The lithium-air battery is the holy grail of energy storage only better.
Now, thanks to a breakthrough made by scientists at Cambridge University, it may also be a lot closer to commercial reality than previously believed.
First things first. What is a lithium air battery?
A battery has three basic parts: a positive terminal (cathode), a negative terminal (anode) and an electrolyte. The electrolyte allows ions to move between terminals, which generates a current. There are many different chemical compositions that can be used to build a battery.
Lithium primary cells use lithium to form their anodes. The cathode can be formed from any of a number of different materials, including iron disulfide, silicon and sulfur dioxide. Lithium-air batteries use oxygen pulled from the air as the reactant in the cell’s cathode (positive terminal) and use lithium for anode (negative terminal).
The key advantage of a lithium-air battery is that the cathode material is external to the cell. The design allows for significantly greater gravimetric energy density.
What does this mean in terms of performance?
A term called “specific energy” is a key metric for comparing the capabilities of different battery chemistries. It represents the amount of energy a battery can store per unit weight and is measured in watt-hours stored per kilogram (Wh/kg). Lithium-ion batteries can store between 100 Wh/kg and 200 Wh/kg. Lithium-air batteries have a theoretical energy density of nearly 10,000 Wh/kg.
“An ‘air-breathing’ battery structure has long been a goal of the R&D community, and has great potential for use in military applications,” according to a study of battery technologies by RAND. “It is unlikely that conventional battery technology can safely exceed a specific energy of 250 Wh/kg.”
If lithium air batteries ever become commercially viable, it may mean game over for the combustion engine.
The commercialization of lithium-air batteries is by no means a certainty. Air-breathing batteries are riddled with technical challenges. Scientists at the University of Cambridge have reportedly solved at least a few of them.
The team’s breakthrough was detailed in a paper published on Friday by the journal Science. The key innovations including replacing lithium peroxide particles with lithium hydroxide crystals and adding lithium iodide as a mediator compound.
Per the IEEE Spectrum’s summary:
Moreover, the researchers used macroporous reduced graphene oxide for their cathode instead of the mesoporous carbon typically used in other lithium-air battery cathodes. This thousand-fold increase in pore size — from pores 10 to 100 nanometers wide to ones 10 to 100 micrometers wide — helped prevent the lithium hydroxide crystals that formed during battery operations from clogging the pores. The scientists introduced the solvent dimethoxyethane to help remove these crystals as the battery charged and discharged. Furthermore, this new design showed a high tolerance for water, suggesting it could tolerate moisture in the air.
These modifications significantly reduced the frequency of unwanted chemical reactions that have hampered efforts to commercialize lithium-air batteries. Cambridge Enterprises has patented the scientists' work.
However, Cambridge is not the only game in town when it comes to commercializing an air-breathing battery.
PolyPlus, a battery research company based in Berkeley, Ca., has designed and successfully tested a lithium-air cell with specific energy in excess of 700 Wh/kg. In addition, EnZinc, a start-up company based in Emeryville, Ca., is developing a zinc-air battery with the U.S. Naval Research Laboratory that it claims “will double the range of electric cars, cut the cost of the batteries in half, and ensure the occupants are safe.”
