CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0110461, filed on Sep. 14, 2018, in the Korean Intellectual Property Office, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates to a secondary battery, and more particularly, to a metal-air battery.

2. Description of the Related Art

A metal-air battery includes a negative electrode capable of ion occlusion/emission and a positive electrode using oxygen from the air as an active material. Oxygen reduction and oxidation reactions occur in the positive electrode, metal oxidation and reduction reactions occur in the negative electrode, and the generated chemical energy is converted and extracted as electrical energy. For example, the metal-air battery absorbs oxygen in a discharge mode and emits oxygen in a charge mode. Thus, since the metal-air battery uses oxygen present in the air as a positive electrode active material, the energy density of the battery may be greatly improved. For example, the metal-air battery may have and energy density which is several times greater than a lithium ion battery.

The positive electrode may function as both an electron transfer path and an ion transfer path in the metal-air battery. As a result, the capacity and performance of the metal-air battery may be influenced by, for example, the material and configuration of the positive electrode (air electrode). Also, the chemical deterioration and deformation of the metal-air battery caused by the reaction products formed during charge and discharge may result in performance degradation and life shortening of the metal-air battery. Thus there remains a need for improved metal-air battery materials.

SUMMARY

Provided is a metal-air battery having excellent performance.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.

According to an aspect of an embodiment, a metal-air battery includes: an anode including a metal; a cathode spaced apart from the anode; and a separator between the anode and the cathode, wherein the cathode includes a first cathode layer including a first conductive material, and a second cathode layer disposed on the first cathode layer and including a second conductive material, and wherein the first cathode layer provides a metal ion transfer path, and the second cathode layer provides an electron transfer path.

A cation conductivity of the first cathode layer may be greater than an electron conductivity of the first cathode layer, an electron conductivity of the second cathode layer may be greater than a cation conductivity of the second cathode layer, the electron conductivity of the second cathode layer may be greater than the electron conductivity of the first cathode layer, and the cation conductivity of the first cathode layer may be greater than the cation conductivity of the second cathode layer.

The metal-air battery may have an allowable overvoltage per current density represented by equation 1:
η/J=R1h+R2l(1)
wherein η is an allowable overvoltage, J is a current density, R1is an ion resistance of the first cathode layer, R2is an ion resistance of the second cathode layer, h is a thickness of the first cathode layer, and l is a thickness of the second cathode layer, and wherein η is greater than 0 volt and less than or equal to about 1 volt, and J is greater than or equal to about 0.2 mA/cm2and less than or equal to about 10 mA/cm2.

The cathode may include a pore-containing layer including a pore.

A porosity of the pore-containing layer may be less than or equal to about 90 volume percent (vol %).

A specific surface area of the pore-containing layer may be greater than or equal to about 10 square meters per gram (m2/g).

The first conductive material and the second conductive material may include a lithium oxide, a sodium oxide, or a combination thereof.

The first conductive material may include lithium titanium oxide (LTO), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium manganese nickel oxide (LMNO), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), lithium zinc germanium oxide (LISICON), lithium phosphorus oxynitride (LiPON), or a combination thereof, and the second conductive material may include lithium titanium oxide, lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium manganese nickel oxide (LMNO), lithium nickel manganese cobalt oxide (NMC), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP), lithium lanthanum titanium oxide (LLTO), lithium aluminum titanium phosphate (LATP), a reduced material thereof, or a combination thereof.

The first conductive material and the second conductive material may independently include an inorganic material having a perovskite structure, an anti-perovskite structure, a layered structure, a spinel structure, a sodium (Na) super ionic conductor type structure, or a combination thereof.

The first conductive material and the second conductive material may each include an inorganic solid compound.

The cathode may include an organic electrolyte-free electrode.

The cathode may include an empty space configured to receive a reaction product produced by the electrochemical reaction, and the empty space may include an electrolyte-free region.

The metal-air battery may further include a gas diffusion layer disposed on a surface of the second cathode layer.

The separator may include a solid electrolyte.

According to an aspect of another embodiment, a metal-air battery includes: an anode including a metal; a cathode spaced apart from the anode; and a separator between the anode and the cathode, wherein the cathode includes a first cathode layer including a first conductive material and a second cathode layer disposed on the first cathode layer and including a second conductive material, wherein the first cathode layer provides a metal ion transfer path and the second cathode layer provides an electron transfer path.

An electron conductivity of the second cathode layer may be greater than a cation conductivity of the second cathode layer, a cation conductivity of the first cathode layer may be greater than electron conductivity of the first cathode layer, the electron conductivity of the second cathode layer may be greater than the electron conductivity of the first cathode layer, and the cation conductivity of the first cathode layer may be greater than the cation conductivity of the second cathode layer.

The cathode may include a pore-containing layer including a pore.

A porosity of the pore-containing layer may be less than or equal to about 90 vol %.

A specific surface area of the pore-containing layer may be greater than or equal to about 10 m2/g.

The first conductive material and the second conductive material may independently include a lithium oxide, a sodium oxide, or a combination thereof.

The first conductive material comprises lithium titanium oxide, lithium manganese oxide, lithium cobalt oxide, lithium manganese nickel oxide, lithium nickel manganese cobalt oxide, lithium nickel oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium lanthanum titanium oxide, lithium aluminum titanium phosphate, lithium zinc germanium oxide, lithium phosphorus oxynitride, or a combination thereof, and the second conductive material comprises lithium manganese oxide, lithium cobalt oxide, lithium manganese nickel oxide, lithium nickel manganese cobalt oxide, lithium nickel oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium lanthanum titanium oxide, lithium aluminum titanium phosphate, a reduced material thereof, or a combination thereof.

The first compound conductive material and the second compound conductive material may independently include an inorganic material having aa perovskite structure, an anti-perovskite structure, a layered structure, a spinel structure, a sodium (Na) super ionic conductor (NASICON) type structure, or a combination thereof.

The first conductive material and the second conductive material may each include an inorganic solid compound.

The cathode may include an organic electrolyte-free electrode.

The cathode may include an empty space configured to receive a reaction product produced by the electrochemical reaction, and the empty space may include an electrolyte-free region.

The metal-air battery may further include a gas diffusion layer disposed on a surface of the first cathode layer.

The separator may include a solid electrolyte.

