Lithium-Air batteries are not new, but they are new to transportation.  Several companies in the battery chemistry and technology field are working towards upsizing lithium-air batteries to work in alternative vehicles.  These batteries promise simpler construction, cheaper materials, and longer-lasting performance.

Lithium-air batteries are currently used in small batteries for hearing aids, along with their companion technology Zinc-air batteries.  Unlike Zinc-air, the lithium-air technology has a better up-size potential for making larger, more robust batteries cheaper.

In a normal lithium-ion battery, positively charged lithium moves through a chemical base (called the electrolyte), over a catalyst (called the cathode).  This moves ions through a circuit.  During recharge, the process reverses itself to recharge the lithium.  Lithium-ion batteries (as opposed to pure lithium batteries, or Lithium Metallic).  A lithium-ion battery excludes water (and air) because of the way lithium reacts to water.

It’s this reaction that powers Lithium-Air batteries.  Rather than recharging through the application of more electricity, the lithium itself is replenished to restore the battery.  This potentially could mean more power over time for the same size and weight of battery.  Using a lithium-air battery, you would “refuel” your car by adding a lithium pellet or powder into the battery, much like filling your car with gasoline now.

In a lithium-air battery, the reaction of lithium to oxygen is exploited.  In this setup, the lithium passes through an electrolyte, but instead of meeting a metallic cathode, it meets air.  This forms lithium oxide or lithium peroxide, giving off electrons in the process.

Some scientists and researchers think that this has great potential in future markets.  In scientific applications of fuel alternatives, the comparison made is usually what’s called tank-to-wheel (TOW) efficiency, which is most often compared to gasoline.  The TOW efficiency of gasoline, for instance, is 12.6% meaning that the energy density of gasoline is approximately 13,000 watt hours per kilogram (Wh/kg) with about 1,700Wh/kg being transferred to the wheels to move the car.  The rest of the energy is lost to heat, non-movement (idling), and other inefficiencies.  By contrast, most electric propulsion systems have a 90% TOW efficiency.

When compared to other metal-air battery types, lithium-air has huge energy potential.  Compared to the most common, zinc-air, lithium has about five times the energy potential by weight (when including oxygen weight for the reaction).  Lithium-air is almost double the potential of all other metal-air combinations, in fact.

The two largest advantages of lithium-air versus lithium-ion for alternative vehicles and EV cars is its huge potential of energy by weight.  Because the third chamber is not metal, but is instead just atmospheric air that can be added at any time, the weight of a lithium-air battery is much lower than that of a lithium-ion battery.  These batteries also have a much longer (theoretical) useful life because the lithium is replenished in order to refuel the battery, rather than the whole battery requiring replacement (as with lithium-ion).

The drawbacks are obvious as well, however.  First, lithium-air is still theoretical and has not become commercially available, though many are working towards that end.  It also requires refueling and new lithium, though some are working on chemical processes to cheaply remove the oxides from the lithium to recycle it.

Regardless, lithium-air is another exciting avenue that science is taking to configure the future of alternative cars and green transportation.

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• IBM Almaden Researchers Say Li-Air Batteries Offer Promise for Transition to Electrified Transportation, But Face Challenges and Multi-Decade Development Cycle (greencarcongress.com)

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