Lithium air battery
Encyclopedia
The lithium–air battery is a class of lithium battery
that employs a cathode which relies on oxygen reduction forming a discharge product. The two classes are the non-aqueous and aqueous lithium–air battery.
The non-aqueous lithium–air battery is a battery
in which a lithium
ion delivering anode
(often but not necessarily Li metal) is electrochemically coupled to atmospheric oxygen
through an air cathode
.
During discharge, O2 entering from the atmosphere is reduced in the cathode and combines with lithium cations that flow from the anode through an electrolyte
. In the ideal cell reaction this forms lithium peroxide
Li2O2 which is inserted in the cathode; this is coupled to the flow of electrons from the battery's anode to the cathode through a load circuit.
Lithium–air batteries have higher energy density
than lithium-ion batteries because of the lighter cathode and the fact that oxygen is freely available in the environment and does not need to be stored in the battery.
With oxygen as an unlimited cathode reactant, the capacity of the battery is limited the space available in the cathode to hold discharge product. The theoretical limit is therefore governed by the energy content of a solid slab of Li2O2. This can in practice not be achieved due the necessity for electrolyte and electron conductor in the cathode. On the battery level this capacity must be matched by the appropriate amount of Li in the anode. Lithium-air batteries are currently on the level of basic research and are not yet commercially available.
positive electrode (cathode), and a gel
polymer
electrolyte
membrane that served as both the separator and ion-transporting medium. Oxygen from the atmosphere enters the pores of the carbon cathode to serve as the cathode active material. In the discharge of the Li–air battery, this oxygen is reduced and the products are stored in the pores of the carbon electrode. As a result, the cell capacity is expressed as ampere-hour
per gram of the carbon in the cathode. The Li ion conducting gel polymer electrolytes used to construct polymer Li–air cells included those based on polyacrylonitrile
(PAN) and polyvinylidene fluoride
(PVdF). The electrolyte can also be organic liquid, dry organic polymer or inorganic solid electrolytes.
is the most attractive since the cell discharge reaction between Li and oxygen to yield Li2O2
, according to 2Li + O2 → 2Li2O2, has an open-circuit voltage
of 2.96 V and a theoretical specific energy
of 5210 Wh/kg. Repeatedly a specific energy of 11140 Wh/kg (40.1 MJ/kg) is claimed which excludes the weight of oxygen gained upon discharge. Therefore this number is irrelevant and misleading in practice. Compare this to the figure of 44 MJ/kg for gasoline (see petrol energy content).
In 2011, MIT researchers reported achieving an energy density of 2500 Wh/kg (9 MJ/kg) in a discharged (oxygenated) Lithium–air battery using carbon nanotube electrodes.
The possible discharge cell reaction and the associated cell voltage in agreement with the experimental discharge data from the test cell is:
2Li + O2 → Li2O2; Go = −145 kCal (Eo = 2.96 V) [1]
Indeed, Abraham et al. showed using Raman spectroscopic analysis
of the products that the discharge product contains Li2O2. This and other authors also claimed a discharge reaction leading to Li2O (Lithium oxide
). The energy stored per unit mass would be raised even more. However, no prove has been provided so far.
Abraham and Jiang also demonstrated that the Li/oxygen battery is rechargeable. They used a carbon cathode that contains catalysts derived from complexes
or oxide
s of metals such as cobalt
. The catalyst is believed to lowering the overvoltage
for the reduction
of Li2O2 or Li2O to form metallic Li and oxygen.
The non-aqueous metal–air batteries represent a class of potentially ultrahigh energy density
power sources useful for a variety of applications. When fully developed these batteries are expected to exhibit practical specific energies of over 1000 Wh
/kg
(3.6 MJ
/kg).
Abraham and co-workers also showed that a magnesium/oxygen battery can be constructed with a Mg ion conducting polymer
electrolyte of the composition, 30PVdF-HFP-62.5 EC/PC-7.5Mg(ClO4)2, with a conductivity of 1.2x10−3 S/cm at 20 °C (68 °F). This Mg/O2 cell showed an open circuit potential of about 1.2 V at room temperature
, lower than the calculated value of 2.93 V, and its discharge voltage ranged between 0.7 to 1.1 V depending on the current density
, carbon cathode and electrolyte composition.
