KR101622092B1 - Cathode Active Material for Metal-Air Cell and Metal-Air Cell Comprising The Same - Google Patents

Abstract

The present invention relates to a cathode material for a metal air cell and a metal air cell including the cathode material.
The cathode material according to the present invention can improve the slow oxidation and reduction reaction rate of the oxygen gas since the metal catalyst layer is formed on part or all of the surfaces of the porous carbon particles or the porous carbon structure.
Therefore, the present invention can accelerate the electrochemical reaction of the oxygen gas more simply than the case of mixing the noble metal catalyst and the porous carbon, and at the same time, the energy density per mass is relatively higher than that in the case of using the nanoporous gold as the anode It is possible to provide a high-cost, low-cost metal-air battery anode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode material for a metal air cell,

The present invention relates to a cathode material for a metal air cell and a metal air cell including the cathode material.

2. Description of the Related Art [0002] A secondary battery exhibiting a high energy density is required due to miniaturization and high integration of portable electronic devices and development of hybrid electric vehicles (HEV) and electric vehicles.

Currently, commercially available lithium ion batteries use only a limited energy density due to technical problems, and thus the development of metal-air batteries having higher energy density is attracting attention.

The capacity of the lithium ion battery is limited by the theoretical capacity of the anode and cathode materials, but since the metal-air battery uses air as the anode, the energy density is greatly increased.

Metal-air cells consist of a metal anode (cathode) and an oxygen cathode (anode). During the discharge, metal ions are formed due to oxidation of the metal anode, and the generated metal ions move to the oxygen cathode across the electrolyte.

In the oxygen air electrode, the external oxygen is dissolved in the electrolyte inside the pores of the oxygen electrode and reduced. In the case of a non-aqueous metal-air battery, the reduced oxygen combines with metal ions transferred from the electrolyte to form metal oxides.

In the case of aqueous electrolytes, water is involved in the discharge reaction to form metal hydroxides.

Metal-air cells, although having a high energy density, have difficulty practically implementing all of the theoretical energy density.

Typically, charging and discharging do not occur smoothly due to the slow oxidation and reduction reaction rate of oxygen gas, and unlike a lithium ion battery, an open structure that allows external air to flow is taken, so that impurities (water and carbon dioxide, etc.) As a result, the irreversible capacity increases and volatilization of the electrolytic solution occurs, resulting in a problem that the performance deteriorates rapidly.

Thus, the anode of the metal-air battery should have a porous, conductive matrix structure in which discharge products must be formed.

Conventional techniques for promoting the electrochemical reaction of oxygen gas include a technique of mixing porous carbon with a noble metal catalyst such as gold or platinum to use as a cathode material, or using nanoporous gold as an anode.

However, merely mixing the porous carbon and the catalyst and using them as a cathode material has a limitation in promoting the electrochemical reaction of oxygen gas. In addition, when nanoporous gold is used as an anode, there is a limit in that an energy density and an electrode price are expensive.

The inventors of the present application have found that when a coating layer containing a noble metal catalyst is formed on the surface of porous carbon particles, the electrochemical reaction of oxygen gas can be further promoted as compared with the case of simply mixing the noble metal catalyst and the porous carbon, The present invention has been accomplished based on the idea that, compared with the case where gold is used as an anode, an energy density per mass is relatively high and an anode for an inexpensive metal-air battery can be provided.

Accordingly, the cathode material for a metal-air battery according to the present invention,

Porous carbon particles; Or a porous carbon structure having a structure in which porous carbon particles are aggregated; And

And a metal catalyst layer formed on the surfaces of the porous carbon particles or the porous carbon structure and lowering the activation energy of the oxidation and reduction reactions of the oxygen gas.

Metal-air batteries are accompanied by an Oxygen Reduction Reaction (ORR) during discharging and accompanied by Oxygen Evolution Reaction (OER) during charging. Therefore, for the secondary battery of a metal-air battery, oxygen reduction reaction and oxygen generation reaction must be simultaneously active.

Therefore, the metal catalyst should be active in both the oxygen reduction reaction and the oxygen generation reaction. The metal catalyst may be one or two or more alloys selected from the group consisting of gold, silver and platinum group metals. The platinum group metals may be selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd) (Pt). ≪ / RTI >

The metal catalyst layer composed of the metal catalysts may be formed on all or a part of the surface of the porous carbon particles, and may be formed on all or a part of the surface of the porous carbon structure.

