The electric bike revolution is powered by Lithium. Lithium ion (Li-ion) batteries are a rechargeable battery with a global market estimated at $11bn, predicted to grow to $60bn by 2020.
The BBC Earth website has a fascinating feature on how lithium has it's first uses in medicine, and over the last decade has become synonymous with batteries. Phones, laptops, basically anything electrical will use lithium-ion, and of course, electric bikes (and cars) need a bigger chunk than most items.
Two interesting facts taken from the article are that most of the world's reserves are in South America, and lithium is one of the original elements from the Big Bang.
(Credit: Nasa/Esa/CFHT/CXO/M.J. Jee/A. Mahdavi)