battery

A positive electrode and a coin cell were manufactured using the same method as in the battery manufacturing example, except that pristine Na ₂ FePO ₄ F was used instead of Na ₂ FePO ₄ F coated with PEDOT as the electrode active material used in the secondary battery manufacturing example.

9 is a graph showing charge and discharge characteristics according to C-rate of a secondary battery manufactured according to a secondary battery manufacturing example and a secondary battery comparative example. At this time, charging was performed up to 4.2V, discharging was performed up to 2.0V, and 1C was performed at 124mA/g.

Referring to FIG. 9, in the case of the secondary battery according to the comparative example of the secondary battery, the maximum capacity exhibited at various C-rates has a value exceeding approximately 20 mAh/g. However, it can be seen that the secondary battery according to the secondary battery manufacturing example has approximately 120mAh/g at C/5-rate, which is close to the theoretical capacity. In addition, it has a capacity of approximately 70.5mAh/g even at 10C-rate, which has a high current rate, which is more than 10 times larger than the secondary battery according to the Comparative Example of the secondary battery. Accordingly, it can be seen that the secondary battery according to the secondary battery manufacturing example has a much higher capacity than the secondary battery according to the secondary battery comparative example.

10 and 11 are graphs showing charge/discharge capacity and coulomb efficiency according to the number of cycles of a secondary battery manufactured according to a secondary battery manufacturing example and a secondary battery comparative example.

Referring to FIG. 10, the secondary battery according to the secondary battery manufacturing example has a high cooling efficiency of 99%, and maintains about 60% of the initial capacity even after charging and discharging 700 cycles at 1 C-rate. In addition, compared with FIG. 11, it can be seen that the secondary battery according to the secondary battery manufacturing example has remarkably improved cycle performance and the excellent capacity retention rate compared to the secondary battery according to the secondary battery comparative example.

Although described with reference to the above embodiments, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the following claims. I will be able to.

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

Claims (18)

Performing a desodiumization reaction of the olivine-based sodium phosphate represented by the following Formula 1;
Coating a conductive polymer on the desodium olivine-based sodium phosphate, wherein the conductive polymer coating is performed by immersing the desodium olivine-based sodium phosphate in a monomer solution of the conductive polymer; And
A method for producing an electrode active material comprising the step of forming a conductive polymer-olivine-based sodium phosphate complex by performing a sodium intercalation reaction on the desodiumized olivine-based sodium phosphate coated with the polymer:
[Formula 1]
Na _x M _y (PO ₄ ) _a (P ₂ O ₇ ) _b X _z
In Formula 1,
x is an integer from 1 to 9,
M is a transition metal or a post-transition metal,
y is an integer from 1 to 4,
a is an integer of 1 to 3,
b is an integer from 0 to 4,
X is N, O, F or S,
z is an integer from 0 to 4. delete The method according to claim 1,
The desodiumization reaction is performed by adding and stirring the olivine-based sodium phosphate in a solution of an oxidizing agent/organic solvent,
The method of manufacturing an electrode active material, wherein the oxidizing agent is used in an amount of 0.1 to 0.5 times the number of moles of the olivine sodium phosphate. The method of claim 3,
The method of manufacturing an electrode active material that the oxidizing agent uses NO ₂ BF ₄ . The method according to claim 1,
The desodiumization reaction is a method of producing an electrode active material that is performed under a temperature condition of 40°C to 60°C. The method according to claim 1,
The conductive polymer is poly(3,4-ethylenedioxythiophene), polyaniline, polythiophene, polyphenylene, poly(p-phenylene sulfide), polypara Phenylene sulfide, polypyrrole, polyacethylene, poly(3-alkyl thiophene), poly(phenylenevinylene), polyparaphenylene vinyl Poly(pphenylenevinylene), poly(thienylenevinylene), poly(pphenylene), polyazulene, polyfuran, polyselenophenes, Polytellurophene (polytellurophene) A method for producing an electrode active material comprising a mixture or copolymer of two or more of these. delete The method according to claim 1,
A method for producing an electrode active material by adding a dopant material to the conductive polymer monomer solution. The method of claim 8,
The method of manufacturing an electrode active material wherein the dopant material includes persulfate. delete delete delete delete delete delete delete delete delete

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