The porous carbon structure in which the metal catalyst layer is formed on all or a part of the surface may be formed with the metal catalyst layer in the aggregated state of the porous carbon particles and may have a porous structure in which the metal catalyst layer is formed on all or a part of the surface The carbon particles may be agglomerated.

In one non-limiting embodiment of the present invention, the carbon structure may be a carbon paper, the carbon structure is generally porous, has a high electrical conductivity and is randomly present, Due to its light weight, it is suitable for use as an electrode in metal air cells.

In one specific embodiment of the present invention, the metal catalyst layer may be formed on the entire surface of the porous carbon particles. Further, in another specific embodiment of the present invention, the metal catalyst layer may be formed on the entire surface of the porous carbon structure.

The metal catalyst layer may have a thickness of 2 to 20 nm and may be formed on all or a part of the surfaces of the porous carbon particles or the porous carbon structure. When the catalyst layer is less than 2 nm, it is difficult to uniformly coat the porous carbon particles and the carbon structure, resulting in a process problem. Also, when the thickness exceeds 20 nm, a large amount of metal catalyst is used, resulting in cost disadvantage and energy density per mass is reduced.

The metal catalyst layer may be formed on the surface of the porous carbon particles or the porous carbon structure by a method known in the art such as an electroless plating method, an electroplating method, a vapor deposition method, a chemical synthesis method, The thickness of the metal catalyst layer can be determined in consideration of competitiveness and the like.

The porous carbon has a regular or irregular structure and non-uniform micropores. Representative materials include activated carbon. In activated carbon, fine graphite has a two-dimensional or three-dimensional higher-order structure, and such voids become pores.

The size of the pores may be micropores (<2 nm), median (2-50 nm) or macropores (> 50 nm), and in one specific embodiment of the present invention, nm (mesoporous structure), and the porosity may be 20 to 45%.

The porous carbon particles may be aggregated to form a porous carbon structure, and voids may be formed between the porous carbon particles. In one specific embodiment according to the present invention, the porosity of the porous carbon structure may be 20 to 45%.

The present invention also provides a metal-air battery including the above-mentioned cathode material. The metal-air battery may include an anode, a cathode, and an electrolyte, and may include a separator depending on the type of the electrolyte.

The metal-air battery may be classified according to the kind of the active metal used as the negative electrode active material.

For example, the active metal may be selected from the group consisting of magnesium, aluminum, zinc, iron, cadmium, lead, lithium, and sodium. In this case, the metal- , Aluminum-air cells, zinc-air cells, iron-air cells, cadmium-air cells, lithium-air cells and sodium-air cells.

The metal air battery may be a rechargeable secondary battery, and may be used as a power source of an electric vehicle (EV), a hybrid electric vehicle (HEV), or a power source of a power storage device, but is not limited thereto.

The positive electrode is a plate-shaped electrode having a relatively thinner thickness than the negative electrode. According to one specific embodiment of the present invention, the above-mentioned positive electrode material is put into a separately prepared binder solution and stirred to prepare a slurry. And then the whole is applied.

The binder solution preparation process is a process of dispersing or dissolving the binder in a solvent to prepare a binder solution.

The binder may be any binder known in the art and specifically includes a fluororesin binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE), a binder such as styrene-butadiene But are not limited to, cellulose-based binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, poly Or a mixture or copolymer of one or more binders selected from the group consisting of polyolefin binders, polyolefin binders, polyimide binders, polyester-based binder mussel adhesives, and silane-based binders, .

The solvent can be selectively used depending on the type of the binder. For example, organic solvents such as isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone and water can be used.

Specifically, a binder solution may be prepared by dispersing or dissolving PVdF in NMP (N-methyl pyrrolidone) or dispersing or dissolving SBR (Styrene-Butadiene Rubber) / CMC (Carboxy Methyl Cellulose) in water.

The current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used.

The current collector may have fine unevenness on the surface to enhance the bonding force of the cathode material, and may be used in various forms such as a film, a sheet, and a foil. In addition, in order to form an air flow path, it may be made of a mesh, a porous body, a grid, a foam, a nonwoven fabric, or the like.

