What use are Lithium Air Batteries?

lithium air batteries

If you’re involved with academia or electric vehicles, then you are probably aware of the rising interest in Lithium Air battery technology.  If you’re not, this may be an interesting article because it alludes to the possibility of some fairly impressive advancements in battery tech.  So, what are Lithium Air Batteries?

History

Lithium Air is not entirely new, it was first proposed in the 1970’s.  Since that time several advancements in battery technology have led us to Lithium Ion (Lithium Iron Phosphate, aka LiFe) cells which are in most electric vehicles today.  The trouble with the current tech in LiFe is the relatively low energy density that it has.

Science

Energy density is the amount of energy in a unit of mass that a substance can hold.  For LiFe batteries that’s about 250 Wh / kg.  By contrast, gasoline has about 13,000 Wh / kg.  But Lithium Air is supposed to have 11,700 Wh / kg or by contrast to LiFe batteries nearly 50 times as much energy density.

Right now gasoline vehicles get, at best, 50 MPG, but at an average of about 28 MPG.  Whereas electric vehicles tend to get an average of 110 MPGe.  By contrast again, this is roughly 4 times more efficiency.

Now consider that the average electric vehicle gets about 80 miles / full charge with LiFe batteries.  Imagine if Lithium Air were a possibility today.  That 80 miles would become a possible 4000 miles / full charge.

The average gasoline vehicle goes about 250 miles on a full tank.  So with an average of 28 MPG that means that the gas tank is about 9 gallons.  This to me implies that there is point where the manufacturer is deliberately making the tank smaller than it could have been.  Supposing that average gasoline car had twice or three times the size of gas tank, it could go anywhere from 500 to 750 miles before needing to refuel.  But in the case gasoline, there is a weight cost for each additional gallon.

Electric vehicles do not have the trouble of added weight when refueled or depleted, the weight is always the same.   But would a manufacturer consider making the range of the vehicle 250 miles to match gasoline or pack as many batteries as possible into the space?

Example

I’ll use my Smart ForTwo Electric Drive, as an example.  The LiFe battery pack for the Smart weighs, let’s say, 600 lbs and has a range of 70 miles.  With Lithium Air that same pack would grant 3500 miles of range.  But would it be more reasonable to cut the pack down to a range of 250 miles, making its weight a mere 15 lbs? Or would it be better to cut the weight by 75% (to 150 lbs ) and make the range 900 miles?

Let me know what you think in the comments.