We don't need the high discharge rate for a car, the quick charge would be nice but lithium batteries like the A123 system batteries can handle an 80% charge in 10 minutes? any faster and your electrical service is going to have a hard time keeping up.
I could see having a bank of capacitors that are used for absorbing the braking energy and that get charged while the vehicle is charging for starting from a dead stop.
The big draw back of capacitors is that as you discharge them their voltage drops drastically.
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