In one specific embodiment of the present invention, the collector may be a carbon paper and a mesh-like metal foil. In some cases, the battery case itself can function as a current collector.

The method of coating the slurry on the current collector may include a method of uniformly dispersing the slurry on a current collector using a doctor blade or the like, a die casting method, a comma coating method, , Screen printing, and the like. Alternatively, the slurry may be bonded to the current collector by molding on a separate substrate, followed by pressing or lamination.

After the slurry coating process, a drying and rolling process may be further included.

The drying process is a process of removing the solvent and moisture in the slurry to dry the slurry coated on the current collector. In a specific example, the drying process may be performed within one day in a vacuum oven at 50 to 200 ° C. The drying process may further include a cooling process, and the cooling process may be a slow cooling process to a room temperature.

After the drying step, in order to increase the capacity density of the positive electrode and increase the adhesion between the current collector and the positive electrode materials, a rolling process may be further performed in which the positive electrode is passed between two rolls heated at high temperature to compress the desired thickness.

The negative electrode may be composed of only an active metal, or may contain an active metal.

Specifically, when the negative electrode active material is an active metal plate or an alloy plate containing an active metal, the metal plate or the alloy plate itself may act as a negative electrode.

When the negative electrode active material is a powder of an active metal, a powder of an alloy containing an active metal, or a compound containing an active metal, the negative electrode can be produced in the same manner as the positive electrode. The compound may be, for example, a metal oxide or nitride containing lithium element, lithium titanium oxide, or the like.

In some cases, the negative electrode may include a conductive material or the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

As the electrolyte, an aqueous electrolyte and a non-aqueous electrolyte may be used. As the non-aqueous electrolyte, a non-aqueous liquid electrolyte, a solid electrolyte, and a gel electrolyte including a metal salt and an organic solvent may be used.

The metal salt varies depending on the kind of the metal-air battery. For example, in the case of a lithium-air battery, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO _{3 , LiCF 3 CO 2, LiAsF 6} , LiSbF 6, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium , Lithium salt of lower aliphatic carboxylic acid lithium, lithium 4-phenylborate, imide and the like can be used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, 4 Methyl-1,3-dioxane, diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative An aprotic organic solvent such as sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyrophosphate and ethyl propionate can be used have.

The organic solid electrolyte includes, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer including an acid dissociation group, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _2, and the like can be used.

The gel electrolyte is obtained by adding a polymer to a non-aqueous liquid electrolyte and gelation. The polymer may be polyethylene oxide (PEO), polyacrylonitrile (PAN) or poly methyl methacrylate (PMMA).

The aqueous electrolytic solution may be a metal salt added to water. Specifically, in the case of a lithium-air battery, it may be an aqueous solution of the above lithium salt.

In the case of a zinc-air battery, it may be an aqueous alkaline solution. The aqueous alkali solution may be an aqueous solution of potassium hydroxide (KOH), but is not particularly limited. In some cases, an aqueous solution of sodium hydroxide (NaOH) and an aqueous solution of ammonium hydroxide (NH ₄ OH) may be used.

Preferably, the hydroxide may be at least one selected from the group consisting of potassium hydroxide (KOH), sodium (NaOH), ammonium hydroxide (NH ₄ OH) hydroxide.

The separator is made of an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The structure and manufacturing method of the metal-air battery are well known in the art, and a detailed description thereof will be omitted.

The cathode material according to the present invention can improve the slow oxidation and reduction reaction rate of the oxygen gas since the metal catalyst layer is formed on part or all of the surfaces of the porous carbon particles or the porous carbon structure.

Therefore, the present invention can accelerate the electrochemical reaction of the oxygen gas more simply than the case of mixing the noble metal catalyst and the porous carbon, and at the same time, the energy density per mass is relatively higher than that in the case of using the nanoporous gold as the anode It is possible to provide a high-cost, low-cost metal-air battery anode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph comparing life characteristics of non-limiting examples of the present invention and comparative examples.

Hereinafter, the present invention will be described in more detail with reference to some embodiments thereof, but the scope of the present invention is not limited thereto.

