1. ENERGY DENSE METAL AIR BATTERIES: TOMORROW’S POWER SOURCE?
Alexander Cross & Catherine Moran
Problems with Current Batteries
Aluminum Air
Magnesium Air
Applications
The overall reaction: 4Al+3O2+6H2O→4Al(OH)3 E0=+2.75V
Made of aluminum metal anode, electrolyte, hydrophobic separator between electrolyte and cathode, and porous carbon cathode with a catalyst
Obstacles to Commercial Production
Obstacle 1: not electronically rechargeable- must be replaced mechanically
Obstacle 2: anode discharges quickly reducing efficiency
Obstacle 3: corrosion between anode and electrolyte- can be lessened with alloys
These obstacles generate heat, which cause water loss in the electrolyte and decreased lifetime of battery
The applications of energy dense batteries are endless.
Batteries that match the energy density of gasoline have obvious applications in electric cars.
Batteries with such high levels of energy density would be able compete directly with gasoline, making electric vehicles more commercially viable.
Another important and less obvious application is that of battery banks.
There are very few commercially feasible battery banks that are on the market, and the ones that are available run on lithium-ion batteries.
With the energy density provided by metal-air batteries, battery banks would be smaller and more viable than previously possible.
As technology has advanced, the need for better batteries has grown rapidly.
Batteries traditionally utilize two electrodes which are two pieces conductive material, which are separated by the electrolyte solution. Electricity is released in the form of electrons when a chemical reaction takes place between the two cathodes, facilitated by the electrolyte solution.
There are several types of battery in production with the most used ones being: lead-acid, nickel metal hydride, and lithium ions batteries.
Lithium-ion batteries are the newest technology on the market and were first introduced to the commercial market in the early 1990s -- more than 20 years ago.
Lithium-ion batteries face definite limitations, one of the most important being their maximum energy density, holding only 200 Watt Hours per Kg they are 10% as dense as gasoline and other carbon based fuels.
Overall reaction: 2Mg+O2+2H2O→2Mg(OH)2  E0=+3.03V
Made of magnesium anode, electrolyte, and a cathode containing a catalyst, hydrophobic additives, and an external waterproof layer to prevent water from entering the cell
Obstacles to Commercial Production
Obstacle 1: discharges quickly, which reduces efficiency of battery and produces heat, requiring a cooling system
Obstacle 2: product of discharge is sluggish and covers the bottom of the anode, reducing the efficiency
Obstacle 3: corrosion between anode and electrolyte- can be lessened with alloys
Zinc Air
Lithium Air
Overall reaction: 2Zn+O2→2ZnO  E0=+1.68V
Made of zinc anode, separator, and cathode made of catalytic active layer and gas diffusion layer.
Currently being used in hearing aids and watches in small scale
Obstacles to Large Scale Production
Obstacle 1: corrosion between anode and electrolyte forms flammable hydrogen gas- better with zinc alloys
Obstacle 2: low lifetime when recharged electronically- better lifetime when recharged mechanically
Obstacle 3: formation of dendrites on anode- can cause battery to explode
Overall reaction 4LiO2+2H2O +LiI→4LiOH+3O2
Made of lithium anode, electrolyte, porous carbon cathode, and iodine mediator
Iodine mediator is used to ensure that side reactions do not take place and to allow the battery to operate in higher water concentrations
Currently the most advanced and highly efficient
Specific type that could be ready for large scale commercial use in 10 years
The Metal-Air Battery Solution
Metal-air batteries are 10 times more energy dense than lithium-ion, a similar density to gasoline.
Most versions are electronically rechargeable.
Work by having a metal anode and porous carbon cathode containing oxygen from the air, with electrolyte between the electrodes.
Current research shows that they could be ready in as few as 10 years.
Example uses of battery pack on a home
Sustainability
Diagram of Zinc, Magnesium, and Aluminum Air Batteries
Both of the applications mentioned above have major implications in terms of sustainability.
Electric vehicles that have similar range to gasoline would be a game changer and would help to reduce our carbon emissions.
Battery banks with the capacity to power homes and businesses would boost the renewable energy sector
Solar panels and wind turbines would be able to produce electricity when environmental conditions make it possible.
This electricity would then be stored in batteries allowing for use when electricity is not being produced, removing the need for on demand carbon based generation methods. ( (
Metal
Voltage (volts)
Energy Density (Wh/kg)
Energy Density (Wh/L)
MgO
3.03
4032
14400
Li2O2
2.98
3487
8050
Li2O
2.93
5252
10600
Al2O3
2.75
4332
17300
ZnO
1.68
1109
6220
Diagram of Lithium Air Battery