TABLE OF CONTENTS There are a number of technologies other than those using chemical batteries which are possible contenders for power storage or generation in electric and hybrid vehicles, and these will be described in this chapter. Some of these technologies are not capable of storing or generating sufficient energy to drive a vehicle over useful distances, but nevertheless some have potential for use as part of the energy storage system to boost acceleration and/or to accept regenerated power during braking.
We will start with descriptions of three methods of storing or generating electrical energy directly, then conclude with two mechanical methods and one thermal method. Of these the fuel-cell shows the most promise at the time of writing, with the flywheel as a longer-term contender.
This storage method makes use of so-called supercapacitor or ultracapacitor technology in which the interface between a conductive electrode and an electrolyte solution forms a boundary layer which can store a charge. This electrode/electrolyte interface has a very small dielectric thickness of a few Angstroms. If this dielectric is combined with a material of high surface area such as carbon black, it produces a low-voltage, high-capacitance, energy storage capacitor in which a theoretical capacitance of one Farad could be provided by a few milligrams of material with an area of about one square centimetre.
Electrochemical double-layer capacitors (EDLCs) of this type have been developed in Japan and Australia using carbon electrodes treated to give an extremely high effective surface area of up to 2...