Lithium battery
Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...
that employs a cathode which relies on oxygen reduction forming a discharge product. The two classes are the non-aqueous and aqueous lithium–air battery.
The non-aqueous lithium–air battery is a battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
in which a lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
ion delivering anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
(often but not necessarily Li metal) is electrochemically coupled to atmospheric oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
through an air cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
.
During discharge, O2 entering from the atmosphere is reduced in the cathode and combines with lithium cations that flow from the anode through an electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
. In the ideal cell reaction this forms lithium peroxide
Lithium peroxide
Lithium peroxide is the inorganic compound with the formula Li2O2. This solid was deployed to remove CO2 from the atmosphere in the vehicles used in Apollo mission.-Preparation:...
Li2O2 which is inserted in the cathode; this is coupled to the flow of electrons from the battery's anode to the cathode through a load circuit.
Lithium–air batteries have higher energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
than lithium-ion batteries because of the lighter cathode and the fact that oxygen is freely available in the environment and does not need to be stored in the battery.
With oxygen as an unlimited cathode reactant, the capacity of the battery is limited the space available in the cathode to hold discharge product. The theoretical limit is therefore governed by the energy content of a solid slab of Li2O2. This can in practice not be achieved due the necessity for electrolyte and electron conductor in the cathode. On the battery level this capacity must be matched by the appropriate amount of Li in the anode. Lithium-air batteries are currently on the level of basic research and are not yet commercially available.
History
In the mid-1990s, K.M. Abraham and co-workers demonstrated the first practical non-aqueous Li–air battery with the use of a Li negative electrode (anode), a porous carbonCarbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
positive electrode (cathode), and a gel
Gel
A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
membrane that served as both the separator and ion-transporting medium. Oxygen from the atmosphere enters the pores of the carbon cathode to serve as the cathode active material. In the discharge of the Li–air battery, this oxygen is reduced and the products are stored in the pores of the carbon electrode. As a result, the cell capacity is expressed as ampere-hour
Ampere-hour
An ampere-hour or amp-hour is a unit of electric charge, with sub-units milliampere-hour and milliampere second...
per gram of the carbon in the cathode. The Li ion conducting gel polymer electrolytes used to construct polymer Li–air cells included those based on polyacrylonitrile
Polyacrylonitrile
Polyacrylonitrile is a synthetic, semicrystalline organic polymer resin, with the linear formula n. Though it is thermoplastic, it does not melt under normal conditions. It degrades before melting. It melts above 300 degrees Celsius only if the heating rates are 50 degrees per minute or above...
(PAN) and polyvinylidene fluoride
Polyvinylidene fluoride
Polyvinylidene fluoride, or PVDF is a highly non-reactive and pure thermoplastic fluoropolymer.PVDF is a specialty plastic material in the fluoropolymer family; it is used generally in applications requiring the highest purity, strength, and resistance to solvents, acids, bases and heat and low...
(PVdF). The electrolyte can also be organic liquid, dry organic polymer or inorganic solid electrolytes.
Properties of metal–air batteries
Of the various metal–air battery chemical couples (Table 1), the Li–air batteryBattery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
is the most attractive since the cell discharge reaction between Li and oxygen to yield Li2O2
Lithium oxide
Lithium oxide or lithia is an inorganic chemical compound. Lithium oxide is formed along with small amounts of lithium peroxide when lithium metal is burned in the air and combines with oxygen:Pure can be produced by the thermal decomposition of lithium peroxide, at 450°C-Structure:In the solid...
, according to 2Li + O2 → 2Li2O2, has an open-circuit voltage
Open-circuit voltage
Open-circuit voltage is the difference of electrical potential between two terminals of a device when there is no external load connected, i.e. the circuit is broken or open. Under these conditions there is no external electric current between the terminals, even though there may be current...
of 2.96 V and a theoretical specific energy
Specific energy
Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...
of 5210 Wh/kg. Repeatedly a specific energy of 11140 Wh/kg (40.1 MJ/kg) is claimed which excludes the weight of oxygen gained upon discharge. Therefore this number is irrelevant and misleading in practice. Compare this to the figure of 44 MJ/kg for gasoline (see petrol energy content).