<Examples>

Gold particles were uniformly formed as a thin film on the entire surface of the carbon paper using an electroless plating method (see X. Ma et al., Materials Chemistry and Physics, 97 (2006) 351-356) . Lithium metal as cathode, TEGDME containing 1M LiTFSi as electrolyte was used, and the separator was used with glass fiber in electrolyte. The air electrode, negative electrode and separator were coiled in a coin shape to fabricate 2032 coil cells.

<Comparative Example>

A coin cell was fabricated in the same manner as in Example 1, except that an air electrode composed of only carbon particles was used.

<Experimental Example>

The life characteristics of the batteries of Examples and Comparative Examples were compared. Referring to FIG. 1, in the case of the battery of the comparative example, the initial discharge capacity was measured at 560 mAh / g, and in the case of the battery of the Example, the initial discharge capacity was measured at 670 mAh / g. That is, it was confirmed that the initial discharge capacity was improved. In addition, it was confirmed that the cell characteristics of the batteries of the Examples were significantly improved as compared with the batteries of the Comparative Examples.

The catalytic properties of the oxidation / reduction reaction of the oxygen gas with gold improves the performance of the electrode. Since the electrode can be made of a small amount of gold rather than the entire electrode, And an increase in capacitance to electrode weight. The reason why the capacity value is smaller than the document value is that a thin lithium metal foil having a thickness of 160 μm is used as a negative electrode. The thicker lithium metal foil increases the electrode capacity (see Il Chan Jang et al., J. Power Source, In Press, (2013)).

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

Porous carbon particles; And
A metal catalyst layer formed on the surface of the porous carbon particles and lowering the activation energy of oxidation and reduction reactions of oxygen gas;
Wherein the metal catalyst layer has a thickness of 2 to 20 nm; And a current collector,
Wherein the current collector comprises a structure of a mesh, a porous body, a grid, a foam, or a nonwoven fabric so as to form an air flow path. A porous carbon structure having a structure in which porous carbon particles are aggregated; And
A metal catalyst layer formed on the surface of the porous carbon particles and lowering the activation energy of oxidation and reduction reactions of oxygen gas;
Wherein the metal catalyst layer has a thickness of 2 to 20 nm; And a current collector,
Wherein the current collector comprises a structure of a mesh, a porous body, a grid, a foam, or a nonwoven fabric so as to form an air flow path. 3. The anode for a metal-air battery according to claim 1 or 2, wherein the metal catalyst is simultaneously active in an oxygen reduction reaction and an oxygen generation reaction. The positive electrode for a metal-air battery according to claim 1 or 2, wherein the metal catalyst is one or two or more alloys selected from the group consisting of gold, silver, and platinum group metals. 5. The metal-organic electroluminescent device according to claim 4, wherein the platinum group metal is one or two or more alloys selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt) Anode for air cells. 3. The anode for a metal-air battery according to claim 1 or 2, wherein the porous carbon particles have an average size of pores of 2 to 50 nm. The positive electrode for a metal-air battery according to claim 1 or 2, wherein the porous carbon particles have a porosity of 20 to 45%. The positive electrode for a metal-air battery according to claim 2, wherein the porous carbon structure has a porosity of 20 to 45%. delete The positive electrode for a metal-air battery according to claim 1, wherein the metal catalyst layer is formed on all or a part of the surface of the porous carbon particles. The positive electrode for a metal-air battery according to claim 2, wherein the metal catalyst layer is formed on all or a part of the surface of the porous carbon particles. A cathode according to claim 1 or 2; cathode; And an electrolyte. &Lt; Desc / Clms Page number 24 &gt; The metal-air battery according to claim 12, further comprising a separator. 13. The metal-air battery of claim 12, wherein the negative electrode comprises an active metal thin film. 13. The metal-air battery according to claim 12, wherein the negative electrode is an alloy or a compound containing an active metal. 13. The metal-air battery according to claim 12, wherein the active metal is one selected from the group consisting of magnesium, aluminum, zinc, iron, cadmium, lead, lithium and sodium. A porous carbon structure having a structure in which porous carbon particles are aggregated; And
A metal catalyst layer formed on the surface of the porous carbon particles and lowering the activation energy of oxidation and reduction reactions of oxygen gas;
The thickness of the metal catalyst layer is 2 to 20 nm,
The porous carbon structure is carbon paper,
Wherein the carbon paper comprises a structure of a mesh, a porous body, a grid, a foam, or a nonwoven fabric so as to form an air flow path.

Images