Battery for Electric Vehicle

 

Now let's have deeper view on batteries for electrical vehicles specially as a possible replacement for fossil fuel. Then we can probably have the insight whether this battery can really replace fossil fuel or not. Regardless of the types, the fule used for road vehicles should have some inevitable characteristics, high energy density and quich recharge time.

 

History of Battery

The figurs below shows the historical develoment of batteries from Pb battery to the current Li-Ion battery. X-axis display tough time span from late 1800 to the short future, and Y-axis show energy density each battery system can have. If we compare Pb battery and Li-Ion battery, we can tell that the weight to hold same amount of energy has been reduced down to one tens during the last 150 years. But still the energy density of gasoline is far far beyond than that of Li-Ion battery.

 

Energy Density

To describe energy density the unit of Wh/Kg is normally used. But this engineering unit cannot bring physical feeling to the public, therefore let's calculate the energy density of battery and gasoline into reachable distance from one recharge or refueling. The current road vehicle has normally reachable distance with one time fueling is moren than 600 Km. For simple calculation purpose, let's take 500 Km as a target reachable distance.

 

 

 

Now the current electrical motor requires 200 to 250 KWh/Km of power (take 250 KW/h for eacy calculation). For 500 Km of running we need to have power of 125,000 (=250 x 500) Wh in the battery. With the recenty possible technology how big (or small) battery we need to keep this amount of energy in the battery ? The 2nd generation of Li-Ion battery has energy density of 200Wh/Kg, this means if we wnat to run 500 Km with 250 KWh/Km motor, we need to have 125,000/200 (=625) Kg of battery on board. Compact class passenger cars has a curb weight in a range of 1000 to 1,200 K, this means more than the half of the vehicle weight should be filled with battery. And the trouble is the weight of battery when it is fully discharged is almost same as fully charged one.

 

Battery Cost

Then how much the cost of the battery ?

Normally the cost is highly dependent on technology (design, production, etc.), market maturity and demand, therefore the cost is just like a snapshot of a given time spot. If we can mention the snapshot of battery cost structure in 2010, probably the picture willbe like this.

 

The current battery cost is arounc 1,000 dollar per KWh. To stack up the battery for 125,000 Wh, we need to invest 125,000 dollar only for battery. With the amount of money in 2010, we can buy a middle class passenger (or even upper class). Do you like to buy a small EV with this much high price ? As seen with a very simple example, it is not matured in battery technology or some other aspects to spread EV into public automotive market yet. But considering our environmental situation and the priciple "EV efficiency is higher than that of ICE", EV can be always justified. I hope the era of EV will definetely come nevethless.

 

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