In 2011, MIT researchers reported achieving an energy density of 2500 Wh/kg (9 MJ/kg) in a discharged (oxygenated) Lithium–air battery using carbon nanotube electrodes.
| Metal–air battery | Calculated open-circuit voltage, V | Theoretical specific energy, Wh/kg (including oxygen) |
Theoretical specific energy, MJ/kg (including oxygen) |
Theoretical specific energy, Wh/kg (excluding oxygen) |
|---|---|---|---|---|
| Li–O2 | 2.96 | 5210 | 18.8 | 11140 |
| Na–O2 | 1.94 | 1677 | 6.04 | 2260 |
| Ca–O2 | 3.12 | 2990 | 10.8 | 4180 |
| Mg–O2 | 2.93 | 2789 | 10.0 | 6462 |
| Zn–O2 | 1.65 | 1090 | 3.92 | 1350 |
The possible discharge cell reaction and the associated cell voltage in agreement with the experimental discharge data from the test cell is:
2Li + O2 → Li2O2; Go = −145 kCal (Eo = 2.96 V) [1]
Indeed, Abraham et al. showed using Raman spectroscopic analysis
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
of the products that the discharge product contains Li2O2. This and other authors also claimed a discharge reaction leading to Li2O (Lithium oxide
Lithium oxide
Lithium oxide or lithia is an inorganic chemical compound. Lithium oxide is formed along with small amounts of lithium peroxide when lithium metal is burned in the air and combines with oxygen:Pure can be produced by the thermal decomposition of lithium peroxide, at 450°C-Structure:In the solid...
). The energy stored per unit mass would be raised even more. However, no prove has been provided so far.
Abraham and Jiang also demonstrated that the Li/oxygen battery is rechargeable. They used a carbon cathode that contains catalysts derived from complexes
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
or oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
s of metals such as cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
. The catalyst is believed to lowering the overvoltage
Overvoltage
When the voltage in a circuit or part of it is raised above its upper design limit, this is known as overvoltage. The conditions may be hazardous...
for the reduction
Reduction
Reduction, reduced, or reduce may refer to:- Chemistry :* Reduction, part of a reduction-oxidation reaction where oxygen is being removed from a compound.** Reduced gas, a gas with a low oxidation number...
of Li2O2 or Li2O to form metallic Li and oxygen.
The non-aqueous metal–air batteries represent a class of potentially ultrahigh energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
power sources useful for a variety of applications. When fully developed these batteries are expected to exhibit practical specific energies of over 1000 Wh
Watt-hour
The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...
/kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
(3.6 MJ
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
/kg).
Abraham and co-workers also showed that a magnesium/oxygen battery can be constructed with a Mg ion conducting polymer
Conductive polymer
Conductive polymers or, more precisely, intrinsically conducting polymers are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymers is their processability, mainly by dispersion. Conductive...
electrolyte of the composition, 30PVdF-HFP-62.5 EC/PC-7.5Mg(ClO4)2, with a conductivity of 1.2x10−3 S/cm at 20 °C (68 °F). This Mg/O2 cell showed an open circuit potential of about 1.2 V at room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
, lower than the calculated value of 2.93 V, and its discharge voltage ranged between 0.7 to 1.1 V depending on the current density
Current density
Current density is a measure of the density of flow of a conserved charge. Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved...
, carbon cathode and electrolyte composition.
See also
- Lithium batteryLithium batteryLithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...
- Lithium-ion battery
- Lithium iron phosphate batteryLithium iron phosphate batteryThe lithium iron phosphate battery, also called LFP battery, is a type of rechargeable battery, specifically a lithium-ion battery, which uses LiFePO4 as a cathode material.-History:...
- Lithium-ion polymer battery
- Nanowire batteryNanowire batteryA nanowire battery is a lithium-ion battery invented by a team led by Dr. Yi Cui at Stanford University in 2007. The team's invention consists of a stainless steel anode covered in silicon nanowires, to replace the traditional graphite anode...
- Power-to-weight ratioPower-to-weight ratioPower-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...