There is some work going on in the cross diciplinary field of material science and electrochemistry to design a structural material that stores electrical energy.

Sense allot of a vehicle's weight is already in its structure if this pans out it could be huge ... hundereds of kilograms of a vehicles weight could be multi-tasking and storeing energy... thus reducing the volume and weight needed for dedicated energy storage devices like batteries... even if the energy density is low most cars have more than 500 kg of potential already there.

One recent group sent me a copy of their pattent... link bellow ... interesting stuff.

http://www.youshare.com/IamIan/0e2e8f907d0809e5.pdf.html