Some preliminary thoughts on the use of batteries (etc) used in electric cars 

1) Li-Battery: PowerStream, "Lir2450 Lithium-Ion Battery," http://www.powerstream.com/LiCoin.htm, 400

Wh/L, 1166 J, 3.6 V, 90 mAh, 0.810 cm3, 24.5 mmOD x 5.4 mm height, $1.36/ea (100-1000 units) in 2003.

Same battery in 2008: 110 mAh and $1.85/ea, also wholesale, i.e. only a price drop of 4% for same energy storage in constant dollars, assuming 3%/year average inflation in the past 5 years.

See spec sheet at http://www.eemb.com/productcenter/Industry/PDF/LIR/LIR2450pdf  and

http://www.eemb.com/productcenter/Industry/PDF/CR/CR34615SL.pdf from EEMB in Hongkong 

2) SupercapaciItor: contains only 0.0025 Wh/g, so that we can forget its use as main energy storage

3) Gasoline would pack ~ 13.2 Wh/g, i.e. about 80x(Li-ion) to 30x(li-thionyl chloride) more energy per unit weight than the Li ion battery

4) Reference lead-acid battery: It is ~ 10x heavier for the same energy storage. But Wh/$ are about the same at ~3.0 Wh/$

5) Hydrogen tank: For storage at 300 bar (~ 4,350 psia) in a 20-liter tank, the H2 energy would be ~18 kWh, i.e. just below the 24 kWh of 120 lbs worth of Li thionyl chl. batteries. However its weight would only be 0.6 lbs + the weight of the tank

Conclusions:

1)      Electric car batteries are typically sized to provide ~ 25 kWh, so that a mileage range of 40-60 miles can be achieved. The cost of such a battery is ~ $9,000-$10,000 regardless whether Lithium or lead-acid based.

2)      Their performance as energy storage devices degrades to ~ 70-80% of original after ~ 500 discharges.

3)      Li-thionyl chloride batteries store about 3x more energy per unit weight than Li-ion bateries.

4)      Hydrogen storage (20 liters) would weigh less and may cost much less, but requires electrolysis and fuel cell units to complete a full car system, which would bring the cost back up to over $10,000

For a gasoline car with a tank holding 10 gal and a 30 mpg performance, the net energy needed to travel the 300 miles worth of gasoline energy, excluding ~25% engine efficiency is ~105 kWh. If a Li battery-powered drive system can supply an efficiency of 90%, then a 120-lb battery (Li-thionyl chloride) can provide ~ ¼ of that energy and ~ ¼ that range, w/o accounting for regenerative breaking or regenerative road vibration.